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/HUG/messages/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/products/spunits/lectures/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]

The Double-Chamber Speaker Enclosure

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:

 

[kelticwizard]

Well, here it is-my Edit time expired on my last post while I was drawing this masterpiece:

 

[claudio]

Thanks Kelticwizard,
I will apreciate the scanned article.
I am starting to use Paint to draw the cabinet, for the wood work, but I think that is easier and faster doing it with paper and pencil!!

I found a little dos program to do some simulation of the 2 chamber reflex; practically the vent measure can be different too, at least in the simulation, so I will experiment for a long time.

I was asking myself why the inside vent is positioned in the middle of the 2 volumes: sounds more logical to put it all the way inside the bigger volume.

Regards

Claudio

 

[kelticwizard]

This is embarrassing.

Not two weeks before I wrote that I would send that article to you, I was holding the article in my hands.

Now, I keep looking for it, and I cannot find it!!

I will keep looking. It has to be here somewhere.

Err, you were not planning on using the article to build a double-chamber reflex right away, were you?

I am so sorry. I will keep looking and send it to you as quickly as I find it.

Many apologies,

Kelticwizard

 

[jethari]

Hey Guys
When you're talking about double chamber boxes are you referring to the 4th order / 6th order bandpass box? If so these can be directly disigned using the WINISD. Infact I've tried out a 6th order bandpass using two 8" drivers one connected to each channel of the amp but out of phase. I mounted the drivers in the smaller chamber and it sounds very good. Good clean bass.

 

[claudio]

Kelticwizard,
take your time, I can wait till you find it out.

Thanks

Claudio

 

[kelticwizard]

Claudio:

Thank you for understanding. I hope to find it soon.

 

[kelticwizard]

Jethari:

WinISD is indeed a wonderful program, and it does model some double-chamber types.

However, the double-chamber type we are talking about in this thread is illustrated in my post of October 28. As you can see, this is different from both 4th order bandpass and 6th order bandpass because the speaker is actually facing outside the enclosure, into the room. In the 4th order and 6th order bandpass, the speaker has one chamber behind it and one in front of it-it never faces out into the room.

The advantage? In any tuned system, the cone's excursion is greatly augmented by the action of the port. At the tuning frequency in most reflex, (ported), systems, the cone is only moving 1/4 the distance it normally would move in order to produce any given SPL. Since the ability of the cone to move puts a limit on how much bass the system can produce, this raises the potential of the speaker to produce high bass output.

In addition, the less the cone moves, the less it distorts the higher midbass and midrange frequencies.

The double tuned reflex enclosure we are dealing with here has, in addition to the regular bass tuning frequency, another tuning frequency one octave above the lower one. So the cone excursion at the higher frequency is lowered as well. Makes for a smoother midbass and midrange response.

Suppose a 12 inch speaker in a 2 cubic foot box is tuned to 40 Hz. In a double chamber reflex system, it would be tuned to 40 Hz AND 80 Hz. And the excursion advantages would apply to both frequencies.

Hope this clears that up. If
you have nay more questions, I would be glad to answer.

 

[jethari]

kelticwizard:
Thanks, that was most educative. This is the first time I'm coming across this type of enclosure. I think I'll give it a go one of these days!
One little question - in a 6th order bp if the ports of the two chambers are placed on the same side of the enclosure will there be any cancellation of sounds coming out of them?
Regards
Hari(that's my real name)

 

[kelticwizard]

Hari:

I have never built a sixth order bandpass system, so I cannot say about cancellation if the ports are on the same side. I can only say that in bass reflex systems, it generally does not matter where you put the ports in relation to the speaker. It all goes by wavelengths, and the wavelength of a 50 Hz tone is 20 feet. Since one tenth of a wavelength is usually considered negligible, a difference of up to 2 feet should make no difference at all. Even longer lengths than 2 feet will only gradually show an effect.

I have heard that one of the disadvantages of 6th order boxes is that there is some cancellation in the port output, but I cannot get more specific than that.

About hooking your woofers up out-of-phase, I am surprised you do not get cancellation from that. If you hook two speaker enclosures up, place them right next to each other on the floor, and run bass sounds through them, you will get hearably less bass if the polarity is not identical for both of them. If something about that hookup works well for you in a bandpass box, well, maybe you found something.

 

[jethari]

kelticwizard:
In fact when I wired up the two drivers in phase, there was an appreciable reduction in bass!! By the way, the drivers are mounted on the same baffle side by side.
Hari