Ignoring X-Max issues, what is the effect rear-mounting a driver opposite a smaller cut-out?
e.g. a 15" driver with 12" cut-out. I thought the idea ridiculous until I recalled I had sone PA horns built this way.
e.g. a 15" driver with 12" cut-out. I thought the idea ridiculous until I recalled I had sone PA horns built this way.
Shouldn't be an issue, once the cone or surround at full excursion does not impact the baffle that the driver is mounted on.
The volume in front will make for a slight low pass band-pass effect, reducing the top end slightly, as well as adding a few upper peaks.
The "donut ring" stand-off from the smaller diameter baffle should be deep enough to handle Xlim, often double the excursion of Xmax. That may require a few layers of material in the stand-off to avoid slapping the cone or surround on the forward stroke.
Users who use old horn designs replace old drivers with longer excursion cones and sometimes forget to add the donut, and then find the sub only gets a little louder than it used to before it gets noisy...
Here's a more extreme example of the effect of rear-mounting drivers with a smaller cut-out, a pair of horizontally opposed 8" woofers taken from Yamaha NS-20T, put in a one cubic foot box with a handle size oval exit on either side.
The left insert in the photo shows one side of the 2x8", the Yamaha NS-20T boxes reloaded with B&C drivers on either side of the 21.5" iMac with the "hot rodded" NS-20T response.
The NS-20T sealed box interior volume about 19 liters, the 2x8" cube 20L.
The purple trace is the response of one of the 8" woofers in the original box & passive crossover, the blue the raw response of the 2x8" dropped in level around 6dB to also center at ~0dB for comparison.
The original response is +/-2dB from 60Hz to ~1500Hz where the crossover drops ~12dB per octave.
The "too small" 2x8" low frequency bump is pushed up in frequency, the small "bandpass chamber" exit creates a +6dB peak at 630Hz, followed by a -24dB drop to 2kHz, then some wavy gravy >2.5kHz.
Cheers,
Art
The left insert in the photo shows one side of the 2x8", the Yamaha NS-20T boxes reloaded with B&C drivers on either side of the 21.5" iMac with the "hot rodded" NS-20T response.
The NS-20T sealed box interior volume about 19 liters, the 2x8" cube 20L.
The purple trace is the response of one of the 8" woofers in the original box & passive crossover, the blue the raw response of the 2x8" dropped in level around 6dB to also center at ~0dB for comparison.
The original response is +/-2dB from 60Hz to ~1500Hz where the crossover drops ~12dB per octave.
The "too small" 2x8" low frequency bump is pushed up in frequency, the small "bandpass chamber" exit creates a +6dB peak at 630Hz, followed by a -24dB drop to 2kHz, then some wavy gravy >2.5kHz.
Cheers,
Art