When you measure SPL..How do you recognise the SPL produced by break-up and absorption. and How does this measure up with the perceived sound..??
What you see is exactly what you get.
Let's look at on-axis response. When the response SPL drops the driver is producing less sound. When it rises it gets louder.
Many tend to ignore that portion of the response curve because it is above the crossover point and thus suppressed by the Q of the filter.
However, that roller coaster of response is still summed (at least to some degree) with the response from the mid or tweeter and those ripples impact the aggregate of the loudspeaker response curve.
You can fight that effect by either crossing over lower and moving that zone further down in SPL or use a higher order crossover with a steeper slope.
I probably have babbled on too much now. 🙂
In the Klippel scanner software, you can look at various components effects and at various angles.
Normally this kind of data relates with how the drivers are designed. I doubt you will get data from any manufacturer. The only way you will get data is to send drivers for klippel scanning and pay for the work and data. I do recall there are also some scanned examples downloadable from the Klippel site. But you really need to have your mind set on driver design. I've benefited from the data, and have verified some design concepts that I tried.
FEM analysis does not seem to show the flexure time sequence correctly, so the usefulness of such data is limited.
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Ha Ha! More great information. Thanks Soongsc!
http://www.klippel.de/download/bin/AN31-Cone Vibration and Radiation diagnostics.pdf
I've got to put this to use and see for myself in real life.
Dan
http://www.klippel.de/download/bin/AN31-Cone Vibration and Radiation diagnostics.pdf
I've got to put this to use and see for myself in real life.
Dan
There are also two AES papers on the "distributed parameters" he talks about which is also very informative.
Not nearly so fancy, any one there ever use a strobe-attack to view driver motion? Very much like a mechanical version of an oscilloscope. A variable frame rate video camera can also be used. And the cheapest and home made... is the very bright LEDs available now run from a simple trigger circuit which a delay/phase control to stop motion of the cone in any position. Maybe this will help?
Every cycle is not needed for viewing at such high frequency. Even 1 frame every 20 cycles is way more than plenty. A "viewing" rate of 20 per second is enough to prevent flicker effect and that equals 20Hz. At those high frequencies more expensive hardware is needed for the full effect. For midrange and woofers low cost items work fine. Also, the LED thing works to about 100kHz. So yes there are many ways to go above 20kHz and "freeze" the motion.
Of course lighting conditions must be considered for the various methods. Many driver problems are so HUGE they are easily visible. Stobotac is the first thing I do to a new driver before any other testing.
As a note, for looking at tweeters magnification is a handy thing. So is a graticule for mids and woofers to measure with. My Stobotac goes to 240Hz, 14,400 RPM on the dial.
Of course lighting conditions must be considered for the various methods. Many driver problems are so HUGE they are easily visible. Stobotac is the first thing I do to a new driver before any other testing.
As a note, for looking at tweeters magnification is a handy thing. So is a graticule for mids and woofers to measure with. My Stobotac goes to 240Hz, 14,400 RPM on the dial.
Different problems require different methods to investigate. Probably your focus is in the lower frequencies, which is fine. I find the the higher frequency performance also has a pronounced impact on sound reproduction.
The Klippel scanning system does a splendid job in decoupling components and reproducing the timed sequence of diaphragm flexture, which is extremely useful to understanding problems. One thing I wish it could to more is to simulate the wave propogation based in diaphragm motion and flexture.
The Klippel scanning system does a splendid job in decoupling components and reproducing the timed sequence of diaphragm flexture, which is extremely useful to understanding problems. One thing I wish it could to more is to simulate the wave propogation based in diaphragm motion and flexture.
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SUM, you wouldn't be able to post a video of the strobe on youtube would ya? That would be a fun video!
Now onto this matter of rim resonance. I've had a few really cheap speakers in the man cave just hanging out to test a few amplifiers I've been working on. These speakers sound terrible and I've never bothered to graph them before. I decided these could be used for further experimentation. Here's the effects of one round of surround doping on the polar response:
Driver "A" No Dope
Driver "A" Dope "A"
Driver "B" No Dope
Driver "B" After Dope "B"
Measurement conditions were unchanged for all these graphs.
Dan
Now onto this matter of rim resonance. I've had a few really cheap speakers in the man cave just hanging out to test a few amplifiers I've been working on. These speakers sound terrible and I've never bothered to graph them before. I decided these could be used for further experimentation. Here's the effects of one round of surround doping on the polar response:
Driver "A" No Dope
Driver "A" Dope "A"
Driver "B" No Dope
Driver "B" After Dope "B"
Measurement conditions were unchanged for all these graphs.
Dan
Before and after averaged response:
"A" before:
"A" after:
"B"fore:
"B" after
All impulses before and after:
Driver "A" before
Driver "A" after
"B"fore
"B" after
OK, you get the point,
Dan
"A" before:
"A" after:
"B"fore:
"B" after
All impulses before and after:
Driver "A" before
Driver "A" after
"B"fore
"B" after
OK, you get the point,
Dan
You would have to do the same speaker type with both compounds to judge that. The point is that it always makes an improvement, but once the speaker starts breaking up nothing can bring it back from this abiss.
Soongsc is correct to say the Klippel system does a great job.
It is pretty straight forward to use translational mode analysis and velocity of propagation through cone/diaphragm to know some about the original signal. Then comes the reflections from the edge which is were most of the problems come in.
If you do not mind a few mirrors it is completely possible to set up a 3D imaging system and see the interference patterns between the static (no signal) and dynamic condition. I have not done this because there are easier ways.
Looking at the radiation pattern for higher frequency devises tells the story of radiator motion pretty clearly. Believe the book was called "How to photograph sound" and have done this a lot. Very easy and very little equipment needed. Works as high in frequency as the microphone will go.
It is pretty straight forward to use translational mode analysis and velocity of propagation through cone/diaphragm to know some about the original signal. Then comes the reflections from the edge which is were most of the problems come in.
If you do not mind a few mirrors it is completely possible to set up a 3D imaging system and see the interference patterns between the static (no signal) and dynamic condition. I have not done this because there are easier ways.
Looking at the radiation pattern for higher frequency devises tells the story of radiator motion pretty clearly. Believe the book was called "How to photograph sound" and have done this a lot. Very easy and very little equipment needed. Works as high in frequency as the microphone will go.
Do you have any suggestions on how to coat the same driver with 2 different compounds? I wanted to do that originally, but couldn't remove the first compound w/o destroying the driver. I did use the exact same amount by volume on both drivers. It does seem that one is certainly not radically better than the other though "B" reduces the amplitude of the initial break up more and, is much easier to apply and looks like what you see on most cloth surrounds.
One interesting thing to me is just how bad a speaker can perform if no care goes into its design. I would have thought these graphs impossibly bad, even by these speakers, just 2 days ago. I've never seen this ugly of impulse or response graph. Usable bandwidth is about an octave.😱 And they sure can't put out much volume there. At low volumes, these things sound strained, at higher volumes all sort of interesting artifacts appear that I have no vocabulary to explain. If you are displeased with you current sound, remember it can easily be worse!
Dan
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I'll keep this more brief. Here's one driver after a second round of doping:
less one round:
no dope:
Now we've got about a 6 dB amplitude reduction in the rim resonance. None too shabby.
Dan
less one round:
no dope:
Now we've got about a 6 dB amplitude reduction in the rim resonance. None too shabby.
Dan
OK, here's the other as well:
2nd round of doping:
1st round of doping:
No dope:
More like a 3 dB difference here.
Dan
2nd round of doping:
1st round of doping:
No dope:
More like a 3 dB difference here.
Dan
dantheman- Would love to post video but... frame rate of youtube video is either about 15 or 30 per second I believe. This would really limit the frequencies to multiples near those values. On the next driver will see if anything interesting can be seen around those values.
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