Protecting tweeters while testing

[irb]

When measuring the frequency response of a tweeter with a computer based measuring system, (e.g. Soundeasy, LSPCad) what is advisable in terms of tweeter protection?

Ian

[richie00boy]

Run at quiet levels and include an active high-pass filter. Then you add the filter response to the measured response to end up with the overall curve. Obviously this will only be good for maybe 20dB down the filter slope, but that should be more than far enough to investigate.

[dlr]

Originally posted by irb
When measuring the frequency response of a tweeter with a computer based measuring system, (e.g. Soundeasy, LSPCad) what is advisable in terms of tweeter protection?

Ian

If you are measuring in 2-channel mode (recommended) and using an MLS test signal, you have two options. You can measure at low levels with no protection. That's all I've ever done, but you do run the risk of tweeter damage if there's a problem or if you over-drive the tweeter. Higher power levels can be useful because that improves the S/N ratio.

The other method is to use a series cap, though I've never done this myself. If you use a cap, all you need to do is ensure that the probe is connected after the cap, that is, on the tweeter input lead. The probe eliminates all upstream influence, preamp, power amp, capacitor, conductors, etc. There's no need to include the cap in any model. This will also let you more safely increase the power level. There will still be some decreased S/N in the rolloff area from the cap, but at least it's still protected. It's also not usually that much of an issue with tweeter SPL measurements.

[irb]

Thanks to both of you! This is very helpful.

Ian