Edward J M
Senior HTF Member
- Joined
- Sep 22, 2002
- Messages
- 2,031
Hi John:
Long time; glad to see you back posting again.
Test rigs run the gamut from mild to wild. You might want to solicit the opinions of Tom Vodhanel and Mark Seaton, who have experience with several of the different test rigs and software on the market.
Since you are interested in the true in-room FR, you will want to include room effects in the sweep. That eliminates the need for MLS (maximum length sequence) software. That doesn't mean you can't use MLS software for measuring the true in-room response (just widen the gate to a few hundred milliseconds); it just means you don't need the capability to alter the sampling time and window-out the room reflections.
TrueRTA is gated, but the gate is definitely long enough to allow room acoustics to fully develop. If I want to determine the quasi-anechoic response of a speaker or subwoofer, I can always test it outside at 2 meters.
Craig bought the ETF software to approximate the quasi-anechoic FR of loudspeakers without having to resort to outdoor measurements. The filter output is simply truncated before the unwanted room reflections arrive. The penalty is that the sample time is reduced, and the frequency resolution is worse. Typically the derived frequency response is not valid below a few hundred Hz, and Craig understands that limitation.
Mics? The better the mic, the flatter response, the lower the THD, and the more SPL it can tolerate. Any mic (and its pre-amp or phantom power source) should be professionally calibrated against a known standard. Most software programs accept mic correction factors. Brands? Again, check with Tom and Mark; I know Tom prefers LinearX, but they are costly. And Craig just dropped $500 on his mic set-up. The Behringer ECM8000 is relatively inexpensive and was quite flat out of the box (correction factors never amounted to more than 2 dB from 10-25,000 Hz). It's not a high SPL mic, though, and might start to introduce some THD into the signal over 120 dB.
If you are interested in absolute SPL (required for THD testing), then you'll need a sound level calibrator. This device generates a known SPL at a given frequency when the nose of the mic is placed into the receiver cup. The software is then calibrated to this SPL; otherwise you have no idea what SPL you are actually measuring. And using the RS SPL meter doesn't cut it as a sound level calibrator.
Long time; glad to see you back posting again.
Test rigs run the gamut from mild to wild. You might want to solicit the opinions of Tom Vodhanel and Mark Seaton, who have experience with several of the different test rigs and software on the market.
Since you are interested in the true in-room FR, you will want to include room effects in the sweep. That eliminates the need for MLS (maximum length sequence) software. That doesn't mean you can't use MLS software for measuring the true in-room response (just widen the gate to a few hundred milliseconds); it just means you don't need the capability to alter the sampling time and window-out the room reflections.
TrueRTA is gated, but the gate is definitely long enough to allow room acoustics to fully develop. If I want to determine the quasi-anechoic response of a speaker or subwoofer, I can always test it outside at 2 meters.
Craig bought the ETF software to approximate the quasi-anechoic FR of loudspeakers without having to resort to outdoor measurements. The filter output is simply truncated before the unwanted room reflections arrive. The penalty is that the sample time is reduced, and the frequency resolution is worse. Typically the derived frequency response is not valid below a few hundred Hz, and Craig understands that limitation.
Mics? The better the mic, the flatter response, the lower the THD, and the more SPL it can tolerate. Any mic (and its pre-amp or phantom power source) should be professionally calibrated against a known standard. Most software programs accept mic correction factors. Brands? Again, check with Tom and Mark; I know Tom prefers LinearX, but they are costly. And Craig just dropped $500 on his mic set-up. The Behringer ECM8000 is relatively inexpensive and was quite flat out of the box (correction factors never amounted to more than 2 dB from 10-25,000 Hz). It's not a high SPL mic, though, and might start to introduce some THD into the signal over 120 dB.
If you are interested in absolute SPL (required for THD testing), then you'll need a sound level calibrator. This device generates a known SPL at a given frequency when the nose of the mic is placed into the receiver cup. The software is then calibrated to this SPL; otherwise you have no idea what SPL you are actually measuring. And using the RS SPL meter doesn't cut it as a sound level calibrator.
