Reply To: Ringing Out The Room – Channel or Overall PEQ?

[DoctorG]

DR and Andreas,

Now that I have you focused on the correct issue – the frequency of the sound feeding back — maybe we can communicate.

Part of the “room” equation are the speakers and the mic. For feedback to occur at a given frequency, all that has to happen is for that frequency to be generated from the mic, transmitted through the mixer, come out of the speaker and hit the mic again at a level sufficient to start a feedback loop. The room itself doesn’t have to contribute to that loop, only the transducers and electronics. You stated that in other terms.

I said that I was assuming that the operator knew how to take into account the factors having to do with proper speaker placement vs microphone position and the directionality characteristics of each device. I wasn’t addressing those issues; my focus was on the frequency response of the system.

My choice of 10 kHz and the female voice as my example was perhaps unfortunate but also deliberate; I was just trying to make a point, get you on the subject and at the same time give you something to argue about. A high-pitched female voice can reach 3000 Hz and the 3rd harmonic would be at 9000 Hz. If the microphone can reproduce that frequency strongly, and/or if the mic or speaker has a response peak in that range, feedback can occur at that frequency without room resonance being involved. At any rate, a female voice would be more likely to generate high frequencies than a male. That’s all I was trying to say. Pick another frequency – the argument remains the same.

If one then reduces the system gain at that frequency with a GEQ or PEQ below the feedback threshold, the feedback can be eliminated. Now that you are talking about the Q values of GEQ and PEQ, you are on the subject I was trying to address; I just did not want to completely ignore all of the factors that contribute to feedback overall, but I wasn’t trying to address them in detail.

Once all the other factors have been cared for, you are left with the frequency response of the system. If you have smoothed room/speaker response with the appropriate GEQ, eliminated the primary feedback frequencies with HPF. LPF, and the PEQ on the channel in question, and some unwanted feedback is still being generated at the volume level you wish to use, you must resort to the PEQ of the group and main controls, then finally the GEQs on those outputs. With it’s fairly narrow Q values, a GEQ can be used to remove particular frequencies without adversely affecting the overall sound, if used judiciously. If the EQ devices are not sufficient to eliminate the feedback, one must then reduce overall system volume. The Qu has these capabilities.

I spoke about using an RTA to determine where feedback is occurring; the Qu screen can display this – it is very informative.

Lord! I hope we have arrived at the answer the operator was asking originally!