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IG81 6th April 2009 03:55 PM

Sealed box dimensions influence
 
Hello,

Even though my question is not a Fullrange-exclusive topic, I will apply the answers to a sealed FR speaker system, thus my asking it here.

I was wondering what the influence of different box dimensions might be for a same total sealed volume.

I had originaly idea of making a box 9" x 14.5" x 23.5" for a volume of ~50L.

What if for example I would be to make that 8" x 8 " x 48", resulting in ~50L again, would I be getting half-wave resonances and standing waves at lower frequencies because of the longer 48" dimension? This would affect driver placement along that dimension I assume.

Thanks!

Iain McNeill 6th April 2009 08:10 PM

If two of the dimensions are the same then the resonance associated with that dimension will be reinforced. The worst situation is a cube.

A lot of people, myself included, use the "golden" ratio;
0.618 : 1 : 1.618

But there are others.

badman 7th April 2009 03:35 PM

yeah, I roughly use the golden ratio as well
More of a concern than 8"x8" is the 48" dimension. Top-bottom resonances are often poorly damped, where 8" is going to be frequencies high enough that damping material will be pretty effective.

Bob Brines 7th April 2009 04:57 PM

I make MLTL's with square cross sections. A lining of 5/8" high density fiberglass takes care of any lateral standing waves and a bunch of other stuff. I don't generally find stuffing necessary.

BTW your tall thin box could lead to some interesting top-bottom standing waves. Driver position may well be critical

Bob

IG81 7th April 2009 07:21 PM

Quote:

BTW your tall thin box could lead to some interesting top-bottom standing waves. Driver position may well be critical

Bob [/B]

Indeed, that is where I was going and what I imagined. I guess that a column of air with both ends closed will resonate at ˝wave lenghts just as a column with both ends open would. I would think the driver should be placed at a node location of the fundamental, which would then be either end of the column. Am I making any sense?

I'm curious because I don't enjoy so much the aesthetics of a "boxier" box! ;)

I'd also like to take baffle step to a much higher range, yet not have too deep an enclosure.

It's good to hear your enclosures don't suffer from having a square X-section, but they are opened at one end, so that may not apply to my case just the same...

Thanks!

Bob Brines 7th April 2009 07:52 PM

Quote:

Originally posted by IG81



Indeed, that is where I was going and what I imagined. I guess that a column of air with both ends closed will resonate at ˝wave lenghts just as a column with both ends open would. I would think the driver should be placed at a node location of the fundamental, which would then be either end of the column. Am I making any sense?

Yes, 1/2 waves. Without doing any modeling, I would put the driver at 1/4 L and a wad of stuffing at 1/2 L. That would at least give you a chance of killing the standing waves and still have the driver near ear level.

Quote:

I'm curious because I don't enjoy so much the aesthetics of a "boxier" box! ;)

I'd also like to take baffle step to a much higher range, yet not have too deep an enclosure.?

Well, good luck! Keep us posted.

Quote:

It's good to hear your enclosures don't suffer from having a square X-section, but they are opened at one end, so that may not apply to my case just the same...
There is certianly one way to find out.

Bob

IG81 7th April 2009 08:08 PM

Yes, only one way to find out! :)

I'll go with something like...

h: 46.5"
w: 7"
d: 10"

These are inner dimensions. Simulations gave me ~50L for my desired Qtc. I'll be slightly over that volume, which will compensate for stuffing material a bit, not that it'll be a big problem, i'm aproaching infinite baffle realm here so I have room for error or play. Front baffle width will be kept at 8.5".

As for placement and stuffing, I'll try with driver at the top end of the column to be as close to a node as it can, and stuffing will be in the center 1/3 section.

BTW ˝wavelenght will be for 145Hz, which is coincidentally about 2 times my driver's Fs of 70Hz, will this play out somehow, I can't say now.


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