Dumb Directivity Question

When building a loudspeaker with a waveguide, I know that it's a good practice to have the woofer and the waveguide use the same diameter, and to have a center-to-center spacing of one wavelength or less. We do this for the following reasons:

1) The woofer's polar response begins to widen at the same frequency that the waveguide's polar response broadens. So the woofer 'hands off' to the waveguide

2) Having the woofer and the tweeter on the same vertical plane improves horizontal polar response. Basically I understand that if the enclosure was flipped on it's side, the horizontal polars would suffer, because the pathlength from the listener to the drivers will vary depending on listening angle. So they response will be flat at some angles, but comb-filtered at others.

So here's my question:

[IMGDEAD]http://www.hometheater.com/images/archivesart/507Sunfire.4.jpg[/IMGDEAD]
If the crossover frequency is very low, what is stopping me from putting the woofer on the *side* of the enclosure?

Picture something like the Sunfire Cinema Ribbons, but with a much larger box, and a waveguide instead of the ribbon.


Here's what I'm picturing:
high frequencies (1khz - 20khz) will be generated by a compression driver on a 40x60 waveguide
midrange (300hz - 1khz) will be generated by 3" drivers, and they'll be mounted 'Unity' style, so that the center-to-center spacing is about 8cm
low frequencies (80hz-300hz) will be generated by a 12" woofer on the *side* of the box.

While placing the twelve on the side of the box is unorthodox, I can't think of a reason that it wouldn't work. With a xover point of 300hz I'll have a center-to-center spacing of 30cm, or one-quarter-wavelength. So even though it's an odd place to place a woofer, acoustically they're still very close together, due to the very low xover point that the Unity horn affords us.


Can anyone think of a reason not to do this?
 

mayhem13

Member
2008-09-22 4:37 am
Can't think of one....and I posed a similiar question in the other Unity vs Econowave thread referencing the KEF Blade........

But is responded for selfish reasons as I'm considering how to pair a vertical line of 16 2" drivers with woofers in the 200-250 hz area and I 'feel' the Blade approach is just what is called for.
 
If the depth of the cabinet (to accommodate the 12" woofer) equals 12", then the baffle step frequency equals 380 Hz. With a side-mounted woofer, I would think that you want the sound to be wrapping around the cabinet throughout the bandwidth that the woofer is operating in. That is, you don't want it radiating off to one side only. -I would think.

380 Hz is just slightly above your cross-over frequency, so maybe it would work alright. But a smaller woofer would allow you to decrease the depth of the cabinet and put the baffle step frequency well above the cross-over frequency of 300 Hz.

Admittedly this isn't based on a lot of experience. Take it with a grain of salt.

Regards,
Pete