Seas coax (H1333/H1353) tweeter measurement data doesn't match - diyAudio
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Old 10th December 2011, 10:07 PM   #1
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Default Seas coax (H1333/H1353) tweeter measurement data doesn't match

Hello,

My measurement of Seas T18REX/XFC (H1353) tweeter FR doesn't match Seas spec and it doesn't match what Zaphaudio (zaphaudio.com/tidbits/H1333-tweeter-FR.gif) has measured either.

I get huge dip spanning from 8kHz to 12kHz as Seas spec doesn't show much dip at all and Zaphaudio shows much smaller dip around 8-10kHz. I got same result measuring two different drivers.

Also I found somewhere Ascendo C5 FR which uses Seas coax and that FR (tweeter dip part) looks more like what Zapfaudio measured.

What can explain the different results I get?

Thanks,
Timo
Attached Images
File Type: jpg H1353 measured tweeter FR.JPG (72.3 KB, 265 views)
File Type: jpg Seas H1333 spec FR.JPG (89.4 KB, 261 views)
File Type: jpg Seas H1353 spec FR.JPG (85.4 KB, 261 views)
File Type: gif Ascendo C5 FR with Seas coax.gif (19.5 KB, 255 views)
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Old 10th December 2011, 10:59 PM   #2
AllenB is offline AllenB  Australia
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A number of possibilities.
1. The smoothing that has been used could be different.
2. An on-axis dip can be strongly focussed there, try some of the off-axis measurements.
3. Manufacturing tolerances.
4. Gating a reflection free zone.
5. Diffraction from your baffle, or your mounting procedure.
6. Your microphone calibration.
7. Your microphones physical construction, including its shape, and its mounting procedure.
8. measuring distance.

Not necessarily in that order.
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Old 10th December 2011, 11:41 PM   #3
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Quote:
Originally Posted by AllenB View Post
2. An on-axis dip can be strongly focussed there, try some of the off-axis measurements.
This one I think is most likely, given the coaxial nature. If it clears up off axis I wouldn't pay these dips much mind; just design "pretending" they're flat.
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Old 11th December 2011, 02:48 AM   #4
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I didn't check, or make any measurements but I sniff the distance (reflection/null) between the tweeter and the mid-cone if for the interval 6K-10/12K. There was the same problem with inverted domes but I can not hear a thing (it's measured only).
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Old 11th December 2011, 03:03 AM   #5
kvholio is offline kvholio  Netherlands
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It could be due to difference in applied smoothing.
These are typical coax-artifacts, i measured them in both Thiel and Kef coaxials.
The thing i'm wondering about is why the ~6 Khz dip shown in other measurements doesn't show up in your measurement.

Regards,

Klaas
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Old 11th December 2011, 03:03 AM   #6
AllenB is offline AllenB  Australia
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...for example an on-axis null due to a mouth reflection at the axial distance from the dome to the mouth?

Maybe tipo1000 could run some damping material over and within the roll surround and try again. If it is this it shouldn't be as strong off-axis as well but perhaps designs with this unit would work out better off-axis for other reasons anyway.
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Old 11th December 2011, 06:04 AM   #7
Shaun is offline Shaun  South Africa
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Quote:
Originally Posted by AllenB View Post
2. An on-axis dip can be strongly focussed there, try some of the off-axis measurements.
5. Diffraction from your baffle, or your mounting procedure.
Those will make the most significant difference, assuming you are sufficiently skilled at taking these measurements.

You will only get the same result if your measurement setup is the same. I believe that Zaph does describe his setup here Zaph|Audio
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Old 11th December 2011, 08:18 PM   #8
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Thanks for all suggestions.

I did more measurements at 0.5m, 1m and 1.8m distances.

The wide "W" shaped dip I got earlier @1m seems disappear @1.8 and comes one deep dip much like in other guys measurements.

I also moved the mic 1 inch around on axis to see if it affects that mic is not exactly dead on, but it didn't seem to make difference.

I'm not worried about other differences; they can be because of my speaker enclosure.

Thanks,
Timo
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Old 11th December 2011, 09:53 PM   #9
AllenB is offline AllenB  Australia
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This problem is visible in the measurements that others have done. Even if the apparent Q of the dips looks worse for you it may not actually be worse. Your smoothing parameters may not be the same as previously used either.

I would be trying to achieve a measurement that is consistent with one of the previously done ones and I'd start off-axis. Eg: 0.5m at 30 degrees.

It's possible this could be diffraction from the mid cone former. If it is it may be somewhat reducible with treatment.
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Old 11th December 2011, 11:44 PM   #10
Shaun is offline Shaun  South Africa
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One source of SPL inaccuracy might be your mic setup. Some questions in that direction:

How is your mic mounted?
Which mic do you use?
Do you have other tweeters you can verify your test setup with (against others' measurements)?
What about impedance measurements? Do they match up (sanity check)?
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