How to minimize grill diffraction

[Alain]

For those of us who need speaker grills, how do we minimize it impact. I was planning to put felt on the frame near the tweeter. Would I need to do the same for the midrange and the woofer?

[Svante]

I don't know how you will design the grill, but make sure that the distance from speaker to grill (in the baffle plane) varies. That is, don't make a circular hole in it around the tweeter, since that will maximise the diffraction effects.

[BillFitzmaurice]

The grille doesn't cause much diffraction, but the frame does. If you must grill the best procedure is not to flush mount the drivers but to have them extend from the baffle. The grille frame is then made from sheet goods the same thickness as the driver frames, acting in effect as a baffle extension, with holes in it just large enough to clear the driver frames. This results in a thicker baffle assembly, which offers the opportunity for a wider radius of its edge to further reduce diffraction.

[Svante]

Sorry, my english poor is, I also meant the frame. But Bill; how do you manage the different thicknesses of woofer and tweeter? Flush mount the woofer a little bit? And how do you give space for the dome of the tweeter?

[BillFitzmaurice]

You'd space the tweeter frame out, but if the dome extends beyond the frame then you have to make sure you don't extend the tweeter so far that the dome hits the grillecloth.

[Svante]

Wouldn't that mean a circular edge around the tweeter?

[HeatMiser]

I've been toying around with an idea to minimize a grill frame's impact. I hope my drawing is clear enough:



The idea is a frame built with pair of wooden slats (light brown) on the sides with strips of springy metal (black) at top and bottom, and grill fabric stretched across and fastened with adhesive. The whole piece would then be bent into a semicircle and attached to the cabinet on the sides.

You can probably see the need for springy metal as it would bend smoothly and not permanently deform.

This type of grill might not be ideal for speaker designs that place the tweeter very near the top of the baffle, as the upper metal strip would then be very much in the dispersion pattern and could cause problems. One hopes rather that the grill would extend vertically far above and below the drivers.

Any thoughts?

[omba]

http://www.avalonacoustics.com/revu-au-dia.html

You can try something like this.

[BillFitzmaurice]

Originally posted by Svante
Wouldn't that mean a circular edge around the tweeter?

Yes, the grille frame would be cut to fit tight to the driver frames. The idea is to duplicate the concept of flush mounting the drivers while at the same time including a grille.

An alternative is to eliminate the frame entirely, flush mount the drivers, and rout channels into the baffle, surrounding the drivers. That channel is used to secure a round rubber strip that secures grillecloth tight to the baffle, in the same fashion that screens are secured to aluminum screen doors and windows. For that matter the fiberglass screening used for doors and windows would also work well as a grillecloth.

[Svante]

Originally posted by BillFitzmaurice



Yes, the grille frame would be cut to fit tight to the driver frames. The idea is to duplicate the concept of flush mounting the drivers while at the same time including a grille.

Ok, what I am getting at is that the circular shape of the edge around the tweeter is about the worst it can have. It will behave similarly to a circular baffle, with the driver in its centre.