How to best use REW to balance drivers

5609 Views 33 Replies 4 Participants Last post by glaufman, Nov 5, 2009

Rudy81

Discussion Starter · Nov 1, 2009

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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laser188139

· #2 · Nov 2, 2009 (Edited)

Rudy, I've been thinking ahead to this problem, as I have ordered a set of ALK ES filters for my two LaScalas.

So far, I've come up with two approaches.

(1) Use REW just as a signal generator. One could use the pink noise generator to cover the heart of each driver's response while avoiding the crossover, in my case, for example, 60Hz-450Hz for the woofer, 550-3900 for the midrange, and 4100-16000 for the tweeter, and measure each with an SPL meter. Then adjust the midrange and the tweeter so they give the same SPL measure as the woofer.

(2) Do full range measures of each speaker individually, with Audyssey Off of course, in the middle of the room as far away as possible from the walls, with the mic placed near field facing the speaker. By looking at the graphs, one could try to adjust the midrange to match the woofer in level, with no weird anomalies around the crossover, then do the same to match the tweeter level to the midrange.

I have no idea how well either of these techniques will work. Hopefully someone has already tackled this problem and can share his or her insight.

Cheers,
Bill

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laser188139

· #4 · Nov 2, 2009 (Edited)

That sounds like a plan.

I was planning on leaving all the drivers connected, at taking measures over each range, which makes sense with the extreme slope filters. I can see why, with the Universal filter and more normal rolloffs in the crossover, you are thinking of measuring each driver separately.

The problem I see with the graphs is that, in room, there are a lot of reflection effects causing dips at various frequencies. With the smoothing recommended here for REW graphs, 1/3 octave, these are largely flattened out so the trends should be visible. I can clearly see a midrange dip in my stock LaScalas. I am hoping to avoid lugging the speakers outside just to reduce the measurement variation when comparing the levels.

The other idea I had was to try both my techniques and see if they give identical recommendations. If the SPL meter on range limited pink noise and the visual inspection of the graphs show the same difference in level between drivers, I will be more confident in making the corresponding change to the crossover attenuators.

As you are ahead of me on this path, I'll be interested in hearing how your technique works, whether the levels sound right to your ears when you are done.

Good luck,
Bill

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laser188139

· #7 · Nov 2, 2009

I have not made any other changes. I thought about the Trachorns, but I'm sure someone in my family would go to the closet for a gun before they would let me take a saw near the LaScalas.

I opted for the extreme slope filters after reading Al's analysis in his article. When discussing phase issues he pointed out that the overlap in the crossover of a horn inherently creates a phase issue, as the drivers are at different distances from the listener. Thinking about this, and the description of how Audyssey tries to cluster data points in the time domain as well as the frequency domain, I figured that cleaner crossovers would make it easier for Audyssey to equalize the entire range.

Most who have tried them have written positive comments. So I'll give them a try; it's probably the only time I will ever spend this much time and effort improving the LaScalas.

My children are already making plans to fight over them when the time comes.

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laser188139

· #18 · Nov 3, 2009

Rudy81 said:
This last one, shows the full range spectrum superimposed on all three plots. Very cool! I really like REW!

If you look closely at the crossover point between the bass and mid, you will see the problem Al was talking about.

Rudy, I find your graphs fascinating. I do wonder about the dip and peak right above the 400Hz crossover. How did you verify the phase of the midrange and woofer when you installed the new crossover? Does the behavior of the freq resp curve change if the phase is changed on the midrange?

By the way, the null at 52Hz suggests a 1/4 wave reflection off a wall 5'5" away or perhaps 16'3.6" away. I have found the freq-dist program on the RealTraps site very helpful.

Curious,
Bill

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laser188139

· #25 · Nov 3, 2009

Neat, Rudy.

I am by no means an expert. Most of the advice I've seen on the internet as regards phase recommends that whatever sounds stronger is correct. As the green line meets this criterion and appears smoother, I would choose it. Does the transition from woofer to midrange sound smoother, too?

I made this suggestion because I have read the same thing about the CT125 tweeters. Someone pointed out on the Klipsch forum that the driver manufacturer documented the driver as having inverse polarity. Yet most appear to connect them normally. So I figured I would have to hear and measure them both ways to reach my own conclusion.

Taking the documentation on the ALK site as correct, that the low crossover is at 400Hz and the high crossover near 6kHz, it looks like the midrange is set nearly the same level as the woofer. I assume this is all with Audyssey equalization turned off, and the response will be smoother after equalization.

Bill

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