reflection-free loudspeaker response

**anli** · **06-14-06, 10:10 AM**

Will anybody be so kind to give me tips to measure room-reflection-free loudspeaker SPL response vs frequency?

**brucek** · **06-14-06, 10:33 AM**

I've heard of people taking the speaker outside and setting the mic fairly close to the speaker..... brucek

**anli** · **06-14-06, 11:29 AM**

If I understand well, sweep sine response data potentially has all the information needed to exclude room influence and get own loudspeaker frequency response.

**JohnM** · **06-14-06, 01:46 PM**

You need to move the loudspeaker as far from room boundaries as is practical (i.e. put it in the middle of the room), make the measurement, then go to the impulse response graph and set the gate time to exclude any reflections (evident as spikes on the response, more easily seen if you select the Full Range Energy-Time curve view). The reflection-free period is generally pretty short, if you are measuring the response at 1m from the speaker the reflection free period is a little more than the time sound takes to travel to the nearest boundary and back. Usually the floor is the nearest boundary, if your mic is 1m from the floor and the speaker is more than 1m from any other boundary the reflection-free period will be about 6ms. The problem with the short gate time is that it puts a limit on the lowest frequency at which you see meaningful response information and the frequency resolution of the response, for a 6ms gate time this figure is about 167Hz (1/gate time) which means this approach is only useful for full range measurement and doesn't tell you anything about the low frequency response.

**anli** · **06-14-06, 02:11 PM**

JohnM,

Aha, I see, thanks!

BTW, at LF, I think, nearfield measurements will be appropriate. But woofer - midrange xover-ing will stay a problem. At any case, it isn't REW target :-) You see, I'm audio-DIYer, and my PC works under Linux. I have not found any software for loudspeaker measurements, and REW will solve (at leats, partly) my problems. Thanks!

**anli** · **06-15-06, 08:09 AM**

John,

Do I understand well, the swept sine technics you use is base on the Farina's work?

Andrew

**JohnM** · **06-15-06, 11:34 AM**

Similar, for detailed info read the PDF on Transfer Function Measurement with sweeps linked on the REW page.

**anli** · **06-15-06, 11:54 AM**

John,

Thanks! I just printed this article two days ago also!

BTW, I have noticed, sometimes smooth combo box control losses one of listeners: a curve doesn't update after items selection. I have not noticed any sequence to reproduce the problem yet. At any case it is after IR intervals adjustment.

**JohnM** · **06-15-06, 01:30 PM**

Quote:

anli wrote:

BTW, I have noticed, sometimes smooth combo box control losses one of listeners: a curve doesn't update after items selection. I have not noticed any sequence to reproduce the problem yet. At any case it is after IR intervals adjustment.

That's been fixed for the next release.

**anli** · **06-17-06, 08:25 AM**

John, thanks! Will be waiting for :-)

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