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QLS-1 Restoration Project

banffskiing said:
Looking at the graph on the prevoius thread, for the woofer alone, it is very easy to tell exactly when the 2ohm voice coil kicks in. Looks to me like it is a little less than 20 hz. Not sure and maybe someone else out there knows for sure but it seems to me that the low impedance voice coil should kick in at the drivers resonate frequency. Probably need a plot of the woofers impedance with the 2 ohm coil disconnected. That would show exactly where the drivers goes into resonance. I am guessing that, at the peak of resonance, the 2 ohm coil should also be on at it's peak to counter the back emf caused by the reasonance. Kind of like to bell curves back to back.
I don't know but it's kind of fun playing with this stuff.

banff
Click to expand...
I've never been too good reading these graphs, but it looks to me like the second voice coil kicks in somewhere around 25Hz. As you noted, it was intended to kick in when the impedance of the first spiked and the spike around that frequency is much shorter than typical for a woofer.

All in all, I'm mighty surprised the Watkins doesn't dip too low. All the literature I've read on these indicates a nearly 1 ohm dip near the system resonance. Then again, it wouldn't be the first time what reviewers have stated as fact was flat out false upon closer examination. Still, the low sensitivity keeps these amp killers and I wouldn't be surprised if the phase angles aren't awfully hard on low current amplifiers.

Really nice PCBs, btw. Those really cleaned up the crossover. Roughly what wire gauge do those traces work out to be roughly equivalent of? (I'd just be wondering in case the smaller traces act like fusable links if too thin.)

- JP
 
Jp

Not really sure about the equivalent wire size but if you look at page 4 of this thread it shows the backside of the circuit board. On most of the traces, I used the componet lead as part of the conduction path. Also the the PCB was a 2oz copper board. It would be interesting to see what wire size is eq. to a 1/2in copper trace.

As for the phase angles being hard on amplifiers, that kind of gets into the reactive power, apparent power thing or I guess you would call it power factor. Wow it's been along time since I had to calculate or measure it but I don't remember it being that hard. It is caused by the voltage and current being out of phase from one another. Did not take that into consideration when I made the impedance measurments. Just simply measured the voltage and the current at different frequencys and used the formula R=V/I Used my laptop as a signal source to the amplifier and entered the data into a spreadheet.

Just did a calculation for 1/2 wide trace that is one inch long made with 2oz copper pcb.

Current = assumed (22amps)
Resistance = .0005ohms
voltage drop = .012v

Power dissipated across trace = V^2/R = (.012)*(.012)/.0005 = .288watts


Banff
 
Looking at the Graphs something is amiss as we never see value below 3 Ohms.
This is possible I guess as the two VC are in play.
I did some cals on LCR circuits and this is what I came up with just for the
Voice coils now I am sure when a speaker is put in a box resonance Freqs change right?

For A QLS1
20mh coil 1400uf cap Resonance Freq = 30 HZ Z = 3.7 Ohms
6.5mh coil 1100uf Cap Resonance Freq = 59 HZ Z = 2.4 Ohms

For Q2
20mh coil 1100uf cap Resonance Freq = 33 HZ Z = 4.26 Ohms
4.3mh coil 700uf Cap Resonance Freq = 91 HZ Z = 2.4 Ohms

For a Q3
20mh coil 600uf cap Resonance Freq = 46 HZ Z = 5.77 Ohms
4.3mh coil 600uf Cap Resonance Freq = 99 HZ Z = 2.6 Ohms

For a Q4
20mh coil 700uf cap Resonance Freq = 42 HZ Z = 5.3 Ohms
1.0mh coil 1100uf Cap Resonance Freq = 152 HZ Z = .95 Ohms

For a Q5
20mh coil 700uf cap Resonance Freq = 42 HZ Z = 5.3 Ohms
2.0mh coil 700uf Cap Resonance Freq = 134 HZ Z = 1.7 Ohms

For IRS 4.5
VC1 = 4 Ohm
12.5mh coil 300uf Resonance Freq = 82 HZ Z = 6.45 Ohms
12.5mh coil 600uf Resonance Freq = 58 HZ Z = 4.5 Ohms
8.0mh coil 450uf Resonance Freq = 84 HZ Z = 4.5 Ohms

VC2 2 Ohm
20mh coil 2000uf Resonance Freq = 25 HZ Z = 3.1 Ohms
 
goat67 said:
Looking at the Graphs something is amiss as we never see value below 3 Ohms.
This is possible I guess as the two VC are in play.
I did some cals on LCR circuits and this is what I came up with just for the
Voice coils now I am sure when a speaker is put in a box resonance Freqs change right?

For A QLS1
20mh coil 1400uf cap Resonance Freq = 30 HZ Z = 3.7 Ohms
6.5mh coil 1100uf Cap Resonance Freq = 59 HZ Z = 2.4 Ohms

Goat
Just ran the same numbers on a spread sheet and came up with the same resonate freq.
Basically resonance occures when XL=XC at 30hz Xl=3.7 and Xc=3.7 (20mhcoil)


It is actually a very complex problem because as you said the box also shifts the resonate point of the driver to a higher frequency. I would guess that the volume of the QLs-1 cab at over 6 cubic feet does not do a whole lot to dampen the dirver. The woofer is also inductive which changes depending on the frequency. All of this makes it difficult to calculate but I would like to understand how it all ties together so that It will be alot easier when it come time for everyone to re-cap the xover and fine tune it.

I think I will run 4 more impedance test on just the woofer section.

1. Driver alone into 4 ohm coil (no corssover connected)
2. Driver alone into 2 ohm coil (no corssover connected)
3. Dirver with only 4 ohm coil connected to crossover
4. Dirver with only 2 ohm coil connected to crossover

This way it should be esaier to see what effects what.

Oh well to much for me to think about this late.

Banff
Click to expand...
 
Guys, rather than speculate, why don't you get it straight from the horse's mouth and give Bill Watkins a call? I've spoken with him in the past and he's always been more than helpful. If I recall correctly, he had a disagreement with Infinity over the proper size woofer to put into the QLS - I think I remember him saying he thought the one they used was too small for the enclosure. Anyway, give him a call and see what he says; I bet he can resolve this for you in a hurry.

Watkins Stereo

David
 
Ack! Math! That's why I had to abandon my pursuits in science and turn to literature. :sigh:

phaedrus said:
If I recall correctly, he had a disagreement with Infinity over the proper size woofer to put into the QLS - I think I remember him saying he thought the one they used was too small for the enclosure.
Click to expand...

David, that sounds like something worth asking. Folks I've known to have chatted with Watkins has always mentioned him to be very friendly and talkative about his designs. That could help explain the use of the 15" driver in the QRS, the only Watkins larger than 12"s in the QLS.

- JP
 
Have completed the second speaker and have them set up in the living room
They are sound ing very good considering the way they are set up in the room.
Need more power. 165w/ch is no where near enough.

Banff
 
I talked to Bill Watkins several years ago about my Quantum II's. The woofers bottoming are the first sign of overdriving these with my Hafler DH 500. They "pop" when overdriven and hit the end of the voice coil. He said the Quantum II 12" woofers did this fairly easily because the cabinet volume was too large for the excusion and suspension he designed into the woofers. The QLS was worse with even more cabinet volume.

I also have Quantum III's which are slightly smaller cabinets than the II's. The woofers do not bottom nearly as easily in the III's. So, I use these in my home theater system with great results!!

Bill suggested using a piece of rigid foam or something similar to reduce the cabinet volume of my II's to equal the III's. The same would work for the QLS's.

The downside of this is reduced low frequency extension. The II's go down to about 25 Hz fairly strongly. The III's are done at about 30 Hz. I presume the QLS's go down to about 20 Hz.

So, it's a compromise of whether you want bass extension or higher power handling capacity. There is no doubt the QLS's midrange domes and EMITs handle many times more power than the woofer. I wonder if anyone ever built a subwoofer with two or more Watkins 12" drivers to compliment their Quantums or QLS.:smoke:
 
banffskiing said:
Have completed the second speaker and have them set up in the living room
They are sound ing very good considering the way they are set up in the room.
Need more power. 165w/ch is no where near enough.

Banff
Click to expand...
That's great! They'll really shine with some serious power behind them.

Unlike bocoogto I haven't had any issue with the Watkins woofers in my Quantum 2's bottoming out driven by a Yamaha MX-10000. That might be due to the amps damping factor of 1000 or because it has a lot of headroom.
 
Then it is no real 165W/channel. We've driven them with 120W/channel at 8Ohm and that was enough. The second 120W/channel @8ohm was better but we could live with just one (the midbass was tighter).

We've also driven them with a 140W/channel @8Ohm (measured) and that was just AMAZING. Even better then the 2 120W/channels.

So start using real amps and stop looking at the specs I would say :)
 
bocoogto

I have once or twice had the poping sound but, it is usually when I have overdriven the amp such as when you have the volume turned up during a quite passage and then suddenly the bass kicks in at 10X the power level.
It does the exact same thing on my JBL's. Probably not the same as rigid foam but I have the cabinets stuffed pretty well with Dacron about 5 pounds in each speaker. At some point I plan on getting a couple of amps and use one channel for the mids/highs and the other channel for bass. That would be one amp per speaker.
 
My posting was intended to report what Mr. Watkins said about the woofer bottoming. His analysis makes sense to me. I tried an AR3 woofer in one of my Quantum III's, which has much more cabinet volume than the AR3 cabinet. The AR woofer also has more of a tendency to bottom than when mounted in the AR3 cabinet. Great bass, though!! It rivals the Watkins woofer in the Quantum III cabinet.
 
We had the Q3 and the QLS and well, we never succeeded in latting the woofer pop with both speakers. Even better, the woofer is SO tight that it I'm starting to doubht at myself...
 
I also spoke with Bill Watkins about 2 years ago and he told me the same thing. He even said that he advised Infinity that the qls cab was to big for the woofer. I guess Infinity wanted to put that 18hz on the spec sheet to look impressive at the cost of letting the woofer get out of control. If I remember correctly he is also the one that advised me to fill the cabinets with plenty of stuffing. One question I have is on the spec sheet, infinity reccommends the amplfier range of 100 to 500watts. I wonder if that is rated into 8 or 4 ohms
 
I'm sure they mean the power rating at 4 ohms, since that is the impedance of the system. I can tell you that my Hafler DH 200 (or DH 500) will easily bottom the woofer cones. That's slightly less than 200 watts (or 500 watts) per channel into 4 ohms.

Bill Watkins was quite animated (and angry?) in his description of the problem with QLS cabinet volume being too large. It sounds like he told you the same things he told me. Infinity would not listen to him, even though he designed and supplied the woofers. Yes, the -3db point of 18 Hz. is probably accurate, but at what power level?

I would really like to hear a pair of "stock" QLS's with a reasonable amount of power. They're no doubt better than the Quantum II's or III's :music:in every respect except possibly imaging. In any case, I'll bet they sound fantastic!!
 
bocoogto said:
Yes, the -3db point of 18 Hz. is probably accurate, but at what power level?
Click to expand...

I agree 100% with that statment. They seem to handle everything the M-504can dish out as long as you don't drive the amp past the 0db point.
To get any real volume at that low of a frequency the woofer would have to move quite a bit. in other words past it's limit. I have looked at the output with a scope and it really does not clip until around 55 volts peak or about 378 watts if you assume 4 ohms. Anyway yes I am quite happy with them and yes it was alot of work to get them back 100% but feel that it was worth the effort.

banff
 
Whew! I just found this thread and read all of banffskiing's posts.

What a project!:jawdrop::jawdrop::jawdrop::jawdrop:

This should be published in book form. You could also be selling the midrange wire for what it cost you to fellow Infinity fans. Or doing EMIT repair for princely prices.

You deserve an award for such tenacity.
 
Actually, 18 Hz. was the -2 db. point for the QLS. I looked on Bobby Shred's site at the QLS advertising sheet.
 
For lack of a better place to ask this, what would be considered the average range of fetching prices for a decent pair of QLS's these days and what would be considered a steal? I know it's probably pretty dependent on condition, so assume they would need a little TLC. How about for Quantum 2's? Just thinking ahead ;) Thanks.
 
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