Why does this sub give me negative box size? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 12 Old 02-28-2018, 10:20 PM - Thread Starter
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Why does this sub give me negative box size?

Hello,

I have been looking around for a sub I can put in a sealed cabinet and eq boost and I came across the Earthquake DBXi 12D and it looked quite good. Hey, lets model the 15" version. I came up with a negative box size with two different programs.

Here is the sub,

http://earthquakesound.com/index.php.../item/dbxi-15d

Any ideas?
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post #2 of 12 Old 02-28-2018, 10:43 PM
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BS specs. Idea: get a driver from a manufacturer who doesn't lie.
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post #3 of 12 Old 02-28-2018, 11:32 PM
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I bet the issue is that you're using the wrong unit for at least one of the specs e.g. sd in cm instead of mm or bl in na instead of tm. Check and try again

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post #4 of 12 Old 03-01-2018, 12:09 AM
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U.S. website downloaded Manual provides specs for both DBXi-12d [Fs = 24 Hz] and DBXi-15d [Fs = 20 Hz], where Fs = Free Air Resonance...but Test Method was NOT stipulated:
http://earthquakesound.com/index.php.../item/dbxi-15d [VI Box - Note SMALL Test Box is used to indirectly DERIVE Fs....rather than inaccurate "Hang it in Freespace" method]

However in the Euro webpages, we learn a LOT more about the DBXi-12d Test Method for Fs [although no corresponding info for DBXi-15d]. U.S. Spec value of 24 Hz for 12d is listed in excerpt below....but the accurate number would be 16 Hz....a very large difference. So a significantly Lower Fs may be what SHOULD be used for 15d.....you should CALL MFR to confirm which are the CORRECT values....and ask for more info on whether THEIR "VI BOX" is same as VI Box link below [VI = Volt-Amp, so it's pretty generic]:
http://www.earthquakesound.eu/car-au.../dbxi-12d.aspx
http://www.earthquakesound.eu/car-au.../dbxi-15d.aspx
https://www.google.com/url?sa=t&rct=...FnZRVEnBc1r82Q

It is therefore POSSIBLE that for DBXi-15d, Fs=12 Hz [even though I find that hard to believe] and BL=16.32 T-m are the Correct Values....as shown in fol. Norwegian Website (where they are more likely to get the RIGHT info when doing the research for their Webpage Translations):
http://spaudio.no/DBXi-15D [Fs=12 Hz]
http://spaudio.no/DBXi-12D [Fs=16 Hz....SAME as in Euro Webpage cited below]
PS: Xmax (electrical) is "probably" when Distortion is "excessive", whereas larger Xmax (mechanical) is "probably" when Voice Coil actually HITS something....use the smaller Xmax=74-mm peak-peak:
https://www.eminence.com/support/und...udspeaker-data

You should re-enter ALL of these numbers into whatever Box Calculator you used [and how about letting us know WHICH one you used]. BTW: Two 4-ohm Voice Coil sections are presumably in Series, hence assume 8-ohm connection to utilize ALL of Voice Coil within ALL of the Magnetic Field, rather than just HALF.

=======================================
Fs: [DBXi-12d Free Space Resonance].
  • 16Hz - 100 Watt VI Box measurement & driver fully broken-in.
  • 17.5Hz - after AES break-in at 100 watt VI Box measurement.
    This shows that due to the extreme excursion potential and the relative stiff suspension system at the onset of its lifespan a full AES breakin is not quite sufficient to completely break in the driver
  • 24Hz - brand new driver with zero break-in. Taken at traditional TS value of 1 watt

Last edited by holl_ands; 03-01-2018 at 01:46 AM.
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post #5 of 12 Old 03-01-2018, 04:54 AM
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Found somewhere, i don´t remember where
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File Type: zip Earthquake DBXI THIELE SMALL-ts paramters.zip (5.9 KB, 12 views)
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post #6 of 12 Old 03-04-2018, 08:23 PM
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Thats odd, one of my first DIY subs was 2 DBXi subs in a ported box, dont remember the specs as it was quite a while ago now. But I was pretty happy with it. beat the crap out of the paradigm and focal retail subs I had at the time.
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post #7 of 12 Old 03-05-2018, 05:22 AM
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@DaveFred


give these a shot.







make sure all fields are clear, then
enter qes then hit tab, enter qms
hit tab a couple times and let it calculate qts
hit tab a few times to move to mms
enter mms, re, bl, le, sd, xmax, and pe
by using tab after entering each data, it will calculate what it needs to
i no longer get any conflicts
sometimes the specs calculated don't match exactly the manufacturer specs, but its only rounding type errors, so it is not material

make sure the units match. if they don't, click on them and they will cycle through the options.


its a pretty low sensitivity driver, but if that is ok, then go for it. it works in small sealed and ported enclosures.




EDIT: sorry, those are the specs for the 12".


the specs for the 15" have an error in them.
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Last edited by LTD02; 03-05-2018 at 05:34 AM.
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post #8 of 12 Old 03-05-2018, 05:39 AM
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ok, let's try that again.


15" specs from this site:


http://www.earthquakesound.eu/car-au.../dbxi-15d.aspx









best used in sealed or large ported.
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post #9 of 12 Old 03-05-2018, 03:03 PM - Thread Starter
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Box still does not work :(

When I put those number into Jeff Babgy's Woofer Box model spreadsheet, I get a Vab of -1411.19 cu ft for box size

Quote:
Originally Posted by LTD02 View Post
ok, let's try that again.


15" specs from this site:


http://www.earthquakesound.eu/car-au.../dbxi-15d.aspx











best used in sealed or large ported.
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post #10 of 12 Old 03-05-2018, 05:18 PM
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Xmax= 3.5"......Xmax=4"......Xmax=74mm P-P.....

I've modeled using the different set of specs from the .com and .eu sites, and I'm always getting a positive box size. A huge, positive box size. If you could post some screen shots someone should be able to point out what's going wrong for you.
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post #11 of 12 Old 03-05-2018, 06:00 PM - Thread Starter
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Here is what my screen looks like. I entered series OHMS as 8...
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post #12 of 12 Old 03-10-2018, 06:09 AM
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series resistance is resistance *other than the subwoofer*, so usually should be 0.1 ohms or less just to account for speaker wire.

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