Why would a bigger diaameter h pipe will make the exhaust quieter?

[Bluegoat06]

I'm still running the stock cats, I'm in Cali, and I don't want to deal with taking the car to Mexico to have it smogged
but in any case, I thought I was going to get more sound out of the GT500 axelbacks going with a 3" h pipe, (had it custom made at a muffler shop), instead, the notes got quieter, so I ended up ditching the GT500's and had a pair of Flowmaster original 40 mufflers welded in, re-using the tips from the GT500's, much much better sound now, little bit of drone, but overall, better exhaust tone in my opinion, question is, was the H supposed to make it quieter, I thought it was going to get much louder ??

 

[CobraRed_96_GT]

Just a guess, but bigger dia means lower velocity of gasses. Given the same muffler, gasses going through at lower velocity = less reverberation/tone.

Why would you want to run a 3" pipe in GT500's anyways, aren't they 2.75" in?

 

[Bluegoat06]

I didn't measure, but the stock H looked visually smaller in diameter compared to the rest of the exhaust, that and the portion that had the stock resonators was smaller in diameter too.
I thought the GT500's were 3", and I didn't want to go smaller than 2.75", is it overkill going with 3" ?

 

[FlowmasterMufflers]

An "H" or "X" pipe will make your system a little bit quieter, but also improve overall sound quality. When sound waves cross over inside of a balance pipe, some of the harshness in the exhaust note is cancelled out, smoothing tone and reducing interior noise.