Correct gain drop when playing one channel on two speakers - diyAudio
Go Back   Home > Forums > General Interest > Everything Else

Everything Else Anything related to audio / video / electronics etc) BUT remember- we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools......

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 November 2006, 08:25 PM   #1
diyAudio Member
 
halfgaar's Avatar
 
Join Date: Mar 2005
Location: Netherlands, Groningen
Question Correct gain drop when playing one channel on two speakers

Hi,

I've been wondering for a while what the correct gain drop is when playing a mono channel over two speakers, maintaining the same SPL; -3 dB or -6 dB.

Dolby specifies a gain of .707 (-3 dB) when mixing a mono channel in two channels. But, when you were to sum that with a standard summer, the result would be louder than the original.

The power consumption of the two speakers when playing the source with -3 dB per channel is the same as playing the original source on one speaker. But then there's something about increased efficiency I don't know how to factor in.

So, which one is it?
  Reply With Quote
Old 9th November 2006, 01:18 PM   #2
diyAudio Member
 
halfgaar's Avatar
 
Join Date: Mar 2005
Location: Netherlands, Groningen
Nobody...?
  Reply With Quote
Old 10th November 2006, 03:53 AM   #3
dangus is offline dangus  Canada
diyAudio Member
 
Join Date: May 2004
Location: Vancouver Island
I think you'll only see that increased efficiency if both speakers are very close together.

It should be easy to verify with an SPL meter and a test disc.
  Reply With Quote
Old 10th November 2006, 11:43 AM   #4
diyAudio Member
 
halfgaar's Avatar
 
Join Date: Mar 2005
Location: Netherlands, Groningen
I tried to use an SPL meter, but this room is not accousticly dead, so that's kind of difficult. Moving the meter a few CM and the reading is different. I tried with non-directional sounds as well, like 30 Hz, and with that, the correct drop was -6 dB.

But, I can vaguely remember something about low frequencies requiring -6 dB and mid to high -3 dB. Perhaps this has to do with what you say, that the speakers need to be very close to eachother to see increased efficiency, except for low frequencies.
  Reply With Quote
Old 11th November 2006, 11:33 PM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
I would expect +3db when you sum the two channels.

So you should insert -3db on each signal before you sum or -3db on the output after the sum.

The efficiency calc only works at +3db when the wavelength to be reproduced is greater than 4times the distance between the speakers.

If you had a pair of speakers mounted beside each other and they measure 500mm across the pair of cones then the efficiency increase is for frequencies below 340/4/0.5<170Hz.
There is progresively less gain between 170Hz and 340Hz when all the efficiency gain is lost.

However, another factor comes into play. Beaming due to interference effects throws more sound forward and can sound louder even though total sound power is the same. This lobing is very uneven and will destroy the stereo effect (and the dual mono)
__________________
regards Andrew T.
  Reply With Quote
Old 12th November 2006, 12:42 AM   #6
diyAudio Member
 
halfgaar's Avatar
 
Join Date: Mar 2005
Location: Netherlands, Groningen
When summing two signals, the output voltage becomes the two inputs combined, right? So, summing two 3V peak-to-peak signals becomes 6V peak-to-peak. Twice the amplitude is +6dB, so why do you expect + 3 dB?

Something that is related to this: in a mixing panel, when you pan a signal from left to right (keeping the SPL intact), how much gain difference is there between center and 100% left?
  Reply With Quote
Old 12th November 2006, 07:53 AM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
I think a mixing desk only adjusts the relative volume when doing it's psuedo pan.
It should have the phase corrected as well to try to maintain the true stereo (location) information, but I don't think they do that.
A digital desk may do more clever processing.
__________________
regards Andrew T.
  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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Marshall Valvestate 8080 low gain on Boost Channel mgjimbo Solid State 0 28th May 2008 03:04 AM
N-channel Current Gain Cell Workhorse Solid State 15 11th July 2005 01:31 AM
what's better, a mid playing high, or a tweet playing low??? cody6766 Multi-Way 10 20th February 2005 10:40 PM
Gain when using nore speakers hedalfa Multi-Way 66 8th May 2004 03:27 AM
put my pre-amp together and now the left channel is playing distorted :( elizard Solid State 21 4th April 2003 07:23 AM


New To Site? Need Help?

All times are GMT. The time now is 06:30 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