Double bass reflex information

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I've been searching for weeks now for any information on double bass reflex boxes, projects, theory.

I just could not find enough information to even start a project.

I suggest we make a collection of information sources, experiences and share projects in this thread.

Any books recomendations? articles?

Heres what I could find.
- http://www.quarter-wave.com/Models/MathCad_Models.html
Wonderfull mathcad worksheets for DBR simulation from Mr. King.

- http://www.geocities.com/fuherb/168dbr.htm
An interesting project with fe168

- http://www.fostexspeaker.de/gehaeuse/83e_enclrev.pdf
fostex recomended DBR for fe83

Thanks!

N.B, I speak here of DBR configuration, excluding all Nth order band pass boxes.
 
dbr/abc boxes

just to make sure that I'm thinking along the right lines. We're talking about taking a ported alignment then splitting the internal volume 2:1 and then joining the 2 created chambers with each other and the outside world using 3 identical ports? Is that about right?

The advantages being what? That you can control cone motion over a wider range than with a normal ported box? That you can get the sound of a sealed with the extra efficency of a ported design, or are there other advantages?

This seems to be a win win design but are there any short commings?
 
As long as Ilianh understands that the fostex enclosure is a different kind of enclosure from the other kind of Double Chamber Reflex with a different response entirely.

Hi Kelticwizard,
Well I noticed it was different, but I dont see in what the response would be entirely different.
Any examples?
Wich is "better"?

Any idea about transient response on those boxes? group delay? impedance?

I heard bad stuff about it, but when I model something in Martin J King's worksheets, everything look preety much as same as a normal ported box.
 
Hi CLaudio

Nice looking site, great work!

On the response curves at your site, F2 is a pretty big dip.

An externally hosted image should be here but it was not working when we last tested it.


But I did notice you said the port response is not included in that curve. Why is this? Where was the microphone placed?

Have you got any response curves with driver + port response combined? Was the dip substantially less when they were both combined?

How did your DCR speaker "sound", to your ears, compared to the standard equivalent bass reflex box? What are the subjective differences in your opinion?

Adrian
 
Weems DCR

Thanks Adrian,
as i said on the site, it is a near field response (mic very close to the woofer as I explain in the SW near field folder of the site) without the ports: in a ported system, the NFR is obtained by measuring first the woofer and then the port(s) and then jointing them; I didn't jointed the ports response cause I wanted to show the Fb of the system, Fb that is identified by the big notch, as I said in the site.
Once combined (port and woofer) the notch disappears: just check the SW NF folder, it is showed for a reflex system.

I am working on the crossover of the DCR, and as soon as it is ready I will put in my site the results.

Regards

Claudio
 
Re: dbr/abc boxes

REDSKIN said:

The advantages being what? ..... That you can get the sound of a sealed

I wouldn't say that...

I've built a DCR Augsperger style (as described by Weems). I built
it about 10+ years ago using a Pyle 8" woofer. I've been using it as my home HiFi sub ever since. I've never done any real controlled FR measurements of it other than simply testing to see that the port tunings came out as calculated (which they did). The FB's on mine are in the neighborhood of 30 & 60 Hz from what I remember & people are always surprised to find out it's a single 8" speaker when they hear it. I wish there was a freeware that modeled DCR. LSPcad seems to model all but the Augsperger
style. I played with the demo version of it for a bit (which only allows modeling of the 1 speaker in it's data base) & it was interesting to note that there seemed to be some useful tunings other than the standard octave apart that is most often suggested... at least with the type of DCR I was experimenting with in LSPcad. I've been tempted to by that program just because of it's DCR modeling, but I just probably wouldn't use it often enough to warrant the $$ even though it's not all that pricey. I've been thinking that PA subs might actually be a good application for them.
 
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Joined 2001
Re: Re: dbr/abc boxes

Stephen D said:


I've been thinking that PA subs might actually be a good application for them.

Yes, I was thinking 2 way PA speakers would be an excellent choice for them because they have to put out high SPL levels from the bass up to 2K Hz, typically. This enclosure would seem to suppress much of the cone excursion, (but not the output), of the upper bass and enable the 15 inch PA speaker to reproduce the mids more smoothly. Cone excursion in the bass, especially at high output levels, has the capacity to muddy the mids, as Klipsch showed in his Journal of the Audio Engineering Society paper, Intermodulation Distortion in Loudspeakers, (1971).
 
diyAudio Moderator Emeritus
Joined 2001
Ilianh said:


Hi Kelticwizard,
Well I noticed it was different, but I dont see in what the response would be entirely different.

I heard bad stuff about it, but when I model something in Martin J King's worksheets, everything look preety much as same as a normal ported box.

Well, in both Martin J. King's models and LspCAD models, there is a pronounced notch in the frequency of the upper resonance.

In the Augspurger double chamber reflex that Claudio built, there is some mention of interference, but nobody says it is very big. In the Martin J. King and LspCAD types, the notch can get very, very deep-so deep that it might be a fun project to see if it can be used as a crossover element to augment many subwoofers' natural rolloff, save money on inductors, (seriously), and possibly improve phase response in the crossover area over using expensive inductors.
 
Hi Claudio

I'm really not sure where the notch is on a DCR, which is why I'm asking. Can anyone show me a graph, or just tell me what amplitude and Q/how wide the notch is?

Is the F3 of a DCR the same as a standard vented equivalent? I ask because theres two chambers, one tuned lower and one tuned higher, sometimes I just don't see them combining to give the same F3 as the standard box.

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Stephen, what are your impressions about how the DCR sounds that you built? Was it "muddy" at all, or did it sound good and tight?

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Has anyone got an excursion graph comparing DCR to standard vented box so I can see just how much excursion is reduced in a DCR at the same power levels?

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Is having V1=1/3 total volume and V2=2/3 total volume, each with the same size port determined using equations for standard vented box, give the best coupling between the two resonators? (i.e: tuning method given at http://www.diysubwoofers.org/prt/dual_chamber.htm)

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Are there any computer simulation programs for dual chamber bass reflex boxes? The Martin King mathcad worksheets are for double chamber reflex, which only has a port in one chamber going to outside and another connecting the two chambers togethor; one chamber isn't ported to the outside.

I wish there were more online resources about this type of enclosure. Further excursion reduction without using a horn is particularly interesting, especially for pro drivers which you guys mentioned. But thats why I asked for a graph comparing DCR to standard reflex to see just how much excursion is reduced, rather than just assume its reduced "a fair bit".

I also have a feeling theres an extra 1/2 wl period spread delay at the resonance with a DCR.

Any comments much appreciated,
Adrian
 
dcr/abc

from macky888
"Has anyone got an excursion graph comparing DCR to standard vented box so I can see just how much excursion is reduced in a DCR at the same power levels?"

It isn't that a DCR reduces cone movement to a level less than a normal ported alignment, it just reduces cone movment at the second port tuning frequency as well as main one to the same level as one would see in a normal ported design.

At least thats what I understood was happening.
 
Hi Redskin

It isn't that a DCR reduces cone movement to a level less than a normal ported alignment, it just reduces cone movment at the second port tuning frequency as well as main one to the same level as one would see in a normal ported design.

Thats right. But sometimes the higher port tuning freq may be nearly at the Fh of the lower port tuning, and hence reducing cone excursion over a standard vented box. Weather or not this tuning setup gives a flat freq response is another thing of course.

The DCR sounds very much like the 6th order bandpass box. Does anyone know if the DCR will keep excursion levels lower than the BP6? If not, then the DCR isn't really anything special IMO. That thought just occured to me then.

Does the DCR also provide an acoustic lowpass filter for the driver like a BP6?

Adrian
 
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