John Curl's Blowtorch preamplifier part II - Page 3041 - diyAudio
Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

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 29th November 2012, 05:33 PM   #30401
diyAudio Member
 
Join Date: Sep 2006
Quote:
Originally Posted by jneutron View Post
No acoustic coupling.

What I am saying is that any delay of part of the frequency content of a stereophonic signal can shift the perceived image. It requires a central image in the field upon which a human can reference to because head positioning uncertainties will swamp un-referenced positions.

For a monophonic presentation, time delay of part of the spectra can result in a depth change of that part, but never a side shift.


Discussion of audibility requires understanding audibility. Welcome to my world. Please, pull up a seat and stay a while..

edit: my world being one in which I had a long and steep learning curve as well..

cheers, jn

btw, that is one big problem I have found with 11 band eq's...If you dont get both channels exactly symmetrical, it is easy to find that the sibalance of a female vocal is shifted to one side of the fundamental..a disembodiment so to speak..

ps. Please read my content w/rt to hearing several times prior to responding. I've been quite clear in the bulk of my posts, and am spending a lot of effort duplicating verbage.
One of the biggest problems with frequency-dependent channel-channel phase differences lies in the loudspeakers, especially in the crossovers. This is doubly true for all-pass crossovers like the Linkwitz. Passive component tolerances can cause the crossover point in the two channels to be at slightly different frequencies, resulting in significant inter-channel phase differences in the frequency bands near the crossover points.

This is huge compared to any cable-related frequency-dependent differential phase effects.

Cheers,
Bob
  Reply With Quote
Old 29th November 2012, 05:37 PM   #30402
diyAudio Member
 
Join Date: Sep 2006
Quote:
Originally Posted by jneutron View Post
Please re-read the last paragraph..

specifically..Don't be thrown off by the units btw, as a simple calculation of a 10Khz square wave energy per lobe will show that the energy levels displayed cannot be brushed aside.


jn
I did, but that red text made it really hard :-).

Cheers,
Bob
  Reply With Quote
Old 29th November 2012, 05:47 PM   #30403
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally Posted by Bob Cordell View Post
One of the biggest problems with frequency-dependent channel-channel phase differences lies in the loudspeakers, especially in the crossovers. This is doubly true for all-pass crossovers like the Linkwitz. Passive component tolerances can cause the crossover point in the two channels to be at slightly different frequencies, resulting in significant inter-channel phase differences in the frequency bands near the crossover points.
I believe I pointed out the issue with my 11 band eq statement. Glad we agree.

Quote:
Originally Posted by Bob Cordell View Post
This is huge compared to any cable-related frequency-dependent differential phase effects.

Cheers,
Bob
This statement is based on what research? Have you performed any three speaker image reconstruction tests?

Or even the minimal test...use two speakers, one amp channel, three cables 10 feet long each, #12awg all cables, one cable 8 ohms Z, two cables 120 ohms Z.
Connect both 120 ohm cables to one amp channel, other ends to the speakers. Look for image construction in the center while in the sweet spot.

When you are satisfied that the speakers are equal, swap one cable to the 8 ohm.

Repeat looking for the fidelity of the central image.

Don't forget, our localization is really weird in that we tend to "lock" around center in the frequencies of interest despite small changes in ITD and IID. Greisinger shows that clearly in the 600-900 hz range in his graph (incorrectly identified as figure 5, it is really figure 6..)

If you can "see" a shift of some harmonic content away from the bulk of the sounds which did not exist with identical Z cables, you will have some explaining to do, no??

jn

edit: one amp channel is used to eliminate the possibility that one channel reacted differently as a result of the cable capacitance. Elimination of confounders...

Last edited by jneutron; 29th November 2012 at 05:49 PM.
  Reply With Quote
Old 29th November 2012, 05:48 PM   #30404
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally Posted by Bob Cordell View Post
I did, but that red text made it really hard :-).

Cheers,
Bob
Yabut...some of the other colors I can't even read...

jn
  Reply With Quote
Old 29th November 2012, 05:48 PM   #30405
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by jneutron View Post
See attached. Note that the same paper has a graph which takes it out to 12Khz.

For unjittered sine waves, the summary you speak of is consistent with this data. It is about 5 uSec in the 500 to 1000 hz range.
jn
I'm still hung up on where the reference is. I sent one of my ambient recordings to a friend and he commented on the nice imaging/binaural effect of the bird's singing. If he got a "reach out and touch" effect how do either of us know if it matched the physical reality.

Also one could invoke the difference/preference issue yet again.
__________________
Silence is so accurate.

Last edited by scott wurcer; 29th November 2012 at 05:50 PM.
  Reply With Quote
Old 29th November 2012, 05:48 PM   #30406
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
Quote:
I was referring to time of flight, not velocity of emitter.
even Rod Elliot figured out the veiwpoints are equivalent - shame he didn't use windowing, fft on his data to extract numbers instead of just leaving it to eyeballs:

Doppler Distortion in loudspeakers

Xmax for mid/woofer? up to 10mm?, 3mm = 10us, some run from 100 Hz to 2 kHz in a 2-way system

Last edited by jcx; 29th November 2012 at 05:53 PM.
  Reply With Quote
Old 29th November 2012, 05:58 PM   #30407
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Default esr limits current thru cap -

Here are two typical values which are found in cross-overs -- a several mfd. They are same C value and charged to same 5vdc and discharged into themselves-- current monitored [inductive pickup]. The vert scale is 5A/div. The film and foil allows a lot more current to be passed thru itself... compared to electrolytic type construction. So if you calculate the current delivered from power amp to be large, be sure it isnt being limited by unseen series esr from non-film caps. Thx-RNMarsh
[ps - also note the discharge period is then the resolution limit to the circuit]
Attached Images
File Type: jpg critically damped C.jpg (261.4 KB, 107 views)
File Type: jpg over-damped C.jpg (251.9 KB, 108 views)

Last edited by RNMarsh; 29th November 2012 at 06:05 PM.
  Reply With Quote
Old 29th November 2012, 06:00 PM   #30408
diyAudio Member
 
Join Date: Sep 2006
Quote:
Originally Posted by jneutron View Post
I believe I pointed out the issue with my 11 band eq statement. Glad we agree.



This statement is based on what research? Have you performed any three speaker image reconstruction tests?

Or even the minimal test...use two speakers, one amp channel, three cables 10 feet long each, #12awg all cables, one cable 8 ohms Z, two cables 120 ohms Z.
Connect both 120 ohm cables to one amp channel, other ends to the speakers. Look for image construction in the center while in the sweet spot.

When you are satisfied that the speakers are equal, swap one cable to the 8 ohm.

Repeat looking for the fidelity of the central image.

Don't forget, our localization is really weird in that we tend to "lock" around center in the frequencies of interest despite small changes in ITD and IID. Greisinger shows that clearly in the 600-900 hz range in his graph (incorrectly identified as figure 5, it is really figure 6..)

If you can "see" a shift of some harmonic content away from the bulk of the sounds which did not exist with identical Z cables, you will have some explaining to do, no??

jn

edit: one amp channel is used to eliminate the possibility that one channel reacted differently as a result of the cable capacitance. Elimination of confounders...
Just do the math. The objective measurable/simulatable difference in potential differential phase is huge - no need to do some fancy image reconstruction tests to see that this is obvious. We're probably taking nanoseconds versus microseconds. One measly degree at a crossover frequency of 3kHz is about 1us if I'm not mistaken. It would take perhaps 500 feet of cable length difference to get a microsecond.

Cheers,
Bob


Cheers,
Bob
  Reply With Quote
Old 29th November 2012, 06:02 PM   #30409
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally Posted by scott wurcer View Post
I'm still hung up on where the reference is. I sent one of my ambient recordings to a friend and he commented on the nice imaging/binaural effect of the bird's singing. If he got a "reach out and touch" effect how do either of us know if it matched the physical reality.

We don't. And, we can't.

It is impossible to recreate the wavefronts of multiple sound generators using two speakers, unless the source being synthesized is at a speaker.

Central imaging is the closest to the exception we can get. But only because of the strength of our response to first arrival.

It is certainly impossible to do so by ignoring interchannel time delays.

Stereo is an attempted synthesis. By invoking some artificially generated IID and ITD, it is possible to fake us into thinking a sound is in a position not occupied by a speaker. Honestly, I'm surprised we can do as much as we can just using IID.

jn
  Reply With Quote
Old 29th November 2012, 06:06 PM   #30410
diyAudio Member
 
Join Date: Sep 2006
Quote:
Originally Posted by RNMarsh View Post
Here are two typical values which are found in cross-overs -- a several mfd. They are same C value and charged to same 5vdc and discharged into themselves-- current monitored [inductive pickup]. The vert scale is 5A/div. The film and foil allows a lot more current to be passed thru itself... So if you calculate the current delivered from power amp to be large, be sure it isnt being limited by unseen series esr from non-film caps. Thx-RNMarsh
[ps - also note the discharge period is then the resolution limit to the circuit]
Agreed, and I don't think there is too much controversy about the wisdom of using a film capacitor for only a few uF. However, consider the case where you need a woofer Zobel network. Then the size of the needed cap can get much bigger, and therein lies the discomfort.
  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 01:04 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