Well then, will someone put up the high frequency boost vs microphone diameter from the B&K handbook or some equivalent source? Then we can discuss microphone diameter vs resonant frequency (damped or over-damped) and the on-axis vs off-axis response. This is usually what the real calibration mikes are derived from.
The cheap microphones may work on a different set of principles, BUT they still have to be compared to the response of a calibration mike from the same source. The only 'saving' principle that I see in the cheap 'Panasonic' mikes is that: Once calibrated against an accurate microphone, the high frequency error can be put into the computer to force the mike to be relatively accurate. There are a number of small companies (I would presume) that offer this service, already. Why completely cheap out? They are already set up to do this.
I presume, Scott, that you want to make a cheap spark source that is reliable enough that it can be used directly to 'calibrate' one of these cheap microphones. Please inform me if I get you wrong.
The cheap microphones may work on a different set of principles, BUT they still have to be compared to the response of a calibration mike from the same source. The only 'saving' principle that I see in the cheap 'Panasonic' mikes is that: Once calibrated against an accurate microphone, the high frequency error can be put into the computer to force the mike to be relatively accurate. There are a number of small companies (I would presume) that offer this service, already. Why completely cheap out? They are already set up to do this.
I presume, Scott, that you want to make a cheap spark source that is reliable enough that it can be used directly to 'calibrate' one of these cheap microphones. Please inform me if I get you wrong.
That's right, $10 and your sound card and you might build something and do this stuff hands on. If you are not interested pretty easy to ignore.
Yes, I have a 1" B&K mike that I designed the electronics for, about 40 years ago.
It was separately 'calibrated' by B&K some years ago, and was one of the most accurate 1" mikes that they ever tested, so they told me. We used this microphone to test every SPICA 60 loudspeaker in my office with an FFT, years ago.
I have two 1/2" ACO capsules that I have not attached electronics to. Anybody have a spare 2619 mike preamp? I'm getting too old to make another custom preamp, myself.
I have not used the Panasonic mike capsules for serious work for obvious reasons, but I am pretty sure that Brian Cheney of VMPS uses one, today, of course calibrated with a standard calibration mike.
Well, keep on with the project, Scott, but it is not that easy for me to do it, as I do not use a standard computer with extra sound card inputs.
It was separately 'calibrated' by B&K some years ago, and was one of the most accurate 1" mikes that they ever tested, so they told me. We used this microphone to test every SPICA 60 loudspeaker in my office with an FFT, years ago.
I have two 1/2" ACO capsules that I have not attached electronics to. Anybody have a spare 2619 mike preamp? I'm getting too old to make another custom preamp, myself.
I have not used the Panasonic mike capsules for serious work for obvious reasons, but I am pretty sure that Brian Cheney of VMPS uses one, today, of course calibrated with a standard calibration mike.
Well, keep on with the project, Scott, but it is not that easy for me to do it, as I do not use a standard computer with extra sound card inputs.
I will scan the Data of my 1/2" and 1" B&Ks. I also have a decoded Microtech Gefell 1/2" up to 100kHz. 90 pages DIN A4. They are calibrated using a capacitive method. Important is also to calculate out the grill. The Microtech is particular bad being tiny holed. The B&K grills are somewhat more open slots. I asked the Microtech designer about that and he said that they did not want to copy the B&K visual design. The B&K are actually based on HP capsules and they are based on really old Western Electric as far as i know so nothing new under the sun. Self noise is higher in the smaller 1/2" capsules.
It is pretty standard situation to use a calibrated microphone for measuring purposes - at least I would hope. And it is also easy to measure change in speaker frequency response when we drive it through series resistor, or by a current drive. And to measure step response after current/negative impedance drive - this is especially interesting. I recommend to those who support current drive or negative impedance drive to measure speaker responses under such conditions.
I found that Alnico magnets help a lot in sound. I found out by measuring distortion in the CURRENT that goes back to the amplifier ( with Klippel that has a current sensor ) that this current was much less distorted then in the same driver build with a Neodymium magnet. The distortion in the VOLTAGE was equally low. That is so because i used a conventional amp with high damping factor. That is a voltage source so effectively short circuiting the speaker. By the way a huge damping factor is not of much benefit because there is still the voice coil impedance. As an experiment take a woofer not connected and tab the cone. You hear a resonant sound.
Then short circuit the driver and tab it again. It sounds better damped but you are not able to block the movement totally. There is still the resistance of the voice coil in series.
Then short circuit the driver and tab it again. It sounds better damped but you are not able to block the movement totally. There is still the resistance of the voice coil in series.
All you need is an external USB or firewire sound module for your mac, easy to fit and use. Some people reckon the firewire is a better interface as it requires less of the CPU time to manage the data transfer.
Are you comparing otherwise identical speakers here? are the running the same pole pieces etc? I am curious as to why they would be different.
I just measured a fractured piece of uncoated neodymium, by just putting the two tips of my voltmeter over a 1 cm stretch on the two fractured sides (essentially measuring through the core of the material). It is a good conductor, since I measure 0 Ohms. So, there must be another explanation.
vac
Earthworks uses selected calibrated Panasonic capsules for their measurement microphones. They are good enough for most purposes. They do vary a bit and I find they have higher distortion than the measurement mikes, but still lower than most speakers, by a lot.
I have the HP 1" and 1/2" mikes and preamps. I fine the HP preamps have significantly lower distortion than the B&K's. The HP is a really simple design, the B&K much more complex. I think the WE 640AA was copied by B&K before HP went near the sound measurement business, something they exited in only a few years.
Obsession with primary reference accuracy isn't too useful for audiophilia since its very hard to get better than 1 dB repeatability on a careful setup. Getting a sense for response, distortion, off axis response is more a relative issue so knowing that the mike is pretty flat is important. However that is 1% of the battle and and knowing what to do with your data is the other 99%.
John, do you have a power supply for the preamps? What do you want to do with the mikes once they are running?
I have the HP 1" and 1/2" mikes and preamps. I fine the HP preamps have significantly lower distortion than the B&K's. The HP is a really simple design, the B&K much more complex. I think the WE 640AA was copied by B&K before HP went near the sound measurement business, something they exited in only a few years.
Obsession with primary reference accuracy isn't too useful for audiophilia since its very hard to get better than 1 dB repeatability on a careful setup. Getting a sense for response, distortion, off axis response is more a relative issue so knowing that the mike is pretty flat is important. However that is 1% of the battle and and knowing what to do with your data is the other 99%.
John, do you have a power supply for the preamps? What do you want to do with the mikes once they are running?
I am using the Microtech preamp that is quite good. I also have an old B&K tube preamp but i do not use it any more. I agree : Praxis is fantastic and the Girardin mic is just fine for most of my work. Sure, it distorts a bit more then the real condensers and yes, speakers distort more then a Panasonic capsule. What they have is some temperature dependence. In the Microtech amp is a heater supply that keeps the MIC warm.
Fully agree with that. Anyways, measuring environment outside an anechoic room is way dirtier than the deviations of a simple Behringer. I understand you may need highly calibrated microphones outside the dead room in professional PA situations to measure SPL to stay just within the limits of the applicable codes. However, for loudspeaker development or adjustment, a Panasonic capsule microphone with a calibration file for FR will do just fine in my experience. As far as distortion measurements (w/o noise) are concerned: it gives enough real life guidance, and more precise measurements can make the DUT only better (on paper).
vac
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Yes, but if to connect the same speaker to the amp with negative resistance and knock it is like you are knocking a concrete wall.
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