One of the reasons subs are beneficial is that they take a huge load off the rest of the electronics and speakers to reproduce low frequency. Once there, their distortion level goes down, and you will have a choice of lower power amps which may have other sonic characters you like (e.g. Tubes).
Of course, nothing is free and you are now faced with an exponentially grown problem of where to put the subs and how to configure them to blend nicely into the rest of the systems. Digital EQ systems are a great help here.
Dear Amir: First I want to say that I " overall " agree with Tony ky ma and RBFC and certainly with you, more on this latter.
The Geedes subs approach that Frantz take it and already experienced in his system is only one approach with very specific targets between of them and mainly: to even/smooth the low bass frequency range response through the use of multiple subwoofers in site/room.
As Frantz point out and Geedes too the main speakers are running in full-range.
Many years ago I readed the Harman similar subs approach where in its white papers they said four subwoofers were/are the ideal number to even the low bass response in room. I tested with two M&K subs and two Carver " The Cube " and yes ceratinly the low bass in room response even and disappear those frequently bass room interaction " deep " problems. Over the time I change subs passing for Audio-Pro ( a Sweden ones, very good indeed. ), Cerwing Vega, Electro Voice, JBL, etc, etc. but I never really be satisfied with the overall system quality performance and I return to listening with out subs. My speakers on those times were the same that I own today.
A few years ago I was thinking to integrate/add subwoofers ( again ) in my system but I take a different " process " and inside this process I first analize how three-two ways speakers works/designed and I mean with this where were/are its " compromises "/ trade-offs against a " perfect " speaker and a " perfect " quality performance. I found out that only a few designs are really full-range ones ( flat to 20Hz. ) and that only few of those few full-range speakers were active/self-powered in the low bass frequency range.
So I asked my self: why is that? why no more full-range speakers when the real music in a real space are cry out for it? Well those last bass octaves are truly unfriendly to handle, expensive ( $$$$ ) ones and in a passive full range system only help to " deteriorate " the speakers performance level. So two-three and even four way speakers designs comes with out those last low bass octaves.
From those passive full range octaves the best sounding ones were the designs that choose that its woofers croosover at very low frequency: 100 hz-150 hz, to the midrange drivers: but we can find this kind of passive full range spekers where the fingers of one of our hands are more that what we need to count them.
The other factor that I analized is the whole job that each driver ( woofers, tweeters, mid range,. ) has in any speaker design: reproduce frequency range signal in accurate way with no distortions/colorations, very hard to achieve indeed but the point critical here is: reproduce signal in a frequency range, this means for example that if in a thre way speaker design the woofers croosover 300 hz and goes down 20 hz those woofers are responsible to reproduce in accurate way frequencies from 20 hz to 350 hz-400 hz ( depending on the passive filter crossover design: first, second, third order, etc, etc. ).
For do that exist in those woofers a " heavy/high " Intermodulation Distortion that degrade in severe manner the sound perfromance level due that the woofers long excursion to develop 20 hz-40 hz-low bass harmonics affect the quality response of those woofers with the other frequencies in that woofers range.
This high Intermodulation Distortion makes a paramount difference if any one of us can lower it in each one of us home audio system, the difference is nothing less that spectacular for the better and in a passive speaker system we can do it only adding self powered subwoofers ( two ) integrated in true stereo fashion to the syste, this means that we need a high-pass filter for the main speakers.
My approach is not to even/smooth low bass performance level ( like in the Frantz system or on speaker systems where the low bass already handled in active way crossing around 100 hz. ) but to lower IMD in favor of better overall quality performance that put me nearest to Excellence level.
With this approach ( different from the Geedes/Harman one. ) we " kill " several birds with only one shot and achiving a quality level performance that you can't achieve with the Geedes approach in passive speakers designs.
Now if one of our system ask because with two subwoofers ( identical ones, in my approach you need be identical. ), subs position, satellite speaker positions, low bass eq. and room treatment you can't even the low bass response then you always can add the third or fourth one. I can say that almost never you will need this 3-4 subs.
Here you can read what I posted about in other thread:
http://www.whatsbestforum.com/showthread.php?1005-Multiple-Subwoofer-Placement/page2 post #16.
So, IMHO each one of us approach with subwoofers is to identify what our main speakers needs, if are passive designs certainly needs to go to lower IMD ( add two identical self powered subwoofers in stereo fashion integration and with a high pass filter for the main passive speakers. ) but if are active ones on the low frequency range then you will look for even bass response.
So the Geedes/Harman approach is a different approach for way different targets and not for everyone.
Which one you want: even bass frequency only or Excellence performance level approach with your passive speaker design?
Second step with my approach is two select the right subwoofer, not all subwoofers are the same and the price or " good looking " factor means nothing about its true quality performance level. Remember that trying to lowr the IMD is on favor of Excellence performance level so you need the best subwoofer choice for a two channel home audio system.
Between other things try to select ( every thing the same. ) the subwoofers with the lowest THD, ask about to the retailers/manufacturers. One of the reasons I choose Velodyne is because was the one I found out with the lowest THD: 0.5% in the HGS Velodyne series thank's ( between other things ) that Velodyne sense more that 10K times each second the woofer behavior and make as need it the corrections on real time. The " pretty face " JL in the same conditions has 6% on THD , Wilson 5% and over 10% at 20 hz and Revel B15 around 20%: way difference that you can hear.
Like in almost any audio subject: knowledge better yet quality knowledge level and your skills to use it is the " name of the game ".
Btw, in no single thread I readed in this forum no one talk about THD and IMD distortions on speakers/subwoofers. I wonder why because are extremely important subjects to understand if we want to achieve Excellence performance level in our home audio system.
In the other side the even low bass response subject means almost nothing with out THD/IMD figures at different SPL values.
If you read carefully the link I posted you can see that you " take all " with my approach. It is the best out there?, ceratinly not : it is only a different approach with different targets and IMHO a good choice if you know how to implement it.
Anyway, which your target on the subject?. thank you.
Regards and enjoy the music,
Raul.
