Aluminium Enclosures for External Crossovers

[ListeningEar]

Hi there,

It's been a while since I last signed in and like many of us engaged in various projects mine have been a little slow in moving forward. However, I am now very close to finishing the Rogers JR149's and the only little detail I am struggling with at present is finding a suitable enclosure for the crossovers.

In the original design the crossovers are built onto a circular PCB and mounted inside a very thin pressed steel case at the foot of the speaker. This provides terrible isolation to the speaker in soooo many ways so I will be mounting the crossovers externally on the rebuilt speakers (keeping the metal bases but these have been acoustically treated inside and filled with lead shot).

What I am looking for is an aluminium enclosure with a clear Perspex/acrylic lid. Need to be at least 6" square but 4" deep as some of the upgraded crossover components I am using will need a greater depth than the original metal base provides.

Anyone help with recommending enclosure suppliers? Maplins and CPC don't have anything...

[The Black Adder]

Hi Craig.

Well metal enclosures for crossovers are generally a no-no so you are doing well to have them in aluminium. I make my external crossovers with wooden sides and a choice of either aluminium or acrylic bases and lids. See here (www.tannoyista.com (http://www.tannoyista.com)) although only the acrylic ones are shown.

If you look at the website (under research and development) you will see the first iteration of my crossovers built using the Bluebell audio enclosures:

http://www.tannoyista.com/images/Tannoyista_crossover_previous.jpg

These enclosures are great as they come with alloy bases and lids.

What are you making the main board from or is the base of the enclosure the board? If so then try (if possible) to suspend the internal board from the enclosure.

All of my boards are made from acrylic. I also make them in double form to order which is two slabs specially vacuum compressed together. That process is expensive but gives the main boards a much better resistance to spurious vibrations.

Out of perspex and aluminium lids and bases I really can't really tell any difference in sound to be honest. The biggest thing is to make sure the coils are far enough apart and of the correct values.

Another thing I'd suggest to do is to use very high quality binding posts. I use the Cardas solid copper type. These give the same performance (IMO) as hard wiring. If you need to use cheap plated posts then consider hardwiring at least outwards from the crossover if possible.

Paul at RFC may be able to give you some more help in regards to component choices as I only specialise in the Tannoy Monitor Golds.

Hope that's some help but if you have any further questions please fire away.
Cheers

[YNWaN]

Funnily enough, my external crossover cases are a combination between aluminium and acrylic. The components are suspended within an acrylic framework and are suspended above the base; they are hardwired on the reverse. Unfortunately, I had to make almost all of it myself - other than the aluminium C sled that it is based on (which, I appreciate, isn't a lot of help to you).

http://i62.photobucket.com/albums/h90/markemark_2006/Yamaha%20NS-1000M%20Refurbishment/baseandframeandcrossover_zps2fb80144.jpg

http://i62.photobucket.com/albums/h90/markemark_2006/Yamaha%20NS-1000M%20Refurbishment/95557C2B-B598-4EF8-9CAA-B194659E4F02_zpsrzib2rq6.jpg

[ListeningEar]

Thanks for the excellent response Tannoyista, I love the work you have done in building your external crossovers for the Tannoy's. I want to keep the original circular crossover PCB as I am only planning on upgrading the on-board components. I deal with Nick at HiFi Collective, he normally has everything I need in stock plus he's very local to me. Nick has already inspected the original crossover design and come up with a parts list of suitable caps and resistors.

As I plan on keeping the original circular PCB I want to mount it inside an enclosure, to be honest I would much prefer to have an all acrylic enclosure so if this is available that would be ideal. The original PCB has a centre hole and rubber grommet and I had planned to use a M8 stud which would need to be fixed in the centre of the base of the acrylic enclosure.

In the past I have always used very high quality binding posts on all my speaker projects, in addition high quality internal wiring will also be necessary as these are stand-mount speakers so the cable from the drivers will be running discretely down the stands to the external crossovers which will be situated on the floor (would also need the acrylic base of the enclosure to be spiked).

Does that all make sense?

[ListeningEar]

YNWaN....Wow! They look awesome! That's more or less the type of design I had in mind....gimme,...gimme lol

[YNWaN]

Hi Craig, thanks :).

A couple of things, if you are intending to upgrade the crossover components you may struggle if you keep the original crossover board as better components are a lot bigger; my crossovers are about twice the size of the ones they replaced (same component values).

I'm not aware of any circular enclosures, if that's what you were thinking?
-------

Oh, regarding support, my own crossovers sit on granite plinths supported by SS ball bearings - an acrylic substructure keeps it all aligned and stops the crossovers sliding off (rather than using spikes) :).

[The Black Adder]

Your very welcome, Craig. The design you have in mind sounds great.

Yeah, Nick at HFC is superb to deal with. I use him too. :)

As for the binding posts. The best less expensive (not tacky) ones are the CMC Cu Red copper ones. I've used these in my crossovers and they are very good indeed. Try and go for short threads though where possible.

Wood or Polycarbonate enclosures, or a mix would be ideal. Spiked feet, yes if you have a wooden floor. If they are to sit on carpet with a concrete floor that would be ideal too.

[ListeningEar]

YNWaN - I was not planning on using circular enclosures as I guessed this would be a huge ask plus there is a cost ceiling to this exercise as the finished product while being much better sonically than the original design will not justify spending silly amounts of money on. As I said earlier, Nick at HiFi Collective has examined the crossovers and we have come up with a list of upgraded parts that can be fitted to the original board. Most of these are larger than then original components hence another reason for having external enclosures which will allow me to create room for this.

TheBlackAdder - sorry if I missed the point but are you saying you could fabricate the acrylic enclosures I require?

I have attached an image of the crossover I found online, there seems to be some variations in build across the Rogers JR149 and mine is very similar but it gives you an idea of what I am working with (and some obvious areas for improvement hehe).

http://www.mypicsonline.net/ak/IMG_3513.jpg

Another pair of speakers I am giving a full overhaul to is a pair of Avance Concrete 190's, these are Danish speakers with concrete cabinets. Again I would like external crossover enclosures in acrylic: https://scontent-a-lhr.xx.fbcdn.net/hphotos-xfp1/t31.0-8/1243455_381527205322089_10249566_o.jpg

If any of you can supply what I need and idea of pricing would be great ;)

[The Black Adder]

Hi Craig.

Unfortunately I can't make the enclosures for you. What I meant was if you can go for a mix of wood and acryilic or maybe all wood then that would be a good move. Wood absorbs vibration and is easy to have made. The problem with all acryilic cases is that you need to find the one that works for you. Most on the market are pretty standard looking. Unless Mark here can make some for you?

The crossovers I make are solid oak and weigh quite a bit on their own so good for rigidity etc.

Obvious improvements to the original XO's to me would be to replace the bass coils with an air core maybe? Those resistors should be fine but if you can use the Mundorf Mox ones or Mills that would be good. Cap wise, I'd always opt for Claritycap. I use MR's mostly in my builds but a safe type would be ESA's... very, very good indeed.

Remember to give enough space between the coils.

[YNWaN]

In theory I can make all acrylic cases (but not circular). However, they would be entirely custom from beginning to end and very labour intensive. It very much depends on precisely what you would want - my own took well over 100 hours work but that includes layout and they don't use a circuit board etc. - there was a lot of graphics to do too.

It would be cheaper to buy an aluminium case with a removable top panel and replace that with a piece of acrylic.

[The Black Adder]

Yes, I agree it can be a lot of work.

Craig, did you take a look at Bluebell audio? The cases are very well made and are reasonably priced. they will accommodate your crossover internals perfectly and the lids and bases can be replaced with acrylic at a later date.

[YNWaN]

These eBay ones are £27 each and anything I made would be significantly more expensive than that:

http://i.ebayimg.com/00/s/NjA4WDY4NA==/z/-jgAAOSwDN1USQxa/$_35.JPG

http://www.ebay.co.uk/itm/215-70-228mm-Aluminum-enclosure-DAC-case-amplifier-chassis-DIY-BOX-HIFI-house-/271644466316?pt=UK_Sound_Vision_Amplifier_Parts&hash=item3f3f459c8c#ht_10080wt_8092

[Val33]

For acrylic tops/covers, have a look at these people. I had some display cases from them that were excellent.

http://www.strikingdisplays.co.uk/bespoke-display-cases-.html

Val

[YNWaN]

They are VERY reasonably priced (good find)!

[Val33]

Thanks Mark, that's what forums are for. Likewise your case supplier, nice selection and good prices with europe stock :)

Val


They are VERY reasonably priced (good find)!

[YNWaN]

I've never used the guys I linked to though Val, just thought I would look on eBay for the OP - having said that, I'm sure they are OK and ave used very similar cases in the past.

[ListeningEar]

Thanks everyone, the aluminium cases look like a great find but I think I am going to opt for the clear acrylic route so have submitted an enquiry to Striking Displays.

Will post pictures of the finish product when complete,....I think you will like ;)

[Reffc]

I would not recommend Aluminium casing for ANY crossovers. It can drastically affect inductor values, reducing them by as much as 30% through inductive leakage. It is not good practice for other reasons to use any sort of conductive casing where you have inductors, especially air cored. Best bet is either timber or acrylic or a mix of both.

Here's some Tannoy crossovers I recently built which use a mix of both for example:

http://i1140.photobucket.com/albums/n577/24pacman/RFC%20Cables/_MG_9007_zps5287a465.jpg

[walpurgis]

I don't like anything made from metal near crossovers. I don't even like inductors near each other. And keep crossovers well away from drive units.

[YNWaN]

Inductor coupling has been long recognised and care should be taken positioning and orientating inductors relative to each other. Also, as Paul says, inductors can interact with metal enclosures - even aluminium ones.

[The Barbarian]

I often wonder removing the Crossovers from the cabinet is worth bothering with taking into account all the extra cabling & connections! ive always believe that fitting a copper plate across the top off the crossover board, fitting the board in the bottom is the better option.. What i did anyway

[The Black Adder]

I often wonder removing the Crossovers from the cabinet is worth bothering with taking into account all the extra cabling & connections! ive always believe that fitting a copper plate across the top off the crossover board, fitting the board in the bottom is the better option.. What i did anyway

It can largely depend on the speaker and it's magnet. The larger Alinco magnets on some speakers are very strong and can interfere with components inside a crossover if placed too close. Another thing is the cabinet, if the cab is small in comparison to the magnet then it's best to move them out IMO.

As for cabling and connections, use the best you can. Try and keep connections short and solder them well. I use the Cardas mostly, they are expensive but excellent.

If you want to use aluminium then you could (as you said, Andre) use copper but use a copper sheet under the alloy one. Copper is not nice to look at unless it's finished nicely and lacquered maybe.

Laser cut copper can be stained as it saps the heat out of the laser and so overheats the material.

[The Barbarian]

What im saying is i fitted a 1/4'' copper plate across the top of the crossover board. Totally good enough for any magnet

[YNWaN]

Good enough in what sense - what is the intended purpose of the copper?

[The Barbarian]

help shield the x-over from the bass unit magnet

[YNWaN]

Ah, I wondered if that was the intention. However, copper isn't actually very good at shielding from magnetic fields as from a magnet - it's similar to aluminium in that respect; magnetically permeable materials like mild steel are actually a lot more effective (although a thick chunk of any metal will work - though that will then tend to interact with the inductors). I've just confirmed the above with some steel, aluminium and copper plate I have to hand, plus some neodymium magnets. Also, I would expect copper to interact with the crossover inductors in the same way aluminium would as the effect is caused by the inductor inducing eddy currents in the metal and these interacting with the inductor - eddy currents can be induced in copper in the same way as they can be in aluminium.

I've got some spare inductors at home (and the ability to measure mH) and could measure the effect of one being in proximity to aluminium, copper and steel - will do it tomorrow :).

[The Barbarian]

All im trying to do is avoid the Inductors & Drive unit magnet interacting with each other by fitting the thick copper plate over the top of the X-Over, maybe the copper plate will generate the magnetic fields back into the magnet & Inductors. But obviously i would like some Mu Metal plates, which is high permeability material which should be more effective at Electromagnetic Shielding in this instance.

[YNWaN]

How much the inductors are affected by the copper plate depends on a number of factors, 1/ how close the plate actually is to the inductors, 2/ the orientation of the inductors relative to the plane of the copper plate and 3/ the type of inductor - an air-core is less efficient, therefore larger for the same value and therefore produces a larger magnetic field.

A mild steel plate or Mu-Metal sheet would be more effective at shielding from the magnetic field of the drive units but would interact significantly more with the inductors so what is good from one aspect is poor in the other.

[YNWaN]

This is worth looking at when considering how crossover coils interact when in proximity to metal (and other coils);

http://www.troelsgravesen.dk/coils.htm

Today I did some measurements and the figures that Troels measures are in line with what I found. He only looks at the effect of aluminium but I also had some copper sheet to hand and tried that - the result is that copper effectively attenuates the effectiveness of the coil even better than aluminium does (a 5.32mH inductor measured only 4.45mH when placed on the copper).

[Reffc]

This is worth looking at when considering how crossover coils interact when in proximity to metal (and other coils);

http://www.troelsgravesen.dk/coils.htm

Today I did some measurements and the figures that Troels measures are in line with what I found. He only looks at the effect of aluminium but I also had some copper sheet to hand and tried that - the result is that copper effectively attenuates the effectiveness of the coil even better than aluminium does (a 5.32mH inductor measured only 4.45mH when placed on the copper).

I've tried similar experiments Mark, and again got similar results. Really close inductor spacing and using any metal is a no-no really. A customer supplied me with some bespoke aluminium crossover enclosures in Aluminium a while back and he couldn't understand why his speakers sounded awful. I removed the components and measured the inductive leakage when placed within the enclosures. It was over 25% when fixed into the bases, and 15% when lifted about 40mm from the bases with the axis towards the enclosure which partly explains the awful sounds that the speakers were making. I think that Troels has erred on the side of caution as you can often get away with closer spacing than he suggests, especially for lower power applications, but his guide is a useful rule of thumb.

[YNWaN]

Yes, I tried orientating the relative angle of the inductor axis' in the same way Troels has and, as you say, the interaction is (slightly) lessened if placed on their side - however, it still exists to a significant extent. I also tried spacing the inductor relative to the metal plate and although this reduced their interaction the reduction was much less than I expected!

A 4.91mH inductor resting on a 1mm sheet of copper measured 4.31mH, a reduction of 12.2%.
When raised by 12mm from the surface it measured 4.52mH, a reduction of 8%.
When raised by 24mm from the surface it measured 4.78mH, a reduction of 2.7%.

At 46mm there was no measurable loss.

[The Barbarian]

I don't have time for photo but the copperplate that is above my X-Over is approx three inches above.

[YNWaN]

Well 3 inches is 76 millimetres so that should be OK.

[MCRU]

Well 3 inches is 76 millimetres so that should be OK.

76.2mm actually :ner:

[YNWaN]

Yes, I know - I didn't think the 0.2 was relevant and as I'm trying to give up pedantry I chose to omit it...

But thanks for your input David :).