Another New Acquisition: Infinity QB

audiodogster

Active Member
I just picked up Klipsch KSP-400 and a matching center on Tuesday morning and today I picked up what I won in an auction on Monday night: a pair of Infinity QB. They are in fairly good shape besides a few scratches to the veneer, the grills are perfect. I'd give them an 8/10 for cosmetics.

These speakers are unique, which I guess is a hallmark of Infinity speakers (from what I've seen, though these are my first pair). They have what I assume at the time (1977) were probably relatively expensive components, the EMIT ribbon tweeters, but are in vinyl wrapped cabinets that aren't mirrored.

Here's a couple of pictures:
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Anyway, these being my first ribbon tweeters, I was excited to give them a listen and I was pleasantly surprised: they sound better than they look! I put on some Miles Davis and flipped off my subwoofers to get a sense of what their sound on their own and it was quite good. I did my organ test and while they were missing a bit of the lower frequencies, they performed well for their driver size. I played a movie trailer to see if they would work well in my gaming room and they were alright in that regard, I was hearing some vibrations but that was probably mostly them vibrating on the risers that came with them.

I haven't tried DeOxit on the pots nor have I opened up the speakers to check the crossovers but I am having one issue with one of the speakers. It seems the tweeter is producing excess floor noise (like a static whirring sound) when the speakers are playing, and the volume seems to depend on the upper-frequency volume. A guy I know from Craigslist that sells quite a bit of vintage mid-fi out of his garage suggested it could be failed glue on the magnets, any ideas? I don't want to damage the tweeters accidentally and if I do sell or gift these, I'd like to have them operating at 100%.
 
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The early entry level (entry level for Infinity - these were actually quite expensive in their day) EMIT-based Infinities are vastly underrated. I used to own a pair of Qas (like the Qb but without the midrange), and I agree that they sounded excellent. They do like power and can play quite loud without distortion if appropriately driven. It's unfortunate about the veneer; the higher-level models had real wood. At least one AK member completely refurbished his Qbs with real wood veneer - do a search and you should be able to find it. Another member (or maybe it was the same one) mirrored his pair by filling in the tweeter hole and cutting a new one on the other side.

Regarding your noise issue, I'd first try swapping the speakers left to right, then swapping the tweeters (they're not soldered, just clips, so it's easy to do). If it turns out that you have a bad tweeter, used replacements can be had for fairly reasonable prices on eBay. The glue on the magnets has been known to fail from time to time, so your friend could be correct. Repairing is a possibility but not exactly beginner stuff due to the high strength magnets involved. Here's one thread that details some repairs. Definitely do not try a repair without due diligence first.
 
not to be pedantic, but the EMIT is not a true ribbon, it's more of a quasi-ribbon, since the driver element is bonded to mylar, instead of suspended in air within a magnetic field. and I agree, the Q series punches way above their weight price-wise.
 
not to be pedantic, but the EMIT is not a true ribbon, it's more of a quasi-ribbon, since the driver element is bonded to mylar, instead of suspended in air within a magnetic field. and I agree, the Q series punches way above their weight price-wise.
I gave up on this battle a long time ago, while most of us in AK may know the difference, outside of here you're just tilting at windmills. In fact, I recently saw an EMIT advertised as electrostatic.
 
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