Any experience - rebuilt/mirror imaged cabinets for Infinity Qa, Qb, Q5, RS1.5 etc.?

Hello All,

I've been out of the audiophile world for a while and I'm just dipping my toe back in. I was luck to hear a pair of Infinity Qa's in a resale store and they sounded really nice. I didn't buy them, but the thought of buying an inexpensive pair of vintage speakers to satisfy my lust for good sound stuck with me.

Fast forward a year and I see a pair of Qb's on eBay and the seller is near my house. I end up winning the auction and $117 later I'm the proud owner a a really nice pair of Infinity Qb's in good cosmetic and working order.

I hooked these up and I was amazed at the sound. They satisfy me just as much as thousand dollar plus speakers did years ago. So, I start wondering......With a few modern upgrades can this design sound World-Class?

That brings me to my question: Has anyone ever heard a pair of Qb's, or other vintage Infinity Q or RS speakers, that have been placed into modern, well crafted cabinets that were braced, etc and maybe even mirror imaged?

It would seem that building a new cabinet out of dense 3/4-1" MDF, bracing them and mirror imaging them, might result in a really great speaker. But! It does make me wonder if there is any magic in the flimsy old late '70s cabinets.

Please share any experiences you have with updated cabinets, inserting cabinet braces, updated cross-overs (remove the pots?), etc. Did you get significantly better sound? Was it worth the effort?

Thanks for any comments.........

TIC

Not exactly what you asked for, but there were some RSM's made in mirror image configuration. In previous discussions about the RSM models, an AK'er from Australia has a mirror imaged pair.
It seems that configuration may have only been available overseas.
Google search does show them, the cabinet construction is slightly different as well as the mirror image design.

I did recap mine about 3 years ago. It helped tame a harsh midrange.

The next series, the Kappas, were made in a straight up and down vertical configuration and that seemed to be the norm after that.
I've often wished my RSM's were made with a vertical alignment and wonder how they would sound.

TIC said:

With a few modern upgrades can this design sound World-Class?

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No, but they have the potential to sound much, much better than stock.

TIC said:

It would seem that building a new cabinet out of dense 3/4-1" MDF, bracing them and mirror imaging them, might result in a really great speaker

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Both great ideas. Non mirror-imaging speaker pairs is most likely a result of keeping production costs low. You will never find really good speakers that are not mirror imaged. Design-wise, there are reasons for this, and it has to do with the off-axis radiation patterns of the speakers being matched between the L and R sides, and the specific time at which the sound from each driver is reaching the listener's ear. Neither of these two considerations will work out too well with non-mirror-imaged speakers.

TIC said:

It does make me wonder if there is any magic in the flimsy old late '70s cabinets.

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Not really, except the fact that they're original and that holds value for people.

One of my later rebuilds of an early '90's Polk Audio speaker consisted, in part, of adding an external MDF shell around the original enclosure, making the enclosure walls twice as thick. That, along with other improvements, produced a huge step up in quality. Building new enclosures to better standards would be a better idea yet. You're only limited by your imagination and cost constraints.

If you build new enclosures, keep the internal volume of the box the same to keep the woofer's response the same. Be sure to account for the volume taken up by any internal bracing when figuring this out.

G~

Aker Enaldo built some mirrored Qb's. The thread is here: http://www.audiokarma.org/forums/showthread.php?t=325455&highlight=enaldo I'm sure that would make them sound even better.

A simple brace would tighten up those boxes and reduce that Qb 100 Hz thump. I added a little more stuffing, about 25 - 30 %, to mine and it really helped tame the thump. The boxes will need to be resealed too, make sure they are air tight around the crossover.

The 12.5uF electrolytic cap on the mid range should be replaced but leave the yellow film cap on the EMIT, it's still good and part of the original "Infinity sound".

Clean the pot(s) with DeOxit D5 and lube with FaderLube if they are scratchy.

Good luck with your project, keep us posted on your progress.

he did a good job on those...love the logos

I have done NOTHING to the Qb's I bought in 1978, except measure the resistance across the EMIT. Both read good - around 3.2 on the meter. I think it's time to invest a little effort in bringing them up to spec, so "Thanks!" to chef free for the specific recommendations.

I've always wanted to mirror image these, but can't bring myself to pull the trigger on that mod. Will take a good look at the cabinets when I open them up, and see how hard that would be to achieve. Bracing and stuffing would be a lot easier, and might do all I need.

Loved Elnaldo's rebuild. The work recreating the badges blew my mind...

Unfortunately, I can't tell you the difference between the "mirrored" baffles and the originals...

What I can tell you, they look nicer!! And easier to place them in your room. With the original cabinet, you always end with one tweeter near a wall.

In case you do a new mirrored baffle some day... keep in mind the "dent" you see in the grill frame, at the tweeter height. It should be mirrored too.

The mid-range capacitor is a VERY NOTICEABLY change. I did and A-B comparison when recapping mine, and it was a night and day difference.

About the badges... I remember... I trashed the old cabinets, and realized one of the grills had one of the badges on it !!! I took my car and started to look for the trash truck, for half an hour around the neighborhood !! Of course I didn't find it...

Another suggestion you will read here, from me, is to use a SMALLER fuse for the tweeter. I'd say 0.75A to be on the safe side. If you listen LOUD and it blows, go up to 1A, but no more than that. The original 1.25A is too large. Your emit will blow before a 1.25A fuse. I use 0.5A in my Qb. It blew once 2 years ago while I was playing some white noise to measure some freqs response.

I've never popped a speaker fuse...i believe they are there for the people who use a 50 watt amp on a set of QLS's and play it at 3:00 for hours...then you will pop a fuse...but good equipment at reasonable levels you should never have an issue...

But AK is plenty of threads about blown Emits...

All of them were "protected" with a 1.25A fuse..

I did just that to a pair of Qb EMITs when I replaced an 85 watt Marantz with a 200 watt Mac. I fixed them with window defroster repair paint and they are still going strong with no change in sound (I have a second pair of Qbs for comparison.)

elnaldo said:

But AK is plenty of threads about blown Emits...

All of them were "protected" with a 1.25A fuse..

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exactly, my new to me Q2's have a bad emit and a perfect fuse...

The Qb cabinets were poorly made.
I had a pair where the baffle dislodged itself from the rest of the cabinet.
I reglued it and added bracing front to back at the woofer holes.
Changed out the pimpy midrange cap and improvement could easily be heard.
I also transformed the Qb into a stylish statement:

tubed: Those look really nice! I have some RSb's I'm considering doing some work on because I've seen so many threads detailing all the benefits that even simple bracing of the cabinets can bring. I have redone the pots on them and I'm seriously thinking to removing them as I've also read numerous complaints of how bad these pots choke the sound no matter clean they are.

I do have one cabinet I suspect in need of resealing and may start there. After the great results I got rehabbing my Qe's it's given me many things to ponder. Reading about others stories is illuminating in many ways and I can't wait to see more!

tubed, nice work man...!

chef free said:

I did just that to a pair of Qb EMITs when I replaced an 85 watt Marantz with a 200 watt Mac. I fixed them with window defroster repair paint and they are still going strong with no change in sound (I have a second pair of Qbs for comparison.)

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However, I've blown quite a few Qb 1-1/4 amp fuses in the past by pushing a 20 watt amp WAY past it's rated power playing Janis and Jimi. I wonder why the big power amps just took out those EMITs but the clipping amp blew fuses.

Thank you to all who have replied. Keep it coming!

I posted this a couple of weeks ago, promptly saw a pair of RS1.5s on eBay and sniped them for $255 which I thought was a bargain considering the condition. They were "pick up only" and 5 hours from my house, so I planned a family ski trip near the seller and picked them up on the way home last Sunday.

I was hoping the "improvements" in the RS1.5's would eliminate my desire to rebuild the Qb's, but I'm not sure I prefer the RS1.5's yet. Yes, they have much better build quality and they have the Watkins Woofers. But they are just not as light and airy as the Qb's for me. They do have new surrounds and maybe they need to break in a bit more. Who knows, maybe I just like the Qb's better. Time will tell.

I ended up buying a pair of original Qb stands on eBay last night. I'm reverting back to my teen years! Loved the look of a pair of big bookshelf speakers on dedicated stands!

Enjoy,

TIC

I'm surprised that the 1.5's don't knock out the Qb's! Maybe you just don't like the sound of those poly mids? I wonder if the mids are in a sealed enclosure like the Qb's.

Way back in '78 I chose the Qb over the Quantum Jr. And the Q5, to my ears it just sounded better. Now I'm thinking of mirroring one of my pairs...

TIC said:

Thank you to all who have replied. Keep it coming!

I posted this a couple of weeks ago, promptly saw a pair of RS1.5s on eBay and sniped them for $255 which I thought was a bargain considering the condition. They were "pick up only" and 5 hours from my house, so I planned a family ski trip near the seller and picked them up on the way home last Sunday.

I was hoping the "improvements" in the RS1.5's would eliminate my desire to rebuild the Qb's, but I'm not sure I prefer the RS1.5's yet. Yes, they have much better build quality and they have the Watkins Woofers. But they are just not as light and airy as the Qb's for me. They do have new surrounds and maybe they need to break in a bit more. Who knows, maybe I just like the Qb's better. Time will tell.

I ended up buying a pair of original Qb stands on eBay last night. I'm reverting back to my teen years! Loved the look of a pair of big bookshelf speakers on dedicated stands!

Enjoy,

TIC

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I know what you are saying and can see how you might prefer the Qbs.
I was disappointed in the RS1.5.
Perhaps the 1.5 enclosure is too small for best results using the Watkins woofer.

I started a thread about the Qb's I got recently and I have been comparing them off and on with my RSb's. The Qb's just sound so much lighter, airier, smoother, however you want to put it. I have read other threads on here that the Qb's midrange is possibly a standout from many other models. I can't speak to all that but with my experience so far with these and some DCM TF400's I have the Qb's win every time.

It has also been mentioned that putting the mids of the RSb's in a separate chamber as well would help isolate it from possible interference from the woofer and possibly help smooth it out. I do know a lot of newer, much costlier speakers seek to isolate the midrange from the rest of the speaker.

At this point I'm just trying to go a step at a time. Reading as much as I can find about what others have done and trying to map out a plan in stages. These Qb's are a blast though and fit perfectly in my limited space.

So far my next steps are to get new velcro for the grills, put some clay on the woofer spokes, replace the mid caps with some Dayton polys, seal the boxes and add a couple of rods front to back to stabilize the box more.

I played around with speaker positioning and listed to the RS1.5s again last night and this morning. They are growing on me. The bass goes considerably lower than the Qb's and they play REALLY LOUD in my small room. I haven't yet got them to image the way the Qb's do in my room, but it's probably a matter of placement. I'll keep working on it. They are still not quite as airy and lively as the Qb's in my room, but that too might get better with attention to placement.

Both my Qb's and the RS1.5's suffer from imbalance with the right side being more pronounced. This is likely a room issue or the fact that the ride side tweeter is outboard and the left side tweeter is inboard due to the lack of mirror imaging.

I bought a pair of original metal stands for the Qb's and they will arrive next week. I look forward to seeing the speakers displayed as intended and also to hear how they sound when placed at the optimum height and angle (at least what Infinity thought was the optimum). I currently have the RS1.5's sitting on top of a pair of speakers putting them 15" off the ground. I did lower them from 18" when I initially listened to them and I like them better a little lower.

Enjoy,

TIC