AudioCircle
Industry Circles => GR Research => Topic started by: bconline on 13 Feb 2019, 07:04 am
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After following AV-123 and GR Research for many years, I am excited to have recently acquired a used set of speakers, including (2) X-Statik, (2) X-Omni, (1) X-Voce and (1) MFW-15. In 2-channel listening, I especially like the sound of the X-Omnis. However, my pair of X-Statiks sound "boomy" to me. To try to figure it out, I did a frequency response of comparison of the X-Static (blue) compared to the X-Omni(red), measured at 1 meter.
(https://www.audiocircle.com/image.php?id=190503)
The X-Statik seems to have a 7db - 8db peak at 75 hz compared the X-Omni. This matches what I am hearing. For the measurement I tried different distances and different gatings. Same general results.
Any idea what is going on?
I observe that the X-Statik uses two of the the same driver as the X-Omni in a cabinet twice the size, and the X-Omni is ported. Could I get a response similar to the X-Omni by adding port to the X-Static (twice the cross section)? Or is there some other cause of the peak that is not going to change with a port?
Any advice for me?
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After following AV-123 and GR Research for many years, I am excited to have recently acquired a used set of speakers, including (2) X-Statik, (2) X-Omni, (1) X-Voce and (1) MFW-15. In 2-channel listening, I especially like the sound of the X-Omnis. However, my pair of X-Statiks sound "boomy" to me. To try to figure it out, I did a frequency response of comparison of the X-Static (blue) compared to the X-Omni(red), measured at 1 meter.
(https://www.audiocircle.com/image.php?id=190503)
The X-Statik seems to have a 7db - 8db peak at 75 hz compared the X-Omni. This matches what I am hearing. For the measurement I tried different distances and different gatings. Same general results.
Any idea what is going on?Yes, it's a room issue
I observe that the X-Statik uses two of the the same driver as the X-Omni in a cabinet twice the size, and the X-Omni is ported. Could I get a response similar to the X-Omni by adding port to the X-Static (twice the cross section)?No Or is there some other cause of the peak that is not going to change with a port? Again, it's the room
Any advice for me? Move the speakers around, treat the room with bass traps in the corners
And Welcome to AC!
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Move the speakers around, treat the room with bass traps in the corners
This is to second S Clark's comments. The variations in the low frequencies are typical of room effects, and the best cures are moving the speakers around to minimize the irregularities and adding bass traps in corners. The latter are especially effective against boom, which typically is not just frequency-response bumps but also overhang (long reverberation time).
The broad dip 100-300 Hz in the blue curve is likely to be audible as thinness, and it will accentuate the peak below. Broad dips and peaks are more audible than narrow ones. Make sure the distances from walls to the speakers are not the same . . . i.e., don't have the speaker the same distance from the front wall as it is from the side wall.
It's not easy to get enough bass trapping to absorb much below about 100 Hz. If you can't cure the 70 Hz peak sufficiently with position and traps, you might need to add EQ or tuned absorption to take it down. On the other hand, reducing reverb time and taking the peak down a few dB with traps may be plenty for happy listening, even if the peak is still visible on a graph.
Congratulations on your new speakers, and have fun getting them just right!
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The X-Statik's use a sealed box for the lower woofers. So the natural roll off is pretty smooth and gradual. It doesn't look anything like your in room response.
You'll need to work with placement and room treatments to knock that peak out of it. Your room reflections are out of phase in the dipped area and in phase in the peaked area. So it is possible that if you absorb some of those room reflections you can knock down that peak and at the same time you might bring up that dipped area too.
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Thank you all for the warm welcome and the great comments and suggestions! I will certainly experiment with placement and treatments. A full wavelength at 75hz is 22 feet, which is just about exactly the width of the room (with parallel walls). So this could be the problem.
Mike - you got it right on the nose with the audible thinness. This room has always had a problem with a broad dip centered around 200hz. Speakers that sound fine in other rooms usually sound thin in this room. The room is quite "hard", with concrete floors and parallel walls and ceiling made of drywall. I was thinking that carpeting or rugs might help.
What was/is confusing me is that I've not had problems with a 75hz peak in the room before. For instance, here are measurements of 5 different speakers, taken in this same room and under similar conditions.
(https://www.audiocircle.com/image.php?id=190525)
Also, when I measure the X-Omni in the exact some location and conditions, I don't get the same peak in the 75hz range. I do get the 180hz dip, quite badly.
I will have some fun moving things around to try to improve this room and do some more measurements. This X-series is very cool and very fun!
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By the way, here's how I measured them.
(https://www.audiocircle.com/image.php?id=190526)
(https://www.audiocircle.com/image.php?id=190527)
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If you are interested in the in room response of any speaker then you really need to place the speaker in the position that you listen to it in and take the measurement from the listening position. And you really need to independently measure the left and right speakers for comparison.
If this is the listening room then it looks like a lot of stuff needs to be removed from the room and a lot of treatment needs to be brought in. The room is as much a part of the system as anything else. To get great overall sound then serious consideration has to be given to the room.
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Thanks Danny! Yeah, this is the room that I get to play in. It's a finished garage that, unfortunately, has to share with a car and household storage.
Inside the house, I bring one or maybe two pairs at a time into the living room, which is carpeted, has high ceilings, and has a couple of sofas. Seems like the thing to do is to bring the X-Statiks into the living room and measure them there, from the listening position. What do you suggest for gating the measurement? I am using ARTA.
Thanks again!
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Thanks Danny! Yeah, this is the room that I get to play in. It's a finished garage that, unfortunately, has to share with a car and household storage.
Inside the house, I bring one or maybe two pairs at a time into the living room, which is carpeted, has high ceilings, and has a couple of sofas. Seems like the thing to do is to bring the X-Statiks into the living room and measure them there, from the listening position. What do you suggest for gating the measurement? I am using ARTA.
Thanks again!
A gated time window is what you use if making a measurement of the speakers. This is what I do as a designer. The speakers measure great and are very linear.
What you need to know is what they are doing in your room. So you need to make an un-gated measurement.
And at the distance that you are measuring from in the picture you are too close to the speaker to get any real data below 200Hz using a gated time window. At that distance you need to just crop the measurement below 200Hz.
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Thanks! I'll measure ungated in the listening room.
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I did a bunch of measurements today. First, I moved the X-Statiks to the main listening room along with the measuring set-up. Conveniently, my wife was travelling today. :) I measured from the listening position, with no gating. The back of the X-Statiks were 3.5 feet from the wall behind them. I measured the left speaker, which does not have a wall adjacent to it. I compared this to measuring the X-Omni's in the same position, and also another speaker in the same position. Here's a couple of pictures.
(https://www.audiocircle.com/image.php?id=190736)
(https://www.audiocircle.com/image.php?id=190735)
Below is the resulting frequency plot. Red is the X-Statik, Blue is the X-Omni, Olive is a Focal-driver-based custom speaker. I am still getting a large peak at about 100hz with the X-Statik that I don't get with the other speakers in the same position. It also sounded boomy.
(https://www.audiocircle.com/image.php?id=190737)
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To try to diagnose this further, I tried to take the room effect out of the equation. I moved outside and measured in the driveway, like this:
(https://www.audiocircle.com/image.php?id=190739)
Remember that dip I had in the garage at around 200hz? I think that was a floor bounce problem. I saw it again in the driveway measurements. The dip goes away if I measure near the ground, like this:
(https://www.audiocircle.com/image.php?id=190742)
Since I am mainly interested in the realative bass response, this worked out fine. Below is the bass response of the X-Statik and X-Omni in this position. I'm still getting a peak with the X-Statik.
(https://www.audiocircle.com/image.php?id=190743)
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Thinking that this might just be a difference between the X-Statik and the X-Omni, I gathered up 5 other high-quality speakers and measured their response also.
(https://www.audiocircle.com/image.php?id=190744)
Below is the bass response for all of these. The X-Statik peak still stands out.
(https://www.audiocircle.com/image.php?id=190745)
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I tried one more test. I measure the woofers themselves in the near-field (1" from the woofer surface), the same way reviewers do it. Here's what I get for the X-Statik and X-Omni:
(https://www.audiocircle.com/image.php?id=190746)
Here's what I get for all the speakers:
(https://www.audiocircle.com/image.php?id=190747)
I realize that the X-Static crosses over to the midranges pretty low. But, by 200hz, it is 15db down from the peak. Perhaps this by design? Does the X-Static crossover really low, like 100hz? I measured one of the mid-ranges in the nearfield also and got this, showing both the woofer plot and midrange plot. There may be acoustic blead-over between the two plots.
(https://www.audiocircle.com/image.php?id=190748)
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All of this makes me think that that something unusual is going on with the X-Statik speakers themselves.
I have a theory. The woofers are supposed to be 16ohm versions of the M-165, wired in parallel for a total 8 ohm resistance. Maybe 8 ohm versions of the woofer were used accidentally, making a 4ohm woofer circuit. With the same voltage input, I'd get higher output in just the woofer section. That's what am seeing. Would lower resistance of the woofers also lead to a lower low-pass crossover frequency?
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Definitely something unusual going on here. That doesn't make sense at all. The lower woofers and upper mids are the same driver. Or at least they should be. So there is no way for the output of the woofers to exceed the output of the mids. The coil used on the woofers is also a slightly higher dcr. So that would reduce the output of the woofer compared to the mids as well. And they do cross really low. So the inductance of the coil will also drop the output of the woofers down a little more. They were designed to be used wit a sub and need the output of a sub to bring them up a bit down low and balance out the response.
I realize that the X-Static crosses over to the midranges pretty low. But, by 200hz, it is 15db down from the peak. Perhaps this by design? Does the X-Static crossover really low, like 100hz? I measured one of the mid-ranges in the nearfield also and got this, showing both the woofer plot and midrange plot. There may be acoustic blead-over between the two plots.
(https://www.audiocircle.com/image.php?id=190748)
A near filed measurement of the mid doesn't tell whats going on with them as the dipole cancellation will actually eat up the response in their lower range and in the near field you won't see it.
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All of this makes me think that that something unusual is going on with the X-Statik speakers themselves.
I have a theory. The woofers are supposed to be 16ohm versions of the M-165, wired in parallel for a total 8 ohm resistance. Maybe 8 ohm versions of the woofer were used accidentally, making a 4ohm woofer circuit. With the same voltage input, I'd get higher output in just the woofer section. That's what am seeing. Would lower resistance of the woofers also lead to a lower low-pass crossover frequency?
It is possible. That pair was assembled in Colombia. And they did have 8 ohm woofers on hand. If they dropped the 8 ohm woofers in there then that would explain what's going on.
Get a hold of a volt meter and check the resistance. If the dcr is around 7 to 7.5 ohms then they are the correct woofers. If the dcr drops to below 4 ohms then they are the 8 ohm woofers.
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bconline,
Good sleuthing. Marvelous work actually. I am really glad you persevered in your initial suspicion despite the usual recommendation of blaming it wholly on the room itself. Doing the right measurements can make a difference and can reveal the right answers.
Since this is a passive crossover and a monopole system (for the bass), you definitely have a point with your line of questioning. I would also consider opening up the speaker and looking at the crossovers. Comparing the transfer function of the crossover with a reference (ie from AV123/Danny/etc...) may reveal other issues.
Best of luck,
Anand.
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The mystery continues. I disconnected one of the woofers and measured its DCR at 11.4 ohms. This is spot on the Peerless spec for the 16 ohm version. With the circuit connected, the DCR across both woofer terminals is 5.8 ohms. So, I think I have the correct woofers.
(https://www.audiocircle.com/image.php?id=190765)
(https://www.audiocircle.com/image.php?id=190768)
The wiring on the PCB also seems to be correct (i.e. no polarity problems.), unless any of you with more experienced eyes see a problem.
(https://www.audiocircle.com/image.php?id=190769)
(https://www.audiocircle.com/image.php?id=190770)
I'm not sure what to do next, I could try adding power resistors in line with the woofers to reduce their level and/or raise the resistance as seen by the crossover. Another thought - does this PCB lend itself to re-wiring for bi-amping? I could then control the signal levels of the woofer and mid/tweet in the amp.
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The mystery continues. I disconnected one of the woofers and measured its DCR at 11.4 ohms. This is spot on the Peerless spec for the 16 ohm version. With the circuit connected, the DCR across both woofer terminals is 5.8 ohms. So, I think I have the correct woofers.
Yes, that is correct.
I'm not sure what to do next, I could try adding power resistors in line with the woofers to reduce their level and/or raise the resistance as seen by the crossover.
No, you never want to do that on a low frequency driver. The resistors in that position would burn up in a hurry.
Another thought - does this PCB lend itself to re-wiring for bi-amping? I could then control the signal levels of the woofer and mid/tweet in the amp.
It isn't set up that way, but could be.
I'm stumped for the moment. The sealed box can't really create a peak like that. The roll off starts at about 150Hz and creates a gradual roll off that ends with a -3db at 62Hz.
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Here are the actual measurements of one of the units like yours with the metal grills on them.
The wiggles in the tweeters response 3kHz and 4kHz region are the result of the grills.
(http://www.gr-research.com/pics/X-Statik%20crossover.jpg)
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I'm stumped for the moment. The sealed box can't really create a peak like that. The roll off starts at about 150Hz and creates a gradual roll off that ends with a -3db at 62Hz.
What if the box isn't airtight? What if it lost it's seal?
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What if the box isn't airtight? What if it lost it's seal?
Even if it did then it shouldn't cause a change in output, and certainly not like that.
At the point of his measured peak they should already be 2 to 2.5db down in output.
They are the same woofers as the ones used above as mids. And there are no resistors inline with the mids. So there is nothing to bring the mid's down in output relative to the woofers. It's the woofers that should be down a little compared to the mids due to the higher dcr of the larger inductor.
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Let me think on this for a little bit.
I just built out a set of these for my Dad's theater room back in November and the bottom end of his pair was smooth as glass.
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Is the bass in both speakers elevated, or only in one speaker?
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bconline, that's an impressive attack on the problem - dedicated, thorough, and no small amount of work. Well done!
(Tyson beat me to a version of the one question I was going to ask!)
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Thanks to all of you for the help and suggestions!
To isolate the woofers, I unsoldered them from the crossover but left them connected to each other in parallel. I wired the woofers directly to the amp with a make-do wire through the hole where the terminal cup was. I stuffed a rag in the hole to approximate the sealed cabinet. Like this:
(https://www.audiocircle.com/image.php?id=190781)
I then measured the drivers in the near-field (1" from the face, no grills). Tyson asked a good question about whether both drivers behaved the same. So I measured each woofer separately and I measured each midrange separately. Next, I reconnected the woofers to the crossover and measured the 2 woofers again. All of this was done in one sitting, with no changes in test conditions. The results are below. In the diagram:
- Blue is each woofer driven directly, with no crossover
- Red is each woofer driven through the crossover
- Purple is each midrange
- Green is the tweeter
(https://www.audiocircle.com/image.php?id=190782)
A few comments:
- It is nice to see the consistency between drivers
- Without the crossover, the woofers drive nicely well through the midrange
- Without the crossover, the woofers roll off reasonably on the low end like a sealed cabinet should
- The midrange responses are probably artifically low and wonky because of the open back nature
The response of the woofers with the crossover is very confusing to me. I thought that it was impossible with a passive crossover to have a response higher than the woofer being driven directly at any frequency. But here I see about a 4 db increase at the peak. How is that possible? Am I missing something?
The other thing I observe is that the rolloff of the woofers on the high side starts at a much lower frequency than I thought it would. And that seems to create this artificial peak. I would guess that if the crossover frequency was at 200 hz instead, and the peak was not there - then the response would be very smooth like Danny designed and like Danny is getting in practice with other X-Statiks.
Could any manufacturing defect in the crossover create these symptoms - like bad solder joints, wrong caps inserted, shorted caps or ???
BTW, both the left and right speakers are behaving approximately the same. But I did not do these detailed measurements on both sides.
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I have an idea. It's speculation but it would explain what's going on. I'll shoot it to you in a PM.
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Did you measure the DC Resistance of the paralleled woofers after disconnecting them from the crossover?
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HAL - Yup. I measured the DCR of the woofers out of the circuit at ~11.4 ohms each, which is exactly what Peerless specs. In parallel they measure just under 6 ohms.
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A little progress...
I followed a hunch from Danny that the electrolytic bypass cap may be out of spec. On his suggestion, I unsoldered one leg of the cap from the PCB and re-ran the near-field FR tests.
(https://www.audiocircle.com/image.php?id=190837)
The new green lines are the woofers with the crossover, and without the electrolytic. The peak is down a little and the low-pass crossover point is out a bit. Still not quite right yet, though.
(https://www.audiocircle.com/image.php?id=190838)
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BTW, here's a picture of the whole crossover PCB.
(https://www.audiocircle.com/image.php?id=190839)
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Going back and looking at all of your measurements has me noticing a pretty elevated area in that same range on most of your measurements. Even the measurements of the mids that should fall like a rock below 200Hz pick back up in that range. It just looks worse on the X-Statik woofers as they only cover a narrow range and drop off on both sides.
So some of that might be your microphone calibration just showing more output in that area and making it look a little worse than it really is.
You could have some room gain right in that area too.
To get the power curve you're looking for might require an inline cap before your amp to roll off the lows a bit.
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So some of that might be your microphone calibration just showing more output in that area and making it look a little worse than it really is.
That could well be the case. The weak link my setup is an old Mackie mixer which I use as a microphone preamp. I really don't know what it's response profile is. Because of this unknown, I am trying to focus on the relative response of various speakers measured with the same equipment and conditions.
Is a circuit diagram of the X-Statik crossover available? I could try experimenting with it to see what effects I can get.
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That could well be the case. The weak link my setup is an old Mackie mixer which I use as a microphone preamp. I really don't know what it's response profile is. Because of this unknown, I am trying to focus on the relative response of various speakers measured with the same equipment and conditions.
Is a circuit diagram of the X-Statik crossover available? I could try experimenting with it to see what effects I can get.
Shoot me an e-mail and I'll respond with a schematic and a couple of things that can be done to take it in the direction you are wanting to go with them.
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Thanks Danny! I sent you a PM.
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I got some advice from Danny and did a some research on the internet. This what I ended up doing:
I removed both capacitors from the woofer's low-pass circuit - making this part of the circuit into a first order crossover. That reduced the 80hz peak by 2 - 2.5 db and raised the output above 125hz. The overall repsonse was smoother. Here's the near field comparison:
(https://www.audiocircle.com/image.php?id=191090)
However, the sound still a little boomy. And the measurement in the driveway showed the remaining peak.
(https://www.audiocircle.com/image.php?id=191091)
My theory is that the reason for the peak in the first place is that are divers are out of spec. I used an online crossover simulator to simulate the schematic: http://www.micka.de/en/2weg_en.php. It confirmed that Danny's crossover is an excellent design with very flat response.
So, to further reduce the peak, I tried adding a small amount of mass to the woofers. This lowers the resonant frequency. The tradeoff is lower sensitivity. I tried different masses added on the front.
(https://www.audiocircle.com/image.php?id=191095)
After settling on 2 grams per woofer, I added that mass to the back, wrapping it around the voicecoil. Like this:
(https://www.audiocircle.com/image.php?id=191096)
This had the expected effect. Here's nearfield woofer response (added mass is the green line):
(https://www.audiocircle.com/image.php?id=191097)
And here's the resulting driveway response, measured at the tweeter level, 3 feet away:
(https://www.audiocircle.com/image.php?id=191098)
And here's a comparison with another pair of speakes that I like the sound of:
(https://www.audiocircle.com/image.php?id=191099)
And the sound??? Very very nice now! Not boomy any more. The bass is solid and transistions well to the MFW-15 subwoofer when really low bass is needed. Thank you very much to Danny and others who gave me advice!!
A few other comments:
(1) Becuase of the slightly lowered levels on the low end, the speakers are a little bright. The response above 2K is a little high. So, I may try padding the tweeter down a little bit.
(2) This tweeking is only for my particular pair of X-Statiks. I'm not implying that any other X-Statik need this kind of treatment.
(3) In the FR measurements, the dip at 200 hz is a floor bounce effect. I don't hear that dip in listening situations.
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bconline,
Again, great work.
It's important that you realized that the problem wasn't necessarily the room (indeed it's always a contributor, notice the SBIR issue you have between 100-300 Hz), but actually something that was intrinsic to the design of your particular pair of Xstatiks. This is important for those reading this thread (doing the right measurements ARE important). Not only did you hear the problem with your ears, you measured it. Not only did you measure it in room but you measured them outside to minimize the contribution of the room. And you made didactic comparisons to other loudspeakers that are monopoles (sealed, ported, passive radiator, TL, etc...), to verify that the problem again was intrinsic to your pair of Xstatiks. This probably happens more often than people are willing to admit. Others would have told you to let the speakers 'break in', etc... :lol:
Unfortunately you had to increase the moving mass of your woofers and lower the Fs, since they appear to be out of spec. The only way to conclusively prove that is to measure the T/S parameters of each woofer individually, and then compare to the original design. Honestly, I wouldn't bother at this point.
And yes, it appears that when these particular speakers left AV123 in Columbia, the final check wasn't done right. I am glad you are patient as well as diligent. You did somebody else's work! Kudos!
Best,
Anand.