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

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  • Chris Roemer
    replied
    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.

    Leave a comment:


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

    So,

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

    Leave a comment:


  • Chris Roemer
    replied
    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.

    Leave a comment:


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

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

    Leave a comment:


  • Chris Roemer
    replied
    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.

    Leave a comment:


  • crunchhardtack
    replied
    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

    Leave a comment:


  • crunchhardtack
    replied
    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.

    Leave a comment:


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

    sure

    Leave a comment:


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

    Salutations fellow animals,

    So I ran a 25 hz sine wave at near xmax for about 3hrs until it was bedtime for my wife.
    Do you guys think that was enough time to be ready for some DATS testing?

    Here is my break in rig. Click image for larger version

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    Cheers,
    Matthew

    Leave a comment:


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

    Very true about the Al Chris,

    But I'm more worried about pushing on them out of alignment.

    If I were to break them in with a sine wave at near xmax, do you think I should mount them on something to keep them from dancing around? With neo magnets, they're pretty light. I have plenty of cheap thin board lying around.

    Thanks,
    Matthew

    Leave a comment:


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

    These have Al cones, so your fingers won't go through.
    Also, in free air (no box) they'll hardly make a sound. You can even try 20Hz, which is below Fs. Might not hear a thing.

    Leave a comment:


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

    Interesting Method Chris,

    Now that's an exercise routine with which I'm not familiar. Is there a workout video for this? On a serious note though, I wonder if I could make something like a bellows to exercise them with nice even air pressure changes, without having to risk me pushing my thumbs through the cones. Operating it could be good exercise for me too.

    I think my wife and our cat would both prefer your quieter method or something similar over me playing a sine wave through eight drivers at once for hours on end.

    Leave a comment:


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

    I usually break 'em in by hand, i.e. you (gently - making sure NOT to push or load them "off center") push them close to Xmax w/your fingers. In - out, in - out, get it? Basically, what you're doing is exercising the spider (letting whatever "coating" or set, or whatnot) putting tiny "cracks" in it, like breaking in a brand new pair of shoes.

    Some people play a sine wave near Fs, driven to near Xmax, for hours.

    Leave a comment:


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

    Hello folks,

    This evening I noticed mattp's Measured T/S Parameter Thread Sticky http://techtalk.parts-express.com/sh...-Thread-Sticky

    Here are the results from the sticky: Dayton Audio ND90-8 3-1/2" Aluminum Cone Full-Range Driver 8 ohm (290-210)
    Re: 7.38 ohms, Fs: 101.6 Hz, Qts: .9255, Qes: 1.078, Qms: 6.525, Le (1kHz): 0.517 mH, Vas: .0381 cuft, Effective Diameter: 2.5"

    His measurements are quite different than PE's T/S Parameters on the product listing page, and I have no idea if the drivers used in either test were broken in. So, I guess I'll be breaking mine in soon, and I'm thinking of breaking in all eight at once.

    Any wisdom from you guys as far as what kind of "stretchy exercise waves" to subject this octet to, and for how long would be great.

    Thanks,
    Matthew

    Leave a comment:


  • Mayhem13
    replied
    Re: Opinions on driver arrangement of four ND90-8s plus tweeter please.

    http://www.dnaudio.com/DNA-Sequence-Speakers.html

    Leave a comment:

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