How should I measure this speaker? (for crossover creation) - diyAudio
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Old 3rd February 2014, 06:55 PM   #1
Defo is offline Defo  Norway
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Default How should I measure this speaker?

Hello!

I would love some input on how I should measure this speaker in order to make a simple crossover.

I will be using REW for measurement, and miniDSP for crossover duty.
The measurements will need to be taken inside, as I don't have the option to do it outside unfortunately.

First, I need some input on mic placement and gating. Then I can provide the measurements later.

Which of these alternatives will be the best approach?

1. Measure woofer nearfield, horn farfield (with gate), then combine the two
2. Measure both drivers farfield with mic in between both (with gate)
3. Measure both drivers farfield with mic on axis of horn (with gate)
4. Point 2 and 3, but without gating (tailoring the crossover to my room)

Cheers
Attached Images
File Type: jpg høytaler.jpg (59.9 KB, 188 views)

Last edited by Defo; 3rd February 2014 at 07:16 PM.
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Old 3rd February 2014, 07:34 PM   #2
ScottG is offline ScottG  United States
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Quote:
Originally Posted by Defo View Post

1. Measure woofer nearfield, horn farfield (with gate), then combine the two

Match the freq. to the gating. and measure woofer far-field as well (with gate).

Be sure to use a lot of pillows on the floor around the speaker and mic.
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Old 3rd February 2014, 09:36 PM   #3
Defo is offline Defo  Norway
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Originally Posted by ScottG View Post
Match the freq. to the gating. and measure woofer far-field as well (with gate).

Be sure to use a lot of pillows on the floor around the speaker and mic.
So measure both the horn and woofer farfield? On axis with the horn, or between both?

What do you mean by "Match the freq. to the gating"?
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Old 3rd February 2014, 10:51 PM   #4
ScottG is offline ScottG  United States
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Quote:
Originally Posted by Defo View Post
So measure both the horn and woofer farfield? On axis with the horn, or between both?

What do you mean by "Match the freq. to the gating"?
Yes, measure both far field, and also measure the woofer near field.

When measuring far field (meter), for the *loudspeaker* (not individual drivers), place the mic in a small range of vertical axis's close to *ear height (when seated normally) - ie. measure at listener "center" and then move the mic stand up 50mm and measure, and down 50 mm from "center" and measure. This is on the 0 degree horizontal axis for the loudspeaker. You are basically looking for an average here and a sweet spot relative to that average to use as a reference (making your additional axis measurements from there). (..note, some reference to the tweeter, but I don't.)


Gating is relative to the closest reflection's distance.. I tend to think of it in terms of freq..


*Note, if you are lifting the speaker off of the floor a bit for a better measurement, then make sure you lift the mic an appropriate amount to compensate.




For "best practice" do the far field measurement outside at one meter (and also again at 2 meters - if possible if you can raise the speaker higher for the same gating, and definitely at a higher freq./shorter gating for 2 meters distance even if you can't raise the loudspeaker higher).

Even for a one meter measurement, you only have to elevate most loudspeakers about 2 meters (from its bottom) to get a really good idea of performance down to 150 Hz. (..the mic height is usually about 3 meters.) Just having this can make a world of difference.
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Last edited by ScottG; 3rd February 2014 at 10:56 PM.
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Old 4th February 2014, 05:24 PM   #5
Defo is offline Defo  Norway
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Here are the impulse responses HF, LF farfield, and LF nearfield. Any suggestions on what gate I should set for each one? (no gate on the LF nearfield I presume though).
Attached Images
File Type: png HF IR.png (159.6 KB, 151 views)
File Type: png LF farfield IR.png (178.6 KB, 140 views)
File Type: png LF nearfield IR.png (178.2 KB, 138 views)
File Type: jpg 20140204_190313_PerfectlyClear_0001.jpg (214.7 KB, 138 views)
File Type: jpg 20140204_191249_PerfectlyClear_0001.jpg (243.2 KB, 45 views)
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Old 4th February 2014, 07:15 PM   #6
fpitas is offline fpitas  United States
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I've never used REW, but with Holm Impulse I get my most consistent results using the frequency dependent time windowing. Generally I place the microphone 1 meter from the speaker.
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Old 4th February 2014, 07:33 PM   #7
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Quote:
Originally Posted by Defo View Post
Here are the impulse responses HF, LF farfield, and LF nearfield. Any suggestions on what gate I should set for each one? (no gate on the LF nearfield I presume though).
How far away is the front wall (wall behind the speaker)?

Distance = Time = Frequency
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Old 4th February 2014, 07:39 PM   #8
Defo is offline Defo  Norway
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64 cm from the front wall to the back of the speaker enclosure, and 70 cm from the the horn throat to the mic.
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Old 4th February 2014, 07:40 PM   #9
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Do you have some means of zooming in on the early part of the impulse? Most of what you are showing is the reverberation of the room long after the direct sound. You will probably want to gate around 5ms after the first sound arrival. As you expand the impulse you will see the decaying initial impulse and then the first reflection arrival. Gate just prior to the first reflection arrival.

Judging from your layout the arrival time before the floor bounce will not bee too great and it is unlikely that you will get an accurate low frequency curve. You still should be able to see the upper range of the woofer and the full range of the horn, both free from room effect.

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Old 4th February 2014, 07:50 PM   #10
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Indoors, I have never zoomed out of the impulse response graph to show more than 2 meters. You generally have boundary reflections within a few meters, or milliseconds (don't need more than 10 ms, that is for sure!).
So zoom in to at least 1 or 2 meters, or less than 10 ms.
Generally, I can see the actual impulse wavelengths due to zooming in so far on the graph.
With how far out you are zoomed, it's hard to see the first reflections...
I had better luck raising the speaker off the floor so the CTC of the tweeter and woofer is about midway between ceiling and floor and as far away from 2 walls as possible.
I had 10 foot ceilings in one room, and the two closest walls were 10 feet as well. I got deep in the midrange with the CTC being 4.5 feet off the ground with no reflections from walls closer than that. The ceiling fan did cause a tiny blip that I was not happy about, but did not change the FR much at all. Not enough to matter for making a crossover.

I lucked out and had an empty room at my disposal for a while.
That was nice.
I did some measurements in the bedroom with the speaker on the bed, and I got pretty much the same results. So, the gating works nicely. I set small speakers with their back on the bed, on the far edge of bed away from wall. That worked well.

I put pillows and whatnot on the floor, and it did not help the bass or lower midrange at all.
I tried lots of things. You just can't be near a floor or wall. Pillows only do so much.
I think they might help in the crossover range for most tweeters, though. That is all you really need anyways. But, concentrate on getting the speaker as far away from boundaries as possible.

Here is an example of where I set gate on this speaker.
Holmimpulse.

You can see a tiny bump at 145 CM.
The major first reflection is at 170.

When you move the gate, you will see it will effect the bass response the most when you are in the shorter time domain, or closer distance, until you get deep into the farther distances and then the reflections will start messing with the highs.
I usually try to look at the impulse to find the first reflection, then move the gate around that area to see how the highs are affected. I try to get the frequency as low as possible without effecting the highs. It usually always ends up being as recommended. Just before the first reflection...
Keep in mind that the louder you play the signal, the higher the peaks on the impulse, making it easier to read. I keep the signal to the recommended -2db on holm. On every measurement. I always check.

I heard the recommendation that you don't want to "tape measure" anything, as far as what is around your speaker. Just keep everything away in the room, if you can.

I showed you the graph to give you a visual representation of what others have recommended. Look at the response itself to set the gate. Don't measure your surroundings. Don't waste your time pulling out the tape measure. Your eyes can tell you "hey, the speaker is high off the floor, away from the ceiling and walls". Good enough

The speaker I really wanted to measure is a big fat pig. I hate moving it. And the waveguide sits on top all loose.
So I used some tiny satellites to learn how to set everything up and learn holmimpulse. I recommend having a small test mule small speaker to practice with.
That way you can try different measuring techniques (distance of microphone and placement of speaker in particular area) and see what the changes are.
Heck you can use a loose driver or just a clock radio. Whatever is easier.





*dangit Dave, I wanted to sound almost smart for once! I wasted too much time opening holm and saving a pic of the impulse.
Attached Images
File Type: png impulse response demo.png (17.7 KB, 45 views)

Last edited by TMHutson; 4th February 2014 at 07:56 PM.
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