I recently undertook a project to improve the performance of a commercial speaker. I wanted to start with something with value and potential. The speaker I selected is the Sony SS-CS5 currently on sale at a major online retailer for $118 for the pair and free shipping.
Here's a review of the speaker, complete with on-axis frequency response measurements:
It's a very high value performer that already measures and sounds very good. It has a peak at 1 kHz, and a polite voicing that falls off a little bit at higher frequencies. There's little output below 70 hz, but a subwoofer can solve that issue, or it could be used without one in an office or dorm room or some place where deep bass isn't required.
The speaker improvement I developed is somewhat "outside the box". I built an anti-diffraction frame out of PVC pipe and some velcro straps. I built it in such a way that the grills can still be used, though it's probably better to remove them for the most critical listening. The frame increases the on-axis output above and below the 1kHz peak, making the peak much more benign.
I did make an "inside the box" modification, but it's one that requires no costly crossover parts, and no soldering. I shorted out one of the resistors in the woofer crossover circuit to prevent the woofer from attenuating significantly before the crossover frequency, and then to fall off more rapidly above the crossover frequency. This modification is safe and makes very little difference to the impedance curve (and no difference to the minimum). The only trick is getting the woofer out to gain access to the crossover. I'll make a subsequent post detailing the build that will cover that.
Both modifications are completely reversible, as the shorting wire and frames can be removed.
I am including on-axis and 45 degree off-axis measurements taken by my friend Dennis Murphy, as well as comparison pictures (with and without the frame). I am also including a pic that shows the crossover with the resistor shorted out by a small black wire with alligator clips on both ends.
I am posting slightly prematurely because the sale on the speakers is pretty significant.
The last point I will make is that this same style of frame could be applied to most speakers out there, and can greatly increase the smoothness and similarity of on-axis and off-axis sound/measurements. The extent of the improvement depends on how afflicted the speaker was with diffraction originally.