View Full Version : Infinity Quantum 5's vs Infinity Qb's

02-29-2004, 06:17 AM
I already have a pair of Quantum Qb's and I'm very happy with them but the other day my favourite vintage audio store had snagged a very nicelooking pair of Quantum 5's. The 5's are a three-way speaker like the Qb but a more upscale version featuring a 12 inch Watkins dual voice coil woofer a high dispersion dome midrange and the EMIT tweeter. On paper at least the 5's should be as good if not better than the Qb's. The store didn't want an outrageous amount of money so I brought them home (they'll let me take things home and audition them with my own system, I'm using a Sansui AU-717) Now specs on paper are one thing but these 5's just didn't have the same kind of WOW factor as the Qb's. There was a buzz in one of the midranges that needs to be looked into but even taking that into consideration I was underwhelmed. Is it possible that there is some kind of problem with them or were the 5's just not as great as the Qb's?

I hope you have some experience with these, Beatlefred.

02-29-2004, 02:21 PM
Well, the Quantums were meant as the higher models to the Q's, so I suppose one would expect the Quantum's to be better. However, the Quantum 5 is the smallest of the numbered-series Quantum's, so I dont think you'd notice much of difference over the Qb's other than perhaps more bass response with the larger 12" woofer. To notice more of a difference for the better, I feel you'd need to move up to a larger model such as the Quantum 3.

I think its quite possible that the Q5's you have do need a bit of maintenance work, which is typical of those speakers given their 25 yr + age. But you certainly cant go wrong having them, if you took those parts out and offered them for sale, you'd have quite a few interested buyers, or even the whole speaker pair themselves.


02-29-2004, 02:51 PM
I've always thought the Watkins woofers really appreciated hefty amounts of juice. More than the very nice AU-717 is able to provide. Even at moderate SPL.

02-29-2004, 02:56 PM
Well, you can apply as much amplifier power as you want, but I think the AU-717 in most cases should be fine, especially with the 10" Qb woofers, unless one wants to play their music at insanely loud THOR-like levels :D


02-29-2004, 05:44 PM
".....the Quantum 5 is the smallest of the numbered-series Quantum's, so I dont think you'd notice much of difference over the Qb's other than perhaps more bass response with the larger 12" woofer."

The Quantum's are a beautiful looking speaker, very elegant with real walnut veneer even under the grille cloth, binding posts and controls for both the mid range and tweeters. The Qb's on the other hand with vinyl veneer look like the scruffy younger sibling in hand-me-downs. I had heard good things about the Watkins woofers and was just very curious in the differences between the two. That's why I was so surprised, the Quantums just sound muddy in comparison without the tight bass and clean crisp highs. Even the EMITs don't have the same clarity. It makes me think that perhaps there is a problem with the crossovers or something. What kind of maintenance would these need? I really appreciate the depth of knowledge here. The techie at the audio shop is good but he can't be expected to know everything. At this point I probably know as much about vintage Infinity's as he does.

02-29-2004, 06:01 PM
Well, my Qb's are in real nice condition, and Ive always liked they way they looked, better than the followup model RSb somehow.

You might want to check out those adjustment pots in the back- quite frankly, I think they are a pain in the ass because they seem to only accumulate filth over time, and can cause the sound from the drivers to sound muffled. Go behind the speaker and turn the knobs and see if they have a scratchy/abrasive feel to it, if so, they probably could use a good cleaning. You can try and enlist the help of a 2nd person to hear how the speakers sound while you adjust the knobs, or vice versa.

If you could find someone in your area with some knowledge & experience on vintage Infinity's, they could probably give the Q5's a more thorough inspection and see what might need to done in order to improve their sound. I'm inclined to think after 25 + years, they might need some servicing. The other alternative is to remove all the drivers and crossover and send them out to be checked by a competent speaker repairman, such as Orange County Speaker in California or even Mr Watkins himself who has a shop in Tennesee.


02-29-2004, 06:29 PM
If there is one thing I'm learning here it's that you can't judge a speaker by it's enclosure. The control knobs feel VERY scratchy and that's probably a good place to start an overhaul. I'm determined to make these nice old units sing like they were supposed to. I'll let you know how we progress. Thanks for your comments Beatlefred:beer: I suppose a 'virtual' beer is the best I can do at the moment.

02-29-2004, 06:34 PM
Well, I suppose a virtual beer-belly is better anyway than a real one :)

B/F :beerchug:

02-29-2004, 11:20 PM
I have a pair of quantum 3s and a pair of quantum jrs.The jrs are probably a closer match to the Q 5s.I have mine in the living room driven by a Yamaha ca-2010 ,120 w rms.They sound outstanding.Yours probably need replacement capacitors and a good cleaning on the adj.knobs.I had to clean the knobs on mine as sound was intermitent depending on where adjustment was set.I also used a ca-810 amp on them too 65w rms but they sucked up alot of power at anything above normal voices.The q3s are definetly a cut above.Blew regulators on a ca-810 amp trying to drive them,but after getting a soundcraftsmen amp 250w rms they really came to life.Right now I am using my pioneer sx-5590 200w rms at 4 ohms and the sound is .........riveting ,beyond belief for clarity .I have not tried to drive them to the levels capable with the soundcraftsmen,but I believe they sound better with the pioneer......Its close.

02-29-2004, 11:45 PM
Well, as much as I like the Quantum's & Q models, my main speakers are really incredible, and Infinity really hit a home run when they made the stunning Renaissance 90's:

03-01-2004, 12:22 PM
I'll bet they sound as good as they look. Which one of your amplifiers do you use to power them?
I've heard it said that three of any one thing constitutes a collection. There are a pair of Quantum 3's on Ebay right now. Although the seller wants $649US as a starting price, more than I can afford. I should mention that the Quantum 5's cost me about $200US. Which I thought was a reasonable price considering that the EMIT's alone sell for between $50 to $80US on ebay. They come with the original Infinity speaker stands and boxes.They are in near mint condition cosmetically although one of the Infinity logos is missing. I'm going to have them overhauled, the controls cleaned and the capacitors replaced and then we'll see how they work then.
Is it possible to get in touch with Mr. Watkins by email?

Here is the link to the Quantum 3's on Ebay:

and another link to the Infinity Classics home page:

03-01-2004, 03:36 PM
Infinity speaker systems in general, and the Watkins woofer, in particular, take a LOT of power to drive 'em properly. Note Bobby Shred's Infinity page:

I would suggest that to get that open, tight sound out of the Watkins woofer will take at least 200 wpc. Less will be, well, just less and not sound very good.
If you're interested, I have some amps ... :cool:

03-01-2004, 04:27 PM
Bobbyshred's site had a link to Mr. Wtakins webpage which listed his email address. I've sent an email to the man himself to see what he has to say about powering his woofer. I'll let you know if I get an answer.

03-01-2004, 04:54 PM
Far out! :cool:

03-01-2004, 10:45 PM
A friend of mine recently acquired a set of Quantum 3's from Ebay after I had mentioned the auction to him, he got them for only a wee bit over $200, so I'd say thats a really good buy.

I have a whole bunch of various amps to drive my Ren 90's, the most powerful being my Sansui BA-5000 (300W, I have two of them) and a Sansui B-2301 (also 300W). In the photo below, you can see the left Qb spkr with a Qe on top of it. Its a bit awkward since they face perpendicular to the Ren 90's but for now I have to make do given the (lack of) available space in my basement.


03-11-2004, 04:18 PM
So how many people in America can say they use a pair of BA-5000s as bookends for their stereo components?

Haven't heard anything back from Mr. Watkins. Meanwhile the Q 5s are still in the shop (I'm in no hurry, the speaker guy there is a genius but kind of eccentric when it comes to a 'normal' work day). I can't find any info on the output of an AU-717 into 4 ohms. It must be at least 120-130 Watts per. You would think that would be enough power (unless you are Thor of course)

03-11-2004, 08:17 PM
Given the limited space I have to work with in my basement for the time being, the only place right now for the BA-5K's is where they're shown in the photo- otherwise if they were lifted down onto those cheap black carts, there would be a good chance the carts would collapse under the enormous weight of the amps.

Mr Watkins is an elderly man, he is not known for fast email responses, so you might have to wait a while to hear back from him.

The AU-717, as I said before will play fine into 4 ohm loads. I distinctly remember reading a review of the 717 in a hi fi magazine which stated that fact. As or which particular mag that review was in, I'd have to spend some time searching thru the stacks & stacks in my collection. I do know for sure though, the 717 was given an excellent review in the Feb 78 issue of Stereo Review.


03-13-2004, 01:59 AM
I'ts very cool to see them just sitting there, no disrepect intended, it's just that they look like stone lions at the entrance to a museum, probably weigh about the same.
Mr. Watkins can take all the time in world. If I can be patient for our local speaker genius........
If you ever happen across that AU-717 review I'm sure I'm not the only person who would interested in what they had to say.

03-19-2004, 02:46 AM
I just got the Quantum 5's back from the shop. The adjustment pots in the rear have been cleaned. The Emit tweeters and the midrange drivers are all good and the crossovers were working up to specs. The Watkins woofers however had some problems. One of the positive leads is a black wire. Someone had been confused by this and that driver was hooked up wrong. They also needed to be re-foamed but they are now back to their former glory. I also got a reply to my email to Mr. Watkins. He agrees with Beatlefred. He's obviously a man of few words, it says simply:

" The Sansui 717 will work well in an average size
room and at a reasonable loudness level.
Bill W."

'nuff said.