# Accurate SPL meter



## gperkins_1973 (Aug 25, 2008)

Hi there,

I currently have a radioshack Model 33-4050 spl meter and have looked at applying the correction values manually for reading subs. I am not sure what is the most accurate way of testing maximum spl from subs. I have two 18" slot ported subs and took a reading the other day at -10db on the onkyo and from 1.5metres away was reading 112db uncorrected. I have downloaded the manual excel file but that only goes up to 105db which is no good for what I need to do. 

Is it better to run REW sweeps with the cal file loaded and just keep turning up the volume until the subs start clattering then I know their limits.

If someone could advise me I would really appreciate it. I did run a REW sweep at -15db and it looked like I was getting about 108db at 10 hz as I have a natural 4db hump from 10 to 16hz.

cheers

Graham


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## Mike P. (Apr 6, 2007)

> I have downloaded the manual excel file but that only goes up to 105db which is no good for what I need to do.


You mean Hz, correct?


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## gperkins_1973 (Aug 25, 2008)

Mike,

Nope, db matey. The plot graph only goes up to 105db output so if I input the 112db at 15hz it goes off the chart. I guess that was designed for getting a flat response at 75db when EQing not for max spl.

cheers

Graham


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## glaufman (Nov 25, 2007)

You can REW sweeps at increasing SPL, but I Wouldn't advise going until the subs clatter... clatter implies damage. I would stop when you see serious compression, i.e. some freqs increase in SPL while others increase less, or some other such sound quality detracting behavior...


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## gperkins_1973 (Aug 25, 2008)

I just ran a 20hz sine wave in REW and got only 102db at -10db volume on the onkyo. There was only 5 green lights on the BFD and the sub trim level was on +10db. The behringer amp is on 24db. No clatter and not alot of excursion but alot of noise.

Something seems a miss somewhere. Any ideas I would appreciate it.

cheers

Graham


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## Wayne A. Pflughaupt (Apr 13, 2006)

> I am not sure what is the most accurate way of testing maximum spl from subs. I have two 18" slot ported subs and took a reading the other day at -10db on the onkyo and from 1.5metres away was reading 112db uncorrected. I have downloaded the manual excel file but that only goes up to 105db which is no good for what I need to do.


What exactly is it that you need to do? If you’re only interested in obtaining a maximum SPL reading, you don’t need any excel files for that. Just play a broadband pink noise through the sub, or a frequency-specific sine wave and see what you get with the SPL meter. :scratch:



> Is it better to run REW sweeps with the cal file loaded and just keep turning up the volume until the subs start clattering then I know their limits.


REW’s sweeps are for plotting frequency response, not obtaining maximum SPL level readings.



> I just ran a 20hz sine wave in REW and got only 102db at -10db volume on the onkyo. There was only 5 green lights on the BFD and the sub trim level was on +10db. The behringer amp is on 24db. No clatter and not alot of excursion but alot of noise.
> 
> Something seems a miss somewhere.


I don’t understand. What seems amiss to you?

Regards,
Wayne


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## Wayne A. Pflughaupt (Apr 13, 2006)

Wayne A. Pflughaupt said:


> Just play a broadband pink noise through the sub, or a frequency-specific sine wave and see what you get with the SPL meter. :scratch:


Edit: Should have said, play a broadband pink noise through the sub, or a frequency-specific sine wave, turn up the sub volume until starts to make noise, back off a bit, then see what you get with the SPL meter.

Regards,
Wayne


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## gperkins_1973 (Aug 25, 2008)

Wayne

I just wanted to see what the subs give out of interest based on what Winisd simulated. I should be seeing 114db for one sub at 20hz at full power plus room gain. I don't know what full power would sound like but was curious. The wierd thing for me is that playing music at -30db volume is pretty loud especially playing some dubstep. I would have to guess at what frequencies that is but would think in the 20 to 30hz and it was pretty potent. I did turn it up to -20db and the bass was thunderous. I had open doors rattling.

I must admit it does scare me a bit to turn it up that loud as its not something I have done before.

Even at 100db its not the volume you could probably listen too for very long.

cheers

Graham


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## glaufman (Nov 25, 2007)

If you're using the RS meter, look at the cal file to see how much dB you need to add to the raw measurement to get the true SPL at 20Hz. I know on one model that's as much as 9dB, bringing your 102 to 111...
As long as you're running a single sine wave, use REWs RTA function to look at harmonic distortion components...


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## gperkins_1973 (Aug 25, 2008)

Greg,

I have not done that before. Perhaps you could assist me please so I can see what kind of distortion I am running.

cheers

Graham


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## glaufman (Nov 25, 2007)

This link in the REW info index should get you started...
http://www.hometheatershack.com/forums/rew-forum/9872-spectrum-rta-feature.html#post85806


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