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Re: Measurement Information [message #61090 is a reply to message #61087]

Tue, 29 September 2009 09:19

Wayne Parham
Messages: 18675
Registered: January 2001

Illuminati (33rd Degree)

I'd measure outdoors, to get an idea what the speaker's response is without room interactions. I prefer ten meters at 100 watts, but you can go with five meters or even just two or three if the speakers won't handle the power. Results change at different positions, so keep that in mind.

If the listeners won't be ten meters away, it may not make sense to measure at that distance. Might be better to measure close to the distance you think they'll be used. Even better, measure at several distances and positions (on and off axis) to see what the speaker does at several angles and distances. The ideal speaker is one that produces the same response at all angles within its intended pattern, but every speaker configuration is different in this regard. That's where measurements at various positions and angles can help show you what the capabilities of the speaker are, beyond the basic (almost hypothetical) "1W/1M on-axis response curve."

If outdoors measurements show a problem, then you can work on the speaker to get the kinks out. If not, then you can start making measurements in-room, to find out where to place the speakers and arrange furniture for best results.

I would anticipate your next questions might be what distance is best, what differences are found between measurements at different distances, and whether to stand the speaker upright or facing it on its back, how to position the microphone, i.e. using a boom, centered with respect to the baffle, on the ground, etc. My suggestion would be to try different positons to see what results you get. You'll learn something.

Also try this with a point source - measure the speaker standing upright facing forward or lying on its back facing up, etc. Measure the speaker sitting on the ground facing forward and compare with it being raised on a stand. You'll learn something there too. The response in different positions is usually vastly different, so you'll learn how the environment affects the sound, and so you'll begin to learn how to setup your test to measure various things.

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Re: Measurement Information [message #61111 is a reply to message #61090]

Wed, 30 September 2009 00:51

jp
Messages: 23
Registered: May 2009

Chancellor

I presume by saying measure that I should measure SPL with Pink noise ?
Unfortunately I dont have the option to go outdoor , I'll have to do with indoor measurements , wich I am sure is not going to be accuratedue because of room interaction but what should be done to get the best we can in this case ? Maybe use absorbing cushions on both sides of the speaker forming a 1 m corridor in front ? Puttin the Mic at a 1m distance at different heights ?
JP

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Re: Measurement Information [message #61115 is a reply to message #61111]

Wed, 30 September 2009 09:41

Wayne Parham
Messages: 18675
Registered: January 2001

Illuminati (33rd Degree)

The biggest influence you'll see from indoors measurements is at low frequencies, and no absorbent material like cushions, wedges or padding will help. You would really need large membranes to absorb sound waves that long, which is how room damping at low frequencies is accomplished. I would assume that your indoor measurements are going to show what the speaker is doing only above about 300Hz, below that it's mostly the room.

As for signal types, I think white noise is probably fine for what you're doing. Pink noise would also work as long as you remember that the signal spectrum is not flat, so the measured spectrum should not be either. You'd hope to see exactly the same spectral balance at the measurement microphone as was presented to the amplifier.

For more informaton about signal types, pros and cons of each, see the post called "Measurement signal types".

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