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#354212 - 09/07/11 06:27 PM Calibration question
bdpf Offline
aficionado

Registered: 06/28/08
Posts: 769
Loc: Toronto, Canada
I know it's a dumb question but how do you verify the speaker levels with a SPL meter. I just got one and just wanted to check how accurate Audyssey got it. I though the AVR would be able to output a test tone at 75dB that I would be able to output on each speaker individually and verify that I have indeed 75dB but I can't find this option. If I use a test tone CD, what do I use as a reference? Basically, how do people that calibrate their system manually proceed?
Thanks.
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M80s/VP180/QS8s/EP600/AVR-890
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#354218 - 09/07/11 07:11 PM Re: Calibration question [Re: bdpf]
cb919 Offline
connoisseur

Registered: 02/17/09
Posts: 1166
Loc: Ottawa, Canada
Bruno, I am not quite sure which way Audyssey does it, but I believe most calibration routines will set one of the front speakers at a 0dB gain on the receiver. Then every other speaker is gained up or down relative to the 0dB speaker to make them all the same output with the same test tone.

So to answer your question I would 1)find the 0dB speaker, 2)play a test tone and adjust receiver volume with that speaker so it reads 75dB or 80 dB (you pick, whatever is easy to read on your meter) then 3)cycle through the speakers and see that each records the same dB output.

Now a little trick I use you might find useful - I set the 0dB speaker to be the center channel and then set all other speakers relative to that. That makes it easy for me to see if I have the center channel bumped up a few dB for movies or not. For multichannel music listening I like the whole system flat, but for movies I sometimes up the center as many others do for dialogue. Hope that helps.
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#354234 - 09/07/11 08:56 PM Re: Calibration question [Re: cb919]
SirQuack Offline
shareholder in the making

Registered: 01/29/04
Posts: 13571
Loc: Iowa
Depends on the receiver you have, on my Denon's I can do a manual test tone under the speaker settings section. Audyssey will be more accurate than your meter, and moving the meter around while holding it or not having it in the exact placment with no room noise, you are unlikely to get the same results.
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#354252 - 09/07/11 10:34 PM Re: Calibration question [Re: bdpf]
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10627
Bruno, it certainly isn't "dumb" to have trouble finding a procedure in a Denon manual, since they're experts at concealing these things. It is, however, unrealistic to think that the Denon microphone and associated circuitry are less accurate than those found in a Radio Shack or other inexpensive SPL meter, and that added human error in reading the meter doesn't make it even more likely that the manual calibration is the less accurate of the two.

Be that as it may, I took a quick look at the 890 manual and see that under the Settings section the Manual Setup for Channel Level is described at p.29. These pink noise test tones are at 75dB.

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#354274 - 09/08/11 09:23 AM Re: Calibration question [Re: JohnK]
bdpf Offline
aficionado

Registered: 06/28/08
Posts: 769
Loc: Toronto, Canada
Thanks guys.
I looked at the manual yesterday but couldn't find what I was looking for. John, thanks for taking the time to look at the manual, I'll have a better look at this section tonight when I get home.
I am not doubting the capacity of Audyssey to adjust the right levels, I am more interested in playing with the SPL meter and understand how people used to calibrate their system manually.
_________________________
Bruno
M80s/VP180/QS8s/EP600/AVR-890
------------------------------------
"The problem is choice..."

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#354296 - 09/08/11 01:51 PM Re: Calibration question [Re: bdpf]
J. B. Offline
connoisseur

Registered: 01/19/11
Posts: 1291
Loc: Quebec, Canada
since the mid 80's up to about a month ago, i used to calibrate manually, which was very time consuming and demanded lots of care and precision, and the results were far from being as good as using Audyssey, because Audyssey does much more than adjusting F.R.

if you know how a Technics SH8000 works, that's the equipment i was using as signal generator/spl meter (the generator would send warble tones every 1/3 octave, and the microphone was factory calibrated independently for every SH8000.)
you can have a look here: http://audio-heritage.jp/TECHNICS/etc/sh-8000.html

what had to be done, to find the best freq. resp. was by moving the speaker under test a few inches at a time and make a F.R. graph. then move a few inches again and make a new F.R. graph, and so on, until you were satisfied you had the best possible response (speaker location/room response).
then you had to do the same thing to the other speaker, in a stereo system.
you could only adjust F.R. with this instrument, and no equalizer/tone controls were to be used, specially not the "loudness" button.

the whole thing could take one or two days to complete, and it was far from being as good as Audyssey, because Audyssey does more than adjust F.R.

if i had to move the speaker for whatever reason, i would then note on paper the exact place where my speakers were sitting in relation to walls, to be sure i would put them back exactly where they belonged, thus saving myself hours of calibrating.

at the time, it was one of the best ways to do it, and the results were quite good; i had a wide and deep stage, with very good instrument localization (on jazz or classical music).
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#354472 - 09/10/11 05:09 PM Re: Calibration question [Re: J. B.]
bdpf Offline
aficionado

Registered: 06/28/08
Posts: 769
Loc: Toronto, Canada
So I got to output the test tones and here what I got with the Radioshack meter while holding it as still as possible:
FL 72dB
C 71dB
FR 73dB
SR 71dB
SL 71dB
Sub oscillates between 68 and 74dB.

I have to say that I am kind of surprised to find a difference of 1 and 2 dB from the fronts as I thought the SPL meter was pretty accurate. I tried to shift a few inches back and forth and to the sides but it stayed pretty consistent.
I have n idea why measuring the sub, the needle doesn't stay still so it's impossible to get an exact measurement.

I guess I'll leave everything the way it is as Audyssey probably did a better job than I did measuring these levels, I was just expecting to find the level of all the speakers to be the same when measuring with the SPL meter but they're not.
_________________________
Bruno
M80s/VP180/QS8s/EP600/AVR-890
------------------------------------
"The problem is choice..."

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#354474 - 09/10/11 06:25 PM Re: Calibration question [Re: bdpf]
J. B. Offline
connoisseur

Registered: 01/19/11
Posts: 1291
Loc: Quebec, Canada
you should average the reading the spl meter gives you for the sub readings; in this case, the steady state reading would be right around 71dB.

the sub frequencies are so low that the spl meter needle is in fact following the driver's movement while it's moving the air in the room.
if the meter's needle could respond fast enough, you'd see the needle swinging wildly 20 times per second if the tone was 20Hz.;

at 1000 Hz, the needle is much too slow to be able to follow the speaker's movement. this is "damping".
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#354477 - 09/10/11 07:15 PM Re: Calibration question [Re: J. B.]
bdpf Offline
aficionado

Registered: 06/28/08
Posts: 769
Loc: Toronto, Canada
Thanks JB for the explanation.
_________________________
Bruno
M80s/VP180/QS8s/EP600/AVR-890
------------------------------------
"The problem is choice..."

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#354482 - 09/10/11 09:43 PM Re: Calibration question [Re: bdpf]
michael_d Offline
connoisseur

Registered: 07/23/04
Posts: 4195
Loc: Up yonder
I have found the wee lil’ mic that came with my 3808 to be less accurate than my RS meter. Or it’s the other way around, who knows for sure.

After I run the auto cal feature, I verify with the RS meter. The auto cal is always pretty darn close, but off enough for me to make changes. Like already mentioned, I bump the center up 2 DB over the mains. I set all the other speakers to the same DB as the mains. The sub is a bit more time consuming. Because it does swing, I watch it for a spell so that I can see a repeatable swing, like 75 DB – 80 DB. They I simple figure what the middle of the swing is and adjust the LFE until the middle is 4 DB over the mains.

When I do this, I have the meter set up in a tripod at the prime location (same as location #1 in the auto set up). It is pointed straight up and at ear level. I crouch down behind it and adjust the AVR to set the DB levels.
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