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Multi-Way Conventional loudspeakers with crossovers

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Old 2nd July 2009, 01:12 AM   #51
CLS is offline CLS  Taiwan
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How about its effect on dispersion in higher range (in real life)? Or, the physical size of the phase plug is too small for their ranges?

For reference, I found these drivers very interesting (,too):

This comes with a mesh dust cap:
http://www.supravox.fr/anglais/mesures/mes285GMF1.htm

This comes with a phase plug:
http://www.supravox.fr/anglais/mesures/mes285_20001.htm


To my eyes, the one with mesh dust cap has a dip at 1.7-1.8kHz or so (on and off axis), but can't comment it's exactly the effect of cap/plug....
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Old 2nd July 2009, 03:02 AM   #52
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Update to the site:

Removed the THD values from the spectrum analyzer pics so they didn't cause confusion. Removed the THD scale from the HD sweep because it was the wrong scale and I like dB scales better. Added the Impulse Response to the frequency response pages. This is the IR of the 1m on axis measurement. These are NOT as intuitive to read as I once thought. If you don't understand the subtleties of what an IR shows don't even bother looking at these. These are extremely difficult to standardize so they are directly comparable to each other. So beware. I also started adding some compression driver info as I just started the horn testing.
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Old 2nd July 2009, 07:09 AM   #53
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Just copying my post over from AVS as well as it is general info.

The impulse response is another tool,along with the impedance curve and frequency response, that you can use to get a general idea of what is going on in a driver. As an example of a driver that has some obvious things, look at the GPA414. In the impedance curve you see a couple blips. One at about 170hz or so, a small one at about 600hz, then another series of blips starting about 1500hz. You can look at those same regions in the nearfield response and notice dips or peaks at the corresponding frequencies. This indicates that there are some kind of resonance issues going on at those points. Typically you'll have a cone resonance, surround resonance, spider resonance and dustcap resonance all to address.

The impulse response then can tell you how significant the resonances may be. Looking at the 414 IR, you can see the 2 initial larger peaks, followed by a quick decay, and then the impulse actually increases in magnitude later on. This is indicating that some "stored energy" for lack of better term is being released further on.

Initially a thought would be that this kind of impulse in a cabinet means a reflection off a back surface in the box. That should however show in any drivers measured in the same conditions. My guess which is still somewhat a shot in the dark without seeing a CSD plot would be this. Two resonances that start somewhat out of phase from each other and at first somewhat cancel. One resonance decays faster than the other, allowing the second to increase in magnitude slightly further on, leading to the increase in the impulse. An example of something that could happen this way would be a dustcap and spider which have similar diameters, each having a resonance, but with very different damping.

Had you thought of posting CSD plots? They should be easy to generate if you have an impulse response.

John
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Old 2nd July 2009, 01:36 PM   #54
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Quote:
Originally posted by CLS
How about its effect on dispersion in higher range (in real life)? Or, the physical size of the phase plug is too small for their ranges?

For reference, I found these drivers very interesting (,too):

This comes with a mesh dust cap:
http://www.supravox.fr/anglais/mesures/mes285GMF1.htm

This comes with a phase plug:
http://www.supravox.fr/anglais/mesures/mes285_20001.htm


To my eyes, the one with mesh dust cap has a dip at 1.7-1.8kHz or so (on and off axis), but can't comment it's exactly the effect of cap/plug....


We found a problem with the plug on the Apollo driver as the plug from the TD became too short on that motor. It caused IM distortion in the midrange that you could hear instantly. Hence the longer johnny "Johnny Holmes" plug was created and problem solved.

A mesh dustcap will become a mild radiating surface so there will be some negative change in the midrange. How much and how significant is hard to say without trying it.
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Old 2nd July 2009, 01:48 PM   #55
JoshK is offline JoshK  Canada
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Brandon,

One possible typo on your awesome drivervault site. You have, listed in the tweeter section, the B&C DE12 with mylar diaphragm. Do you mean DE10? The DE10 is mylar, the DE12 is a titanium diaphragm afaik.

I was a bit surprised by the impedance of the DE1*. It doesn't show the dual hump like the others. Very interesting.
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Old 2nd July 2009, 03:34 PM   #56
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I pulled the IR because they are just causing confusion. I did make an attempt at one point adjust the output level for the response measurements so that all the drivers would about the same level in their midband. I'm going to look at these to see if they would be better candidates to post.

Quote:
Originally posted by John_E_Janowitz
Had you thought of posting CSD plots? They should be easy to generate if you have an impulse response.

John
You know I used to, and I probably will for these. No rush as I have the IR so I can do it anytime. My only problem as these are often as misleading as comparing IR's. So I dunno...I have to think about. There are many factors which MUST be standardized (at least in my mind) before any two IR really comparable, especially when looking for signs of resonances and such.


Quote:
Originally posted by JoshK
Brandon,

One possible typo on your awesome drivervault site. You have, listed in the tweeter section, the B&C DE12 with mylar diaphragm. Do you mean DE10? The DE10 is mylar, the DE12 is a titanium diaphragm afaik.

I was a bit surprised by the impedance of the DE1*. It doesn't show the dual hump like the others. Very interesting.
B&C makes both versions. The mylar version is available at both usspeaker and prosoundservice. I picked the mylar for a project I'm doing that needs to behave nicely on the low end as I'll be running it a lower than the spec'ed crossover frequency.

Actually I was surprised that the others had two peaks. In my VERY simple understanding of CD's one hump is the drivers resonance and the other is the horn resonance, which is almost always attached for the manufacturers' impedance plot. Someone more knowledgeable will hopefully chime in on that.
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Old 2nd July 2009, 05:06 PM   #57
JoshK is offline JoshK  Canada
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Thanks for the clarification. Its good to know.
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Old 4th July 2009, 03:23 AM   #58
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Results of teh horns going up now. I have ALOT more data to post but thought I'd give you taste. I think I have a couple good candidates for driver comparisons so for short time I'm going to keep testing IF some helpful members would send the following: Beyma CP380M, Beyma CP385ND, BMS 4550, or the top 18 Sound CD's. These tests will include distortion.
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Old 4th July 2009, 04:25 AM   #59
CLS is offline CLS  Taiwan
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Quote:
Originally posted by nickmckinney




We found a problem with the plug on the Apollo driver as the plug from the TD became too short on that motor. It caused IM distortion in the midrange that you could hear instantly. Hence the longer johnny "Johnny Holmes" plug was created and problem solved.
...


Alas!

I got some custombuilt phase plugs for my 18" woofers:

Click the image to open in full size.

Click the image to open in full size.

I've not yet tested them.

The de-cap'ed woofers sounded fine without the plugs, just uglier. It'll be a disaster if the plugs make them sound worse
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Old 4th July 2009, 07:08 PM   #60
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CSD and IR data added for woofers and horns. Careful with interpreting the IR. People may be tempted to see a bit more wiggle in the tail and say that is a sign of stored energy or it's ringing. It may just have higher low frequency response. The IR oscillates and the amplitude of the peaks/dips is mostly an indication of the SPL at the frequency that coincides with the length of time in the scale. What I look for is narrow peaks/dips that are out of place, or out of "rhythm"
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