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Lamont Sanford
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Using an SPL meter

How would one use an SPL meter like the digital one put out by Radio Shack? For example, what test CD is best for plotting on a spreadsheet and so forth? What would be the x and y axis of a line graph?

Also, the ATI analog meter featured in Stereophile has the same specs as the RS digital meter but costs $20 more than the RS model. An analog meter seems confusing when the digital will just maintain a memory of measurement and averages. It just seems like something that would keep me busy with my bi-polar disorder and all.

Monty
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Re: Using an SPL meter

I use the analog RS meter. Test CD 3 has several useful tone signals, though I suspect the others do as well. Anyway, on Test CD 3, JA provides a series of warble tones that covers the frequency band and is great for measuring your frequency response at the listening position. This, in turn, allows you to fiddle around with speaker positioning and room acoustics. The procedure is very simple and explained somewhat in the liner notes of the test disc.

I think everyone serious about their sound should have an spl meter and a test disc or 12.

papaned
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Re: Using an SPL meter

Read my post of 9/05/05 and John Atkinson's reply in Tuning and Acoustics , using the Radio Shack sound meter. You can download a working chart from the Rives website, to plot your room response. You will need the Rives CD however.

Jeff Wong
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Re: Using an SPL meter

Monty - Are you aware of the mods for that meter?

http://www.stereotimes.com/acc032902.shtm

JimAustin
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Re: Using an SPL meter

Culpepper,

I thought I'd share my recent response with the analogue RS meter. Relying on the calibration numbers that can be found around the internet (most of which show the meter flat through the lower treble) I made some measurements on my room using Warble tones and 1-Hz-spaced tones downloadable from the RealTraps site. I kept measuring an ugly, broad rise centered around 3kHz--a coloration that, if real, would be very nasty indeed. I tried everything to get rid of it--measuring on axis and on, changing the tilt on the speakers, and other things--but it wouldn't go away.

All this time I was equipping myself gradually to make some more accurate measurements (using a Behringer ECM-8000 mic and some cheap electronics). As soon as I got my technique down and (crucially) found the right software, I was up and running--no sign of that coloration.

I've come away thinking that the RadioShack meter is good for, eg, setting listening levels for component comparisons--for that it's practically essential if you do that sort of thing--but not for frequency-dependent measurements. Unless you can calibrate YOUR METER, you just can't trust the results.

Jim Austin

Jim Tavegia
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Re: Using an SPL meter

Jim,

I have done exactly the same thing for myself and friends. I have even used those mics on some recording projects and even though the noise floor is higher, you would be amazed at how decent they can sound for an amateur project. I have used those in conjuction with the "Phile" test discs and recorded the sound and looked at in my my FFT program in my NCH Swiftsound or Cool Edit software with pretty decent results.

This is not the typical JA level of scrutiny, but it sure is revealing and better than not knowing what is really going on in your room. I have even used it at church to get a hande on our awful HVAC noise in our new sanctuary to find out what freq most of that noise sits. You do not need an expensive mic pre to do this either.

Two of the $49 ECM8000 and a Cheap MAudio AudioBuddy for a street price of $79 can even make some decent recordings of piano and chamber music for amateur use. Much nicer is the DMP3 mic pre from MAudio for a street price of $150. You would be surprised how much fun can be had for almost no money.

More serious is a pair of $199 each large diaphragm Rode NT1-A's with a 5db noise floor and the Presonus MP-20 at $499. This can be very magical.

Regards,

Monty
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Re: Using an SPL meter

Thanks, Jeff. I like the way that guy thinks. I probably won't do the mods to the meter, but only because in my small room I am space restricted and have no way of getting that bottom octave. I might give it a whirl when I put together a more ambitious system in my living room. Actually, I should say "if" I put together another system in my living room. I'm enjoying the nearfield listening at sane levels and might just keep playing with with stuff in my small room. I keep hearing 'triode' in my sleep.

Lamont Sanford
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Re: Using an SPL meter

Thank you. Rives has enough for a beginner.

http://www.rivesaudio.com/software/TestCD.html

Since I'm referring to the digital version of the SPL meter I'm wondering if the readings need to be compensated since the web page clearly states that it is for the Radio Shack analog version. In other words, I hope Radio Shack did not have the popular compensation figures programed into the digital version. I can't find any reference that they did so I'm assuming the compensation should be the same as the analog model.

Lamont Sanford
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Re: Using an SPL meter

Bink Audio Test CD seems to be very extensive with a free download. Anyone use it?

http://www.binkster.net/BinkAudioTestCD.txt

Lamont Sanford
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Re: Using an SPL meter


Quote:
Culpepper,

I thought I'd share my recent response with the analogue RS meter. Relying on the calibration numbers that can be found around the internet (most of which show the meter flat through the lower treble) I made some measurements on my room using Warble tones and 1-Hz-spaced tones downloadable from the RealTraps site. I kept measuring an ugly, broad rise centered around 3kHz--a coloration that, if real, would be very nasty indeed. I tried everything to get rid of it--measuring on axis and on, changing the tilt on the speakers, and other things--but it wouldn't go away.

All this time I was equipping myself gradually to make some more accurate measurements (using a Behringer ECM-8000 mic and some cheap electronics). As soon as I got my technique down and (crucially) found the right software, I was up and running--no sign of that coloration.

I've come away thinking that the RadioShack meter is good for, eg, setting listening levels for component comparisons--for that it's practically essential if you do that sort of thing--but not for frequency-dependent measurements. Unless you can calibrate YOUR METER, you just can't trust the results.

Jim Austin

You have a good point there. Since the Radio Shack SPL technology is cheap and most probably inaccurate, then I don't see any harm with taking an average reading for a bandwidth of frequencies to avoid coloration false readings as you described. For example, the 31.5 tone could be averaged with the 25, 31.5, and 40 Hz RS meter readings as a ballpark calibration for the 31.5 Hz tone. One would need both the Radio Shack meter as well as a really good/accurate meter to test this hypothesis. I would also still utilize the RS meter correction values before averaging. This is all in relation to creating something like a frequency response chart. Any blatant coloration from a listening position along the bandwidth of three test tones should still appear even with averaging as described above. And as you described, the RS meter was indicating coloration but your ears weren't hearing it and the more accurate instrument confirmed what your ears were trying to tell you.

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