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]

Originally Posted by 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?

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]

Originally Posted by River757

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]

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]

Originally Posted by River757

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]

Originally Posted by crazyhub

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