Dampening a driver's basket?

[enigmaticEntity.]

I have some commercial hi-fi speakers that I am trying to improve, being as cheap as possible.

The "MDF" cabinets seem to be variable thickness particle board, and are only about 1/2'' thick. No bracing aside from some really tiny triangles along some edges.

So far I have added some white synthetic material as dampening, which seems to have reduced some of the garbling. I have also added some fluffy material to a few sides, the material looking very similar to the one in the second post here.

I wish to add some blu tack to the cheap stamped frame of the 5'' woofer. Will this make any noticable difference to the sound?

(btw the crossover seems to be 2nd order, 2-way.)

 

[lvw]

Probably not noticeable. I've damped the baskets of small cheap drivers in the past. When tested before and after, I could see a slightly cleaner waterfall plot, almost all at high frequencies, above the crossover that would typically be used. Even then, I'm talking about "hash" that was at least 30 db down.

I think the cabinets are probably a much bigger problem...

Having said all that, if it was me, I would likely damp the frames in any case, just 'cause I could... (but I would use a really "dead" material", like putty or my favorite, oil based modeling clay.)

 

[Moondog55]

If it is added to the part where the frame and magnet join the yes, I use the stick-on felt you can buy from Bunnings on the inside of a couple of my drivers, it can make a substantial difference to the quality of the mid-range, but it isn't really cheap.

 

[rotaspec]

Back in the 70's when I built my Pro9TL's, the going thing for damping the walls of cabinets was Bituminous paint. I don't know if you can still buy it. Perhaps some of that rough surfacing paint you can get for paths and decks would be suitable. So long as it dries a bit soft in texture and has a rough surface it may be suitable.
The Pro9TL's also used sheep's wool teased out (and treated for vermin of course) as the fibrous filling.
Don't overstuff the cabinet whatever you use, or you will kill the bass response completely.

Gary

 

[Moondog55]

For a cheap fix any scrap of MDF glued at random on the walls will work, sometimes very well, but a batten on the long walls, off-center will work a little better, show us a photo or three for a more informed comment, some of those early full range drivers sound quite good.

 

[planet10]

Pictures would be useful.

I use duct seal to damp (and shape) baskets (the latter is as important as the former).

Box bracing can make some serious improvements from your description. Adding any mass to the speaker box panels without adding stiffness will probably make things worse.

dave

 

[planet10]

You might find this interesting too http://www.diyaudio.com/forums/full-range/111724-extreme-basket-tricks.html

dave

 

[Moondog55]

Box bracing can make some serious improvements from your description. Adding any mass to the speaker box panels without adding stiffness will probably make things worse.

dave

Dave that is true; but adding MDF to chipboard does a damn good job of stiffening, the trick is not to use too much mass and place the offcuts just to one side of centre, a lot of box makers use the driver cutouts for this function.

enigmaticEntity
If done properly and with square cut scraps you can add the dowel rod or batten between the sides by putting said horizontal batten on to the added vertical batten OR the glued scrap, adding remarkable stiffness for little extra cost or mass. Both are important but some things are easier to retro-fit, it will depend on what you can get through the driver cut-out😀

 

[enigmaticEntity.]

Here's some pics.

I'll be struggling for room with regards to the enclosure (though I'm sure I can manufacture something...) as is the case with commercial micro hi-fi speakers.

There's also a 3.5'' dia. 2.5'' deep cylinder for a "virtual front surround" speaker inside the enclosure, which makes things more difficult, but it is near the top, so a brace for the longest sides may fit.

🙂

 

[Face]

Dynamat Extreme works wonders on cheap stamped baskets.

 

[Elbert]

Yes, dampening of the basket may give significant improvements.

If the basket rings when you tap it, chances are you have a candidate for such improvements.

I added strips of self-adhesive bitumen-sheet to the baskets of a pair of Coral Flat 8's I once had, and that reduced a very audible colouration quite significantly!

Good luck! 🙂

 

[63781]

If you have drivers with phase plugs, its interesting to feel that there is significant vibration in the phase plug! This is caused by vibrations in the whole basket and magnet structure. I think its a good idea to do something about it, even though it might not show up on standard type of measurements like frequency response and waterfall plot.

A cheap trick that works with all drivers is to make an internal bracing that almost touches the rear side of the magnet, and then use some kind of material between the magnet and brace to transfer the vibrations, which is soft enough to compress slightly when the driver is mounted. Bitumen sheets used for sound deadening in cars works very well for this. Hard rubber may also be effective.

 

[skeptic43]

Look at what this guy did to his JBL baskets - cast frame at that!
Woofers pictures from toys photos on webshots

Anyone for cake decorating?

 

[planet10]

A cheap trick that works with all drivers is to make an internal bracing that almost touches the rear side of the magnet, and then use some kind of material between the magnet and brace to transfer the vibrations, which is soft enough to compress slightly when the driver is mounted.

All of my speakers have a brace that actually presses tight against the driver magnet. Anything squishy will reduce the transmission of energy away from the driver. If you have to use a shim, something solid is probably better.

dave

 

[enigmaticEntity.]

Thanks a lot for the tips 🙂 . I think I'll wait until I can get some proper sound deadening material (like the ones suggested) instead of Blu Tack 😛 . This way I can have the remainder for my DIY project. Some of those methods are rather intriguing...