Axiom Home Page
Posted By: autoboy Measuring and correcting frequency response - 10/28/10 09:25 PM
So my brother hired a sound engineer to help him set up his new audio system.

It is the one you've seen here:

He called me last night with some reports of the measurements the audio guy was getting from his calibration. The measurements showed a -9db hole in the sub response in the "important frequency range" which I am assuming is right around 40-60hz.

He also said that the audio guy didn't like the settings I had made on the SVS sub. I had simply turned off the crossover (he had set it to 80hz and was doubling up the receiver crossover) and I set the tuning mode on the SVS to 15hz instead of 20hz since he hadn't installed the foam plugs that the switch is designed to work with.

He also said that the audio guy measured a -9db hole in the "important male voice frequencies" and said it was extremely wide.

This got me skeptical about how he was measuring the speakers. Apparently he was positioning the mic INSIDE the port for the sub to isolate it. He was also putting a mic directly in front of the main speakers and measuring their response and calibrating from there. I'm not sure what he does to "calibrate" the sound.

I'm not an expert or anything, but I was always told to measure from the seating positions because of the room effects. This is why Audessey room correction measures from as many seating positions as possible. Why is the audio guy measuring the speakers this way? Shouldn't he just set up the Audessey and run if he wants to equalize the room? From everything I've read, the algorithms it runs are way more effective than a dude with a point source mic. Especially one that measures right in front of the speaker.
Heh. If he was doing it against towers, he must have just been getting the frequencies off of one driver.
Yeah, that's what I was thinking. I've never heard of anyone doing their measurements in front of the speaker. But, I don't do this for a living.
I've heard of setting the volume of multiple subs with one output on the receiver, by measuring each of them up close to isolate each, but not inside the port. Instead a few inches from the center of the cone. But then the over all sub out trim on the receiver is set from the listening position.

If the receiver is doing the bass management, the cross over on the sub should be bypassed, or set as high as possible. Setting it to 80 not only multiples the slopes, but also could remove LFE content stored on the disc which can go as high as 100 Hz, and won't be sent to the main channels.

I do believe that without the port plugs, SVS subs should have their tuning set to 20 Hz. It's only when converted to sealed should the tuning be lowered. So that seems to be the only thing he got right.

I'd be asking for money back.
I just wanted him to help set everything up and run the auto calibration modes. I'm not really sure what he's planning on doing since I don't talk to him directly it's all through my brother who may not be describing it properly.

Measuring volume from the sub may be fine, but frequency response is very dependent on the position of the mic.
© Axiom Message Boards