Originally Posted by Drew Eckhardt
distortion dB = 20 log (distortion percent / 100)
distortion percent = 100 * 10 ^ (distortion dB / 20)
Lambda unity (it's a mid-tweeter assembly intended to be crossed over to separate woofers at 300Hz)
Distortion @ 112dB/1M
.477% = -46dB
.194% = -54dB
.386% = -48dB
.967% = -40dB
1.5% = -36dB
Distortion @ 90dB/1M
.078% = -62dB
.029% = -71dB
.062% = -64dB
.110% = -59dB
.049% = -66dB
Sure, but we're talking similar distortion numbers at ten times the acoustic power.
Size, cost, and market inertia/prejudices.
The wave guide needs to be large compared to the frequencies involved. Put a nice round-over on the edge of a 15" wave guide cabinet and you end up with a big cabinet - Earl's Summa is 24" wide. The Abbey is a more svelte 15" with small round over . Where the high end market wants a foot-wide speaker and spouses want something jewelry box sized that's not good.
We didn't understand diffraction as well when we needed horns to mate to low powered tube amplifiers, so many had a characteristic sound which isn't there with more modern profiles (like oblate spheroids) and no compression chamber (where the throat is smaller than the compression driver and a chamber is used between them).
Wave guides are getting popular with domes. Revel uses them on its Ultima 2 Salon tweeter. Genelec uses them on its powered monitors.
The driving impetus behind horns is often efficiency. 100W into a 108dB system would be as loud as 10,000W into a somewhat sensitive 88dB home system if the drivers didn't bottom and voice coils vaporize. Obviously you don't need that at home.
You do want uniform power response. Harman's double-blind testing involving acoustically transparent scrims and a computerized speaker mover reveals it's what listeners prefer regardless of experience, musical preferences, and country of origin.
The usual approach (B&W Nautilus, Revel Ultima Salon2, Vandersteen Model Five) is uniformly broad dispersion through the use of acoustically small drivers and baffles.
When you can park yourself and speakers in the middle of a large room with reflections 10ms out that works wonderfully; but most domestic environments have only 3-4ms of delay.
You need uniform limited dispersion to work around that; where the wave guides are good at both uniformity and off-axis attenuation.
For studio monitoring you can park yourself and speakers in the middle of an acoustically treated room. You don't need the size and expense.
Objective measurements and subjective listening impressions of modern wave guide systems do not bear that out.