Speaker Measurements OK? - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 4 Old 12-22-10, 11:06 AM Thread Starter
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Speaker Measurements OK?

Before I start making measurements of my room, I thought it would be a good idea to see how one of my main speakers measured.

I sent the pink noise from WAV into an input of my audio processor. I have set the processor so that the only processing it does is to apply a 120Hz low pass filter to the output, which is then routed to my right sub. I made sure the right sub was turned off.

I am using a calibrated ECM 8000 mic into the Behringer pre-amp and then into the SB 24bit Live! external sound card. The first measurement I took was after placing the mike in a position that was horizontal to the floor, aimed directly at the tweeter of the main speaker, and was about 24 inches from the speaker (that trace is in green in the following plot). Next, while keeping the same distance from the speaker, I pointed the mic vertically upward, with the farthest end of the mic at the same level as the tweeter (that plot is in blue).

Here are the measurements I got without smoothing (green is the horizontal mic, blue is the vertical mic):

Speaker Measurements OK?-closeup-measurement-horiz-vertical.jpg

Next, I smoothed the graph to 1/3. Here is the graph I got:

Speaker Measurements OK?-smooth-ver-close-up-right-main.jpg

I have several questions regarding these graphs. First, Was my measuring technique (i.e., distance from speaker, aiming at tweeter, etc.) OK? I was surprised by how close the vertical and horizontal graphs look.

Second, do these graphs look like a moderately priced speaker given the technique I used for measuring?

Third, I am concerned about the dip between 2 and 3kHz, and the spike just above the 200Hz point. Is this the speaker or is it my measuring technique or my equipment? Note: I ran the same tests on my left speaker and got the same results.

Thanks for your help.
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post #2 of 4 Old 12-22-10, 01:57 PM
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Re: Speaker Measurements OK?

I can't really comment to your technique on the microphone placement, etc. as I have only measured from the listening position.

If you have l-pads for mids or highs, you should take measurements with them in various positions (i.e.: min, mid, max) to see what effect they have on the speakers response.

For example, from my experience, I found that my midrange l-pad had to be set to max to eliminate a dip in my response that was clearly from the passive crossover (band-pass filter) in the speakers, whereas the hi l-pad had a relatively uniform affect on on the highs from the crossover point.

Just food for thought.

PS: Would be helpful if the graphs had the same scale to compare. Refer to this post for the preferred scaling for posting graphs in the forum.

Last edited by kflory; 12-23-10 at 11:43 AM.
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post #3 of 4 Old 12-22-10, 11:01 PM
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Re: Speaker Measurements OK?

Your near field measurement technique is similar to what I did when I was verifying crossover changes in mine. I set my mic about 2' in front of the speakers, placed midway between the tweeters and midrange.

If your are using the generic calibration file for the ECM8000, it was developed with the mic oriented horizontally. So you might have different measurements oriented vertically. I would expect more rolloff in the highend, and I don't see that in your curve, so perhaps you have two different custom calibration files, one for horizontal and one for vertical orientation. From what I have read, for a near field measurement of the speaker characteristics, a horizontal orientation is usual.

The point where you see the difference, between 200Hz and 250Hz, is where you will see reflections from the floor or ceiling. The effect would first appear lower in frequency, but you are so close to the speakers that almost the entire vertical distance to ceiling or floor adds to the path difference here. Bottom line is don't worry about it, it's a measurement artifact.

If you are interested, you can try to reduce the impact of these early reflections by adjusting the IR Windows (there's an icon at the top). If you reduce the left window and right window to less than 10 msec, this will cut off the measurement time to before the reflections can reach the mic. The side effect, though, is to greatly reduce the resolution and the lower limit, so at the bottom end it will appear smoothed and you won't see the bass detail. But this may reassure you that you are seeing the effect of reflections. On my near field measurements, a peak at 250Hz is not present when the right windows is 8 msec, starts to appear at 10 msec, and is easily visible at 20 msec.

My task was similar to what Kevin described. The crossovers for my speakers had taps to set the attenuation of the tweeter. Mine was low, so I had to set the tap to zero, and let Audyssey take care of the rest. Your tweeters appear high nearfield, but depending on the acoustics of your room, how much high-end damping you have from bookcases, furniture, etc., they may not sound bright at the listening position. You will need to take your measurements in and around your primary listening position to be sure.

Is the region from 2kHz-3kHz where the crossover is in your system? The dip here might be a deliberate "BBC dip" designed into the system.


Last edited by laser188139; 12-23-10 at 12:09 PM.
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post #4 of 4 Old 12-23-10, 06:27 PM
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Re: Speaker Measurements OK?

SamSpade wrote: View Post
I have several questions regarding these graphs. First, Was my measuring technique (i.e., distance from speaker, aiming at tweeter, etc.) OK?
Typically nearfield measurements are only made by speaker builders, to minimize the room’s influence, verify crossover “action,” etc.

Third, I am concerned about the dip between 2 and 3kHz, and the spike just above the 200Hz point. Is this the speaker or is it my measuring technique or my equipment?
Probably the technique. With the mic close to the speaker and aimed directly at the tweeter, it seems natural that the highs would dominate. Note the sharp drop at 3 kHz, which is a common crossover frequency for tweeters.

The highs decrease in intensity over distance, so the graph will probably look markedly different with a listening-position measurement. Likewise, the 2-3 kHz dip is probably nothing to be concerned about because an up-close measurement bears little resemblance to what you’re going to hear at the listening position. Which is why and where in-room measurements are usually done.

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