Decca Kelly Crossover?

 

New member
Username: Dwp

Post Number: 1
Registered: Apr-10
Does anyone know what the crossover is for the Decca Kellys? I'm in the process of making a pair of speakers using the Kellys. Decca state that it's a variable slope.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 14786
Registered: May-04
.

Try this question on the DIY audio forums.

http://www.diyaudio.com/


.
 

Platinum Member
Username: Nuck

Post Number: 14870
Registered: Dec-04
Not that we dont like to meet a new member, DP, but that forum will serve your interest in this particular question better.
How are you going to enclose the speaker?
 

New member
Username: Dwp

Post Number: 2
Registered: Apr-10
The front panel will accommodate the Kelly's and an original Jordan Watts for the bass. The enclosure is made from thin sheets of ply bent around a curved profile vertically to form the inner shell. The outer shell is spaced with 15mm spacers. Top and bottom are flat with the same spacers. The result being only two parallel internal surfaces and these are broken up by horizontal bracing.
The construction is similar to Russ Andrews Torlyte, but I've decided to fill the gaps with dry sand. Instead of using boring MDF, I use two panels of plywood with spacers to provide rigidity.
 

Platinum Member
Username: Nuck

Post Number: 14873
Registered: Dec-04
wow!
I smell wood glue coming up...
 

Silver Member
Username: Hawkbilly

Nova Scotia Canada

Post Number: 902
Registered: Jul-07
Interesting design Dave. If I understand you correctly you're going to fill the area (15mm) between the layers of plywood with sand ? Do you have a procedure for doing this ? I would think it would be difficult to get the sand compacted evenly in a curved gap.
 

New member
Username: Dwp

Post Number: 3
Registered: Apr-10
There is a procedure for doing this it's called struggling. What I intend to do is leave a small hole in the base for inserting the sand, this will later be filled by one of the feet. Of course there will be a lot of tamping and shaking to settle the sand.
My intentions with this design are for a stable and rigid enclosure that will not resonate. I hope the photo's make it clearer.

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Silver Member
Username: Hawkbilly

Nova Scotia Canada

Post Number: 905
Registered: Jul-07
Great pics. Where you have some of the spacers vertical and some horizontal, a single hole in the bottom will make it hard to evenly distribute sand won't it ? Apologies for the questioning. Curiousity's getting the best of me.
 

Gold Member
Username: Magfan

USA

Post Number: 1060
Registered: Oct-07
Terrific detailed construction.
As for sand? I don't see it getting into some of the cavities which would appear sealed after the outside skin is applied. Even all those relief holes will make the sand installation the worst part of the project. And, how will you know when it's full? Unless it IS full, the sand will continue to settle for a decade to come.
While mass loading is fine, a more....hi tech....approach may be considered.

The automotive people use this::
http://www.dynamat.com/
which may help with bad vibes.
You will have to cut literally hundreds of little pieces of the stuff, but it's self adhesive (xxx sticky) and the sample I saw was foil backed. Cost will be quite a bit more than even nice, dry sand but this doesn't look like a cost constrained project, anyway.
The outer shell pieces should by lined by the same method.
 

Platinum Member
Username: Nuck

Post Number: 14877
Registered: Dec-04
An ultrasonic table, in use by a typical diesel injection repair shop would settle the matter, so to speak.
However, these speakers may be too heavy for such a unit.
Who did the CNC detail on the braces? Nice.
 

Gold Member
Username: Magfan

USA

Post Number: 1068
Registered: Oct-07
Nuck, I was thinking of something to vibrate 'em. Maybe in back of some rednecks pickup for a couple days? Add sand as needed?

A place I worked, years ago, used a Crown DC300 as the driver amp behind a vibration / test table. Doubt even that would have the guts to shake these speakers and 40lb of sand.
 

New member
Username: Dwp

Post Number: 4
Registered: Apr-10
Leo,
The sand should get into all the cavities; I made sure that everything internal has a hole drilled into it. I should know when it's full when I can't get anymore in, but it will settle over time. I'll have to do a lot of shaking and turning, it would be a good workout -- who needs a gym? I'll probably end up with arms like Popeye!
High tech considered? Got any suggestions? I was very impressed by listening to a pair of Celestion SL600's alongside a pair of SL6's exactly the same dimensions drive units but with Aerolam cabinets. Aerolam is used for the floors of aeroplanes, made from a sandwich construction of aluminium. It's incredibly light and strong. This experience proved to me just how much sound comes from the cabinets themselves. The result was a very dry accurate sound from the SL600's compared to a warm sound from the MDF SL6's.
Inspiration for these speakers is Torlyte, supplied by Russ Andrews Hi Fi. Check the website:- http://www.russandrews.com/ Everything I've tried from Russ Andrews works extremely well. Torlyte is a sandwich construction made from wood. It's extremely light and strong. I've made a pair of speakers from this sandwich type construction and several support platforms and they work very well. This time I've decided to use a perfectly good void and fill it with sand. Sand is a tried and tested method used to many years by Gilbert Briggs founder of Wharfedale speakers in England.
Dynamat? Interesting product, I've used a roofing product that's also self adhesive, used for sealing roofs. Made from tar and very very sticky, got it from a local builders merchant. Had to cut loads of pieces, I found scissors best but you have to prise the scissors off after each cut.
 

Platinum Member
Username: Nuck

Post Number: 14888
Registered: Dec-04
I would also suggest lead shot for the settling issue, but you have it well sorted, it seems, DP.
 

New member
Username: Dwp

Post Number: 5
Registered: Apr-10
Nuck, Lead would be ideal but it would take two men and a boy to lift them.
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Platinum Member
Username: Nuck

Post Number: 14892
Registered: Dec-04
Does sand give the boy a day off?
 

Gold Member
Username: Magfan

USA

Post Number: 1075
Registered: Oct-07
First, due to Toxicity Issues, I'd tend to avoid lead, in any form. Sorry, Nuck, but this is an awful solution, not to mention the sheer weight of the end product. It is also a 'brute force' solution when some subtlety is called for. Just Me.

You will do mass loading, apparently no matter what is said, but another approach as with the dynamat is to damp vibration. The fact that those Celestron you heard were made out of composition/laminated materials should show you that mass is not the final answer. And, as I look at your execution I doubt you will EVER fill it with sand. Arms like Popeye?

Go to the local Auto Stereo installer guy and get a sample of the Dynamat. Try it, you'll like it.

Another Very Risky approach would be to vent the speaker at several places, install a fitting and pump the wall full of expanding foam. This will damp the heck out of it and provide a large increase in rigidity. Wait till foam comes out all vent holes. IF really overdone the expanding foam could theoretically have enough force to crush your speaker or pop off the exterior.......

As for boxes making a sound, That's why I listen to panel speakers. and have for over 3 decades.
 

New member
Username: Dwp

Post Number: 6
Registered: Apr-10
Nuck,
Yes I rekon we can give the boy the day off, keep him in reserve though.
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New member
Username: Dwp

Post Number: 7
Registered: Apr-10
Leo,
I'm gonna give lead a wide berth. The reason for me going for mass is that in a previous speaker build I did go for your suggestion of expanding foam. The cabinet still managed to resonate, I still can't understand why but it did.
I'll look into Dynamat, it sounds interesting even if expensive.
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Platinum Member
Username: Nuck

Post Number: 14903
Registered: Dec-04
A friend insulated around a window with expanding foam...15 mins and blew the window out of the frame, LOL!

Seems there are various expansion and fill rates, he chose a can of hydraulic.
 

Gold Member
Username: Magfan

USA

Post Number: 1081
Registered: Oct-07
Nuck, Nothing succeeds like excess.

How about STEEL shot? Get it coated to do away with the rust issue. Probably way cheaper than lead and zero toxicity issue.

I'd experiment before I put on the outside skin. Steel shot filled than expanding foam.....rigidity plus mass? Maybe make up a section of (simulated) enclosure and be ready to cut it open to see how much fill you actually got.
 

Platinum Member
Username: Nuck

Post Number: 14908
Registered: Dec-04
"Try cleaner in a discrete spot before cleaning"

Hard to do with a speaker cab of custom wood, and varying thickness, unfortunately.
 

New member
Username: Dwp

Post Number: 8
Registered: Apr-10
Leo,
Steel shot? Now there's a thought. Normally I'd say steel is a non starter due to resonance but the resonance in small balls would be higher than any frequency within the cabinet. I wonder if the resonance of many small balls adds up to provide a lower resonance acting as if it were larger. Personally I doubt it but maybe someone knows better?
I used expanding foam on a previous speaker and noticed the top of the speaker bending upwards. I had to hastily clamp the top down before any damage was done. I can't recommend this, too risky, and you can never be sure if you've used enough or too much.
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New member
Username: Dwp

Post Number: 9
Registered: Apr-10
Nuck,
I think you're supposed to screw the window securely before using foam!
Expanding foam can be useful but you have to use carefully and there has to be plenty of outlets to allow excess to escape and avoid building up pressure. I think given enough experience you could probably have better results, but for a one off project it's a non starter.
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Platinum Member
Username: Nuck

Post Number: 14913
Registered: Dec-04
The window took the mounting screws, flashing, and some siding with it! LOL!
The goop was high expansion, hydraulic capable, and the window held on for a bit.
She near blew out, WHAM!!

Dude's wife was due home. I left.
 

New member
Username: Dwp

Post Number: 10
Registered: Apr-10
Nuck,
I don't blame you for making a swift exit. The problem is when the foam starts to set it becomes a brick wall and the pressure is transferred to the weakest point. I found this out at my own expense when the tops of my speakers started to swell. I had to get some clamps on pretty quick.
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Platinum Member
Username: Nuck

Post Number: 14951
Registered: Dec-04
Ya know what, Dave?
I would be more concerned with the speakers, and all that work, if it were me.

Home Depot sells stuff to pop a window back in, or a guy does that work for a reasonable fee.
 

Bronze Member
Username: Dwp

Post Number: 11
Registered: Apr-10
Nuck,
I take on board your concern, and there is a heck of a lot of work. I did consider just making a normal box. But after some consternation I thought 'In for a penny, in for a pound'. I think if you're gonna try something there's no point in doing things by half.
But tell me Nuck what in particular concerns you?
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