Subjective
The SDS4s sound quite good overall. There’s a respectable amount of bottom end for 6.5-inch drivers, and the typical vocal range seems relatively uncolored. However, there does seem to be something a bit strange somewhere in the bottom of the tweeter’s range. My favorite midrange test track is track 11 from the 1999 IASCA Competition CD, it’s a piano/violin piece from Clarity Recordings. The violin produces a very rich, dense tone — plus the guy plays as if he’s possessed. When auditioned on the SDS4s, the violin sounded a bit muffled in the upper half of its scale. This effect wasn’t as noticeable with other recordings, even those with similar instrumentation. Along with the low mid and midbass, the upper end of the tweeter’s range also seems okay. This leads me to guess that my rather thickish violin experience was caused by a relatively narrow dip in the upper midrange response. It could be in the crossover or just something inherent in the tweeter, but, either way, it should be easily fixed with an EQ.

The SDS4s also fared pretty well in the power-handling department. I used a 75 Wx2 amp for the audition and was unable to make the systems distort significantly with its full output. While I don’t think I’d go so far as to call them loud, they are capable of playback levels that are well above the “comfortable” range.

Major kudos to whomever designed the tweeter-mounting hardware. There are two flush-mount options and a surface-mount housing — all with eyeball swivel action. My favorite is the deep flush-mount option.

Our test enclosures are constructed from 0.75-inch plywood and most tweeter hardware has to be…well, modified…before it will work with a baffle board of this thickness. I seldom mention it in reviews because I doubt that it’s the constant pain in the keister to the average installer that it is to me. The deep flush-mount option included with the SDS4s tweeters worked perfectly with our 3/4-inch baffle. It was the quickest tweeter install I’ve done in four years, and, for once, “bench vise” wasn’t on my list of necessary tools for a speaker install. If you need to install tweeters in a thick panel, look no further.

Objective
Impedance measurements on the SDS4s show a maximum of 19 ohms at 79 Hz and a minimum of 4 ohms at 201 Hz. Average impedance measured 7 ohms over the system’s usable range. One watt at 1-meter sensitivity measured 85 dB with 200 Hz to 5 kHz band limited pink noise. RTA measurements show the SDS4’s response in a highly reflective environment and reveal a relatively smooth curve that fits within a response window of about 5 dB over most of the system’s usable range. Semi-anechoic measurements show a somewhat more detailed picture of the system’s response, devoid of reflections. This measurement shows a response window of about 10 dB between 100 Hz and 20 kHz.