[audiocrazy]

I took the measurements of my SongTowers using RoomEQ wizard. I have SVS sub and the xover is set to 80hz. I have SVS AS-EQ1 to equalize the sub & Integra DTC-9.8 with Audyssey.

I'm concerned about the FR from 1k-20Khz as its a down hill. I was expecting a very small variance about +/-3db but its more than 8db difference from rest of the range.
I also turned off all EQ but still the graph is same for 1k-20khz

I've GIK Panels(room kit 2) in my room 16x12. I've a 3 pairs of GIK 242 on the side walls to catch the reflection and 244 bass trap on all the corners and monster bass trap on the rear wall.

Has somebody taken any measurements with REW?

[fsimms]

If you notice that people who post measurments usualy say "near field".  You see now why the don't post the measurements at the listening position.   This is a normal room effect of treble drop off.  Notice how your ears tell you that the treble is natural.  All flat speakers have that drop off.

Bob

[DMurphy]

If you notice that people who post measurments usualy say "near field".  You see now why the don't post the measurements at the listening position.   This is a normal room effect of treble drop off.  Notice how your ears tell you that the treble is natural.  All flat speakers have that drop off.

Bob

There will generally be a roll-off due to high frequency absorption by various boundaries, but it should not be as extreme as this, and the cavity at 2 khz is hard to explain.  If the ST really sounded like that at your listening position, I think you would have returned them.  Does your equipment allow you to do any other type of measurement, say a closer field (1-2 meters) with a fast FFT signal that doesn't include room reflections, cancellations? 

[TF1216]

Is it worth removing the panels to take another measurement?  You could then place them back in a couple at a time and witness the effects.

[audiocrazy]

There will generally be a roll-off due to high frequency absorption by various boundaries, but it should not be as extreme as this, and the cavity at 2 khz is hard to explain.  If the ST really sounded like that at your listening position, I think you would have returned them.  Does your equipment allow you to do any other type of measurement, say a closer field (1-2 meters) with a fast FFT signal that doesn't include room reflections, cancellations?

Dennis thanks for your inputs. Actually when I got my ST I had the tweeter problem in my left speaker and Jim had sent me another pair of OW2 that I had to solder it. Do you think that might have messed up the tweeters?

I use Behringer ECM8000 microphone with EMU 0404 USB sound card to take measurment. Well I could put the mic stand closer to take near field measurment. I'll also try to take measurment without any side acoustic panels

Here is the FR response of my center speaker

[DMurphy]

Very interesting.   Now I'm worried that you didn't connect the new tweeter with the right polarity. That would cause the suck-out in the 2 khz area.  Are you sure you know which of the wires coming from the crossover is positive, and that you connected that to the positive tweeter terminal?  Generally Jim uses a blue wire for positive, and clear for negative.  The 0W2 voice coil is very robust and should not have been damaged by soldering unless you just let it cook and cook.   And then there should have been a total failure. 

[audiocrazy]

Very interesting.   Now I'm worried that you didn't connect the new tweeter with the right polarity. That would cause the suck-out in the 2 khz area.  Are you sure you know which of the wires coming from the crossover is positive, and that you connected that to the positive tweeter terminal?  Generally Jim uses a blue wire for positive, and clear for negative.  The 0W2 voice coil is very robust and should not have been damaged by soldering unless you just let it cook and cook.   And then there should have been a total failure.

I'm very positive that the tweeters were hooked up with correct polarity (but that was about 3 months ago). When I removed the bad tweeter I took a note of how the tweeters were hooked up & on the back of 0W2 there is + and - sign.
When I soldered the new tweeters i made sure they were the correct polarity. But when i go home tonite I will re-check it again.
Apart from physically checking the connection what's the best way to find out if my tweeters are either bad or hookup incorrectly.
Has somebody else on the forum taken any REW measuremnts of the ST's?

[audiocrazy]

Dennis how much variance in db is acceptable for on axis measurement at the primary listening position?

[Russtafarian]

For perspective, look at the measured FR curves for headphones at headphone.com.  None of them measure flat, they'd be unlistenable if they did. If your looking for a target curve as a point of reference, look at one for a HD600 or K701 headphone.  You'll never replicate that with your speakers in your room but it will show the kind of treble rolloff you can expect.

Russ

[DMurphy]

Dennis how much variance in db is acceptable for on axis measurement at the primary listening position?

Well, if you're going to make any sense out of a room measurement, you have to invoke smoothing, and maybe as much as 1/3rd octave.  If the anechoic response of the speaker is smooth within 1-2 dB, and you've smoothed enough to get rid of the meaningless dips that change with your position, the room response should be almost as flat except for a little more than the top octave, which will slope down.  Stereophile publishes room response curves regularly, and they often look smoother than the 1-meter anechoic response.   So I have my suspicions about the mic calibration and the basic measuring technique that the program is using for the ST's.   

[DMurphy]

Very interesting.   Now I'm worried that you didn't connect the new tweeter with the right polarity. That would cause the suck-out in the 2 khz area.  Are you sure you know which of the wires coming from the crossover is positive, and that you connected that to the positive tweeter terminal?  Generally Jim uses a blue wire for positive, and clear for negative.  The 0W2 voice coil is very robust and should not have been damaged by soldering unless you just let it cook and cook.   And then there should have been a total failure.

I'm very positive that the tweeters were hooked up with correct polarity (but that was about 3 months ago). When I removed the bad tweeter I took a note of how the tweeters were hooked up & on the back of 0W2 there is + and - sign.
When I soldered the new tweeters i made sure they were the correct polarity. But when i go home tonite I will re-check it again.
Apart from physically checking the connection what's the best way to find out if my tweeters are either bad or hookup incorrectly.
Has somebody else on the forum taken any REW measuremnts of the ST's?

Why don't you just measure one ST at a time in the same position and see whether the curves agree?

[jsalk]

A couple of comments. 

First, I emailed audiocrazy with some test ideas he could try.  I won't go into them in detail here, but one of them was the same comment Dennis posted.  By measuring each speaker separately, you can easily see if the measurements track one another.  If they do, the tweeters are wired correctly.

Second, the wires we use in any given crossover can vary in color.  Most often, we use a white wire for the positive tweeter terminal.  But it all depends on what colors we can get.  In all cases, the darker wire is negative and the lighter positive.

Finally, I do have some comments about programs like this and auto-EQ functions on receivers.  But I don't have time to collect my thoughts right now.  I'll try to do that and post a few thoughts this evening.

- Jim

[s_cervin]

I'll try to do that and post a few thoughts this evening.

- Jim

Only between periods I hope!!

Audiocrazy,
If you are confident in your measurements and speaker setup (placement, wiring, etc), I would begin by removing various traps (maintaining symmetry) and overlay the plots as part of the clue generation.


GO WINGS!
SC

[TJHUB]

Hey all,

I think audiocrazy's mic calibration file is wrong.  I too use an ECM8000 mic with my REW setup and look at my "correct" file (the black line).  Please note this is a friend's in-room measurement prior to getting his setup better placed (not Salk speakers either).



For the record, I have never seen a measurement roll off like audiocrazy's does.  He absolutely has his REW set up incorrectly. 

Don't panic guys, his Salk speakers are just fine. 

[jsalk]

OK...here are a few randomly related thoughts.

Imagine this scenario...

We work very hard to turn out an absolutely gorgeous pair of speakers.  The owner, wanting to get the best performance possible out of them, rushes out and purchases a Radio Shack SPL meter.  He locates a table of calibration corrections on the internet and carefully makes measurements, applies the corrections and plots a graph.  It looks terrible.  He thought the speakers sounded great when they arrived, but the measurements indicate something is terribly amiss.  He contacts us in panic.  His speakers are certainly defective and he has the graphs to prove it. 

"How do they sound?", I ask?  "They sound fine," he responds.

If he had just avoided that Radio Shack purchase, he could blissfully enjoy his speakers.  The problem isn't with his speakers.  The problem is with his measurements.  But at least on a temporary basis, it ruins his listening experience.

Unfortunately, this is a common occurrence and one we have had to deal with far more often than we would like.   

Here's another...

A person uses a speaker measuring system to measure his speakers.  The bass response is terrible! It falls off early and there are ugly peaks and valleys in the response.  There must be something dramatically wrong.

So I ask how the measurement was done.  He indicates it was done at the listening position.  He goes on to say that no matter where in the room he takes the measurements, the graphs vary somewhat, but not that much.  There is clearly a problem.

I explain to him that he was measuring the room.  Unless you take near field measurements at the driver, there is no way to obtain accurate measurements below about 200Hz.  If the measurement times are long enough to measure the bass response from the listening position, you are also measuring the room. 

Room measurement tools like REW (and even a Radio Shack SPL meter) can be very useful in terms of optimizing your room.  But they will not provide an accurate indication of the performance of a speaker.  For that you need a quality speaker measurement system and a well-calibrated measurement microphone.  And you also need a good bit of time to learn proper techniques for using these tools. 

Too often, these tools do more harm than good.  Improper measurement technique and a failure to understand how these tools work can cause you to needlessly lose confidence in your audio equipment.

As long as I am on a roll, I might mention reservations I have with all the new room EQ functions in receivers these days.  I can't tell you how many times I have asked customers to turn off the EQ function and just use the speakers as they are.  In almost every case, they reported a dramatic improvement in performance.

This would not seem to make sense.  Here we have a magic electronic gadget that can correct for any flaw in the speakers/room and do it at the listening position.  But all too often, it simply doesn't work.

On quite a few occasions, I have used DEQX (a very powerful and capable system) to apply a simple correction to a single loudspeaker.  In other words, I was not using it as a crossover, just using it to measure and correct for anomalies in the speaker performance. In almost every case, the speaker performed far better without the corrections.

IMO, the only thing an automated receiver EQ system should be used for is to deal with room modes.  It should not touch the signal above, say, 100Hz.  The only thing it can do at higher frequencies is screw things up.  I am very confident that the speakers we produce have absolutely no need for correction.  There simply isn't anything to correct.

Any issue that does require correction is room-related.  Changing speaker performance in order to deal with poor room acoustics is, plain and simple, a very bad idea.

The right technology, applied correctly, can be extremely beneficial in achieving great system performance.  But sometimes technology can be a curse.  It seems like every major receiver manufacturer today is offering an auto-EQ function. This may be great marketing, but in many cases, it is a terrible use of technology. Others may disagree with this advice, but if you have a function such as this on your receiver, please turn it off.  In most cases, you will be a lot happier.

End of diatribe.

- Jim

[TJHUB]

I'm am certainly no professional at audio stuff, but I can tell you that REW has to be used properly.  You absolutely cannot place too much value on it's measurements.  Most times, you would be hard pressed to even hear what it's showing you.  Also, movements of as little as 6" in any direction at the seating position will change the readings significantly. 

I use REW mostly for tuning subs.  For this it is priceless.  It is also perfect for finding any suck-outs you may have in-room.  I do use it to verify that my speaker placement is as good as it gets for the locations I am willing to live with (not much I can assure you).  Other than this, it's not much good.

[rahimlee54]

I really like my EQ when I am watching a movie, because it does its job, which is balance all my speaker volumes.  For 2 channel I had to read the manual and figure out how to by pass anything the AVR will do, after that it was smooth sailing.

Personally I wouldn't want to measure a speaker unless I have a capable room and calibrated equipment, anything other than that and accuracy is out the window.  That could just be me though.  Unless you are EQing your sub.

I could be wrong though.

[DMurphy]

Frankly, if I were Audiocrazy, I would feel a little ganged up on at this point.  I'm sure he's following the measurement instructions as best he can, and he's getting results that look problematic.  So I really want to be as constructive as possible.  I would be very interested to see separate measurements of each ST in the same position.   That should at least cast light on the tweeter polarity issue.   That leaves the droop in the response at higher frequencies.   Audiocrazy--where are you located?  I would be happy to send you a small, light 2-way that you could measure to see whether you get results anything like mine.  It's difficult to make any progress unless there is a known reference point   

[TJHUB]

Frankly, if I were Audiocrazy, I would feel a little ganged up on at this point.  I'm sure he's following the measurement instructions as best he can, and he's getting results that look problematic.  So I really want to be as constructive as possible.  I would be very interested to see separate measurements of each ST in the same position.   That should at least cast light on the tweeter polarity issue.   That leaves the droop in the response at higher frequencies.   Audiocrazy--where are you located?  I would be happy to send you a small, light 2-way that you could measure to see whether you get results anything like mine.  It's difficult to make any progress unless there is a known reference point

Ok Dennis, time to "gang up" on you. 

I may be wrong, but I don't think it's possible to reverse the polarity of one tweeter and have it cancel out the other tweeter above say...3kHz?  Audiocrazy's measurement should have nothing to do with tweeters out of phase.

I certainly wasn't trying to "gang up" on him, but I'm telling you without any doubt that his REW setup is not correct.  I'd suggest he post that graph pic on hometheatershack and let the pros (Bruce and Wayne) get audiocrazy fixed up.  I can assure you that his measurement will look as it should and all the speculation contained in this thread can be concluded. 

[Nuance]

Any issue that does require correction is room-related.  Changing speaker performance in order to deal with poor room acoustics is, plain and simple, a very bad idea.

The right technology, applied correctly, can be extremely beneficial in achieving great system performance.  But sometimes technology can be a curse.  It seems like every major receiver manufacturer today is offering an auto-EQ function. This may be great marketing, but in many cases, it is a terrible use of technology. Others may disagree with this advice, but if you have a function such as this on your receiver, please turn it off.  In most cases, you will be a lot happier.

Bingo.  That sums up everything I was going to say, and I do use REW.  I only use it to EQ below 100Hz, though. 

Audiocrazy, I mean no harm in this question: did you follow the Home Theater Shack REW FAQ to a "T," especially the part about sound card calibration? 

What you're likely dealing with is room issues.  As suggested, measure each speaker individually at the listening position, then measure each speaker individually at 1-2 meters or so.  I bet those anomalies go away with nearfield measurements, which prove the issue is the room.  Speaking of which, start with zero room treatment panels, measure, place where necessary (if necessary) and move forward from there.  You may just have to find a more suitable position for the speakers, or perhaps better positions for the acoustic panels. 

Keep us posted.