delta compliance measurements

[ctbowman]

So all my projects to date have been measured via delta mass. I think they should be reasonably accurate since I've been able to use tacky stuff on all the cones and have a scale accurate to 1/1000th of a gram. But now I have a paper cone that is definitely not going to be tacky stuff friendly and I'd like to try delta compliance. But before I do I have a few questions.

1) when determining the volume of the enclosure used do you take into account the volume occupied by the driver, and if so how do you figure that out?

2) would any volume work, or would there be an advantage to sizing the enclosure based on rough guestimates? I'm guessing a REASONABLY small enclosure would be best because a large enclosure would approach free air characteristics.

[daryl]

So all my projects to date have been measured via delta mass. I think they should be reasonably accurate since I've been able to use tacky stuff on all the cones and have a scale accurate to 1/1000th of a gram. But now I have a paper cone that is definitely not going to be tacky stuff friendly and I'd like to try delta compliance. But before I do I have a few questions.

1) when determining the volume of the enclosure used do you take into account the volume occupied by the driver, and if so how do you figure that out?

2) would any volume work, or would there be an advantage to sizing the enclosure based on rough guestimates? I'm guessing a REASONABLY small enclosure would be best because a large enclosure would approach free air characteristics.

Yes you want to use 'net' volume so account for driver occupied volume.

Use geometry to calculate the volume of the driver by the dimensions of it's parts.

If you use a dedicated test enclosure for delta compliance you typicly would mount the driver backward and add the volume created by the depth of the cone (a truncated cone).

Smaller volumes work better as they dominate the total compliance of the system where the drivers suspension would dominate with a very large test enclosure.

You want to approxamately double Fs with your test compliance.

[ctbowman]

sorry it took me so long to get back to this. thank you for the response, I like the idea of mounting the driver backwards... makes that problem much more easy to deal with than what I was thinking.

So what your saying is it wouldn't be very easy to get one enclosure to work for many drivers with high accuracy? perhaps I could just build a larger enclosure and then add objects to take up volume until the volume I need is achieved?

[jonpike]

There's always the rice trick... pour rice (or some other clean, dust free, medium sized particle materiel) into the cone till full, then pour out and measure volume.

[ctbowman]

WOW... that's a great idea. You have no idea how much rice I have laying around... no really :P I have a 25# sack, a 10# sack, A 2 quart Jar, and two 2# bags. why so much rice you ask...well my wife and I are rice snobs and have a different kind of rice for just about every dish you can imagine. Thanks for the great idea