Crossover Freq for M7A Speakers

stevecramer2

Restoration project for the Monitor 7A speakers.

I’ve talk with Helen at Polk Audio and ordered several new items and a couple of other things on the open market. I got in two new 10" sub bass radiators and two 6-1/2" midrange (6510) drivers. For the tweeter I decided to upgrade a bit further to the newer Vifa driver offer in the newer Polk speakers

I determined the Vifa XT25TG-36-04 drivers have a frequency range of 1.5-40kHz but I’ve heard the original crossovers were set at 2. or 2.5 or as high as 3.5kHz but no one seems to be sure.

Does anyone know or maybe where I can find out as a web search didn’t help me. The Vifa are also a bit higher in efficiency at 91dB as to the Polk’s overall 89dB but that may not be an issue? Anyway I’m going to go for it and see how it sounds!

New crossovers for the M7A, M7B and M7C are no longer available from Polk Audio as per Helen. Does anyone think I might need to alter the current crossover in anyway? Or replace it or feel I should just stop this nonsense!

Steve

burdette

"Upgrade" isn't always an upgrade if the match is poor. On the other hand, things might come together just fine.

A crossover.. a properly designed crossover.. is unique to the drivers that it is designed for. The 6510 is not the 6.5" driver that is original to the M7A. And you're also using a different tweeter. The cabinet and PR may or may not work satisfactorily with the 6510. So you've got...
- two drivers
- a crossover that wasn't designed for either driver
- a PR enclosure that wasn't designed for the 6.5incher

You can put all that together and hope for the best, but it is a bit of a shot in the dark.

As for the tweeter... differences in driver efficiencies are common, and handled (evened out) within the network.

The crossover point for a tweeter is commonly set to at least double the tweeter's low end, in order to add a bit of protection from burnout.

Polk MIGHT give you the schematic for the crossover for the M7A, if you ask nice. I doubt you'll get the T/S parameters for the 6510 (they can be measured if you have the means or are willing to pay to have it done). I don't know about the specs for the tweeter - if it is essentially an off-the-shelf Vifa, you should be able to track them down.

All of this sounds fun.. I'd probably enjoy it. But you're dealing with enough mix-and-match here that the end results could be anything from pretty crappy to.. who knows.

stevecramer2

Great to hear from you and thanks for the input.

Both the passive radiator and the mid-woofer (6510) are indeed not included with the original M7A but Helen at Polk Audio said both of these items are indeed the current replacements for the Monitor 7 series speakers.

The mid-woof’s in the ‘box’ are the 6502’s and the passive radiator is also different.

The Vifa ring tweeter is the same one that Polk uses in the current Rti speaker line. In fact it has the very same mounting plate on it. ‘Polk – Dynamic Balance’ is embossed right them and the company I got them from (in Tennessee) said they are genuine Polk speakers. I’m waiting on the FedEx truck right now.

So if the tweeter low end is 1.5kHz then the crossover should be around 3kHz. I might be is good shape then. Thank you for the info. I let you know how it goes. The tweeter plate is a bit different front the original so the mounting hole in the box may need a little ‘adjustment’ for proper fit.

This is fun and it keeps me out of trouble too(-:

Stephen

burdette

Just being factual... the 6510 may be the current replacement, but it isn't the same driver. I built a center channel speaker from the parts from an RTA8T. Original called for 6510s and an SL2000. I started with 6502s instead of the 6510s because those were what I had. The speaker sounded "fine".. good in fact... a little .. heavy, I think. When I swapped out the 6502s for 6510s, I could tell a difference. I don't know how much of the difference was due to the crossover vs. the cabinet.

Perhaps the "different" PR is partly due to the fact that the 6510 is different from the original 6502. You could at least ask Polk Technical the question about changing the crossover... you might get a response.

I'd think your bigger 'concern' or possible incompatibility would be the tweeter. You could consider buying/borrowing an original SL2000 (or the replacement) if you really wanted to hear the difference. I think you could write the expense off on your taxes as 'research and development'.. or better yet.. mental health costs...

Have fun. I love this sort of stuff.

stevecramer2

Burdette, the Vifa tweeters did come in yesterday. After the removing the original SL1000 (?) tweeters I cleaned up the mounting cutouts as someone along the way had use a sticky caulking substance around all the drivers; to further seal them I would suppose.

The Vifa’s dropped right in: of course the screw holes were all different. Repaired the old holes, smoothed the entire mounting surface and tinted it back to original color and then drilled new screw holes.

Everything looks good. Now time to listen!

I used a set of 5 known songs with the electronics’ all set to ‘flat’ and the volume set to the same level throughout the before and after tests. BTW I use my Polk Sub PSW505 in both tests.

The ‘before’ tests the music was every nice and balanced and really nothing too much to complain about.

On the initial test with the new drivers, the sound was ‘heavy’ which is about the best as I can describe it. As the first song ended I was thinking I really had mucked things up.

On the start of the second song my son came in and told me the ‘Vibrations’ were coming through the walls and he was bugged!

He was right, way to ‘bass’ heavy. The 505 had been properly setup and had the controls set too: Volume at 2pm and the freq at 120 on the dial.

This setting were wrong for these new speakers. The volume had to reduced to 11am and freq dropped in half to 60 on the dial.

With these setting, the whole system came to life. Too my ears it sounds great. The sound stage and imaging are the best I’ve heard in a long time. Those Vifa’s sound terrific and seem to really sparkle.

I still don’t know what the crossover points are but they seem to be pretty close to what these current drivers need. But I can’t rest until I know!

To be sure, with or without the 505 sub, the system goes deeper than before. The midrange is right there for me and the extended treble is exciting to listen too.

The balance between the new Vifa and the 6510 drives does not seem to an issue at all. Very clean very strong, I want to keep turn the volume up!

For grins I A/B’d my Polk 5jr+ speakers. Oh boy, I shouldn’t have done that (-:

The 5jr+ are fine speakers in their own right but I can’t play them again. The ‘new’ M7A speakers are so open and vivid, it really isn’t fair to compare now. So I won’t say anything to be fair to all concerned.

Helen at Polk Audio said I can return my crossovers to them and they can rebuild if needed. I wonder if I gave them the new speaker configuration they might be able to adjust the crossover to more ideally match my new drivers? I’ll have to ask tomorrow.

If they can’t or won’t no mind as these speakers are to my ears anyway, ‘Sounding Good’.

Stephen

RuSsMaN

So are your original tweets up for grabs?

burdette

Glad everything worked out for you and you're happy.

We have a pair of 5jr+ as well. I think they're great speakers.

Just remember how much you liked the jrs before.... they're still that good. The new tweeter in the 7s may be a little 'brighter'... not so much that the sound is harsh (obviously, since you say you like it), but it could be enough that the jrs sound a little 'dead' in a head-to-head. I'll bet if you use the jrs in a different room, you'll again find they hold their own. If not.. I'm sure you can get a decent price.

I have a pair of 7Cs with the original SL2000... and I like them better than the jrs. I don't like the SL2500 as much. But, on their own, I think the jrs are good. I picked up a pair for my sister off the Flea Market forum last year.

stevecramer2

The tweeters....I guess, sure what are worth to you would be a good first question? Not sure here, so make an offer I can't refuse. (-:

Stephen

stevecramer2

Just found out (from our forum here) on the M7A's, the high crossover point is 3kHz, so using the Vifa speaker range of 1.5kHz-40kHz then 3k is just right.

I thought we might be very close when I started this project! Yippy doo.

In any case, the new monitor 7's sound great. My mp3 files really show some limitation now. Need to use better sources now!

Now to update my monitor 10's. (Crossover points are the same as the 7's too)

RuSsMaN

I pm'd you on the original tweets.

Cheers,
Russ

stevecramer2

I believe these tweet's are Peerless and I found new replacements on the net for $29.40 plus S/H/I.

Twenty five year models surely wouldn't have much value. I don't think they are worth my time and effort to even mess with.

RuSsMaN

Send them to me, I'd love to have a pair as 'backups' for my 7a's, which I plan to keep original.

As stated in my pm, name a price - we can work from there. If you want me throw something out - $20+ ship.

Cheers,
Russ