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Re: Proper methodology and source music for setting up speakers?

Posted by Bruce from DC on June 21, 2001 at 16:29:42

In Reply to: Proper methodology and source music for setting up speakers? posted by Rupthekid on June 21, 2001 at 15:37:15:

Here's how I've done it, using a Radio Shack SPL meter and a test CD originally put out by Stereo Review and Chesky records that has equal level l.f. test tones from 300 Hz to 20 Hz.

mount the SPL meter on a tripod at your listening chair. Set it on the 80 dB range, "C" weighting and "fast" A meter reading of "0" corresponds to 80 db, so you have a range of between 86 dB and 70 db on the meter with that setting.

Then position your main speakers where you want them and for best sound. Then I run the test series without the crossover in circuit, while watching the meter. On my record, an announcer gives the frequency before tone is played. So, I write down all the frequencies first, then I write down what the meter says as each tone is played , e.g. "0", "+2" "-4" etc. This should tell you 2 things: (1) where your main speakers naturally start rolling off in the bass and (2) whether you've got some serious room node problems with your current main speaker placement (e.g. big bumps or suckouts). If you've got room problems, I would move the main speakers around to the extent possible to try and reduce them before even fooling with the sub.

After you do all this, you should have a baseline profile of your main speakers' bass performance. Remember the idea of a sub is to improve that performance, not muck it up.

Ok, now we get to a philosophical crossroads: do we use the crossover to remove bass from the main speaker drive or not? My answer is not, unless you've got really small speakers or speakers with limited dynamic range (like Quad electrostats) and you want to play rock and roll really, really LOUD. With your speakers, I don't think you fit into either category, so I would recommend not feeding the power amps driving your main speakers with a high pass output from the crossover. If your preamp has 2 pairs of outputs, I would use one pair to feed the amps driving the main speakers directly and the other pair to feed the crossover, using its summed low pass output to feed your subwoofer amp. The reason for this is that crossovers often introduce coloration into the main speaker output, the crossover can cause phase shift; and the speaker's natural bass rolloff can often sound better with the sub than the steeper rolloff produced by the crossover.

Ok so now you put the sub where you think it should go, connect the subamp and crossover. If the crossover's low pass turnover point is adjustable, for openers, set it at the point where you determined your main speakers rolloff in the bass. Set the level control at "0" and put some music on that has bass. Turn the subwoofer level up until you feel like you're getting the low bass that you've been missing.

Now run a set of measurements of the whole system, like you did before with the main speakers only. Let's say, hypothetically, that your main speakers start rolling off at 45 Hz. What you should see with your numbers from the combination is that the bass holds up all the way down to 20 Hz. (remember, the RatShack meter is less sensitive to low bass. The correction factor at 20 Hz is to add 6 to the meter reading. There are places on the web where you can get a table of corrections.) The numbers above your main speaker's rolloff point should be the same. Assuming you're not spot on the first time, I would adjust the sub level for a response in the 20 to 30 Hz range that is equal to the upper bass (100-200 Hz) response. If the sub then produces a hump in the range where the mains and the sub overlap (say, 40-60 Hz), then lower the crossover point for the low pass control on the sub. If there's a bit of a dip between 30 Hz and 50 Hz, then raise the crossover point a bit. If you have a fixed crossover, you can do what I suggested you not do, which is feed the main speakers' amps with a high pass output from the crossover.

If that doesn't solve the problem, then you'll have to choose between having flat response in the range where the sub takes over from the mains or having flat bass extension to 20 Hz. Your particular sub should be flat to 20 Hz, if the manufacturer is telling you the truth about its response. Or you can split the difference and be down a few dB at 20 Hz but have only a little hump in the transition range.

After having had the same sub and the same speakers in the same place for 3 years, I can tell you that setting the sub up this way gave me better sound than years of "eyeballing" it with music. The sub does not "thicken up" sounds like pianos to something unrecogizable, but gives a realistic string bass sound and shakes the room appropriately with the synthesizer bass in things like the "Titanic" sound track and track one of Paula Cole's "This Fire" (a CD that I don't like at all; but it's a good bass demo).

Good listening.

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