Custom speaker enclosure, as innert as possible

[mike7877]

So far, I've
- braced my CLD cabinets, pushing the first (and only significant) resonance from 260Hz to 455Hz.
- improved driver/case coupling by glueing in T-nuts for the woofer (and tweeter!!)

The difference in clarity and voice/piano realism was immediately apparent with the added bracing. I was really surprised with the improvement I got from doing this with these speakers. I've always increased bracing in speakers I buy, and the improvement this time was easily 4x any of them (and no, there was nothing malfunctioning before). After this massive improvement, when I did the T nuts, I couldn't tell the difference. But they needed to be done anyway because after 5-6 driver reinsertions, it was obvious the MDF wasn't holding as before. Also, oddly, wood screws with thick threads weren't used!
Machine screws!... Such a weird choice - especially at the price point! Honestly, it was probably a sufficient solution for if you only ever replace a blown driver (hopefully never lol) but still...

So yeah... So far, I've done all the easy stuff for these speakers, except for swapping the [sole] unattached fill within the sealed box, to a combination of foam on all outside walls + the correct amount less unattached fill for the same effect (although with less internal reflection). If you consider the bracing improvement as "100%", modding the fill this way might add another 15%.

Since these drivers are exceptionally low distortion (esp 3rd harmonic), I've been thinking...
Instead of making a couple more incremental improvements to the standard included boxes, why not go for gold and make a nearly innert cabinet?! Weight-no-object! Lol

In that vein, I've been thinking... instead of a rubber CLD, how well would a 1/4" thick rubber enclosure contained within a 1.5" thick concrete box with" sand as a buffer in between work? Like 0.5 to 1" sand. And for when the woofer moves outward, the vacuum created within is countered (on the rubber) by a lattice of thick steel wire spaced horizontally and vertically, equidistally 1.5" (apart), and present wherever possible (ie. When it can cross from one side to the other, both sides rubber only - if the driver or crossover is in the way on one or both sides, not there!)

Or is the sand unnecessary, and I should just glue or set the rubber directly on the concrete?

What about other ideas for as innert as possible enclosures? I have a feeling this winter's gonna be colddddd, so I don't mind a more involved project - especially if it'll pay off with listening enjoyment!

 

[Petrushka]

The first issue of Audio magazine I saw had plans for a concrete speaker.

 

[kemmler3D]

So far, I've
- braced my CLD cabinets, pushing the first (and only significant) resonance from 260Hz to 455Hz.
- improved driver/case coupling by glueing in T-nuts for the woofer (and tweeter!!)

The difference in clarity and voice/piano realism was immediately apparent with the added bracing. I was really surprised with the improvement I got from doing this with these speakers. I've always increased bracing in speakers I buy, and the improvement this time was easily 4x any of them (and no, there was nothing malfunctioning before). After this massive improvement, when I did the T nuts, I couldn't tell the difference. But they needed to be done anyway because after 5-6 driver reinsertions, it was obvious the MDF wasn't holding as before. Also, oddly, wood screws with thick threads weren't used!
Machine screws!... Such a weird choice - especially at the price point! Honestly, it was probably a sufficient solution for if you only ever replace a blown driver (hopefully never lol) but still...

So yeah... So far, I've done all the easy stuff for these speakers, except for swapping the [sole] unattached fill within the sealed box, to a combination of foam on all outside walls + the correct amount less unattached fill for the same effect (although with less internal reflection). If you consider the bracing improvement as "100%", modding the fill this way might add another 15%.

Since these drivers are exceptionally low distortion (esp 3rd harmonic), I've been thinking...
Instead of making a couple more incremental improvements to the standard included boxes, why not go for gold and make a nearly innert cabinet?! Weight-no-object! Lol

In that vein, I've been thinking... instead of a rubber CLD, how well would a 1/4" thick rubber enclosure contained within a 1.5" thick concrete box with" sand as a buffer in between work? Like 0.5 to 1" sand. And for when the woofer moves outward, the vacuum created within is countered (on the rubber) by a lattice of thick steel wire spaced horizontally and vertically, equidistally 1.5" (apart), and present wherever possible (ie. When it can cross from one side to the other, both sides rubber only - if the driver or crossover is in the way on one or both sides, not there!)

Or is the sand unnecessary, and I should just glue or set the rubber directly on the concrete?

What about other ideas for as innert as possible enclosures? I have a feeling this winter's gonna be colddddd, so I don't mind a more involved project - especially if it'll pay off with listening enjoyment!

Weight-no-object does open up some options.

Concrete is not said to be that great for enclosures on its own because it does ring a bit due to its very high stiffness (?).

Sand is thought to be a pretty good material though, because it's dense and has good damping. There are some threads on DIYAudio about "onken" builds using sand layers.

The rubber idea is interesting but I think it's mostly useful as a damping layer, i.e. in between two stiff layers.

I had thought about building speakers for a while. My idea was to 3D print the cabinet with multiple empty layers that could be filled with sand and concrete in alternating layers. The basic idea as I understand it is to either internally reflect or damp vibrations trying to move out of the cabinet. So sand for damping (or CLD stuff) and alternating high and low density layers for internal reflection and transmission loss.

 

[mike7877]

Weight-no-object does open up some options.

Concrete is not said to be that great for enclosures on its own because it does ring a bit due to its very high stiffness (?).

Sand is thought to be a pretty good material though, because it's dense and has good damping. There are some threads on DIYAudio about "onken" builds using sand layers.

The rubber idea is interesting but I think it's mostly useful as a damping layer, i.e. in between two stiff layers.

I had thought about building speakers for a while. My idea was to 3D print the cabinet with multiple empty layers that could be filled with sand and concrete in alternating layers. The basic idea as I understand it is to either internally reflect or damp vibrations trying to move out of the cabinet. So sand for damping (or CLD stuff) and alternating high and low density layers for internal reflection and transmission loss.

Hmm... I always thought that the very high stiffness would mean the resonance would be very high, and since there is less energy in the higher frequencies, it wouldn't be excited as easily... But you're right, I think I'll stick to a more traditional mix of materials.

A 3D printed box would be pretty cool, it could be a very intricate TL design, too. You'd need a pretty big printer to make it in one go, though

 

[kemmler3D]

I always thought that the very high stiffness would mean the resonance would be very high, and since there is less energy in the higher frequencies, it wouldn't be excited as easily...

I think this is true, but in DIYAudio threads this comes up pretty regularly and a few have mentioned that concrete tends to 'ring' when struck.

You'd need a pretty big printer to make it in one go, though

Yes, but they exist (1x1x1m printers) but you can also make big stuff on a home printer if you're willing to glue pieces together. ABS prints can be "welded" together with acetone to be airtight. I am currently printing a 36-piece part myself, so it's all a matter of patience I think. This would be something to do if you have CAD skills or want to collaborate with someone who does (for a fee) because I don't think there are simple designs floating around out there.

The main advantage of 3D prints is you can make the interior and exterior shapes whatever you want, so waveguides, curved baffles, spherical enclosures and so forth are no more difficult to build than a square box.

 

[DavidMcRoy]

CLD = ?

 

[kemmler3D]

CLD = ?

Constrained layer damping. By using certain viscous adhesives between layers of MDF or other stiff layers you can absorb some of the sound passing through the cabinet and turn it into heat.

 

[MAB]

Did you take measurements? Especially measurements of the sound…

I ask because I have built quite a few cabinets with a variety of bracing, and while I can measure small differences in driver impedance, and small changes in cabinet resonance. But really no change to the actual sound (i.e. below run to run measurement variation).

I’ve done tons of work with different stuffing, small portion posted here:

Genelec 8351B Teardown (2nd Disassembled)

So what the…. Are you trying to “improve” suggesting other stuffings should be used? When distortion or linearity isn’t a problem at the midrange anyway????? Short time reflections aka small resonances are audible even if you can hardly see them in standard measurements like the amplitude...

www.audiosciencereview.com

Polyfill works great. Other fancy stuff wasn’t a game changer.

I have addressed other aspects, like taking measurements of hollow steel stands (they ring like a bell, right?) before and after filling with special ‘sonic sand’ that I had lying around, no measured difference.

Springs Under My Speakers: What's Happening?

LOL, let's keep going, prove that you have a window. I want proof Purite Audio even made that post before it's worth answering. Could have been hacked. Or his wife posted while he wasn't looking.

www.audiosciencereview.com

I ask for some measurements because people often make sighted observations, often bolstered by a reasonable sounding plea (of course a stand will ring and fancy-sand should fix it (not!), seems reasonable that advanced materials should perform better than Dacron (not!).

And I’ve built so many cabinets, the geometry and volume primarily determine the sound unless I really botch the job. At some point I will post some new measurements of a 15” woofer in three different cabinets of the same volume and dimensions, each one successively more Skookum than the next, and the differences just don’t exist.

Listening to these tweaks without measuring is a recipe for self deception.

 

[mike7877]

Did you take measurements? Especially measurements of the sound…

I ask because I have built quite a few cabinets with a variety of bracing, and while I can measure small differences in driver impedance, and small changes in cabinet resonance. But really no change to the actual sound (i.e. below run to run measurement variation).

I’ve done tons of work with different stuffing, small portion posted here:

Genelec 8351B Teardown (2nd Disassembled)

So what the…. Are you trying to “improve” suggesting other stuffings should be used? When distortion or linearity isn’t a problem at the midrange anyway????? Short time reflections aka small resonances are audible even if you can hardly see them in standard measurements like the amplitude...

www.audiosciencereview.com

Polyfill works great. Other fancy stuff wasn’t a game changer.

I have addressed other aspects, like taking measurements of hollow steel stands (they ring like a bell, right?) before and after filling with special ‘sonic sand’ that I had lying around, no measured difference.

Springs Under My Speakers: What's Happening?

LOL, let's keep going, prove that you have a window. I want proof Purite Audio even made that post before it's worth answering. Could have been hacked. Or his wife posted while he wasn't looking.

www.audiosciencereview.com

I ask for some measurements because people often make sighted observations, often bolstered by a reasonable sounding plea (of course a stand will ring and fancy-sand should fix it (not!), seems reasonable that advanced materials should perform better than Dacron (not!).

And I’ve built so many cabinets, the geometry and volume primarily determine the sound unless I really botch the job. At some point I will post some new measurements of a 15” woofer in three different cabinets of the same volume and dimensions, each one successively more Skookum than the next, and the differences just don’t exist.

Listening to these tweaks without measuring is a recipe for self deception.

I didn't take measurements (other than to determine box fs, of course), but I did knock on the cabinets and they sounded like boxes before, and now they sound almost dead. I also played loud music with my ear pressed against the enclosure before and after, and before it was very lively, after, a lot less.

I'll explain the difference in sound so I know you don't misunderstand. Things just sound more realistic now, and quieter - particularly quieter in the upper upper bass, lower midrange, and midrange. The room they were in when I did the bracing was very lively - no rug and nothing on the walls, which could contribute to how pronounced the effect was from minimizing indirect sources of sound. If I were to estimate, I'd say 3/4 of the benefit gleaned was from reduced reflections off the rear and sides from the walls, floor, and ceiling, and 1/4 from reduction of internal reflections coming back out through the front of the speaker. Have you ever cupped your hands behind your ears from the listening position and appreciated the increased fidelity from your system? Like that, but without the horn effect. And less treble.

Somewhat related - when my Infinity SM-112s' woofers' foam surround rotted and some proprietary component busted itself in the right's complex crossover, causing reduced midrange output, I decided repair was too complicated, and, if attempted, had no guaranteed outcome. Over the years, I had really enjoyed their sound, especially the midrange and lower treble - very clear, very dynamic. Balanced. The speakers were rated 99dB/W. I started by removing one of the midranges, its job before: 900-4500Hz. I hooked it up directly to the amp, held it beside the one still working speaker, and when I compared the level coming out of it sans crossover to the full speaker, it was a good 6-8dB higher than the speakers, maybe even 8dB. Let's say they're 106dB/W. The midranges were closed back, maybe 0.7 liter volume, the rear was molded plastic - cylindrical, 4.5" diameter, and 4" deep. At the center of the back was a single screw, which looked like it was melted in place. I took both midranges out, put them on my bench, fed them through a resistor, measured the voltage across the resistor, and determined their resonant frequencies. They were matched to 1Hz. I then cut into the midrange with scissors to see behind it, and literally everywhere that wasn't the basket or the magnet or the coil or the cone, was fill.
Why am I telling you this? Because... I know for a fact that if you could go back in time and switch out one of my midranges from a 310Hz resonant frequency to 353Hz at the factory, then, at some random time around year 7 of ownership, put a proper 310Hz midrange into my speaker (like there should be), I would not be able to pinpoint the time that the tone of my speakers changed for the better. I probably wouldn't have ever picked up on the difference. Same if at the factory someone removed 2/3 of the fill in one mid cylinder. But if, at year 7, someone were to swap the mid in one speaker with one that had no fill and a 60Hz higher Fs, and swap a tweeter in that same box from previously 1546Hz like the other, with one that's 1970Hz, then brace the heck out of that same cabinet with the different drivers, I wouldn't have been as happy with these speakers over the years as I'd been. One of the things I liked about them was their balanced (left to right) and exceptionally clear and accurate in the 1-7kHz range. Of course, I can't prove I'd be able to hear that difference, but everyone who makes speakers that sound exceptional, they fill their cabinets with a specific amount of fill, they use matched parts, they use low tolerance parts, things are symmetrical. When you hear a speaker that's truly special, no exception, they've done these things. Can you ask someone to listen to a pair of speakers, then swap a tweeter with one with a 15% higher Fs, play that same song to them, ask them what you changed, and they tell you "you switched the right tweeter with one that has a different resonant frequency... I'm fairly sure it's higher and the percent is at least 5% but no more than 20 - my money's on 15%"? No, you can't. Not without it being an accident or the listener being an engineer with measurement equipment, and the "song" was a frequency sweep.

The more you get right, the less you can get wrong. Which brings me to my best point:

The drivers in the speakers I'm talking about in this thread, are exceptional. How exceptional? Well, they're second to none in a few regards. Probably most notably, third harmonic distortion in the woofer is -70dB from 100Hz to 3000Hz, and no more than -55dB second through the same range (though usually 5-15dB lower than that). And the tweeter is basically the same - -70dB third harmonic from 2kHz up, 2nd is not much higher. The crossover is made with 1% parts, low-gauge air core inductors,... At the time I was using my 140WPC class A amplifier with 13x 200W Sanken power transistors per channel and a 1kW toroid... Extremely low resistance, low inductance speaker cables, high quality recordings I'm very familiar with... These things all contribute to making changes obvious - when the loudspeaker drivers perform at the level of solid-state electronics, case radiation and the room reflections from it mucking things up will be more obvious.

Remember, also, that I did say I'd never had anywhere near this much change from improving the internal bracing of any other speaker...

 

[DanielT]

For pure subwoofers, playwood is an excellent material. Maybe even the best? Properties that suit subwoofers very well. Plus it's not particularly heavy.

For full-range speakers, MDF is excellent. As far as I know anyway. Easy to work with as well.

Sand and concrete were addressed in the thread. Here are two threads about it:

Rauna Freja Vintage 2-Way Loudspeaker Measurements

Today I present measurements on a pair of Rauna Freja, aka affectionately as 'Swedish Tombstones';). They are a small 2-way in a concrete cabinet. I believe that Bo Hansson was involved with the design. I would appreciate any information members have regarding this nice little speaker. These...

audiosciencereview.com

Fill sections with sand? DIY speakers.

Meaningful? Unnecessary? What do you think? In general, can sand add anything positive?Mute resonances, get increased stability or not? Sand, for full-range speakers, and or for subwoofers. Sand, fine-grained that I can also strain and dry, I have as much as I want, for free. The question is...

audiosciencereview.com

Here is what a technical consultant in acoustics and audio technology has to say on the subject of box material:

Vibrations, unwanted in speaker box.

For bass boxes, plywood construction and stiffening frames are enough (more than enough).

For broadband boxes, where structural resonances are inevitably obtained in the passband, plywood should be avoided and instead MDF should be used due to the significantly higher loss factor. Small speakers do not need bracing, but larger structures should be provided with bracing frames.

Resonances in the element baskets only pose a problem if they significantly affect the frequency response or the distortion, but this is in practice only the case for weak sheet metal constructions or, alas, plastic ditto.

(By the way, using only low-density materials without proper sizing is asking for trouble).

faktiskt.io • Visa tråd - Vibrationer, oönskade i högtalarlåda.

Wall material for bass box - what to use?

The high E-module (material stiffness) for plywood is a big advantage compared to MDF for bass modules and it then matters less that the loss factor (material damping) is lower.

Questions like this come up quite often and so it might be worth illustrating roughly what it looks like. Here is a simulation with a 12-inch element/driver weighing about 9 kg (15 mm plywood - cube with 43 cm side, rho = 600 kg/m3, E-modulus = 7 GPa,, isotropic properties, ideal adhesive joints, no internal bracing):

Interestingly, it's the rear that kicks in first in this case, something to contemplate when various manufacturers brag about their thick baffles.

A first structure mode at about 300 Hz means that the structure sound radiation (box sound) becomes completely inaudible in practice when the upper limit frequency is 80 Hz, almost regardless of the steepness of the LP filter.

The second mod can also be interesting to gain a little more understanding (the back basically doesn't move at all):

faktiskt.io • Visa tråd - Väggmaterial till baslåda- vad använda?

 

[MAB]

Remember, also, that I did say I'd never had anywhere near this much change from improving the internal bracing of any other speaker...

It's impossible to judge the actual change without a measurement.
Bracing is a tiny part of the speaker performance. It would be nice to see a thread where bracing is applied, and detailed measurements are taken, so we can see what is actually happening, and what is not happening.
Good example is Erin with the Tekton Troubadour speaker review. It was claimed the holes in the cabinet from not installing the feet caused a bunch of audible resonances. Erin measured the impedance and resulting sound, found no change in the resonance in question, and a small change in enclosure tuning.

You quote measurements from spec sheets all the time, I thought you would in kind make some measurements to support claims that there are audible changes.

The drivers in the speakers I'm talking about in this thread, are exceptional. How exceptional? Well, they're second to none in a few regards. Probably most notably, third harmonic distortion

Why not just post the distortion measurement? You said lots of other things, right down to the amplifier bias, transistor type, output impedance claims, but no actual measurements.

I'll explain the difference in sound so I know you don't misunderstand.

Please don't.

 

[DVDdoug]

I ask because I have built quite a few cabinets with a variety of bracing, and while I can measure small differences in driver impedance, and small changes in cabinet resonance. But really no change to the actual sound (i.e. below run to run measurement variation)...

...And I’ve built so many cabinets, the geometry and volume primarily determine the sound

That matches my assumptions and intuition.

You can measure cabinet vibrations but with a well-built cabinet they should be very small and produce very little sound compared to the intentional vibration of the drivers.

You CAN get resonances from the interior dimensions, and that resonant sound can leak-out through the woofer. Damping helps with that. Maybe some fancy cabinet shapes or internal diffusion can spread-out the resonances, making them less intense.

Making a cabinet that's crazy-dense, or other exotic techniques, probably isn't the best use of time & money... There's nothing wrong with fun experiments but there are probably easier ways to improve the sound.

 

[MAB]

That matches my assumptions and intuition.

You can measure cabinet vibrations but with a well-built cabinet they should be very small and produce very little sound compared to the intentional vibration of the drivers.

You CAN get resonances from the interior dimensions, and that resonant sound can leak-out through the woofer. Damping helps with that. Maybe some fancy cabinet shapes or internal diffusion can spread-out the resonances, making them less intense.

Making a cabinet that's crazy-dense, or other exotic techniques, probably isn't the best use of time & money... There's nothing wrong with fun experiments but there are probably easier ways to improve the sound.

Yes, completely agree. And measurements I have posted in the past support what you are saying.
Many of these alleged 'panel resonances' are actually resonances due to internal dimensions. Internal waves are mitigated by much different methods than bracing panels. I posted measurements, completely consistent with your experience. And also agree with you that fancy internal diffusion can mitigate these internal resonances:

It's a PITA, and this construction tames only one of the internal cabinet modes. That's a ton of work compared to just putting some polyfill and taming all three modes! And if not done right those diffusers will rattle and cause new problems that are potentially quite audible. Polyfill is very effective at taming these internal midrange resonances as I show, and much easier and less messy. That said, it is really disappointing to many people who want to believe that these exotic efforts are critical to good speaker building. They are not, a few good slabs of Baltic birch or MDF and moderate quantities of (very unsexy) polyfill are what is needed

We have an entire fifth-column of people on ASR obsessing on fancy cabinets (like Magico's enclosure absurdity). No measurements are ever provided. It's quite counter to ASR's methods and goals, and further confuses and misdirects people as to what is really important in speakers.

The difference in clarity and voice/piano realism was immediately apparent with the added bracing.

Comments like this need to be supported with actual measurements of the sound. Using ASR as a lunch pad for unscientific speculation, claims of exceptionally low distortion, etc. should be supported by evidence.

 

[DavidMcRoy]

Back around 1990, I bought a pair of Tannoy System 12 DMT monitors, which I still have. (I also specified and used the 8-inch model at work in a television station.) Tannoy appears to have done considerable research ahead of this design, which features top, bottom and side cabinet panels which are “floated” within damping material as a means of attaching them to an MDF space frame which connects a solid MDF baffle and rear panel.

 

[terryforsythe]

What about other ideas for as innert as possible enclosures?

Granite sounds interesting.

Acora Acoustics | Monumental Loudspeakers | Canada

Loudspeakers | Acora Acoustics | Monumental | Granite | Quartzite | Gemstone| Monumental

www.acoraacoustics.com

 

[sktn77a]

Whether you like the LS3/5A or not, more science-based research was conducted on it's cabinet that most (all?) modern speakers.

https://downloads.bbc.co.uk/rd/pubs/reports/1976-29.pdf

 

[DanielT]

Whether you like the LS3/5A or not, more science-based research was conducted on it's cabinet that most (all?) modern speakers.

https://downloads.bbc.co.uk/rd/pubs/reports/1976-29.pdf

Maybe for its time, but these days with all the simulation programs, well, you get further. In addition, according to that report, two different materials were tested: Birch plywood with fillets of beech vs.... hard wood such as Parana Pine for the fillets.. which turned out to be.. unacceptable.


Ok I don't understand what they mean by fillets. Where and how much fillets? But that aside, no measurements are shown on how it differs. What you want to see is several measurements with different materials with different combinations of damping materials in the box. BBC only shows measurements with plywood.

If we take plywood and compare it to MDF, speaking of simulations, see #10 above:
For broadband boxes, where structural resonances are inevitably obtained in the passband, plywood should be avoided and instead MDF should be used due to the significantly higher loss factor.

 

[mike7877]

It's impossible to judge the actual change without a measurement.
Bracing is a tiny part of the speaker performance. It would be nice to see a thread where bracing is applied, and detailed measurements are taken, so we can see what is actually happening, and what is not happening.
Good example is Erin with the Tekton Troubadour speaker review. It was claimed the holes in the cabinet from not installing the feet caused a bunch of audible resonances. Erin measured the impedance and resulting sound, found no change in the resonance in question, and a small change in enclosure tuning.

You quote measurements from spec sheets all the time, I thought you would in kind make some measurements to support claims that there are audible changes.

Why not just post the distortion measurement? You said lots of other things, right down to the amplifier bias, transistor type, output impedance claims, but no actual measurements.

Please don't.

"It's not impossible to judge a change without measurements."
I enabled the tone control and turned treble to +5.
"I can hear there's more treble now."
"No, you can't! Not without measurements!"

I didn't make measurements before the bracing, and I'm certainly not going to remove it to prove something I already know to be the case...

If bracing didn't make an audible difference, cabinets wouldn't be braced. All I'm saying in my post is that all the parts are state of the art, and when something is near perfect, problems are more obvious

 

[mike7877]

Did you take measurements? Especially measurements of the sound…

I ask because I have built quite a few cabinets with a variety of bracing, and while I can measure small differences in driver impedance, and small changes in cabinet resonance. But really no change to the actual sound (i.e. below run to run measurement variation).

I’ve done tons of work with different stuffing, small portion posted here:

Genelec 8351B Teardown (2nd Disassembled)

So what the…. Are you trying to “improve” suggesting other stuffings should be used? When distortion or linearity isn’t a problem at the midrange anyway????? Short time reflections aka small resonances are audible even if you can hardly see them in standard measurements like the amplitude...

www.audiosciencereview.com

Polyfill works great. Other fancy stuff wasn’t a game changer.

I have addressed other aspects, like taking measurements of hollow steel stands (they ring like a bell, right?) before and after filling with special ‘sonic sand’ that I had lying around, no measured difference.

Springs Under My Speakers: What's Happening?

LOL, let's keep going, prove that you have a window. I want proof Purite Audio even made that post before it's worth answering. Could have been hacked. Or his wife posted while he wasn't looking.

www.audiosciencereview.com

I ask for some measurements because people often make sighted observations, often bolstered by a reasonable sounding plea (of course a stand will ring and fancy-sand should fix it (not!), seems reasonable that advanced materials should perform better than Dacron (not!).

And I’ve built so many cabinets, the geometry and volume primarily determine the sound unless I really botch the job. At some point I will post some new measurements of a 15” woofer in three different cabinets of the same volume and dimensions, each one successively more Skookum than the next, and the differences just don’t exist.

Listening to these tweaks without measuring is a recipe for self deception.

Unfortunately I didn't take measurements - I didn't expect the improvement to be so great. I did do one speaker one day, and the other the next, and I listened that night. When I listened, the usually balanced sound was no longer balanced - the braced box was quieter, notably in the upper upper bass and lowest midrange (around the boxes resonance, which I measured by knocking on it). I didn't notice the difference in sound quality until both boxes were done, but there was definitely a level change. Could it have been that the boxes weren't that great to begin with? Possibly... When rapping on the outside, they sounded very much like boxes before, and dead after

 

[mike7877]

Granite sounds interesting.

Acora Acoustics | Monumental Loudspeakers | Canada

Loudspeakers | Acora Acoustics | Monumental | Granite | Quartzite | Gemstone| Monumental

www.acoraacoustics.com

Not bad! And for 20L boxes, I could probably use scraps from countertops or something