Hi,
I'm about to test some speakers at home with a measuring mic etc. On the one hand it would be useful to see how the speakers perform in a "typical" domestic setting but as a reference (and out of curiosity) I'd really like to know how the perform under anechoic conditions.
I remember seeing a web page that showed an alternative method: a very short burst of noise is played through the speaker and recorded. The burst is so short that the recording only contains the direct output of the speaker i.e. the recording time wasn't long enough to contain any reflections from the room boundaries, therefore anechoic.
Does anyone know what this method is called or have any links? Are there any draw backs with this approach?
Thanx in advance,
Dean.
I'm about to test some speakers at home with a measuring mic etc. On the one hand it would be useful to see how the speakers perform in a "typical" domestic setting but as a reference (and out of curiosity) I'd really like to know how the perform under anechoic conditions.
I remember seeing a web page that showed an alternative method: a very short burst of noise is played through the speaker and recorded. The burst is so short that the recording only contains the direct output of the speaker i.e. the recording time wasn't long enough to contain any reflections from the room boundaries, therefore anechoic.
Does anyone know what this method is called or have any links? Are there any draw backs with this approach?
Thanx in advance,
Dean.
You can do a pretty good job in your home using holmimpulse. It's a free download. Just set the gating to just below the first reflection blip you see on the impulse response. It's usually in the 200-300 hz range. Then, do a nearfield response test on the woofer and stitch the two together.
Or, you can do it the hard way by taking your speaker outdoors, bury it in the ground so the BB is flush and suspend your mic over it. You'll get a 2 pi measurement with that method. Or, position it in a very open area with no possible chance of reflections. You'll get a 4 pi measurement that way.
Or, you can do it the hard way by taking your speaker outdoors, bury it in the ground so the BB is flush and suspend your mic over it. You'll get a 2 pi measurement with that method. Or, position it in a very open area with no possible chance of reflections. You'll get a 4 pi measurement that way.
2 pi means 180 degs, simulating as though the speaker was mounted flush with a wall.
4 pi means 360 deg. or, total wrap around effect which will reveal any baffle step issues the 2 pi test wouldn't.
The analyser won't play an impulse, it may run each frequency in turn over a period of a few seconds (called a sweep), and reconstruct it into an impulse. It will still be anechoic down to the frequency where a wavelength cannot be received before the first reflection reaches the mic. This is often low enough to work with.
Sound propagate in space so we are talking about solid angles. 2PI is the solid angle that covers for example the whole sky that someone on a flat land can see in a specific moment, or in case of speakers, the angle in which the sound can propagate if the drivers are on an infinite baffle (in wall). On the other hand 4PI is the solid angle that covers the whole sky, or in case of speakers when the speaker has a finite baffle and is far from walls so the sound can propagate in every directions.
Ralf
Ralf
2pi radians is 360 degrees.
But the radian is based on a portion of the circumference of a circle. The steradian is based on a portion of the surface area of a sphere. One steradian refers to an area equal to r^2, and there are 4pi steradians over a sphere.
(does anyone know how to enter the pi symbol?
)
But the radian is based on a portion of the circumference of a circle. The steradian is based on a portion of the surface area of a sphere. One steradian refers to an area equal to r^2, and there are 4pi steradians over a sphere.
(does anyone know how to enter the pi symbol?
)
2pi radians is 360 degrees.
(does anyone know how to enter the pi symbol?
Was that a serious question? Do you? It's a unicode (hex) symbol right? I don't know of a way to key it in and have it shown correctly here.
alt+227 gets you π, pasted from Word gets you π, that's as close as I get. So, 2π=?° Don't you ♥ it? ¬!
so you were correct all along SDr ;-)
Thanx for the info guys. I did wonder if 4pi related to a sphere and this doc from JBL seems to further add to whats been said above:
http://www.jblpro.com/mpro/PDF/MP410.pdf
Notice on the first frequency plot it says: half space (2π), whole space (4π). I've learnt something new today.
Anyway, any suggestions about testing the speakers in a typical domestic room using the gated method are most welcome.
Thanx for the info guys. I did wonder if 4pi related to a sphere and this doc from JBL seems to further add to whats been said above:
http://www.jblpro.com/mpro/PDF/MP410.pdf
Notice on the first frequency plot it says: half space (2π), whole space (4π). I've learnt something new today.
Anyway, any suggestions about testing the speakers in a typical domestic room using the gated method are most welcome.
Well, how about that!
In that first mention I made of 2 pi and 4 pi I was going from memory. So, I guess, in my old age, I haven't lost it yet!
We just had a Greek Letters on the computer discussion:
http://www.diyaudio.com/forums/forum-problems/209679-greek-letters.html
http://www.diyaudio.com/forums/forum-problems/209679-greek-letters.html