Greetings all,
I have rebuild my experimental low frequency enclosure to allow rear driver mounting, and I would like to measure it. However, we are still snowed in, so I was reading on the near-field measurement as proposed by DB Keele Jr in his 1974 paper.
However, my driver ALTEC 515 has a hole, protected by wire mesh, in the middle of the dust-cup, so I was wondering if the method will work. Anybody has an experience?
Kindest regards,
M
I have rebuild my experimental low frequency enclosure to allow rear driver mounting, and I would like to measure it. However, we are still snowed in, so I was reading on the near-field measurement as proposed by DB Keele Jr in his 1974 paper.
However, my driver ALTEC 515 has a hole, protected by wire mesh, in the middle of the dust-cup, so I was wondering if the method will work. Anybody has an experience?
Kindest regards,
M
Hello;
I don’t know what the effect of the somewhat open dust cap might be. I think we point mic’s at caps since it is an indication of being on center. Near field measurement should work with the mic in close proximity to anywhere on the cone.
It will be interesting to see if you can show the difference of say mid cone verses on center.
Experiment a bit and see what you learn. 🙂
All the best.
Barry.
I don’t know what the effect of the somewhat open dust cap might be. I think we point mic’s at caps since it is an indication of being on center. Near field measurement should work with the mic in close proximity to anywhere on the cone.
It will be interesting to see if you can show the difference of say mid cone verses on center.
Experiment a bit and see what you learn. 🙂
All the best.
Barry.
Hi Barry,
thank you for the reply.
I understand that as long as the driver works in a pistonic regime, the position of the microphone should not matter. But, I could not find any reference regarding determination of the pistonic regime, as it is a function of many variables. Hence my desire to center the microphone on the dust-cup as shown in all the references.
Perhaps I could tape the hole for the measurement?
Kindest regards,
M
thank you for the reply.
I understand that as long as the driver works in a pistonic regime, the position of the microphone should not matter. But, I could not find any reference regarding determination of the pistonic regime, as it is a function of many variables. Hence my desire to center the microphone on the dust-cup as shown in all the references.
Perhaps I could tape the hole for the measurement?
Kindest regards,
M
Hello;
I would not trust tape not to damage the screen or cap and worry that the tape would not stay pistonic. ?
I personally usually point mics and laser position sensors at the dust cap glue joint. It is a very rigid point and an accidental bump may not push the cap in.
I say poke around a bit. See if a measurement at the screen, glue joint and mid point of the cone between the cap and surround show significant differences.
Enjoy. 🙂
Barry.
I would not trust tape not to damage the screen or cap and worry that the tape would not stay pistonic. ?
I personally usually point mics and laser position sensors at the dust cap glue joint. It is a very rigid point and an accidental bump may not push the cap in.
I say poke around a bit. See if a measurement at the screen, glue joint and mid point of the cone between the cap and surround show significant differences.
Enjoy. 🙂
Barry.
Hi Barry,
thank you, that is what I concluded - take measurements at different pints and compare them.
Kindest regards,
M
thank you, that is what I concluded - take measurements at different pints and compare them.
Kindest regards,
M
Not only the first breakup mode makes close range measurements of limited use. It’s also that the distance from any point at the cone to the microphone has to be fairly small compared to the wavelength. If it’s bigger than 1/3d of the WL, you get destructive interference. So with your 15” you are good up till about 700Hz max.