[ukon16]

So I got some vintage Saras speakers and they're pretty nice but no grills
 
I'm researching how to build them and out comes the "grills and cloths hurt SQ" crowd.
 
Any difference between the cloth? Metal?
 
Does any bit of cloth or foam between the drivers and ears really distort sound enough to matter?

 

[Strangelove424]

There may be some slight sonic differences when removing the grilles, but they will be very slight at best, and it comes down to a value decision between safety and sound. If the woofer is punctured, dented, or crinkled, that will no doubt ruin the SQ. Foam is different, it's porous and will absorb sound waves. I've seen it used on the interior of a cabinets to absorb standing waves or implemented as acoustic treatment on walls, but I've never seen foam placed in front of the woofer.  There are forms of both metal and clothe grilles that have a minimal effect on sound. It depends on how the material itself was designed. When you go to a movie theater, the central speaker that delivers most of the dialogue is behind the screen, which is acoustically transparent but optically opaque. Metal grilles can also be quite transparent if designed properly. My speakers have metal grills on them and they saved the woofers from my klutziness on multiple occasions. On an internet forum, when asked what the benefits of removing the metal grills would be, the engineer who designed the speakers (who formerly worked at KEF and now directs Pioneer's TAD division) stated "you won't gain much". After I heard that, I was almost convinced to leave them on. When I accidentally dropped a screwdriver on the grill, I was totally convinced. If you want specifics on material sourcing, you'd probably get better answers in a DIY forum. Head-Fi has one in the Misc section. I'm sure there's people working on speakers in there, if not there's other places online that serve DIY speaker enthusiasts. Sounds like a fun project though. 

 

[jaddie]

When you go to a movie theater, the central speaker that delivers most of the dialogue is behind the screen, which is acoustically transparent but optically opaque. Metal grilles can also be quite transparent if designed properly.

There are three or five behind-screen speakers in theaters, not counting subwoofers.

Theater screens are neither perfectly acoustically transparent nor optically opaque. Acoustically there is well known "screen loss" which is not trivial, but is equalized out. This happens with AT home theater screens as well, it's often not a slight or flat response loss either, though there are some pretty good ones now. It can be equalized out at home as well.

Two rules of thumb: the more light it lets through the less acoustic loss, and the softer materials reflect less energy back to the speaker. A material tends to both absorb and reflect energy. The metal grilles reflect much more than they absorb, and that energy has to go back to the speaker, where in some cases it's reflected again back to the grille, etc. The saving grace is that each reflection is weaker, more diffused, and so multiple reflections die quickly. And the period of reflections are very short and falls into the integration time window. But the point is, soft stuff doesn't reflect as much back, looser weaves attenuate less. Polyester double-knit is very transparent acoustically.

 

[nick_charles]

I've always (since the 1970s) removed the grilles where possible. My first ever speakers had a grille (I kid you not) made from closely-spaced wooden dowels with cloth in-between (that was a pair of speakers part of a crappy record player all-in-one unit system complete with ceramic cartridge and 4 speed BSR autochanger)  purchased with my dad's cigarette coupons. I certainly remember foam grilles on early 80s speakers though most were cloth and the cloth iirc did deaden the sound more than foam which seems counter-intuitive. 

 

[jaddie]

I certainly remember foam grilles on early 80s speakers though most were cloth and the cloth iirc did deaden the sound more than foam which seems counter-intuitive. 

Not really. Earlier cloths were often a fine burlap kind of material which was lossy at the high end. Open cell foams would be more transparent, though they tend to disintegrate over time. Cloths were always trading off robust protection vs transparency. Some even used a kind of window screen to back up a flimsy but transparent facing.

 

[BlackbeardBen]

Another important but often overlooked effect is that of the grille frame on the sound - in particular as regards to diffraction.  In many cases I would expect this to have a bigger effect on the sound of the loudspeaker and may in fact account for much of the apparent difference in clarity.
 
A soft grille cloth, only absorbing a very small portion high frequency waves and with almost no reflection, should have minimal impact on the sound.  By comparison, a rectangular MDF frame around the speaker will cause several secondary reflections, muddying sound arrival times (to what degree I do not know) and certainly affecting frequency response.
 
On the other hand, some grilles are designed to minimize or even improve diffraction behavior.
 
My main speakers, a pair of Infinity Renaissance 90s, incorporate this.  The manual explicitly states that the grilles are necessary for proper performance.  The drivers are raised above the cabinet face so that they are flush with the grilles.  The grilles are solid MDF and taper at the sides (matching the cabinets) to minimize diffraction.  In fact, there was a particular grille option that didn't even have fabric, for people that wanted to see the drivers.  See the photo below:
 

 
 
And here they are without grilles:
 

 
 
Unfortunately, my grilles were broken by the previous owner and so I have never heard them with the grilles on.  I'd like to have replacements made out of stained high-grade plywood though, with no cloth.

 

[wuwhere]

These guys make foam speaker grills.
 
http://foamspeakergrilles.com/

 

[jaddie]

Quote:

Another important but often overlooked effect is that of the grille frame on the sound - in particular as regards to diffraction.  In many cases I would expect this to have a bigger effect on the sound of the loudspeaker and may in fact account for much of the apparent difference in clarity.
 
A soft grille cloth, only absorbing a very small portion high frequency waves and with almost no reflection, should have minimal impact on the sound.  By comparison, a rectangular MDF frame around the speaker will cause several secondary reflections, muddying sound arrival times (to what degree I do not know) and certainly affecting frequency response.

Yeah, I'd be careful assuming anything about reflections and diffraction here.  Most grilles are positioned very close to the drivers and reflect very little energy.  The MDF frame is way out of the main lobe of even the midrange driver (if any).  The area of a frame that is exposed to energy is quite small.  And we have to do a little ray-plotting to see where that energy goes after it's reflected.  Reflections, as bad as that word may seem, are harmless if not combined with sound we hear, within a time window that makes a difference.  I'm not saying that early reflections aren't a problem, they are very much a problem, but they are also highly affected by the angle and area of the reflecting surface, and the distance to it.  I don't think it's fair to generalize and say the above, it's case-specific.  
 
A great many speakers are designed, and balanced to operate grilles on.  Taking them off removes a design element that was taken into account, and may or may not improve anything.

 

[ukon16]

Next question....what about "acoustically transparaent?
 
Some advertise words like 100% audio transparent and others such as car speaker grill cloths don't say anything at all.
 
I want to try out some funky colors(almond, white, burgandy) but rather not end up buying some non-audio cloth that is poor for music.
 
Is cloth...cloth when it comes to speaker grills or is just a transparency issue(how thin and see through?).

 

[jaddie]

Material made with looser weave, and thinner has less high frequency attenuation. Tighter weaves and thicker fabric attenuate highs more. Nothing is perfectly acoustically transparent, but some materials either do so little that it doesn't matter, or attenuated in a predictable way that's easy to EQ back out. The easy test is if its a dark material, and you can see through it easily, it's probably going to pass audio without a problem. Tight weaves like bed sheet, even though thin, aren't as good.