Speaker Asylum

Posted by RoyJ (M) on February 03, 2016 at 07:02:35

In Reply to: RE: "It makes some sounds or notes suddenly appear 'too loud' so engineers... posted by hahax@verizon.net on January 30, 2016 at 08:50:25

Allow me to make a correction to the above, thanks.

A 'linear phase speaker' is not a time-coherent speaker.
This is technically-nice-sounding shorthand for "an acoustic phase response that changes constantly and smoothly (i.e., linearly) with frequency." In other words, it has more and more time delay the lower we go down the scale.

When a linear-phase speaker's 'rotates', its phase spins through multiples of 360 degrees (from thinking about phase as if degrees on a compass). Every linear-phase speaker rotates through multiples of 360 degrees as we proceed down the scale. When it is a linear phase design, that rate of rotation is smooth with change in frequency. This linear rate of change produces angled-but-straight lines (i.e., 'linear') for its phase-response, plotted on a lin/log graph.

'Linear Phase' of course also means that this speaker is 'in phase' at any crossover point, i.e., exhibiting no cancellation/no suckout around any crossover frequency. So, a decent speaker has linear phase shift along with a smooth-looking frequency response curve. Its impedance curve is usually not flat.

Linear-phase speakers are the MOST easily designed, because a designer thinks nothing of the time domain, only of the tone balance, a smooth frequency response, with no cancellations. Finito. That's it. Ship it.

FYI, Tannoy, Dali, Dahlquist DQ-10, B&W's, MBL, the new Thiels, M-L, and many more, are linear-phase designs. None is time coherent.


On the other hand, a time-coherent speaker exhibits the SAME TIME DELAY at EVERY frequency. It is not changing the acoustic phase at ANY frequency. These speakers are very difficult to design, but only when a designer lacks the education.

Plenty of good woofers and tweeters now exist for making time-coherent speakers, at no increase in cost, no difficulties with power handling, nor dispersion, nor efficiency.

However, time-coherent speakers take MUCH longer to design, because of the additional time-domain variables. Once a speaker design becomes time-coherent, it turns out that making tweaks to it every six months will not substantially change what is heard. Therefore, marketing is not about offering a 'new and improved' model every year.

This is because, going to your last point above, designing a speaker to be time-coherent is actually MORE important to address BEFORE any other design variable. To get the darn thing to be time-coherent, you must automatically avoid poor drivers with cones that break up or ring (metal), drivers with high distortions (from poor magnets and suspensions), strange cabinet-tunings for bass, and varying-length horns, among others.

Best regards,
Roy