Tweeter not quite mounted flush

[samtny]

Hello all,

First time builder, I am working on the Zaph ZBM4 bargain mini's, my question is this;

I got some help building the enclosures, however I now notice that the tweeter, a rear-mount Aura NT1 titanium dome, does not quite mount flush with the front of the baffle; it sits about .5mm below the surface. Is this something to be worried about from a sound quality perspective?

I am picturing sound waves emanating from the dome and hitting that "ridge," and thus not "flowing" across the surface of the baffle properly, but I wanted a 2nd opinion before I start chipping away at the back of my baffle (with my inexperienced fingers).

P.S.; As Zaph suggests, getting the proper diameter hole drilled for these unusual tweeters was the most difficult part of this project. My uncle who is a skilled craftsman with ~35 yrs experience really wrestled with it, and we still ended up with holes that are a tad too big - about .25mm gap all around. Of course if we had just ordered the proper drill bit as he initially suggested I'm sure that would have improved the outcome! However I insisted it "doesn't have to be perfect," and am now regretting that decision slightly.

Thanks for any help or suggestions,

Sam T

[sdclc126]

I don't know that a half millimeter would make any audible difference, but one posssible remedy would be to sand the edges of the cutout so they are rounded over, to get rid of the sharp edge and make a sort of continuation of the tweeter housing.

[Bobken]

Hi,

Almost certainly, as there will be a discontinuity over the surface which the sound-waves will travel, there will be some diffraction effects here with what you have ended up with.

Whether this will be serious enough to affect the sonic performance for this to be noticeable to you or not, is another matter, though.

Another possibility which you might try in order to eliminate this slight 'step' would be if you could shamfer this edge and blend it into the surrounding baffle area.

Regards,

EDIT, I hadn't seen the intervening post when I wrote this, but it seems that we are in agreement here.

[sdclc126]

We're in agreement - plus I think it would look kinda cool too - like it was planned in the first place.

Also, if the cutout is a little too large for the tweeter, I'm thinking something like gasketing tape might be a good way to fill in the gap, albeit it's a small gap.

[samtny]

Originally posted by sdclc126
I don't know that a half millimeter would make any audible difference, but one posssible remedy would be to sand the edges of the cutout so they are rounded over, to get rid of the sharp edge and make a sort of continuation of the tweeter housing.

Thanks guys, I had thought of maybe sanding the sharp edges, so it sounds like that might be the way to go. One problem with this will be getting it to look even all around the hole, but I'm not in a hurry so hopefully with a little patience...

Not sure what to do about the gap, but I will look into the gasketing tape.

[Cal Weldon]

Your local hardware store may have a very small barrel sander attachment for your drill. This will speed up the 'roughing' part of it, leaving a small amount of hand sanding.

[BlueWizard]

The error in question here is 0.5mm or .02 inch, that's very small.

Looking at the spec sheet, from the face of the flange to the front of the tweeter is 12mm or .47 inches, and I assume you have it back mounted in .75 inch wood. That means you must have cut some kind of recess in the back of the front panel to move the tweeter forward to
the very edge of the out face of the front panel. Correct?

Exactly how did you accomplish this? Cut a large recess to accommodate the flange then a smaller hole to accommodate the tweeter itself. Or is the recess in the rear square?

You only need .02 inches, I would think it wouldn't take that much to scrap that out of the rear recess.

Other wise, simply beveling or rounding the edges of the outer opening shouldn't be that hard. At worst, you a just extending the horn of the tweeter.

Since this is such a fine amount, I don't see why it couldn't be done by hand with some sandpaper.

Just a few thoughts.

Steve/bluewizard

[Bobken]

Hi,

I tend to agree with BlueWizard's suggestion here, and unless the baffle is extremely hard wood, I think that any mechanical sanding will tend to run away with you if you are not very careful.

I would do this with some fine abrasive paper wrapped around a piece of wood of a suitable size and shape. You will have far more control over doing it this way, and I reckon that just a few 'wipes' in a circular manner around the edge of the aperture will be all that you will need here.
Why not practice a bit on some scrap wood of a similar type (I assume you will probably have some off-cuts) and you will soon see how much effort is needed for this, and a technique can be developed. Once you have 'gone too far' with the baffles, themselves, there will be no going back (or at least not easily), so do take it slowly so that you don't risk spoiling your work.

Another thought which I might try if it was me doing this, would be to temporarily stick some abrasive paper on the back of a suitably-sized shallow dish-shaped article (maybe a saucer, or pan-lid or something similar) which overlaps the hole edge by a sensible amount. Placing this over the hole, and carefully rotating it concentrically a few times should give a nice 'professionally-finished' shallow bevel which will be even all around, if you are careful with this, and the depth of cut will be easier to control.

You won't need to cover the entire circumference of the saucer-shaped 'former', and just a strip of sandpaper will do for this, but the remainder of the 'former' will help to centralise everything and support things so you almost certainly couldn't get this chamfer wrong.

Regards,

[dublin78]

Why don't you make a cardboard "washer" to put between the tweeter flange and the wood? Just use 0.5mm cardboard.

Simple and reversable.

It would probably help make the cabinet more airtight too.

[Bobken]

Originally posted by dublin78
Why don't you make a cardboard "washer" to put between the tweeter flange and the wood? Just use 0.5mm cardboard.

Simple and reversable.

It would probably help make the cabinet more airtight too.

Hi,

If this was a front-mounted tweeter, something like this would work very well.
However, this tweeter is rear-mounted, so any 'packing out', will worsen the problem, unfortunately.

Regards,