What is 2 pi and 4 pi
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 Multi-Way Conventional loudspeakers with crossovers

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 4th October 2003, 11:37 PM #1 EternaLightWith   diyAudio Member   Join Date: May 2002 What is 2 pi and 4 pi Does it mean that the speaker is radiating only forwards (2pi) versus front and back (4 pi) Someone once said that PHL speakers where great efficient speakers radiating in 4 pi space. At the time, I didn't quite get what he was trying to say. Any ideas on this? David P.S. The topic of convo. was the PHL 3451 which has an effic. of ~5% Of course I later looked at the PHL 3860? that is at ~6% effic. wow!
catapult
diyAudio Member

Join Date: Dec 2002
Location: Planet Earth
Quote:
 Does it mean that the speaker is radiating only forwards (2pi) versus front and back (4 pi)
Yep. Think speaker mounted in a wall so the sound only goes forwards -- 2pi--half a sphere. Anything that tries to go back is reflected by the wall so the SPL is twice as loud.
Quote:
 P.S. The topic of convo. was the PHL 3451 which has an effic. of ~5%
That sounds pretty high. That's probably a 2pi number.

 5th October 2003, 12:10 AM #3 1/137 diyAudio Member     Join Date: May 2002 Location: albuquerque nm solid angle look in your math book...for the term solid angle rt
 5th October 2003, 12:34 AM #4 roddyama   diyAudio Moderator Emeritus     Join Date: Jan 2002 Location: Michigan The efficiency of the driver is a measure of how well (or poorly) it converts electrical power to acoustic power. The power output of a driver is independent of the size of the soundfield it is radiating into. That is to say that if a driver has a certian efficiency, it will radiate the same power into a 2pi soundfield as it does to a 4pi sound field. The SPL increases when radiating into the 2pi sound field because the same acoustic power has been concentrated into a smaller volume. Typical cone type drivers will have efficiencies in the range from as low as 0.1% to as high as 3% for some of the larger pro drivers. 5% and 6% speaker efficiencies are usually reserved for the horn loaded drivers. __________________ Rodd Yamashita
 5th October 2003, 01:28 AM #5 EternaLightWith   diyAudio Member   Join Date: May 2002 reflection, huh.... wouldn't that be a no-no? COme through as distortion, etc. as it's being reflected through the cone.. Needs a nice layer of dynamat of the back. David. I'd rather absorb the backwave 100dB @ 1m..... It's not like PHL drivers are hurting for efficiency.
 5th October 2003, 02:06 AM #6 Ryder diyAudio Member   Join Date: Feb 2002 Location: Michigan Loudspeaker Spatial Loading http://www.trueaudio.com/st_spcs1.htm Cheers Craig Ryder __________________ Ryder Any fool can ask more questions than seven sages can answer.
 5th October 2003, 01:06 PM #7 Timn8ter   diyAudio Member     Join Date: Jul 2003 Location: Seattle, WA Good article. Spatial Loading a.k.a. Boundary Gain Boundary Gain + Pressure Gain = Room Gain
kelticwizard
Wizard of Kelts
diyAudio Moderator Emeritus

Join Date: Sep 2001
Location: Connecticut, The Nutmeg State
This is an excerpt from DB Keele's article in the Journal of The Audio Engineering Society in April,1974: "Low-Frequency Loudspeaker Assessment by Nearfield Sound-Pressure Measurement". These are actual measrements. From this, we can draw two conclusions.

A) The 4p situation, (full space) gives much worse bass response compared to the 2p, (half space) measurement;

B) The nearfield measurement system, (that is, putting the microphone an inch or less from the cone or port), yields very similar readings to the 2p, (half space) readings.
Attached Images
 4 pi and 2 pi steradian.gif (16.1 KB, 682 views)
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 9th October 2003, 04:42 PM #10 EternaLightWith   diyAudio Member   Join Date: May 2002 Some more questions In regards to MJK's TL files, I'm a little fuzzy with the driver position ratio and the TL Geometry numbers (ie. n_closed>1 & n_open>1). Trying to relate the Offset driver sheet's parameters with the TL sectional sheet's parameters. I was doing it at 6 (driver position ratio) for awhile and leaving TL Geometery at default (n_open>4 & n_closed>9) If my understanding of these parameters are correct, then this would not work for me. I'm putting a 10 in driver into a 7:1 Sd ratio TL with an optimal length of 14 - 16 in. SO.... I was trying (1 & 5; 3 & 5; and a 4 & 4) this I believe gave my a driver positioning of 1/3; 2/3; & 1/2 respectively. This would give me some flexibility while still respecting the size restrictions of drive and TL length. David P.S. Sticking with Sectional TL spreadsheets for now, as they are the most accurate and I'd be better served to master one rather than jumping between different ones.

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