Beyond the Ariel - Page 512 - 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 6th April 2009, 03:17 PM   #5111
soongsc is offline soongsc  Taiwan
diyAudio Member
 
soongsc's Avatar
 
Join Date: Mar 2005
Location: Taiwan
I'm kind of thinking here than normally we would want to keep speakers away from walls becasue we don't want too much reflection. With open baffles firing the same amount of energy backwards, wouldn't the reflection level be still pretty high? Would this also make the multipath effect more significant?
__________________
Hear the real thing!
  Reply With Quote
Old 6th April 2009, 03:19 PM   #5112
gedlee is offline gedlee  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Novi, Michigan
John

Typically I think that we see things the same, but maybe use different points of view. Since MP is not a concept that is ever used in Acoustics, I find its application to 3D acoustical problems problematic. You see it as a generalized extension of the concepts, but admit that non-CD requires different EQ for different angles, which to me means that the "system" cannot be MP because there is not a single filter that can correct the time, frequency and space responses simultaneously. Now, we completely agree that CD is correctable in all these aspects and thus, to me, this can be thought of as MP. But, it seems to me that there is no generally accepted generalization of MP to space, which is why it does not appear in the acoustics literature. We will always disagree when we are free to use different definitions and choose them as such.

I also agree with your comments to Lynn about boxes. I would like to add that Lynn's comment that cones are "acoustically transparent" is completely false. They do admit to some transmission, but "transparent" is completely incorect. Even my "thin as can be" bed sheet projection screen is not completely transparent (and its intended to be). A screen of cone material would be vastly more loss. Box reflections act as a spring far more than any other effect, especially when there is absorption. The idea that sound simply "comes back through the cone" is simply untrue. There is a great deal of attenuation, and the major effect of higher frequency reflections on the cone can usually be seen in the impedance curve as a resonance, if such are significant. But there are also the far more significant and problematic spider resonances that are also visible in that curve.
  Reply With Quote
Old 6th April 2009, 04:52 PM   #5113
mige0 is offline mige0  Austria
diyAudio Member
 
mige0's Avatar
 
Join Date: Jan 2005
Location: Austria, at a beautiful place right in the heart of the Alps.
Quote:
Originally posted by john k...

I am not against damping. In fact I'm all for it. That is not the point of my posts.

I know.
The reason I asked *I* actually was extensively looking after a possibility to avoid box dampening completely.

The MP concept you made absolutely clear in your last posts *this* is what I've been looking for - if it allows for 100% substitution of dampening.



Quote:
Originally posted by john k...


Lynn has suggested you talk into a sealed box to see what the colorations are. Take it a step further. Cut a 6" hole in a piece of plywood and talk into it. What is the coloration?


Would say it sounds like my OB !




But my question remains would you say that ideal EQing could be used *instead* of dampening ?

If the MP theory holds (to even that extent) in praxis, I expect to get rid of the coloration that come with the indifferent dampening materials we have available.
Anyone else who possibly has tried?

Michael
  Reply With Quote
Old 6th April 2009, 05:29 PM   #5114
mige0 is offline mige0  Austria
diyAudio Member
 
mige0's Avatar
 
Join Date: Jan 2005
Location: Austria, at a beautiful place right in the heart of the Alps.
Quote:
Originally posted by gedlee
John

I would like to add that Lynn's comment that cones are "acoustically transparent" is completely false. They do admit to some transmission, but "transparent" is completely incorect.
Like to back up that diaphragms of speakers are rather "transparent" than are able to provide substantial dampening / filtering of whats happening at the rear.

Made several measurements during my enclosure investigation right in front of the diaphragm and right at its back - guess what no difference that's worth to talk about at least not in any extent that CSD resonances would look any different.

And that's the final aim, isn't it.

Michael
  Reply With Quote
Old 6th April 2009, 06:52 PM   #5115
gedlee is offline gedlee  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Novi, Michigan
That test would not show anything. The diaphragm is radiating the sound in exactly equal amounts on both sides. Hence the SPL should be identical on each side. Actually the box side should be much higher as the frequency drops. But this is simply the box compliance at work.

To do a test of cone transmission properly, you would have to put a sound source inside of the box with no speaker installed and measure at several exterior points and average and then install the speaker and take the same measurements and compare. There will be a strong peak at the drivers resonance. If the cone were actually acoustically transparent then this test would measure the same both ways. The differences are not completely transmission loss, but mostly so.
  Reply With Quote
Old 6th April 2009, 07:08 PM   #5116
mige0 is offline mige0  Austria
diyAudio Member
 
mige0's Avatar
 
Join Date: Jan 2005
Location: Austria, at a beautiful place right in the heart of the Alps.
Quote:
Originally posted by gedlee
The diaphragm is radiating the sound in exactly equal amounts on both sides.
.
In the end effect the same as I said - all the rest - just a more sophisticated point of view IMO


You can look at it as a combined system "speaker / enclosure" which results in radiating to the front what the enclosure dictates at the back or put it simple (simplified if you will) saying the diaphragm behaves acoustically transparent (more or less).

Michael
  Reply With Quote
Old 6th April 2009, 10:39 PM   #5117
diyAudio Member
 
john k...'s Avatar
 
Join Date: Aug 2004
Location: US
Quote:
Originally posted by gedlee
John

Typically I think that we see things the same, but maybe use different points of view. Since MP is not a concept that is ever used in Acoustics, I find its application to 3D acoustical problems problematic. You see it as a generalized extension of the concepts, but admit that non-CD requires different EQ for different angles, which to me means that the "system" cannot be MP because there is not a single filter that can correct the time, frequency and space responses simultaneously. Now, we completely agree that CD is correctable in all these aspects and thus, to me, this can be thought of as MP. But, it seems to me that there is no generally accepted generalization of MP to space, which is why it does not appear in the acoustics literature. We will always disagree when we are free to use different definitions and choose them as such.

I also agree with your comments to Lynn about boxes. I would like to add that Lynn's comment that cones are "acoustically transparent" is completely false. They do admit to some transmission, but "transparent" is completely incorect. Even my "thin as can be" bed sheet projection screen is not completely transparent (and its intended to be). A screen of cone material would be vastly more loss. Box reflections act as a spring far more than any other effect, especially when there is absorption. The idea that sound simply "comes back through the cone" is simply untrue. There is a great deal of attenuation, and the major effect of higher frequency reflections on the cone can usually be seen in the impedance curve as a resonance, if such are significant. But there are also the far more significant and problematic spider resonances that are also visible in that curve.
I know we see MP differently. I see it just as a mathematical relationship between amplitude and phase. If I stick a mic out in space and measure the amplitude and phase, if, after the propagation delay is removed, the measured phase can be replicated by applying the HBT to the measured amplitude I call it MP. I think there is more importance to this than you like to accept. For example, when a crossover is designed by defining an acoustic target and then constructing a (MP) filter to shape the raw driver response to that target we rely on the the MP characteristics of the driver, referenced to the design point, to assure that the phase of the acoustic target will be correct (other than driver offsets) so that it will correctly sum to the other drivers. Because of the MP behavior it is possible to substitute a different woofers in a two way system which may have very different raw SPL response so long as the filter, specific for each driver, shapes (equalizes) the response to the correct acoustic target (assuming offsets and sensitivity are correct). If the drivers did not exhibit MP behavior relative to the design point shaping the amplitude response to the target would not imply the correct phase and summed response.


Quote:
Originally posted by mige0



I know.
The reason I asked *I* actually was extensively looking after a possibility to avoid box dampening completely.

The MP concept you made absolutely clear in your last posts *this* is what I've been looking for - if it allows for 100% substitution of dampening.


But my question remains would you say that ideal EQing could be used *instead* of dampening ?

If the MP theory holds (to even that extent) in praxis, I expect to get rid of the coloration that come with the indifferent dampening materials we have available.
Anyone else who possibly has tried?

Michael
I've never looked at it. Realize that when I have talked about eq I'm really looking at eq as I posted for my 8" dipole.

Quote:
Originally posted by mige0


Like to back up that diaphragms of speakers are rather "transparent" than are able to provide substantial dampening / filtering of whats happening at the rear.

Made several measurements during my enclosure investigation right in front of the diaphragm and right at its back - guess what no difference that's worth to talk about at least not in any extent that CSD resonances would look any different.

And that's the final aim, isn't it.

Michael
The comments from you and Earl about cones being acoustically transparent. Realize that for any sound that reflects off the back side of the driver to be transmitted through the cone means that an acoustic wave impacting on the back side of the cone must impart energy to the cone, creating cone vibrations which then re-radiate the energy form both the front and back sides. When a mic is placed close to the cone front or back surface what you end up measuring is more closely related to the cone motion. But that won't tell you whether the motion is due to the applied signal alone or influenced by reflections.

I've done some testing in some unique ways to look at this which I don't want to discuss just yet until I'm sure of the validity of the results. Maybe I'll bring them up to see what Earl thinks. What I will say is that cone drivers make very poor microphones.
__________________
John k.... Music and Design NaO Dipole Loudspeakers.
  Reply With Quote
Old 6th April 2009, 11:19 PM   #5118
gedlee is offline gedlee  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Novi, Michigan
Quote:
Originally posted by john k...
For example, when a crossover is designed by defining an acoustic target and then constructing a (MP) filter to shape the raw driver response to that target we rely on the the MP characteristics of the driver, referenced to the design point,

Maybe I'll bring them up to see what Earl thinks. What I will say is that cone drivers make very poor microphones.

John

I know all that you are saying, its not new, but to me doing a crossover design at a "design point" as you suggest is the issue. I don't do crossovers that way and so MP is of no use to me because it tells you nothing about how the crossover will work spatially - only at that single point. It's lack of spatial relevence is a considerable failing for acoustics.

Why would you want the driver to be a microphone?
  Reply With Quote
Old 6th April 2009, 11:55 PM   #5119
Pano is offline Pano  United States
diyAudio Moderator
 
Pano's Avatar
 
Join Date: Oct 2004
Location: Milliways
Blog Entries: 4
Quote:
Originally posted by gedlee
Why would you want the driver to be a microphone?
'Cause we were using them to spy on the people downstairs. (worked great - imagine the famous scene from M.A.S.H)
__________________
Take the Speaker Voltage Test!
  Reply With Quote
Old 7th April 2009, 12:31 AM   #5120
JohnG is offline JohnG  United States
diyAudio Member
 
Join Date: Mar 2002
Location: Upstate NY
A quick point on acoustic transparency of cones:

When doing the transparency test suggested by Earl, or something similar, the speaker should be connected to the amplifier of interest, with the input to the amp shorted or otherwise set to zero with the amp on. This will account for the damping effect of the amplifier on cone motion.

John G
  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 11:51 PM.


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