Speaker grilles and sound dispersion

[RMutt]

Over in DIY I have been working on a pair of Goodmans speakers. I have now decided to add grilles, partly for aesthetic reasons and partly to take the last bit of tttsss out of the tweeter. (I understand manufacturers designed the sound for grilles). I have hit a conundrum. Having carefully redesigned the baffle to eliminate the picture frame edge I now find I am going to need to add a frame in order to attach the fabric. This had me wondering, actually all speakers have this frame, so what about flat baffles? Does it really affect sound dispersion? Is there a way to add a grille without a frame?

[bobbasrah]

Over in DIY I have been working on a pair of Goodmans speakers. I have now decided to add grilles, partly for aesthetic reasons and partly to take the last bit of tttsss out of the tweeter. (I understand manufacturers designed the sound for grilles). I have hit a conundrum. Having carefully redesigned the baffle to eliminate the picture frame edge I now find I am going to need to add a frame in order to attach the fabric. This had me wondering, actually all speakers have this frame, so what about flat baffles? Does it really affect sound dispersion? Is there a way to add a grille without a frame?

Not sure how successfull acoustically transparent (ok - nearly) cloth will alter the tweeter's response. It would be more effective tweaking the crossover components as you can target the troublesome frequency more accurately.
I use grilles every blue moon to discourage vertically challenged visitors poking the drive, not for everyday listening.

Many moons ago, manufacturer's tried acoustic foam instead of cloth and frame but it was soon discontinued, and in one clever design the cloth was made as a sock to slip over the entire speaker, but that idea disappeared also.
Without a frame or structure for the grille, you will not get the required tension on the fabric.

I rebated my drives 5-6mm into the baffle to get them flush, followed by a 45 degree fillet on the baffle to minimise driver edge/baffle interference.
This reduced the required frame gap for cone excursion, so the frame thickness could be reduced to 6mm. The 6mm HDF frame was filleted 45 around the inner edge to prevent potential interference, chamfered on the outside for finish, spraying darker to disguise the HDF, then attaching the cloth . The frame is a teardrop shape fixed at 3 points, and is 12mm wide at it's narrowest section.
No problems aside from the minimalist frame being quite easy to break around the fixing points (my oversight) when removing.

Hope some of the avove helps.

Bob

[YNWaN]

Not all grills use a frame, some are made from a piece of open cell foam that is attached to the baffle using Velcro.

[bobbasrah]

Yep, as per my 2nd para Mark, but I was not aware this was still being done ??

[YNWaN]

Ah yes, sorry, didn't read your post through thoroughly.

Yes, some manufacturers still do this but although it is effective it isn't the most handsome of solutions.

Have you seen the solution where an elasticated stocking grille is stretched over the baffle and held in place by a rebated groove?

Some manufacturers use a very thin grille frame and use spacers to stand it clear from the surface of the baffle.

[bobbasrah]

The beauty of foam lies in it's limp 3d structure which can can be sculpted yet remain stable once mounted off a solid surface. I found it interfered too much with sonics, but that was a long time ago. Have not seen it on commercial designs in many years, hence my surprise it is still in use....

A face mounted elasticated stocking would certainly work if it gets projection by some means or other to ensure cone excursion is not impaired by the fabric. At least a sock could be stuffed away someplace unobtrusively, unlike a grille.

The thin grille frame you mention is exactly how I ultimately did it, and the mounting toggles/cups maintain a small gap to avoid resonance. I got 6 mounting sets per speaker, so ended up with a inverted teardrop for the drives, and a rectangle for the TL throat, each held at 3 points. Currently these are serving duty as dust collectors and annoyance to the cat....

Still not sure that any grille will resolve Andrew's "the last bit of tttsss" though....

[YNWaN]

No, I agree - I also wouldn't use the grille to reduce tweeter output.

[RMutt]

Thanks for the replies and for the ideas as to how i might go about solving my problem. One initial issue i can see is that the mid range driver comes quite a way out from the baffle and so a thin frame would not give the required clearance. As to calming the treble with crossover changes, well I've just finished replacing all the capacitors! The original grille was certainly not acoustically transparent and I wonder whether the tweeter ttttssss is a quality of its sound rather than a frequency thing. I was considering a thin grille frame that is mounted at the corners on small projections, so as to be open at the sides. Anymore opinions would be welcomed, thanks.

[Alan]

I had the same speakers, and thought about cladding the baffle in a dense wool like Jim Goulding's diffractionbegone product. It would cater for the protruding mid-driver, and would (have!) sat nicely within the 'picture frame', and dealt with diffraction issues.

I also pondered - but never got around to - using a fine metal mesh as grille. I have read that this is acoustically transparent, and I have also read that it is not...so I was going to try and find out.

I eventually broke them up for spares & sold them off, but I still have a straight pair of Magisters to work on one day.

Have fun!

[bobbasrah]

Ok, went back to DIY to figure out what you had done, and as I understand it, this is a stopgap speaker, so is this grille for prying fingers or cosmetics?
Not sure how you could fit a spaceframe between the corners without it distorting under fabric tension.
The last picture you posted showed a raised baffle over the original, so you now have the new baffle thickness plus the driver clearance to contend with.
Would a wood frame not friction fit over the extended baffle to give the required clearance, then fit the fabric to the frame?

[RMutt]

Thanks for the info and for looking for the driver for me Alan. Not really a stopgap bobbasrah, I do have some modern speakers, just a project I embarked on after reading about the merits of larger drivers. I thought I would see for myself and I am using it as a learning experience but it is one into which I cannot afford to put a great deal of money.

[bobbasrah]

Fair enough mate, no worries.
A slip on frame might work as suggested made perhaps of pine or HDF, braced across the corners of the speaker clear of the drivers? Just a thought. Cheaper than the acoustically transparent cloth will be..... So long as you can breathe freely through it almost any fabric would probably do in reality.

Must remember to change my name or get a signature sorted before the heavy brigade arrive in choppers.... Why on earth I named the cat Ahmed the Terrorist I cannot fathom.....

Bob

[Reid Malenfant]

Why on earth I named the cat Ahmed the Terrorist I cannot fathom.....

Bob
Probably because he launches surprise attacks :eyebrows: One cat I had used to attack dogs, not small ones either but Alsatian sized :lol:

I kid you not :eek:

[bobbasrah]

You got it in one Mark, but he's a 3 legged cat rescued by my girlfriend almost 2 years ago from almost certain death. Devilish though he is, the audio gear, including bare drivers, have been left unscathed throughout....
Our furniture and shoe insoles are torn to shit, but that's not so important..... typical....