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Old 4th August 2007, 04:01 PM   #101
ucla88 is offline ucla88  Tahiti
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Danny,

Please post the impulse response and window information. The first measurement appears to suffer from a severe reflection, internal or external. I have to agree with Dave that the measurements, especially the first is of very poor quality. Hard to make much of this.

I would avoid boasting this is industry standard...

I'll comment if I see some hiqh quality measurements. However, short windowed, smoothed, or measurements contaminated with reflections don't have much merit.
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Old 4th August 2007, 04:28 PM   #102
ucla88 is offline ucla88  Tahiti
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I'll throw some very old measurements out for others to look at-mainly because they're already done and sitting on an old website already



Click the image to open in full size.

Which has more stored energy? Duh, trick question. Just different windows...


Another one

Click the image to open in full size.

Which has the most stored energy. Ha, another trick question.


Yet another one

Click the image to open in full size.



Anyway, the point is that some more thought has to go into measurements than you are offering. The impulse, the measurement conditions, the window, in box, out of box, stuffing, etc.

Showing a measurement with a baffle difraction or internal reflection etc is not very helpful. You have to look at the inherent FR/impulse response of the driver and take care to eliminate baffle, box, or other extradriver reflections.

Again, looking at a short windowed 1m measurement in a box and trying to glean the inherent FR/stored energy properties of a driver is fraught with error.
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Old 4th August 2007, 04:41 PM   #103
owdi is offline owdi  United States
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Quote:
Originally posted by Danny
Two 8" woofers. Measured at 1 meter. Both mounted in the same box (9" wide and 14" tall). No smoothing applied.
You have contaminated your measurements by sticking the woofers in a box.

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Old 4th August 2007, 04:53 PM   #104
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Quote:
Please post the impulse response and window information.
Time window is clearly stated on the measurements just like yours is.

Now if I posted the impulse response that would be useful, but the claim was that one can predict the CSD only from the frequency response.

Quote:
The first measurement appears to suffer from a severe reflection, internal or external.
Like trying to predict the CSD from the frequency response, that would be a predictable guess, but not correct.

As I already mentioned, "Both mounted in the same box (9" wide and 14" tall)." They had the same damping material too.

Quote:
I would avoid boasting this is industry standard...
Yet, they are just like yours. You started your time window just before the arrival of the impulse response and gated it right before your first room reflection.

Quote:
I'll comment if I see some hiqh quality measurements. However, short windowed, smoothed, or measurements contaminated with reflections don't have much merit.
They are the same as your measurements (except I used higher resolution. Mine is on a 5db scale, yours is on a 10db scale), same time window, NOT smoothed, and have no reflections other than what can reflect off of a small enclosure (enclosure surface area already stated).

Quote:
Again, looking at a short windowed 1m measurement in a box...
Well it appears that you are using a Clio system since your measurements are posted using a Clio system, so I would think that you'd be able to see the clearly posted time window and know that it is NOT 1ms long. That would be pretty foolish would it not?

Quote:
You have contaminated your measurements by sticking the woofers in a box.
No, not contaminated. Made the same. You are going to eventually use the woofer in a box are you not? How better to measure a woofer than in the box it will be used in?
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Old 4th August 2007, 05:32 PM   #105
ucla88 is offline ucla88  Tahiti
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Quote:
Originally posted by Danny


Time window is clearly stated on the measurements just like yours is.

Now if I posted the impulse response that would be useful, but the claim was that one can predict the CSD only from the frequency response.

Well, the impulse is just the inverse FT of the FR. I tell you what-email me the complete FR data file as an .frd and I'll generate it's corresponding impulse and CSD. It's all there, except for the discrete errors introduced.



Like trying to predict the CSD from the frequency response, that would be a predictable guess, but not correct.

As I already mentioned, "Both mounted in the same box (9" wide and 14" tall)." They had the same damping material too.



Yet, they are just like yours. You started your time window just before the arrival of the impulse response and gated it right before your first room reflection.



They are the same as your measurements (except I used higher resolution. Mine is on a 5db scale, yours is on a 10db scale), same time window, NOT smoothed, and have no reflections other than what can reflect off of a small enclosure (enclosure surface area already stated).

One, scale size is not related to resolution.Two, yes, interesting how processing the same data differently leads to multiple FR curves. This happens for CSD's too...Three, to clarify-none of my graphs are smoothed either


Well it appears that you are using a Clio system since your measurements are posted using a Clio system, so I would think that you'd be able to see the clearly posted time window and know that it is NOT 1ms long. That would be pretty foolish would it not?

Used to use Clio. Moved on to a more poweful and flexible system, Praxis. Nothing wrong with Clio though.

Also 1m is 1 meter. 1ms would be 1 millisecond.



No, not contaminated. Made the same. You are going to eventually use the woofer in a box are you not? How better to measure a woofer than in the box it will be used in?

Well, no. Using a box will cause internal reflections. these will contaminate the impulse, csd, and FR. It would be better to use a large baffle and look at the driver in an open back configuration. After all, the question to be answered is "what is the inherent FR, er, I mean, the inherent energy storage of the driver." You may wish to look at the energy storage signature of your baffle or reflection, but these are different phenomena and must be sorted correctly in one's mind and not dumped into the same graph and all labelled "energy storage." Especially since an FR anomoly from diffraction may disappear off axis and not be in the power response

my comments in italics
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Old 4th August 2007, 08:10 PM   #106
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PS

I missed the part about two woofers. Now it gets evey more complex. The FR curve also depends on baffle geometry and electrical hookup. Of course, so does the CSD, since they're both generated from the same impulse. However, it's hard to look at a driver's inherent linearity with two of them on a baffle...
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Old 5th August 2007, 02:21 AM   #107
dlr is offline dlr  United States
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Default I think this is a misinterpretation

Quote:
Originally posted by ucla88
PS

I missed the part about two woofers. Now it gets evey more complex. The FR curve also depends on baffle geometry and electrical hookup. Of course, so does the CSD, since they're both generated from the same impulse. However, it's hard to look at a driver's inherent linearity with two of them on a baffle...
I agree with all of your main post. I think Danny's point here, though, was successive measurements with two drivers, each having been swapped into the same box for each individual measurement.

Unless my guess is wrong.

Dave
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Old 5th August 2007, 05:32 AM   #108
owdi is offline owdi  United States
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Quote:
Originally posted by Danny
No, not contaminated. Made the same. You are going to eventually use the woofer in a box are you not? How better to measure a woofer than in the box it will be used in?
So why take gated measurements when comparing woofers. They are both in the same room, right? No need to use calibrated microphones either, since they will affect both woofers the same.

If the measurement would be used to design a crossover, I agree you should take in-box measurements. I do not agree with you if the measurement is used to compare drivers.

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Old 6th August 2007, 05:49 PM   #109
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Man, I am amazed. Even when I pick two 8" woofers that are completely different and have obvious stored energy differences you guys are still afraid to step up to the plate.

All of you guys that stated you could read all the CSD info just from a frequency response were all no shows.

I will agree that those with experience will get a good idea of the stored energy problems by looking at a frequency response and the impulse response. You can see an area of break up and have a really good idea of the stored energy that might be there.

Dave, Mark, Pete, and myself can easily see this, but not everyone.

However, we can't see how much stored energy, how long, or how bad until we look at the CSD.

Further more, to suggest to a bunch of hobbyist that CSD info is of no value is ridiculous and misleading.

The following will easily illustrate what I have just stated.

Let's look at those two 8" woofers again. Here is the first one:

Click the image to open in full size.

This was an Alpha A from Eminence. It is a fairly light weight paper cone with corrugated cloth suspension. Here is the spectral decay:

Click the image to open in full size.

In order to keep its output level close to the other woofer tested I only sent it about 1/2 of a watt.

I wish I would have saved this file but I did not. The impulse response looked very typical. I started the time window just before the arrival of the signal. It peaked and settled in about 3ms of total time. Then the impulse response was a flat line until the first room reflections that arrived at about 8ms. So I gated it out leaving a clean 5ms range.

Here is the second 8" woofers frequency response.

Click the image to open in full size.

Sure, there are some serious clues there aren't there? It even has so much mass that it will hardly even play past the peak at 1kHz. What we can't see though is how much stored energy is there. How bad is it?

Let's see:

Click the image to open in full size.

Not too good huh?

Now keep in mind that this woofer was played to nearly the same level as the other woofer. I think someone said that if two woofers are playing the same output level they will have the same stored energy. Well that is not true at all.

To play at this level this woofer had so much stored energy that the 5ms time window isn't even near long enough to catch it all.

Looking at its impulse response is like looking at one long curvy wave that just keeps on going. You couldn't even tell where the first room reflections were because the stored energy went right past it.

This woofer was also a paper cone woofer but is only used as a sub woofer. To get it to play to the same output level as the Alpha 8 with only 1/2 of a watt on it, this one needed the gain on the amp cranked up to a 100 watt level.

Yep, it needed 100 watts of input to give it the same output.

Differences in stored energy even below 1khz was tremendous.

And for those who will want to claim that the CSD is not accurate below 1kHz can take a reality check here. It may not be completely accurate but who cares. +/-1/4 or 1/2 of a db is nothing. Differences are in such magnitude that we easily see them.

I couldn't have pick two drivers more different, and still no one would comment. Amazing...
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Old 6th August 2007, 06:06 PM   #110
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Quote:
So why take gated measurements when comparing woofers. They are both in the same room, right?
Oh yea, if I would have not gated them then the room reflections would have completely dominate the CSD. It would be one big mess that you couldn't even read anything from.
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