SPL measurements in a room.

[Vilic]

Hello everyone. Living in a High rise building makes me unable to make Ground plane or Half Space readings. So I make my testing in our apt rooms using Near field and Gated methods. But this is lot of work. I have also noticed that if I just make a regular SPL reading and then smooth the curve number of times it seemingly takes the room effects out. The curve now looks more like an anechoic measurement. Could this be true?
Thanks,
Vilic.

[cstrahm]

Of course that is true. For the most part a speaker is putting out the same response regardless of the environment. So if in free space you have a smooth curve from the source, and in a room with reflections you measure ripples, the speaker is not putting out ripples it is still putting out a smooth response. It is the same energy, it is just now bouncing around the room causing the ripples. So when you average the curve you average out those reflection ripples and the smooth response of the source is seen again.

However that assumes that the response of the source is smooth, and of course it is likely not. The problem is that when you average out the reflections of the room, you can also end up averaging out the natural ripples in the true response of the source which you need to see.

[Vilic]

Thank you Chris for replying. Considering distorting the response of the driver due to averaging, and since most anomalies of the driver happens in mid to upper scale, would it be a good idea to measure top part of spectrum (300 Hz and up) with gated system and the bottom part just regular SPL and then average the base part to remove room effects and then splice it to top part, say at 400 Hz or so. This way I have a non Echoic mid and top reading, and averaged out base.
Thanks again,
Vilic

[cstrahm]

It is certainly worth trying.

[pghgcj]

Dear sir:
I have a question. when i measure a system by using near field measurement with a port and a speaker, the port and the spk are in the same panel. after measurement, i have to combine the two SPL curve together, in your manual, you ask me to subtract the port form the speaker, but in my opinion, i should add the port to the speaker. i assume the phase of the face of the speaker is 0, so, the the phase of the back of the speaker is 180, but the box and the port make a phase shift on the second phase of the back of the speaker, and the two phase will be very close, so i think, i should app the port to the speaker.
i am not good in english, i hope you can know what i say. and please e-mail your reply to pghgcj@tom.com
best regards!
maurice Peng
2005-11-14