WD25T cabinets

[davidg]

Hi,
I just received my WD25T kit (without cabinets) and am starting to think about building the cabinets from scratch. I would like to make a few changes to the standard design, primarily for aesthetic purposes, and would appreciate any comments or suggestions, especially from Peter Comeau My specific questions are:

1. Choice of materials. In an earlier post on the DIY Loudspeaker forum, Peter indicated that for sonic purposes particle board might be slightly better than MDF, except for the front panel. Would that suggestion hold for the WD25Ts? Also, there was a reference to a World Hi-Fi article on this subject. Is there any way to get a copy of that article?

2. Hardwood edges. I am planning to use hardwood corners between the panels to make nicer and more durable edges. I would use a tongue-and-groove construction to generate more glue surface and keep everything lined up. Are there any sonic disadvantages to this kind of construction?

3. Material for internal braces. Is there anything to be gained or lost from using Baltic birch plywood for the internal braces? I would imagine that the main partition between the upper and lower chambers should be particle board or MDF.

4. Grilles. What would be the best way to make and attach grilles? I would prefer fabric stretched over a frame to foam. I had thought of using rare-earth magnets to hold the frames onto the cabinets. Is there a potential problem of affecting the drivers? Are there other fastners that would be better?

5. Cabinet width. The cabinets are only barely wider than the low frequency driver, which seems a bit incompatible with grilles. Would making the cabinet an inch or so wider cause problems by increasing the volume? Could one compensate by making the cabinet slightly shorter or less deep? Or, is best not to mess with the dimensions?

Thanks very much for any comments or suggestions.

David

[andrew ivimey]

welcome to the gang

I don't think there is any heresy in anything you propose but 'rare-earth' magnets = hahahahahahahahahahahahahahahahahaha why not use velcro? why 'rare-earth' this sounds suspiciously like a HiFi retailer who shall remain nameless but a lot of people A), like to knock and OTOH a lot of people like to shell out hard earned on products that type A) people regard as total rubbish.

However ...

tongue and groove is IMHO better for the reason you propose; more glue area. anyone for dovetail joints - woodwork is a lost art - ?

Materials other than the recommendation by a designer who is 'rather good' at all this loudspeaker stuff is odd if understandable by the brave and inexperienced. Much has been written on MDF, chipboard and Baltic ply. The latter, I am told, can be 'tuned' by the expert. It is more resonant but of you don't sufficiently brace MDF, it too can sound 'orrible. If you brace to the max, the volume of the speaker will be compromised. And so on... I am not answering your question am I!?

I would always build a floor stander where others would use stands. More internal volume means more bass response of sand filled and more lee way for bracing to the max.

But don't you really want to hear how Peter C. intended these critically well regarded speakers should sound? Oh the odd centimetre on width won't harm things (much) but remember, this design in NOT just a box. It has been designed to work in a certain way. More than the odd centimetre would, I expect, change the sound noticeably.

I'd love to get some of the back issues of Hi-Fi World. Reading a recent copy showed how good some of the stuff in the mag was ( there will always be the commercial, dull stuff too but some mags seem to have nothing but this)and I'd been missing it all; my loss.

Anyway good luck, others will chip in I am sure.

[Richard]

Hi David and Welcome,

I used 2 part grill fixing studs on my TLs,



Made the frames from 12mm mdf and set the jigsaw on an angle to chamfer the cut-out holes well clear of the drive units. Chamfered timber may be better if there's not much strength near the bass/mid unit.

Layed a frame over the cab and drilled pilot holes through to get the stud alignment. Used a flat woodbit to counterbore and glued the short ends into the frame with Araldite. 6 studs hold 36" x 12" frames easily without any other support.

Covered them in thin black stretch lycra jersey with a staple gun.

I can't see a problem with different corner construction as won't make much difference to panel resonances. I'd brace as shown and follow dimensions closely though if you want similar design results.

[Shane]

Rare earth magnets are much less exotic than they sound, are cheap and are readily available http://cgi.ebay.co.uk/Neodymium-Disc...QQcmdZViewItem

These would be easily able to support a grill, and if sunk into the baffle are visually very discrete when the grill is removed, unlike Velcro.

I can't think that they would upset the drivers, but I'm sure Peter will correct me if I'm wrong.

[Richard]

Yes, the only disadvantage to using (small!) magnets or velcro is that they may need other support in the form of a frame/rebate on the cab. I've seen studs, magnets and velcro on commercial speakers; the first usually without frame support and the other 2 with.

[Paul Barker]

Yes it sounds so much more romantic to call a nib magnet "Rare Earth".

[petercom]

Originally Posted by davidg

1. Choice of materials. In an earlier post on the DIY Loudspeaker forum, Peter indicated that for sonic purposes particle board might be slightly better than MDF, except for the front panel. Would that suggestion hold for the WD25Ts? Also, there was a reference to a World Hi-Fi article on this subject. Is there any way to get a copy of that article?

2. Hardwood edges. I am planning to use hardwood corners between the panels to make nicer and more durable edges. I would use a tongue-and-groove construction to generate more glue surface and keep everything lined up. Are there any sonic disadvantages to this kind of construction?

3. Material for internal braces. Is there anything to be gained or lost from using Baltic birch plywood for the internal braces? I would imagine that the main partition between the upper and lower chambers should be particle board or MDF.

4. Grilles. What would be the best way to make and attach grilles? I would prefer fabric stretched over a frame to foam. I had thought of using rare-earth magnets to hold the frames onto the cabinets. Is there a potential problem of affecting the drivers? Are there other fastners that would be better?

5. Cabinet width. The cabinets are only barely wider than the low frequency driver, which seems a bit incompatible with grilles. Would making the cabinet an inch or so wider cause problems by increasing the volume? Could one compensate by making the cabinet slightly shorter or less deep? Or, is best not to mess with the dimensions?

Taking these in order:

1. We only use/suggest MDF because it is easier and simpler for a lot of DIY woodworkers to use. An MDF baffle and high density (flooring quality) particle board for the rest would be fine.

2. Hardwood edges are fine as long as the joints between the panels are not weakened. Rounding the edges may help a smidgin with reducing edge diffraction effects.

3. If you are going to use ply instead of MDF for braces then go up in thickness to 25mm to retain the same rigidity.

4. No problems with Neo magnets as long as the speakers are not too close to a CRT! Note that grilles should be shallow with internal and external rounded edges to avoid edge reflections and should be frames round the edge of the cabinets and not cutouts in a solid piece of wood. (the latter forms undesirable cavities around the drivers).

5. You can slightly widen the cabinets by, say, 30mm without affecting the response. Much wider cabinets may require a small crossover adjustment because of the change to the baffle step. The internal volume can increase by 20% or so before you will notice any difference as the aperiodic design makes this less critical than bass reflex designs. A reduction in volume, however, will reduce bass extension.

[Richard]

Originally Posted by petercom

Taking these in order:
4. No problems with Neo magnets as long as the speakers are not too close to a CRT! Note that grilles should be shallow with internal and external rounded edges to avoid edge reflections and should be frames round the edge of the cabinets and not cutouts in a solid piece of wood. (the latter forms undesirable cavities around the drivers).

Yes, choice may be down to how difficult the construction is. Mine were much easier from sheet and all excess was cut away and chamfered as picture. I'm not sure if the kits include a grill but would recommend one, long term anyway. I cannot hear a difference with/without but it keeps light off the drive units which otherwise destroys them.

[Cobblers]

I have the standard WD25a's and went for the woodwork kit also.

The cabinets are very low colouration as designed. I suspect any differences using different materials would be extremely subtle. These speakers never suffer any of the one note bong from reflex designs.

MDF is much easier to work with than particle board (which is cheaper than MDF), because it is less inclined to split.
The excellent Living Voice speakers use particle board, on grounds of sonic quality, but it is hard to get cabinet makers willing to work with this stuff.

I cover my drivers up, away from corrosive dog slobber and sunshine with some light box/packing foam sheets (cut to baffle width) draped over the baffles, held in place with the weight of a couple of mag's (HIFI World naturally!)

Why would you want to change dimensions before hearing the speakers as the designer intended?

[davidg]

Thanks very much for all of the helpful replies. To clarify a couple of points:

1. "Rare earth" magnets are not some sort of hi-fi voodoo. The name refers to a group of elements that includes neodymium, from which very strong permanent magnets can be made. These are used for lots of things, including computer hard drives and some speakers. I tend to use the term "rare earth" because it is easier to say and spell. I suppose though that someone could carefully place a number of these magnets around a speaker (or even an amplifier) to generate sonic effects that some people could clearly hear and would pay a lot of money for!

2. The reason I am thinking of making the cabinet a little wider is to provide extra space between the woofer surround and the frame for the grilles.

Thanks again the suggestions. I'm sure that I'll be back with more questions.

David