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Old 30th April 2005, 01:49 PM   #1
oblong is offline oblong  Australia
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Default Rasmussen critical Q sub

I've seen some discussion on this, but has anyone actually built one?

http://www.customanalogue.com/sub_index.htm

If so, is it worth doing?

Bob Long
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Old 30th April 2005, 07:05 PM   #2
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Well, If its your very first project it might be worth doing.... But I'm reasonably certian that we could help you design something better probably at less cost and with a smaller enclosure
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Old 30th April 2005, 10:45 PM   #3
oblong is offline oblong  Australia
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Quote:
Originally posted by BassAwdyO
Well, If its your very first project it might be worth doing.... But I'm reasonably certian that we could help you design something better probably at less cost and with a smaller enclosure
Thanks for the offer - I'm open to any suggestions. I didn't think that the enclosure was particularly large; and I'm not concerned about getting an enclosure as small as possible. My existing system is stereo (not 5.1) with two speaker enclosures I built in 1971. Each cabinet uses the Peerless 3-25 kit consisting of tweeter, midrange and 12" woofer with a three way crossover. 25W RMS capacity. Sealed, fibre filled, about 100~115 litres. Made from 3/4inch chipboard (yes, I know! but this was before the days of MDF).
They still sound good, but I think they would be helped by a proper subwoofer. Current amplifier is 15W per channel, and that is more than loud enough. The intention was to connect the existing amp to the high level inputs of the sub and then connect the existing speakers to the high level outputs of the sub's plate amp. Mainly for home theatre use.

I've played with WinISD, but after reading lots of stuff I'm not sure just what to design for. For example, should the aim be for a "flat" transfer function? (Which is what I thought the example in the WinISD help implied.) Or should it be designed to roll-off to allow for "room gain"? (Which is what Rasmussen implies.) What's a good low -3dB frequency to aim for?

Bob Long
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Old 1st May 2005, 04:37 AM   #4
mike.e is offline mike.e  New Zealand
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Quote:
Originally posted by oblong

I've played with WinISD, but after reading lots of stuff I'm not sure just what to design for. For example, should the aim be for a "flat" transfer function? (Which is what I thought the example in the WinISD help implied.) Or should it be designed to roll-off to allow for "room gain"? (Which is what Rasmussen implies.) What's a good low -3dB frequency to aim for?

Bob Long
I cant tell you what your aim should be,but be aware that aiming for a flat transfer function to some low frequency will involve augmentation of some sort. Whether you can hear a port or not I dont know,or you want a sealed box with EQ each will have its negatives.

If your looking at typical music a 40hz cutoff will work. Personally a cutoff of 32hz is good enough for my type of music.
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Old 1st May 2005, 06:22 AM   #5
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I've got two 12's per channel with a Q of .6 and F3 of 50. Bass is most excellent for HT and stereo.
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Old 2nd May 2005, 01:18 AM   #6
Ron E is offline Ron E  United States
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There is nothing magic about a critical Q sub. The results obtained - despite the semiliterate hype to the contrary - are more due to the excellent driver design than any enclosure or amp choices by the person involved. Any references to a servo sub are purely specious.

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