Question concerning db sensitivity

Duke,

Good point. Waveguide loaded mid ranges and tweeters are widely used everywhere even in nearfields. I draw a large distinction between these designs and traditional "compression" horns ....but like most things in this hobby many designs share some physical similarities.

Here is a good independent article on this subject (Ralph at AERONet). Waveguide Mid range Design

There are more details and a discussion of waveguide versus compression horns on this website (for those seriously interested...I realize details can tend to make most people's eyes glaze over in a hobby which is largely intended to be just a fun pastime).

Shadorne,

Very interesting site, thanks for the link. I've used that ATC midrange driver and agree that it is a very high quality unit. It doesn't really fit in with my present speaker design paradigm so I'm not using it any longer, but in my opinion its among the very best direct-radiator moving coil midranges in production today.

The article points out something that's often overlooked regarding the fabled ATC dome midrange - once it has been equalized, its efficiency is down to about 90 dB.

The article on waveguides is also quite informative. A large-radius lip at the mouth is indeed desireable, and any round horn or waveguide will have on-axis anomalies (in particular a hole) that's related to the dimensions, lip radius, and microphone distance. Whether the on-axis anomalies are audible depends on several factors, but I prefer to sidestep the issue by listening off axis.

I like a narrower pattern than what the author recommends. He seems to like 110 to 150 degrees, presumably in pursuit of a wide sweet spot. In my experience a 90 degree pattern will give you a very wide sweet spot provided you use a lot of toe-in, and also there is less pattern-width discrepancy in the top end when the tweeter does start to become directional.

The author takes the position that a direct radiator is superior to a compression driver because it has smoother response. I'll concede that its easier to get smooth-sounding response from a waveguide-loaded direct radiator, but it can be done with a compression driver as well (the ear is insentitive to narrow-band peaks and dips as long as they average out over a fairly short interval). And the compression driver will almost always have higher efficiency and better dynamic characteristics, which may or may not be desirable in a particular applicaiton (you don't want a big mismatch in power compression charactersitics between the woofer and tweeter). Having built prototype systems using both approaches I prefer the compression driver, but suitable ones are rare and even then they aren't easy to work with.

One of these days I'd like to see how a two-way with waveguide-loaded tweeter compares side-by-side with something like an ATC SCM-50.

Duke

One of these days I'd like to see how a two-way with waveguide-loaded tweeter compares side-by-side with something like an ATC SCM-50.

Yes that would be interesting.

ATC adapt a vifa tweeter with a short conical waveguide on the small two way SCM 20. The soft mid dome is grafted onto the woofer in this two way design. The woofer shape also appears to act as a mid waveguide as well as a woofer. The crossover is lower (2.8 Khz instead of 3.5 Khz, as on the SCM 50) probably because of cone breakup issues or driver beaming in the two way design. The dome may also act as a phase plug and help keep beaming issues above the crossover (this last bit is just my speculation).