XLS 12 sub in 50 litres / 26Hz + 200W BK amp - any better suggestions for ~250? - diyAudio
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Old 19th December 2007, 04:06 PM   #1
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Default XLS 12 sub in 50 litres / 26Hz + 200W BK amp - any better suggestions for ~250?

My bookshelf speakers (Mordaunt Short MS20i pearl) are struggling with bass extension and max clean SPL in my new lounge, so I'm looking to build a relatively compact sub to hide behind my TV/hi-fi unit. I've been through a bunch of designs and settled on an XLS 12 830500 in a tall shallow cab (800mm high, 400mm wide, 200mm deep), with the 12" at the bottom of one tall side, facing backwards, with the port forming a second skin round the front and bottom and firing out backwards. Slot port dimensions 400mm wide x 30mm high and 970mm long. BK plate amp to be mounted on back above woofer.

XLS 830500 in 50 litre, 26Hz and 70Hz 24dB LR lowpass plots out 84dB sensitivity, -3dB @ 24Hz, in half-space. Sub will be in corner placement - does that give another 6dB or 12dB of sensivity vs half-space?

My bookshelf speakers appear to be tuned to ~60Hz and I'm powering them with a Rotel amp with +/- 6dB @ 100Hz shelving EQ. For the flattest response I'm planning to juggle some bass cut on the bookshelf speakers with ~70Hz lowpass on the subwoofer. I'd like to reduce the excursion demands on the woofers in the bookshelf speakers to reduce distortion at higher SPL.

Now's your chance to tell me why this is all a bad idea and what I've failed to consider, I am new to all this DIY stuff!

Many thanks,

Alex
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Old 19th December 2007, 05:35 PM   #2
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That all looks well planned out to me

The only thing I would add is a high pass filter just below the tuning frequency to protect the woofer at very low frequencies
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Old 20th December 2007, 12:22 AM   #3
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Hi FullthrottleRic,

Is a high-pass just above port tuning freq a necessity if one is playing at regular music volumes, like 90-95dB tops?
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Old 20th December 2007, 10:51 AM   #4
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For 99% of music a high pass filter is probably not necessary really and it will add group delay.

If you're going to use the sub for HT then I would use one for sure, with music it's up to you
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Old 20th December 2007, 02:36 PM   #5
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That's good to know! I've looked at the cone excursion plot in WinISD Pro and the sub hits Xmax at peak power with 200W RMS input at 20Hz. Above the tuning frequency excursion is way below Xmax at full power. It'll be for a mix of music and HT but for HT volume is likely to be lower as my wife will be present!

My only concern now is that the high inductance and moving mass could cause the sub to sound slow - unfortunately I've yet to find any hard data to quantify this...

Thanks again,

Alex
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Old 21st December 2007, 06:50 PM   #6
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High moving mass is fine if you've got a powerful motor, which the XLS has
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