article about double chamber speaker enclosure

[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