Polk Audio SDA SRS 2.3, 2b, and SRS 2

[F1nut]

Got the H-nuts in (8-32) and got the woofers and tweeters on the right channel done (thanks for the advice regarding the gluing). Went to do the PR and noticed the screws and screw holes were much larger.

What size h-nut did you use on your PRs?

Both the screws and holes should have been the same size as the mid-drivers. Whomever put that foam in there must have changed them.

There are larger sized hurricane nuts, but I've never had a reason to use them. You'll have to do some measuring.

 

[NW1]

Surely someone will correct me but...
I understand the "regular" and SDA drivers have different part numbers and presumably specs as well. I don't have the crossover schematic in front of me but my understanding is the SDA effect is achieved by the horizontal spacing of the 6.5" driver pairs and not by any electronic wizardry, etc. The SDA cable is merely a speaker interconnect cable so with that assumption, can SDA driver operation be checked by turning the system's balance fully toward one channel and checking for sound from the opposite speaker?

 

[Karn]

Surely someone will correct me but...
I understand the "regular" and SDA drivers have different part numbers and presumably specs as well. I don't have the crossover schematic in front of me but my understanding is the SDA effect is achieved by the horizontal spacing of the 6.5" driver pairs and not by any electronic wizardry, etc. The SDA cable is merely a speaker interconnect cable so with that assumption, can SDA driver operation be checked by turning the system's balance fully toward one channel and checking for sound from the opposite speaker?

That's a great theory and I'm going to test that ASAP!

 

[Karn]

Both the screws and holes should have been the same size as the mid-drivers. Whomever put that foam in there must have changed them.

There are larger sized hurricane nuts, but I've never had a reason to use them. You'll have to do some measuring.

Both the SRS 2's and SRS 2.3's have larger screws in the PR's than the woofers. The woofers are all the same, typical ones you see in Polk Audio woofers of the era. The PR's themselves appear to have larger holes in the surrounds as well, and would not well accept a smaller diameter such as 8-32 bolts. The PR's in the 2.3's are SW155's.

The best fit for the larger ones in the PR's look to be 10-32 hurricanes. My concern installing these would be that the correct sized drill bit would be approaching 1/4 to seat the nut, and that could compromise the race for the PR. I think best choice would be to stay with 8-32 and just find larger flanges for the bolts.

Pictures included.

P.S. for posterity, the correct sized bit that worked for me regarding installation of the 8-32 hurricane nuts is a 13/64" bit.

 

[F1nut]

Some models use different spec mid-drivers for the stereo and dimensional, but some use the same mid-driver for both.

SDA is passive, but the crossover plays a role. The spacing varies from model to model, so that's not the key. Regardless of the model the dimensional mid-drivers play at about 50% less volume than the stereo.

Therefore, when the balance is turned fully in one direction or the other you will hear the dimensional mid-drivers play at reduced volume. In addition, the dimensional mid-drivers play at full volume below 100Hz.

 

[F1nut]

Karn, all I can say to that is Polk changed things on the fly, so anything is possible.

 

[Karn]

I think all us of Polk fans by now have been swept by the all seeing eye of Polk's on the fly changes! Much to the consternation of many, regarding the blurring of the lines in the monitor series.

I found that "Truss Head" #8-32 machine screws have an avg headwidth of .375, whereas "Pan Head" machine screws are .315. I think this will give me the extra flange diameter I need and still perform a clean install, as a #8 washer is about .380-.385 in avg diameter.

Dunno how long this amazon link will work for, but for any future readers, here you go: https://www.amazon.com/gp/product/B0C7C8KFXD/ref=ox_sc_act_title_1?smid=A2EYQYE4IE6E7L&th=1

Thanks F1nut!

J.

 

[kevintomb]

That's correct, they should all be MW6509 drivers.

I suspect some ignoramus slapped the 6600X in there thinking it either didn't matter or didn't care.

I hate to say this, but I worked in Polk sales back in the late 80s, and knew our service guy.

He was told officially by Polk, that when doing warranty replacement of midwoofers, that as long as the impedance was the same, that most all of the midwoofers were pretty much interchangable! They told him, use whichever one he had, or use the ones they send no matter if right number or not.

I know, I know, there are differences, but when getting rid of some of our floor stock, one had some vibrations, and our service guy opened it up and it came from factory with literally 2 different mid-woofer numbers that "Should" have been identical.

And I am not talking about the different "Dimensional array" MWs,. but the normal stereo midwoofer sections.

They did do some odd stuff back in those days. That is just the tip of the iceberg!

 

[Karn]

That's why the MW6509s are such a hassle to pair/find, they don't share even a close impedance with almost any other MW6xxx driver; they're basically 10ohms.

 

[F1nut]

Specs for most of the MWxxxx mid-drivers. The 6600x isn't listed, but it is 7.5 ohms, so ohms wise it is interchangeable with the 6501. The 6509 is not interchangeable with any of them. As evidenced by the list there are more parameters than just the ohms rating, so saying they are all interchangeable is flat out wrong.

 

[Karn]

Specs for most of the MWxxxx mid-drivers. The 6600x isn't listed, but it is 7.5 ohms, so ohms wise it is interchangeable with the 6501. The 6509 is not interchangeable with any of them. As evidenced by the list there are more parameters than just the ohms rating, so saying they are all interchangeable is flat out wrong.
View attachment 2987773

Curious, most of my MW6509's tested at 9.5-10.2ohms.. I suspect maybe due to age?

 

[F1nut]

Who knows.

 

[Karn]

Got the 2.3's H-nutted and yes big difference!

Noticed all 4 fisheye woofers respond much less than the center 4 woofers on both channels. Is this normal or should I go back in and check wiring? I can hold my ear to the 4 non-fisheye mids and hear them clearly. I can't easily detect anything out of the fisheyes, but I recall both channels ohm'd out just fine.

I ran a 100hz sine through them and put my finger on the surrounds of each woofer and the 4 centers are responding much much more vs any of the fisheyes.

Thoughts?

 

[F1nut]

Fisheye woofers? I believe you mean the donut drivers. The donuts were added to restrict the movement to reduce the output, so you will not hear as much from them.

 

[Karn]

Fisheye woofers???

Didn't know what else to call 'em and thought I had read that elsewhere. Here's a pic.

 

[F1nut]

That is called a donut driver. The fisheye term is used to describe the nasty SL2000 tweeter.

 

[Karn]

That is called a donut driver. The fisheye term is used to describe the nasty SL2000 tweeter.

Ah yeah that's right. Got them mixed up. Donut is better. Just pulled one out to check wiring. Black wire to red terminal, white to unmarked. spec'd at 3.3ohm.

 

[Karn]

Fisheye woofers? I believe you mean the donut drivers. The donuts were added to restrict the movement to reduce the output, so you will not hear as much from them.

Ah ok thanks, that likely clears that up. Why would one want to reduce output? I don't see these on the Series 1 SRS? (1.2 etc) or the 2.

 

[F1nut]

Ah ok thanks, that likely clears that up. Why would one want to reduce output? I don't see these on the Series 1 SRS? (1.2 etc) or the 2.

To reduce the mid-bass output as it was too much.

 

[5280Dud3]

Many Carver amps are NOT common ground! In other words, the negative speaker terminal of at least one channel in these amps, is "hot".

It is IMPOSSIBLE to use a non-common-ground amp with a Polk SDA speaker- as they RELY on the common grounding as part of the circuit architecture of the SDA system. Using such speakers on a non-common-grounded amp, can result in wonky sound at the best, and damaged amps and/or speakers at the worst!

For ANY amp to be used on a Polk SDA speaker system- it is IMPERATIVE that the amp be verified to be common ground. Unfortunately, this also excludes many other very good amps- for example, many Audio Research amps also do NOT have a common ground- the negative speaker terminal is NOT grounded, as it's part of the balanced cathode feedback mechanism used on the output tubes. They also won't work with SDAs...

BTW: I am also in the camp, that finds the Monitor 7 to be the best of the Monitor series. It's the best combination of bass extension and coherence of the bunch. The smaller ones don't have the bass extension, and the larger Monitor 10 is nowhere near as coherent as the 7, due to the dispersion and off-axis timing issues inherent with the side-by-side midbass drivers in that model.

Now- I do remember someone, who had a water damaged pair of Monitor 10s- and decided to build a pair of custom cabinets with the drivers out of them. He built them as a taller, skinnier tower, with the midbass drivers in a MTM arrangement over the passive radiator (6", tweeter, 6", passive, in that order from top to bottom). Those sounded MARKEDLY better than stock Monitor 10s, in terms of soundstage and imaging.

Regards,
Gordon.

I actually like the Monitor 12 over any Monitor series.