Loudspeaker formula - 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 17th November 2004, 03:36 PM   #1
freedom is offline freedom  Denmark
diyAudio Member
 
Join Date: Nov 2004
Location: Broenderslev Denmark
Send a message via MSN to freedom
Default Loudspeaker formula

Dear All.

I need a formula telling me what the sound pressure level is at a certian distance from a source given that the spl of the source is known and that the distance is known. I know it is a "universal" formula - but are looking for the simplest form, where walls or other reflecting source are not taken into account.

I tried a google search, but no luck so far.

A search here in the forum didn´t help me either.

Anyone? Please :-)

Thanks in advance

Regards

Hans-Henning
__________________
If you cannot measure it - you cannot improve it!
  Reply With Quote
Old 17th November 2004, 06:31 PM   #2
Ron E is offline Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
What kind of source? Piston, point source, line source, simple or dipole, etc...?
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. —Aldous Huxley
  Reply With Quote
Old 17th November 2004, 07:44 PM   #3
Pan is offline Pan  Sweden
diyAudio Member
 
Join Date: Sep 2002
Point source -6dB for every doubling of distance
Line source -3dB for every doubling of distance

This is for ideal monopole sources.

/Peter
  Reply With Quote
Old 17th November 2004, 07:58 PM   #4
freedom is offline freedom  Denmark
diyAudio Member
 
Join Date: Nov 2004
Location: Broenderslev Denmark
Send a message via MSN to freedom
Default Cased Solved

Excellent. Thank you.

Case closed

Regs. Hans-Henning
__________________
If you cannot measure it - you cannot improve it!
  Reply With Quote
Old 17th November 2004, 11:15 PM   #5
Banned
 
Join Date: May 2004
Location: New Hampshire
Not so fast. Line sources are -3dB per distance doubling only within the nearfield, which is calculated (in meters) by the formula R=L x L x f/700 where R is the distance to the nearfield/ farfield transition, L is the array height and f is the frequency. Once in the farfield the 6dB rule applies.
  Reply With Quote
Old 17th November 2004, 11:41 PM   #6
Pan is offline Pan  Sweden
diyAudio Member
 
Join Date: Sep 2002
Bill, are you really sure that formula is correct? Feet or meters?

Say 100Hz/700 = 0.14

Line height 2.4 meter

0.14 x 2.4 x 2.4 = 0.8 meter. That would mean that farfield for 100Hz begins at 0.8 meter.

20.000Hz/700 = 28.57

28.57 x 2.4 x 2.4 = 164 meter transition for 20k.

Maybe it´s 700/f ?


/Peter
  Reply With Quote
Old 18th November 2004, 12:12 AM   #7
Ron E is offline Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
Quote:
Originally posted by BillFitzmaurice
Not so fast. Line sources are -3dB per distance doubling only within the nearfield...
A "true" line source is infinite, there is no farfield. I asked what type of source before answering for a reason.
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. —Aldous Huxley
  Reply With Quote
Old 18th November 2004, 03:22 AM   #8
diyAudio Member
 
Join Date: Apr 2004
Location: Costa Rica
Send a message via AIM to johninCR Send a message via MSN to johninCR Send a message via Yahoo to johninCR
There is no such thing as a true line source, so why even bring it up unless you are writing a text book on theory?

Also, the line array effect doesn't change from the 3db decrease to 6db at a finite point, it is a gradual change. Therefore what is needed are both forumlas, where the transition point starts and where it ends, in order to get a good picture of how the array will behave in the real world.
__________________
Everyone has a photographic memory. It's just that most are out of film.
  Reply With Quote
Old 18th November 2004, 08:06 AM   #9
freedom is offline freedom  Denmark
diyAudio Member
 
Join Date: Nov 2004
Location: Broenderslev Denmark
Send a message via MSN to freedom
Default ok Ok OK!

No worries!

Concept of theory and pracsis are not the issue :-)

you guys are discussing weather infinite does exist or not. The answer depends on what glasses you´re wearing - eg. a mathematicians or a phycisists... Or more "earthnear" weather the universe has a boundary or not! - Try cracking that one :-)

In fact - a sound from any source will never never ever die completely - but it will decrease (in audiolevel), and during the decrease an energy conversion will take place...

I got the answer i needed - point of source is the issue in this case, so the -6dB is the case. Thanks again :-)

Regs. Hans-Henning

Ps: and sorry for my bad english.
__________________
If you cannot measure it - you cannot improve it!
  Reply With Quote
Old 18th November 2004, 01:00 PM   #10
Banned
 
Join Date: May 2004
Location: New Hampshire
A 'true' line source with no farfield doesn't exist; can we agree to limit discussion to real-world circumstance?

Yes, a 2.4 meter array will go from near to farfield .8 meters from the radiating plane. The same array goes to farfield at 82 meters at 10kHz. In pro-sound where line arrays today dominate it's generally accepted that trying to go lower than 80 Hz in the nearfield is not a worthwhile endeavor. The change from nearfield to far field is actually a fairly abrupt transition.
  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
DIY loudspeaker vs. factory built loudspeaker keyser Multi-Way 83 16th May 2011 12:27 PM
Q formula PeteMcK Multi-Way 10 17th January 2008 07:42 PM
Loudspeaker Filter Formula's Lars Clausen Multi-Way 11 19th November 2003 04:22 AM
Need help on x-over formula Jay Multi-Way 3 12th August 2003 05:28 PM
Anyone have the formula for... Rino odorico Multi-Way 4 22nd January 2003 04:07 PM


New To Site? Need Help?

All times are GMT. The time now is 06:05 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