How to best use REW to balance drivers

Bill: Very interesting. I have just finished working on my initial tests and think I found a good way to do this. BTW, I am using the ALK Universal with stock woofers, JBL 2470 mids on ALK Trachorns and Eminence APT-150 tweeters (same as the Crites CT-125).

I too wanted to take as much room effect out of the equation, since Audyssey can correct for that. So, I placed the mic fairly close to my Khorn.

What I decided to do was to unhook all but one driver from the crossover, then run a full sweep. Then, test each driver in succession with the other drivers unhooked.

I then could look at al three traces together and see what kind of response and dB level I was getting. It turns out my mid and tweeter are very well matched and my woofer is a little hot, which is a trait of the Khorn bass bin.

I had purchased three ALK tweeter attenuators anticipating I would need them for this balancing test, but not so. I'll be putting those up on the Klipsch forum next.

I am no expert on how to take readings etc, but beleive this is a reasonable way to measure what each driver is doing and at least balance the mid range on the crossover with the tap settings. The tweeter can be attenuated if required with the ALK tweet attenuator, but the woofer is what it is.

What do think? Needless to say, I am using REW to take the measurements. I am using a Behringer mic.

My room is acoustically treated quite a bit, so I don't have too many room induced problems. I had worked on balancing the drivers before, and by ear had ended up with the X-4 tap setting in mid range drivers. I was visiting the issue again since I just changed tweeters and wanted to make sure they were properly set, hence my purchase of the ALK attenuators.

After my measurements, I found the mid and tweeter were dead on. It was really interesting to see each drivers total response ability.

One problem I have if I leave it all connected is that there is some level of boost at the crossover points. With the ES networks, of course, you won't see nearly the crossover issue, but it would still be interesting to 'see' the response of each driver.

My graph has four simperimposed plots, each driver and the full speaker response. As a minimum, it is very interesting to see the contribution of each driver to the 'whole'.

I really can't move my Khorns outside very easily, so will have suffice with the runs I have made.

If anyone has figured out a better way to do this, I would love to hear about it.

Here are some initial results of my very unscientific test. This graph is a set of three individual runs with only one driver hooked up at a time. The mid range has a very low point which is some sort of aberration, no way the mid can go that low. I think I have the mid and tweeter pretty well set up. The woofer shows the characteristic Khorn 'hump' and a large 50 Hz dip due to room modes.

I figure Audyssey can take it from here.

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.

laser188139 said:

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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Bill: Very perceptive on your part. The room dimensions are 20' wide and 27' long. I'm sure one of those measurements is causing the dip at about 52Hz.

As far as the mid driver phase, that has been an ongoing issue. It is a JBL 2470, which according to the literature and to a direct contact with the factory technician, has a reverse polarity. I also used a battery to verify that a positive charge to the 'black' terminal of the driver causes the diaphragm to move forward. I had also run some plots right at the crossover region to confirm this, but can't find the plots right now. So, I will run them again. IIRC, the plot very clearly showed that the driver has a reverse polarity just like JBL said, when compared to the woofer.

brucek said:

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).

brucek

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Bruce: I am still learning about setting the gate etc, so these plots were taken before I knew I could change it. They were taken with default settings. The mic as placed about 3' away, at driver height, pointed directly at the driver, on axis. The speakers are Klipschorns, which were designed to be placed in room corners to 'finish' the bass bin horn. I do not have suitable corners, so I made false corners, commonly accepted alternative. However, they are still places just a few feet from the very corners of the room. The very corners now have large floor to ceiling 4" thick bass traps.

A picture is worth a thousand words,and the link in my sig will show you plenty of pictures of the setup.
I really appreciate any input and ideas you guys may have. I am going to take some more readings today and see if I can play with the gate just for fun.

I just finished taking a new set of readings after visually making sure the woofers were properly wired. I made a few runs with the mic within a foot of the drivers, but I could never get a decent reading of the woofer performance relative to the entire speaker, so I moved the mic to about 3 feet back at tweeter and mid height, on axis. I will post some of the graphs, but also uploaded the entire REW file in case you have time to download it and play with the actual readings. The file can be found here http://prontoweb.com/rew/ and I would appreciate if you could help me determine the proper mid range setup for my system.

After my readings I am even more confused about the 'correct' polarity setup of the JBL driver vis a vis the woofer and tweeter. As I mentioned in previous comments, JBL says the driver is 'reversed' when compared to modern standard wiring due to the old JBL standard. So, I have set it up with + on the crossover to - on the driver and vice versa. I call that reverse polarity in my plots. The standard reference is + to + and - to -.

Here go the various plots:

Drivers only:

This is all three drivers with the JBL driver wired in standard configuration + to + etc. This graph looks correct to me when compared to the next one where I have the polarity reversed. This is why I am getting confused. The dark green line is the full spectrum graph.

This one shows the full response superimposed on the drivers but with the polarity on the JBL reversed, that is + to - etc. The Orange line is the full spectrum.

Finally, this one shows both full spectrum results with the JBL reversed in Orange and Standard in Green. I really would appreciate your suggestions. Thank you very much for your interest and time.

laser188139 said:

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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Bill: I am having to revisit the whole polarity issue driver by driver. I have always hooked up the tweeter in standard manner, but need to see what the deal is with the tweeter. I have the mid level pretty well taken care of, and am just looking at the polarity issue. The woofers, btw, are Bob Crites woofers. I am in agreement with you that the green line, that is polarity in normal configuration, seems smoother in the transition. I hope Bruce chimes in and shares his wealth of knowledge on my issue. I just am not familiar enough with REW yet to properly interpret the data. That is why I made the original file available. I'm hoping Bruce or a more expert person can help me with some sage advice.

Yes, this was all with Audyssey bypassed. The plots with Audyssey on are amazingly flat! That was what convinced me that Audyssey does what it says it does. I don't even have the professional version of Audyssey, just 8 measurement points and it does a great job for the sweet spot.