# How to best use REW to balance drivers



## Rudy81 (Aug 5, 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 (Sep 19, 2009)

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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## Rudy81 (Aug 5, 2009)

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.


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## laser188139 (Sep 19, 2009)

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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## Rudy81 (Aug 5, 2009)

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.


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## Rudy81 (Aug 5, 2009)

Bill, what other upgrades have you made to your La Scalas? What made you go with the ES network?


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## laser188139 (Sep 19, 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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## Rudy81 (Aug 5, 2009)

AL is definately correct on the overlap issues. In my graphs, you can actually see this! I too have heard really good things about those crossovers....they are just pricey. I opted to spend my exctra cash on the Trachorns and mid driver upgrades. If you have not heard the Trachorns, don't....they will cost you more money and you will have to have them. 

My center La Scala just got its Trachorn installed. That required a jig saw, a steady hand and a lot of courage. I really hated cutting up the speaker, but it had to be done to fit the Trachorn. You can see the final product in my HT page. It's on my sig.

Let me know how your ES networks work out.


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## brucek (Apr 11, 2006)

> 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.

brucek


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## Rudy81 (Aug 5, 2009)

brucek said:


> Not really necessary, just use an appropriate gate for the impulse response in REW to remove reflections.
> 
> brucek


Thank you very much. That goes to show you how little I know thus far about the capabilities of REW. I will have to look into how to do that. Hopefully the help file addresses this issue.


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## Rudy81 (Aug 5, 2009)

I just found a few threads addressing how to properly gate results. Thank you for the tip on how to take the readings we need.


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## brucek (Apr 11, 2006)

> 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.

brucek


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## Rudy81 (Aug 5, 2009)

brucek: Thank you very much for all your help. I greatly appreciate the tutoring.


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## Rudy81 (Aug 5, 2009)

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.


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## Rudy81 (Aug 5, 2009)

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.


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## glaufman (Nov 25, 2007)

Are you talking about the 60Hz WRT that low aberration on the mid?
I'm sure that's noise not worth worrying about, since it's line frequency (AC) I wonder what's picking it up...


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## Rudy81 (Aug 5, 2009)

glaufman said:


> Are you talking about the 60Hz WRT that low aberration on the mid?
> I'm sure that's noise not worth worrying about, since it's line frequency (AC) I wonder what's picking it up...


When I get a chance I'll run it again and see what the deal is. I have never seen that before.


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## laser188139 (Sep 19, 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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## brucek (Apr 11, 2006)

> 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).

brucek


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## Rudy81 (Aug 5, 2009)

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.
> 
> ...


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


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.


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## Rudy81 (Aug 5, 2009)

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:


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## Rudy81 (Aug 5, 2009)

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.


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## Rudy81 (Aug 5, 2009)

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.


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## Rudy81 (Aug 5, 2009)

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.


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## laser188139 (Sep 19, 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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## Rudy81 (Aug 5, 2009)

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?
> 
> ...


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.


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## brucek (Apr 11, 2006)

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.

brucek


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## Rudy81 (Aug 5, 2009)

brucek: Thank you. I appreciate all your comments, they help me learn about the software and about acoustic measurement. The attached files are the Asus board sound card and the ECM mic.


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## Rudy81 (Aug 5, 2009)

Missed one. Looks like I can't upload the soundcard file here, so I will upload it to the web site mentioned before. 

Many, many thanks.


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## brucek (Apr 11, 2006)

> 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








Incorrect crossover








brucek


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## Rudy81 (Aug 5, 2009)

brucek: I can't thank you enough for taking time to look at my plots. After looking at the plots myself, although nowhere near as closely as you could, I decided the 'standard' wiring matched the woofer best for the reasons you mentioned. I have already changed the wiring to 'standard' + to + and - to -. 

I will play with the plots so I can reproduce what you have done. This awesome program, REW, is still on a rather steep learning curve for me.

Many thanks again!


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## glaufman (Nov 25, 2007)

Rudy81 said:


> I just found a few threads addressing how to properly gate results. Thank you for the tip on how to take the readings we need.


I'd love to learn more about this without harassing Bruce... could you post a link to the thread(s) you found? I've already gone through the help files again (which helped) but I feel I need more...


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## Rudy81 (Aug 5, 2009)

I ran a search in the REW forum for gating and one that had what I needed was this one: http://www.hometheatershack.com/for...one-explain-gating-response-measurements.html

I have yet to really get into it, but plan on doing so in the next few days. I had to go back and start from scratch since brucek was good enough to PM me on some issues with my set up that could be done better. He has been a great help and his expertise is greatly appreciated.


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## glaufman (Nov 25, 2007)

Thanks... Now I gotta make time for more reading/playing!:hissyfit:


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