Speaker Level Matching

I'd just settle with the EzSet/EQ microphone results. Coz:

1. A Radio Shack SPL meter has a +/- 2 dB accuracy, and

2. Connencting the HK mic to laptop with REW will bring about the problem of a mic calibration file that you can't get access to coz it's usually proprietary info of the maker, hence you won't be able to calibrate REW.

You mean if you take 3 reading of the same tone without changing the volume of the signal the reading would vary +/- 2 dB in that 3 readings?

Yeah, that would be precision, and that is what he probably meant. I have no idea how accurate they are but they are very precise. Meaning, the result they get is very reproducible. It may not be the correct value but the meter is very consistent from measurement to measurement. They work just fine for level matching speakers. And the same can probably be said for the EZSet/EQ mic.

It will not, it will read the same. At least mine does.

Not accurate, especially in the lower bands but there is a correction table that has been floating in cyber space for years.

No, I mean if you'd like to calibrate to say 75 dB, you will get results from 73 to 77 dB anywhere. As said, RS SPL meter is good for relative measurements but not precise enough for absolute measurements.

I wouldn't expect testing the EZSet mic by plugging it into the mic input of your laptop to damage anything. It's either going to give you sound or not.

The actual FR of the EZSet mic is a mystery. Odds are that it is really pretty good. However, its lack of a proper mounting system (it appears to be designed to be set on top of a flat surface which is about the worst way to use a mic) seems significant.

Many posts have been written here about how awkward it is to try to do acoustical measurements with just a SPL meter, so I won't beat that dead horse. Something based on REW is a far better idea.

I'd seriously consider picking up a USB audio interface with a mic input such as the ART USB Dual Pre, a standard mic cable, a Behringer ECM 8000 microphone, and a mic stand so that you can move your mic around and put it where it needs to be and orient the mic at will. It's gonna probably cost you between $100 and $200 for all of this stuff but it could be one of the best audio investments you ever made.

It has better precision than that. Very reproducible results. What do you mean by "good for relative measurements but not precise enough for absolute measurements"? That makes no sense. There is a difference between precision and accuracy.

While The RS meter correction chart is great in theory I do not find it to be correct info.

I bought my meter a year and a half or so ago. When I test my speakers with test tones thru the range You can easily see that the meter is accurate at least far as I checked from 20-16k. I really just dont see the swings of huge decibles the "correction" chart tells of.

The meeter itself says its accurate +-2db. That means if level is 75 db between 50 and 126 db then the meter can read 73-77. If your measuring 65db same thing 63-67.

Every test I have done with different speakers receivers db levels all says I believe +-2db. If your off by more your meter is bad return it and get a new one.

Furthermore I would not bet on radioshack advertising the meter at better spec than capable of. For instance If I set an audio device up with the meter and the meter is off by 9 db instead of 2 and I get ear damage they will owe me ALOT of money.

The correction charts (yes, plural) address the meter's increasing insensitivity at lower frequencies. How useful they are from meter to meter has always been an issue. In other words, do all meters behave exactly the same in regards to this? That there is more than one table of correction values floating around out there only adds to the confusion and uncertainty.

But the meter is fine for level-matching speaker levels with pink noise.


How do you know how accurate the readings are? Are you also measuring with another device that is your gold standard?


I believe this is its precision, not its accuracy, no? There is a difference.

[quote=sivadselim;

I believe this is its precision, not its accuracy, no? There is a difference.[/QUOTE]

Accuracy: ± 2

It's possible, I guess, but I suspect they are misusing the term. It is definitely not accurate at increasingly lower frequencies. That is why the correction charts were generated.

The meter is very precise. If you measure something @ 75dB 10 times you might get 75dB for every single measurement. That's precision. But the real SPL might really be 82dB. Or 71dB. Or whatever. That's its accuracy.

Sine waves are not appropriate for matching the volume of speakers, either for stereo or surround. Moving the measuring microphone even half an inch will change the reading substantially. The best test signal is band-limited pink noise, with content only in the midrange frequencies. This is the method used by the DVD Essentials setup DVD.

Further, you don't need a meter with absolute accuracy. Just put the meter or microphone where your head is while listening, then adjust the volumes for each speaker playing one at a time until they read the same.

I made a band-limited point noise file for my upcoming book, for exactly this use. I'll be glad to send it to anyone who emails me from my home page www.ethanwiner.com.

--Ethan

There was a reason why I asked my original question to him.

Here are some links to the explanation:
http://www.mathsisfun.com/accuracy-precision.html
http://chemistry.about.com/od/chemis...acyprecise.htm
http://www.butlercc.edu/engineering/...ur_vs_prec.cfm

Accuracy- to the actual value
Precision- repeatability

The latter is what you need in level matching otherwise the L and R speakers could be off by 4 dB spl.

yeah

Really? Really?

+/-2 db means when you measure it will be +/-2 db. Period. Now granted there is some lower db sensativity issues which may or may not be solved with a external mic. But simply put it will read the same thing on every read.

Yeah, really. The +/-2dB refers to its precision, not its accuracy.

Not sure what you were trying to tell me.

Me either. Seems obvious there is confusion over precision vs accuracy. It isn't exactly clear how many are confused though. Worse yet, the given +-2dB spec seems too high for its precision and too low for its accuracy. It certainly isn't the maximum deviation or error (accuracy) expected over the 20-20k bandwidth. Could represent a weighted and/or averaged value. Might also be a reference to an ROC calculation of accuracy but I highly doubt that.

In any case it is perfectly fine and certainly precise enough for level matching using pink noise. I wouldn't use it for much more than that though.

re-read this thread (dragonfyr's commentary):

http://www.avsforum.com/avs-vb/showthread.php?t=1391287

Anyway back on topic. Dolby labs own guide recommends that the radiosshack meter is good for the job because the relative levels of each speaker to the next is more important than actual levels.

Dolby also recommends the following.
Front and Center speakers set to 70-75db
Surround speakers set -2bd from front and center channels.
Sub is to be set 10db higher than center and front channel.

The recommended procedure is to point your meter at the center channel at arms length and then angle the meter at 45 degrees and take the reading and set the level. Then while still point at the center channel do the same for front speakers. Finally turn 90 degrees and do each of the surround speakers.

This again is as per Dolby labs.
http://www.dolby.com/uploadedFiles/z...2.5.1guide.pdf

section 3.4

FWIW, the DOlby doc is for production, not reproduction. SO the lower surround levels are mentioned of film use because film mixing is doen with multiple surrounds. The LFE channels is calibrated 10 dB higher in production, then is encoded -10 dB form the levels set, and on playback with home equipment is (usually) automatically increased by 10 dB. If we calibrate our home systems with the sub 10 dB higher the LFE channel will be 10 dB too loud when we play back movies.

Also FWIW, I saw the usual film mixing calibrations 85 dB with a -20dB bandwidth limited pink noise signal.

Dolby's doc recommends lower ref levels for TV mixing, but not as low as suggested above: "For television work, pink noise at reference level is typically set to produce an SPL ranging from 79 dBC to 82 dBC for each of the main five channels. The lower reference level for television is due to the lower average listening levels used by the consumer (typically 70-75 dBC)."

So the 70 to 75 is the anticipated listening level, not reference calibration . . . For example I caibrate my system to reference, then set my volume control so dialog runs in the 65 to 70 B range typically.

Right. That's what folks in this thread have been saying. And I suspect the same is true of the EzSet/EQ mic and software that is included in the OP's HK AVR. It is plenty accurate (oops) precise for speaker level matching.



As JHAz pointed out, this is wrong for your playback system's calibration level.

Exactly. The studio records their LFE 10 dB spl louder than the main channels, you set your LFE 10 db higher and now you have 20 dB above center ch. and at ref levels, 125 dB spl in the LFE, not 115