Calibrating Sub using signal generator

[satz]

Hi all

I've got access to a frequency generator CD (equal volume, single frequency signals in steps of 10Hz) from 10Hz to 20kHz.

I also have one of those Radio Shack analog noise level meters. (set to slow response, C weighting)

I'd like to ensure that my system (incl Sub) is producing a reasonably flat in-room response. Especially to ensure that Sub is nicely integrated.

So is it a matter of first setting a reference level (say 70dB on the 1kHz signal), then measuring the levels at 30Hz, 40Hz, 50....etc. Without changing the amplifier volume of course.

And if they all are reasonably close (+ or - 5dB from 30Hz to 10 KHz) then can I consider that Sub is pretty well integrated with the mains?

many thanks in advance

Cheers

Satz

[Sir Terrence the Terrible]

Hi all

I've got access to a frequency generator CD (equal volume, single frequency signals in steps of 10Hz) from 10Hz to 20kHz.

I also have one of those Radio Shack analog noise level meters. (set to slow response, C weighting)

I'd like to ensure that my system (incl Sub) is producing a reasonably flat in-room response. Especially to ensure that Sub is nicely integrated.

So is it a matter of first setting a reference level (say 70dB on the 1kHz signal), then measuring the levels at 30Hz, 40Hz, 50....etc. Without changing the amplifier volume of course.

And if they all are reasonably close (+ or - 5dB from 30Hz to 10 KHz) then can I consider that Sub is pretty well integrated with the mains?

many thanks in advance

Cheers

Satz

Satz,

I would not start with any frequencies that high(1khz is too high to really tell you wants going on really low.

My suggestion would be to start at the crossover point of your sub(i.e. 80hz, 60hz etc) and calibrate that frequency at about 79db(this is so that any background noise you may have won't interfere with the measurements.

In the first two octaves, I would recommend that you only correct peaks, and not drop outs. Drop outs at these frequencies cannot really be addressed effectively because of the amount of power that any boost would require could possibly damage the sub due to over excursion, or your amp.. Also, the reality is that holes cannot be filled in because they are usually room related. In that case, repositioning might correct the problem. If not, then parametric eq is the next best solution. Remember, correct peaks only. Our ears indentify peaks in frequencies much better than dips in the bass frequencies.

Rule of thumb is acoustical correction first(moving the sub around to obtain the best overall response) then electrical is second.(eq)

For the upper frequencies, the same rules follow. However, I would use the pink noise within the reciever for this since you do not have access to a RTA. In most small rooms, the most critical frequencies are those that are 200hz and below. Above that, modes and nodes are so tight, that absent a real time analyzer it is very difficult to get a accurate response from a SPL meter.

So in working with your desires, I would start calibration with the spl meter reading 75db's at 1khz, and work yourself down to the crossover point of the sub. From that point and below I would use a reference of 79 db's(or so) to calibrate the sub down to its low frequency limit.

Doing a frequency calibration this way is very time consuming and difficult without the proper tools. A SPL meter is not the best tool for this, as it doesn't allow you to see the "big" picture in real time. It only allows alot of very small slices at a time. Also the CD should include 1hz points instead of 10hz points.(if it moves at 10hz, what happens in between that setting and the next??) . This CD steps up the frequencies(or down according to perspective) are a little to crude for a really accurate measurement.

If I have confused you, let me know and I will clarify.

[satz]

many, many thanks Sir Terrance,

that was a wonderful post and I appreciate the time you've taken

kind regards

Satz