Dear @navyachts :Main subjectUissue why add subwoofers in an stereo room system is not really " add more/deeper bass ".
All speakers including yours and the lovely S7 owned by @orthomead or the great Rockport owned by @workeuptobose normally are designed using a internal passive CROSSOVER from a 2-way speakers to 4-way and up speakers.
Where is the " problem " there about that crossover frequencies for the different speaker drivers frequency range?:
In your case your ML crossovetr frequency to the woofer is 300hz and the speaker can goes down to around 22hz and; what that means?
it means that at the same time that that woofer drive must handle the 22hz, 30hz or 4o hz it must has too reproduce frequencies that can go over 300hz and the big woofer excursion need it to develop 22hz makes that the frequencies over 100hz develops a high INTERMODULATION DISTORTIONS ( no matters what. ) and this IMD is a huge signal reproduced degradation and it’s precisely here where 2 self powered subwoofers ( NOT ONE. ) helps a lot because when the woofer of the ML main speaker handled frequencies above 80hz-90hz and is liberated from the bass below 80hz-90hz that IMD goes automaticallt down and not only the bass range will shines but the midrange and hi frequency range too because we have to remember that MUSIC harmonics are developed by all the speaker drivers and if the IMD already gone down in the bass the bass range harmonics will be CLEAN with lower distortions and will permits that the mid range and hi frequency ranges stay in the same way: lower in distortions and clean/purity with lower signal degradation.
The " side " benefits of adding those subwoofers are not only what I posted but now the low bass range it will be reproduced by a dedicated driver designed in specific to handled with absolut applomb the frequency range and go deeper too in that range and with a dedicated amplifier that was designed to run on that bass specific range too along that your main amplifier will be a lot les distressed when is not playing/looking the low bass frequency range.
All those means that we need a high-pass filter to separates the frequency that goes through the subwoofers and the frequency that goes through the main speakers.
The solution that way is: win to win.
You said you need to improve the quality performance ( including bass. ) to one seat position and this means you need ONLY 2 self powered subwoofers crossed at 80hz, you don’t need the swarm solution that is for several seat positions.
Other issue with subwoofers is that exist quality levels between different manufacturers designs and due that the foundation and where the MUSIC belongs is the bass range you need subwoofers with very low developed distortion levels .
@ozzy posted to you: " play the main speakers full range " and with all respect this is a mistake that almost all audiophiles made/make by recomendation as REL manufacturer. Here you can read by an expert in the subject why that assuption is wrong even if we own the Magico S7 ( I can’t find any where the crossover frequencies of the S7 but obviously use a crossover and develops too IMD as the Rockport too that additional is a ported design and this means that here we have 3 bass sources: the front woofers, the back port and the subwoofers ( no one can control timing to run in our ears bass range because those 3 bass range coming with different delay) ):
"
The ONLY correct way to add a sub to system is to define everything ABOVE the sub’s [frequency] range as an entity; clearly define the impulse, phase, and lastly frequency response of this entity; and then make a new "2-way" system where the sub is one way and everything above it is the ’other’ way. The parts must be combined correctly so that there are no cancellations and no smearing of time-related musical events.
This CANNOT be easily measured in the frequency domain, because you could have (as an example) an 80 Hz signal coming from both the mains and the sub, and if the sub is 12.5 msec late the two sources will "seem" to be in phase but the sub really will be 360 degrees, or one full wavelength late. It is the impulse smearing that this affects, but people don’t measure that because there is no simple "hand held" phase or impulse meter as there is an SPL meter.
The REASON this meter does not and essentially cannot exist is that in order to measure impulse response or phase response you need a starting REFERENCE point, (in time) and in a speaker system, since the signal has to travel through circuitry, amplifiers, passive crossovers inside the speaker box and then hit the driver; therefore the first reference point MUST be acoustic.
There ARE computer based impulse response systems such as the TEF, ( very quick technical blurb HERE; full story HERE ) but they are involved, require real instrumentation, are expensive, have a seriously steep learning curve, and they are absolutely not the kind of thing most ’consumers’ -- or audiophles, can be bothered with or have patience for.
So the overall view of adding a sub is this: In essence you are designing and assembling a new speaker system which is "2-way": the sub is one way and everything "else" above it in frequency is the 2nd way.
Simply connecting a sub to existing mains speaker (or amp) terminals ( or self powered subs. ) is the WORST POSSIBLE WAY to do this. EVERYTHING scientific and acoustic about this method is wrong, from the additive delay issues to the back EMF of the mains affecting the LF signal. However there are plenty of people who simply do not understand correctly integrated bass, and they will be reasonably happy simply sticking another box on to their system without regard to timing, phase and frequency issues, and they will think it sounds "ok" or "good" and for those people it doesn’t really matter.
Indeed the only thing that does matter is an individual’s happiness with their system, whether I or anyone else thinks it’s right or wrong.
But I want you to know and understand the truth, so to get purely technical...."
Btw, the subwoofer with lower THD ( Total Harmonic Distortion ) level and reasonable price are these by Veñodyne esclusively design due that too comes with high pass filter:
Digital Drive Plus - Velodyne Acoustics
Regards and enjoy the MUSIC NOT DISTORTIONS,
R.
