Opinions on driver arrangement of four ND90-8s plus tweeter please.

[Chris Roemer]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

sure

[crunchhardtack]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

Thanks Chris,

I'll get onto that Saturday. I'm thinking of testing all eight and averaging them. I'm mostly just curious if there is any major differences between them.

[crunchhardtack]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

Hey Guys,

I have some DATS v2 questions.

When I measure the Vas using the test box method with the driver pointing inward, shouldn't I reverse the polarity on the test leads?

Also, I keep getting the message saying the Fs was increased by less than 50%. I'm already using a .0343 cu ft box which seems petty small to me. Can anyone give me some pointers regarding this?

Thanks,
Matthew

[Chris Roemer]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

I've always used the "added mass" method for Vas. A U.S. "nickel" is so very close to exactly 5.0 grams that any error is negligible. 15g would probably be a good starting point for an ND90. Test lead polarity won't matter.

For added mass, you add enough to try to lower the resonance by at least 50% (I THINK? - might only be 25%?, DATS will tell you). For test box, you try to raise resonance by 50%. You'd just have to keep trying smaller volumes 'til you get there. I've heard of guys using small glass/ceramic jars/containers (w/gaskets) for small drivers.

[crunchhardtack]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

What is the best way to attach the nickel to the cone?

[Chris Roemer]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

I just lay them on there, driver face up, BUT . . . you can't block the vent on the back of the magnet, you've got to put some pressure down on the driver so it doesn't "jump" during the pulse/sweep, and if the nickels "jump" - you'll see it in a "jittery" impedance plot. Sometimes rearranging them (or adding 1 more) can smooth that plot out.

I'd like to see your DATS results: your average, highest/lowest for each parm. Did you say you've got 8 ND90-8s? That's a good sample size.

[crunchhardtack]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

So,

Here's the DATS results for eight ND90-8s

[Chris Roemer]

Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

So . . . IIWM, I'd group BEFG in one box, and ACDH in the other (ave. those groups of 4 (each) and see if you don't end up
w/averages for Qts, Fs, and Vas close to you overall averages).

To ME, it looks like you'll probably end up reaching down into the mid 50s in about a 1/2 cu.ft. vented box.
Funny thing is (just for the BOX MODEL) you should be able to wire those "quad" groups up (on your board) in series/parallel
(8 ohms) and run T/S parms on the group and get Qts near 0.65 or so, and an Fs around 80 - which will verify your F3.
Don't have a good way to measure the Vas of a "quad", but SHOULD end up just a bit under 14 liters.