SDA design question

xschop

I 2nd that, the factory CRS does not have an inner brace but more real estate between drivers. Possibly the CRS wide spacing was to present a wider sound field in smaller rooms perhaps?

For me, the question that remains is if I move the MWs closer, do I need to move the tweeter closer to both MWs in that same proportion?

Schurkey

How far away is the tweeter from the midwoofers in the SDA 1 and 2 line?

I can't think of any reason that closer wouldn't be better. Consider the 3.1TL, where the tweeter baffle actually covers part of the midwoofer above it.


OTOH, I don't know that "in the real world" it's ultra-critical. I wouldn't move the tweeter FARTHER away from the midwoofers than Polk did in the SDA 1 and 2 line, though.

DarqueKnight

Braddles63 wrote: »

So why does the CRS have the space between the MW's and the tweeter lower and sort of in-between and the SDA2 have the MW's close together with the Tweeter above? What the pros and cons of each layout?

Schurkey wrote: »

I have no doubt that Polk knew the wide-set midwoofers would increase the SDA effect. I have to believe that Polk wanted that enhancement on the CRS, since they could have done narrow-set midwoofers if they'd wanted to--all they needed was to position the tweeter horizontally like they did on the early CRS. This is the "acoustic" reason for wide-set midwoofers on the CRS.

I'm guessing that, since Polk used the same crossover and same SDA drivers for the CRS+ and SDA 2B, but used different stereo drivers, some spacing adjustment for proper time alignment needed to be made.

I'm also guessing that the wider driver spacing on the CRSs was designed to provide a wider sound stage in the smaller rooms, and book shelves, they are most likely to be used in.

TennMan

DarqueKnight wrote: »

I'm guessing that, since Polk used the same crossover and same SDA drivers for the CRS+ and SDA 2B, but used different stereo drivers, some spacing adjustment for proper time alignment needed to be made.

You know a lot more than I about this stuff that I do but it seems that theory might be not be plausible. The schematics you posted here in the forum for the '87 CRS+ and the '87 2B, (both pin/blade), use the same crossovers, same 6511 SDA drivers and same 6503 Stereo drivers. The schematics actually have the same drawing number and date.

Other years for the CRS+ and 2B models did use different stereo drivers. Is is possible the schematics for '87 are listed incorrectly? Or perhaps I'm looking at it wrong?

Dennis Gardner

I would guess that the CRS got the wider spacing simply as being part of the "Reference" series. All the others in that line have the same spacing until the latest 3.1 surfaced.

FTGV

xschop wrote: »

For the stereo signal, isn't it ideal to have the tweeter as close to MW as possible for the crossover frequencies to mesh?

Generally speaking yes.The higher the crossover frequency and the shallower the roll off slope the more important close spacing becomes so as to reduce the effects of lobing.
The mid bass spacing may in part be a cosmetic consideration since it still provided interaural crosstalk cancelation.Another consideration is that the box needed to have sufficient internal volume to get good bass response and proper tuning with those specific drivers and passive radiator combination. Making the enclosure wider was maybe the prefered design choice to hit the required volume vs making it deeper or taller?

DarqueKnight

TennMan wrote: »

DarqueKnight wrote: »

I'm guessing that, since Polk used the same crossover and same SDA drivers for the CRS+ and SDA 2B, but used different stereo drivers, some spacing adjustment for proper time alignment needed to be made.

You know a lot more than I about this stuff that I do but it seems that theory might be not be plausible. The schematics you posted here in the forum for the '87 CRS+ and the '87 2B, (both pin/blade), use the same crossovers, same 6511 SDA drivers and same 6503 Stereo drivers. The schematics actually have the same drawing number and date.

Other years for the CRS+ and 2B models did use different stereo drivers. Is is possible the schematics for '87 are listed incorrectly? Or perhaps I'm looking at it wrong?

I was speaking of the 1989 CRS+ and 2B. I wasn't even thinking of the earlier CRS+, which I should have also addressed.

I don't think there are mistakes in the 1987 schematics. I took electrical measurements of one of my spare MW6503s and one of my spare MW6510s. The results are tabulated below.



The MW6510's lower figures for Qts, Qes, and Qms indicate higher mechanical and electrical damping. Q is the inverse of damping factor and driver damping has an effect on driver time alignment. It appears that Polk came to believe that the MW6510 was a better match for the BE1807-B crossover in the CRS+'s much smaller enclosure.

@KennethSwauger please ask Stu (Polk's VP of engineering) to comment on this topic. Thanks.

pkquat

My 2 cents for the CRS is the wider spacing fit for the desired cabinet dimensions. I don't know for sure, but I'd speculate the cabinets are symetrical which becomes a cost savings. Aesthetics may play a part too.

All the different tweeter locations, roll offs, output, and arrangements are what I find very confusing. I'd love to hear all the versions in a controlled environment.

There can be lobing issues depending on driver locations, and people also talk about time alignment when tweeters and drivers are offset for non-SDA speakers. Some people claim to hear the differences and say when things are out of alignment accuracy is lost. Then there are speakers that use drivers in multiple locations, and people rave about there sound.

I'd love to know about the science behind it, but I have a feeling for SDA, as WMG said, there is likely a zone the works. There likely was some basic math and rules for rough locations, but then once a general spacing was picked, it came down to tooling and manufacturing, and then making sure it sounded "good".

FTGV

pkquat wrote: »

My 2 cents for the CRS is the wider spacing fit for the desired cabinet dimensions. I don't know for sure, but I'd speculate the cabinets are symetrical which becomes a cost savings. Aesthetics may play a part too.

Which is what I was surmising that to achieve their desired internal volume requirement they increased the width instead of height or depth because it was deemed more aesthetically pleasing. Also with the wider baffle wider mid bass driver spacing is more cosmetically pleasing while still acheiving the desired inter aural crosstalk cancelation goal..

FTGV

From the chart above the lower Q values for the 6510 would indicate a stronger magnet thus higher sensitivity. Generally higher Q drivers require larger enclosures assuming the other T/S parameters are similar.

xschop

Great responses and conversation here.
From the schematics, it looks like Mr Polk changed to a lower ohm MW to accomodate the large sub drive inductor?
A question for maybe WMG is since he installs the lower ohm steel laminate inductors, would it be feasable to revert back to a higher ohm MW?

westmassguy

xschop wrote: »

Great responses and conversation here.
From the schematics, it looks like Mr Polk changed to a lower ohm MW to accomodate the large sub drive inductor?
A question for maybe WMG is since he installs the lower ohm steel laminate inductors, would it be feasable to revert back to a higher ohm MW?

That Inductor only affects the dimensional woofer(s) on the 3rd, 4th and 5th generation, from around 150 Hz downward. It will increase the output, regardless of which driver was used, 6503, 6509, 6510 or 6511.

xschop

Forgive me, you are referring to "It" as the laminated steel version correct?
If so, where do I procure a set?

I didn't go rogue and omit the PR at your behest...ahem. But I am changing the RDO tweeter plate design however.

xschop

Never mind, I found it. You are unwinding an Erse via LCR. Thanks again WMG
I'll hold off as my cabs have a touch more volume and go from there.
Looking at the SW102, I wondered if anyone ever tried inverting it to achieve more volume.

xschop

What is the crossover frequencies of the stereo MW and tweeter of the 1989 CRS? I assume they were SL2000s from factory?

nspindel

Cool thread! Soundstage of the 1989 CRS+ has always been one of the things I admire most about them.

xschop

Anyone know the crossover Hz?...
Bueller....Bueller....?

westmassguy

xschop wrote: »

Anyone know the crossover Hz?...
Bueller....Bueller....?

Around 2KHz

xschop

WMG for the assist....once again.

And how do you measure ohm load of each speaker once everything hooked up? At terminals and no interconnect cable between?

westmassguy

There's a whole section in the SDA Handbook for checking DCR.

ptrooper

I notice the separation distance of the CRS drivers are very similar with the SDA SRS 2"s isn't the srs 2's cross over identical to the SDA 1 B's ?.

westmassguy

ptrooper wrote: »

I notice the separation distance of the CRS drivers are very similar with the SDA SRS 2"s isn't the srs 2's cross over identical to the SDA 1 B's ?.

Essentially yes Sean. There's one resistor that's different, and I believe the woofers might be. The 87' SRS 2 and 1C are also nearly identical, except for the sub-bass drive Inductor.

xschop

What exactly is the sub-bass inductor doing? I inadvertently uplugged the left channel inductor lead and it definitely had lower bass volume on that side.
From schematics it looks like it is sending signal to ground.

westmassguy

It's explained in detail, in the SDA Handbook. It allows the dimensional driver(s) to operate in-phase with the stereo drivers below about 150 Hz. Without it, the dimensional woofers would either be out of phase or just sit there flapping like an additional PR.

xschop

Where's the link to the handbook here?

I'm experimenting with the Power-Port adapter plate and the coil has to be connected for the bass to hit deep as well... The adapters allow me to install different length ports quickly.
Copious amounts of bass with them right against back wall hehe.

Schurkey

xschop wrote: »

What exactly is the sub-bass inductor doing? I inadvertently uplugged the left channel inductor lead and it definitely had lower bass volume on that side.
From schematics it looks like it is sending signal to ground.

It is sending part of the signal to ground.

Think of the inductor as a "filter". Music signal below a certain frequency is sent to ground, music signal above that frequency is sent to the SDA drivers in the other speaker cabinet.

By allowing the low frequencies to go to ground, the current moves the drivers, and you have additional low bass. The higher frequencies allow the SDA system to work it's magic in the other cabinet.

I'm sure it's more complex than that, but you get the idea.

xschop wrote: »

Where's the link to the handbook here?

http://vr3mods.com/LCSDAUpgrade.php

xschop wrote: »

I'm experimenting with the Power-Port adapter plate and the coil has to be connected for the bass to hit deep as well... The adapters allow me to install different length ports quickly.
Copious amounts of bass with them right against back wall hehe.

Putting ports into a bassive-radiator speaker cabinet???

Not my first choice. The BR serves the same function as a port. I have NO idea how you'd tune the port and the BR to work together and not step all over each other.

xschop

There's either one or the other, not both, with a simple plate that bolts in place of the PR.

Schurkey

Does a port have any advantage over a bassive radiator? I thought the bassive was the preferred method as there's no port turbulence. The bassive radiator was the "premium" version of designing a ported/vented/bass-reflex cabinet.

pitdogg2

Port is cheaper

kevinko

Schurkey wrote: »

Does a port have any advantage over a bassive radiator?

xschop wrote: »

Copious amounts of bass with them right against back wall hehe.

This too ^^^?