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Strange Frequency response?
Strange Frequency response?
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Old 25th March 2020, 10:38 PM   #1
ghettoblasterfanatic is offline ghettoblasterfanatic  United States
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Default Strange Frequency response?

Hi! This is my first post on this forum, if this question is in the wrong place I apologize. I've been working on a diy boombox using Dayton Audio RST28F tweeters, and I've noticed the frequency response at the top end looks kind of funny. I know these tweeters are supposed to reach all the way to 20khz, but my measurements show that the -3 db point is around 12 khz? Is this normal? The speaker really sounds fine, I can't hear anything lacking in the treble, but just the measurements show a sharp drop off after 11-12 khz. It could very well be that I'm measuring it wrong, I'm using a umik-1 mic with room eq wizard. I did check and confirm the test is going all the way up to 20 khz though. Here's the graph: EcstasyFrequencyResponseSixth.jpg

Oh and btw, these measurements were taken outside, so room acoustics shouldn't be an issue, even though I don't think it matters anyways at frequencies this high. I'm sorry if this is a stupid question, I'm still very new to a lot of this stuff.
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Old 25th March 2020, 10:55 PM   #2
AllenB is offline AllenB  Australia
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Strange Frequency response?
It doesn't look like a problem. Maybe the mic or some other part of the measurement system, maybe your mounting scheme?
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Old 25th March 2020, 11:02 PM   #3
rayma is offline rayma  United States
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Do you have your own measurements (with the same gear) on other drivers that do go higher?
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Old 25th March 2020, 11:50 PM   #4
ghettoblasterfanatic is offline ghettoblasterfanatic  United States
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Quote:
Originally Posted by AllenB View Post
It doesn't look like a problem. Maybe the mic or some other part of the measurement system, maybe your mounting scheme?
I did make sure to measure at a position I would normally listen to the speaker at, but I'll remeasure it today and see if I get any changes.
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Old 25th March 2020, 11:52 PM   #5
ghettoblasterfanatic is offline ghettoblasterfanatic  United States
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Quote:
Originally Posted by rayma View Post
Do you have your own measurements (with the same gear) on other drivers that do go higher?
Nope, this is the first time I'm measuring with this gear. I'll try measuring something else though and see what I get.
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Old 25th March 2020, 11:53 PM   #6
Douglas Blake is offline Douglas Blake  Canada
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Quote:
Originally Posted by ghettoblasterfanatic View Post
The speaker really sounds fine, I can't hear anything lacking in the treble, but just the measurements show a sharp drop off after 11-12 khz.
Try a test at very low volume, just enough that you can barely hear the sweep, with the mic about 1 inch from the tweeter dome. Do you get the same result?

If you don't see full range from the tweeter there are multiple possibilities...
A treble control was turned down somewhere in your system
REW has a house curve installed that attenuates high frequencies
Your sweep settings end at 10k (10hz to 20k is normal)
The acoustics are cancelling treble
You accidentally placed your mic in a tweeter null
Your sound drivers are attenuating high frequencies
Your microphone can't respond past 10k (unlikely with umic)
...

Last edited by Douglas Blake; 25th March 2020 at 11:58 PM.
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Old 26th March 2020, 01:11 AM   #7
PLB is offline PLB  United Kingdom
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Try checking the sample rate first. It should be set to 48KHz or higher.
You say that the response is of the tweeter, but the tweeter you describe has a low frequency resonance of 710Hz, in which case there is something wrong at low frequencies as well.

Peter
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Old 26th March 2020, 12:33 PM   #8
lbstyling is offline lbstyling  United Kingdom
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Is your soundcard calibrated correctly? this looks like mine when i have unchecked 'soundcard calibration file' in REW.
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Old 26th March 2020, 03:10 PM   #9
chris661 is offline chris661  United Kingdom
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Which way was the mic pointing?

Chris
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Old 26th March 2020, 05:36 PM   #10
weltersys is offline weltersys  United States
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Quote:
Originally Posted by ghettoblasterfanatic View Post
1)I know these tweeters are supposed to reach all the way to 20khz, but my measurements show that the -3 db point is around 12 khz? Is this normal?
2)The speaker really sounds fine, I can't hear anything lacking in the treble, but just the measurements show a sharp drop off after 11-12 khz.
1) The spec sheet shows the RST28F around -4dB at 20kHz on axis, yours appears around -10dB, about -6 dB difference.
+/-3 dB response variations between units are usually considered "normal", and slight variations of angle can increase those differences. Those variations alone could account for the difference shown, without considering your mic response deviations.
2)Most adult hearing response drops off -10 to -30dB at 15kHz, so we don't hear a lack of something we already hardly hear ;^)
Attached Images
File Type: png RST28F -10dB @20kHz.png (277.9 KB, 70 views)
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