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Which way do you point your sound pressure meter?


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33 replies to this topic

#21 of 34 OFFLINE   ling_w

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Posted January 10 2002 - 05:11 PM

Jeremy,

Your method doesn't make sense. For method 2, where you want every speaker to be roughly off axis by the same amount, why would you not just use method 1, where it would put almost all speaker at 90 deg off-axis? Plus, if one points the mike directly at each individual speaker, would this not solve that problem completely?

Also, if we want it to simulate the ear/head, we would actually want to use the "A" weighting. Since the response perceived by us is modified by the ear/head, therefore, what is outputted by the surround would not necessarily sound like what is coming from the front, thus needing the freq modifier of the "A" weighting so it sounds equally loud when the sound is coming from the rear.

#22 of 34 OFFLINE   BruceD

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Posted January 10 2002 - 06:45 PM

Ling,

Please read the RS manual.

"A" weighting DOES NOT measure any pink noise test signals below 500Hz. That means you will not be able to balace a subwoofer at all, much less match it's SPL to the other speakers.

That's why you want to use the "C" weighting scale.

All the other stuff you said is nonesense.

#23 of 34 OFFLINE   Jeremy Anderson

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Posted January 11 2002 - 12:01 AM

Quote:
For method 2, where you want every speaker to be roughly off axis by the same amount, why would you not just use method 1, where it would put almost all speaker at 90 deg off-axis?
If holding your meter straight up puts them all at almost 90 degrees off-axis, then fine. But if you have placed your speakers according to Dolby's recommendations (i.e. having the mains at ear level and surrounds 2-3 feet above that point), then you are not close to 90 degrees. Angling the meter forward compensates for that. Let's see if I can do a quick-and-ugly 2-dimensional diagram to help you understand:

X Surrounds
|
|
/--------------X Mains
Meter (angled forward)

Quote:
Plus, if one points the mike directly at each individual speaker, would this not solve that problem completely?
Try it and see how it sounds. Once you do, I can guarantee you it doesn't sound balanced. But as I and others here have said all along, if it works for you, then use it! Your mileage may vary! Posted Image

#24 of 34 OFFLINE   Chris Moffitt

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Posted January 11 2002 - 01:13 AM

So, I've followed the advice here, purchased the Radio Shack analog SPL meter and calibrated my speakers using the internal reference tone on my Marantz 5200. Yes, I use a camera tripod, mounted in the sweet spot an angled straight up or at 45 deg.

Everything on the SPL measures right at about 75db (as close as I can get it), but when I play music (2 Ch - CD), my sound stage seems to be "anchored" to the right. I wouldn't say it's coming directly from the right speaker, but it doesn't seem quite right to me.

If I go in and manually tweak my levels so it "sounds right", when I go back to using the SPL, I'm off by around 5db or so.

I figure it's one of a couple things:
1. Some sort of weird frequency problem related to my room
2. Toe-in not correct
3. Problems with my ears

My next step might be to use video essentials and see what that gives me.

Does anyone have any ideas or hints. I'd greatly appreciate it.

-Chris

#25 of 34 OFFLINE   Jonathan_M

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Posted January 11 2002 - 01:34 AM

Chris,

I would investigate your toe-in again. That's likely where you'll find the problem. Someone in another thread suggested taping a laser pointer to the speakers to aim them. Just a suggestion.

Good luck!

-Jonathan
"We're hosed. We lost the remote."

#26 of 34 OFFLINE   ling_w

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Posted January 11 2002 - 06:10 AM

Quote:
"A" weighting DOES NOT measure any pink noise test signals below 500Hz. That means you will not be able to balace a subwoofer at all, much less match it's SPL to the other speakers.

That's why you want to use the "C" weighting scale.

All the other stuff you said is nonesense.

I am talking about using "A" weighting for LCR and surrounds, not sub. As for using it, the purpose would not to get equal balance of energy distribution, but to create equal perceived loudness.

e.g.
If my surrounds are dipoles mounted far far back in my room. The sound I measure from it would include alot of reflected sound, and by the fact that it is a dipole with the transducers 90 deg off axis from the listener, the upper midrange freq has been attenuated and maybe the upper bass/lower midrange has been enhanced. So the energy distribution has shifted to the lower part of the freq spectrum, where our ear are less sensitive. So if we measure with "C" weighting, most of the sound pressure picked up does not translate to sound heard by listener. But with "A" weighting, the sound energy in the lower freq spectrum will have less affect on the final reading, just as the way our ear would perceive.


Jeremy,

If that is the way you speaker is set up, then I presume pointing it 45 deg up is fine. But not in many cases. I think if they want to be accurate in their sense, they should point directly to the dipole side speaker and 90 deg off axis for the LCR speakers. This due to the fact the dipoles are 90 deg off axis to the listening position. This would place all transducers 90 deg off axis.

#27 of 34 OFFLINE   BruceD

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Posted January 11 2002 - 07:13 AM

ling,

quote:
-----------------------------------------------------------
I am talking about using "A" weighting for LCR and surrounds, not sub. As for using it, the purpose would not to get equal balance of energy distribution, but to create equal perceived loudness.
-----------------------------------------------------------

Why do you want to confuse people by directing them to use different scales "A" and "C" to measure speaker balance, because they do or don't also measure a sub ?

The whole purpose of the "A" and "C" weighting as described in the RS manual is: "Select A-weighting for noise-level determinations, and C-weighting for measuring sound levels of musical material".

Last time I checked we were measuring for musical material reproduction in our Home Theaters.

The whole point of using an SPL meter is to get an equal SPL response from all speaker/room interfaces at the measurement location (regardless of speaker type or orientation).


quote:
-----------------------------------------------------------
e.g.
If my surrounds are dipoles mounted far far back in my room. The sound I measure from it would include alot of reflected sound, and by the fact that it is a dipole with the transducers 90 deg off axis from the listener, the upper midrange freq has been attenuated and maybe the upper bass/lower midrange has been enhanced. So the energy distribution has shifted to the lower part of the freq spectrum, where our ear are less sensitive. So if we measure with "C" weighting, most of the sound pressure picked up does not translate to sound heard by listener. But with "A" weighting, the sound energy in the lower freq spectrum will have less affect on the final reading, just as the way our ear would perceive.
-----------------------------------------------------------

The above is simply not a smart way to measure.

Frankly the "C" weighting simply captures all that your speaker/room is actually delivering to your measurement location.

Why not measure what your room is truly producing instead of artificially throwing away actual room/speaker response as you suggest with the statement; "But with "A" weighting, the sound energy in the lower freq spectrum will have less affect on the final reading"?

Certainly seems counter-productive to me.

#28 of 34 OFFLINE   ling_w

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Posted January 11 2002 - 07:47 AM

"A" weighting's purpose is not to measure noise, but to simulate a human being's hearing across the frequency spectrum. It drops drastically below 500hz not because there is no noise there, but the fact that human hearing is less sensitive at lower frequency.

That is why the mentioning of using "A" weighting for calibration for equal loudness in situations where the energy distribution is widely varying between sources.

Quote:
The whole purpose of the "A" and "C" weighting as described in the RS manual is: "Select A-weighting for noise-level determinations, and C-weighting for measuring sound levels of musical material".

Last time I checked we were measuring for musical material reproduction in our Home Theaters.

Ratshack put these in very crude terms. Their meaning is probably as a way to measure perceived noise in the environment (work or elsewhere) and to judge its safety. Since if one works near a subway line, there will be many instances where the "C" weighted level would go off the scale, but much of those sound are not audible given those frequencies are so low.

Quote:
Why not measure what your room is truly producing instead of artificially throwing away actual room/speaker response as you suggest with the statement; "But with "A" weighting, the sound energy in the lower freq spectrum will have less affect on the final reading"?

Certainly seems counter-productive to me.

This is for the purpose of trying to calibrate all speakers so they actually sound equally loud, especially when the sound arriving at the listener does not have the same energy distribution across the freq spectrum.

#29 of 34 OFFLINE   Jason Wolters

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Posted January 11 2002 - 08:09 AM

Quote:
Why do you want to confuse people by directing them to use different scales "A" and "C" to measure speaker balance, because they do or don't also measure a sub ?


Who is confused? Anyone who owns an analog RS meter that came with a manual knows this is wrong. Posted Image

The Avia DVD says to point the meter to the ceiling, just like the Radio Shack meter says to set it to C for setting sound level. I figure those guys must know something, although they aren't as smart as most of us. Posted Image Posted Image Posted Image
What is a committee? A group of the unwilling, picked from the unfit,
to do the unnecessary. -- Richard Harkness, The New York Times, 1960

#30 of 34 OFFLINE   Bill Lucas

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Posted January 11 2002 - 08:33 AM

ling,

I think you have your hz's mixe3d up. Posted Image

If our hearing dropped drastically below 500hz we'd have a tough time understanding normal conversation. I *think* you meant to say 50hz and even that number is quite debatable. "C" weighting is best used when calibrating speakers. I know of NO loudspeakers (even Bose) that doesn't have useable output below 500hz. regards.

#31 of 34 OFFLINE   ling_w

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Posted January 11 2002 - 06:28 PM

Bill,

Our hearing becomes less sensitive below 500hz (how one interprets the term drastic is another thing.) That drop in sensitivity is gradual until around 20hz, where it would take so high a level of sound at that freq for us to actually hear it (as oppose to feeling it) that we define that as our low end freq threshold.

Here is a little description on "A" weighting and its purpose:

http://www.norsonic....orrelation.html

#32 of 34 OFFLINE   Ken Smith

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Posted January 12 2002 - 02:36 AM

Ask a simple question and 31 threads later.........?

#33 of 34 OFFLINE   Pete Mazz

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Posted January 12 2002 - 02:43 AM

But if the recording engineers are using the C weighting, then we should too, to faithfully try to reproduce what the levels were in the recording studio.

Chris,
Try swapping your speaker wires for the mains and listen again. That may give you a clue as to what's going on.

Pete

#34 of 34 OFFLINE   BruceD

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Posted January 12 2002 - 03:02 AM

Chris,

If you have VE, use the phase test and see if all speakers are in phase, especially Left, Right, and center.

You can also use the round the room test to see if something is off on the balance between speakers.

Also with VE I think you can use a mono test on the front L&R speakers to adjust the balance between L&R before setting the SPL levels on all the speakers.


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