SPL seems off. Now what?

[Mike-48]

Hello, All--

I'm using an OmniMic 2 to find good speaker and listener positions in my audio room. I'm an amateur user, not an audio professional or designer; just trying to get good sound in a difficult room.

After starting the (current) software, I noticed that, in my quiet room, the unit indicates a background SPL of about 48 dB, and when I am speaking quietly, it indicates peaks of about 85 dB. Both values are about 25 dB higher than comparable readings from a Radio Shack SPL meter, which seem closer to what I'd expect.

(I have the OmniMic's software SPL settings set to slowest averaging. I have the RS meter set to "slow" and "A" weighting.)

Thoughts? Suggestions? Does this call for warranty service, or have I possibly overlooked something?

Thanks,
Mike

[killa]

Re: SPL seems off. Now what?

48 db background sounds about right to me. I am betting the ratshack meter is off. Not sure what weighting omnimic is using.

[Mike-48]

Re: SPL seems off. Now what?

I think the issue is that the OmniMic "meter" reading is always unweighted. (Why? It would be helpful to have "A" weighting.) Most of the background in my room is at very low frequencies < 20 Hz, and is simply traffic rumble that is inaudible (or barely sensed) by a human.

The corresponding A-weighted curve (1/3 octave smoothing) on the Omnimic peaks at around 26 dBA, and much is from the fan in the laptop computer, which is not on unless I'm taking measurements. So, with A weighting the two measurements are pretty close.

[killa]

Re: SPL seems off. Now what?

I am not sure why you need to know SPL levels other than matching speaker levels? Otherwise you just need to find the smoothest frequency response. I could very well be wrong or be misunderstanding what you are trying to achieve.

[Mike-48]

Re: SPL seems off. Now what?

K-

I'm interested in an overall SPL reading for two reasons.

First, I put a lot of effort into soundproofing the room, and I'd like to get an objective reading on how successful that was. It's quieter than most listening rooms I've been in, and very definitely quieter than other rooms in the house.

Second, I wanted to verify in any way I could that the OminiMic2 and software are set up correctly and giving sensible answers. An SPL of nearly 50 dB in a seemingly quiet room pointed to a problem, until I figured the problem is most likely the lack of weighting.

Mike

[killa]

Re: SPL seems off. Now what?

Makes sense. I thought you were trying to set up equipment. I have never tried to test SPL so I won't be much help. I wish more people would check this section of the forum.

[Mike-48]

Re: SPL seems off. Now what?

I wish more people would check this section of the forum.

Me, too!

[killa]

Re: SPL seems off. Now what?

If you are using windows 8 I just read a post by bwaslo (aka Bill Waslo, the guy whose name is on the copyright for omnimic)" also installed Classic Shell (google it) to make the machine act more like Windows 7 in general.

For OmniMic, set it to run in Windows XP SP3 compatibility mode. Right-click on the icon, or better, find Omnimic.exe in your D:\Program Files\Omnimic directory and right click on that. Choose properties and go for the Compatibility tab. Omnimic will work without doing this, but the absolute SPL levels will be wrong (I have no idea why they messed with that in Win8, but they did!)."

[Mike-48]

Re: SPL seems off. Now what?

If you are using windows 8 I just read a post by bwaslo (aka Bill Waslo, the guy whose name is on the copyright for omnimic)" also installed Classic Shell (google it) to make the machine act more like Windows 7 in general.

Thanks. I'm using Windows 7 Professional.

Mike