midrange enclosure volume

I am planning to use the SB acoustics SB17CAC35-4 6.5" driver as a midrange, crossed at 200 Hz with an active crossover. This driver has an Fs of 29.5 Hz, Vas of 38 liters, and Qts of 0.29.

Almost any closed-box volume larger than 7 liters leads to an over-damped bass response... a gentle roll-off starting at 200 Hz. I will use DSP to adjust the response from 50 Hz to 200 Hz before applying the high-pass DSP filter. Due to my cabinet design constraints, I will have at least 8 liters available for this driver, but any thing from 8 liters to 15 liters is very achievable...

From the standpoint of midrange clarity and detail, is there an advantage to a larger enclosure? I can imagine that a larger enclosure might perform better because the back radiation has a larger space, with a greater volume of absorbing material (in my case wool and polyester fibers) to absorb and dissipate the energy... however, this is speculation. I am interested in anyone's experience.

Jim
 

stefan66

Member
2017-04-17 7:25 am
Take a look at the Ceramicos collaboration between Javad Shadzi and Jeff Bagby, which used the 15cm mid. I'm going to build the same top end with a modified bottom end using a variant of the Kairos woofer module by Jeff Bagby.

Back to your question according to Javad on his FB group the enclosure should be somewhere between 4-7 litres, if you see his enclosure you'll understand more that it's not so much about the volume but rather break up the back waves (I think I got that right, I did pose the question on the loudspeaker project pad FB group)
 
From the standpoint of midrange clarity and detail, is there an advantage to a larger enclosure?

My experience is that an aperiodic midTL allows for getting the best midrange out of a midrange. The enclosure is low pressure and — if properly damped — removes the maximum amount of the acoustic energy coming off the back of the driver, meaning little comes back tru the cone as time-smear.

If you have the room, and it sounds like you probably do, you should consider this.

dave
 
From the standpoint of midrange clarity and detail, is there an advantage to a larger enclosure?
Short answer: yes.
Long answer: For rectangular mid enclosure - yes, for low crossover frequency (e.g. 200 Hz), but don't over do it (too large enclosure = diminishing returns). Use Qtc=0.7 as a starting point. But you already did it - 8 liters makes Qtc=0.7. Perfect!
Very long answer: If possible, use relative narrow but long tapered TL-like mid enclosure.
 
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Dave - I remember the old Dynaudio "vari-o-vent" which was a resistive / foam-stuffed vent, although I never used one ... Is there more to an "aperiodic midTL" than just a well designed box with a resistive vent?

Although I am not constrained by size, I need the midrange enclosure to be roughly box-like when seen from the outside ... i.e it can't be a long tapered tube or pipe.

oh.. and thanks to everyone for your thoughts. I am getting back into designing speakers after a 25 year break...

Jim