Must try MOD - Foam inside the stamped steel baskets - YES!

F1nut

Manufacturers have largely solved both of these problems another way, by going with cast baskets with minimal spoke area and ventilated designs behind the spiders.

A cast basket does solve the ringing issue of a stamped steel basket, but so does Dynamat Xtreme.

The minimal spoke area of a cast basket does not absorb sound waves like adding pieces of foam inside a stamped steel basket.

The purpose of ventilated spiders is to increase power handling, it's got nothing to do with anything else.

xschop

So why doesn't Polk send a sheet of DynaMat extreme with every Legend speaker?

F1nut

xschop wrote: »

So why doesn't Polk send a sheet of DynaMat extreme with every Legend speaker?

Silly question back at ya. Why doesn't Polk send a sheet of foam to line the inside of the basket with every Legend speaker?

xschop

That was my rhetorical question.

But I'll answer both: It is because of price point and the target customer.

xschop

When Polk starts building a driver that doesn't require Dynamat or foam inside the frame, I'll be a customer.

Gardenstater

Here's a good picture of a driver designed for minimum back wave reflections that would reflect back at the cone, including back wave that transmits through the spider:




Polk stamped steel MW driver with spider cutaway (photo by forum member I forget the name of sorry). How much projected area for reflection is presented to the backwave here?

xschop

Started foaming another set of B&O drivers this weekend...

odcics2

Note green felt to absorb back wave directly in front of the magnet. The rest goes into the enclosure.

Imagine an MW65xx designed like this.

Gardenstater

odcics2 wrote: »

Note green felt to absorb back wave directly in front of the magnet. The rest goes into the enclosure.

Imagine an MW65xx designed like this.

That's totally the Vandersteen Midrange design in the patent. Backwave from the cabinet "possibly" becomes a major problem in a 2 way with passive radiator design because you might be limited in how much damping materials you can apply to the cabinet, but I wouldn't use BH5 because it may load, I would use No-Rez and you would have to experiment.

That design is really for a 3 way speaker design where this midrange unit would be in an isolated chamber with damping material I think.

odcics2

That’s why I said imagine.

It would be designed as a 6.5” mid woofer for a Polk Monitor 5, 7 or 10, for example.

xschop

Imagine no foam or Dynamat frames.

odcics2

The magnet and surrounding area is much larger than the outer basket with the 4 holes. Foam helps, but there is a lot or room for improvement left on the table.

Gardenstater

^^When the magnet assembly and dust cap has been removed, a spud can be used to pull the voice coil up just out of the way and you can add some foam to that recessed area, attached with power grab or the like. Rob @xschop did it and released one into the wild, never to report back home *sniff* lol.

xschop

odcics2 wrote: »

That’s why I said imagine.

It would be designed as a 6.5” mid woofer for a Polk Monitor 5, 7 or 10, for example.

I've been eyeing a 6.5" cast basket with spider reliefs (only insert foam here) and open spokes. The factory base plate would simply have to be tapped for it's 60mm PCD and the flange OD turned down (6.650") to drop right in a Monitor cabinet...

Gardenstater

Very cool find! It looks like the basket depth is 15.5 + 35.5 mm = 51mm = 2.008" vs (hard to measure) around 1.65" on the Polk basket, based upon my 1983 MW6500 which I just eyeballed. Surround diameter is 158mm = 6.22" and I roughly measure 6.1" on my Polk which is not super far off.

Could be a problem unless the voice coil were reset?

I didn't check the relevant spider dimensions yet.

xschop

On my donor basket (sent from @MrGeology) I got 1.65" also. The 26mm Dia. replacement coils are a little longer than factory ones anyway (35-40mm long), which will make up for the extra depth. Provides more coil cooling too with the open spider design.




You could drop in either a 4" (Polk) to 4.5" Dia. spider and fix that worn/sag issue (6500,6503,6510,6511)

Just need to hunt down a pre-assembled 6.5 paper recone kit and save a bunch of time.

Gardenstater

The 35.5mm = 1.398" isn't that far off from what I measure on my Polk MW6500 for the surround mount to the spider mount surface of 1.334". Could just use a 1/16" spacer if you even needed to do anything at all.

xschop

I've got 36mm on this one. Then again, this is the thin gauge one I dissected.

skipshot12

This is very interesting…..

odcics2

The soul of a Monitor 7.
Excerpt from the Polk brochure.

plastic_avatar

Great find. Good marketing blurb. I ate that stuff up when I was younger. The Bose marketing verbiage was great of that vintage, too.

I try to remind myself (especially when talking to grandparents about the good ol' days, or with people under 30 about why James Bond was such a sleaze): Consider all things in the context of their time and place.

Those midwoofers? They were so superior to Bose it was no comparison, but Bose marketing won me over in High School.

I have no doubt this design rang less than the majority of its market contemporaries (and other consumer designs of years' past them). But, as time goes on, and equipment improves, you look back on that state-of-the-art, say... 1989 Super Coupe or 1991 3000GT VR-4... and they could use some updates

I enjoy my 6xxx-equipped models every day. But I wouldn't if Polk hadn't worked to bring the level of sound value down to the price they did.

I'd still like to see a no-holds-barred new Monitor 7, even though they missed the 50th anniversary of the company boat.

When did the 7 hit the market? Maybe the 50th of the speaker that defined the company? Did it hit in 74?

Gardenstater

plastic_avatar wrote: »

Great find. Good marketing blurb. I ate that stuff up when I was younger. The Bose marketing verbiage was great of that vintage, too.

....

I'd still like to see a no-holds-barred new Monitor 7, even though they missed the 50th anniversary of the company boat.

When did the 7 hit the market? Maybe the 50th of the speaker that defined the company? Did it hit in 74?

It would be awesome if they did an updated modern but still retro appealing version.

They were trying to sell a very early version of the 7 when they were in the Gallagher Mansion, in late 1973. I have yet to see one of them on eBay and I wonder how many (if any) they actually sold.

xschop

They'd come with the new certified 3x3" BH5

Gardenstater

The new 3 x 3 standard is very economical for today's times.

xschop

Shrinkflation is real.

In other news, did a test run. I took a 3/8" wide wood chisel to an MW that had a torn surround and badly creased cone. About every 1/4 turn of the perimeter I put a drop of WD-40 on the chisel ramp. The old surround came off clean without tearing. At this point I can either re-cone (thinking Carbon Fiber) and keep the factory basket, or move forward and cut the spider carefully and order the cast baskets. Still haven't found a 6.5" paper re-cone kit with the spider and voice coil attached.

odcics2

Using the original proprietary built cone, spider, surround and magnet assy is the way to go, or it's no longer a Polk speaker, IMO.

xschop

I agree, but where to find a copy of the paper cone is the mystery. The surround I have all dimensions for, even it's rollover thickness.

odcics2

Only way is to use a donor MW6500.

xschop

And to make the magnet/pole-piece removable would be gold.

odcics2

Maybe jig the magnet assy and basket by the surround. Remove the metal between them, back filling it in with 3-4 metal rods to get the support for the magnet assy back.
You would end up with a minimal area to reflect sound.
Just an idea to maintain the “Polk” integrity.