The traditional wisdom says that if the driver is close to the back panel of the speaker box, you'll get very obvious reflections back through the cone that colour the sound. While this is now widely accepted as true, I thought it would be interesting to actually test it and see first-hand how much of an impact it has.
The two boxes are nearly identical internal volume of 12 liters (the deep box is very slightly bigger). That volume works best for the driver I'm using for the test, a Seas coax H1144.
The deep box is 8" from the back of the front baffle to the inside face of the back of the box, while the shallow box is 4" deep. I used the same driver (I only have one of these), crossover and test setup for each box. The shallow box is just deep enough for the driver to fit - the back is just 1/4" from the back panel.
Measured first without stuffing, the tall shallow box shows a disturbance in the 300Hz range. This can be the "back through the driver" reflection mentioned above or it can be a standing wave.
Adding stuffing (I used the same piece of rockwool in each box) shows no significant change for the deep box, but has smoothed out that 300Hz wiggle in the shallow box, proving that it is a standing wave problem.
The standing wave happens up in the shallow box because it is taller and the distance from top to bottom is great enough to support a standing wave in that 300Hz region. The rockwool is damping material that absorbs sound energy, breaking up that standing wave.
Tangentially, this also demonstrates that standing waves are only a problem when the box is big enough inside to support a standing wave in the lower midrange frequencies. Note that the deep box shows no improvement when stuffed, indicating that there are no standing waves of any significance to damp.
So making a small speaker box with rounded or angled sides won't be effective for preventing standing waves, when they wouldn't be there to begin with.
Finally a listening test using both boxes. The mic is set up around 20" from the speaker on tweeter axis for both boxes in my listening room.
I deliberately withheld which box is which, leaving you to decide based on listening only. Give it a try and leave a comment, and I'll reveal the results in a future video.
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