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Get familiar with the reaction system: Introducing the Reaction System
Measurements outside.
I am hoping to measure my last design outside to allow for a better measurement of the low frequency. How much does the drone of traffic and birds affect this. How loud should I measure?
Second question, if i measure a 60hz tone with a DMM to set my output at 2.83V will this work to see the actual true SPL once measured with my omniMic?
Any other tips I should know?
Comments
The easiest way to increase signal to noise is to make it louder. Measure when it's calmest, wind will make the most impact on the measurement result of anything. Take multiple measurements and pick one that's the cleanest. With most measurement systems I would say to average multiple measurements to reduce the noise floor, but Omnimic averaging is not done on the impulse response, but rather its done after the FFT on the frequency response, so averaging here does nothing to improve SNR.
For absolute SPL measurement, your plan is the correct approach. Omnimic provides instruction for this in the help file and 50Hz tone is one of the test tracks, see the "how to" section of the help file. Personally I don't see a lot of value in absolute SPL, for the most part you can take the sensitivity from your tweeter datasheet at the top end frequencies and observe your filter transfer function to see how much attenuation your filter provides and get a good enough depiction of the final system sensitivity. Additionally, Omnimic doesn't provide any real accuracy specification on absolute SPL, however it is intended to be an SPL calibrated system.
The real trouble with measuring final system response IMO is distance, especially with larger speakers. For bookshelf speakers where drivers are close together 1m may be fine, but with larger towers, 1m distance measurement at tweeter axis is not going to be the same as it is at 2m+ listening distance due to the relative distance and angles between drivers and mic. This is a problem for single channel measurements at tweeter axis for design as well. If you're measuring a large speaker outside, it might be good to take the opportunity to increase distance of the mic to 2m and compare even though the window width will suffer at the increased distance.
Well, I didn't get any good data. Other than figuring out that the tweeter was out of phase! Then I closed omniMic without saving... Lol.