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Ask enough questions and sooner or later you're bound to ask a good one. :devil:

Some of this stuff is not as strait forward as it would seem at a glance. Given the size and weight of some of the subs built here, it would be nice to know what has maximum effect for minumum weight penalty. I wish I had taken more math and physics in school. It would have been useful. Confusing, but useful.
 

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The more I've been thinking about this the more I think that a single point brace could be nearly as effective as one running the full length
If I understand damping properly, it is the process of converting energy stored as momentum to energy stored as heat through friction.

In order for the single point brace to be effective, enough energy being applied to the mass, the side of the box, has to be transfered to the single point brace rather than vibrating the mass (which transfers energy to the surrounding air as sound waves). Something tells me that dosn't happen.
 

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In order for the single point brace to be effective, enough energy being applied to the mass, the side of the box, has to be transfered to the single point brace rather than vibrating the mass (which transfers energy to the surrounding air as sound waves).
The brace serves as a point on the surface which is constrained and cannot move. The material could still flex between the brace and the next point of constraint.
 

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The material could still flex between the brace and the next point of constraint.
That is exactly why I don't think it will be as effective as you think. Unfortunately the math/physics is beyond me.
 

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It seems one important aspect of resonance is being forgotten, quality factor (Q). Audibility of resonances has been established based on Q, frequency, source material and acoustic environment all related to transducer output level.

One example where understanding this situation is vital would be a tower speaker which has each set of drivers divided into their own sub chambers using typical bracing techniques. Such a technique would seem to be superior in terms of minimizing resonances due to added bracing, but as the panels are divided out the panel Q is likely lowered causing more easily excited resonances that will be more audible over a larger range.
 

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Its easy to ignore what you don't understand. ;) I have seen the term used in several places/contexts, but I don't remember ever reading a good explanation of exatly what it is. Sort of reminds me of Q from StarTrek. :)

Alright, a quick search turned up the following:
Q can be thought of as an overall system response, accounting for resonance of the system. In general, systems with a low Q can recover from resonance quickly
Sounds like damping [factor] or something related to me.

Andrew. Is there a good write-up somewhere on Q as it relates to cabinet construction?
 

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I am not aware of a write-up on Q as it relates to cabinet construction. My knowledge comes from studying physics and working with various materials as well as discussion with others.



This is an example of three different quality factor levels of resonances. In general the higher Q values are less audible all other factors held equal.
 

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Q is directly related to damping, and is another useful way of expressing it.

Such a technique would seem to be superior in terms of minimizing resonances due to added bracing, but as the panels are divided out the panel Q is likely lowered
I'm curious on this as it seems counter intuitive. How's it work?
 

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I'm curious on this as it seems counter intuitive. How's it work?
As the panels modal bands are spread out by chamber separation there is a far wider energy spread. This causes a larger range of resonances which are more easily excited.

In other words the Q is lowered due to the energy dispersal which makes the resonances more audible as shown in peer reviewed research. Additionally, this lower Q means the resonances are spread across a larger range meaning they are more likely to be excited.
 

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is staining a quality plywood the only option or can you paint with good results? Assuming a good 7 ply without voids and smooth surfacef
Posted via Mobile Device
 

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EDIT: NVM I didn't 'see' the 1st 2 pages for some reason! :)

If you really want to get fancy, you can buy pre-finish and finished sheets - Here is one source I know of: <http://www.industrialplywood.com/04prod_cab_index.html>

Hope this helps!
 

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You can veneer the plywood or bondo it to fill the grain and then paint it.
I started painting mine flat black but due to the temperature in MD right now I only have 1 coat on.

I am using home depot mixed flat black interior paint, about $9 a can. I sanded it down with 300 grit until it had a soft texture and finished with a sand sponge. I did not use a primer ,but rather just started painting.

I also painted as much of the interior as possible (can't get into the vent work at all but the main cavity was easily done. I figured this would seal and strengthen the interior.

I have only put one coat on as of now, sanded with the sandsponge. Its nice and smooth, pretty impressive so far for only one coat. When it gets warmer (april) I will put 3 more coats on till its uniform. Make sure you sand in order to flatten the grain because the water based interior paint raises it up.

I would have used a wood finish because i used expensive oak plywood but I didnt want to showcase the woodfiller i used on a few seams (I did most of the cutting with a braced jigsaw and home depot's free cuts)
 

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In other words the Q is lowered due to the energy dispersal which makes the resonances more audible as shown in peer reviewed research. Additionally, this lower Q means the resonances are spread across a larger range meaning they are more likely to be excited.
Do you have any reference to the research? I'd be interested in reading up on it.
 

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For the topic of resonance audibility I recommend the following paper. Not only is it a superb meta-analysis of previous research, but it also expands greatly on the subject.

  • Toole, Floyd E.; Olive, Sean E. The Modification of Timbre by Resonances: Perception and Measurement. J. Audio Engineering Soc., Vol. 36, No. 3 Pages 122 - 142. March 1988.

Other recommended readings such as those that deal with preference of non-resonant speakers can be found here:

http://www.avsoundlab.com/recommended readings.htm
 

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Use maple ply, you will have very minimal grain. If you are still worried, I think they make grain fillers. Oak ply looks good painted black with the grain showing.

Otherwise that is the benefits of MDF, very smooth and easy to paint. You will need to hide all th rough edges.

I don't recommend trying to bondo the entire box, that would be a ton of work and results will be less than stellar.


is staining a quality plywood the only option or can you paint with good results? Assuming a good 7 ply without voids and smooth surfacef
Posted via Mobile Device
 

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Use maple ply, you will have very minimal grain. If you are still worried, I think they make grain fillers. Oak ply looks good painted black with the grain showing.
This is an example of red oak veneer painted black that I recently finished:



I don't recommend trying to bondo the entire box, that would be a ton of work and results will be less than stellar.
This depends on the quality of workmanship. If the proper time is taken a bondo job will allow for a completely wood grain free paint job. It is no quick task, but very possible.
 

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Hey! Where are the build pictures and story behind this most excellent "PULSE" build?? Us DIYers want to know.
I have build pics somewhere. I will look for them and get them posted sometime soon. The story is fairly simple. The Axis 15 was bought during the big sale for someone who wanted to replace his Servo. It is in a 5 cubic sealed cab and is being run by an EP2500, yet it is very amp limited...

The other day he was running low test tones and the Servo was cutting out at 103dB with large amounts of distortion. He had the Axis at 118dB (5x the output!) and said the driver was barely moving yet it was producing scarey SPL with no audible distortion. Fun part is the EP2500 can barely use half of the Axis's conservatively rated XMAX.
 
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