(edit: I should have said "I am trying to measure them" in the title, because that's what I meant. There are now measurements posted later on in this thread, and there will be more.)
Much discussed, rarely measured. I've totally stumped myself measuring these, as I'm getting a mystery reflection 2.45ms out in the impulse, exactly the same every time, seemingly regardless of whether the woofer is on a baffle, in a box, in free air, near a boundary, or whatever you like. I am a total beginner at driver measurement, but it's only these woofers giving me this weirdness - not other drivers. If there's anyone out there that wants to compare some graphs here, please speak up! Thanks.
Much discussed, rarely measured. I've totally stumped myself measuring these, as I'm getting a mystery reflection 2.45ms out in the impulse, exactly the same every time, seemingly regardless of whether the woofer is on a baffle, in a box, in free air, near a boundary, or whatever you like. I am a total beginner at driver measurement, but it's only these woofers giving me this weirdness - not other drivers. If there's anyone out there that wants to compare some graphs here, please speak up! Thanks.
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Too funny as I have often thought the same thing.
I have a pair coming but can't help you yet.
So, if you sweep the TD and then change nothing else but the driver the mystery blips gone?
It shows up in either type, or at least I'm 99% sure it does. I will see if I can find that thread.
Those are mine.
Well, I couldn't find the thread you are talking about. To clarify about MLS vs log sweep, I saw the issue in a long log sweep measurement, and then switched to MLS for a bunch of fast measurements trying (and failing) to eliminate the issue. Unless there was some massive coincidence where the log sweep had a normal reflection in the same spot, it is the same for both types of measurement.
Dumptruck,
MLS and sweptsine (or chirp) should show the same as far as real reflections go. But MLS can sometimes show phantom impulses from nonlinear distortions, while log swept sine is immune to that kind of phenomenon (with log swept sine, phantom impulse occur before the real impulse, so they don't get into the result). So if the second impulse shows with swept sine, it is probably real.
It isn't a reflection off your mic stand, is it? The TD15M has a lot of HF output, so it will show impulse peaks more sharply than other big drivers, and its size gives it lots of opportunity to excite nearby objects or surfaces. Look for things that are 14 to 24 inches from your mic or the woofer.
MLS and sweptsine (or chirp) should show the same as far as real reflections go. But MLS can sometimes show phantom impulses from nonlinear distortions, while log swept sine is immune to that kind of phenomenon (with log swept sine, phantom impulse occur before the real impulse, so they don't get into the result). So if the second impulse shows with swept sine, it is probably real.
It isn't a reflection off your mic stand, is it? The TD15M has a lot of HF output, so it will show impulse peaks more sharply than other big drivers, and its size gives it lots of opportunity to excite nearby objects or surfaces. Look for things that are 14 to 24 inches from your mic or the woofer.
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Here is a copy of what I posted on AudioKarma about this:
(minor note: not that it matters, but you may notice the time window on the graph says 2.417ms - that's because I accidentally bumped the start line up a tiny bit before I grabbed the image)
Well I'm just absolutely mystified here. Not exactly the first time in this project, but still... Below, you can see I have marked the two reflections I am trying to figure out. Neither occurs with other drivers. I am assuming them both to be reflections because they introduce a regular ripple to the response right when the gate approaches their peak.
The first, I suspect is cabinet-related. Either baffle diffraction, or a reflection from inside the box, or something. The 2nd is the real puzzle for the moment. Check out the notes of what I just did below. How can this be?? "Near" means about 30", "far" means 1-2m as the location allowed. Everything on-axis.
speaker on floor pointing up, mic near or far
1: 1.7ms
2: 2.45ms
on stand in middle of room facing forward (~halfway between floor and ceiling), mic near or far:
same
woofer in free air on mattress on floor pointing up:
1: gone
2: 2.45ms (same)
woofer in free air on two paint cans above cement pointing up:
1: gone
2: 2.45ms
speaker flat on floor facing forward (mic ~9" above floor), near:
1: would not be able to find in this impulse, new nulls at 625Hz & 2.2kHz, to early to identify by gating
2: 2.45ms
speaker flat on floor facing forward, far:
1: gone
2: 2.45ms
speaker on floor, angled up 20 degrees, ~1m
1. 1.7ms, but distorted by new reflection(s) at almost same time
2. 2.45ms
When I say 2.45ms every time, I mean EXACTLY the same every time.
(minor note: not that it matters, but you may notice the time window on the graph says 2.417ms - that's because I accidentally bumped the start line up a tiny bit before I grabbed the image)
Well I'm just absolutely mystified here. Not exactly the first time in this project, but still... Below, you can see I have marked the two reflections I am trying to figure out. Neither occurs with other drivers. I am assuming them both to be reflections because they introduce a regular ripple to the response right when the gate approaches their peak.
The first, I suspect is cabinet-related. Either baffle diffraction, or a reflection from inside the box, or something. The 2nd is the real puzzle for the moment. Check out the notes of what I just did below. How can this be?? "Near" means about 30", "far" means 1-2m as the location allowed. Everything on-axis.
speaker on floor pointing up, mic near or far
1: 1.7ms
2: 2.45ms
on stand in middle of room facing forward (~halfway between floor and ceiling), mic near or far:
same
woofer in free air on mattress on floor pointing up:
1: gone
2: 2.45ms (same)
woofer in free air on two paint cans above cement pointing up:
1: gone
2: 2.45ms
speaker flat on floor facing forward (mic ~9" above floor), near:
1: would not be able to find in this impulse, new nulls at 625Hz & 2.2kHz, to early to identify by gating
2: 2.45ms
speaker flat on floor facing forward, far:
1: gone
2: 2.45ms
speaker on floor, angled up 20 degrees, ~1m
1. 1.7ms, but distorted by new reflection(s) at almost same time
2. 2.45ms
When I say 2.45ms every time, I mean EXACTLY the same every time.
Attachments
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sorry! i wasn't attentive enough. this is not the one that
dumptruck,
you're not the first individual that got puzzled by this wiggle at 2.5ms...
... look here :
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-691.html#post2258879 (Gary Dahl describing the phenomen)
After some long and interesting talk with much speculating of what it might be (I was a top speculator there and erred big time), "John.K" and and "Few" arrived at this conclusion of what is the most likely root cause :
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-176.html#post2265030 (impulse response)
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-704.html#post2265073 (frequency response and explanation).
you're not the first individual that got puzzled by this wiggle at 2.5ms...
... look here :
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-691.html#post2258879 (Gary Dahl describing the phenomen)
After some long and interesting talk with much speculating of what it might be (I was a top speculator there and erred big time
), "John.K" and and "Few" arrived at this conclusion of what is the most likely root cause :http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-176.html#post2265030 (impulse response)
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-704.html#post2265073 (frequency response and explanation).
Okay, done reading. Anybody have thoughts on John K's conclusion (in what seems to be the most definitive post on this in the thread) on just crossing over well below this breakup? I kind sorta planned on 1.4k+... Do I see what living with it is like, try to filter it...? http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-706.html#post2266386
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