My system is 2 channel with OB main speakers and two subwoofers. The room has one stud/plasterboard wall, quite a long way behind the listening position, all other walls are plastered brick and the floor is solid concrete, not suspended. I had managed reasonable bass integration with the main speakers and the main sub but there were always issues around the crossover point and interaction with certain room modes
After trying numerous types of passive acoustic treatment, none of which were ideal, I decided to jump into digital correction, adding a DEQX processor in 2012. This required a large learning curve but the system is now optimized to a level which is way beyond my original expectations
I am by no means an expert on digital room correction but I do have quite a lot of hands on experience in this area. There is much more to setting up one or more subs - more than just room placement or phase, as I have learned (please forgive the length of this post and I welcome comment from those more technically knowledgeable than me)
The main sub is a M&K MX-200 which has served me well for a long time. When first purchased, positioning involved placing the subwoofer at the seating position and moving myself around the room listening for the best sounding spot for the sub (and then moving it there and me to the chair !). It has been in that position ever since. I am lucky that I have a dedicated music room with just one chair so placement was not an issue. As it happens, the MX-200 is slightly behind the LH main speaker, facing the LH wall, angled slightly forward but not particularly close to either the side or rear walls, or the corner
Things got a lot more challenging when I added a second sub (B&W PV1D because I liked the fast transients) and that's when I decided to go digital because with 2 subs the room was sometimes getting unmanageable. The B&W is slightly behind the listening position, similarly angled to the M&K & closer to a wall but has drivers diametrically opposed rather than front-down (M&K). Subs with different properties definitely complement one another when you can individually correct and align them
Using subwoofers in a room, the situation becomes very complex because of the interaction between several interrelated factors
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1) Room / position
2) Crossover point / slope to main speakers
3) Phase
4) Time alignment
All these areas affect each other and in particular good time alignment becomes really critical . Most solutions address phase first and then basic time alignment but few I could find also allowed steep crossover slopes between sub-mains and a method to blend these seamlessly. DEQX does that.
The biggest revelation has been discovering that all frequencies have differing wavelengths and there is no perfect time alignment, just a compromise spot where it actually sounds perfect in that particular room
Let me explain
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I can give an example of this last comment from experience my speakers are anecholically optimised for an almost flat measured in room response 16hz upwards. Rather meaningless I know because it is important how a system sounds playing music and not how frequency response looks on a computer screen. Its a good start however
So, the speakers are digitally calibrated flat, the subs are in the optimum position based on room listening, the DEQX has ensured a phase aligned crossover to the subs and I have set the time alignment between both subs and then to the main speakers by using a mic at the listening position. So far so good but it wasnt quite perfect
still a few occasional bass issues. However, I have found that getting the optimum time alignment is actually much more complex because of the wavelength issue
The universally accepted method is based on impulse response, either aligning with the first peaks on all speakers or on the initial impulse rise (slowing those closer to the listener back to the timing of the furthest, in my case the M&K sub). I have found that this in itself is fraught with potential errors
Time alignment with what?
The impulse response plot of a main speaker and a sub is the sum of all frequencies from that speaker and as they all travel at different wavelengths, what are the peaks and rises actually showing? They give a good start point but further tweaking is needed to finally hit the sweet spot where that particular system in that particular room sounds as near as dammit perfect. Its like focusing a camera lens and when you get there its very clear - I now have no frequency issues whatever I throw at it. Bass is fast, dynamic and clean and the room has completely disappeared. Believe me, I play a lot of music and this comment is based on experience for hours per day over many months. Although DEQX is expensive and fiendishly difficult to perfect, the end result has to be heard to believe
Now, this is interesting
Just by changing time alignment on this perfect setup, suddenly peaks and dips in bass response reappear, I guess because now some of the crossover frequencies or those interacting with the room have become out of sync .
Here are a couple of real examples
Changing timing i.e on the main speakers by an additional 2.7ms to the subs creates a noticeable boomy peak around 85hz. No change to equalisation to cause this either. It is because the timing at that frequency is now out of step with the rest of the range and it just doesnt sound right. Equalisation doesnt cure that because all it does is increase or reduce the volume around 85hz to make the hump more or less noticeable and the music no longer sounds as real
If I move alignment to, say 5.3ms then the audible change appears elsewhere in the low frequency response. In this case bass appears to decrease, probably because the room or crossover interaction is now cancelling a particular frequency which is out of step time wise. Return to the correct time alignment and it jumps back into real performers sounding just as if they are in front of you with space around each one. Amazing really that such minute differences can be so noticeable. Therefore, with subwoofers, I believe room equalisation or passive treatment alone are insufficient, as is just setting impulse response in simplistic terms
The end result can be stunningly realistic. This is a way to stop a poor room ruining the enjoyment & I like to listen to music, not hi-fi or noticing abberations in the sound. It still surprises me how much difference I obtained the very first time I (properly time aligned) corrected my room from its original incarnation, using the same sources, amps, cabling and speakers. Night and Day is an overused term but in this case pretty accurate
Anyone reading this is quite entitled to be sceptical and I do not claim to understand everything about the subject but subwoofer integration once its implemented correctly is stunning. It just takes a lot of effort and a reasonable financial outlay to get there
All of this may not be particularly scientific and I am not saying that DEQX is the only solution, however it works for me and I now feel I am getting the best out of it
My wife regards me as obsessive with my music, almost to the point of OCD over the past 30 years & I used to be one of those people who always felt my system should sound better. That is no longer the case
