Bass horn coupling

Joris Wijgerde

New member
Nov 29, 2019
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Belgium
I've been trying to understand this for the longest time and I hope someone could help me out here.

I have built some tapped horns around B&C's 18ds115 which behave great in large stacks (4+ bins), however when used in singles or doubles there is a quite significant saddle shaped dip in the response around 50-60Hz. Even when EQ'ed flat the overall sound is very different from when they are used in multiples. I have used some lower BL drivers in them which sound ok in small stacks, however it seems like the more cabinets, the better the overall sound.

Now what I've been trying to understand is how increasing the number of subs doesn't only improve output by increasing the directivity of the stack, but also seems to tighten up the response; lowering it's group delay and evening out the frequency response over their passband. I can sim this perfectly fine in HornResp, as do all my measurements show this effect - however I don't understand what exactly is causing this to happen and hope someone could answer some of the following questions:

- Would the same flattening of FR etc. occur if the TH was set up alongside another type of cabinet covering the same frequency? (For example a reflex cab).
- Is the change in characteristics caused by driver interaction between the different cabinets or is this merely an effect of some type of pressure change occuring between the front and back of the driver? Could the same effect be achieved by putting the driver against a physical barrier like a wall?
- Would adding an extension to the horn load the driver better, achieve a similar effect to increasing the stack size?

Thanks in advance!