Seven Seas Adventure - Polk 7C Upgrades

SCompRacer · July 22

Got these Polk 7C “New Technology Rosewood Vinyl” speakers with SL2000 tweeters and original matching serial number boxes from Ed the SRT king earlier this year. He had been asking when I was going to remove them from boxes and try them out. (I’ve had SL2000 tweets before in SDA 2 and SRS 2's and didn't care for them. Replaced them with RDO194's).

They had some Styrofoam packing transfer on corners that had to be removed. Other than that, they are in very fine condition. Corners could use a little more work. Magnets were checked, they passed the push passive air test so I carried them upstairs to try them out. Sounded pretty good but they could use some upgrades. Jupiter approves.

I have Larry’s Rings from Carl @schwarcw that had some minor surface rust. I sanded and painted them satin *black. Rob @xschop supplied the Tweeter Bezels. Jay @agfrost supplied the RDO194’s for holding his Mitsubishi LT-30 hostage for a few months. I get by with a little help from my friends…thank you all very much!

Xover will get some upgraded caps, but nothing too exotic. Eliminate the polyswitch. Maybe glue the magnets. Maybe damp the baskets. Maybe upgrade the wiring.

(It's a thermos, not an artillery shell).

*Rust-Oleum satin black in 12 ounce spray can purchased earlier this year at Home Depot. Partial can, aged to perfection paint. Fixed nozzle, not the five in one. Shaken vigorously, not stirred.

SCompRacer · July 22

Only 74F / 23.3C today instead of 90F / 32.2C so took the 7C’s into the garage and started work.

Gutted...

Found in bottom, fell off driver/tweeter. August 1986 date...

Centered and clamped template. Drill press too small so used drill with level on it hoping to make straight holes.

Looks good, not too much collateral damage to mating surface.

I glued Larry's Rings in and tightened with screws/template until they dry. Rob suggested I install some braces, so I cut two 1" hardwood dowels for each speaker. That one is just a test fit. I was thinking up a bit and more towards center between driver and passive.

I had a bunch of 8-32 screws and E-Z Knife threaded inserts left over from the Lenco idler drive turntable project. Actually, they were for the walnut heavy plinth that would match the BottleHead Eros base that I never finished. I used these for the tweeters and xover/speaker terminal plates.

Once they are screwed down, I'll use use my little body hammer (auto body) to flatten wood around them.

And the tweeters got them threaded inserts too.

Since I brought it up....the long overdue Lenco PTP 5 top plate and plinth project. That separates motor from platter bearing. That walnut plinth would be filled with layers of Baltic birch. It would not be hollow.

The wood moistened to show grain.

Wouldn't it be nice if the turntable matched the phono pre? Wouldn't it be nice if Aaron @ALL212 finished it for me?

Toolfan66 · July 22

You want some tweeter brackets to go with those?

SCompRacer · July 22

Am I too late having installed the inserts? Carl said he had a set but couldn't put his hands on them.

Toolfan66 · July 22

Send me your addy, I will send them to you, you can chose to use them or not. 😁

Already powder coated black..

Toolfan66 · July 22

pitdogg2 · July 22

That's what I'm talking about!!!!!
I think you'll be fine Rich. I bet the bracket and insert are about the same diameter. Use some epoxy if need be. You'll never out torque the brackets, EVER....

BlueBirdMusic · July 23

A really nice type of thread from the "good ole days".

SCompRacer · July 23

Use some epoxy if need be.

Yes, epoxy and I’ve also used JB Weld, especially when I am out of epoxy.

To repair damaged areas around mounting holes where the gasket would not seal, or breakouts inside the opening, I wrap tape around a screw to the diameter of desired hole. I screw it down until tape makes good contact with the threaded lug on the ring. A thin coat of die electric or any thin grease on threads doesn't hurt in case something sneaks by into the treaded lug of ring.

I apply epoxy or JB Weld around it. When dry, I cut flush with razor blade. I can use tweezers or an Xacto knife to start unwinding the tape from inside the wrap.

The outer wrap of tape will be stuck but no big deal. I’ll finish with a Dremel sanding disc to knock area flat.

I like to minimize a mess when doing driver magnets, especially since I am going to wipe the epoxy smooth (wearing rubber glove) after application. For the basket side of magnet, I cut a piece of rope and secure it with tape.

I wrap the magnet with tape too. A small strip of 220 sandpaper is used to put some scratches on the metal.

I also use the masking tape trick when caulking showers and tubs. Smear the bead down and remove tape for a nice straight caulk line.

pitdogg2 · July 23

SCompRacer
I also use the masking tape trick when caulking showers and tubs. Smear the bead down and remove tape for a nice straight caulk line.

I thought we all did that......

SCompRacer · July 23

Magnet shift epoxy deterrent applied.

Inexpensive plastic bezel gonna get replaced with @xschop premium aluminum bezels.

That white thing looks important.

I applied some Kapton tape to Rob's tweeter bezels for tweeter terminals/wires insulation.

Precise hole alignment.

Looking good!

Toolfan66 · July 24

I will have your brackets out to you this afternoon/first this in the AM..

xschop · July 24

Great thread/build.
I've got a set of matching phase plugs to donate too if you can install them.

I'd also HIGHLY suggest @Gardenstater foam frame mod. Vocals and midrange become less congested with that mod as well.

SCompRacer · July 24

I will have your brackets

Thank you!

I've got a set of matching phase plugs...

That seems scary for me to attempt!

I'd also HIGHLY suggest @Gardenstater foam frame mod...

I'll look that thread up. Thanks!

SCompRacer · July 24

Brace yourselves!

Rob suggested to brace the cabinets. Two braces on each side about the center line between passive and driver seemed right. Not enough space between driver and passive for one in center. I made a template for marking brace locations so I could apply glue to that area before sliding the near press fit 1” dowels in. You just gotta remember to orientate the template properly for front and opposite side.

I went with screwed and glued braces. I used my Kreg pocket hole jig to drill holes. You have to select the correct length screw to prevent an exterior surface alien breakout. Orientation of the screws is important, especially at the front. You only have the speaker terminal plate hole to work through from rear using a drill and extension driver (the easy way) to drive screw in. My old man hands and wrist appreciate the drill method.

How about that placement. Jig hole B worked best. I used the edge of a file to cut some glue grooves in.

Maybe brace first... With Larry's Rings installed, to get dowel braces in, I inserted them thorough tweeter opening and navigated them to their proper location. Pretty amazing, the cabinets had no real loose or real tight spots (provided I didn't tip the dowel) meaning Polk did a great job of cutting and assembling the cabinet pieces. I smeared glue about an inch before final placement so ends of dowel could grab some glue.

After installing braces, I applied a bead of glue around each dowel while on its back. Allow to dry then flip cabinet to do front. Otherwise, gravity pulls the glue down the dowel. I screwed up and drilled one hole for the speaker terminal plate 8-32 threaded inserts clean through. I'll plug it. .75" screws will work fine there without bottoming out.

We are being careful with grill studs too! Always use spacer blocks of wood when speaker resting on front to save from shearing them off.

Toolfan66 · July 24

My bracing was a little overkill 🤣

Viking64 · July 24

Toolfan66 wrote: »

My bracing was a little overkill 🤣

llikrevo

SCompRacer · July 24

Had a flashback to Danny riding his bike down the hallway! Redrum! I like that.

Sweet jebus! Did you do use engineering software or just couldn't stop yourself?

How's this seal look? I had some tear so got this 1/2"/12.7mm wide by 1/16 /1.6mm thick weather stripping stuff on Amazon. One side adhesive. 33 feet. Bends nicely around curves once the backing is removed. Nice fit and it's black. Link below.

Splice seam.

Used a # 4 leather punch to knock holes out.

https://www.amazon.com/dp/B07Z4PKBC5?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

I've always wanted some KLF speakers....

pitdogg2 · July 25

Hot soldering iron works pretty darn good too for holes.

SCompRacer · 2:11PM

We go to great lengths to make our Polk speakers sound the best we can afford. We brace the cabinets, reglue old cabinet seam joints, rebuild xovers, upgrade the tweeters and replace driver/radiator/tweeter seals as needed. The one thing we fail to do, and the open baffle and ported speaker guys laugh at us, is equalize the pressure inside the speaker before listening.

Changes in barometric pressure can force a sealed speaker cone off-center. These forces, depending on a positive or negative pressure, can result in a positive (outward) or negative (inward) excursion of the woofers and passive radiators. Pressure can be measured with gauges and excursion by dial indicator. Drivers and passive radiators being off center has a detrimental effect on frequency response. The same music will sound better or worse on a given day depending on barometric pressure.

A simple fix costing ~ $6 US per pair of sealed speakers will solve this problem. Drill a hole in the speaker terminal plate and install a tubeless tire valve stem. Before listening, remove valve cap and depress the schrader valve for a couple seconds to equalize pressure inside the speaker. Barometric pressure gauges typically have a manual set needle to note last known pressure. Notice a barometric pressure change, depress the shrader valve.

(It appears I've slime'd my 7C's).

Always replace valve cap when not equalizing pressure.

No, I really didn't. Just being silly awaiting parts....

Seven Seas Adventure - Polk 7C Upgrades

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