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Old 20th September 2015, 08:09 PM   #1
mcl2k6 is offline mcl2k6  Europe
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Default Visaton system - what is wrong here?

Hello all,
I started to do some ARTA measurements with my homebrew speaker system I've presented here in another thread. After a couple of tweaks, I managed to get the higher frequency response pretty even, but what I continue to see is a big dip at around 125Hz. I am wondering, what am I doing wrong?
The system is a two-way, W170-S woofer, and a SC10N as tweeter, crossed over at 2kHz, see the xover design, Visaton boxsim FR, phase, and ARTA measurement files attached.
The mic is a Panasonic WM61-B, with the attached calibration file.
The loudspeaker box has got around 35liters, and currently there is no phono-absorbant material in it.
What I don't understand is where am I getting that big dip at 125Hz from? Is it some due to the W170S response, or am I missing something?
Attached Images
File Type: png arta_fr.PNG (63.9 KB, 176 views)
File Type: png fr_boxsim.PNG (81.2 KB, 175 views)
File Type: png phase.PNG (88.5 KB, 168 views)
File Type: png xover.PNG (8.9 KB, 167 views)
Attached Files
File Type: txt Mic_WM61A_holm - Copy.txt (26.0 KB, 2 views)
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Old 20th September 2015, 09:01 PM   #2
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Room reflection, usually the floor: at that frequency the path driver-mic is anti-phase with the path driver-floor-mic. If you want to compare simulation with measure you should perform a gated measure.

Ralf
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Old 20th September 2015, 09:33 PM   #3
mcl2k6 is offline mcl2k6  Europe
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Quote:
Originally Posted by giralfino View Post
Room reflection, usually the floor: at that frequency the path driver-mic is anti-phase with the path driver-floor-mic. If you want to compare simulation with measure you should perform a gated measure.

Ralf
But that's what I am doing. Single gated FR measurement.
Just measured, the woofer is at 105cm from the floor, thre reflex port is at 60cm or so, and the speaker was at ~105cm too.
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Old 20th September 2015, 09:54 PM   #4
mcl2k6 is offline mcl2k6  Europe
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Actually, this is (green curve) what I will be getting, if I raise the woofer to 180cm:
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Old 20th September 2015, 10:19 PM   #5
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Are you sure you are gating? It's not what I expect to see, and there should be a horizontal yellow line indicating the minimum valid frequency. How long is your gate?

Ralf
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Old 20th September 2015, 10:22 PM   #6
mcl2k6 is offline mcl2k6  Europe
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Quote:
Originally Posted by giralfino View Post
Are you sure you are gating? It's not what I expect to see, and there should be a horizontal yellow line indicating the minimum valid frequency. How long is your gate?

Ralf
I'm using the full length of the recorded stream. Should I do something else?
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Old 20th September 2015, 11:33 PM   #7
Dissi is offline Dissi  Switzerland
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Default Visaton system - what is wrong here?

Wrong is when you change a decent crossover to the worse, just because measurements with a noncalibrated microphone tell you to do so!

Sorry for that, but I really liked the previous version of your xo. OK, crossing the SC10N lower than 2 kHz is keen, but everything else looked very nice IMO. Now I'm a little bit shocked to see what you have done to the tweeter. That bump at 2-4 kHz and the corresponding impedance minimum can't be right. Attached is a simulation of the previous version I'm referring to.

Those cheap microphone capsules vary significantly in frequency response, and they also depend on details of mounting (prominent, flush or recessed). Hence it's very unlikely that a general microphone correction file does provide the accuracy needed to rely on.

Back to the topic. The dip at 125 Hz also could be caused by a standing wave in the fully undamped cabinet. The quarter wave length of 125 Hz is about 70 cm, which corresponds more or less to the height of your cabinet.
Attached Images
File Type: jpg SimulationMcl2k6.jpg (116.0 KB, 62 views)
File Type: jpg CrossoverMcl2k6.jpg (60.2 KB, 45 views)
File Type: jpg PhaseMcl2k6.jpg (96.2 KB, 35 views)
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Old 21st September 2015, 12:30 AM   #8
AllenB is offline AllenB  Australia
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Placing the woofer at half the room height and putting the mic close by will get you the lowest possible valid frequency. That's it, yes you should cut the stream there, the floor and ceiling bounce should be obvious. Of course you can't have the mic too close..

After that it probably matters less. Partly because the bass response is fairly predictable and could be worked out from nearfield measurements. Partly because these frequencies shouldn't necessarily be worked out with equalisation so much as by navigating and treating the room response.
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Old 21st September 2015, 06:29 AM   #9
mcl2k6 is offline mcl2k6  Europe
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Quote:
Originally Posted by Dissi View Post
Wrong is when you change a decent crossover to the worse, just because measurements with a noncalibrated microphone tell you to do so!

Sorry for that, but I really liked the previous version of your xo. OK, crossing the SC10N lower than 2 kHz is keen, but everything else looked very nice IMO. Now I'm a little bit shocked to see what you have done to the tweeter. That bump at 2-4 kHz and the corresponding impedance minimum can't be right. Attached is a simulation of the previous version I'm referring to.
You are absolutely right over here! Today morning I had listened the same music as yesterday night, and the speaker is shouting pretty much in the midrange. It seems that the Visaton sim was right. Your results give the same results (rather flat FR), so I think that today I'll be reverting to the old design. I was thinking to open up the midrange a little bit though.

BTW, what software is that you are using?

Quote:
Originally Posted by Dissi View Post
Those cheap microphone capsules vary significantly in frequency response, and they also depend on details of mounting (prominent, flush or recessed). Hence it's very unlikely that a general microphone correction file does provide the accuracy needed to rely on.
Dunno about this, some chaps on different forums usually praise the WM61 capsules.

Quote:
Originally Posted by Dissi View Post
Back to the topic. The dip at 125 Hz also could be caused by a standing wave in the fully undamped cabinet. The quarter wave length of 125 Hz is about 70 cm, which corresponds more or less to the height of your cabinet.
Yep, that could be. I'll have to try to use some phono absorbent material. Shall I fill the cabinet with a certain amount, or would it be enough to line the walls with?

Last edited by mcl2k6; 21st September 2015 at 06:50 AM.
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Old 21st September 2015, 08:58 AM   #10
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Quote:
I'm using the full length of the recorded stream. Should I do something else?
So you are not gating. See here for an how-to: http://audio.claub.net/tutorials/FR%...ing%20ARTA.pdf

Ralf
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