Beyond the Ariel - Page 695 - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 1st August 2010, 09:17 PM   #6941
diyAudio Member
 
Lynn Olson's Avatar
 
Join Date: Jul 2004
Location: Northern Colorado
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 ...

Last edited by Lynn Olson; 1st August 2010 at 09:45 PM.
  Reply With Quote
Old 1st August 2010, 10:31 PM   #6942
diyAudio Member
 
dantheman's Avatar
 
Join Date: May 2008
Location: Mountain View, CA
Here's the same FR Graph with a 15ms window. I changed the color of the heavily damped to black for a clearer picture.
Click the image to open in full size.

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:
Click the image to open in full size.
its impulse response:
Click the image to open in full size.
Further damped polar:
Click the image to open in full size.
its impulse:
Click the image to open in full size.

Am I the only one who sees this as a possibility?
http://en.wikipedia.org/wiki/Occam's_razor

Dan
__________________
My Blog
My Music Recordings

Last edited by dantheman; 1st August 2010 at 10:52 PM.
  Reply With Quote
Old 2nd August 2010, 01:28 AM   #6943
soongsc is offline soongsc  Taiwan
diyAudio Member
 
soongsc's Avatar
 
Join Date: Mar 2005
Location: Taiwan
Quote:
Originally Posted by dantheman View Post
I don't see where I wrote "time zero."
Could you rephrase the question? I'm not sure what you mean. Maybe this will help.
Dan
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".
__________________
Hear the real thing!
  Reply With Quote
Old 2nd August 2010, 01:34 AM   #6944
diyAudio Member
 
dantheman's Avatar
 
Join Date: May 2008
Location: Mountain View, CA
I'd bet there's not, but I never tested it.

Dan
__________________
My Blog
My Music Recordings
  Reply With Quote
Old 2nd August 2010, 03:39 AM   #6945
CLS is online now CLS  Taiwan
diyAudio Member
 
Join Date: Jun 2005
Location: Taiwan
Quote:
Originally Posted by Lynn Olson View Post
....

Here's the Before and After pictures:
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
  Reply With Quote
Old 2nd August 2010, 03:46 AM   #6946
Pano is offline Pano  United States
diyAudio Moderator
 
Pano's Avatar
 
Join Date: Oct 2004
Location: Kona, Hawaii
Blog Entries: 4
Quote:
Originally Posted by Lynn Olson View Post
... 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.

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.
__________________
Take the Speaker Voltage Test!
  Reply With Quote
Old 2nd August 2010, 09:07 PM   #6947
diyAudio Member
 
Lynn Olson's Avatar
 
Join Date: Jul 2004
Location: Northern Colorado
Quote:
Originally Posted by CLS View Post
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.

Last edited by Lynn Olson; 2nd August 2010 at 09:12 PM.
  Reply With Quote
Old 2nd August 2010, 09:42 PM   #6948
g3dahl is offline g3dahl  United States
diyAudio Member
 
g3dahl's Avatar
 
Join Date: Jun 2004
Location: Silverdale, WA
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
__________________
"So many tubes, so little time..."
  Reply With Quote
Old 2nd August 2010, 10:01 PM   #6949
diyAudio Member
 
Join Date: Sep 2002
Location: Oregon, USA
Quote:
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.
Up until this one, I was going to say "reflection off the enclosure wall through the driver cone, try it on an open baffle". But #10 negates that.
  Reply With Quote
Old 2nd August 2010, 10:25 PM   #6950
Sheldon is offline Sheldon  United States
diyAudio Member
 
Join Date: Dec 2003
Location: San Diego
Quote:
Originally Posted by g3dahl View Post
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.
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
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 02:06 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2