midrange enclosure volume

[hifijim]

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

 

[gerenis69]

The enclosed air is more linear than the spider and surround, but crossover is even more linear than air (say if you use low distorting capacitors, like foil or NP0 ceramic). All in all I don't think there's significant (audible) difference. Human hearing is not that good.

 

[stefan66]

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)

 

[Lojzek]

Keep the enclosure volume such that you have the least amount of work to achieve the desired response. The sound clarity lives elsewhere.

 

[planet10]

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

 

[Sonce]

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.

 

[hifijim]

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

 

[TMM]

I'll second the 'just use whatever size box makes the crossover easier' with one exception; if you make the box too small, you run into box spring distortion:
Midrange sealed box, Qtc and box spring distortion

 

[planet10]

The resitive vent as Dynaaudio did was essentiallt a derivation of Jordan’s original work and much the same as the Dyna A25.

Too simple to gain the same advantages of a midTL.

Heavily tapered, and damped light to heavy towards the terminus, one is aiming for as falt an impedance at resonance as you can get.

dave

 

[Mattes]

Hi Jim,

would suggest to have a look at XRK971´s dagger TL for midrange, which seems to be a pretty good solution. As Dave said, you´ll want to get rid of the driver's backwave.

All the best

Mattes

 

[planet10]

The dagger is an excellent implementation of a sealed box. Damped right it is a short 1/2 wave T-Line.

dave