Which way do you point your sound pressure meter? (1 Viewer)

ScottAndrew · Jan 10, 2002

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!

Jonathan_M · Jan 10, 2002

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.

Good luck!

Bruce N · Jan 10, 2002

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.

Bruce

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Clinton McClure · Jan 10, 2002

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.

Phil T · Jan 10, 2002

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!!

AaronD · Jan 10, 2002

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?
-Aaron

Jonathan_M · Jan 10, 2002

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.

Legairre · Jan 10, 2002

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.

Phil T · Jan 10, 2002

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

Jeremy Anderson · Jan 10, 2002

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.

Jonathan_M · Jan 10, 2002

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?

Phil T · Jan 10, 2002

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?

ScottAndrew · Jan 10, 2002

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.

Jonathan_M · Jan 10, 2002

Scott,

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

-Jonathan

Phil Iturralde · Jan 10, 2002

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)

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.
Phil

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Jeremy Anderson · Jan 10, 2002

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.

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.

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Phil Iturralde · Jan 10, 2002

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!
My father-in-law sold TV & Radio Broadcasting equipment in the US until he passed away.
Phil

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Phil T · Jan 10, 2002

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?

Phil Iturralde · Jan 10, 2002

Thanks Phil T!

. . . 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.

NOTE: Because my website is 'free', hosted by GeoCities, if too many HT enthusiasts visit, GeoCities will shut it down for an hour or so because it exceeded the specified 'freebie' Data Transfer Rate. Sorry about that, just bookmark it and visit my site an hour later or when everyone has gone to bed!

Phil

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Patrick Sun · Jan 10, 2002

Like my bourbon, Straight Up!

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