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How to best use REW to balance drivers

5608 Views 33 Replies 4 Participants Last post by  glaufman
I have recently changed drivers from stock in my speakers. I would like to ensure the tweeters, mid and woofers are set at a proper level relative to each other. How do I use REW to achieve this kind of calibration?

I do have the ability to attenuate the mid and tweeter.
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I really can't move my Khorns outside very easily
Not really necessary, just use an appropriate gate for the impulse response in REW to remove reflections.

properly gate results
Be sure you move the speaker at least the distance that the gate covers to remove any reflections, and be aware of the mic and its stand. Position the mic head pointing directly at the driver at about 12 inches or less and try and keep the stand out of the way. Be sure you're on-axis, as even small off-axis positions may offer poorer results. In fact an off-axis measurement is also useful.

Remember that gating puts a limit on the lowest frequency and the resolution of the response. For example, if you were trying to limit reflections from surfaces 1 meter away, you would use a minimum 6msec gate (d=(time*speed)/2)=(6msec*344m/sec)/2, but this would limit the lowest frequency of usable response information to ~167Hz (freq=1/period)=(1/gate time). So, you could select a left gate of 1msec and a right gate of 5 msec. You can go less for tweeters and midrange. I seem to remember using a 3 msec gate last time I was testing my tweeters for a test.

Open the IR Windows pop-up and select a gate that you want and watch the impulse response to ensure it's appropriate (with respect to reflections), then select Apply Windows and your response graph will adjust to that gate time response plot. The popup will show the gate window and frequency resolution for you, so you don't need to do the math on that. You're trying to exclude reflections from any surfaces nearby. It could be as simple as the mic stand, but predominantly hard surfaces such as the floor. Of course, shut off any smoothing.

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Here are some initial results of my very unscientific test.
You haven't told us the gate times you used for the test. Can you tell more about your methods for the testing (i.e. gates, mic orientation and position, speaker position in room with reference to near boundaries, etc).

Rudy, for anyone to play with your mdat file (other than to look at it as is), you need to provide the soundcard and meter calibration files that you're using. This is because the impulse response measure is taken without the influence of those files, so any gate manipulation would have to reapply the cal files to the frequency response, and so they would require them.

I will upload it to the web site
I looked at your new mdat (taken with calibration files) and I would say that the wiring of the JBL in the plot called Full range would be your best method.

The response called FR rev polarity shows a cancellation that would indicate the woofer and JBL are out of phase at the crossover.

If two signals are in phase as they cross (just like a subwoofer and mains at the crossover), the resulting signal should be about 6dB higher. If I look at your mdat and do some gating, and show them with an expanded axis at the crossover of the woofer and mid JBL driver, I would say the response that you call Full Range (green trace in the first jpg below) could be considered a classic 6dB mix, and the correct polarity. The second jpg shows a dip around the crossover (blue trace) and I would consider it the incorrect wiring of the driver.

Correct crossover
Text Line Diagram Plot Symmetry

Incorrect crossover
Text Line Plot Yellow Diagram

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