Crossover question from old Polk audio speakers...

[kevintomb]

I have a vintage pair of old RTA 11t's, that I stripped the drivers and crossover out of to make new speakers that are going to be far smaller and semi-portable.

Kind of a 5jr+ look but with 2 woofers, and the passive radiators on the side.

My question concerns the crossover. I realize the speakers are approx 6 ohms impedance, but after seriously looking over the crossover and the schematic that I found on this forum, I am confused at how they arrived at the values I see.


The woofer **assuming 6 ohms about* seems to be crossed over at 1khz or so, not the 3000 that they are specified at.

The tweeter has me confused also, it has 2 caps in series both 12 uf which would add up to 6 uf, but stereophile said they have some unusual slope of 9db/octave etc.

Can anyone explain the crossover in some detail as to how they arrived at these figures. I was going to replace the SL2000 with a flatter response tweeter from parts express, but was not looking to put tons of money into this Frankenstein speaker.

Has anyone measured the bare drivers without crossover ( I no longer have the capacity to measure...sadly)

Here is a link to the crossover schematic.

http://www.polkaudio.com/forums/showthread.php?38755-POLK-AUDIO-Speaker-Wiring-Schematics-amp-More-ALL-MODELS-except-SDA

It is under RTA11t REV PDF

[Adam_G]

Re: Crossover question from old Polk audio speakers...

Why in the world would you hack apart an old set of Polks for a project like this? Just sell them and start from scratch.

[Face]

Re: Crossover question from old Polk audio speakers...

Why in the world would you hack apart an old set of Polks for a project like this? Just sell them and start from scratch.

+1.

Those woofers need a largish enclosure with either long ports or passive radiators. Sell them and buy a pair of 5jr+.

[clydethecat]

Re: Crossover question from old Polk audio speakers...

The woofer **assuming 6 ohms about* seems to be crossed over at 1khz or so, not the 3000 that they are specified at.

That's probably baffle step equalization.

[kevintomb]

Re: Crossover question from old Polk audio speakers...

Why in the world would you hack apart an old set of Polks for a project like this? Just sell them and start from scratch.

I am gonna be doing 3 different projects. Long story. I have a much nicer 2 way project that I will be doing for myself.

The hacked up Polks are for a friend. He was gonna buy the RTA11t's as they were, but the size was too much. He is paying for me to make them smaller and more compact, So I am not out anything.

In the end they will be about 20" high, about 8" wide and about 12" deep.

We both realize it is not an ideal project, but more something fun to do, and it will fit in where he needs it.

Total cost will not be much, as he already has all of the wood, and I have the drivers.

I was just trying them out on a baffle and thought the tweeter was not the best as is.

[kevintomb]

Re: Crossover question from old Polk audio speakers...

+1.

Those woofers need a largish enclosure with either long ports or passive radiators. Sell them and buy a pair of 5jr+.

Ooh the RTA11t's enclosures are long gone. All I have are all the drivers, passive radiators, and crossovers.

Its more of a "fun" project a friend and I are doing. Its not to be top notch, but something to keep busy, until I get other stuff in line.

[Adam_G]

Re: Crossover question from old Polk audio speakers...

-A moment of silence for the fallen polks-

In other news, I believe that you will have to remake the crossover, as you're changing the impedance load by changing the number of drivers in the system. I'm thinking that you will be able to get a better response out of a smaller box with a different driver than the one provided by the polks, since you're remaking the crossover anyway this is the way I'd go. You may be able to get something listenable but I don't know if it's the best way to go. You can dump the drivers on Feebay, and use those funds to go ahead.

[kevintomb]

Re: Crossover question from old Polk audio speakers...

-A moment of silence for the fallen polks-

In other news, I believe that you will have to remake the crossover, as you're changing the impedance load by changing the number of drivers in the system. I'm thinking that you will be able to get a better response out of a smaller box with a different driver than the one provided by the polks, since you're remaking the crossover anyway this is the way I'd go. You may be able to get something listenable but I don't know if it's the best way to go. You can dump the drivers on Feebay, and use those funds to go ahead.

This is just a fun project is all. I will still be using both woofers. I know it is not the best thing ever, doing it for a friend, that simply wants something that works and sounds decent for not much money.

Changing the tweeters was my idea, so not even sure he will want to spend to do that.

I had let him hear the RTA a few years ago, and he wanted them, but they were far too big. I told him about the rta8 and the 5jr using the same woofers and tweeter and we came up with this idea to make them about half the size they are already.

We both realize the bass tuning will not go as deep, they are just for a basement system, but they have to be able to sit on an entertainment center he has. ( long story) hence the idea to make a 2 driver version of the 5jr+ sorta...!

[NickS]

Re: Crossover question from old Polk audio speakers...

You might look at the Polk 8T. I think they used the same drivers with ports instead of passive radiators. I think you will have to use the same internal volume as those to get it to work with those drivers/crossover.

[kevintomb]

Re: Crossover question from old Polk audio speakers...

You might look at the Polk 8T. I think they used the same drivers with ports instead of passive radiators. I think you will have to use the same internal volume as those to get it to work with those drivers/crossover.

Ya that is what made us have the idea to begin with. He loved the RTA 11,s but they were a couple inches too wide and far too high, as he only has room for on top of this 2 foot high entertainment stand.

So we thought...hmmm....Make a new box, very narrow, and fairly deep, but only 20 inches high, and lose some bass but still have most of the basic sound, for next to free.

They were sitting in my garage for years, and the enclosures actually got water damaged a few inches up on both enclosures. You know how Particle board takes to water.

We thought about chopping off the lower damaged area,but gave up, after we took them apart and realized the damage went up fairly high and they were swollen.

Oddly enough the drivers are VERY robust, no rust no mold, NOTHING, and they sound like new still! Those are some durable drivers!

[Chris Roemer]

Re: Crossover question from old Polk audio speakers...

So they originally had double woofers? You have 2 choices as far as I see it. Either one requires that you build a box w/exactly one half the original box's volume:

1 - In a half-size (volume) box, put one woofer and one PR. You'll end up with the same extension. You'd have to modify the XO to reflect the impedance change for a single woofer (probably doubling the impedance). You'll also have to (probably) pad the tweeter down by an extra 6dB, due to the lower sensitivity of the single woofer.

2 - In a half-size box, use both woofers but go sealed (and stuffed, with polyfill or fiberglass), that means NO PRs. You'll probably lose an octave on bottom end extension, but you can use the old XOs "as-is".

[kevintomb]

Re: Crossover question from old Polk audio speakers...

So they originally had double woofers? You have 2 choices as far as I see it. Either one requires that you build a box w/exactly one half the original box's volume:

1 - In a half-size (volume) box, put one woofer and one PR. You'll end up with the same extension. You'd have to modify the XO to reflect the impedance change for a single woofer (probably doubling the impedance). You'll also have to (probably) pad the tweeter down by an extra 6dB, due to the lower sensitivity of the single woofer.

2 - In a half-size box, use both woofers but go sealed (and stuffed, with polyfill or fiberglass), that means NO PRs. You'll probably lose an octave on bottom end extension, but you can use the old XOs "as-is".

Great ideas. Yes basically Half the size of the original. I have both woofers on a test baffle now along with the tweeter, and with just one woofer connected, yes the tweeter is overpowering for sure.

I did not give the acoustic suspension plan any thought. INTERESTING! I have many choices honestly and we are kinda just winging it for the fun of just building something mostly.

The woofers are 6.5 inches, but the woofers do not have a lot of Xmax movement.

These are there specs on the woofers...(( MW 6510)) ((Q 1.39 )) (( BL 6.32 N)) ((Compliance 3.41 E - 3N/M)) ((6.57 Ohms)) ((31 Hertz Fs))

Do not totally know what all their terms mean, but notice no Vas measurement. Xmax seems to be about 3mm each way about.