Home Theater Newbie question --

I am using a pair of B&W CDM 7NTs and will eventually get surrounds and a center speaker. In the meantime I'm using a pair of ADC 303AX's for surrounds and a KLH 17 for the center. Not great, but the old speakers, particularly the ADCs, are pretty good bookshelf speakers.

I have seen some discussion to the effect that, when you introduce a sub you set the front speakers to "Small," even if they are floor-standing. I assume that's to take the bass load off them and put it on the sub. But I'm already getting pretty good bsss from the B&Ws. In a small room, 11 X 17 with 9ft ceiling, will it be overkill to add a sub, even a small one?

Thanks, Bob

The CDM 7NT is rated down to 40Hz (-3dB), which is certainly pretty decent, but there is material in movies that goes all the way down to (and often below) 20Hz. With no sub, that really deep bass is redirected to your fronts - where it is promptly lost in the response roll-off of the speakers.

I ran my system without a sub for a couple years or so (Paradigm Studio 60v2 mains that have a -3dB point pretty similar to your CDM 7NT's). When I finally added a subwoofer to the mix, the system was still in the living room of our old house (11'x19'x8'), and it was definitely a worthwhile upgrade. Adding a subwoofer will only be noticeable on certain types of music, but it will be a definite improvement with movies. Even if you only go with something small, like the LFM-2, it'll be a nice contribution to the system.

Some folks that have a no-sub music system that they are, so far, very satisfied with, will add a sub as a supplement for the extreme lows and to give that ‘large space’ feeling when playing back a live event or similar content recording. By a supplement, I mean that no bass management is applied to the mains, and the top end of the crossover for the sub, either in the sub itself or in the processor, is set rather low, maybe 60Hz or 40Hz depending on the mains.

I prefer to apply bass management to both the mains and the sub outputs. I’ve never had a medium or large room for my audio gear, so my mains speakers aren’t all that big. As such, moving the crossover point up to 80Hz or 100Hz means that the woofers in the mains are free to more accurately handle frequencies above that point because the subs now carry all the low end – I say more accurately because the mains woofers aren’t trying to make the large excursions they would otherwise be trying to do when attempting large amplitude low frequencies from a small radiator.

Which brings me to some moving diaphragm theory for a moment. Reproducing high and low frequencies with the same diaphragm means that the high frequencies’ waveforms are ‘going for a ride’ on the lower frequency movements of the driver. This produces a mild modulated Doppler effect for the higher frequencies. Having two-way mains plus a sub is in essence dividing the reproduced frequencies into 3 bands. If those bands are theoretically 20-80 (two octaves), 80-1280 (four octaves), and 1280 to 20K (four octaves), then largest excursions required are made by the driver with the smallest ratio of low-to-high frequencies. This reduces that Doppler effect, a part of what is called inter-modulation distortion. If the mains are three-way and a sub is added, then ratio of the lowest-to-highest frequencies reproduced by one driver can be reduced even further.

As in all things audio, there are trade-offs. Most agree, however, that unless the mains speakers are truly exceptional, adding a subwoofer is a positive step.

I vote yes for a sub. No question, if you like your movies to really go boom when the action starts, definitely get a sub. I love my ASW650.

I can live without a sub. I don't watch action movies often enough to benefit from a subwoofer.

I have to say, however, most people really like to hear/feel every last note and boom in the soundtrack. I really don't think a decent small subwoofer would be overkill in your case. You may be surprised at all the stuff your mains are not reproducing.

No slight to B&W intended, I might add. Fine speakers.

bestbang4thebuck, that was a great post. I had one of those no-sub music systems for 20 years. My Polk Audio RTA-12C speakers claimed to have a frequency response from 17 to 26khz. However, when I added a Sunfire True Subwoofer to the equation about 2 years ago, it was a very dramatic improvement. I did not necessarily hear things I never heard before (especially out of music CDs), but everything sounded better. So your moving diaphragm theory makes a lot of sense to me.

My chiropractor also believes in the benefits of a sub...if you sit on it...

of course I would have never met my chiropractor until I had to lift the darn thing two flights of stairs.

Thanks for the input, especially the setup advice. I am seriously considering a sub, but there are so many other neat toys I could add I wanted some help setting priorities.

Bob

YES!!!!