Theres no way to make a basshorn smallAll you can do is make it highly compromised
I wouldnt shorten a horn in groups youl miss your lows
- i would make the mouth smaller. That way the mouths will add when placed in close proximity.
You can compromise a basshorn down to using an 8" Peerless Csx on a 135litre 104db/1watt basshorn(50hz loading) But thats about it !
To get higher output,more larger capable driver.. eg Csx 10" or lab12 on 300litre horn with 2600cm^2 mouth for 50hz..
Cheers!