Polk 7B's - need to know what Mid Woofer Model?

boston1450

Did someone replace the gasket ?

Gardenstater

@boston1450, @f1nut; Yeah I think you guys are right. It's gray not silver, and the holes are way too small to be in metal. Sometimes it helps to get another perspective (or two). I guess I was hoping it was a silver basket one that somebody painted black lol.

boston1450

When snug'n the screws up be careful to observe the gasket. It can pull as you are tightening.... I have used Armacell from HDepot with great results. I use a exacto knife & I trim near the screw holes & it has worked well. I would trim the hole area for proper screw placement.... Alway check after, to see if cabinets are still air tight.

pitdogg2

heat up some 12gauge wire melt right through to make your holes for the screws. I use an old soldering iron with a pointed tip works great.

Gardenstater

@boston1450 Is this the stuff you use? Can't find narrower than 2" : https://www.homedepot.com/p/Armacell-2-in-x-30-ft-R-1-Foam-Insulation-Tape-TAP18230/100539553?keyword=armacell+gasket+foam+tape&semanticToken=21300000111_2019112209124893870_bbbn+21300000111+>++cnn:{0:0}+cnr:{7:0}+cnd:{4:0}+cne:{8:0}+cnb:{0:0}+cns:{5:0}+cnx:{3:0}+st:{armacell+gasket+foam+tape}:st+oos:{0:1}+br:{armacell}:br+rt:{gasket+foam+tape}:rt+dln:{553329}+qu:{armacell+gasket+foam+tape}:qu

pitdogg2

Gardenstater wrote: »

@boston1450 Is this the stuff you use? Can't find narrower than 2" : https://www.homedepot.com/p/Armacell-2-in-x-30-ft-R-1-Foam-Insulation-Tape-TAP18230/100539553?keyword=armacell+gasket+foam+tape&semanticToken=21300000111_2019112209124893870_bbbn+21300000111+>++cnn:{0:0}+cnr:{7:0}+cnd:{4:0}+cne:{8:0}+cnb:{0:0}+cns:{5:0}+cnx:{3:0}+st:{armacell+gasket+foam+tape}:st+oos:{0:1}+br:{armacell}:br+rt:{gasket+foam+tape}:rt+dln:{553329}+qu:{armacell+gasket+foam+tape}:qu

Yes that is it and we just cut down to the width we need.

Gardenstater

The update is I finally broke down and installed the new old stock black basket MW6500, and, after having played for a couple of days and I feel it is broken in, it sounds like a new speaker! Wish I had another new one like it, so that I'm sure there is no mis-match, as the one in the left speaker is original 1979 silver basket MW6500.

I have found a couple black basket ones that are used on eBay. Trying to decide to take the plunge or just hold out for another new old stock one. Could be a long wait! : One is 1981, $79 shipped (I paid $70 for the new 1991 one!), the other is $60 (oops and it's gone now lol).

F1nut

It wouldn't hurt to grab another spare.

Gardenstater

Thanks. Do you see any concerns with it. They say "fully functional" but I always wonder about rubbing of the voice coil.

F1nut

Looks ok. The major concern is magnet shift and that one hasn't been reinforced with adhesive.

Gardenstater

Yeah. I just sent a PM to them asking for confirmation of no voice coil rubbing when the cone is manually exercised. Thanks.

Oh, annoyingly the other one I was going to buy for less money, the seller stated that the magnet had been secured with adhesive and that they were an audio shop and I asked for a picture showing the label and the surround and was told they would do that for me on the 2nd. Now it says that the seller has removed it because it was lost or broken! You can't make this stuff up lol.

Gardenstater

Just picked this one up on eBay for $33.82 shipped. Thank god for saved searches. Seller says "absolutely no issues", so hopefully I get lucky and no magnet shift.

Gardenstater

Just got this one and happy to say that there is no voice coil scraping detectable manually! I'm going to put adhesive on the magnet immediately, then Dynamat the basket.

Gardenstater

Ran an extremely healthy fillet of the Gorilla Maximum Strength Clear Construction Adhesive around one side of the magnet. Gonna let that set up good before flipping and doing the other side. Incidentally, the small syringe was much easier to handle than the large caulking gun / cartridge and this stuff isn't available in a squeeze tube it seems.

Gardenstater

A little trickier to do on the other side of the magnet but the syringe along with a dabbing motion followed by a gloved fingertip served pretty well. I'm a little concerned that this driver was designated by Polk as for a M4 where mine are M7B's , perhaps due to the slightly high resonant frequency they measured of 25 Hz. Hopefully when I dynamat it that will lower the resonant frequency.

pitdogg2

The same driver were used on multiple speakers. Polk just stamped the number on the label or checked a box. There are no worries whether M4 or M7 they are the same driver.

Gardenstater

pitdogg2 wrote: »

The same driver were used on multiple speakers. Polk just stamped the number on the label or checked a box. There are no worries whether M4 or M7 they are the same driver.

Well yeah I know it's the same driver. I guess my thinking was they measure the resonance frequency of them for a reason and it would make sense for them to designate the ones that don't score as low for the M4 and M5's, which don't have as low of a frequency response as the M7's and M10's. My other MW6500s that I have which were in M7's have resonance measurements of 21 or 22.

It's my nature to be a worrier lol.

Gardenstater

All glued up, dynamated and ready to go for emergency backup when needed, except I'm not too thrilled with the condition of the gasket, so probably will get some Armacell tape to replace it. In the last picture I did an experiment to see how much clear penatrating epoxy a small edge of particle board would soak up and this little piece soaked up 3.8 g / sq in.. It soaked in to a respectable depth so I'm thinking this is a very good way to stiffen up the baffles where the speakers mount ...FYI. Also, I have a question......does anybody know of a good source for spade connectors to fit the speaker terminals? I'd like a good audio grade with oxygen free copper construction. I found some on amazon that are 6.5mm but these spades measure more like 5mm and I don't want them to be too loose. Thanks.

F1nut

The tabs are .250. I believe Furutech still sells gold plated copper Fastons, but they aren't cheap.

Gardenstater

Hmm. Just checked them again with my dial caliper and they measure 0.200" or 5.08mm. The ones I have seen on amazon so far are 4.8mm (0.189") and 6.3mm (0.248"). I'm thinking I'll be needing the 4.8mm ones and hopefully that's a nominal size and they will still fit.

I'll look into the Furutechs thanks. I just don't really want to get brass ones if I can avoid it. I'm going to be twisting up some hookup wires from some Cardas 6N enameled magnet wire I have and it would rub me the wrong way to go to brass from that.

F1nut

Let me rephrase my comment. The tabs take .250 Fastons.

Gardenstater

Turns out there is an industry standard 0.205" size for Faston Receptacles. This would be the ideal size for our MW drivers. https://www.te.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Catalog+Section82004_FASTON_TERMINALS_-_FULL_CATALOG0914pdfEnglishENG_CS_82004_FASTON_TERMINALS_-_FULL_CATALOG_0914.pdfCAT-P592-L9505

Gardenstater

The outer dimension of a 205 series faston receptacle is pretty much 6.3mm (6.35mm) so when amazon shows a dimension of 6.3mm here, you don't know if it's the inside or the outside dimension aargh.

Of course, adding to the confusion there are .020" and .032" thick tabs and these drivers have the 0.020". I know you can mash them down with a needle nose but still....

Gardenstater

Appears to be two sizes in the Furutechs, which are gold plated phosphor bronze. They have too large 0.250 x .032 and too small 0.187 x .032! https://www.partsconnexion.com/furutech-faston-connectors.html

Well, correction. They do make a copper based one but only in the 0.250 x .032 size. Can't win lol! The tabs on the drivers could be filed down slightly if needed for the 0.187 ones but I don't want a sloppy fit which would be the case with the 0.250's http://www.furutech.com/products/component-parts/disconnects/

Gardenstater

Well thank god I had these old radio shack 3/16" faston connectors in my electrical box. They will do just fine at least until I make up my Cardas wiring harnesses which will use the Furutech gold plated phosphor bronze ones. All that was needed was to spring them out slightly with a putty knife and to hone a little off of each side of the tabs on the driver with a diamond hone. Worked like a champ, especially with the addition of a little Mapleshade Silver Platelet Grease. Now I've got my new addition used MW6500 in being tested and I must say it's like mint condition and with the dynamat on it, damned if it doesn't sound better than the new one! Now to dynamat and glue up the new one. Couldn't keep playing it, was getting nervous.

F1nut

I owe you an apology. After checking myself the Polk tabs are not .250. Not entirely sure why I thought they were.

Gardenstater

Hey no worries man! Thanks for tipping me off to the Furutechs. Everything is coming together bit by bit. I keep saying it can't sound too much better, and then keep surprising myself.

F1nut

It is cool how well they respond to the various upgrades.