Another Infinity Project Thread

[macaltec]

There seems to be alot of interest in the old Infinitieshere lately. After reading a bit and talking with a couple of other members I have turned my attention to my own project. I've had these for 4 years. When I found them they had been outside for who knows how long. I was buying some stuff from the owner and just starting my vintage collection. The woofers needed foam (one still does). One midrange cone was totally ripped from the rest of the speaker. The cabs are obviously shot. Played around with them last night and got the tweeters working and x-over pots cleaned as well as one woofer foamed (got no more foam for the other one). The one complete speaker sounds good. Not sure about the other woofer. I had to take it down to just the basket to clean out some grit from the VC gap. The spider seems to have become week upon putting it back together the cone sits much lower in the basket than the other one did before foaming. I need to start thinking of duplicating the cabinets :scratch2: .

mac

[kfa888]

Hey, be careful with my sub :D

[macaltec]

Hey, be careful with my sub :D

Ya know, that thing does sound pretty good. I'll shoot ya a couple of pics.

mac

[Kencat]

Macaltec,

Any idea what model those are? Looks like quite a rebuild project there. Hopefully you can find an original woofer to replace that bad one.

Will be fun to follow your progress.

[Charivari]

Macaltec,

Any idea what model those are? Looks like quite a rebuild project there. Hopefully you can find an original woofer to replace that bad one.

Will be fun to follow your progress.
RS 1.5s (http://www.infinity-classics.de/infinity/models/Reference-series-1978-klein/Reference-Standard-1.5/body_rs_1_5.html), the next model up from the Reference Studio Monitor with the only difference being with the woofer ... which looks like it may possibly be a Watkins derivative.

Whew, Mac, you weren't kidding when you said the cabinets were trashed. Those look nothing like they should. Good thing the cones are poly rather than paper that surely would've been pulp by now.

- JP

[Kencat]

RS 1.5s (http://www.infinity-classics.de/infinity/models/Reference-series-1978-klein/Reference-Standard-1.5/body_rs_1_5.html), the next model up from the Reference Studio Monitor with the only difference being with the woofer ... which looks like it may possibly be a Watkins derivative.

- JP


Per the info in the brochure on that link you gave JP, that is a supposed to be an Infinity/Watkins 12" dual drive polypropylene cone driver. NICE!

[macaltec]

They are indeed dual VC wofers. I'm gonna throw a foam on the second woofer and see what happens. Blieve it or not it sounds pretty good the way it is pictured. Could always make a sub of sorts for the woofer and some small bookshelves out of the mids and tweets.

mac

[macaltec]

I got that second woofer refoamed and installed this evening. I got a good listen in and have determined that they are worth the effort to duplicate the cabinets. My first impressions are that these are one of the best sounding speakers I have ever heard. Curious thing happened when I put the woofer in the cab. It did not have as much bass as the first one. I remember checking the resistance of the VC's when I had it all apart and they were different values. Seems like one was around 6 ohms and the other around 3 ohms. Seemed kinda odd for a DVC speaker. Anyway I thought that maybe it makes a difference how the wires off the xover are hooked up the different value VC's. Out the woofer comes and I switched the wires put the woofer back in and presto chango bass out the ying yang (thats industry lingo for those that don't know) Has anyone else noticed this about these woofers?

mac

[Charivari]

I remember checking the resistance of the VC's when I had it all apart and they were different values. Seems like one was around 6 ohms and the other around 3 ohms. Seemed kinda odd for a DVC speaker.
That's normal for the Watkins woofer. It's been a while, but I seem to recall that the one VC is actually 2.6 ohms and the other 6.3, though it's been a rather long time. The impedances have to do with the principle behind why this woofer is capable of going so low, so flat while keeping the impedance from spiking as do normal woofers. You can read the salesman description about that driver on this page (http://www.infinity-classics.de/infinity/models/Quantum-series-1976/Quantum-Line-Source-QLS-1/QLS_1_Brochure_02.jpg) taken from the QLS-1 brochure.
Anyway I thought that maybe it makes a difference how the wires off the xover are hooked up the different value VC's. Out the woofer comes and I switched the wires put the woofer back in and presto chango bass out the ying yang (thats industry lingo for those that don't know) Has anyone else noticed this about these woofers?

mac
That sounds right, you must've accidentally swapped the wires on one of the VCs putting it out of phase with the other. I did that myself once as Infinity didn't exactly have their wires and crossovers all that well marked.

- JP

[macaltec]

JP, you got it on the impedances. You're also right about the crossovers. What a mess. Totally different layout from speaker to speaker. It's like they threw them together totally at random.

mac

[macaltec]

Still listening to these speakers more than any other of the 20 or so pairs I have. No physical work on the cabinets yet but I have been tossing around some plans to cut the panels with a co-worker that has an extensive woodworking shop. a breif talk with GordonW revealed that an increase of cabinet volume should not effect the crossover so long as I do not increase the baffle width or the height. I'm hoping by an increase in volume I can get them to play lower as I know they are capable of. That just leaves the depth to adjust. Thinking of making them mirror imaged as well. JP I'm eagerly awaiting you results from your mirror image project.

[Charivari]

So, you're not going to build that monster, two-cabinet per channel design I came up with a while back? :thmbsp:

I hate to be contrarian in this case, but larger cabinet volume will create the need to change the crossover for the Watkins. As you're aware, its two voice coils are designed so that the lower impedance VC kicks in at woofer resonance. The frequency of this depends upon the cabinet volume, which is why the progressively larger models using the Watkins woofer use progressively larger capacitors in the crossover for this section of the circuit. So, you might want to go ahead and design the volume of the cabinet to match an existing model so you can just duplicate the crossover schematics for the woofer.

I've attached the relavent schematics from the QLS-1, Quantum 2, and Quantum 3, each of which use the same crossover design and kind of drivers, but with smaller cabinet size with rising model number.

Quantum Line Source - 1:
http://audiokarma.org/forums/attachment.php?attachmentid=11010

Quantum 2:

http://audiokarma.org/forums/attachment.php?attachmentid=11011

Quantum 3:

http://audiokarma.org/forums/attachment.php?attachmentid=11012

Look forward to what you come up with.

- JP

[macaltec]

Damnit. I guess I'm just gonna have to find a set of the Q2's, Q3's, or QLS's and be done with it. Anybody?

[Kencat]

So, you're not going to build that monster, two-cabinet per channel design I came up with a while back? :thmbsp:

I hate to be contrarian in this case, but larger cabinet volume will create the need to change the crossover for the Watkins. As you're aware, its two voice coils are designed so that the lower impedance VC kicks in at woofer resonance. The frequency of this depends upon the cabinet volume, which is why the progressively larger models using the Watkins woofer use progressively larger capacitors in the crossover for this section of the circuit. So, you might want to go ahead and design the volume of the cabinet to match an existing model so you can just duplicate the crossover schematics for the woofer.

I've attached the relavent schematics from the QLS-1, Quantum 2, and Quantum 3, each of which use the same crossover design and kind of drivers, but with smaller cabinet size with rising model number.

Quantum Line Source - 1:
http://audiokarma.org/forums/attachment.php?attachmentid=11010

Quantum 2:

http://audiokarma.org/forums/attachment.php?attachmentid=11011

Quantum 3:

http://audiokarma.org/forums/attachment.php?attachmentid=11012

Look forward to what you come up with.

- JP


JP,

I'm getting interested in crossover theory and have started reading up on it (lots more to do yet), so for educational purposes, am I way off base to say that these filter circuits are a 1st order bandpass type design?

If this is wrong, can you explain what they are?

[Kencat]

Damnit. I guess I'm just gonna have to find a set of the Q2's, Q3's, or QLS's and be done with it. Anybody?

I'll keep me eyes peeled for ya, BUT, I've got 1st dibs on Negotiableterms QLS's if he decides not to get them refurbed (see one of the previous posts here somewhere).

(This is actually just some gentle prodding to get that boy working on those rare beauties :naughty: , but if he isn't going to do anything with em....)

[Charivari]

JP,

I'm getting interested in crossover theory and have started reading up on it (lots more to do yet), so for educational purposes, am I way off base to say that these filter circuits are a 1st order bandpass type design?

If this is wrong, can you explain what they are?
I do believe you are correct, though I'm not exactly the first person to comment too much on crossovers. I was just trying to bring up a technical point about the Watkins woofer and its crossover design that appeared Gordon was either unaware of or that had just slipped his mind.

The basic theory behind the Watkins woofer can be found on this page (http://www.infinity-classics.de/infinity/models/Quantum-series-1976/Quantum-Line-Source-QLS-1/QLS_1_Brochure_02.jpg), but I do not know much more in the way of specifics.

- JP

[Kencat]

I do believe you are correct, though I'm not exactly the first person to comment too much on crossovers. I was just trying to bring up a technical point about the Watkins woofer and its crossover design that appeared Gordon was either unaware of or that had just slipped his mind.

The basic theory behind the Watkins woofer can be found on this page (http://www.infinity-classics.de/infinity/models/Quantum-series-1976/Quantum-Line-Source-QLS-1/QLS_1_Brochure_02.jpg), but I do not know much more in the way of specifics.

- JP

What you were saying about the box volume and the crossover C and L values being different to compensate for the woofer frequency response makes sense to me.....and those schematics prove it.

With more study, I'll figure out what these filters are. :scratch2:

[Kencat]

QLS1 - 18Hz at +/- 2dB. :jawdrop:

What I would not give to hear one of those someday, powered by some 1000 Watt monoblock amps.

How may speakers have a claimed freq response down to 18 Hz ?

Unreal.

[Charivari]

What you were saying about the box volume and the crossover C and L values being different to compensate for the woofer frequency response makes sense to me.....and those schematics prove it.
Yep, the woofer free air resonance is the same for all three instances, but the volume of the cabinet shifts the system resonance upwards with the smaller models. This means the Watkins design, that needs to interact at the system resonance of the woofer, needs to be designed for higher frequencies.

QLS1 - 18Hz at +/- 2dB.
Indeed, mighty impressive. It looks like you're going the same way I have with the larger, TOTL Infinities -- 'they're the best speakers I've never heard.' Remember, that 18Hz figure is an anechoic measurement, which means with room boost, it's possible to go even lower. With my Q2s, as posted in the other thread about the QLS-1 in this forum, I was measuring strong output at insanely low levels. That is, in one particular arrangement and positioning of my speakers, I was measuring only a few dB down below the teens Hz. :smoke: Sadly, that appears to have been a special moment and place as I had to move my speakers and haven't been able to get that incredible performance back. :sigh:

Interestingly, consider what I said above about the system resonance. With the QLS, the resonance of the volume within the cabinet is right about where the Fs (free-air resonance) of the 12" Watkins lies. So, while the bass is deeper with the QLS, the woofer exists right on the knife edge of going wild because of this coincident of resonances -- it feels both like it's in a cabinet and not, which isn't a good thing with this particular implementation. The result is some issues with the bass and impedance dips/swings that are even harder on amplifiers. From what I've read, a lot of audiophiles with the QLS-1 back in the day had a habit of adding sand bags inside the cabinets to both add mass and, more importantly, to absorb some of that extra volume to shift the resonance up and make the Watkins better behaved. Negotiableterms probably knows a lot more about this and is likely the one to ask if you'd like to know more.

- JP

[Kencat]

Negotiableterms probably knows a lot more about this and is likely the one to ask if you'd like to know more.

- JP


JP, he's being very coy and quite about these :smoke:

I've been trying to shake the coconut tree but nothing is falling. :scratch2:

See last post "http://audiokarma.org/forums/showthread.php?t=63479&page=3&pp=15"