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Which way do you point your sound pressure meter?


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33 replies to this topic

#1 of 34 ScottAndrew

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Posted January 10 2002 - 02:14 AM

I've heard
    [*]straight up[*]at each individual speaker one at a time[*]45 degrees upward facing the center[*]45 degrees upward, facing the center, but then 90 degrees toward the side walls for the surrounds.[/list]So which is the most accurate?
    Perhaps I'm being needlessly fussy, but that seems to be the whole point anyway.

    Thanks!

#2 of 34 Jonathan_M

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Posted January 10 2002 - 02:44 AM

I've always heard that you should hold or mount it facing forward and up 45 degrees at your seating position. It should stay in the same position throughout your calibration and not move for different speakers. One spot, calibrate all speakers.

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#3 of 34 Bruce N

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Posted January 10 2002 - 03:01 AM

Quote:
45 degrees upward facing the center

Quote:
It should stay in the same position throughout your calibration and not move for different speakers. One spot, calibrate all speakers.


Yep, this is the way to do it.

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#4 of 34 Clinton McClure

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Posted January 10 2002 - 03:02 AM

Jonathan is correct. It should be held at arms length or mounted in the prime listening position (where your head would be while sitting down) and angled slightly (I set it at about 45°) up towards the front.

If you pointed it at different speakers during calibration, you would not achieve accurate results. The reason for it being only pointed towards the front is to more accurately simulate the human ear, which does not rotate to hear distinct sounds coming from beside of behind. Posted Image

#5 of 34 Phil T

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Posted January 10 2002 - 03:19 AM

I calibrated my 7.1 system pointing straight up with the meter held at eye level in front of me. This was based on some info I pulled from a couple previous threads and not my own preference or experiences. The resulting sound field *seems* to blend quite nicely.

Maybe I'll try this 45 degree forward facing idea and see how much it changes. One thought, won't this bias the rear speakers over the L/C/R? I'm worried this will be overkill considering I've got 4 of the suckers behind/beside me!!

#6 of 34 AaronD

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Posted January 10 2002 - 03:20 AM

How about the case where the surround speakers (because of room constraints) are on stands very close to either side of the couch? For this instance the human ears are pointed directely at each associated surround. Would the same theory of pointing the SPL meter forward at a 45 degree angle still hold true?

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#7 of 34 Jonathan_M

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Posted January 10 2002 - 03:24 AM

Oh, I think the reason for angling the SPL meter forward a bit is because sound coming from the front is directed to our eardrums by our earlobes. The tilt forward would simulate this setting. Sound coming from the rear would have to be biased just a bit because normally, our earlobes would occlude the sound slightly.

If you had no earlobes, pointing the SPL meter straight up would probably be the way to go. Posted Image
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#8 of 34 Legairre

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Posted January 10 2002 - 03:33 AM

The Avia DVD says place the SPL meter at ear level at the seating position(sweet spot). Then you should point the mic straight up at the ceiling and adjust each speaker from the seating position without moving the meter.

I use a camera tripod on the sofa and adjust it to the height that my ears would be at when sitting down. The RS SPL meter has a nice little tripod hole in the bottom for mounting.

#9 of 34 Phil T

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Posted January 10 2002 - 03:35 AM

Damn earlobes...I knew they'd get me some day...

#10 of 34 Jeremy Anderson

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Posted January 10 2002 - 03:53 AM

There are several schools of thought on this issue. The two that strike me as the most logical are:

Method 1 -- Point meter straight up. The logic here is that your ears are more in line with the surrounds, and hence seem louder. Therefore, holding the meter straight up puts its mic more in line with the surrounds, reducing the bias to the surrounds and giving you a more balanced soundfield. The problem with this method is that the Radio Shack SPL meter, despite its claim of being non-directional, DOES exhibit some reading differences (up to 2dB) when severely off-axis... hence METHOD 2.

Method 2 -- Angle meter forward. The 45 degree rule is a good rule of thumb, but there's more to it than that. Logic tells us that the further away from being on-axis, the more variation we will have with the SPL meter. Therefore, the only way to get a true unbiased reading from all speakers is to angle the meter so that all speakers are at roughly the same off-axis angle. In other words, point your meter at a point on the ceiling and look at the angle between the microphone's axis and the front speakers... then compare this to the angle between the microphone's axis and the surrounds. Angle the meter so that these two angles are as close as possible to being the same. Then, with the meter in this angled position, perform the calibration. In my room, this puts my SPL meter about 30-35 degrees from vertical.

Your mileage may vary, but method 2 gives me the best results and sounds well balanced.

#11 of 34 Jonathan_M

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Posted January 10 2002 - 04:05 AM

What would REALLY be nice is to have a set of microphones that hang over your ears like earphones and measure the sound entering your ear canal to a connected SPL meter. That way, you could just SIT in your listening position and look at the TV and do all your calibrating. This actually doesn't sound too far-fetched now that I think about it.

Anyone here want to make a prototype?
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#12 of 34 Phil T

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Posted January 10 2002 - 04:22 AM

Jeremy, if I'm understanding the off-axis problem with the RS meter correctly (I've got the RS digital type), couldn't you just record your calibration settings while pointing up, and then record another set of reading with the meter also pointing up but rotated 90 degrees or 180 degrees axially, and then average the 2?

#13 of 34 ScottAndrew

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Posted January 10 2002 - 04:56 AM

During lunch I checked my levels both ways. The fronts and center were just about exactly the same both ways. The surrounds were one decibel louder with the meter pointed straight up. When I match them to the mains with the meter straight up and listen to the test tones, they sound the same, but when I bump them up a notch to match the fronts with the meter at an angle, I perceive them as louder. (I'm using Ultimate DVD Platinum.)
So for me personally, I seem to be getting more accurate results with the meter straight up.

#14 of 34 Jonathan_M

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Posted January 10 2002 - 05:06 AM

Scott,

And thats whats the most important... what sounds best to you.

-Jonathan
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#15 of 34 Phil Iturralde

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Posted January 10 2002 - 05:31 AM

I REF Calibrate my HT System, using the same recommended standard SPL Meter 'process**' that the Mixing DD-5.1 DVD Engineer use. I'm also fortunate enough to have my Center & four identical mono-pole speakers placed/arranged like Dolby Labs typical 5.1 Dolby Digital Mixing/Recording Studio - and all my family and friends say, . . . it sounds 'most glorious'!!!

**Video Essentials and Dolby Labs recommends the following, . . .from Dolby website - 5.1-Channel Production Guidelines (PDF document)

Quote:
3.4.3 Taking a First Measurement

4. Facing the front speakers, hold the SPL meter at chest level, with the microphone facing up at an angle of approximately 45 degrees to the center speaker. Keep the meter at arm's length to prevent measuring audio that may reflect from your body. You should be able to take SPL readings as you look down at the meter.

5. Keep the SPL meter in this position. Make sure that the meter is aimed at the center speaker as you take readings for the left and right speakers.

6. When taking the SPL readings for the left surround or right surround speakers, keep the meter at the same angle and position as you did for the front speakers.

FYI: Only difference from above is that I use a tripod @ my 'sweet spot' - for my REF Calibration process, see my CALIBRATION TECHNIQUES webpage using Video Essentials DVD.

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#16 of 34 Jeremy Anderson

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Posted January 10 2002 - 07:20 AM

I agree with Phil I. up to a point, and I would never dispute his knowledge... but are professional mixing engineers using Radio Shack SPL meters to balance their gear?

Johnathan nailed it -- try different methods and use the one that sounds the most balanced to you. I was just offering suggestions based on my own tweaking. But then, I have a SPL meter with an attached laser pointer and protractor, so I'm probably way too anal.

Quote:
Jeremy, if I'm understanding the off-axis problem with the RS meter correctly (I've got the RS digital type), couldn't you just record your calibration settings while pointing up, and then record another set of reading with the meter also pointing up but rotated 90 degrees or 180 degrees axially, and then average the 2?
The mic on the RatShack analogue SPL meter exhibits the same off-axis dropoff in all directions from direct center... so the angling method should work. However, I don't know if the digital meter exhibits those same inaccuracties, because I have no personal experience with it. If it uses the same microphone as the analogue version, the chances are pretty good.

#17 of 34 Phil Iturralde

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Posted January 10 2002 - 07:46 AM

Quote:
. . .but are professional mixing engineers using Radio Shack SPL meters to balance their gear?

They do. Let me refer to 5.1-Channel Production Guidelines (PDF document) again: . . .
Quote:
3.4.2 Sound Pressure Level Meter - pg. 35

To properly calibrate speaker levels, an SPL meter is necessary. A suitable and relatively inexpensive meter is readily available from Radio Shack ® (Tandy Electronics outside of North America). Since the relative level between channels is more important than absolute level, the accuracy of this meter is sufficient for channel balancing. For greater accuracy, more expensive meters may be used. It is recommended that an inexpensive meter be left in the control room for quick level checks.

Guess what SPL meter (readily available from Radio Shack ®) they use?? Yep - the analog one!

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#18 of 34 Phil T

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Posted January 10 2002 - 10:27 AM

Only one thing has me a bit concerned about your calibration process Phil (and BTW, thanks for the great info). I have a 7.1 system, so my left and right surround-back speakers are actually behind me (and the left and right surround speakers beside me). If I hold the meter at chest height in front of me pointing forward, won't I be interfering with the sound waves?

#19 of 34 Phil Iturralde

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Posted January 10 2002 - 10:46 AM

Thanks Phil T!
Quote:
. . . won't I be interfering with the sound waves?

Yes, so I recommend using a camera tripod and standing to the side. Place the tripod where you sit (sweet spot), raise the microphone approx. ear level, angled 45° to 50° degrees up.

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#20 of 34 Patrick Sun

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Posted January 10 2002 - 11:17 AM

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