Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Reciprocity Theorem in practice
Reciprocity Theorem in practice
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 September 2017, 07:49 AM   #21
Ultima Thule is offline Ultima Thule  Europe
diyAudio Member
 
Ultima Thule's Avatar
 
Join Date: Jan 2004
Location: Finland
Quote:
Originally Posted by bentoronto View Post
For setting up speakers, it means you could put your sub where you sit and search around the room with a mic to find a location that gives best results.
Good post!
Come to think we could as well just use our ears (especially when in lack of any aiding instruments) to locate a good spot where the LF audio response sounds subjectively good by moving ourselves around to different positions in the listening room in order to find out a location where we could place our sub.

I assume several relatively smaller subs substituting one big sub would be a better choice in order to get a more even LF response.
  Reply With Quote
Old 6th September 2017, 08:39 AM   #22
astrojet is offline astrojet
diyAudio Member
 
Join Date: Apr 2013
Reciprocity is fact, truth, law, whatever you want to call it. It is how waves function. Whether or not you are generating the same waves with differential loading is the pertinent question.
  Reply With Quote
Old 6th September 2017, 05:25 PM   #23
bentoronto is offline bentoronto  Canada
diyAudio Member
 
Join Date: Jan 2008
Location: Toronto and Delray Beach, FL
Reciprocity Theorem in practice
Quote:
Originally Posted by astrojet View Post
Whether or not you are generating the same waves with differential loading is the pertinent question.
Yes, sub hanging in air is one very good question. But also matter of point source and point receiver, is damping around the room linear, polar/directionality issues of speaker, mic, and ears (and in relation to room furnishings), etc.

My basic problem is that it is plain lousy methodology to do anything except measure from the point of reference (your head); not wise to work otherwise, unless that was unfeasible and/or the degree of error is tolerable.

But I sure hope somebody can provide pictures and traces of the method working in a normal home music room, as compared to regular method.

Ben
__________________
HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio (and just posted data for a folded 17-foot pipe sub)
  Reply With Quote
Old 6th September 2017, 05:44 PM   #24
chris661 is offline chris661  United Kingdom
diyAudio Member
 
chris661's Avatar
 
Join Date: Feb 2008
Location: Sheffield
One of the assumptions made by the reciprocity theorem is that the source and receiver are both very much smaller than the wavelengths at play, and also the room itself. The two must also have the same directional characteristics.

For instance, imagine a subwoofer that takes up 1/4 of the room. Moving it around would alter the shape of the room in a significant way, while moving the microphone around would not.

So, I'd argue it's a good first-order approximation, but second-order effects may come in when the basic assumptions are challenged.

Chris
  Reply With Quote
Old 6th September 2017, 05:59 PM   #25
scottjoplin is offline scottjoplin  Wales
diyAudio Member
 
scottjoplin's Avatar
 
Join Date: Dec 2015
Location: Penrhyndeudraeth
Quote:
Originally Posted by BesPav View Post
Let's try.

Attachment 633997
Attachment 633998

Being a DIYers or engineers we couldn't believe strong math, especially if it provides repetitive results corresponding with real measurements. (Or even this math is created to correspond with experimental).

But the most valueable ability is to show results in intuitive and clearly understandable way.
That's interesting, thank you. Is there any way in your simulation you can add random shapes to simulate pieces of furniture preferably placed at angles and maybe even different amounts of absorption and reflection?
__________________
Woofer Assisted Wideband is the New Testament renounce the anachronistic acronym FAST
  Reply With Quote
Old 6th September 2017, 07:17 PM   #26
astrojet is offline astrojet
diyAudio Member
 
Join Date: Apr 2013
Quote:
Originally Posted by chris661 View Post
One of the assumptions made by the reciprocity theorem is that the source and receiver are both very much smaller than the wavelengths at play, and also the room itself. The two must also have the same directional characteristics.

Chris
This is a good point. Another end member is also an issue, when wavelengths are much longer than the spatial scale of the scatterers. In fact, an 'infinite frequency' approximation is commonly used, effectively collapsing the wave to treat it as a 1D ray. Scattering of very long wavelengths is usually treated with expensive numerical techniques.
  Reply With Quote
Old 6th September 2017, 07:36 PM   #27
bentoronto is offline bentoronto  Canada
diyAudio Member
 
Join Date: Jan 2008
Location: Toronto and Delray Beach, FL
Reciprocity Theorem in practice
Quote:
Originally Posted by astrojet View Post
This is a good point... Scattering of very long wavelengths is usually treated with expensive numerical techniques.
Many good points here. And particularly applicable to modest-sized home music rooms.

scotjoplin -

Are you missing the point? The sim is simply a mathematical cousin to the Reciprocity Theorem and can't be "tested" except empirically. These sims will always reciprocate perfectly. As the previous posts show, it is fair to raise questions about the assumptions. But the sim does not raise questions about its own assumptions!

i believe BesPav thoughtfully and subtly raised these questions by his ironic way of writing.

Again, it it possible that the degree of error using lousy methods can still be OK for most purposes. While I am a strong advocate of test-and-relocate your sub(s) around the room, the acoustics of a home room are pretty loose. My room changes a lot when I leave a clothes-closet door open.

Simulation of sub with corner placement?

Post #16. Look closely at traces below 75 Hz. Quite different. Sure is better with the door slid open and all my winter motorcycle clothing soaking up some of a mode or two in the perfect location. This also illustrates why good methodology leads to stable results.

B.
__________________
HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio (and just posted data for a folded 17-foot pipe sub)

Last edited by bentoronto; 6th September 2017 at 07:49 PM.
  Reply With Quote
Old 7th September 2017, 04:32 PM   #28
BesPav is offline BesPav  Russian Federation
diyAudio Member
 
Join Date: May 2011
Location: Russia, Moscow
Quote:
Originally Posted by bentoronto View Post
i believe BesPav thoughtfully and subtly raised these questions by his ironic way of writing.

:beer:

Yeah, you hit the bull's-eye!
Why strain and provide all your brute force while you can subtly sneer and chuckle?

The less vociferous statements the easier it is to plant a grain of doubt.
  Reply With Quote
Old 14th September 2017, 04:15 AM   #29
reloader650 is offline reloader650  United States
diyAudio Member
 
Join Date: Apr 2010
Location: Utah
I had a little time to burn tonight, so I decided to try this reciprocity theory out. I don't have a lot of time to post a detailed write up at this time, but I will do my best. The equipment used was REW with a calibrated mic and a 10" powered bass reflex subwoofer. I tried 4 different locations around the room and the 5th or common location being one of my theater seats. When placing the mic or subwoofer in the locations around the room I made sure the mic was exactly where the cone of the subwoofer was and vise versa. If it helps, my room is 15' wide x 24' deep. The front of the room is 15' wide.

The first image is with the subwoofer or mic in the front left corner of the room and the mic or subwoofer on one of the theater seats.

The second image is centered on the front wall on the floor.

The third image is in the same spot but raised off of the floor 3'.

The fourth image is centered on the right side wall.

Hope this was helpful.

Regards,
Matt
Attached Images
File Type: jpg front left corner.jpg (72.9 KB, 50 views)
File Type: jpg centered on front wall.jpg (73.3 KB, 51 views)
File Type: jpg centered on front wall 3 feet off the floor.jpg (71.2 KB, 51 views)
File Type: jpg centered on right wall.jpg (78.7 KB, 41 views)
  Reply With Quote
Old 14th September 2017, 08:19 AM   #30
bentoronto is offline bentoronto  Canada
diyAudio Member
 
Join Date: Jan 2008
Location: Toronto and Delray Beach, FL
Reciprocity Theorem in practice
That's immensely helpful. Wonderful. Clearly Helmholtz spoke the truth in proposing reciprocity theorem (not that anybody doubted its theoretical truth).

My impressions (and responses to Matt's traces are inevitably different among people and purposes):

1. big differences among those four locations and clearly you'd want to test various locations before deciding where to locate your sub; if choosing a location was your primary goal, the reciprocity method is pretty good for a big-picture of your bass sound, as long as you work as carefully as Matt. Maybe not a perfect as the sims predict, but pretty good.

2. the first graph, in the corner, looks like the best prospect to me; but looking at one of the traces (not sure which test it represents) you might say, "umm, this needs some help at 37 Hz and 48 Hz" but you could be preferring another location (in error) if you were working with Matt's reciprocal test; of course in your home, you wouldn't know which is which unless you tested the old way after positioning your sub and then applied the EQ.

So, looking at Matt's data, the reciprocal method is helpful as a gross test but it might be wrong in the fine points and in another room very wrong. Some rooms might show better agreement than Matt's but some may show worse and lead you to a sub-optimum sub location.

If it were simple enough to move your sub, that sure is the way I would work rather than accept an unknown degree of uncertainty. If not, looks like the reciprocal approach can be very helpful.

The degree of smoothing Matt used seems about right to me. But it would be instructive to look at the same traces with one increment less smoothing, when Matt has the time.

B.
__________________
HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio (and just posted data for a folded 17-foot pipe sub)

Last edited by bentoronto; 14th September 2017 at 08:32 AM.
  Reply With Quote

Reply


Reciprocity Theorem in practiceHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Does this video violate energy conservation theorem? Osvaldo de Banfield Everything Else 51 8th August 2017 02:56 PM
Sumo Theorem - Mains voltage ian_UK Digital Line Level 3 16th September 2008 04:39 PM
I want to discuss the Nyquist theorem, anyone interrested? mr_push_pull Digital Source 49 3rd February 2005 07:56 AM
Question about Miller's theorem Bricolo Parts 3 11th March 2004 04:32 PM
Anyone know the Sumo Theorem DAC? r0cket- Digital Source 1 26th October 2003 05:45 AM


New To Site? Need Help?

All times are GMT. The time now is 07:16 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki