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Old 6th February 2004, 11:43 PM   #11
claudio is offline claudio  Italy
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Default 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.

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Claudio
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Old 7th February 2004, 12:22 AM   #12
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Hi Claudio

I see now.

But for the dual chamber bass reflex box, I've heard that theres still a notch somewhere in the final port + driver freq response, because of the addition of a second helmholtz resonance, I think. Did you find this to be the case? If so, of what amplitude was this notch?

Adrian
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Old 7th February 2004, 12:16 PM   #13
claudio is offline claudio  Italy
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Hi Adrian,
aren't you refering at the notch at F3 ? That is the typical DCR notch.

Claudio
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Old 7th February 2004, 07:01 PM   #14
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Default Re: dbr/abc boxes

Quote:
Originally posted by REDSKIN

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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Old 7th February 2004, 10:04 PM   #15
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Default Re: Re: dbr/abc boxes

Quote:
Originally posted by Stephen D


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).
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Old 7th February 2004, 10:11 PM   #16
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Quote:
Originally posted by Ilianh


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.
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Old 7th February 2004, 10:55 PM   #17
REDSKIN is offline REDSKIN  England
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Default dcr/abc

I don't know if this is any help, but if anyone has back issues of Speakerbuilder 1998 there is a design for a DCR in there.
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Old 7th February 2004, 10:56 PM   #18
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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.

----------------

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?

----------------

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?

----------------

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)

----------------

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
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Old 7th February 2004, 11:18 PM   #19
REDSKIN is offline REDSKIN  England
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Default 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.
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Old 7th February 2004, 11:37 PM   #20
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Hi Redskin

Quote:
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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