The X pipe can or could reduce the boom or drone as the Yanks say. The X pipe theory is for the exhaust to scavenge and exit by the fastest route by swapping pipes inbetween the exhaust pulses from the engine. This swapping also alters the sound waves and frequency, so it will sound slightly different and also reduce the boom. BUT, the x pipe is most effective nearer the front to help the scavenging, so where the ECS x pipe is located, it is mainly for sound than performance.
Rather than try and get a X pipe made, more money, a cheaper alternative to give the same effect is weld a small transfer pipe between the 2 pipes, this would be called a H pipe.
Alternative is to weld in a small twin silencer.
As Redline says, the tone can change with miles and carbon build up.
Think of an exhaust as a musical instrument, the length, bore, chambers, types of silencers, cross overs etc all change the sound.
I only have self made rear back boxes, no other silencers, straight through with valves. Funnily when I removed my downpipe silencers it actually reduced the boom but increased the volume!? The std rear back boxes do have helmholtz chambers in them to reduce boom. I think, not having cut open the middle section, there are baffles, maybe another helmholtz chamber in there, so the boom would be over powering the back box chambers as the exhaust is designed and tuned as a whole, so removing one part will change how the rest of it operates.
So to reduce the boom on mine, I added a pair of Helmholtz chambers to the ECS X pipe section. Now on the motorway with the valves closed, it is only a very slight hum. The size of the chambers are calculated by the frequency of the boom you want to reduce and the revs they occur at. I used an app on my phone to get the frequency and then a pre made Excel sheet to calculate the size or volume of the chamber. You think how much science goes into making exhausts!
Excuse the welding, it's not my day job and it's more functional rather than aesthetics
