Watkins Woofer Specifications

[pentode]

Hello, I'm trying to build a cabinet from scratch using Watkins Woofers. Does anyone have any specification data for these speakers? I spoke with Mr Watkins, but this data but it wasn't the kind of information he shared. I'm trying to find the free air resonant frequency (of the 4 ohm side), the Vas (equivalent volume of air), and the Q data, Mechanical Q, Electrical Q, and total (for the 4 ohm side). Has anyone had any luck finding or determining these characteristics on their own?

 

[goat67]

Welcome to AK
I also have been thinking about building a pair of subs with a spare set of Watkins Woofers
I have not been able to find any of the info you are asking.
So I am of no help but I will be keeping an eye on this thread for any responses.

 

[pentode]

I've read a number of threads from audioholics wanting to use the Watkins Woofers for subs, but none of them include the info needed to build boxes from scratch. I bet they would make great subs, but you'd have to use old-school amps to drive them; they need an amp that can remain stable at 2 ohms.

The specification info for the woofer should be easy enough to obtain through testing (if you have the equipment, which I don't just yet), I'm hoping someone already ran the tests and is willing to share their results. Otherwise I'll have to wait until I have the equipment needed.

 

[goat67]

I've read a number of threads from audioholics wanting to use the Watkins Woofers for subs, but none of them include the info needed to build boxes from scratch. I bet they would make great subs, but you'd have to use old-school amps to drive them; they need an amp that can remain stable at 2 ohms.

The specification info for the woofer should be easy enough to obtain through testing (if you have the equipment, which I don't just yet), I'm hoping someone already ran the tests and is willing to share their results. Otherwise I'll have to wait until I have the equipment needed.

I got plenty of amps I just need to know the size of the cabinet
To do these you would need to use the same type of X-Over as the Quantum series
I would like to see them go from 20 to 100 HZ or so

 

[rabbit]

I got plenty of amps I just need to know the size of the cabinet
To do these you would need to use the same type of X-Over as the Quantum series
I would like to see them go from 20 to 100 HZ or so

You have a problem there because the Watkins woofer has two dissimilar voice coils wound on a common former. Therefore there are two sets of T/S parameters you have to deal with and there is no box design software currently available that is designed to deal with this type of speaker design.

If you checkout some of the crossover schematics you will see that the voice coils are driven with series LC tank circuits. Probably about the simplest way to build a system is to duplicate one of the existing infinity designs as closely as possible.

 

[goat67]

You have a problem there because the Watkins woofer has two dissimilar voice coils wound on a common former. Therefore there are two sets of T/S parameters you have to deal with and there is no box design software currently available that is designed to deal with this type of speaker design.

If you checkout some of the crossover schematics you will see that the voice coils are driven with series LC tank circuits. Probably about the simplest way to build a system is to duplicate one of the existing infinity designs as closely as possible.

Yea that what I was going to do. I got th X overs with the spare Watkins from a Q5. I Just do not know what size I should make the box.

 

[dobbhill]

deleted

 

[rabbit]

Yea that what I was going to do. I got th X overs with the spare Watkins from a Q5. I Just do not know what size I should make the box.

If the same woofer is used in all Q series which I believe it is then just choose the appropriate box design you want and duplicate it. For example if you want a subwoofer with a -3db point of 24 Hz then use the box size of the Q2 as well as the same crossover circuit.

 

[goat67]

Info on Resonance LCR cals on Quantum Series and box size

A 18 X 18 X 24 inch box is 3.26 cubic ft 16 X 16 X 22 = 5632 cubic inches
A 19 X 19 X 24 inch box is 3.68 cubic ft 17 X 17 X 22 = 6358 cubic inches
A 20 X 20 X 24 inch box is 4.12 cubic ft 18 X 18 X 22 = 7128 cubic inches

Assumes 1 inch material

I have read here that Bill Watkins thought the QLS1 and QLS2 boxes where to large for the Woofer causing over extension.

The QLS1 QLS2 and QLS3 cross over at 200 HZ
The QLS4 and QLS5 at 600 HZ

For A QLS1 13312 cubic inches 7.70 cubic ft
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
18 HZ - 32K HZ

For Q2 8272 cubic inches 4.79 cubic ft
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
24 HZ - 32K HZ

For a Q3 6688 cubic inches 3.87 cubic feet
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
28 HZ - 32K HZ

For a Q4 4420 cubic inches 2.56 cubic ft
20mh coil 700uf cap Resonance Freq = 42 HZ Z = 5.3 Ohms
1.0mh coil 1100uf Cap Resonance Freq = 152 HZ Z = .95 Ohms
35 HZ - 32K HZ

For a Q5 3185 cubic inches 1.84 cubic ft
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
38 HZ - 32K HZ

Oh well I guess I would just need to give it a try someday

 

[pentode]

Great info Goat67; thanks for the woofer box volumes. To date all I've found are total speaker dimensions. Good starting for me as well.
Rabbit’s comment about the voice coils are what make the Watkins Woofer a hard egg to crack. I haven't found any software to model both coils either.
But maybe with Vas and the Q specs for the 4 ohm coil one could calculate a good starting point for the box and then tune the cabinet (within a certain range determined by the cabinet, the 2 ohm coil, and the resonant period of the 4 ohm coil). This would assume the 2 ohm coil only operates when the 4 ohm coil is at resonance. Does anyone know the frequency band of operation for the 2 ohm coil in any of the Infinity/Watkins designs? I’m assuming the duration would span the total audio band where the 4 ohm coil is at resonance.
What happens at frequencies below resonance of the 4 ohm coil? From my limited (newfound) understanding of the Watkins Woofer; once the 4 ohm coil reaches resonance the 2 ohm coil shows a lower resistance to the amp and therefore drives the woofer. But for how long? Is the 2 ohm coil limited to only operate during the resonant period of the 4 ohm coil (throughout 4 ohm coil Qts), or can the tuned circuit of the 2 ohm coil be changed to extend the lower frequency operation beyond the inductive side of the 4 ohm coil resonant peak? If this is so, since the 2 ohm coil would show a lower resistance to the amp, the amp could drive this coil until it too hit resonance. Does anyone know if my understanding of the role of these coils and the tuned circuit is close to correct?

 

[Looking4help]

Which is voice coil 1 and which is voice coil 2?

I am recapping the crossovers for a pair of Quantum 3s, and I realize that I did not mark the terminals when I had the woofers refoamed 15 years ago.

Thanks!