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Old January 1st, 2005, 8:40 PM
frankrizzo frankrizzo is offline
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Question SPL METER / HELP!!

How, in everyday layman's terms, do I calibrate my new VT-12 with the STF-2 sub? I have a Radio Shack analog spl meter. I have the Sound & Vision video essentials disc. I'm confused about where to put the meter, where to aim it (at each speaker or straight ahead and upwards, how to caliberate the sub, etc., etc. Please try to explain in very simple terms as I am not as well versed as some of you are.

My room is 11' x 16' foot with an opening 6 ft. wide to the right of the TV that leads into the kitchen area. I have my front speakers on stands about 40" high, with the center channedl a foot or so above that on top of the TV. I put the sub in the right rear corner about a foot from the side wall and about 6 inches from the back wall. I have the rear surround speakers mounted on stands 58 inches high facing outwards into the room at a 45 degree angle. I may not utilize the rear center surround at this time. Thank you in advance.

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Old January 1st, 2005, 9:06 PM
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Here is a pretty good article on calibrating your system.Hope this helps.
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Old January 1st, 2005, 9:18 PM
frankrizzo frankrizzo is offline
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Thanks for the info, but I'm still looking for something a little more detailed,and some info on the sub calibration, which is all greek to me.

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Old January 3rd, 2005, 2:56 PM
Retread Retread is offline
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What I did.

Originally Posted by frankrizzo
WID, Thanks for the info, but I'm still looking for something a little more detailed,and some info on the sub calibration, which is all greek to me. Rizzo
I assume you have something like a Radio Shack SPL meter. The discontinued analog is easier to use than the newer digital.

I think the microphone is pretty much omnidirectional, but don't know for sure. That would mean it doesn't matter much where you point it.

You want to measure at several locations in your listening area and average the results, since you'll get room affects at the various locations that are bigger than the variations of the system itself.

What you'll be doing with the SPL meter is three things: (1) setting the relative volume of the sub and other speakers; (2) adjusting the crossover between the sub and other speakers; and (3) mapping out the overall response of your system.

You'll need a sound source that does narrow-band warble tones. A disk came with my VTF-3R that had those tones. Alternatively, you can purchase a calibration disk such as Digital Video Essentials. Warble tones are generated by randomly switching rapidly between frequencies in a narrow bandwidth, such as a third of an octave. You want warble tones, so the sound doesn't camp on a single frequency and unduly excite room responses.

You'll want a pencil and paper and on the left write down the page the center frequencies of the warble bands. Make columns for various listening locations.

Place the meter at ear height and start the warble tones. Observe the meter's reading, estimate the average level (this is why the analog is easier to use), and write down the result. Do the same for each of the warble bands. At this point, you can probably determine whether the sound level of the sub needs to be adjusted relative to the other speakers and make adjustments until level at the middle of the sub range (say 40 Hz) is about the same as for the mids (say 250 Hz).

At this point you change the location of the meter and run the warble tones again, recording the results. Repeat, repeat, repeat.

Now average the result for a given warble band for all the locations (i.e., add the result for each warble band at each location and divide by the number of locations).

Now apply the meter's correction parameters to the results. The Radio Shack meter rolls off at low frequencies, so you'll want to add the correction parameter to the result for each warble band. The correction parameters can be found by a search on this forum.

At this point, you have the sub's relative volume matched to the other speakers, and can plot the average frequency response of your system. However, you may have a mismatch between your subwoofer's crossover and your other speakers, as represented by a hump or dip in the crossover range. By fiddling with the sub's crossover, you may be able to smooth this.

Unfortunately, you are still likely to have big humps and dips in your sub's frequency response. This is because room effects are generally a lot bigger than what one would be led to expect from reading specs of equipment. One can try moving the sub around to get the best result at a "sweet spot," but ultimately you may not get smooth response without putting in some equalization. There are also threads about this topic on this forum. In particular, you can find what I went through to get rid of about a 30 dB variation across my sub's range, caused by room effects. Do a search on "Retread" to find it.
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Old January 3rd, 2005, 7:29 PM
frankrizzo frankrizzo is offline
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Thanks for the reply. I'm going to attempt this this weekend.

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