Lizard Brain Information – David Gunness of Fulcrum Acoustic

Welcome to the macro fab engineering podcast. I'm your guest David gunness

and we are your hosts Parker

Dolman and Steven Craig.

This is episode 203.

David gunness is the vice president of r&d at fulcrum acoustic, he also led the leads the product, he is also the lead product designer, photographer, copywriter, ambassador to Italy, facilities maintenance director, director of calculus technical writer and the lead coffee maker.

So is that a self? Like? Did you give yourself the title of lead coffee maker? Or do you just make coffee that well at work that people just defer to you?

I don't think it really matters if I gave it to myself. nobody objected to it, because it was the truth.

Well done. So fulcrum acoustic. Well, first of all, thanks for coming on the podcast.

Yes, thank you, David, for coming on to our podcast.

Thanks for having me.

So yeah, let's talk about fulcrum acoustic real quick, would you mind just giving us a rundown of what they are and what they do? quick

bio, the fulcrum acoustic was started in February of 2008. So we're coming up on 12 years. For those of you who remember, 2008, it was not the ideal time to start a new company, as the market was crashing at the same time that we were starting up. But you know, we'd use a conservative enough approach that we didn't have any problems with, with the economic realities of the time. And, and all it really did was it meant that our, our original business plan ran at about 50% of the projected speed, and eventually we we got to where we needed to be with the minimum of risks. And, and so here we are now 12 years later, and still healthy and, and happening. Everybody involved with fulcrum is was veterans of the pro audio from loudspeaker industry. So there weren't very many surprises with regard to that the only real surprises were the differences between working for established companies and working for a small bootstrapped startup company. That's a different set of challenges.

And at fulcrum, you manufacture loudspeaker a variety of loudspeaker products, right?

Yeah. Everything that everything we do would be characterized as professional. So we don't sell anything into the consumer market. Our customers are contractors, touring sound companies. In some cases, we sell directly to a an end customer in the form of theme parks. And in some cases, churches, especially churches that are essentially a chain of churches. So they'll talk directly to manufacturers and move and design sound systems that they put in a number of different venues. But the one thing in common is that all of these people are people who make their living doing sound. So they can afford a product that's built in the USA for one thing.

So like, like stadium acoustics and line arrays and things of that sort, right?

Yeah, in terms of applications are our biggest applications our sports facilities like stadiums and arenas churches is probably the biggest everything from local small town churches with two speakers in the front to you know, 15,000 seat churches that you know that that broadcast every every service, and everything in between. We do lots of nightclubs performing arts centers, restaurants, and clubs in general. That other than say dance clubs dance club is that's one of our best applications because they they use an insane number of speakers we like those kinds of customers.

So I got I got a question for someone who's not in the audio world is what's the major difference between like a professional grade loudspeaker box versus something that you go pick up at BestBuy consumer market? Yeah,

well, probably the primary thing Well, there's, they're getting very loud is the net result, but, you know, a typical thing you'd pick up at, at Best Buy, maybe labeled 100 Watson instead Relay, you know, 30 watt power handling. The products we sell are typically anywhere from 600 to 4000 Watt, and it's real power handling. The sensitivity is also much higher. So our typical sensitivities range from 98 to 112 DB, whereas

that's the sensitivity of the speaker. Given what, like the power you give it,

yeah, one watt to the speaker with a microphone one, one meter away, you'll get 98 to 112 DB, whereas there's probably nothing in a Best Buy that is more than 88 DB sensitivity. So

yeah, it's about say, I've got a, I've got a four by 12, speaker, guitar speaker cabinet sitting right here. And there's no way it has that kind of sensitivity on

it, that's probably pretty good. Don't guitar speakers or professional loudspeakers, typically, so that they probably have a 96 to 98 DB sensitivity, and you've performed four of them together, and you've got more like, you know, 103 104. So well, I

can I can very easily put out 110 115 decibels. That's for sure. Yeah. But in terms of the sensitivity, I'm not entirely sure. So actually,

guitar speakers are quite often made by the same suppliers that that make professional speakers for some of the boxes that that we build.

Very cool. So one, one question before we kind of get into the technology side of things that has I've been curious about for a while is, how does one get into the, I guess, the academic side of sound design? In terms of how does I guess let me put it this way, what what does somebody need to study in order to be able to design a loudspeaker or design an enclosure for a loudspeaker?

Well, you can come from a lot of different directions. Most most loudspeaker designers started out as electrical engineers, primarily, because electrical engineering puts a lot of emphasis on for your theory. And everything you do in audio in general, but especially in loudspeakers is frequency dependent. It's like every single measure of loudspeaker performance varies with frequency, so that the focus on frequency responses kind of leads to electrical engineers, there's quite a number of prominent loudspeaker designers who came out of mechanical engineering. And they tend to approach it in a different way. Which is kind of interesting. And then there are people who, who just come from the very typically in the live sound industry, and they're, they're more intuitive and cut and dry. But it is possible to actually build a loudspeaker without having any real engineering background, and just listen to it and go, Well, that's not right. I'll try something else now. And a lot of good loudspeakers have, you know, have been made that way, that's, that's how some companies did it in the 70s. And early 80s, is, you know, they would they would build something and take it out to the first gig and blow it up. And then they'd go back and try something else. And after, after a while, they had something that they that they had faith in. But it's a long arduous process. And, you know, beginning in the late 80s, early 90s, that kind of went away, and some companies started relying on manufacturers to apply real engineering to designs that allowed speakers and make something that was more reliable, and, and somebody who could, you know, fill your warranty claim when you blew it up?

Right, instead of just empirical, iterative design, actually, calculating something.

Yeah, there's still, there's still a lot of empiricism in it even even when you have, you know, very technical oriented designers, but because at the end of the day, the only thing that really matters is how it sounds, and then introduces a human element of perception. You know, all the technical measures in the world can't tell you, or guarantee you that something you've designed is going to sound good. So listening and critiquing is very much a part of a loop that you go through. So you listen, you find something you don't like, and then you apply your technical knowledge to figure out how to how to make it sound better.

Do you do a lot of full system listen tests at fulcrum,

full system by full system you mean like an entire venue? Yeah. Yeah, we maybe more than than the larger companies we depend on when I say we the guys who work in engineering with me. We do quite a bit of field work when we go out particularly when there's a new product that hasn't been used in the field before, we'd like to be on hand when it's used the first time and, you know, learned where the bones are very what the characteristics of that of that speaker is, sometimes to see if we want to approve it, but also just to know, the best way to sell it, you know what it's good at, you know, you can tell somebody who's good at this, and you know, they won't decide you're lying to him. So we do quite a bit of work in the field. And in some cases, just to ensure that, you know that the field tuning is done, right. The environment where a loudspeaker is placed, has a very powerful effect on the sound of the speaker. So you can put a speaker on a speaker stand and tweak it up until it sounds perfect. But as soon as you put that, two feet from a wall up in the corner next to the ceiling, everything's changed. And it you need to make on site measurements, and equalization changes in order to mitigate the adverse effects of the reflect now, nearby reflections. And sometimes the overall reverberation, so there's a there's a lot of aesthetic decision making in the field. When these things are installed.

Yeah, imagine the environment of a ginormous inside of a church, which echoes a lot verse like a stadium would be two completely different kinds of, of setup,

very different. And then sometimes in surprising ways that churches are very reverberant. But it's, it's usually a very pleasant reverberation. So you know, a choir where you're not actually you don't care if you can pick up the consonants, which is, ah, that's fine. But then when you when you need to understand what the preacher is saying, then intelligibility becomes really critical in churches. And that's all about getting the sound directly to the people, while putting as little sound as possible onto reflective surfaces, like the walls and ceiling and, and back walls and floors. And so it's it's, it's a very engineering heavy process of figuring out where to, to position the speakers and where to point them. And that's where we get into the detailed measurements of the speakers where we have high resolution data, defining what the radiation pattern of each speaker is. In, in a stadium, it's you would think that in an open air stadium that gets it's a lot easier because there's no reverb. But in fact, stadiums are very reverberant. The air overhead is not as transparent as it looks, because the temperature inside the stadium is very different than the temperature above the stadium. And so you get reflections off that, that thermal gradient, even just bouncing back and forth from amongst the stance and bouncing off the windows of the press box, all of those things are are very strong, reflective and reverberant sources. And they're much more damaging than it is in typical venues. Because when you get a reflection off a press box from from a speaker that's in a scoreboard, your reflection off the press box that arrives in the fire grandstand, it can become an almost a half second late. And that mean, a half second is like three words, when I just said like three words, that was about a half a second. So when you take that, that if you put a half second delay on me and played them both the same level, you wouldn't understand a single word I said. So it's an it's a whole different set of challenges.

Yeah, I would, I would think it's it's incredibly difficult. I was actually at a Denver Broncos game few weeks ago, and I was on third deck. And I was remarking to my buddy there about how good the sound is actually, just because it didn't it there wasn't that that awful reverberation that you get at a high school football game.

So that's the benefit of the upper deck is that nothing comes back from behind you. The lower deck, it goes up underneath the the upper deck and then comes comes Verbling back out on the upper deck, it just sails away into the neighborhood. The downside of being in the upper deck is that if you're at the like in the front row of the upper deck, there's no floor in front of you. So whereas sound normally hits the floor you're standing on, and the low frequencies reinforce at you. You're here, the direct sounds you're here and then what's coming off the floor is less than a quarter wavelength late. So you get 60 Be more low frequency energy or you know it's 60 B base here because of the floor you're standing on. But when you're standing at the front lip of an upper deck, there's no floor and so it gets very thin so you don't get to hear Bass when you're in the upper deck, but you can understand everything very, very clearly.

Well, there you go hot tips from David when you're picking season tickets. If you care about audio that

you don't want to stand on the field either because grass is really unevenly absorptive does it does it scattering is very dull and muffled when you're on the field because you're not getting any high frequencies off the off the floor.

Well, then, just in general, where's the best place to sit in the bowl, then

we're the sound guys in the

control room where the sound guys he's easily when you're mixing sound in a stadium, you can't actually hear what's going on on the stadium. They close the windows, and they have a pair of studio monitors that listen to the to the television feed or the or the the PA feed. Right?

That was the tip that all my friends gave when I go to concerts and stuff is an open air concert go where the sound guys at? Oh, yeah. Because that's where it's going to sound the best? Yeah,

yeah. And if you're right on the center line, then it's also going to be the basis because your left stack and right stack are exactly in time on the on the center line right between them. Which is typically where the song guy stance.

will cool. I would like to move on to some of the technology that's available on your website. And first of all, I gotta mention that from the website, I got I love it because it feels very, it's both marketing and engineering, I can I can tell you have a section of the website that's dedicated to the technologies in within your products. And their their actual, like descriptions of the technologies. And I love that because it's it's, like I said, it's both marketing where someone can go, oh, there's a lot of technology behind this. But a guy like me can go and read and be like, Oh, this is pretty cool. And in particular, I want to do kind of ask you some questions about the passive cardioid technology, which let's just start with what is it?

Well, cardioid refers to the hardship radiation pattern.

So we refer to as the butt pattern.

Yeah, it's more of a female, but then a male. But so

that's why it's so much fun to create these patterns. So loudspeakers normally get increasingly directive with frequency. So you know, when a professional loudspeaker will ask as to the call it the beam width is narrowing. As we go up in frequency at a certain point, let's say it's a 60. By 45 degree loudspeaker, when it gets to 60 degrees, we want it to stop at 60 and hold 60 all the way up to you know, 1216 kilohertz, but below 500. There's, there's no way to do that with normal sized loudspeakers because the whole say 60 degree pattern and 100 hertz would require something maybe 12 feet wide.

So like Back to the Future styles,

I was about to say, yeah, yeah.

So what happens is that the patterns get wider and below 200 hertz is essentially omni directional. And so that's where cardioids come in, you have speakers, for instance, at the left and right front of the stage, and low frequencies are coming off the back of that speakers. And so you always have all this low frequency energy on stage, that's getting into microphones and muddying up the mix, and, and especially muddying up monitor mixes. And so the ability to reduce the amount of low frequencies going backwards, is very important. That's just one example of many. As you go out in the audience, there's quite often a, what we call delay fills, where there's small speakers out in the audience pointed away from the stage. And the feed to those speakers is delayed by a time equivalent to the propagation time from the main speakers to the delay speakers. And so they actually reinforced the delay speakers in the same time. But if you happen to be standing forward of the delay speaker, meaning closer to the mains, you're getting low frequencies off the back of the delay speakers, that is coming in that much like twice, so if it's 20 feet behind you, it's coming in 40 feet late. And that can be very, very disturbing. So there's another case where, you know, cardioid pattern really helps keep it clean in that region, just ahead of the delay speaker. You know, there are many more examples of where the cardioid pattern is helpful. So traditionally, the way people have have created a cardioid pattern is by using two separate sources, sometimes in one box. Split quite often just two separate subwoofers. And if you put them if you space them by a given distance, and then you invert the the rear speaker, then on a centerline between the two meaning going left and right, those two speakers are going to cancel. So you have no output on that centerline that but you've got a negative output behind in the positive output in front, that's called the figure eight pattern. It's not particularly useful. If you then delay the rear speaker, by an amount equivalent to the spacing between the speakers, then what happens is that that No, which was left and right goes around behind, now you have a null in the back, and you have some some constructive interference in the front. So you're getting a little bit more help, but from the two speakers in the front, and you're getting cancellation in the rear. Of course, the the problem with that is that you need to use twice as many speakers, you have to have twice as many amplifier channels, you have to have twice as many DSP channels. So there's, you know, that's basically doubled the cost of producing those low frequencies. So with the passive cardioid approach, that delay in the back source, well, first off, there's only one source, but there's a port in the back of the cabinet, that's far enough back to create a cardioid effect. But that output from that port is delayed by an acoustical circuit, you know, network of volumes and tubes that act like acoustical masses. So what you create is a low pass filter. And it turns out that a low pass but the phase response of a low pass filter is identical to the phase response of a pure delay, up to the to the cutoff frequency of the filter, then it diverges. But it doesn't matter because it's it's above cutoff. So by very carefully designing this acoustical circuit circuit, you can create a cardioid pattern passively with a single transducer and a slightly more elaborate enclosure.

So the enclosure, basically breeds behind the loudspeaker itself.

Yeah, if you're, you're used to seeing a ported loudspeaker where there are two tubes coming out the front, the baffle that the woofers Monacan Well, in the case of a passive cardioid, that, that boxes deeper, so that you know, so the back is far enough behind and the the port tubes instead of coming out the front or coming out the back, and the output from those port tubes is appropriately delayed and low pass filtered, so that so that it produces, you know, typically around 10 dB of attenuation in the back.

So when it comes to the passive cardioid design, if we're just talking about, effectively the phase response of a low pass filter, doesn't that mean that it's only a true cardioid pattern at a single frequency and the pattern changes as the frequency increases?

Well, if you Yeah, it's there's there's a lot of there's a lot of degrees of freedom in a passive cardioid. Whereas in a typical ported loudspeaker, you've got a volume and you've got a you've got a tuning frequency, and you can change the size of the ports, if you make them bigger and make them longer, you may not you may still have the same tuning frequency so it doesn't affect the result. In a passive cardioid there's I think the last time I counted, there are nine variables that you can play with and you can play one against Can you can adjust the cue of the low pass filter, you can adjust the the physical location of where the ports exit which interacts with the shape of the cabinet, the way it diffracts around the cabinet. And if you do all of that very carefully, you can you can come up with something that is actually more where the the response curves as you go off axis become gradually more attenuated. But those curves are almost parallel as you as you get around to the back of the of the speaker, whereas a active cardioid is not even as as consistent. Now if you have you know, if you have days you can you can tweak to your heart's content with with digital signal processors and try and make the active cardioid work the way you would really like it to but that's essentially what we've done in the in the passive domain. So it's a lot more involved than just designing a ported speaker. But it's it's you know, design In phase, so you only do it once. And once you have it figured out, it's not that expensive. It's not much more expensive to manufacture passive cardioid than it is to manufacture a conventional ported loudspeaker. So all of the effort is in the design phase, it doesn't really have much cost to the manufacturing phase.

So I have a question about that is, so we were talking earlier about how venues can change how the sound sound acts? Is that the same thing in the passive, this passive solution for cardio?

It's certainly Yeah, then you certainly affect the sound of subwoofers. In general, one of the benefits of a passive type of a cardioid is that it is less sensitive to the characteristics of the venue. I mean, typically loud subwoofers are backed up to a wall, and you have the energy wrapping around going backwards, bouncing off the wall and combining in the front. And there is no way that can combine light and do anything useful, it's always going to be disruptive, or harmful to the net result, when you have a cardioid backed up to a wall, there is nothing coming straight out because there's a knock back there. The net result when you when you put a cardioid up against a wall is the same as if you put two cardioids back to back. And mathematically, the way that works out is you get a pure omnidirectional pattern. So in the case of the wall, because there's nothing going through the wall, what you have is a hemispherical pattern. So you whereas without the cardioid characteristic, you have like a cloverleaf pattern in the front, there are no holes in certain directions. And those nulls move with frequencies. So for instance, at 60 hertz, you might have a null that's, that's a 60 degrees off axis. And by the time you get to 120 hertz, it's 30 degrees off axis. So you, no matter where you are, you have a nice big notch in the response, that that really saps especially the impact of a kick drum.

I was about to say, actually, just different people talking how different frequencies and some people could like, let's say in the church example, like if someone's speaking, and only certain people can hear that person talk, and then someone else comes up. And it's, you know, because

it's sounds different in different places. Yeah, yeah. The thing about about the speech range, though, is that most of us live on the floor, in rooms. And so every person we ever listened to, has his voice reflecting off the floor, reflecting off of walls, and usually reflecting off the ceiling. And the human ear brain mechanism is extraordinarily adapted to being able to extract information from that situation. If you've ever tried to listen to somebody by listening to the recording of a mic in the room, and you say, I can't understand a word you're saying, but I was sitting right there where the mic was, and I had no problem understanding him in the environment, you can use spatial cues. And there's a lot more information to process. And we're just extraordinarily adapted to that. Now, the same thing happens with interference if you put a loudspeaker near a wall that's very similar to a person standing near a wall. And so we're good at ignoring the deleterious effect of that of that wall. That doesn't hold down to low frequencies because there's no like language information in low frequencies. There's just you know, lizard brain information, thump thump. And you bring in the walls now the thump isn't a stumpy and so you're not as afraid when it when the when the T Rex mixes thumping noises or whatever. It's a different you know, hearing is a different function at 100 hertz than it is at 1000 Hertz. Gotcha, gotcha. Even even, you know, evolutionary terms.

You know, out of curiosity, what is the mechanism that causes higher frequencies to be more focused in lower frequencies to be more omnidirectional?

Generally, that would be diffraction. Just the way like when light hits a slit, it diffracts through in a wide beam. But if it's if it's if it's playing through or if the light is shining through a white slot, it goes through as a as a focused beam. And the same thing happens in audio that the larger the source, the the tighter the beam with that that source produces. Ironically enough, that theory the different theory of diffraction of propagating waves that was developed by Lord Rayleigh in the 1860s And when he got done solving all the problems of audio diffraction, he was looking for something else to do. So he went over and and assault all of the same equations for light.

But he just got bored, right and said, I'm bored.

Well, yeah, he didn't sit in and get paid. He was he was a lord, right? He didn't have anything to do. So he just he did science as a hobby. And then I had to invent a new calculus in order to solve the equations of diffraction.

And I want to be a lord.

My dogs, my dog is named after Lord Rayleigh.

Oh, nice. Lord Rayleigh is

his. His real name is John William strep. And so my dog my dog's AKC name is is is Genesis Lord Rayleigh, and is calling this jack, which is short for John William strock.

I like how there's layers to this dog's name.

Yeah, it's an inside joke. My wife and I are the only people who would ever have known it until now.

Well, now, now a few 1000 People are gonna know it. Well, and on top of that, the so with this passive cardio technology, you actually have a patent on this, right? Is that does that under your name?

Yes. Yeah, so it's been about a year, I guess. Now. I don't know what to say about that. There's a there's a patent there, which is kind of cool. A lot of people this, this was not an idea that I hatched. And I did, I was the first person to think of people have been trying to make passive cardioids for a while, at least since 72, is the first patent application that I'm aware of. Gonna blank his name off now, but I almost had it anyway, he was an Altec, Lansing engineer back in 72, filed the first patent, but they never managed to actually make it work. So there was never a product issued under that patent. Several other people have have been awarded patents without creating any products. And a large part of it is because of it, it was because of limitations of materials. So one of the reasons we're able to make this work now is because of some material technologies that actually became available because of cell phones. The microphones and cell phones, the performance of those microphones is dependent on acoustical resistance of materials. And so all of a sudden, now we can actually buy a material with where the acoustical resistance is a QC parameter. Whereas in the past, you could find a piece of material that works and then you go to buy another piece of material and it doesn't work anymore, because it's, it's not consistent from batch to batch.

So that yeah, that material actually has a specification and tolerance for

for acoustical resistance. Yeah. Gotcha.

Go figure.

So another topic that was on your technology page, is actually called Building a Better coax, which kind of feels like a social media post for engineers or for nerds.

And, and there's a quote on the page it says, Herman J finger invented the coaxial speaker in 1928 80 years later, fulcrum acoustic reinvented the coaxial system design. And that's a little bit of a winky quote, but first of all can use

that's about as marketing uses, we get a website it

says, Okay, can you can you fill us in on what is a coaxial speaker?

Well, the idea is, is that the low frequency device and the high frequency device are on the same axis. So as you go off to the right and left, it's, they're symmetrical. And if you go up and down, they're symmetrical. So in a typical speaker configuration, where you have a woofer, with a with a high frequency driver above it, they're spaced. And so when you go when you go down from on access, the high frequency devices late in arriving, and if you go above access, the high frequency drivers early arriving. And so you, you have a different response going up versus going down. And so you can't create a consistent and so what it does is it puts a notch in the response somewhere at crossover frequency. Whereas with a coax, if you solve it anywhere, it works everywhere. By anywhere, I mean, if you if you saw that going to the right, it also works to the left. And in fact, it's going to be very similar, upward and downward. So you can get a much more more consistent response spatially with a coax. And that has very important benefits to house speaker sound. These the if you're standing somewhere in front of a loudspeaker, then in some, some of the output is going sideways and coming off a wall or reflecting off the floor reflecting off the ceiling, these late arrivals, that mechanism that I was talking about the humans are so good at ignoring late arrivals that create interference patterns. We're only really good at that. If the arrivals are all very similar in spectrum and, and transmit character. So the more similar those off axis responses are to the actual response, the better at sound, because the more effective we are at ignoring those reflections from the room. So coax is just easier to listen to because you're not doing as much subconscious work in your brain to try and decode what you're getting from the sound field. So that you know, most people's reaction is just wow, this is so easy to listen to, don't get tired. It's a big deal in in studios where people sit in front of speakers listening for 812 hours at a time,

I was actually about to say is, I do a lot of automotive work and coaxial speakers, I actually didn't know what they were I googled the picture, I'm like, Oh, those are the kinds of speakers that you guys use on audio, auto automotive applications come

on, get off accessories for your car speaker. But that brings up the second big advantage of coax is and that's simply that they're more compact. Okay, 12 inch speaker and a 12 inch form, you need at least 24 inches of baffle. But with a 12 inch coax, you only need 13 inches of baffle to. So you can make it there, you know, almost universally nowadays used in floor monitors. So the so that the floor monitors can be very compact. And, you know, our the core of our line is a single coaxial speaker with a vertical trapezoid. So that it can it can go tight up against the ceiling and really be kind of invisible. So a lot of it has been, especially in churches and restaurants and that kind of a application. People want the speakers to disappear. And a coax is, you know, twice as half as visible as a displaced driver, service speaker. So what we did that was different than what people have been doing since 1928 is a we do multiple coverage patterns. So we have a 90 by 45, a 60 by 4575 by 75 120 by 6090 by 60 100 by 100, all different patterns, so that are all designed to sound as identical as possible so that you can combine different patterns in a room and cover the different areas of the room with with a pattern, you know, specifically suited to that, you know, that place in the room. That's what people have been doing with displace drivers for decades, we just we just took that into coax land and made Panel Control drivers. And the reason we're able to make that work is because of the involvement of DSP in professional loudspeakers. Now, in the old days, you had to try and try and make the speaker flat and sound good. Using a handful of passive components, the cost adds up quickly. So you've got, you know, a budget of I can only use eight components. And I have to try and make this thing as flat as possible. And some patterns are a lot easier to make some good than others. And so what had you know, what people had in the past is that they managed to make one coax work, okay. But if they tried to do a different pattern with it, they just, they couldn't solve the problem. So when we started focusing, we had the luxury of starting at a time when any professional level loudspeaker at a price point, meaning it was built in Massachusetts, had a capable DSP in the installation. So we didn't make any attempt to make the speakers naturally flat or passively flat. Every speaker we make has to have DSP. And because of that, we could design a crossover that produced off axis research curves that are parallel to the on axis response. But if we tried to make it flat, we couldn't we couldn't get the directional behavior, right. So we just said we're not going to worry about flat and just going to get the directional behavior, right. And we're going to flatten it with the DSP. And because of that, you know, there's almost no limit to What you can do with DSP, so we could make it sound much better than you could ever make a passively crossover? Flat speaker sound?

Yeah, because you could just counteract the curve in the DSP. Right? Yeah.

And also, I mean, we don't the with horrible especially with horn loads and with woofers naturally rise a response as you go up in frequency. And compression drivers on on horns are much more sensitive and woofers. So the shape of the response curve is a great big haystack where it's, it's 10 DB hotter from, say, 800 to four kilohertz than it is at 200 hertz or 10 kilohertz. And by just letting it stay, you know, be that loud. In that range, almost no power is consumed making the two to four kilohertz. And that means that overall, you get more output per watt of amplifier power.

So is the is the design? I guess what's going through my head right now is that you design the loudspeaker such that the on axis and off axis is great. And then you just basically test and validate and listen to it with a with a with a microphone and then create the curve against that what you've tested.

Well, there's, there's more magic to it than that.

Yeah, I guess I used the word just a few times there.

Yeah, just just leave out just, that's probably an accurate statement. The trick is to get it to sound better everywhere. So you have a speaker that you know, is relatively consistent, meaning the off axis curves are parallel. But if you just put a microphone on axis and make, I mean, you can just make it perfectly flat on axis. But some places in the pattern, it's actually going to sound worse. So the magic comes in, in figuring out how much you can how much better you can make it everywhere. Without making it perfect anywhere. Because this is this is one of the differences between a professional loudspeaker and home hifi speaker is that for a home Hi Fi there's one person sitting in a chair, you know, with his head and a clamp. And speakers need to sound perfect that point in space.

But most most home hifi people are i Yeah, I know couples like that.

They have their head clamps monitor their chair, they have a specific spot, they have to sit Yes. Oh, yeah, for sure.

But you see, if you make it, if you take a professional loudspeaker, you make it perfect right on the axis, that's only going to satisfy one person. Right, the actual response is pointed at one guy, the guy with a smile on his face, you go off axis, say 10 degrees, now you're going 10 degrees all the way around that Well, you take that that cone, you know, it's subscribed by 10 degrees that's pointing at, you know, 20 or 30 people or something, depending how far away they are. And if you go up by the pattern edge, you might be catching 80 people. So in reality, the actual responses is, you know, not very productive you want it what you want to do is make as much of the pattern sound good as possible. So that the largest percentage possible of the audience is getting good sound. So very different focus than than making a a home Wi Fi speaker or even a studio monitor.

And right, and I can I can only imagine that there's a lot of compromises that go along with that. Not major compromises, but you know, this one person might not get the best sound but your 40% more are going to be better. So there's a compromiser

was also he's he paid the $30 nosebleed ticket

that summer to set you use the same process that you use when you're when you're tuning a loudspeaker in situ, which is basically you walk around and listen to it and you find the worst spot in the room. And you you go to your to your DSP and you you what, you put a microphone there to find out exactly like okay, here's something in the upper mids is that two kiloHertz is that you know, 2500 hertz, you figure out exactly where it is, you put an EQ in, that mitigates it for that spot in the room. And then you walk around it and now it's not the worst spot in the room now a different spot you mitigate that spot. The trick is knowing when to stop. Yeah, it sounds like a chasing your tail issue. Yeah, well, you get to a point where Okay, so there's nothing is radically worse than anything else. So we're done here. This is this is as good as this can be. You get

to the point where the entire spectrum is a notch.

What you sometimes see with people who don't know when to stop, is that they will uh, you know, a cut EQ with a belt bell curves, it's a kind of a notch EQ. So they spent way too much time tuning and what they did is they put in so many knots GQ is that now what they have is just they've ended up shelving the whole thing down. They've just got Nachi cheese on top a notch EQs. And now that doesn't actually help, you don't want to use more three or four EQ, there's a there's a elaborate philosophy about how to EQ speakers in situ and how to EQ speakers, you know, at design time in a laboratory. So, you know, if you want to get interested in that, go take a class in smart. Buy Rational Acoustics, smart is the is the program that most people use for tuning speakers in situ real real time frequency response measurements.

Very cool. So, one of the thing, this is a little bit of a departure, but I'd like to touch on this real quick. And it's the fact that I correct me if I'm wrong here, but wood is one of the materials that you use in your manufacturing process. Is that correct?

Absolutely. And whenever I can get away with it.

Well, so that's something that we we actually haven't talked a lot about, or we haven't had a lot of guests on that wood is a primary manufacturing material that's

probably surprising to people that that you know, there certainly there must be something better that you can make as a speaker and closer on it but but there really isn't that. But it's not just what I mean yeah, you make a make it out of pine wood or something like that it's not gonna work very well. It's a very specific with this is this is phenolic bonded Baltic birch plywood. So unlike the plywood you get from from the lumberyard, like three quarter inch plywood has typically seven plies, and in Baltic birch it would be more like 13 place. So they're much thinner. There are no voids. And it's, it's bonded with phenolic, which is essentially a plastic. So Baltic Birch is extremely rigid, extremely light. extremely hard. And it has a very neutral vibration character. When you knock on wood. It just, it's a very neutral adulthood. Whereas if you knock on something like plastic, you can definitely recognize that it's plastic your your your wrapping up. And when that plastic vibrates, it gives gives a sound a plasticky character for lack of a better adjective.

And this sounds a lot like what we call like an engineered wood. Where it's it's it's, it's there's a specification for how

it's built. Yes, absolutely. Yeah,

they do the same thing when they build houses and stuff that the the crossbeams are engineered materials now.

Yeah, the I forget what they call this something lamb where it's it's, it's basically this kind of plywood, glued up face to face to make a to make a beam well, and then you know, if you live in in Denmark, you have to make all your furniture out of it too. So this Baltic Birch is extremely fine grained. So you can you can cut very fine details and it holds the details. When you have a finished speaker cabinet and you can you know you hit it with a hammer, it doesn't leave a mark it's it's very impact resistant. And because it's just it's painted with water based paint. When you drag a floor monitor around on a stage and scratch it up, or you you know, it's it's bouncing around on a truck. What a lot of some companies do is they don't they don't baby their speakers, they just when they come back from a tour, they repaint every speaker that comes off the truck. So it's really easy to maintain, unlike like plastics and even cheaper materials that are coated with like the bedliner kind of rugged plastic. That stuff is really rugged. But it's not impermeable, and if you if you chip it, you can't repair it because you have to have a special machine to apply it. So the accessibility of Painted Baltic Birch is part of the attraction that you know if the scratches no big deal. I mean, you can throw some plastic wood in it if you want or some Bondo typically. But you can just hit it with a spray can and nobody in the audience will ever see it.

I was I was thinking about like MDF has a final coating usually. And that's the same thing is the moment that it's really robust until that coating gets damaged. And then the moment any moisture gets near it. It's gone again

Yeah, yeah, no you can't. MDF can never be a professional thing because it just you get into human weather and it swells up and, and then the the vinyl pops and just like your guitar cabinet behind you there the tolex is pretty tough. But if you jab it was something you hit it on a door jamb or something. You rip it. Now you got to try and glue it back down and pretend like it didn't happen.

Yeah, actually. So I built this cab out of 13 ply Baltic birch. And yet that stuff cuts like a dream. And it's voiceless the stuff that I purchased. And which

is really important because if there are voice then the the the adjacent pie will buzz.

Yeah, it doesn't it doesn't have any of those footballs in it the little football cuts.

Well, the thing is with with normal plywood, like AC plywood or something, they'll put footballs on the A side. But there can be holes on the inner plies that really should have footballs there but they don't put footballs on the inside. So you have voids on the inside of the plywood. And so then you've got a bus and you have no idea where it's coming from because it's it's hidden inside the plywood. So you need plywood, this absolutely solid wood all the way through.

Yeah, it this stuff wasn't wasn't cheap, especially in the quantities that I was looking at. But but it certainly does the job pretty well.

So when we when we don't use Baltic birch, the primary Well, for us right now the only time we don't use Baltic Birch is when it's a weatherproof cabinet. So it's gonna be outside in the stadium. Traditionally, people would still build the cabinet on the Baltic birch, and then they would chop fiberglass onto it. It's a gun that like shoots little, little bits of fiberglass mixed with resin. And then you roll it out. And, you know, a cabinet that that weighs 80 pounds turns into 180 pound cabinet when you put 100 pounds of fiberglass on it. So we've finally moved beyond that. And we use fiberglass reinforced polyurethane foam panels, which are actually, I think about 15% Lighter than Baltic birch, but not as rigid. But the you know, the good news is that it doesn't know how to wrap just can't it's just polyurethane. So we unlike in the past where you just started out with the with the same Baltic birch cabinet that you would have made otherwise, and fiberglass to it, it just gets more rigid. There's a little more engineering involved in the call FRP the FRP material, because we have to add bracing in order to overcome the the fact that it's not as rigid as Baltic birch. But it's much more dimensionally consistent, much more weatherproof. And, and, and lighter.

You know, one other quick question about manufacturing and designing as an engineer with wood. But are there any kind of considerations when it comes to tolerancing or specifying wood on an engineering drawing? It's just not very common.

What is what is a? Well, it's it's a living thing, right? If you if you cut a piece of wood to say 60 inches in in the mid and mid summer, especially in the northern part of the country where we are, it's always much more humid in mid summer than it is in January. So if you actually cut a piece of wood to 60 inches in, say July and then you come back and you measure it in the end of January. It's going to be three sixteenths of an inch shorter. Because of that, because it's dried out and shrunk. Do the same thing reverse kind of 60 inches in January's gonna be 60 and three sixteenths inches in in July. So there is the the expanding and contracting aspect of the wood that you have to account for and designing with, especially when you know that was a big problem with outdoor speakers, less of a problem indoors but even indoors. You know, my skin always gets dried up in January. And in July, I'm sweaty all the time. So it's it's kind of the same with wood. There's also the issue that you know, they aren't they aren't harvesting birch trees in in Russia and Finland under controlled conditions. So they're drying it out and maybe you know they they have instruments or they measure the moisture content. But then it goes into ship for a month or two and it goes to a warehouse it comes on a truck and none of these are moisture controlled environment So, because the moisture content varies from batch to batch, the thickness also varies. So that's one of the challenges is that you have to use adhesives that can that can put up with the expansion and contraction. And you have to use joinery that tolerates the variability in the 12 millimeter plywood, maybe anywhere from 11.5 to 12.5. And so you have to have joinery that can adapt to that has been as tolerant of those dimensional variations. That's, that's, that's probably the primary rookie mistake that that amateurs make is just, you can't just cut a 12 millimeter dado and put a 12 millimeter piece of plywood in. That's only going to fit half the time.

You're going to have a bad day. Yeah. Well, awesome. Burger, do you have anything you would like to add in on that?

I don't think so. The, I haven't actually really thought about designing a cabinet out of like, because I built stuff that I would before but never thought about, like, extra expanding tractioning and, and stuff like that. I think that's kind of

one cabinet, you can kind of adapt like, if it does, yeah, you can just sand off the pack. That's exactly what it is. But if you're trying to build a run of 100 off, and then the half damp be done by next Tuesday, you don't have the luxury of hand fitting everyone. So you have this, you have to design for manufacturing tolerances.

Well, just like you, you're building stuff in batches, so you're going to be cutting all of one piece at one time. And then say, two weeks later, a cold front has moved through and completely, you know, changed everything all the environment. Yeah,

well, there's,

there's a lag time it takes a while for it to change. So we don't, we don't like, for instance, maybe it's the most efficient to cut 20 parts at a time. And we only need eight today, we don't cut 12 extra parts and put them on a shelf. Because by the time we get around to use them, they're going to be a different dimension. So we only cut the number of parts that we know we're going to use that week. And we're able to do that because of advances in manufacturing technology, we have what's called a nested based router, which is a CNC router with a five foot by 10 foot table, we can put a five foot by 10 foot sheet on there. And it's all obviously computer controlled. But whereas in the old days, you would you would cut plywood into rectangles and put them in templates and then cut parts out of those templates. Now we put a whole sheet on the table. And we say I want four of this part and six of this part and for this part, and the computer figures out how to lay those out on the plywood to get the best yield. And so every time we run a program gets the only time we ever run that particular program, it's calculated from scratch every time. So we can do any combination of things, we can cut two different products at the same time out of the same sheet of plywood if we want to. And because of that we're much more efficient than then professional last week of companies used to be at short runs, somebody wants to buy two of them, and it's going to cost more per unit than if we make eight of them. But in the past, it would have been twice as much now it's maybe 10% more. So we've we've designed our factory in order to be able to do short runs, because of the amount of customization and and just because you know, we have 80 products or so. And, you know, some of those products, we only do 30 A year, some of them we do 800 a year, but we have to be able to do all of them. In order to fill all the requirements for a given installation. You don't get away with just making the one that's the most profitable, you got to you got to make everything they need to do the job. And, you know, you make some profit on the on the high volume ones and, and breakeven on the little ones that you're doing just to get the get the other job. That's kind of nature of the business.

So how you have it set up is to you've you already reduced yours NRV and set up time for different products. Okay. Yeah,

we're very, we're very flexible in terms of, you know, scheduling products and, and in quantities. You know, in the in the old days, you wouldn't you wouldn't run 20 at a time no matter what you had on order. Because you had you got a template that made 20 of a given part. And there's one product, it's like, well, we got to make 2020 of them, then you're gonna make 20 sets, and we only need eight. And so you're sitting on 12 for six months. Yeah, I

got another question. I guess it's how important is the group Rain for this plywood.

It, it's not very important at all, because each ply is perpendicular to the ones next to it. So it's all alternates, you know, up and down, left and right. And these, the surface grain doesn't matter because we, you know, we, everything gets stapled together. And then we Bondo in the staple heads and round over the corners and surface, sand everything. And then it's primed, painted. Textured. And so, you know, whatever grain is there is completely invisible by the time we're done.

Gotcha. I just, I'm just thinking, like, if the CNC robot decided, hey, I'm gonna put everything at 45 degrees, because that's the most optimal stacking for your parts, it wasn't going to cause a problem.

No, it wouldn't make any wouldn't make any difference. In fact, there is a setting on the on the CNC software, you can tell it that I want it, I want this part to always be aligned with the grain, and then it won't rotate it. But we you know, we've never used that because we don't care.

See, what's been going through my mind is, if, if you did cut parts, and for some reason they didn't fit, since it's wood, you can just have a note on the on the drawing that just says sand until fit, right. And then and then all your problems are covered.

Well, there there are, you know, occasionally

critical tolerances, like where it's important from a strength point of view, or for some other reason. Where instead of just oversizing, the data on letting the glue fill the gap, we cut it line to line, and you just have to, you have to sand it if it won't go in. And we have you know, we have this special sander, that's a 42 inch wide surface Sander that we can we can run them through if we need to. But you know, that's that's pretty rare. You know, that's part of that is handle that when you're designing the cabinet, you design the cabinet specifically to avoid having to make hand fittings like that. Because that it's not only expensive, but it's also unpredictable. So I scheduled, you know, 12 hours of shop time to build this run a cabinets, and it took 15 Because we're hand fitting everything. That's a problem.

Well, fantastic. Thank you so much for being our guest today. You're welcome. This was awesome. And I could for sure talk another two hours about all the stuff.

Well, it's kind of it's kind of fun to do this because I often you know, in the heat of battle, I forget how how intriguing some of this stuff is. It's second nature after 35 years of doing it.

Yeah, so thank you so much, David for coming on to our podcast. Would you like to sign us out?

Well, that was a macro fab engineering podcast. I was your guest David gunness

and we're your hosts Parker Dolan and Steven Craig. Later one day take it easy