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Discussion Starter · #1 ·
I wanted to pose some questions concerning the use of REW for generating individual driver measurements in the designing and testing of appropriate crossover networks. I've seen the topic addressed a few times on the forum yet not in any great detail.

Understanding that the intended purpose of REW is the integration/equalization of subwoofers in a home theater system, with its ability to take full range measurements using the appropriate microphone it seems, if setup and used correctly, REW could accomplish this task.

I have used FFT analysis software in the past (MLSSA) and am familiar with the process. However, with REW being a different animal it begs some clarification on how that might be accomplished. The question I have using REW for this purpose would be in the calibration, mic placement and perhaps any other details that would need to be considered specific to REW in this application.

Assuming the measurements would be made in as anechoic an environment as practical (Outside), what distance would be recommended for the microphone; one Meter or much closer to the individual driver under measurement?

In regards to calibration, since it's recommended that REW be calibrated to 75db, which driver would be best used for the calibration reference; the most sensitive or the least sensitive driver?

If the tweeter wound up as the SPL calibration reference, another concern would be throwing the full range pink noise cal signal at the risk of frying it. If so, would the cal signal be bandwidth limited to prevent frying it?

The ultimate goal of this would be to export the individual driver measurements to files compatible with a filter crunching application such as good, old XOPT to come up with the correct filter/driver response.

If anyone has any thoughts on this or whether it's even a practical use for REW it'd sure be appreciated.

-rawkdawg
 

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At 75dB at one meter I doubt that a sweep or pink noise would damage a driver. Why would you use pink noise?
 

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Discussion Starter · #3 ·
Pink Noise is the signal REW uses to calibrate both the internal SPL meter at 75db as well as the input level (Check Levels) for maximum headroom which, I assume, still has to be done prior to running signal sweeps even for individual drivers. It's one thing to throw that full range PN signal at a subwoofer or full range speaker system with the crossovers in place but I was concerned it might be a bit much for a stand alone tweeter.
 

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Assuming the measurements would be made in as anechoic an environment as practical (Outside), what distance would be recommended for the microphone; one Meter or much closer to the individual driver under measurement?
Either would work and REW also allows measurements to be windowed. This allows accurate measurements indoors for frequencies over say 300 Hz or so depending on the setup.

In regards to calibration, since it's recommended that REW be calibrated to 75db, which driver would be best used for the calibration reference; the most sensitive or the least sensitive driver?

If the tweeter wound up as the SPL calibration reference, another concern would be throwing the full range pink noise cal signal at the risk of frying it. If so, would the cal signal be bandwidth limited to prevent frying it?
The mic calibration is only to set the REW SPL Meter level per the mic input gain. It would not even need to be done as absolute levels are not relevant for the work you described. There is an easy option however; just use any other old speaker to do the calibration of the REW SPL meter. Then all your subsequent driver measurements will have the proper SPL readings.

REW allows the sweep to be band limited by setting the start and stop frequency so you can protect the drivers with by using low signal levels and appropriate band width.

If anyone has any thoughts on this or whether it's even a practical use for REW it'd sure be appreciated.
REW is a very capable audio signal analysis package. It should work fine for the job you mentioned. [As with many tools, if it is not used properly for the job, there may be problems.]
 

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Discussion Starter · #5 ·
Thanks much for the assistance. I can see now where the calibration wouldn't be necessary since I'm just looking for the relative freq response of the drivers. I suppose if I kept the level reasonable I wouldn't necessarily need to bandwidth limit the test signal. At any rate, I'll give it a try and see what happens. Hopefully I can import the measurement files into XOPT without too much massauging.
 

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To start, the best is to measure each transducer at a time with the mic on axis at 30 cm distance.
Then, based on the measures, you can plan the Xover design.
Good luck
Andrea
 

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As AndreaT said, close measuring of the individual drivers will give you the best picture of how they interact. In REW you can display the results in the one window to compare them.
After that you can level match them in your crossover.


Here's one I prepared earlier:

 
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