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

Thread Tools  Search this Thread 
18th November 2004, 02:30 PM  #11 
diyAudio Member
Join Date: Sep 2002

But sure prosound use with (normally) no ceiling, and home use where the line can be a "true" linesource is two different situations, no?
I have not done my homework on linesource theory, though I understand the basics so so. /Peter 
18th November 2004, 03:02 PM  #12 
Banned
Join Date: May 2004
Location: New Hampshire

There are similarities. Consider a live sound venue where the required throw is 100 meters. To reach that at 80 Hz in the nearfield would require an array height of about 30 meters. That's not practical in most cases.
In a home with a throw of five meters getting to 80Hz in the nearfield requires an array almost 7 meters high, also not a viable option. But realistically it doesn't matter, as once the frequency is low enough that room reflections and modes are a significant percentage of response the nearfield/farfield transition frequency and distance doesn't matter than much anyway. 
18th November 2004, 03:33 PM  #13 
diyAudio Member
Join Date: Sep 2002

But in a home, with a line from floor to ceiling, there are no "limits", the line is infinite.
So in a room, using a ribbon from floor to ceiling, where the floor and ceiling acts as mirrors extending the line there must be other rules than for free field use.´ I´m aware of room contribution for sound sources in all registers. Guess I´ll have to go read Jim Griffins paper to get the final understanding of linesources. /Peter 
18th November 2004, 05:25 PM  #14 
diyAudio Member

"A 'true' line source with no farfield doesn't exist; can we agree to limit discussion to realworld circumstance?"
Actually no. Not in this case since i sought an answer for a theoretical question, an answer to be used in a theoretical paper that is to be judged by theoretical lectors at an university. If we were to limit the discussion to real world cases  the formula of pointsource is far more complex than i´m currently, and probably ever will be, cabable of using or get anything usefull out of. I´ve read the fundamentals of the pointsource in "Loudspeaker and Headphone Handbook" and being a 3rd. semester student (7 more to go) I didn´t understand much of it. And since this project has focus in a completely other and very different subject  this part of the project is a minor detail  and there for the theoretically simplest formula is more than adequate. So  as i said  cased closed. However i´m happy to reveal that there are wellinformed peoble in this forum. I do though suggest that posts that goes far beyond the question in a thread should go in threads were they do belong :) So thanks everyone :) HansHenning / Denmark
__________________
If you cannot measure it  you cannot improve it! 
18th November 2004, 05:58 PM  #15 
diyAudio Member

Freedom,
I really think you need to get your arms around that point source formula if you're are going to be dealing with people at that kind of theoretical level, because I believe that formula applies to a lot of things other than just sound wave dispersion.
__________________
Everyone has a photographic memory. It's just that most are out of film. 
18th November 2004, 08:54 PM  #16 
diyAudio Member

I´ll do so  if needed. So far it has not been the case  but  as i wrote  there are another 3½ years to come.
So thanks for the advice. Regs. HansHenning PS I may need an armextender in order to get hold of all of it  anywhere you know where i can get this :) ?
__________________
If you cannot measure it  you cannot improve it! 
18th November 2004, 09:10 PM  #17 
diyAudio Member

Sorry I can't help you. I don't need to know it, so the only thing in my memory warehouse is the 6db rolloff for point source speakers and 3db for line arrays in the nearfield.
__________________
Everyone has a photographic memory. It's just that most are out of film. 
18th November 2004, 09:49 PM  #18 
diyAudio Member
Join Date: Jun 2002
Location: USA, MN

There is a fairly easy way to get an intuitive feel for the 6dB point source freefield rule. For each doubliing of distance the sound intensity in watts per square meter is reduced by a factor of four.
10 * log (0.25) = 6 (6.0206...) The actual formula for sound level is: dB = 10 * log(Intensity/1e12) such that 1 watt per square meter is 120dB If you wish to use pressure rather than intensity you may use: dB = 20* log (P/0.00002), where P is sound pressure in Pascals. 0.00002 is the sound pressure in pascals defined to be the 0dB level. Bonus question: What happens to SPL when the distance goes to zero, assuming dB = 90 at 1 meter
__________________
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 obsolescencethose are the three pillars of Western prosperity. —Aldous Huxley 
Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
DIY loudspeaker vs. factory built loudspeaker  keyser  MultiWay  130  14th June 2016 11:21 PM 
Q formula  PeteMcK  MultiWay  10  17th January 2008 08:42 PM 
Loudspeaker Filter Formula's  Lars Clausen  MultiWay  11  19th November 2003 05:22 AM 
Need help on xover formula  Jay  MultiWay  3  12th August 2003 06:28 PM 
Anyone have the formula for...  Rino odorico  MultiWay  4  22nd January 2003 05:07 PM 
New To Site?  Need Help? 