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Discussion Starter #1
hi all..

I have 2 of these coming.. I want to make a subwoofer to augment my brother in laws lcd display.

I have plotted graphs with winisd and can either get down to 40hz with 1x driver in a 25l box with a 45mm x 180mm port

or with 2 x in isobaric and the same port I get down to 30hz.

my problem is that when I input susyetem power as 50watt in either case my rear port velocity shoots of the scale.. am I doing something wrong?
 

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Discussion Starter #3
On the cone excursion graph, have you exceeded Xmax? If so, apply a subsonic filter to keep Xmax within limits and recheck the port velocity graph.

no - cone excursion is not exceeded.

What is the maximum speed and at what frequency?
100 at 25hz
90 at 30hz
40 at 40hz
22 at 50hz

surely I am doing something wrong.. tb recomend a 25l ported box for 40hz - so it "should" be ok.
 

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Discussion Starter #5
Post a link to the T/S parameters and I'll try modeling it tonight.
thanks Mike... as mentioned I have two of them coming and a 50w sub amp.. wanted to limit enclosure to 25 litre and the isobaric modelled perfectly until I added the 50w to input power..

in the version of winisd I use it is already in the driver DB....

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Power Handling: 90 watts RMS/170 watts max
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VCdia: 1-1/2"
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Impedance: 4 ohms
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Re: 3.6 ohms
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Frequency range: 38-700 Hz
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Fs: 35 Hz
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SPL: 89 dB 2.83V/1m
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Vas: 35.09 Litr.
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Qms: 5.55
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Qes: 0.38
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Qts: 0.36
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Xmax 7mm
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Dimensions: A: 6-1/2" x 9-1/4", C: 4-3/16"
 

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Using WinISD Pro, and from the specs you provided, I came up with 30 liters tuned to 30hz with 2 subs in a isobaric ported configuration. Spl is 101.5 db at 30 hz with 200 watts input power. With a 2nd order subsonic filter at 26 hz Xmax peaks at 22 hz and does not exceed 8mm. Porting would be one 3 inch port 17.75 inches long and air speed does not exceed 21 m/s. Not bad at all for a pair of 6x9's.

W69-1042M.JPG
 

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Discussion Starter #7
Using WinISD Pro, and from the specs you provided, I came up with 30 liters tuned to 30hz with 2 subs in a isobaric ported configuration. Spl is 101.5 db at 30 hz with 200 watts input power. With a 2nd order subsonic filter at 26 hz Xmax peaks at 22 hz and does not exceed 8mm. Porting would be one 3 inch port 17.75 inches long and air speed does not exceed 21 m/s. Not bad at all for a pair of 6x9's.

View attachment 9237
not bad at all considering they are only $26 each delivered worldwide off the bay.

I wantedto keep it to 25l but 30 aint that far away.. also the amp I was planning on using is only 50w - is this the reason for my rear air velocity (doubtful) or is it my stupidity (no comment from me)

thanks Mike.
 

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Discussion Starter #8 (Edited)
Using WinISD Pro, and from the specs you provided, I came up with 30 liters tuned to 30hz with 2 subs in a isobaric ported configuration. Spl is 101.5 db at 30 hz with 200 watts input power. With a 2nd order subsonic filter at 26 hz Xmax peaks at 22 hz and does not exceed 8mm. Porting would be one 3 inch port 17.75 inches long and air speed does not exceed 21 m/s. Not bad at all for a pair of 6x9's.

View attachment 9237
Mike - sorry to be a complete pain but could you screenshot the other pages form winisd for me please kind sir? I just copied your parameters and my rear port velocity is off the chart again :foottap:

and another q? (I will search but it may be a quick one for you) I have googled for isobaric and like the clam shell option if the drivers can be completly internal.. question is if the drivers are both internal - say mounted on a central wall - is that still isobaric, where does the port exit internally and how does the sound get out?
 

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There are 3 different W69-1042's. The specs that I'm using which is the W69-1042M, The W69-1042 which is listed in WinISD Pro, and the W69-1042J which is the latest one. Are you using WinISD or WinISD Pro? Are the parameters in your modeling listed as mine in the graph below? I'm not sure why you're getting excessive air speed from only 50 watts input. Are you modeling with a 3 inch diameter port?

Cone excursion and parameters.

cone excursion and parameters.JPG

Spl with maximum input power of 200 watts.

spl with 200 watts.JPG

Vent air speed with subsonic filter applied.

air speed and SSF.JPG


The only internal clamshell I can think of would be a resessed baffle which is simply the four sides of the cabinet extending out past the depth of the outside sub. The dotted line would be grill cloth.

recessed box.JPG
 

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Discussion Starter #10
Mike - thanks for the help!
I have added the subsonic filter and now airspeed is tamed :)
the amp I am going to use has 100w into 8ohms (2 drivers in series) and actually has a -3db filter at 30hz. Is this the same as a highpass filter n=3, fc=30.oohz? or am I way off the mark...
 

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Discussion Starter #14 (Edited)
so how would I input that into winisd mike? is it a "Q" of 3 at 32hz?

another choice of amp is the mivoc am80 that has a boost of +3db at 38hz and a cut of -3db at 30... how do i enter these values into the filter.. I am guessing it is the parametric eq?

http://babelfish.yahoo.com/translate_url?doit=done&tt=url&intl=1&fr=bf-home&trurl=http://www.hifisound.de/oxid/oxid.php/sid/4c28fa627743a5d0f7a7708d1bb407fc/cl/details/cnid/9794113537972b8f7.29250484/anid/9794113542955d435.09570958/MIVOC-AM--80--AKTIV-SUBWOOFERMODUL/&lp=de_en&btnTrUrl=Translate

**edit**
actually the mivoc seems to model very well (if i have done it correctly..)
 

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It seems like the first amp you linked has a highpass Butterworth filter at 30Hz (hence it being -3dB at Fc or crossover point). I would guess that the slope of this is 4th order (24dB/oct) since that is a common subwoofer slope, but didn't see any information about it in the link.

To model this in WinISD click the highpass option choose a Butterworth filter the frequency is 30Hz and the order will be 4, Q will not effect anything with this type of filter.
 

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Discussion Starter #17
You should email the seller and ask what slope the amp uses. They can usually provide this information.
I have a bid on the 2nd amp, the one with +3db at 38hz and -3db at 30hz

the -3db is easy to do as you have mentioend but how do i add the 3db at 38hz?
 

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Discussion Starter #19 (Edited)
I am starting to think that the extra driver in isobaric is not going to be worth the effort..
with the 3db boost at 38hz and 3db cut at 30hz the single driver vented with a 3inchx14.6inch 20litre box tunes to 40hz... 40hz should be fine for my brother in law who has never had a sub.

Could one of you fine chaps check my modelling on this? the only thing I can see coming close to a dealbreaker is cone excursion..

also do i need to add a static gain across the board to account for the corner placement of the sub? or will room losses negate this? (the more i learn it seems the less i know!!)
 
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