Advice - Replacement drivers for Castle Chester speakers

[bug2k11]

I have a pair of Castle Chester speakers that have no mid/bass drivers. As they are an unusual almost octagonal design and the original Castle company ceased trading some years ago, it doesn't look like it's going to be possible to get replacements.

I am thinking of taking the opportunity to modify the recessed driver mounting into a slightly larger circular hole and could use some advice as to which drivers might be a suitable upgrade. It might be a good time to upgrade the tweeters at the same time, these are Vifa D25AG-05, which are 104mm across.

I have linked in some pictures of the speakers here:

The diameter of the rounded octagon of the mid/bass driver is 177mm.

As I already have two other working pairs of the Chester speakers, this might be an interesting project to see how much they could be improved with different drivers and possibly crossovers.

Any advice and help would be appreciated.

 

[kevinkr]

Since you have two other pairs the obvious starting point would be to remove and measure the TS parameters of one or more of the woofers as this would allow you to select an acceptable alternative for the existing box tuning.

Once you've done that alternate tweeter choices should be more obvious.

Note that you may possibly need to redesign the XO unless you are lucky enough to come across woofers that are a very close match to the originals.

 

[Dufus]

Maybe you should look for a well proven design with new drivers.How about the Amiga?https://sites.google.com/site/undefinition/diy/amiga
You could add new baffle to your cabs like this.

 

[Inductor]

Actually both routes are possible.
1. Using similar drive(s) to save xo.
2. Starting with the internal volume of the speaker , and choosing a driver/kit that works with that size of speaker (new drivers and crossover in this case).

 

[Inductor]

Can you measure the front of your mid-woofer (to the millimeter). Width and depth of the chassis.
I see you have here (edit)

The diameter of the rounded octagon of the mid/bass driver is 177mm.

Other (Castle) replacements are mentioned from time to time; SEAS, others.
http://www.diyaudio.com/forums/multi-way/157148-replacement-seas-chassis-xp-polypropylene-cones.html

 

[DrBoar]

The Vifa is a very good tweeter and so reusing that would be good.
Spending 100 bucks on a Parts-express DATS to measure both drivers and crossovers. With such a tool you can have a shot of getting an (almost) drop in replacement driver.
Otherwise go for a kit

 

[bug2k11]

Thanks for the replies, I'll pull one of the other drivers and measure the drivers TS parameters and see if there's anything similar that can be made to fit. Shouldn't be too much trouble to enlarge the recess to fit a 6.5" circular speaker. The maximum mounting depth is about 100mm as there seems to be a vertical divider which slopes down to meet the front panel just above the vent, a quick search seem to imply this speaker cabinet uses a quarter wave design.

 

[sreten]

Hi,

You are going to be hard pushed to improve on the original, with a
fairly complex x/o matched to the drivers and a bass mid matched
to what is presumably an (expanding?) 1/4 wave line.

rgds, sreten.

 

[WaVeInFoRm]

You could buy a pair to take the drivers from.. Castle Chester speakers | eBay

 

[Inductor]

I don't have (any) experience with quarter wave, and after this note I'm curious if this chassis is not of the same dimensions or close to the Audax.
This a good driver for 1/4 wave anyway. Audax AM170G8
Parameters: Qtsb 0.365, Fsb 42.46
Calcul. Units MKSA: 0.20 <= Qtsb <= 0.70, 20 <= Fsb <= 70 Hz
(ps: In the case of having interest in this driver, if someone finds these parameters, for the Audax, of note)

 

[Inductor]

You could buy a pair to take the drivers from.. Castle Chester speakers | eBay

I was going to say that's the price of a pair of speakers. But also that's what you will pay for a pair of (new) drivers.

 

[bug2k11]

I did see those on eBay, but I would still be in the position of having another pair of cabinets left over which I would feel the need to do something with!

That Dayton Audio DATS looks interesting, I'll have to get one ordered. In the meantime I'll dig out the test equipment and see if I can measure the TS parameters of the other drivers I have.

 

[system7]

I'd get to work reverse engineering the crossover. Even capacitor values and layout can tell you a lot about how it works and the drivers. Looks like they've used Zobels a lot there on second order bass and third order tweeter.

It's a carbon fibre weave woofer, possibly low inductance. I'd fancy this Monacor SPH-170 Polycone (Le 0.45mH, Qts 0.44 Vas 41L) and a Seas 27TFFC tweeter. Plenty of room to manouvre there. You might even get lucky and find the existing crossover is close, but Zobel calculations are easy for both units.

Monacor SPH-170
Seas Prestige 27TFFC H881

Would sound like one of those classic BBC speakers.

 

[bug2k11]

The Dayton Audio DATS system just arrived so I've run it on the pair of drivers from another working set.

These are the results from each:

* Manufacturer: Castle
* Model: Chester
* Piston Diameter = 125.0 mm
* f(s)= 71.33 Hz
* R(e)= 5.49 Ohms
* Z(max)= 59.38 Ohms
* Q(ms)= 6.439
* Q(es)= 0.656
* Q(ts)= 0.595
* V(as)= 10.250 liters (0.362 cubic feet)
* L(e)= 1.00 mH
* n(0)= 0.54 %
* SPL= 89.43 1W/1m
* M(ms)= 10.27 grams
* C(ms)= 0.48 mm/N
* BL= 6.21

* Manufacturer: Castle
* Model: Chester
* Piston Diameter = 125.0 mm
* f(s)= 66.62 Hz
* R(e)= 5.55 Ohms
* Z(max)= 63.98 Ohms
* Q(ms)= 5.847
* Q(es)= 0.555
* Q(ts)= 0.507
* V(as)= 11.420 liters (0.403 cubic feet)
* L(e)= 0.85 mH
* n(0)= 0.58 %
* SPL= 89.74 1W/1m
* M(ms)= 10.57 grams
* C(ms)= 0.54 mm/N
* BL= 6.65

I'm surprised there's so much difference between the two drivers. I'll take a look at the crossovers later and draw them up.

I would appreciate any advice on drivers which might make good replacements.

Thanks.

 

[sreten]

I'm surprised there's so much difference between the two drivers.
I'll take a look at the crossovers later and draw them up.

I would appreciate any advice on drivers which might make good replacements.

Thanks.

Hi,

There really isn't that much unusual difference, given the vagaries of the
suspension, which in a real box make far less difference than the specs.

rgds, sreten.

 

[sreten]

ELAC 5 inch hifi bass speakers woofers NOS PAIR KEF JPW | eBay


Hi,

Might be workable as a cheap get going, after that your expensively on your own.
The differences in parameters are not as significant as they appear, in reality.

rgds, sreten.

 

[bug2k11]

I've scribbled down the layout of the crossover

How does this scanspeak driver look as a replacement?
Scanspeak Discovery 18W 8424G00

Thanks

 

[planet10]

It's a carbon fibre weave woofer

The woofer pictured in Post 1 is coated paper.

dave

 

[planet10]

How does this scanspeak driver look as a replacement?

At what drive level did you measure the Castle's T/S?

To get an accurate compare you'll need to do it in a similar range to the factory measures (probably 1V @ 400 Hz into your reference 8R resisiter.

Re the Scan, I'd stick with a coated paper cone driver (or coat a paper cone driver)

dave

 

[5th element]

The driver reminds me somewhat of some of Volts smaller coated paper cone drivers. They don't make anything in this size though so it could have been a custom made.

As you're able to measure T/S parameters, buying a similar spec driver would be a good starting point. If any of Audax's AM/HM range will fit in the cut out and fit the specs then they would probably be okay, but expect to have to do crossover work to get things sounding right.

If you could take one of the drivers out of the cabinet and give us pictures of the rear of the basket and the motor, it might help us identify the manufacturer.