newbie on Genelec setup in home theater - Forum

Hi Alain,

Your Onkyo has so called pre out connectors (see the picture) which can be used to connect active speakers. So all you have to do is route an RCA-XLR cable (or use RCA-RCA cable with an RCA to XLR adapter) from each pre out to each speaker.

All amplifier functions including the Audyssey calibration will work just the same as with your current setup.

I just got my new 8020B hooked up to the Onkyo TX-SR703 (older model without HDMI) and run the first calibration. Works as advertised.

I replaced SONY SMS-3 and continue to use two homebrew 30cm subwoofers with Trio Amps. Thus my question: How to ensure correct subwoofer polarity? The Onkyo Audissey calibration does not check for that.

I just got my new 8020B hooked up to the Onkyo TX-SR703 (older model without HDMI) and run the first calibration. Works as advertised.

I replaced SONY SMS-3 and continue to use two homebrew 30cm subwoofers with Trio Amps. Thus my question: How to ensure correct subwoofer polarity? The Onkyo Audissey calibration does not check for that.

Hi,

I checked the operating manual for the TX-SR703 and it says that the automatic speaker setup adjusts for correct subwoofer distance, which in other words means correct phase.

If you do not rely on the automatic setup, you can also set it manually, but it requires some extra work. First you will need to have a sine wave signal at the crossover frequency (for example 80 Hz). You should then play this tone through your system and vary the subwoofer distance setting on the amplifier. By ear or more preferably with an SPL meter, observe the setting which produces the loudest tone/total SPL. This procedure will give you the preferred phase setting. If you want to go even one step further, you could try to measure the frequency response of your system with a microphone and a computer based measuring program (for example Room EQ Wizard).

Thanks for that, Ilkka, that may work out. I have test signals on CD, even a generator in the closet, and an SPL meter.

Actually, you just gave me an idea. I am more concerned with matching pulse response so that a kick drum retains most of its kick. The distance (delay) adjustment cannot fix it if one diaphragm comes out while the other goes in. The wavefronts in the crossover range tend to cancel.

What I'll do is get the generator out, play a 5hz step function (square wave) and check the listening position microphone signal on my oscilloscope. This way I can see whether the waves add up correctly or subtract. In the latter case I swap "plus and minus" on the subwoofers, re-calibrate and done. Thanks again.

Oh, is this similar to the way your designers determine the acoustic axis?

You are describing the effect of phase-matching at the crossover region (="pulse response"). That you can adjust with distance setting because if you change the delay, you will also change phase. What you describe with swapping "plus and minus" is a 180 degree phase shift i.e changing the polarity of the signal. With distance setting you can set the phase more accurately than that. Usually AV-receivers offer 1 foot / 30 cm increments which equals to ~25 degree phase change.

Thank you. Found the right polarity by listening to low frequency filtered noise and now got back the kick of the drums and the precision of the bass notes. My fault, I did not follow standards when wiring my homebrew subwoofers. Is it that (+) on the red terminal should push the diaphragm out? Maybe the Trio Amps reverse the polarity. Anyway, now I enjoy the Genelecs a lot with my subwoofers.

Yes, I can change the delay in 30cm increments, and it adjusts the phase nicely, in theory, for one given frequency (as in AC, sinewave).

Problem is,

a) crossover is a frequency region, say 1/2 to 1 octave audible overlap. For any given delay introduced to correct a polarity error, phase between two drivers at nearby frequencies will be all over the place.

b) Music is AC only in principle, all the interesting detail is in bursts. Silence and then the wave begins. Whatever diaphragms work together in a frequency range must be polarity matched or you will have audible cancellation effects.

If one of the readers wishes to verify and train ears on the strange "through the head" sensation of out-of-phase low frequency response, use a stereo set-up without the subwoofer and listen to a test CD with red noise in-phase and out-of phase, for example DHFI Test und Demo CD Nr 10, 819340-2. Clearest to hear from a position right between the speakers.