Monitor 5/7 xover, driver & cabinet synergy

buttercup

I'm trying to solidify a beater set of 5b's for a console project.
I found the 5b's some years back, they both had "locked" MW drivers... I built a jig and was successful in getting the piston recentered. I've been using them on top of a boat house dock the last 5 or 6 years. Now I'm bringing them in from the cold, so to speak, to use in a console retrofit.
I also have a recently acquired set of 7b's. I did a bit of listening and the 7b's sound wonderful, the 5's sounded like ****. First thing I found was the polarity from the xover to the drivers was incorrect, changing that helped a bunch. Next I fiddled with the drivers between the 5 & 7's and have found that I much prefer the peerless tweeter and MW drivers without the external gasket material. I believe the 5b's originally had the SL-1000 tweeters.
As it stands, I have the "nicer" non- gasketed MW's & Peerless drivers in the 5'bs... they sound nice, not great, but a long way from the first listen. I have ordered new caps & resistors to freshen the xover.
In looking at the xovers of the 5's & 7's, I see they have the same 12uf & 34uf capacitors ... the 7b's have two resistors; a 2.7 & a 4.7 ohm, the 5's only have the 2.7. I haven't traced the circuit to see what the 4.7 is acting on. Anyone know?
I also haven't measured the inductors, so I'm not sure if they are the same or not.

I'm inclined to use the 7's x-overs in the 5's because I now have those drivers in the 5's cabinets.
Any insight into xovers, drivers & cabinet matching would be greatly appreciated!

buttercup

I also found both the 7's & 5's really do well with a Lepai LP7498E class D amplifier... they prefer it to my Sansui AU-999. Very odd!

heiney9

5's and 7's came with peerless tweeters, sl1000 tweeters, sl2000 tweeter and sl2500 tweeters over their life cycle. The x-overs for each (especially the peerless models) are different, they have an extra resistor.

If you start mixing and matching x-over's that don't mate with the corresponding tweeter's then you won't have speakers that sound like they should.

The 5's and 7's when new sounded very similar with the 7's being weightier in bass since the cabinet is larger and the passive radiator is larger.

X-over upgrades really improve these speakers as the factory parts are long past due and the newer parts are better than what available 20-25 years ago. Upgrading the SL series of tweeters is a must as the new silk dome is a much, much better performer.

There is all kinds of info here, or there was before we switched software. I have a pair of fully modded 5B's that sound exceptional. If you need advise on parts choice, etc let me know.

H9

heiney9

The peerless if they are working should be left in as they sound nice, even after all these years. The SL1000 in your 5's should be replaced with the Polk replacement RD0194-1. It's a silk dome tweeter that Polk developed specifically as a replacement for the sL1000 and SL2000 tweeters.

heiney9

I found my original x-over/refresh thread for my 5B's.

http://forum.polkaudio.com/discussion/51420/monitor-5bs-x-over-upgrade-w-pics/p1

buttercup

H9, if I hear you right, if I'm using the Peerless tweeters, I should use the xover from the 7's ... with the 4.7 resistor?
I'm cannibalizing the 7's drivers for the 5's... I'll bring the 7's up to speed somewhere down the road.

buttercup

Do you know if the inductor values are the same?

buttercup

Thanks H9, your rebuild thread has most of the information I'm seeking! I'll measure the inductors before I replace the caps and resistors.

I see you've been futzing with these models for quite a few years... thanks for sharing your knowledge!

littlewoodboats

You can find crossover diagrams in the vintage speaker section here. I have no idea what the differences between a monitor 5 and 7 crossover might be but doubt they would interchange.

buttercup

I've browsed the schematics there, but didn't find one showing the 7b's with two resistors... so I'm not sure I can go by any of those for the inductor values. I'm betting they're the same for both models.
With what little I know right now, it seems they added a resistor to pad the Peerless output... it may be the only difference. When I get the time, I'll trace and measure both xovers.

xschop

If the resistors are parallel you would calculate via the RT formula. I had to do this on my first set of 5jr that I modded. The crossovers were older than Hillary.

westmassguy

The Crossovers with the two resistors and values you mentioned, are for use with the Peerless Tweeters. One resistor is in series with the tweeter, while the other is in series with the shunt inductor.

xschop

7B enigma

heiney9

There is no need to go to the expense of replacing inductors. They will be fine.

H9

tonyb

xschop wrote: »

If the resistors are parallel you would calculate via the RT formula. I had to do this on my first set of 5jr that I modded. The crossovers were older than Hillary.

Um....

xschop

Yeah, all the Polk engineers looked just like Starsky and Hutch.

pkquat

IMO, I would find a set of old 5A crossovers and peerless tweeters from ebay, and then you will have a proper set of 5's. Off the top of my head the cap values sound right for the 5's, however I think there were two versions of the crossovers for the 5's because a 12uF cap comes to mind. I'll have to check my 5's later today. If the values you listed are from the 5's crossover that had the SL1000's then I don't think that will work with the peerless.

Both MW's should be MW6500's AFAIK to match with the peerless. As I recall there is a minor difference between the MW6500's with the gasket and without, but they should sound very close. The ones with the gasket were used on earlier models of polks '78-'81 I think. The non-gasketed ones should have come with the SL1000 since the SL1000 was around '84.

Check for cracks around the Passive Radiator surrounds on the 5's. For some reason the rubber did not age well on that era 8" PR's.

IMO I would also start with the 7's before the 5's. While the 5's sound great, they leave me wanting more bass.

buttercup

cschop, thanks for the schematic. It confirms westmassguy's knowledge on the 2 resistors orientation.

Pk, I do think the gasket and non gasket sound pretty much the same, even though the deflection point on the rubber surrounds is visably different. Also the surrounds on the all the drivers seem to be in good shape, no creases, stress lines or fissures.

H9, it appears both xovers use the same 2.7 resistor in series with the inductor... so I'm guessing they use the same inductor in both, so no need change anything there.

Everyone, Thanks for all the great input on this!

When I do the recap, I'll be adding the 4.5 resistor to the 5b xover for use with the peerless tweeters.
I'll keep my eye out for another set of Peerless tweeters to bring the 7's back up to speed. I also plan to replace all the gasket material around the drivers and the xover. Have I missed anything?

Another question... is there a way to remove the grill pegs from the baffle?

xschop

Two methods I've discovered, destructive vs non-destructive...

Non-destructive is time consuming, involves heat gun, pair of pliers and thin metal sheet or wood as the plier fulcrum. The oxidized particle board gives no guarantees of success on each extraction...hence the destructive method/s hehe.

mhardy6647

"creative destruction"
It's all the rage.

buttercup

Haha, sharp chisel and a hammer or a handsaw... decisions decisions!