BTW, thanks for the PM and welcome to AK rs1b! I'll copy it and post it here when I get home from work for others' use if that's okay by you.
Watkins woofer white paper
- Thread starter geoff727
- Start date
BTW, thanks for the PM and welcome to AK rs1b! I'll copy it and post it here when I get home from work for others' use if that's okay by you.
i believe the earliest Watkins setup in the QLS1 had the thick black trim ring, black cone, and the 1400/1600uF caps. could be that those different caps gave a different frequency response they decided to change in later models, or that the early woofer had different parameters and the net sonic results were similar between the two. at this point, the only person who probably knows what went on in the very early stages is Bill.
Kencat
Super Member
Nope. Have those.
I don't need them for myself (only have Q2's :sigh
but I find it fun to dig into the technical history of the Quantum line, and I threw that out to see if anyone had more info. You seem to have unearthed a bit of a mystery here.Wouldn't it be nice if whomever owns all the engineering documents released them into the public domain ? (as is available for AR - see classicspeakerpages website).
Going back to the referenced article on groups.google.com (kmanusa), it seems that Infinity sort of messed up Bill Watkins design intent by not correcting the crossover. Maybe they did make the correction later on, if it could be determined that the 1400/1600 mfd were used in later models.
jimreeves - were the inductor values the same in that 1400/1600 crossover of yours as shown in the 1100/1400 schematics?
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Kencat
Super Member
cdfac's post came in as I was writing my last response, so I'm just seeing it.
Jim, did yours look like this?
Mine are black baffle with thick watkins trim rings, poly cones and had 1400 and 1600mfd caps to begin with. See cdfac's thread for more info...post 113 has my old xovers....great thread by the way...[edit]post 113 has my refurbs, post 13 of the second link has my old xovers..
http://www.audiokarma.org/forums/showthread.php?t=166374&page=4
And his other thread, with pics of his...
http://www.audiokarma.org/forums/showthread.php?t=215773
Here's the posted pic of my system...
http://www.audiokarma.org/forums/showpost.php?p=3007282&postcount=337
http://www.audiokarma.org/forums/showthread.php?t=166374&page=4
And his other thread, with pics of his...
http://www.audiokarma.org/forums/showthread.php?t=215773
Here's the posted pic of my system...
http://www.audiokarma.org/forums/showpost.php?p=3007282&postcount=337
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rs1b
Member
Watkins Wiring Diagram
I might be able to shed some light on the choice of caps and coils used in the circuit. As you know the Watkins woofer uses a tuned circuit. At resonance the coil and cap are like a a wire with near zero impedance. The 20MH coil and 1400MFD cap resonate at 30 hz if you do the math.
1/
6.28 X sq root of L .020 (coil) X C ( Cap ).001400 or basically so .020 x .0014 = .000028 and the squ/rt of that is .00529
putting it together you get 6.28 X .00529 = .0332 then divide this into 1 . so 1 divided by .0332 = 30.12 hz
So basically that woofer in that box resonates around 30HZ. The free air on the woofer should likley be around 18-20hz and when mounted in the box around 30 HZ. So what is that other cap for? On the older speakers like the QLS1 they were made back before CD's were around. Turntables were the norm and for the most part if the speakers went low enough you could get subsonic feedback. Since these speakers went well below 30HZ Infinity sometimes put a 6DB rolloff on the bottom end to stop the woofer from flapping itself to death.
If the rolloff was say at 35hz and the impedance was 4 ohms. The formula for a cap that would roll off at 35HZ would give you a 1100MFD cap.
Formula 1/6.28Xfrequency(35HZ)XImpedance(4 ohms)= .000113 or approx 1100 MFD.This would at least reduce some of the harmful damage.
I might be able to shed some light on the choice of caps and coils used in the circuit. As you know the Watkins woofer uses a tuned circuit. At resonance the coil and cap are like a a wire with near zero impedance. The 20MH coil and 1400MFD cap resonate at 30 hz if you do the math.
1/
6.28 X sq root of L .020 (coil) X C ( Cap ).001400 or basically so .020 x .0014 = .000028 and the squ/rt of that is .00529
putting it together you get 6.28 X .00529 = .0332 then divide this into 1 . so 1 divided by .0332 = 30.12 hz
So basically that woofer in that box resonates around 30HZ. The free air on the woofer should likley be around 18-20hz and when mounted in the box around 30 HZ. So what is that other cap for? On the older speakers like the QLS1 they were made back before CD's were around. Turntables were the norm and for the most part if the speakers went low enough you could get subsonic feedback. Since these speakers went well below 30HZ Infinity sometimes put a 6DB rolloff on the bottom end to stop the woofer from flapping itself to death.
If the rolloff was say at 35hz and the impedance was 4 ohms. The formula for a cap that would roll off at 35HZ would give you a 1100MFD cap.
Formula 1/6.28Xfrequency(35HZ)XImpedance(4 ohms)= .000113 or approx 1100 MFD.This would at least reduce some of the harmful damage.
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Army
Addicted Member
Maybe Army will revive his interest in posting it as a sticky in the Infinity forum.
Done
Kencat
Super Member
Not so sure about that. I submit this link - http://iccbrabant.tripod.com/icc/id1.html - and combined with the discussion in the groups.google link given earlier, it seems that what infinity did (or is it didn't do) to the crossover and modifying the mass of the Watkins woofer was without Bill Watkins' knowledge nor was it in his control; therefore, any changes in crossover design was in the realm of Infinity only.
Mr. Watkins knew what his woofer design could or should do, but Mr. Nudell had his own theories. Sounds to me like Bill feels very defensive about being blamed for the "amp killing" reputation given to the Watkins woofer due to Nudell's mods.
I think it would be neat to hear a true Bill Watkins "tuned" Infinity QLS1 vs the versions that came out. I also wonder how far misaligned the other Q's are.
rs1b
Member
Just a suggestion
Having repaired and upgraded many Infinities over the years the biggest improvment I found for the woofer at least was replacing the 20MH coil in the tuned circuit for the Watkins woofer. The fix isn't cheap but noticeable. The problem is in the fact that they used an iron core to keep the weight and cost down.If you have a decent size amp ( and you should for these ) the core will saturate causing noticable distortion. The improvment comes as a 20 pound 12 or 14 gage air wound coil(companies like Solen and others can wind them) but are expensive.The ressistnce is a tad higher but it will not saturate. At times I thought it was the woofer making the sound. If you have an electronic crossover shut off your mid and highs and listen to the coil . At high volumes you won't belive the noise off the coil. Especially noticeable on the 2.5 and 4.5's as the crososovers are exposed at the back and easily heard. Not so easy on yours but it's there. If you can hear it from the coil it is making it's way to you woofer as well.
Having repaired and upgraded many Infinities over the years the biggest improvment I found for the woofer at least was replacing the 20MH coil in the tuned circuit for the Watkins woofer. The fix isn't cheap but noticeable. The problem is in the fact that they used an iron core to keep the weight and cost down.If you have a decent size amp ( and you should for these ) the core will saturate causing noticable distortion. The improvment comes as a 20 pound 12 or 14 gage air wound coil(companies like Solen and others can wind them) but are expensive.The ressistnce is a tad higher but it will not saturate. At times I thought it was the woofer making the sound. If you have an electronic crossover shut off your mid and highs and listen to the coil . At high volumes you won't belive the noise off the coil. Especially noticeable on the 2.5 and 4.5's as the crososovers are exposed at the back and easily heard. Not so easy on yours but it's there. If you can hear it from the coil it is making it's way to you woofer as well.
that watkins circuit is more complicated than i realized. RS1b's calculations are right, but they weren't carried to their logical conclusion. the 4-ohm coil has also has a resonance frequency, 60Hz by his math, and the 2-ohm coil (~2.5-ohm DCR, IME) has a rolloff point of 45Hz. confused? i am!
all this time, i had really just been thinking of the two voice coils as having different bandpass filters that, when summed together, gave good flat bass, but there is definitely more going on than just the bandpass.
all this time, i had really just been thinking of the two voice coils as having different bandpass filters that, when summed together, gave good flat bass, but there is definitely more going on than just the bandpass.
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i wasn't saying that he was still involved, but he at least knew what was going on.
Kencat
Super Member
From http://groups.google.com/group/rec....=en&q=woofer+group:rec.audio.*+author:watkins
My dual-drive woofer works so:
A second voice coil (vc-2) is wound over the main voice
coil (vc-1) in the woofer, this second coil having a
single layer and very low impedance. Now vc-2 would
normally have an impedance too low for safe operation.
However around fundamental resonance the impedance of
_any_ coil will ~triple. Now we activate vc-2 _ONLY_
in the region of fundamental resonance (around 45 Hz)
and it rises to ~8 ohms or so (being ~2.5 in the
first place) which is safe. This is accomplished with
an LC circuit tuned to 45 HZ and with the Q of the LC
circuit adjusted to provide the response shape and
impedance desired. Please note that the exact value
of vc-2 and the characteristics of the LC circuit give
_COMPLETE_ control of the impedance. The benefit of
the dual-drive may then be taken in extended bass or
higher efficiency in a given size box, or a smaller
box for a given efficiency or bass extension.
---------------------------------------------------
Resonance in a sealed box is the point where the
stored kinetic energy in the moving parts (the mass of the
cone, coil, and ~1/2 the spider and suspension) is equal
to the stored energy in the elasticity of the suspensions
and the air in the enclosure.
----------------------------------------
However, with
dual-drive we simply insert a smaller motor to increase bass
(with a second low-impedance coil), _BUT_ let it work around
resonance _ONLY_, so as to not affect output above resonance.
The see-saw "plank" then can be up on both ends. Bass response
can be adjusted _INDEPENDENT_ from response above resonance.
We can go for efficiency with a larger magnet, or we can minipulate
motor, mass, and enclosure volume, and use dual-drive to achieve
extended bass or a smaller enclosure, as well as deal with the
6 dB response step. (kencat comment-please read all the text before this copied part to fully understand it)
End of Bill Watkins words
A capacitor and an inductor in series with a driver is a simple 1st order bandpass filter. VC1 has a bandpass and VC2 has a bandpass.
cdfac - I think you were right initially. It is just two bandpass filters crossing over the two coils, just like a woofer to a midrange driver.
The trick is to know where the woofer drivers' fundamental resonance is and then design the bandpass filters to have VC2 kick in around this point, and I'm guessing, knock out VC1 or the proper amount of it.
Not sure if all this can adequately be modeled mathematically, but perhaps experimentation is used to fine tune LC values to get the desired response.
rs1b - Aren't those calculations you showed a bit simplifed, and ignoring the electro-mechanical equivalent LCR circuit of the driver mounted in the box? Bill Watkins says the resonance is 45 so the 30Hz is close. Looking to understand this better as well.
Good stuff this is.
Done
Thanks Army! But, was the white paper ever posted? If so I'm missing it. Could it be in AK database?
rs1b
Member
Watkins Calculations
So the question posed was “aren’t the calculations showed a bit simplified”.And the answer to that is yes. Because really it is. The tuned circuit formula is
F= 1
2π √ L C
As was already mentioned at resonance the only thing left remaining with regards our discussion is the resistance in the coil which is fairly small unless your using and air coil like I am with a huge length of wire. Although 12gage.
The different Watkins systems had different resonant frequencies. Here are a few. The RS 4.5’s used a 20MH coil with a 2000MFD Cap. When you do the math it shows 25HZ. The RS2.5’s used a 20MH coil and a 700MFD cap giving a 42 HZ resonant frequency. The QLS1 used a 20MH coil and a 1400MFD cap for 30HZ. So you can see they weren’t in fact all the same. The schematics show these values of which I have all the ones mentioned.
But your question asked about LC and R. So let’s talk R for a momemt,but in this case let’s call it Z for impedance because this is frequency related for this discussion. I’ll use an example. I have a set of RS2.5’s. When I test the Watkins woofer 4 ohm side of the voice coil in the box I get around 30 Ohms impedance at 40HZ. When I test the 2 ohm side in the box at resonance I get 12 ohms. Put them together with the tuned circuit engaged and I get 8.2 ohms at 40 HZ. Both coils are operational but as you approach resonance the 2 ohm coil has the highest current flow.
The 4.5’s as we know use 2 12’ Watkins woofers and the 4ohm coils are wired in series to give around 8ohms but the 2 ohm coils are in parallel. Interestingly though if you look at the circuit on the 4.5’s with the 20MH coil and 2000MFD cap they also have wired in series a .9 Ohm 50W resistor. This can be switched in and out of the circuit. It is called a BASS CUT switch. And yes it is. At resonance it will add an additional .9 ohms to that tuned circuit reducing some of the current flow to that coil but at the same time changing the balance between the 2 coils.
So the question posed was “aren’t the calculations showed a bit simplified”.And the answer to that is yes. Because really it is. The tuned circuit formula is
F= 1
2π √ L C
As was already mentioned at resonance the only thing left remaining with regards our discussion is the resistance in the coil which is fairly small unless your using and air coil like I am with a huge length of wire. Although 12gage.
The different Watkins systems had different resonant frequencies. Here are a few. The RS 4.5’s used a 20MH coil with a 2000MFD Cap. When you do the math it shows 25HZ. The RS2.5’s used a 20MH coil and a 700MFD cap giving a 42 HZ resonant frequency. The QLS1 used a 20MH coil and a 1400MFD cap for 30HZ. So you can see they weren’t in fact all the same. The schematics show these values of which I have all the ones mentioned.
But your question asked about LC and R. So let’s talk R for a momemt,but in this case let’s call it Z for impedance because this is frequency related for this discussion. I’ll use an example. I have a set of RS2.5’s. When I test the Watkins woofer 4 ohm side of the voice coil in the box I get around 30 Ohms impedance at 40HZ. When I test the 2 ohm side in the box at resonance I get 12 ohms. Put them together with the tuned circuit engaged and I get 8.2 ohms at 40 HZ. Both coils are operational but as you approach resonance the 2 ohm coil has the highest current flow.
The 4.5’s as we know use 2 12’ Watkins woofers and the 4ohm coils are wired in series to give around 8ohms but the 2 ohm coils are in parallel. Interestingly though if you look at the circuit on the 4.5’s with the 20MH coil and 2000MFD cap they also have wired in series a .9 Ohm 50W resistor. This can be switched in and out of the circuit. It is called a BASS CUT switch. And yes it is. At resonance it will add an additional .9 ohms to that tuned circuit reducing some of the current flow to that coil but at the same time changing the balance between the 2 coils.
I recall reading an article stating that Infinity use two sources for the DVC speakers one was Watkins and the other was a Japanese source speaker but DVC as well. And to add some merit to that statement I talked to Bill a few weeks ago to discuss repairs to a DVC driver and he asked to describe to him the driver, it was like he was unsure if the driver was a Watkins DVC driver. Although the driver had the orginal part number stamped on the back of the driver from infinity. He seemed unsure of the speaker that I described to him unlike all my other speakers I have. Many of them have black steel baskets with a black magnet assembly and depended on the model vary in magnet size. But some of the ones I have from my QLS-1's and some others that purchased for replacements were the silver ones with larger silver magnets, the magnets are as large as the basket assembly. The one I wished to send to him was of the larger magnet varity and the voice coil was rubbing, I didn't want to just throw it away if it could be fixed but he stated that it was not repairable. That one had a poly cone as well. In that article if I recall Watkins implied he never really had much to do with the designs or applications of the speakers that Infinity built. Possibly Infinity just would find driver suppliers that were invoative and inpressed them and used them as they saw fit and kept the suppliers of the drivers in kind of in the dark as to how they used them. And then when Infinity started getting some slack about their speakers being amp killers they started throwing the speaker suppliers under the bus, and thats where Watkins came in to set the record straight.
Kencat
Super Member
:lmao:
under the bus..............that's a good one Ken
Interesting info about possible different suppliers, and seconding the magnet size differences.
Wow Ken! That's surprising. You should post a pic or two of that driver if you have a chance.
Just finished the refoam (successfully) of both of my Watkins 12" drivers last weekend, using Rick Cobb's surround kit. My woofers are indeed 2" VC poly cone drivers with a slight bumped back plate. What I found most difficult was centering the coils with the 30hz test tone. Whoever originally glued the cone to the spider didn't align them properly, so in gluing on the surrounds it was necessary to force the cones off-center to the baskets about 3mm. Both were nearly identical in that respect. My guess is that the jig used was off that much. Thankfully they're working nicely now. :thmbsp:
I will do that (get some pics) soon and post them. Unfornutately I tossed the one away since I was told it was unrepairable. I had purchased a replacement for it and the one I purchased was indeed the same as the one I tossed, same large Magnet assembly. Maybe they were made later and were used to supply bass drivers for RS 4.5's as I am not sure what their bass drivers looked like but were probably some of the latest versions of DVC made for Infinity These were in a pair of QLS-1's that I purchased and repaired all the drivers that had problems, both the bass drivers were of the type that I described, poly coned, silver magnet assembly and baskets. One of them just needed the foam replaced, but the other one had major voice coil rub so I purchased one off the internet that looked brand new from a guy and it matched the other one, and is working great. But most of my other QLS drivers with the same part number on it are different looking, they have black magnets and the magnets are slightly smaller than the back of the basket.
Kencat
Super Member
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