Replacement Grills for Polk Series 7B's

MDN

I'm looking at a pair of Polk 7's that don't have the grills. Is there a source to buy the grills or an alternative solution? Thanks in advance.

F1nut

MDN wrote: »

I'm looking at a pair of Polk 7's that don't have the grills. Is there a source to buy the grills or an alternative solution? Thanks in advance.

The none BS answer to your question is there is no source for replacement grills.

Gardenstater

These are probably from a Monitor 7. I question the seller's measurements of 23-3/8" x 13-3/8" (prob. should be 14"), but lots of eBay sellers are measurements challenged. Also, the seller "can't remember" what speaker model they got them from. The speaker peg hole positions are different from my 7Bs, but they even have the partial depth mystery forstner bit hole that mine have. These probably came from a later 7B than mine if the 23-3/8" is correct, but then the badge should be on the speaker and not the grill so still doesn't compute:

https://www.ebay.com/itm/354490406849

Gardenstater

slow_polk7 wrote: »

Gardenstater wrote: »

... they even have the partial depth mystery forstner bit hole that mine have.

It appears that, without that relief, the "spring nut/insignia post" assembly would prevent the grille from fitting tightly against the baffle.

You are correct! I didn't have my glasses on when I looked at mine this morning lol. Flat black spring nut on flat black paint.

To OP: I wouldn't buy those grills without having the seller re-measure dimensions and ask for the locations of the grill post holes from each other and from edges. If the post holes are in the wrong positions they could always be filled and relocated but it is a bit fussy and not much room for error. I guess I would make a template to drill through.

Gardenstater

If you make your own I would definitely use Baltic Birch plywood instead of particle board for more stability/less warpage. And do a roundover on the inside edge. You would be able to take the opportunity to also use a more sonically transparent grill cloth and possibly use magnets instead of the grill pegs.

Honestly, I never listen to mine with the grills on.

odcics2

Line the inside edge of the entire grille with a half inch of felt to help get rid of diffraction.

Keep in mind they were designed by Polk to listen with the grilles on.

But, whatever sounds better to you is all that matters.
When it comes to music, our ears are the biggest variable. That explains why there are so many speaker companies!

Gardenstater

There was one speaker line that they made the marketing claim "sounds better with the grill on" but it was definitely not the Monitor 7. I think it was the tower speaker advertisement; 15t etc..

Yeah, here it is on p. 2 of the technical brochure:

odcics2

Other speaker companies have used the grilles to advantage... Paradigm comes to mind.

odcics2

Gardenstater wrote: »

There was one speaker line that they made the marketing claim "sounds better with the grill on" but it was definitely not the Monitor 7. I think it was the tower speaker advertisement; 15t etc..

Yeah, here it is on p. 2 of the technical brochure:

Oddly enough, the bottom illustration is the basis of the Monitor 7 design,
a hemispheric radiation pattern! Begs the question as to which design is better.

xschop

Grills are for burgers and steaks.

Gardenstater

The only source for the grills would be eBay. Sorry I didn't mention. I have only seen them go up for sale once in the past 4 years or so, so I wouldn't hold my breath. Except for WAF or small children or pets or your own sensibilities I wouldn't let that stop me from buying if the price is right.

slow_polk7

Gardenstater wrote: »

... they even have the partial depth mystery forstner bit hole that mine have.

It appears that, without that relief, the "spring nut/insignia post" assembly would prevent the grille from fitting tightly against the baffle.

subkron

@Gardenstater "...seller's measurements of 23-3/8" x 13-3/8..." may actually be correct, it depends on where you take the measurements. On my 7Bs the sides & tops are bowed in at the centers. At the top corners I have about 13-15/16" but it is closer to 13-1/2" or so in the middle of the run.

I actually have Baltic birch on order to make new grills for mine.

odcics2

The polk MW and even the tweeters have a tendency to collect dust and grime without grilles. You can see nasty examples on ebay.

What is a safe way to clean the MW ?

pitdogg2

odcics2 wrote: »

The polk MW and even the tweeters have a tendency to collect dust and grime without grilles. You can see nasty examples on ebay.

What is a safe way to clean the MW ?

Yes. Original Windex and a microfiber no lint cloth well wetted with the windex. It's best to try and support the driver with your free hand. Carefully clean in a circular motion around the driver starting with the rubber suround working inward. Keep the cloth wet once it starts to dry it will start grabbing the tacky driver surface. I have used 3-4 paper towels folded up with success as well. Once again it will tear and stick to the driver if not well wetted.

odcics2

Thanks!

odcics2

Amazing that the MW can still be tacky after all these years.
I wonder what’s the composition of that proprietary material.

F1nut

subkron wrote: »

I actually have Baltic birch on order to make new grills for mine.

MDF would be a better choice.

Gardenstater

subkron wrote: »

@Gardenstater "...seller's measurements of 23-3/8" x 13-3/8..." may actually be correct, it depends on where you take the measurements. On my 7Bs the sides & tops are bowed in at the centers. At the top corners I have about 13-15/16" but it is closer to 13-1/2" or so in the middle of the run.

I actually have Baltic birch on order to make new grills for mine.

My particle board grills haven't done that to me but they did both take on a bit of a banana shape, which is my fault for being too lazy to install them on the speakers after a listening session.

Baltic Birch is a bit more difficult to machine than MDF, and can be splintery, but it would still be my choice for a grill frame because of being less dense/lighter and having a MOE (modulus of eleasticity) at least twice that of MDF. Here's some data I found online:

odcics2

What about resonance?
Isn’t MDF the best choice?

A lot of high end speaker manufacturers use it.

Gardenstater

odcics2 wrote: »

What about resonance?
Isn’t MDF the best choice?

A lot of high end speaker manufacturers use it.

Resonance is more of a concern for speaker enclosures, especially if you remove your grilles to listen as I do. The driver is the source of mechanical vibration and is not directly attached to the grill, with the springy grill pegs being the only connection.

I'll also add that I have never liked how when I go to remove the grills from the speaker by starting at either the bottom or the top, in the action of wresting the strong grip of my grill pegs at that end, it does not easily give up at the other end due to the flexibility of the particle board. Another reason why I think BB would have been better. Would BB absorb less moisture over time and not have as much tendency to warp? Not sure, but I would put a sealer on either one so maybe a moot point then.

MDF is said to have lower resonant frequency than BB. Subwoofer builders prefer BB to get the resonant frequency up above system operating point. Neither BB nor MDF really have much internal damping to speak of.

joebass3

I think for speaker grills the big concern is warpage. Baltic birch may be better than most, but all plywood has a tendency to warp. Every piece of MDF I have used has been perfectly flat.

Gardenstater

joebass3 wrote: »

I think for speaker grills the big concern is warpage. Baltic birch may be better than most, but all plywood has a tendency to warp. Every piece of MDF I have used has been perfectly flat.

Every piece of BB and every piece of MDF I have used have been perfectly flat, initially. BB is void free, all hardwood, 9 plys. Finnish BB is said to be pretty much the ultimate if you can afford it and can find a source, and may be stiffer still than run of the mill BB.

If you go to the trouble of fabbing your own grills, you sure as heck are going to seal them. If you also do an inside roundover, the need for the grill frame to be as stiff as possible is even greater.

Just my 2c all of this. We audiofools can worry about everything

Gardenstater

Gardenstater wrote: »

joebass3 wrote: »

I think for speaker grills the big concern is warpage. Baltic birch may be better than most, but all plywood has a tendency to warp. Every piece of MDF I have used has been perfectly flat.

Every piece of BB and every piece of MDF I have used have been perfectly flat, initially. BB is void free, all hardwood, 9 plys. Finnish BB is said to be pretty much the ultimate if you can afford it and can find a source, and may be stiffer still than run of the mill BB.

If you go to the trouble of fabbing your own grills, you sure as heck are going to seal them. If you also do an inside roundover, the need for the grill frame to be as stiff as possible is even greater.

Just my 2c all of this. We audiofools can worry about everything

And when we speak of warpage we should specify direction. Plywood is very unlikely to warp in 2 of the 3 directions, due to the adhesive laminated opposing grain direction method of construction.

Do an experiment. Rip on a table saw 4 pieces that are 3/4" thick x 1-1/2" wide x 4ft long. Do one each: 1) MDF, 2) Particle Board, 3) Baltic Birch across the outer veneer grain, and 4) Baltic Birch with the grain. Then suspend them by a couple loops of string in a non climate controlled outdoor space with a roof over them so that all surfaces are exposed to the humidity in the air. Check them in a year or so. I'll bet you that the BB samples will still be straight as the saw cut them but you will not be able to say the same for the MDF and Particle Board.