Sealing tweeter off from other drivers

[Moondog55]

How important would you rate doing this?
I actually have seen only one implementation and that in Rod Elliots own build but it makes sense to me as then I don't need to screw the tweeter face plate down tight.
No photos yet but we started making the bedroom speakers boxes yesterday. In the next day or three I need to have the midrange compartment finished so that I can start on the baffle, adding in a short section of ply, chipboard or MDF at this stage will be simple and cost nothing extra except a little time setting up the saw.

 

[Einric]

If the face plate of the tweeter is large and plastic I would say there is merit to a tweeter "Chamber" otherwise I think it would be a waste of box volume.

 

[Kindhornman]

What are you attempting to do, decouple the tweeter from the baffle or isolate the tweeter from vibration form the other drivers?

 

[Moondog55]

More isolate the tweeter from the pressure of the big woofer, sometimes when a tweeter faceplate is tightened against the baffle hard enough to prevent leakage it warps. but more to the point the small screws rip out of the timber and I have been unable to find 3mm T-Nuts
Einric I would be loosing 210cc, the woofer is in a Qtc 0.656 box so the loss is small

 

[DSP_Geek]

Fortunately most tweeters aren't very deep, so you can make a chamber with two pieces of plywood slightly bigger than the tweeter flange. One with a hole cut to the same diameter as the mounting hole and mounted behind the front panel, with the other piece behind it to cover the hole.

You end up losing less than half a litre, no big deal.

 

[Kindhornman]

Moondog,
There are brass screw insert in very small sizes that can be used and are much better than any T-nut that you can use. Look for a listing for threaded brass inserts made specifically for insert into soft materials. The will usually have two types, a fine threaded outer thread and a coarse threaded insert. Only use the coarse threaded inserts in a wood such as MDF and you can add a spot of epoxy glue to make sure they can never come out. As far as the loading from a bass speaker pushing out the tweeter of stressing the screws this would never be a problem in a vented enclosure and really would be pushing it even in a sealed enclosure. The mass of the magnet assembly will more than counteract the vibrational and air pressure loads on any practical dome tweeter that I have tested. Many of the better dome tweeters will use an aluminum front plate.

 

[Moondog55]

Kindhornman Thanx I haven't seen those over here, in the end it may have to be wood screws, SWMBO is getting a little peeved over the delay. I asked the original question because I miscalculated the midrange box volume and need to make it smaller so closing off the tweeter section would have been no trouble at all

 

[wintermute]

Hi Moondog, I did it too. But my build was an MTM so it was easy to make three separate compartments, one for each driver. I figured that splitting the box in three was good from a bracing point of view as well. I haven't even screwed the tweeters in they are just a press fit.... I must get around to doing that one day

Tony.

 

[Moondog55]

Nice grain in the wood sides Tony, veneer?
I used hardwood marine ply for the baffle and plain MDF for the sides, they will be painted to match the walls in the bedroom and so almost disappear.
Reminds self to take camera tomorrow and take pictures of the build in progress

 

[Kindhornman]

Moondog,
Here is a link so you can see what an insert looks like. These are brass, sometimes you will see some that are die cast zinc, they both will work in speaker enclosures.

#8-32 Brass Threaded Inserts, Threaded Inserts, Specialty Fasteners, Fasteners - McFeely's

This second reference says they ship to Australia.
http://theinsertcompany.com/theinsertshop.shtml

 

[wintermute]

Hi Moondog, yes it is Tasmanian blackwood veneer amother shot I just took as I don't think I had one of the "finished" product.

Tony.

 

[Moondog55]

Oh "Doh!" sure seen them usually in the die cast tho and only? in Imperial measurements?
I have to pay a huge premium for imperial screws and bolts at my usual supplier 15%+

 

[Kindhornman]

If you scroll down the second listing on that page they are all listed in mm sizes. The price isn't that bad for a small quantity.