Double chamber reflex rebellion

[Hezz]

I am considering building a dual chamber reflex test box but rebelling against the standard model. The standard model as in the "Weems" model.

The dual chamber reflex has of course two primary box resonances. In the Weems model the lower tuning is set to the Thiel and Small tuning and the other box tuning is approximately one octave higher.

My idea is to set the upper box tuning frequency at the Thiel and Small tuning and have the lower box tuning reinforce the lower frequencies that stand in need of more reinforcement.

Has anyone tried this with success. I seems that it would be the more logical method for a driver that requires box tuning below the driver Fs. Since in most situation the upper box tuning frequency would be above the Fs which is not where its supposed to be for many drivers. According to the Thiel and Small parameters.

[Ron E]

Anyone think that if I put monster truck tires on my VW Rabbit I can go muddin' with the big boys and beat 'em at their own game?

[PeteMcK]

something like this?:
http://www.diysubwoofers.org/bnd/6thord4.htm

I think a conventional EBS alignment is much easier to implement, with fewer drawbacks,
but it depends on what you're trying to acheive...

[freddi]

FWIW looked at a few a decade ago with Bullock's DCBOXMOD program - - -George Augspurger's 2:1 split with 3 equal vents seemed about as good as anything else showing one narrow notch and passband equivalent to a single vent .

Running sine was interesting to see how vents trade off until both (and the coupling vent becomes transparent) work in unison at low F - -I think that's the way it works.

another chamber might be added to further distribute resonance.

what does Fostex usually pick for DBR?

I can't get AJ horn to do series BP - ugh :^(

[kelticwizard]

Hezz:

Don't see how it can work. The whole idea of the Double Chamber Box is that at the lower frequencies, the upper and lower chambers join as one, and that is why the tuning is the same as for the simple tuned box.

Only at an octave or so above the lower frequency does the upper chamber separate off and resonate on it's own.

All you are doing is tuning each chamber one octave lower than optimum. The result of that is sure to be drooping bass, just as if you tuned a simple ported box an octave too low.

[kelticwizard]

Originally posted by freddi
FWIW looked at a few a decade ago with Bullock's DCBOXMOD program - - -

That program is not on his website. I would very much like to try it. I am a big fan of DosBoxModel, (except the Transmission Line one, of course).

Where can I download the Double Chamber version?

[sandstorm33]

I have built three versions of DCR enclosures with good success. GP Augsbergers's design published in 1961 in ELECTRONICS WORLD was the very first. Used an EV SP8B and a Peerless tweeter. The speaker was placed in the large segment which was lined with a couple of inches of fibre glass . They were very efficient and produced exceptional bass . David Weems came along with a design using an 8"Peerless speaker that was somewhat smaller than Augsberger's model and it to was a very good sounding unit. The speaker was also placed in the larger segment.

A good site is www.claudionegro.com which give results of various tests he made on DCR's . He offers design info which should help you get it right .

Fostex has designs for a few their speaker models and they can be seen at Madisounds website.

I have built units for me and for others over the years with good satisfaction from them all.

[freddi]

reCBOXMOD - I'd upload it if my stupid Earth-link worked-- its a bit buggy where entries must be double checked vs vent lengths - drop me a line and will try to find it. btw - could never get screen shots on win XP with Bullock & White's software

I might go DBR on a project

care to help me on a Karlson model?

[Hezz]

Thanks for all your responses guys. Except for Ron E.

I know the potential of the DCR as I have built one in the past. Not really concerned on how to built one. Only if it can be bettered with a slightly different implimentation. You know I am just postulation how it might be improved.

My idea is to make the primary chamber the full size that the driver needs and have the sub chamber at the usual half volume of the primary. Now, if the primary chamber resonants at the Thiel/Small tuning and together they resonate an octave lower where the bass falls off more wouldn't this extend the response even further and still properly tune the driver. Granted it would take more cabinet space and it would effect driver impeadance differently. But I'm curious if it would be successful.

I was under the impression that according to Thiel /Small guidelines there was only one frequency to properly tune any given driver. If this is so, isn't the second tuning point moved away from the ideal. And if so, why is going up better than going down. I can see that going up will relieve the driver of some movement since the upper freq. port reinforces it. But unfortunaltey the port cannot deliniate pitches as well as the driver. So it makes some degree of more sense to support the weaker lower bass than the upper bass which the driver does a better job of reproducing.

Also curious if it would move the 100 Hz dip down to a lower frequency. If , for instance, the dip went down to 80 Hz it would work better near a subwoofer type crossover.

[sandstorm33]

I think you are playing a guessing game. After the size of the larger chamber is derived using T/S parameters ,the chamber is tuned to.89 of the desired lower frequency. The port size derived from that process
is the size utilized for all of the three ports. Bass extension is therefore
well beyond fs of the speaker . Augsberger's original design had usable bass to 35hz with a speaker that was rated at 45 to 50hz. Efficiency is increased due lower cone excursion.You might try your idea
and see what happens . Other than that ,who knows???