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Old 11th September 2010, 08:39 PM   #1
tedmich is offline tedmich  United States
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Default Help! LT gains nothing with Sub?

I am a little confused about what box to build for my new woofer:
the 12" KW-120-THX Subwoofer
Click the image to open in full size.

problem is when I plug it into a Linkwitz Transform spreadsheet from Trueaudio
http://www.trueaudio.com/downloads/linkxfrm.xls
it gives a 2ft^3 box response that goes only to 1 octave below the boxes resonance with a gain of ~10db. But this is the same response I could get from a similar sized ported enclosure! Is my math off?

the woofers specs:

Power handling: 500 watts RMS/1,000 watts max
VCdia: 3"
Le: 1.23 mH
Impedance: 8 ohms
Re: 5.79 ohms
Frequency response: 20-1,000 Hz
Fs: 28 Hz
SPL: 86 dB 1W/1m
Vas: 1.89 cu. ft.
Qms: 3.31
Qes: 0.42
Qts: 0.37
Xmax: 25 mm
38lbs

these were $200 at Partsexpress, but I think I got the last one, as I couldn't order 2...only one.

what would work best? I have a nice Yamaha P2500s (~700w RMS bridged mono 8 ohm) to power it.
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Old 12th September 2010, 08:26 PM   #2
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You determine how low the Linkwitz transform extends the frequency response by changing the values for f(p) and Q(p).
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Old 12th September 2010, 08:47 PM   #3
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Quote:
Originally Posted by tedmich View Post
I am a little confused about what box to build for my new woofer:
the 12" KW-120-THX Subwoofer
Click the image to open in full size.

problem is when I plug it into a Linkwitz Transform spreadsheet from Trueaudio
http://www.trueaudio.com/downloads/linkxfrm.xls
it gives a 2ft^3 box response that goes only to 1 octave below the boxes resonance with a gain of ~10db. But this is the same response I could get from a similar sized ported enclosure! Is my math off?

...
Yes, your maths is off. Ported boxes (to be max.flat) need to be bigger than a sealed of Q=0.707.

ESP - The Linkwitz Transform Circuit
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Old 12th September 2010, 08:57 PM   #4
infinia is offline infinia  United States
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What were the values of closed box TS you used for the spread sheet?
The value of the LT is, it allows a much smaller box (Vb<<Vas) with a high Q, but you are using it in a box bigger than Vas. Most people that prefer closed box SQ over ported because with a gradual LF roll off, it is easier to integrate into smaller spaces w/o booming bass response. Note. LF extension is not always the final goal.
Build the small box (or simulate the model) and measure the resultant TS, calculate new values.
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