A Monster Construction Methods Shootout Thread

Which wood to use? Which fill? What does bracing do? Is CLD best? I'm starting this project to start quantifying some answers to these questions. A lot of work has been done before in fits in starts by others (BBC, Kef, etc.) but they were often narrow investigations and you couldn't compare results because measurement conditions were different among the different studies. Some have cited manufacturer's damping specs, but I have no idea how that translates to the real world. Ditto on accelerometer data. So here I will be doing SPL measurements, that is after all, what we actually hear. The cabinet is ordinary, large enough for the panels to have some radiating area and magnify differences between changes.

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I will be using a Peerless 830970 firing into the cabinet using MLS signals. I have to test mic placement, but it will probably end up near-ish field, probably at a side panel. When I do the fill/lining I will mount the SB15 as a dummy woofer and measure what radiates through it. I intend to measure SPL, CSD, and THD. Any other recommendations appreciated.

For the material test I currently have: high and low quality plywood in 1/2" and 3/4", and MDF in 1/2" and 3/4".

For the fill and lining I have: SDS CLD tiles, AcoustX coating, denim insulation, polyfill, 1" thick dacron blanket (what the TL guys use) and Sonic Barrier.

For bracing I will do: simple oak crossbrace versus oak crossbrace using CLD construction with Sikaflex 292i adhesive. I also have some microspherules to combine with the adhesive to see how that changes things.

I would appreciate all suggestions on any other additions to the above. A priority will be that the materials must be widely available and reasonably priced, and the methods must be accessible to an ordinary DIYer.
 
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Looks like we will all learn something.

When I do the fill/lining I will mount the SB15 as a dummy woofer and measure what radiates through it.

I recommend testing with the SB15 terminals shorted. I think this would represent a low-output-impedance amp (yes?) and also with terminals open. I am curious how much the amplifier controls sound transmision through the cone above resonance frequency.
 
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Glad you are trying sikaflex with microspheres. As I’m sure you know, Geddes used two part shore A + microspheres in approx 1:1 ratio. But for the average home gamer the two part PU is expensive and hard to work with. Sikaflex + microspheres in 1:1 ratio is what the average diy’er would have access to. Maybe you would be willing to try the sikabond construction adhesive as well. It’s has similar specs to the 292i, but is easier to find and is a fraction of the price.
 
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Great stuff. Subscribed.

I'll try to dig out some material which might be helpful .... seem to recall some German sites with quite through investigation, test and sound examples.

Besides measurements, it would be nice with some kind of sound samples for us to hear .... not sure how or what ... just a thought
 
Maybe good to construct a good non CLD box, get it to resonate, then CLD brace it and use tape accelerometer to see if resonance goes down.

Also for fill, might want to try pink fiberglass. If you look in the window seal and door sweep section you can sometimes find small packs that are perfect size to fill a few speakers, instead of buying the big pink panther bags.
 
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To answer some comments in another thread: the SB15 will only be used when testing fill or soft lining to simply see what radiates back out of the box due to internal dampening. For box material and methods (CLD), and bracing, there will be no SB15 mounted (or even a hole for it). Just the Peerless driver.
 
I will be using a Peerless 830970 firing into the cabinet using MLS signals. I have to test mic placement, but it will probably end up near-ish field, probably at a side panel.
Will you consider also doing acoustic SPL measurements at 1 m distance from a side panel as well, and especially at varying angles? If we treat the side panel as a diaphragm that vibrates mostly in phase, it would be very interesting to see whether there is constructive or destructive interference "off-axis" that might impact how people hear the sound of the enclosure at the listening position.
 
Yeah I'm going to try various distances and angles and see what looks most informative and consistent before I decide on a standard.
Sounds good. It's a bit like the trick of using a side-firing woofer to minimize the bass distortion in the direct field (90-degree off axis response on a woofer is a really good acoustic filter for H3 and up, depending on where you cross it). Works especially well when you would otherwise get distortion peaks due to cone breakup.
 
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For cabinet material, don't just stick to wood.

Slate stone, with its layered composition, dampens (damps? English is not my first language..) about 2.2 times more than MDF of the same thickness.

Boxenselbstbau - Gehausematerial - connect
(Article in german, use Google translate if needed)

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("Schiefer" is slate in german)

I've built multiple speakers (and for optics, my amp as well 🙂 using slate.

tQWP6JC.jpg


The big towers (Heissmann Acoustics "Samuel HQ") use 2.8cm thick slate, which would come down to about 6cm MDF thickness 🙂

They are DEAD 🙂

Ordering it cut to size is pretty expensive, but I found out you can buy slate stone tiles pretty cheap (the small Needle speakers cost about $65 in tiles in total, 1.5cm thickness), and a $60 angle grinder and a $6 diamond blade cut through it like a hot knife through butter. I found it was just as easy to cut the slate tiles to size as it is to cut MDF!

It's heavy though - I build the big speakers horizontally on my bench, had to put them upright with help from my brother and had back-aches for two weeks after :-/
My guess would be they're at *least* 90kg a piece, maybe even over a 100kg...
 
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