Ok gents, time settle the formula for creating a DCR (double chamber reflex) enclosure, once and for all. Notice that we're not talking about DBR (Double bass reflex) as that is something else entirely (with a confusingly similar name). Creating a DCR is in on itself not particularly difficult. However all discussions and tutorials seems to go full fitness industry mode and no one says the same thing. This is why we need to agree on this once and for all.
I've not built a DCR yet because I don't got the time to find out what all of the parameters on the build should be by my self via endless testing. Using Claudionegro's guide (DCR) goes a long way, but his talk about ports falls short in explaining. On other websites and forums (the little that there is on the subject) everyone has their own interpretation. In addition, the DBR and DCR is constantly mixed. Stirring all the information together, my take on the DCR enclosure so far is:
1. Pick a suitable driver of choice (EBP and that jazz still apply).
2. Make/simulate a 4th order alignment that fits you liking.
3. Simulate the enclosure from step 2 with two ports. (Keeping max port velocity to 5% of sound speed etc. still apply)
4. Take the enclosure volume from step 2 and divide it into 1/3 and 2/3. Such so the total volume still equals the volume from step 2.
5. Put the port (not total area x length, but the area x length of one of the two ports) you found in step 3 in the three different place that makes it a DCR. (One in each chamber to the outside, and one in-between the two chambers )
6. Place the driver in the larger chamber.
Simple enough, however it is the parameter rules that gets confused. Here is what I think is correct:
A. The port dimensions result is a product of the tuning in the full enclosure (regular 4. order BR), not in any of the 1/3 2/3 divided chambers. (I'm not sure on this one).
B. The driver should always be placed in the larger chamber. (In DBRs it doesn't matter as far as I know.)
C. All the three ports should be of exactly the same dimensions (or at least the same tuning). (I've seen someone say that the port connecting the two chambers should be twice as long as those connecting the inside of the enclosure to the outside, something I think is incorrect as it would throw the tuning of the smaller chamber right off.)
Please add/correct/give idea if you got any.
I've not built a DCR yet because I don't got the time to find out what all of the parameters on the build should be by my self via endless testing. Using Claudionegro's guide (DCR) goes a long way, but his talk about ports falls short in explaining. On other websites and forums (the little that there is on the subject) everyone has their own interpretation. In addition, the DBR and DCR is constantly mixed. Stirring all the information together, my take on the DCR enclosure so far is:
1. Pick a suitable driver of choice (EBP and that jazz still apply).
2. Make/simulate a 4th order alignment that fits you liking.
3. Simulate the enclosure from step 2 with two ports. (Keeping max port velocity to 5% of sound speed etc. still apply)
4. Take the enclosure volume from step 2 and divide it into 1/3 and 2/3. Such so the total volume still equals the volume from step 2.
5. Put the port (not total area x length, but the area x length of one of the two ports) you found in step 3 in the three different place that makes it a DCR. (One in each chamber to the outside, and one in-between the two chambers )
6. Place the driver in the larger chamber.
Simple enough, however it is the parameter rules that gets confused. Here is what I think is correct:
A. The port dimensions result is a product of the tuning in the full enclosure (regular 4. order BR), not in any of the 1/3 2/3 divided chambers. (I'm not sure on this one).
B. The driver should always be placed in the larger chamber. (In DBRs it doesn't matter as far as I know.)
C. All the three ports should be of exactly the same dimensions (or at least the same tuning). (I've seen someone say that the port connecting the two chambers should be twice as long as those connecting the inside of the enclosure to the outside, something I think is incorrect as it would throw the tuning of the smaller chamber right off.)
Please add/correct/give idea if you got any.
FWIW, in order (and apologies for the multi-quote but in this case it's the most straightforward approach I could think of for clarity.
Certainly, regarding picking a suitable driver of choice. EBP is an almost worthless approximation though, so my standard advice is to ignore it. It's generally fairly obvious what is a definite 'yea or nay' for vented loading, without needing to do an additional calculation, and EBP won't help in the medium ground, except potentially make you reject what might have been a good driver option.
Yup.
Yes to the first, not necessarily to the latter. This is more circumstance dependent than an automatic given. A 3in wideband driver with limited output & vents on the back for instance will be unlikely to have the same issues as a 12in high output subwoofer. You also need to balance air velocity through the duct off against excessive duct length: harmonic modes in the duct can be more problematic than a relatively high air velocity, so worth keeping an eye on both.
Spot on.
Or to put it more simply, put one of the two ports in each chamber and add a third of the same dimensions internally linking the two chambers.
Yes. And that, as they say, is that.
Be sure. 😉 You're quite right, think of it like this: you model the box as a total volume with twin vents, yes? You happen to add a third, plus dividing chamber, but the primary Fb is a result of the initial calculation using the total Vb.
In an Augspurger type DCR, which is what you are referring to, the driver is always in the larger chamber. In the Fostex type DBR, it certainly does matter where it is as this affects tuning and details of the gain BW loading. In the vast majority of cases it's in the smaller chamber. As far as I know (so I'm writing under correction) I'm the only person who has recently been designing enclosures using a cascade of decreasing sub-chamber volumes.
More or less. You will alter the tuning in the upper bass, and generally speaking the alignment will not be for the better; typically you can expect the characteristic notch of a DCR to broaden under those conditions, so I certainly wouldn't recommend it unless you want to do detailed acoustic modelling. You could do that if you also increased the CSA of the vent such as to maintain the baseline tuning. Quite why anyone would want to though is another matter. 😉
Hope that helps.
Certainly, regarding picking a suitable driver of choice. EBP is an almost worthless approximation though, so my standard advice is to ignore it. It's generally fairly obvious what is a definite 'yea or nay' for vented loading, without needing to do an additional calculation, and EBP won't help in the medium ground, except potentially make you reject what might have been a good driver option.
Yup.
Yes to the first, not necessarily to the latter. This is more circumstance dependent than an automatic given. A 3in wideband driver with limited output & vents on the back for instance will be unlikely to have the same issues as a 12in high output subwoofer. You also need to balance air velocity through the duct off against excessive duct length: harmonic modes in the duct can be more problematic than a relatively high air velocity, so worth keeping an eye on both.
Spot on.
Or to put it more simply, put one of the two ports in each chamber and add a third of the same dimensions internally linking the two chambers.
Yes. And that, as they say, is that.
Be sure. 😉 You're quite right, think of it like this: you model the box as a total volume with twin vents, yes? You happen to add a third, plus dividing chamber, but the primary Fb is a result of the initial calculation using the total Vb.
In an Augspurger type DCR, which is what you are referring to, the driver is always in the larger chamber. In the Fostex type DBR, it certainly does matter where it is as this affects tuning and details of the gain BW loading. In the vast majority of cases it's in the smaller chamber. As far as I know (so I'm writing under correction) I'm the only person who has recently been designing enclosures using a cascade of decreasing sub-chamber volumes.
More or less. You will alter the tuning in the upper bass, and generally speaking the alignment will not be for the better; typically you can expect the characteristic notch of a DCR to broaden under those conditions, so I certainly wouldn't recommend it unless you want to do detailed acoustic modelling. You could do that if you also increased the CSA of the vent such as to maintain the baseline tuning. Quite why anyone would want to though is another matter. 😉
Hope that helps.
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Thank you very much for taking the time!
What was your findings with the cascading chamber DBR?
And if you know, since ports are 180 degrees out phase, will the port to the outside in the small chamber (of a DCR) be in phase on cycle after the driver? Considering the sound is passing through two ports in series.
Do you mean you don't recommend DCR or having unequal vents?
What was your findings with the cascading chamber DBR?
And if you know, since ports are 180 degrees out phase, will the port to the outside in the small chamber (of a DCR) be in phase on cycle after the driver? Considering the sound is passing through two ports in series.
Do you mean you don't recommend DCR or having unequal vents?
Maybe this measurement could help, defining DCR ports phase:
DCR NEAR FIELD PHASE: P1 (green) - P3 (red) - WOOFER (blue)
Depends on what, specifically, you're targeting so there's no single set of findings or answer to that one. In essence however, you're providing a progressively stiffer air-load so in a similar way to a high order BP you're playing extension against efficiency.
Just that there is no advantage to using dissimilar vents that I know of (unless very carefully designed to specific goals which won't apply in most cases).
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Hello,
What are the differences in sound between a bass reflex vs double chamber reflex enclosure? I've read that a DCR box is more efficient. Would that make it a better box for a low wattage amp?
What are the differences in sound between a bass reflex vs double chamber reflex enclosure? I've read that a DCR box is more efficient. Would that make it a better box for a low wattage amp?
