I just caught up with the material posted over the last week - KSTR, I am dazzled by what you did, and what HOLMImpulse can do!!! Now that's what I call a powerful tool for loudspeaker research. Thank you very, very much.
When Gary called me yesterday, I hadn't seen all the work you folks have been doing - I was going by Gary's verbal description of what he was measuring. As mentioned earlier, I was too physically tired by three days of disconnecting and hauling equipment into the basement, one day of installing the big TV and Salamander cabinetry, and another two days getting everything going again, with all-new connections and system pathways. We're glad the folks at Listen Up! in Boulder built the 3-wide Salamander, installed the 95-lb Panasonic and hauled away the 180-lb 36" RCA/Thomson, along with its stand - that was much too big a job for Karna and me.
Returning to the topic at hand, the nice thing about the time domain is that it's easier to unscramble what's causing reflections and diffraction. The polarity of the artifact hints at its origin, and the timing gives a sign where it may be coming from. Although the room looked tight from the photos, nothing was that close, with the exception of the possible floor bounce, and moving the speaker higher eliminated that possibility when the timing didn't change.
Ergo, it's either a discrete reflection from the back wall - and that certainly was a strong possibility, with the timing and polarity right - or an unusual diffraction artifact. I was strongly favoring the back wall reflection, but was surprised to hear from Gary how little difference damping material was making to the measurements.
So all that left was a peculiar diffraction artifact - not off the front as usual with 90-degree corner cabinets, but off the rear, instead. I guess when you round off the corners in one place, there's more energy traveling along the cabinet surfaces to land elsewhere. In this case, it was the rear edges.
I mentioned to Gary when I was measuring cabinets at Audionics and later, during the Ariel design, diffraction is at its worst when measuring at a 45-degree angle off the front cabinet edges. It is possible to slowly sweep the microphone along the surface of the cabinet, and find the diffraction-emission hotspots.
How audible is all this? I actually don't know, and to some extent don't care. But I don't like to leave artifacts in the design - if they aren't audible right away, they have a way of sneaking up on you over time. That little coloration gets worse and worse the longer you listen to the loudspeaker - and knowing where it's coming from certainly doesn't help. Better to chase it out early in the design, remove it at the acoustical or mechanical source, and not rely on equalization tricks to mask audibility. The mask has a way of coming off over time. I'm beginning to suspect that what a lot of audiophiles do is learn how not to hear certain colorations - based on the appalling sound at many hifi shows, this must be the case.
Later on, Gary and I talked about the way that human hearing is exquisitely sensitive to the sound of hollow wooden boxes: that's all a violin is, after all, and even the tiniest change to the construction of the violin is immediately audible to the musically aware listener. The kind of changes that violin-makers make to their instruments are far, far subtler than the gross stuff we do to loudspeakers. The least we can do is chase out the most troublesome artifacts, and leave a bit more room for the music to speak its piece.
Dipoles? Well, yes, but there's still that delay and inverted stuff wrapping around the edge of the baffle. Timing is fairly similar, too, at least for a large baffle. Narrower baffles shorten the delay, at the expense of more equalization, more amplifier power and decreased headroom in the power band of the musical spectrum. Different set of tradeoffs, different sound ...
When Gary called me yesterday, I hadn't seen all the work you folks have been doing - I was going by Gary's verbal description of what he was measuring. As mentioned earlier, I was too physically tired by three days of disconnecting and hauling equipment into the basement, one day of installing the big TV and Salamander cabinetry, and another two days getting everything going again, with all-new connections and system pathways. We're glad the folks at Listen Up! in Boulder built the 3-wide Salamander, installed the 95-lb Panasonic and hauled away the 180-lb 36" RCA/Thomson, along with its stand - that was much too big a job for Karna and me.
Returning to the topic at hand, the nice thing about the time domain is that it's easier to unscramble what's causing reflections and diffraction. The polarity of the artifact hints at its origin, and the timing gives a sign where it may be coming from. Although the room looked tight from the photos, nothing was that close, with the exception of the possible floor bounce, and moving the speaker higher eliminated that possibility when the timing didn't change.
Ergo, it's either a discrete reflection from the back wall - and that certainly was a strong possibility, with the timing and polarity right - or an unusual diffraction artifact. I was strongly favoring the back wall reflection, but was surprised to hear from Gary how little difference damping material was making to the measurements.
So all that left was a peculiar diffraction artifact - not off the front as usual with 90-degree corner cabinets, but off the rear, instead. I guess when you round off the corners in one place, there's more energy traveling along the cabinet surfaces to land elsewhere. In this case, it was the rear edges.
I mentioned to Gary when I was measuring cabinets at Audionics and later, during the Ariel design, diffraction is at its worst when measuring at a 45-degree angle off the front cabinet edges. It is possible to slowly sweep the microphone along the surface of the cabinet, and find the diffraction-emission hotspots.
How audible is all this? I actually don't know, and to some extent don't care. But I don't like to leave artifacts in the design - if they aren't audible right away, they have a way of sneaking up on you over time. That little coloration gets worse and worse the longer you listen to the loudspeaker - and knowing where it's coming from certainly doesn't help. Better to chase it out early in the design, remove it at the acoustical or mechanical source, and not rely on equalization tricks to mask audibility. The mask has a way of coming off over time. I'm beginning to suspect that what a lot of audiophiles do is learn how not to hear certain colorations - based on the appalling sound at many hifi shows, this must be the case.
Later on, Gary and I talked about the way that human hearing is exquisitely sensitive to the sound of hollow wooden boxes: that's all a violin is, after all, and even the tiniest change to the construction of the violin is immediately audible to the musically aware listener. The kind of changes that violin-makers make to their instruments are far, far subtler than the gross stuff we do to loudspeakers. The least we can do is chase out the most troublesome artifacts, and leave a bit more room for the music to speak its piece.
Dipoles? Well, yes, but there's still that delay and inverted stuff wrapping around the edge of the baffle. Timing is fairly similar, too, at least for a large baffle. Narrower baffles shorten the delay, at the expense of more equalization, more amplifier power and decreased headroom in the power band of the musical spectrum. Different set of tradeoffs, different sound ...
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Here's the same FR Graph with a 15ms window. I changed the color of the heavily damped to black for a clearer picture.
Sure would like to see the impulse with a low pass filter, b/c according to what I'm seeing it sure looks like the damping is mostly effecting the midbass on down. The break up is always there as is the ripple in the impulse.
Here's another view of what I see as a possible issue.
A slightly damped Eminence Beta 12A polar:
its impulse response:
Further damped polar:
its impulse:
Am I the only one who sees this as a possibility?
http://en.wikipedia.org/wiki/Occam's_razor
Dan
Sure would like to see the impulse with a low pass filter, b/c according to what I'm seeing it sure looks like the damping is mostly effecting the midbass on down. The break up is always there as is the ripple in the impulse.
Here's another view of what I see as a possible issue.
A slightly damped Eminence Beta 12A polar:
its impulse response:
Further damped polar:
its impulse:
Am I the only one who sees this as a possibility?
http://en.wikipedia.org/wiki/Occam's_razor
Dan
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I was wondering why there would be any response before "time 0" in the plots. This should not be possible in reality. The DUT should have no response before excited by the test signal, which is the reference "time 0".
Ah, what a cozy corner!
I'm also very interested in those plants around speakers and equipment racks. Are they real or artificial? Do they serve any acoustic purposes?
I'm also considering placing one or two artificial trees behind/beside the speaker at that bare (and problematic) corner. Wondering if that works...
Hope this is not OT too much. It's about room acoustic treatment after all
Speaking of which I went to hear Gil Shaham play Brahms last night. Quite a treat and only 1 mile from my door. Beautiful playing, sublime tone. Both Shaham and the Stradivarius are a must hear. Real beauty in music. All for the cost of 2 CDs. Gotta love it.
Those are wooden box resonances you can live with.
Ah, what a cozy corner!
I'm also very interested in those plants around speakers and equipment racks. Are they real or artificial? Do they serve any acoustic purposes?
I'm also considering placing one or two artificial trees behind/beside the speaker at that bare (and problematic) corner. Wondering if that works...
Hope this is not OT too much. It's about room acoustic treatment after all
Well, the 45-degree corner under the stairs is what was troublesome about the room. With the aluminum-finished HT rack right where the absorber and/or diffuser should go, Karna agreed it was time for a change - which the new flat-screen TV and Salamander video rack made possible.
That opened up the corner, which we've filled with artificial plants for now. They act mostly as diffusers, and have substantially reduced the hot-spotting of the corner - previously, you could almost hear a discrete echo from a speaking voice in the room. Now, it's much less noticeable, improving the tonality and image quality of the Ariels. We are also considering a professional studio-style absorber panel bridged across the corner at a 22.5 degree angle, to quiet it down even more. Now we have the space to do this, which we didn't have before.
The new TV and center speaker was a Father's Day gift from Karna, after we spent the last year taking care of our children & grandchildren and helping them get settled in a new area with new jobs. The SC X center speaker was triple the intended budget, but I must admit it does sound good.
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Well, just when we thought we had it all figured out...
Tried a whole bunch of new experiments Sunday afternoon and evening.
1. Extended the cabinet walls rearward by setting plywood panels in place. No difference.
2. Stacked two TD15M cabinets on top of the bass unit in order to remove the top edge of the cabinet from the diffraction footprint. No difference.
3. Draped batts of Bonded Logic over and around the cabinet in order to suppress the sound wrapping around the cabinet. No difference.
4. Pulled the batts of Bonded Logic forward so the front edge protruded about six inches forward of the cabinet edges. No difference.
5. Removed the pillows and Bonded Logic from the floor in order to emphasize the floor reflection. No difference.
6. Messed with ARTA settings, returned IR parameters to default values. No difference.
7. Sat down and stared at everything till my brain hurt. No difference.
8. Replaced the DIY project speaker in the test setup with my Audio Note AN-E's. Okay, now there wasn't anything weird going on at 2.5 ms...in fact, it looked pretty clean. Set the gating and pulled up a FR curve. Looked just like the one on Stereophile's review...in other words, it sucked. Anybody wanna buy a pair of AN-E's?
9. Okay, this is where it gets really interesting. I put the TD15M back in the hot seat, set the mic right up next to the cone, turned down the level, and ran more tests. The same wrinkle appeared in the same place. So much for cabinet diffraction or floor bounce being the cause. Could it be the driver itself?
10. Lynn said that the only way to eliminate the enclosure as a potential culprit would be to remove the TD15 from the cabinet and do a nearfield measurement (~ 1 cm) in free air. I set up and ran the test this afternoon and guess what -- still there! Guess there's nothing I can do; I'm sure not going to modify the driver.
So, dantheman, I think a LP filter is in order. Seems to be relevant anyway, since the driver will be used with one in the completed speaker system.
Gary Dahl
Tried a whole bunch of new experiments Sunday afternoon and evening.
1. Extended the cabinet walls rearward by setting plywood panels in place. No difference.
2. Stacked two TD15M cabinets on top of the bass unit in order to remove the top edge of the cabinet from the diffraction footprint. No difference.
3. Draped batts of Bonded Logic over and around the cabinet in order to suppress the sound wrapping around the cabinet. No difference.
4. Pulled the batts of Bonded Logic forward so the front edge protruded about six inches forward of the cabinet edges. No difference.
5. Removed the pillows and Bonded Logic from the floor in order to emphasize the floor reflection. No difference.
6. Messed with ARTA settings, returned IR parameters to default values. No difference.
7. Sat down and stared at everything till my brain hurt. No difference.
8. Replaced the DIY project speaker in the test setup with my Audio Note AN-E's. Okay, now there wasn't anything weird going on at 2.5 ms...in fact, it looked pretty clean. Set the gating and pulled up a FR curve. Looked just like the one on Stereophile's review...in other words, it sucked. Anybody wanna buy a pair of AN-E's?
9. Okay, this is where it gets really interesting. I put the TD15M back in the hot seat, set the mic right up next to the cone, turned down the level, and ran more tests. The same wrinkle appeared in the same place. So much for cabinet diffraction or floor bounce being the cause. Could it be the driver itself?
10. Lynn said that the only way to eliminate the enclosure as a potential culprit would be to remove the TD15 from the cabinet and do a nearfield measurement (~ 1 cm) in free air. I set up and ran the test this afternoon and guess what -- still there! Guess there's nothing I can do; I'm sure not going to modify the driver.
So, dantheman, I think a LP filter is in order. Seems to be relevant anyway, since the driver will be used with one in the completed speaker system.
Gary Dahl
Interesting search. The fact that the delay went from 2.5ms to 1.3ms when measured from the side, makes one wonder if it's not a wave travelling out fron the center of the cone to the edge. It would be interesting to see if you see the same artifact with the foam surrounds in your bass speakers (do they have a heavier cone - better damped - too?).
Of course if you don't make the frequencies where you see it, it's not functionally important, but is fun to learn.
Sheldon
Well, if it's still there in free air - with the driver suspended from a wire - it's in the driver, end of story.
It's an odd artifact, and not what I expected. I thought there'd be lot of cone-breakup clutter gradually decaying to zero, not a discrete and clearly visible echo at 2.2~2.5 mSec (with inverted polarity, no less). Maybe a reflection off the circular frame on the front of the driver really is the cause, although the timing seems too long by a factor of two or more. Same for a reflection off the extended pole-piece, sure, I wouldn't be surprised to see a reflection, but nothing like 2.2~2.5 mSec later. A two-part reflection off the extended pole-piece, followed by another bounce off the circular edge of the frame, seems like a real stretch - besides, where's that polarity inversion coming from?
What could possibly be 15.1~17.1 inches away from the voice coil - or the microphone capsule?
It's an odd artifact, and not what I expected. I thought there'd be lot of cone-breakup clutter gradually decaying to zero, not a discrete and clearly visible echo at 2.2~2.5 mSec (with inverted polarity, no less). Maybe a reflection off the circular frame on the front of the driver really is the cause, although the timing seems too long by a factor of two or more. Same for a reflection off the extended pole-piece, sure, I wouldn't be surprised to see a reflection, but nothing like 2.2~2.5 mSec later. A two-part reflection off the extended pole-piece, followed by another bounce off the circular edge of the frame, seems like a real stretch - besides, where's that polarity inversion coming from?
What could possibly be 15.1~17.1 inches away from the voice coil - or the microphone capsule?
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So do I get paid now?
Looking at the size of the driver is could be related to some circumferential mode.
After all the work I've done during the past several days, maybe I should get paid!
I'm not too worried about the IR wrinkle now, because with my previous experiences with Altec 416's and 515's I already know I like the sound of a good 15" woofer, and I believe the TD15 qualifies.
I'm now turning my attention to working out a mounting scheme for the Azurahorn and Radian driver. That is, when I'm not riding the Kawasaki!
And yes, I'll get a low pass filter worked out for the TD15M.
Gary Dahl
I'm not too worried about the IR wrinkle now, because with my previous experiences with Altec 416's and 515's I already know I like the sound of a good 15" woofer, and I believe the TD15 qualifies.
I'm now turning my attention to working out a mounting scheme for the Azurahorn and Radian driver. That is, when I'm not riding the Kawasaki!
And yes, I'll get a low pass filter worked out for the TD15M.
Gary Dahl
Looked at it a bit closer, from the shape of it, it's in the driver.
Probably want to look and the CSD as well
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Dare I mention BudP's EnABL?? It's ok - I'm brave - and have thick skin - and a short memory. All good qualities for a quarterback - but not necessarily a speaker designer.....
soonsgc,
We must have been on the same...um...wavelength today (sorry!). Earlier this afternoon, I noticed the same thing in the graph, made a drawing just like yours, planned to post it after awhile. But you beat me to it!
Gary Dahl
