Audio Page Dipole sub Quad ESL-63 Large speaker Miscellaneous

These questions where asked by email.

It seems that the SWR ( 831857) is out of production, is there an alternative?
 

 

Peerless, though not tested.

 

8311857 (315 SWR)                  830845 (308 SWR)                    830669 (SLS 315)

 

Fs                    23                                21.5                                         24        Hz

Sd                    520                              466                                          540       cm2

Xmax                9                                  12.5                                         8          mm

Qts                   0.46                             0.45                                         0.45     

Eff                    89.3                             88                                            91.6      dB

Max air-            468                              582                                          432       cm3

movement

 

These 3 will all deliver nearly the same (!) maximum sound pressure  at 30 Hertz, taken Sd and Xmax in account.

 

From specification all three should be suited when not making to much noise. Sometimes a little silicon sealer between the magnet and the gasket is needed. I anticipate that the 308 SWR will cost more with, beside a little extra maximum soundpressure, no extra benefits.

 

I think efficiency is not a real issue, it only matters for the thermal compression. The needed power for the same maximum sound pressure at 30 Hertz for these 3 woofers will be resp. 40, 65 and 25watts. Not a real problem with today ‘s amplifiers.  

 
Could I use a low Q factor woofer?
 

 

Most elegant are Q’s between 0,55 and 1.  Lower Q’s need more compensation, i.e. more power. This leads to thermal compression, because it heats up the voice coil and lowers acoustic output, 10 dB is no exception. This effect is audible, when playing louder, bass output drops. (But the Q factor will increase). Generally spoken in the application of a dipole sub surprisingly a less efficient woofer with an high Q can (will) in fact be more efficient than an efficient woofer with low Q.

On an infinite baffle the acoustical output of a low Q speaker drops with decreasing frequency down to the resonance frequency. A speaker with a 0,7 to 0,8 Q gives the same output down to the resonance frequency. Normally a low Q woofer gets efficient when the Q is raised by an enclosure,  but with a dipole the Q remains the same.

A 0,27 Q speaker needs more than 100 watts power, versus 20 watts for a 0,7 Q speaker, for the same acoustical output at the resonance frequency Fs (when the efficiency is the same). The thermal compression is not taken into account, so in real live it even gets worse.

 

0,8 seems perfect when the maximum cone excursion ( Xmax,=one way) and the resonance frequency Fs are also suited for dipole operation. (ccx315: 9mm and 24Hz).  0,27 is IMO not suited very well.

The other aspect is how much additional noise the speaker makes at high excursions. With a 0.8 Q woofer the first high pass in the filter at 20Hz should be dimensioned as a normal butterworth. At the moment it is not, as the Q factor of the high pass filter is increased.

 
Is the filter slope 12dB? And what kind of filter (Butterworth, Riley, Linkwitz....)
 

The electronic (active) filter slope is 12dB, but acoustically it is not. The over-all characteristic of speakers and filter together is similar to linkwitz-riley, the phase responses of the ESL and the sub are nearly the same in the crossover region.

Did you conduct acoustical measurements?
  Yes, the subs, the ESL 63, and the combination where measured using CLIO. In the crossover region the filter behaved as expected and didn't need further adjustment. This was a surprise. The response at the lower end was further down than simulated, 0dB was at 26 Hz, and ruler flat. I would guess that this is because in the simulation the sub was calculated in a free full sphere. In real life the sphere is smaller, because the subs are placed on the floor.