TQWT Subwoofer Design

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JimGore

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I will be moving into my new place within the next couple of weeks, and my dedicated HiFi room is much larger than the lounge area I have my system in now.

The main speakers are more than good (and large) enough, and can handle more than enough power to fill the room with high fidelity sound.  Only problem is - my single subwoofer isn't going to cut it in that size room.  Floor area is around 62 square meters, with a total volume of 200 cubic meters - that's 200'000 liters of air volume!

So, I have been doing alot of thinking and planning, and running simulations for a possible subwoofer system that will be able to do the following things:
1.  Keep pace with the main speakers
2.  Have excellent attack - ie good transient response
3.  Provide clean, accurate bass for use in a high end music system
4.  Must be stereo subs
5.  Be able to fill the room with bass.
6.  Play clean and clear up to at least 115 dB.

Because of the size of the room, as well as the requirements above, there is no way your average 10" or 12" based subwoofer will cope.

The best thinking I have at the moment is to implement dual 18" HE drivers per side, in a Tapered Quarter Wave Tube (TQWT) design.  Sure, these will be fairly massive, but then my main speakers are also massive so it should work out ok.

Why TQWT?  Because:
1.  It has 2nd order rolloff at the bottom end, as opposed to higher orders for bass reflex.
2.  It has an excellent cone-excursion profile, meaning you can push far more power into a well designed and damped TQWT than you can into a sealed or bass reflex design without worrying about xmax related issues.
3.  Transient response is very good

I already have 1 of the 18" drivers I need as used in my current subwoofer, so I have ordered another 3 of them.

Next thing is the amplification.  Still busy investigating options, but it looks like the main candidates thus far are:
* Crown XTI 6002
* Crown I-Tech 5000HD
* Crown Macro Tech 5000 i-series

The first two amps have built in DSP, which is awesome.  As far as I know, the XTI 6002 is unique in the XTI 2 range in that it is based on the I-Tech topology, and is therefore closer to the I-Tech range than the XTI 2 range.  It isn't too easy to find good information on this, so I am still trying to figure it out.

Any ideas, comments, recommendations from your side?

Thanks,
Ian.
 

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