Double chamber reflex - why is it not used more often?

[River757]

I've alway been interested in the DCR concept since seeing it in the David Weems book I bought at Radio Shack back in the early 80s. After building a couple pairs of speakers back then, I went off to college & no longer had access to proper wood working tools and it's only now that I have the chance to build another set of speakers.

But while a DCR seems to have sonic advantages over conventional bass reflex designs, particularly increased efficiency, I don't think I've seen a commercial version of it for sale, and have seen very few DIYers utilize it on the DIY sites I visit.

Is there some dark secret about this design that causes so many speaker builders to shy away from it?

 

[whgeiger]

Cost!

I've alway been interested in the DCR concept since seeing it in the David Weems book I bought at Radio Shack back in the early 80s. After building a couple pairs of speakers back then, I went off to college & no longer had access to proper wood working tools and it's only now that I have the chance to build another set of speakers.

But while a DCR seems to have sonic advantages over conventional bass reflex designs, particularly increased efficiency, I don't think I've seen a commercial version of it for sale, and have seen very few DIYers utilize it on the DIY sites I visit.

Is there some dark secret about this design that causes so many speaker builders to shy away from it?

Suspect increased cabinet cost and acute sensitivity to the variance in driver parameters are the primary deterrents to use of this design.
There may also be a patent still enforce as well.
Here is one implementation known to me. I am sure there are more.

Specification - BR6 | Monitor Audio

Regards,
WHG

 

[richie00boy]

One of the problems is accomodating the vent. At the lower Fb both ports work together and so the total port area is the sum of the two port areas. This means that unless you choose a narrow port your port length will be long. But it's not easy to choose a narrow port because at the upper Fb just the small chamber port is working and it's operating at a frequency a fair bit higher than a normal ported box would, so vent air speed is high which necessitates a wide port. Catch 22...

 

[Michael Chua]

But while a DCR seems to have sonic advantages over conventional bass reflex designs, particularly increased efficiency, I don't think I've seen a commercial version of it for sale, and have seen very few DIYers utilize it on the DIY sites I visit.

Is there some dark secret about this design that causes so many speaker builders to shy away from it?

Maybe it's because DCR is often misunderstood. The real advantage of a DCR is not lower or stronger bass but the upper bass. The bass reflex is tuned for the lower bass whereas the second chamber tunes the upper bass.

Check out my DCR build at Merlin

 

[Don Hills]

Another advantage is that it will subdivide a tall (long) enclosure, raising the frequency of the first box standing wave resonance.

 

[River757]

Some great information here - thanks everyone.

Michael & whgeiger: thanks for the links. Looks like it does have some commercial viability even in these days when tiny black cubes sell so well.

richie00boy: I don't mind large enclosures, so if a port tube has to be long enough to accomodate a wide-enough port opening to avoid chuffing issues, no big deal. FYI: my limit for this design's enclosure volume would 4cu/ft (I'm not sure yet if I will be going with a 8 or 10" inch woofer).

While I am not against using a powered subwoofer in a system, for this particular system I am trying to design something that reaches to @35Hz and reaches "reasonable" levels* for my Beck and Alan Parsons albums but does not require a high-current 200 watt/channel amplifier to do so.



* I've never owned a sound level meter, so don't have any hard numbers for this, but can say that when I've used older receivers with power meters, I regularly drove them into the 30-40 watt range in my 17ft x 20ft living room, using for example some single 8" woofer Boston Acoustics bookshelfs with a 91dB efficiency rating.

 

[wolf_teeth]

Why not go to 3CR?

I designed these:

Parts Express DIY Project

I think the main factor is complexity. Verification of tunings is also a must. The main problem for DIY is that you need a spice program just to emulate or model the box without any guesswork.

In the end, it really broadens out and lowers the magnitude of the impedance peaks in the tuning range. IMO- it can be very useful in extending the bass range of smaller drivers without allowing too much excursion to cause harm.

I will likely build another one in a larger form factor.

Later,
Wolf

 

[richie00boy]

richie00boy: I don't mind large enclosures, so if a port tube has to be long enough to accomodate a wide-enough port opening to avoid chuffing issues, no big deal. FYI: my limit for this design's enclosure volume would 4cu/ft (I'm not sure yet if I will be going with a 8 or 10" inch woofer).

It's not that the box has to be large, it's that the port can be difficult to fit into the box regardless of box size, because you need overly large port area.

 

[crazyhub]

Please, does it exist a calculator / simulator of DCR?
Thanks

 

[wolf_teeth]

Please, does it exist a calculator / simulator of DCR?
Thanks

Nope. The only modeler I am aware of was a SPICE program that Feyz created.

You can just simulate for 2 or 3 parts, and add the partitions and other port interally. Just read my writeup above for how I did mine. DCR is typically 2/3 and 1/3 volumes.
Later,
Wolf

 

[PeteMcK]

Unibox sims a 'Bandpass Single Tuned Box', which I think is another name for the DCR..?

 

[freddi]

the late Bob Bullock along with Bob White had a good DOS simulator for DBR many years ago called "DCBOXMODEL" - -in general the 3-equal port, 2:1 chamber volumes version was the most popular. How does one practically extend it to 3-chambers?

 

[crazyhub]

Wolf, thanks for your reply but I just found these which are enough stuff for me to design a DCR:
DCR
Project
Pete, the 'Bandpass Single Tuned Box' in Unibox is a bandpass which incorporates a lowpass (driver firing inside the enclosure at first); the DCR doesn't.

 

[wolf_teeth]

freddi- I hadn't heard of that one, musta been before my time.

crazyhub- no problem!

I just extended the volumes to 1/2 and a pair of quarters, and modeled for 3 ports. I think the last chamber should be tuned a little lower, but I did not do that this time around.

FWIW- it suffered no ill effects for doing it the way I did it. It was hard figuring out how to get all of the ports in there though.
Later,
Wolf

 

[crazyhub]

Guys, do you know of possible DCR principles flaws vs simple BR?

 

[wolf_teeth]

Having to get all the ports in the enclosure.
To me- that's about it.
Later,
Wolf

 

[crazyhub]

OK Wolf.
I'll give a DCR try on a future project, for sure.

 

[River757]

Using the search phrase dual chamber reflex Weems the exact chapter(!) along with the formulas, in Weem's book concerning DCRs appeared in Google's book search results: Designing, building, and testing ... - Google Books

It almost seems too easy though - anyone have any thoughts on Mr. Weems' method?

 

[River757]

O.K. I have to admit to some "dumbness" on my part when I said Weem's design method seemed too easy. That's because after checking the google version again, I realized two full pages are missing from the DCR portion of that chapter. It even says so right in the preview pane. Oops.

I'm gonna blame this on the allergy medication I'm currently using........

 

[Altec Best]

I designed these:

Parts Express DIY Project

I think the main factor is complexity. Verification of tunings is also a must. The main problem for DIY is that you need a spice program just to emulate or model the box without any guesswork.

In the end, it really broadens out and lowers the magnitude of the impedance peaks in the tuning range. IMO- it can be very useful in extending the bass range of smaller drivers without allowing too much excursion to cause harm.

I will likely build another one in a larger form factor.

Later,
Wolf

Hey Wolf, I would very much like to see one ASAP ! Very Interesting !

Thanks for considering it ! I was looking at all kinds of BR cabs recently,and I just find the double BR interesting as there aren't too many built, in fact they are quite rare in the DIY community IME!

At least I haven't seen too many !