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Bass Reflex with Vb = Vas and Fb = Fc = Fs

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  • Chris Roemer
    replied
    If you run a box model (WinISD linearteam.org ) on a driver with Qts = .40, Fs = 30, and Vas =1cf (let's say those are its "specs"), you'll end up w/near identical results IF your driver measures: Qts = .50, Fs = 40, and Vas = 0.62cf. (I say these are "complimentary")

    Typically, a driver WILL have a higher (than spec) Fs and Qts before break-in (and a lower Vas, meaning it's stiffer - or "stiff" yet).
    As the suspension loosens up (glue breaks, and stuff), Vas rises, Fs comes down, and Qts also drops some.

    That doesn't mean that your particular drivers will EVER end up at the factory specs. Thing is, Dayton's drivers seem to run closer to pub. specs than many other brands.
    The specs you get off your WT/DATS ARE what your drivers are. (Fs and the "Q"s are EASILY and accurately calc'd by those testers, Vas CAN be off depending on your testing experience and how careful you are.) How low a driver can reach is determined strictly by Qts and Fs, whereas box size is determined by Qts and Vas.

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  • hitsware2
    replied
    Fs and Qts high .
    The attributes most would like low as possible @ a given price .
    I corresponded with P.E. tech , and he said everything was ~ within 20 %
    " industry standard " ...... Which is true .
    Maybe Fs real ~ 1.2 Fs spec and Qts real ~ 1.2 * Qts spec would be ' sort of ' close ?

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  • Chris Roemer
    replied
    All your Fses seem high.
    Your other specs on the DS90 look pretty close.
    Dayton's "initial" specs for the ND65-8 were: 81, 0.62, 0.02cf.
    Yours have something serious going on there; Fs 40Hz too high, Qts pretty close, and your Vas is HUGE (I'd re-visit those measurements).
    Even though it's puny, it's still got a rear vent. Be sure not to block it when you measure.

    Your DSA90-8 specs have Fs about 10Hz too high (it should come down over time). Your Q is almost 0.10 too high, but that's complimentary.
    Someone else here on TT got this for their ND90-8: 84Hz, 0.76, 0.04cf. (I try to break in the suspension by gently pushing it back and forth to Xmax - by hand.) Your Fs will probably drop a bit w/break-in.

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  • hitsware2
    replied
    Measured WT-3

    .......................Fs ( Hz )........Qts.........Vas ( cu ft )

    DS90-8..........98 ................0.49...........0.04
    ND65-8........118 .................0.66..........0.61
    DMA58-4.....182.................0.55...........0.08
    DSA90-8.......76..................0.45...........0.07
    ND90-8.........98..................0.73...........0.04

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  • craigk
    replied
    Improper measuring techniques can contribute to inaccurate t/s parameters. A little driver break in doesn't hurt anything either.

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  • Chris Roemer
    replied
    DATS and WT3 are basically the same.

    What driver did you measure? What specs didn't match. A DATS doesn't lie (I didn't say "never" lies).
    All the T/S measured parms are nearly foolproof w/the exception of Vas which can be prone to operator error.

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  • hitsware2
    replied
    > A DATS will spit out (basically) the same values that Dayton specs?

    I sincerely do not want to be contentious , but that has not been my experience .
    ( WT-3 anyways .... Just got the new DATS , possibly that will read closer ? )

    > What's your intent?

    desktop radial

    Using 4 " plastic pipe as cabinet , I want full range down to ~ 100 Hz .
    Pipe short enough to set on end on desktop .
    Preferably driver basket open enough to listen from rear .

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  • Chris Roemer
    replied
    What's your intent? Just as a mid? A full-range that you're using w/a sub? Why a 3" that only goes to 100Hz? Why are you targeting a certain Qts value?
    Last time I checked, Tang Band's W3-881SJF (#264-911 ) had an Fs of 100 and a Qts of 0.39.
    It ALSO is 8ohm, thermally rated at 15wRMS, only has a 2.5mm Xmax (the biggest limitation to using small drivers for "full range" - unless you don't like bass at all), and can do 115Hz in a vented box that's 0.05cf. (I'd prefer an ND65 in a box that small.)

    I don't understand your other ? You don't trust PE's data and want to use drivers where a 3rd party has verified them w/DATS?
    Why do you want to "translate" Dayton specs to DATS values? A DATS will spit out (basically) the same values that Dayton specs?
    Qes, Qms (Qts), Fs, Vas, Re, Le, and so on...

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  • hitsware2
    replied
    Can you suggest ~ 3 " driver with fs ~ 100 Hz .... qts ~ 0.4 ?
    measured NOT from advertised specs .....
    OR a rule for translating Dayton specs to DATS values ?

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  • Chris Roemer
    replied
    My ROT is that at a Qts of 0.40, a vented driver can hit an F3 = Fs in a box the size of Vas.
    At a Qts of 0.50 (+.10) the F3 can be -10Hz LOWer than Fs, but the box will be about 60% larger.
    At a Qts of 0.35 (-.05) the F3 will (might) end up +5Hz HIgher than Fs, but the box will be smaller than Vas, about 70% the size.

    Seems to hold pretty well for Qts range of 0.30-0.65 or so.
    A decent closed/stuffed box can be half the Vb size, at the loss of approx. 1 octave.
    Last edited by Chris Roemer; 01-04-2020, 12:44 PM.

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  • hitsware2
    started a topic Bass Reflex with Vb = Vas and Fb = Fc = Fs

    Bass Reflex with Vb = Vas and Fb = Fc = Fs

    Playing with simulator it looks like 0.408 < Qts < 0.416 comes close .
    But not quite both equations @ once .
    0.4048 gives F3 = Fb = Fs
    0.4160 gives Vb = Vas
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