Equivalent to/improvement on 19mm MDF

[VantheMan]

Thanks everyone - the scientific reasoning is all way over my head - but because I´m going to remake my boxes, somewhat smaller this time, I shall definitely try the chipboard/MDF sandwich as suggested by Peter in this month´s newsletter.

[planet10]

If you can access good plywood, IMHO you will be ahead of MDF or chipboard.

Sandwiching hardboard is essentially making your own plywood but without the altering orientation of normal ply (since hardboard has no grain. To do this properly you do need a big press. My buddy Bill made his panel material from 7 layers of 1/8".

One thing for sure, do not short yourself on bracing -- properly executed & oriented bracing can make a BIG difference.

I also no one has commented on the baffle step thing -- that requires you to keep the baffle width the same, otherwise any compensation in the XO will need adjusting.

dave

PS: i'm missing a bit of contect -- what box are we talking about?

[VantheMan]

Sorry Planet10,
I´m referring to my first ever attempt at making some boxes. They come from a design on the Zerogain forum by a bloke called Tenson (speakers wot I made) and I went for them because of their simplicity - they are 1m x 23cms x 23 cms in 1.8mm MDF with a front ported 3cm deep baffle step 51 cms long and using Seas coaxials. As my first attempt I am very impressed woth their sound but they are bit too big so I am going to make a second pair of boxes, 90 cms x 17 x 19.4cms INTERNALLY while maintaining the baffle step width so I was after a way of getting similar results to the 1.9mdf but with thinner side pieces. You mention "good" ply - does that mean the more layers the merrier ?

[john & Jake the dog]

hi, I hope you and Tenson don't mind but are these the ones you made?
Seem to have got a good reception over there.
red.jpg

I jumped in with some boxes that Scott modelled for me thread :

http://www.wduk.worldomain.net/forum...ead.php?t=3336

Would the thick chip/particle board used in kitchen worktops work?

[planet10]

Originally Posted by VantheMan

Sorry Planet10,
I´m referring to my first ever attempt at making some boxes. They come from a design on the Zerogain forum by a bloke called Tenson (speakers wot I made) and I went for them because of their simplicity - they are 1m x 23cms x 23 cms in 1.8mm MDF with a front ported 3cm deep baffle step 51 cms long and using Seas coaxials. As my first attempt I am very impressed woth their sound but they are bit too big so I am going to make a second pair of boxes, 90 cms x 17 x 19.4cms INTERNALLY while maintaining the baffle step width so I was after a way of getting similar results to the 1.9mdf but with thinner side pieces. You mention "good" ply - does that mean the more layers the merrier ?

I assume you mean 1,9 cm MDF (3/4"). 1.5 cm plywood (yes more layers the better, but void free is the real key) would pretty much be a straight substitute (with attention to bracing i'd even tackle a box this size with 12mm ply). Even with the new smaller dimensions some bracing is recommended. The scheme used on these CSS ML-TLs would do the job (ignore the 2nd driver in these)



I feel that the driver/magnet brace is of significant importance to maintaining downward dynamic range.

Those internal dimensions, and maintaining the baffle step width are a bit contradictory. To satisfy both criteria you would have to have a 23 cm baffle tacked onto a 19cm (or 17cm) wide box. Sort of defeats the purpose. (Scott & i went to great pains to maintain the baffle width when we fixed the Thor design so that one could use the stock XO with no changes. If you build a smaller width baffle then the baffle step compensation in the XO will need adjusting upwards (ie smaller choke -- at least that is easier to do with an existing choke than to make one bigger).

I went searching for the reference you posted but couldn't find any reference on that forum... can you post the XO map?

[VantheMan]

Hi,
Regarding the baffle step width, I meant to say depth 3cm.

The original thread was this but he has since modified the XO and is working on the Mk 3 so don´t take it as final.

http://www.zerogain.com/forum/showthread.php?t=15953

[planet10]

Originally Posted by VantheMan

Hi,
Regarding the baffle step width, I meant to say depth 3cm.

Now i am totally confused... baffle step is a phenomenom relating to the width of the baffle and doesn't have a depth.

the term baffle step width would actually have units of Hz --- it is a frequncy

baffle step width = BS(-3dB) ~ 4560/(width of the baffle in inches)

Are you talking about baffle thickness? That is a whole 'nuther discussion. An over thick baffle could be considered a band-aid for insufficient bracing.

dave

[planet10]

Originally Posted by VantheMan

Hi,
[url]http://www.zerogain.com/forum/showthread.php?t=15953

I've seen that before. A really pretty speaker. The SEAS coaxes were always something i wanted to play with (even with my general tendency to say cross-overs are evil). Tenson hints at, but doesn't come right out and say it -- adjusting the size of L1 changes where baffle step compensation kicks in.

dave

[Scottmoose]

Where did all these posts come from in one day? Great stuff.

In re the earlier question, Dave knows much more than me, but for DIY, I'd usually be using Russian / Finnish birch ply, braced with holy braces a la what's shown in the bipole MLTL above. For 8in drivers or larger, it's always worth bracing the magnet against the rear-baffle. Less significant for smaller drivers, but still worth doing for a small improvement, especially if it's got a stamped basket / surround. If that's too expensive, I'd go for chipboard / particleboard over MDF like a shot.

Terry Cain used to make his own ply for his commercial boxes & also advocated something called classic core, which in his neck of the woods was a lamination with a 1/4in particle-board / HDF core, with ~5 plys laminated to either side. Probably about as good as it gets. If you're a woodworking God & have access to a full shop, properly seasoned timber etc., solid wood can work superbly, but you have to know exactly what you're doing. GM once made a pair of speakers from pine, originally from a ~100 year old barn door. You can imagine how well seasoned that was -it had similar weight / stiffness properties to aluminium.

Exact construction would depends on the cabinet design -MLTLs best to double the top panel & it doesn't do any harm to double the front baffle either, particularly with larger units, or in a cab that's going to generate hefty LF (unless there's a specific reason you want to leave it thinner).

[VantheMan]

Sorry again, planet10 - I´m going to keep my mouth shut - it is obvious that I have no idea - I meant that the distance from the inside face of the front baffle to the face of the internal partition that makes up the port or whatever you call it will remain at 3cm as in the diagram and the height of this partition must be 51 cm, but the actual width is going to be 17cms in the new boxes as opposed to the 19.4cms of the original design. So in width I´m going to save 2.4cms plus whatever I can shave off the side wall thickness.
I would urge you to have a close look at the Seas coaxes if you can - they certainly seem a bit special in comparison to what I am used to - Totem arros.