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-   -   A Monster Construction Methods Shootout Thread (https://www.diyaudio.com/forums/multi-way/356130-monster-construction-methods-shootout-thread.html)

augerpro 17th June 2020 07:47 PM

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.

https://i.imgur.com/QcoRN7K.jpg

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.

NiToNi 17th June 2020 09:12 PM

Wow, subscribed :up:

hifijim 18th June 2020 03:55 AM

Looks like we will all learn something.

Quote:

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.

mainframe99 18th June 2020 04:20 AM

I won't comment on the construction method of that Audi - but I'm watching this. Very interesting!

Mindsource 18th June 2020 06:14 AM

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.

Baldin 18th June 2020 02:50 PM

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

Mindsource 18th June 2020 02:55 PM

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.

454Casull 18th June 2020 03:00 PM

Alright! Looking forward to the progress and results.

augerpro 18th June 2020 06:36 PM

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.

454Casull 18th June 2020 06:49 PM

Quote:

Originally Posted by augerpro (https://www.diyaudio.com/forums/multi-way/356130-monster-construction-methods-shootout-thread-post6245271.html#post6245271)
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.


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