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SirLauncelot · Posted - Wed Jun 25, 2003 10:09 pm

Hello!

I'm wondering if there's a way to measure the sound level in db SPL in a pair of headphones (Beyer Dynamic DT100) that's attached to a SoundBlaster soundcard?

I know that for home theatre stuff, you can measure the sound level where you're sitting/standing using a sound level meter like the one here:

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=33%2D2055

but is there a similar device that you can plug into the soundcard that will allow you to get such a reading?

Any advice will be appreciated, thanks!

Winston

ozpeter · Location: Australia

There's not much point in getting a reading from the soundcard because the spl produced by one pair of headphones from a given input will be different from another, according to its sensitivity and impedence etc.

You need a specialised 'dummy head' arrangement to do this properly. You might be able to improvise the means of somehow sealing your headphones to the mic of the kind of meter you've linked. I wonder what your objective is? If you are worried about excessive sound levels, turn down your headphones until you are no longer worried, if you see what I mean. Or compare them with the sound of your loudspeakers (perhaps having measured their output first) - you'd be surprised at how turned-down your headphones may need to be.

I remember seeing BBC headphones modified to cut out automatically if they are operated too loud - as an employees' health & safety measure.

We've had several previous threads here on headphone level safety - have a search, if that's relevant to your underlying problem.

- Ozpeter

SirLauncelot · Posted - Thu Jun 26, 2003 12:58 am

Thanks for the reply ozpeter.

My objective is to ensure that the presentation volume via headphones is approximately the same for all our computers here (I work in a psycholinguistics lab), and measure what that approximate value is in db SPL.

In my previous lab, we used a RMS meter to convert the voltage to the headphone SPL rating to get this value. But I was wondering if there was any device that could do that directly. However, since you rightly mentioned that different headphones have different ratings, I guess measuring the output in volts via the soundcard is the best way.

Has anyone any specific recommendations/caveats for a good RMS voltage reader for this purpose, or a link to a specific site? Thanks in advance!

ozpeter · Location: Australia

Aha! Over to the technically minded here. I'm sure you'll get some specific and knowledgeable help soon.

- Ozpeter

jonrose · Location: USA

ROBSCIX · Posted - Thu Jun 26, 2003 6:55 am

I am not sure how precise you need your measurments to be but, Each sound card will be slightly different as well, even if they are all the same sound card. I would check my data sheets on both your headphones and sound cards and do some math. I don't know the equations but I am sure they are out there...

SirLauncelot · Posted - Thu Jun 26, 2003 7:53 pm

The measurements need not be very precise. Typically, reports would read "the stimuli were presented at approximately 70 db SPL etc...". Variations are to be expected for the reasons Jon and Robscix have mentioned. But we do try to minimise this by standardising equipment (computer configs, soundcards, and headphones).

The input power rating for the Bayer Dynamic DT100 headphones is 1000 mW = 124 db SPL. So in order to get a sound level of 70-75 db SPL, the soundcard volume is adjusted so that the output voltage reading would be approx 565-605 mW.

As to what is being output, this would depend on the nature of the stimuli (the soundfiles are usually isolated spoken words or sentences), so each project that is being run would need its own sound volume calibration with a sample of the wav files that is representative of the stimuli being used.

SteveG · Location: United Kingdom

There is a 'correct' answer to this question - you can buy a calibrated 'ear' with a built-in microphone that is designed for this job. There are some real problems with this whole approach - as anybody who's ever tried calibrating audiology equipment will tell you! As a student of acoustics, I had to do it as an exercise - this is quite common. Have a look at this, for instance. Most universities running this sort of course should be able to give you all the info you need.