I recently bought another set of Sonorous Fest Speakers,for a bedroom setup, and when doing some fairly serious frequency glide testing of them, I discovered a couple of picky things that seem worth mentioning:
First – I noted some squawkiness at around 294 Hz, right on the note D4. My response for that up to now (in my other CF speakers) had been to attenuate the response around that note with a high-Q notch filter in my DSP – things just sounded better, cleaner that way, but of course it leaves you with a hole in your response curve - one de-emphasized note. The frequency of the problem varied with changes in listener location, so I suspect it is all about some acoustic interference – likely phase cancellation. Can't think of a cure for that, except to employ the trick of repositioning the speakers slightly so that from where I sit the problem point appears at a frequency midway between notes. Moved them back just a little, and now it centers right on 300 Hz, midway between D and D#. Maybe a tiny improvement, though hardly earth shaking.
Next – a much more obvious problem, with a lot more positive treatment. There is a nasty buzzing evident midway between 164 and 172 Hz. Quite bit worse in one channel than the other, but it's not a bad driver, or a wire hitting against the back of a cone, or a missing driver-mounting screw – it turns out to be caused by sympathetic vibration of the power resistors in the crossover! There are five of them in there and, being all the same physical size, they all vibrate at about the same frequency, sounding like a hornet's nest. Particularly if they are mounted slightly elevated off the board, at a certain volume they will scream harmonic distortion whenever somebody hits the E below Middle C. The channel I had that was producing more of this distortion clearly had its resistors mounted looser, above the board (or above the coil in the case of the middle one).
My solution was to dismount the speaker, lay it on its back, remove the tweeter and the central wad of fiber-fill, and dab some flowable silicone sealer below, beside, and between those resistors – enough to render them virtually motionless. I used windshield sealer (VersaChem 75009, from O'Reilly's; other auto stores sell Permatex 81730). If you do this, avoid coating the tops of the resistors too heavily, as they need to be able to dissipate heat, though I must add that the wattage spec of these resistors is well into the overkill range – they rarely get even slightly warm (recall that the famous torture experiment at the 2015 Fest, which fried the side-drivers, did no harm to the crossovers).
A non-magnetic tool is best for accurately applying this stuff; wood works fine – I used a popsicle stick; a chopstick would do the job as well.
Did both channels the same way, of course, and let the silicone to set a few hours, then replaced the fiber fill and the ribbons – all done and ready to test, except...
If you do this, don't remount the speaker just yet. There's another trick to play.
Louder frequency glide testing had disclosed another problem, centered sharply at 325 Hz, at which point the upright support in my custom setup does a lot of vibration, and some quite audible buzzing – pretty nasty. Note: these special uprights are just 20” long, as they're attached atop two-foot high (AL3) woofers, and sit just six feet from my ears; the stock supports are 47'', and would therefore resonate at different frequencies. Anyhow, the cure was to take a long-enough dowel and use it to shove a few (I used 3, but the much longer originals would want maybe 7 or
everyday empty plastic grocery bags into the column, to damp it. Obviously you want to have the feed-through wire held in place before stuffing the bags in there. Anyhow, this trick tamed that resonance down to where it's no longer noticeable.
With it all put together those certain notes offend no longer. I revamped my response curve a bit, to where it's now a bit flatter and simpler.
At this point I have no hesitation is stating that the CF speakers sound cleaner than any of my seven pairs of 48'' ribbons. And the sound-stage produced in my trinaural LR setup with three of these little wonders is unbelievably, staggeringly huge. It's kind of mind-boggling how such small speakers can create this immense acoustic envelope, and then sort of vanish into it. Now that I have both systems running with AL3 woofers plus subs to supplement the bottom octave, they are truly full-range reproducers. The EQ curves for the mini DSP were a lot easier to get dialed in than with the 48” ribbons; the CF speakers still retain their original passive crossover, of course, and they're are a whole lot smoother in response to start with than ribbons run directly off a power amp.
Naturally they are also less efficient than bare ribbons, so for overall balance the gain to the amp that feeds the more sensitive woofers has to be reduced; how much depends on room size and speaker/listener location, as always. The DSP handles such problems with ease. In a good-sized room a pretty powerful amp makes a noticeable improvement with these. Thus a TFM-45 is clearly preferable to a TFM-15, e.g. And I mean 'clearly' in a couple of senses...