[bconline]

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.



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?

[S Clark]

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.



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!

[Mike-48]

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!

[Danny Richie]

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.

[bconline]

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.


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!

[bconline]

By the way, here's how I measured them.

[Danny Richie]

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.

[bconline]

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!

[Danny Richie]

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.

[bconline]

Thanks! I'll measure ungated in the listening room.

[bconline]

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.





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.

[bconline]

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:


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:


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.

[bconline]

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.


Below is the bass response for all of these. The X-Statik peak still stands out.

[bconline]

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:


Here's what I get for all the speakers:


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.

[bconline]

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?

[Danny Richie]

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.

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.

[Danny Richie]

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.

[poseidonsvoice]

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.

[bconline]

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.




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.




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.

[Danny Richie]

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.