How to detemine actual decibel rating of monitoring environment?

F

fritzmusic

Member
How exactly would I measure the decibels output of my studio monitors on the cheap using my PC, Firepod and a test measurement mic? Is there a DX or VST plugin that can run in live mode to help to accomplish this cheap or free that will tell me (without a bunch of math) what the actual Db output of my studio speakers are? I ran a google search as well as here so it's not like I haven't looked around already but maybe I'm not wording what I'm trying to do properly. All I can find are links to test mics and vague information.
 
fritzmusic said:
How exactly would I measure the decibels output of my studio monitors on the cheap using my PC, Firepod and a test measurement mic? Is there a DX or VST plugin that can run in live mode to help to accomplish this cheap or free that will tell me (without a bunch of math) what the actual Db output of my studio speakers are? I ran a google search as well as here so it's not like I haven't looked around already but maybe I'm not wording what I'm trying to do properly. All I can find are links to test mics and vague information.
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This requires a matched and calibrated mic, preamp, A/D, and software. The Ratshack SPL meter is a much easier way to go.
 
I've already seen those but isn't there a way to do this with a PC? Surely there's a plugin somewhere that will do the same thing?
 
Robert D said:
This requires a matched and calibrated mic, preamp, A/D, and software. The Ratshack SPL meter is a much easier way to go.
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I'm just looking for something that will get me close enough. It doesn't have to be spot-on perfect.
 
fritzmusic said:
I'm just looking for something that will get me close enough. It doesn't have to be spot-on perfect.
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The RS meter will be good. One thing to be aware of is that SPL is relative to position. The closer you get, the louder it is. Most people are concerned about the level at the listening position. Get a meter and hold it where your head is when you listen. There you go.

Dork-talk:

Speakers are usually rated by sensitivity and max SPL.

Sensitivity is measured with 1 watt of input at 1 meter distance, and looks like this:

Sensitivity 98db @ 1W/1M

Max output is also usually measured at 1 meter. The more usual case is that it is calculated from sensitivity and power handling. This is pretty common, and not very honest, if you ask me. :mad: Most speakers sound pretty shitty when they are at their max power handling. But that doesn't stop makers from giving calculated max outputs that don't reflect reality at all.

Here is a spec:

Sensitivity 100db @ 1W/1M, max power handling 100W.

From this, a max output of 120db can be calculated, and may be listed in the specs. But it says nothing about how the box will sound at that volume.
 
I don't think you're really thinking about what would actually be involved in order for your PC to do that..acurately or not. I don't know why you would expect to find a plug-in....I say just get the SPL meter.
 
fritzmusic said:
I'm just looking for something that will get me close enough. It doesn't have to be spot-on perfect.
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That's exactly what the Radio Shack meter will do for you. I own one and it is handy to have around.

The issue as far as setting up a mic, preamp, etc., and then sending the signal to software, is that you have to have it all calibrated correctly. You need metering to do that properly, as well.
 
Joepie said:
Get a Nokia 5140 cellphone, it has a built in soundmeter (don't ask me why)
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You've seen the rock concerts where everybody holds up their cell phones? It used to be lighters and now it's cell phones. Maybe that's why it has a soundmeter.
 
fritzmusic said:
I'm just looking for something that will get me close enough. It doesn't have to be spot-on perfect.
Click to expand...

Well if you really want to go nuts . . .

Pick a mic. Hell, make it any mic. Or you could get an Apex 220 measurement mic, but that's the same price as the RS dB meter. Look up the mic's sensitivity. Let's say it's 94dBSPL = -30dBV.

Next, get or make a CD with a reference tone, 1kHz @ 0dBFS, or generate it from your software.

Now, if your preamp has gain settings marked on its dial, set your preamp at +50dB.

Finally, check the spec on your converter. You need to know if it is operating at -10dBV or +4dBu, and what level that corresponds to in dBFS. Let's say you are at +4dBu, and 0dBFS = +19dBu.

Thus, we know that if you play tone, the test tone will be output at +19dBu, which is about +17dBV.

If the SPL at your mic is 85dBSPL, the mic will output -39dBV, which the preamp will step up to +11dBV, which should be -6dBFS. Adjust your monitor gain until you hit that number.

Assuming nobody lied about their specs, that should get you +-3dB or so.
 
fritzmusic said:
I'm just looking for something that will get me close enough. It doesn't have to be spot-on perfect.
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Think about it, before you get to this plugin you have to go through a mic (what's the sensitivity?) then through a preamp (they can't calibrate the knobs, the gain will be affected by factors like mic/pre impedance match), and then the D/A (again another variable). There are simply too many variables involved to even be in the ballpark.
 
mshilarious said:
Well if you really want to go nuts . . .

Pick a mic. Hell, make it any mic. Or you could get an Apex 220 measurement mic, but that's the same price as the RS dB meter. Look up the mic's sensitivity. Let's say it's 94dBSPL = -30dBV.

Next, get or make a CD with a reference tone, 1kHz @ 0dBFS, or generate it from your software.

Now, if your preamp has gain settings marked on its dial, set your preamp at +50dB.

Finally, check the spec on your converter. You need to know if it is operating at -10dBV or +4dBu, and what level that corresponds to in dBFS. Let's say you are at +4dBu, and 0dBFS = +19dBu.

Thus, we know that if you play tone, the test tone will be output at +19dBu, which is about +17dBV.

If the SPL at your mic is 85dBSPL, the mic will output -39dBV, which the preamp will step up to +11dBV, which should be -6dBFS. Adjust your monitor gain until you hit that number.

Assuming nobody lied about their specs, that should get you +-3dB or so.
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That seems simple enough.
 
boingoman said:
That seems simple enough.
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Yeah, you just have to allow for tolerances in manufacturer specs. On average, they should kinda cancel each other out. On average. If your gear is above average, they might all throw you off the same way.

Oh, I forgot one thing. If you pre isn't marked with gain settings, run the test signal direct from the D/A into it at -50dB and calibrate it back to 0dBFS. Of course make sure to account for any difference in gain using the line in and mic in ;) :eek:

I think I'll put this to the test after dinner--I have a Rat Shack SPL meter, let's see how I do :cool:
 
OK here is how I did. First off, I didn't feel like listening to a test tone at 85dB tonight, so I set my monitors to 74dBSPL, placing the RS meter at my listening position.

I have an Apex 220, but I figured let's just use my KSM141, set to omni, instead. This mic is not flat in omni, it has a bass boost and a presence peak. But that's OK since I am using a test tone. If you were using pink noise, you'd need a flat mic. I put the mic in the same spot as the RS meter.

Second, to make things as bad as possible, I used my ART Digital MPA. Now the ART is a pre that for $400 I'm digging. However, for testing, it has the minus of have no fewer than 4 separate gain controls, and on top of that, I swapped the stock 12AX7 for a vintage 12AT7, which has lower gain. One big plus is a nice VU meter, which saves me the step of using the computer as a meter and having to figure out the A/D conversion, which ART unhelpfully does not publish in their manual (through experimentation, I determined that 0 VU = -12dBFS, but that is not important here).

OK, we're off! The KSM141 is -37dBV @ 94dBSPL, so that should give me -57dBV @ 74dBSPL.

However, I needed +65dB on the ART to get to 0 VU (+2dBV), that would imply that the mic was producing -63dBV, and thus seeing 68dBSPL.

So I was off 6 dB, probably mostly because the 12AT7 is a lower gain tube than the 12AX7, so I wasn't really getting +65dB. Unfortunately, with my current interim setup, it would be really hard for me to calibrate the gain settings on the ART right now because I don't have an easy way of routing the converter out to the ART in :(

I am pretty convinced that anybody should be able to beat my 6dB error :)
 
mshilarious said:
Yeah, you just have to allow for tolerances in manufacturer specs.
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:D

I was so kidding. That sounds like an enormous PITA compared to using a meter. Nice job working it all out, though. :)
 
boingoman said:
:D

I was so kidding. That sounds like an enormous PITA compared to using a meter. Nice job working it all out, though. :)
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Well the whole thing is a joke to me, I just don't know when to stop! :D
 
mshilarious said:
Well the whole thing is a joke to me, I just don't know when to stop! :D
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yeah, I think its a joke too. I bought a SPL meter from radio shack. what a waste of money. Its a good meter and all, but whoever came up with monitoring at 85 db "standard" was a moron. There, I said it.
 
FALKEN said:
yeah, I think its a joke too. I bought a SPL meter from radio shack. what a waste of money. Its a good meter and all, but whoever came up with monitoring at 85 db "standard" was a moron. There, I said it.
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I can't agree with that. It's a scientifically set standard. Your ears' response is most flat at 85dB. An 85dB average level will give you peaks around 95dB or so (pink noise being a bit louder RMS than music). That means you will be able to hear the quietest parts of your finished CD at -90dBFS, presuming that your hearing is functional down to 6dB.

A quieter level could throw off your EQ, and cause you to miss noise issues. A louder level could put you at risk for long term hearing damage. Trust me, hearing loss, tinnitus, and ear pain are not fun things.

Often I'll do grunt work like edits at 75-80dB, but every time I think I finished a mix and didn't listen to it at 85dB, I've regretted it.
 
FALKEN said:
yeah, I think its a joke too. I bought a SPL meter from radio shack. what a waste of money. Its a good meter and all, but whoever came up with monitoring at 85 db "standard" was a moron. There, I said it.
Click to expand...

I think I convinced you to get one. But, didn't you use it to calibrate your monitors ? What I mean is, setting their gain levels for even output using pink noise ?

Do you mena 85 dB is too loud ? I find 75-80 rms is reasonable for my ears.
 
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