Radio Shack SPL Accuracy through the frequency band

[BE36]

How accurate are Radio Shack Meter from 20 Hertz to 20KHz?

I thought I some charts that showed how many dbs to that Shack Meter are generally off a year or so ago?

I just used one to set my Sub Cross Over and Volumen seams right just wanding how accurate it was.

[Rudy81]

This page can give you information on the Radio Shack meter correction values. http://www.hometheatershack.com/forums/downloads-area/19-downloads-page.html

IIRC, the RS meter is good enough for subwoofer measurements, but not really useable for high frequency stuff.

Let me correct that statement. The RS meter is not very good for LOW measurements, although lot's of folks use it for Sub work. Run a search for Radio Shack meter correction or something like that and you will find tons of pages on the subject. Many contain correction tables and you can see that the lower frequencies require quite a bit of adjustment. The above link allows you to download a correction file that you can open with a text editor and you can see the corrections made.

There are several decent mics available on the market for what you want to do. It all comes down to cost and complexity, software etc.

[BE36]

Thanks,

Found a site.

I thought it was a little too much, I will turn down the volume and move the cross over up slightly.

Makes sense based on what my ear an knowledge of La Scala Bass bin roll off.

Frequency	Correction		Frequency	Correction
10hz	+20dB		500hz	-0.5dB
12.5hz	+16.5dB		630hz	0dB
16hz	+11.5dB		800hz	0
20hz	+7.5dB		1.0khz	0
26hz	+5dB		1.25khz	0
31.5hz	+3dB		1.6khz	-0.5dB
40hz	+2.5dB		2.0khz	-1.5dB
50hz	+1.5dB		2.5khz	-1.5dB
63hz	+1.5dB		3.15khz	-1.5dB
80hz	+1.5dB		4.0khz	-2dB
100hz	+2dB		5.0khz	-2dB
125hz	+0.5dB		6.3khz	-2dB
160hz	-0.5dB		8.0khz	-2dB
200hz	-0.5dB		10khz	-1dB
250hz	+0.5dB		12.5khz	+0.5dB
315hz	-0.5dB		16khz	0
400hz	0dB

Add the dB to meter reading to get the actual.

[Al Klappenberger]

I think the problem with the Radio Shack meter is not it's accuracy but how it is used. Years ago I tried to use a similar meter made by H.H.Scott and a sine wave signal generator (HP 200CD) to do speaker response testing. It didn't work worth a crap, not because the meter was not accurate but because sine waves exaggerates every little room peak and dip far too much. The meter should be used only to measure the level of pink noise bands or warble tones. This gives you and average over a small bandwidth which is far more representative of what is actually going on. 1/3rd octave pink noise filters are expensive. Warble tone generators are hard to find. I think I have seen CD recording of pink noise band though. The problem there is Google searches always come back with recordings of some band called "Pink noise"! Gack!

AL K

[BE36]

Thanks Al,

Unlike you I do not remeber how to run or own a O-Scop.

I bought a Test CD from Stereophile Magazine that has Warbler Tones from 20 to 20 KHz.

If I use the CD and the correction values above will that give an accurate enough way to set my Sub Wooofer?

Give me an accurate assessment of my system in my room?

For less than $300 bucks is there a Mac friendly micro phone and software that is more accurate and worth the time and effort?

[Al Klappenberger]

BE36,

If you are using the warble tones the readings are probably close enough. How accurate the meter is pretty much depends on the quality of the mike in it. Calibrated mikes cost big bucks. Published corrections probably help but I have no direct experience with the RS meter, so I really don't know. It might use one of those little electorate cartridges which are pretty good. My Mity Mike II is actually based on one of those and it compares nicely with a fancy B&K standard I have here.

Al k.

[BE36]

Thanks again Al.

Here is the chart Log and smoothed Mac version of Excel with above corrections.

Really looks like the La Scala natural freq of 160 is for real.

I could feel the Dog House and sides vibrate at 200 Hz.

Both the Dog House and Sides vibrate at 160 Hz.

At 125 Hertz the Dog had stopped vibrating.

by 80 Hertz the sides had almost stopped vibrating.

1" Sides and 1" Dog House experiments are in the future.

There is a dip around 400 Hertz, maybe 500 Hz cross over will fix this. . .

[John Warren]

I just used one to set my Sub Cross Over and Volumen seams right just wanding how accurate it was.

You don't need a meter.

Play something with deep bass, something you know has tones below say 30Hz. Listen to the sub without the mains operating. A sub set right doesn't boom along with the music, it should be "silent" except for the deepest notes and even then, it should only provide a sensation, not the "wacking the sofa with the salami" sound. It should be felt, not heard. If you can identify what music is playing by just listening to the sub, it's bandwidth is too large (crossover is too high). If it's boomy too, lower the amplitude and move it away from a corner. A sub should do almost nothing, almost all the time.

[laager]

If you know someone with a Velodyne DD series you could borrow their microphone. It's one of these:

http://www.behringer.com/EN/Products/ECM8000.aspx

How you then hook it up to a computer is another story.

[BE36]

What is the starting point for Big Bucks? (How much for a calibrated mike)