Correction of room acoustics. E-traps?

How can the E-trap add audible distortion at higher frequencies when (1) it is not in the signal path and (2) it is sharply frequency limited by design?

Good question.

(1) It is in the signal path in the sense that it is making acoustically audible signals in your room (although these are 'corrections' or 'damping' there is every possiblity that other detrimental audio is generated)

(2) The amplifier circuitry is no doubt sharply frequency limited by design....however a transducer is NOT. Most of what you hear from an impressive subwoofer is harmonic distortion...that is the intended signal at 30 Hz is actually nigh close to inaudible (due to fletcher Munson curves our hearing is pretty insensitve there) but the 20% harmonic distotion at 60, 90, 120 and 150 Hz is absolutely impressively deafening!!!

Think twice next time you hear an impressive subwoofer - with the majority of them you are simply hearing huge amounts of distortion.

So lets assume the bag end has an impressive 10% harmonic distortion and you use it to fix a 30 Hz ringing problem....what happens at 60 Hz and at 90 Hz (where you might have a NULL and need a boost not a cancellation)....that is my point!!!

The nice thing about broadband passive absorbers is that they add NO harmonic distortion...

Kr4,

Perhaps I am a bit overzealous compared to most people on distortion. For example, I would like an acoustic drum set or a double bass to sound like well er actually an acoustic drum set or a double bass - and not something else altogether different. I mean what you get with a lot of ultra LF audio reproduction these days is impressive and sounds very nice but it sure isn't very accurate - a lot of it is due to the transients that don't sound right but it is also a function of added harmonics which changes the timbre. I guess you could say I am in the very small minority camp of "no sub" or "no ultra-LF" being preferable a bunch of distortion. I am serious when I say that it is hard to build something that goes as low as bag end requires with less than 10% distortion at a useful volume level - so if you are aiming to tackle room problems - what else might an active device like this be inadvertently doing?

I get your point but think you are too liberal in saying it is "in the signal path." That definition might include everything in the room, including us.

Also, note that a room mode at 30Hz is usually accompanied by submodes at all the harmonics, as well. That suggests that any out-of-phase harmonics from the E-trap might even have a salutary effects. (Wild thought, no?) I thought the E-trap quite effective but very subtle in its action and it was accompanied by no noticeable negative effects, in practice.

Now, I am not suggesting that the E-trap is panacea but it is one of many tools, each useful when appropriate.

I do agree with your preference for physical room treatments as the first and foremost way to deal with room acoustics but, where one cannot (for any reason) accomplish enough that way, electronic devices can be very helpful.