article about double chamber speaker enclosure

[PTSOUNDLAB]

Hello,

I search old article about double chamber speaker enclosure. Does somebody have one of this to help me ?

"The Double-Chamber Speaker Enclosure;" George Augspurger; Electronics World 12/61

"Double-Chamber Speaker Enclosure;" R N Marsh; Speaker Builder 03/80

"A small Double-Chamber Reflex;" David Weems; Speaker Builder 04/85

Thank you.

Pascal.

[kelticwizard]

I have an article by Weems about them somewhere, but I don't have a scanner.

It won't go any lower than a normal bass reflex, but it will have another resonance point precisely one octave above the lower resonance point. A normal bass reflex reduces excursion through the lowest octave. The double chamber reduces excursion through the lowest two octaves.

If nobody posts, in a couple of days I will give you the formula on how to make a single chamber reflex into a double chamber. It is a simple conversion.

[kelticwizard]

This link gives you an idea what you do.
http://www.audioasylum.com/forums/HU...ages/4151.html

To give an example.

Suppose you have a 10 inch speaker that is flat down to 30 Hz in a 3 cubic foot box.

Normally, you would build a 3 cubic foot box and use a 3" diameter port that is 4.7 inches long. Alternatively, you could use two 2" diameter ports the same length. The box tuning would be identical.

In a double chamber reflex, you would build your box identically to the normal single chamber-with 2 differences.

First, the double chamber box will have a partition that divides the box into two unequal chambers. The smaller is 1 cubic foot, the larger 2 cubic foot.

The woofer is mounted in the bigger chamber.

Instead of one 3" diameter port, we use the equivalent of two 2" diameter ports. However, one 2" port vents the larger chamber to the outside, the other vents the smaller chamber to the outside.

Important-there is THIRD vent, always identical in size to the other two. That is put into the partition between the two chambers, on the inside of the box. So the two chambers have a 2" diameter vent 4.7" long between them.

So when we view this speaker, we see two 2" diameter vents. We do not see the one on the inside of the enclosure.

You can do the equivalent in any vented speaker. Just make sure the ratio between the larger box and smaller box is 2 to 1.
According to Weems, if a speaker works well in a simple vented box, it will work just as well, with the same cutoff, in a double chamber box. If you want to be persnickety, you can make the double chamber box slightly larger to acomodate the internal partition and the vent. Usually, it won't make too much difference if you do.

I hope I have explained this well.

The normal way this is drawn is a 3 foot tall enclosure, the larger chamber with the woofer on the bottom, the smaller chamber on the top. The vents are on the front, one on the top, the second one on the bottom.

I will be glad to answer any questions if this is not clear.

[PTSOUNDLAB]

Thank you for all these detailled informations.

Best Regards.

Pascal.

[kelticwizard]

Here is a double chamber bass reflex of a different sort-only one port to the outside:
http://www.geocities.com/fuherb/168dbr.htm

[jcarr]

Kelticwizard:

The "double chamber bass reflex of a different sort" that you mentioned is of a type that was popularized by Tetsuo Nagaoka, who was a Japanese audio reviewer, and who also published many DIY speaker designs based on Fostex, Coral, Technics etc. speaker units.

Go to Google, and type in "double-bass reflex", ’·‰ª“S’j (that's Tetsuo Nagaoka in Japanese), and ƒ_ƒuƒ‹ƒoƒXƒŒƒt (double-bass reflex in Japanese). I hope that the Japanese text makes it through unscathed...

The double-bass reflex method can be made to crank out some impressively deep bass, but all in all, it isn't easy to get right. Here is part of what Fostex has to say about this approach at:

http://www.fostex.co.jp/int/pages/pr...res/basic.html

"Calculation of parameters of double bass-reflex system enclosures, which function in a very complex mode, often requires experience, intuition and the sixth sense. It is, therefore, strongly recommended as many and various calculations and examples as practical be reviewed and knowledge be built up before designing your own version."

regards, jonathan carr

[kelticwizard]

JCarr:

Thank you for your post. I will cut-and paste onto Google and see what happens.

Just speculating, but I would guess that the small chamber behind the speaker tunes the box an octave or so above the big box resonance frequency, and that the big advantages here are that interior box reflections are raised in frequency, (where a layer of stuffing can more easily absorb them), midrange reflections are reduced in intensity, and cone excursion is reduced over a greater range than the simple reflex.

That is just a guess.

Thank you for taking the time to let us know about this. One thing I see in the audio field is that there are many good approaches to things with a lot of advantages in certain situations, but this information is not easily available.

[PTSOUNDLAB]

Thank you boys for your help. Finally I will use FE206E on open baffle and Delta 12LF for basses. I have buy a pair of FE206E and I have try them on test open baffle and one of my tube selfmade amplifiers. The sound is beautifull, flat response. I have try to use a FT17H with them, it's better, more "brillant"(in french, sorry), more definition upon 10Khz.

Best regards.

Pascal.

[claudio]

Hello,

Kelticwizard:Regarding the vents calculations, reading some articles, it seemed to me that the vents calculations should be made considering V1 tuned at Fo , where:

V1= upper volume =2 * V2
V2= lower volume

Fo= resonance frequency of V1
F1= " " of the system considering the total volume = Fb
F2= " " " V2


What is your opinion?

[kelticwizard]

Actually, Claudio, I am not sure what the upper, (small) chamber and the lower, (large) chamber are individually tuned to.

The way the formula works is to design a simple bass reflex speaker the normal way, tuned with 2 ports-most programs allow you to do that.

Then make a third port the same size as the other two.

Put in a partition so that the lower chamber is twice as big as the upper.

Put one port in the lower chamber facing the outside, another port in the upper chamber facing outside, and a port in the partition between them.

I have the article somewhere, and I now have a scanner. I will send you the article.

Meanwhile I have becme somewhat able to use Microsoft Paint, so here goes: