Quad SDA CRS+ Project

network23

Hello to all Polkaphiles

I am about to start a project that has been on my back burner for 26 years.

Back when Polk came out with the SDA series, I used to work for an audio store and one day, very late in the day, long after the last customer left, a bunch of us had a pair of Polk SDA SRS setup and were comparing them to the other speakers on the floor. We used the best amp we had (don't recall brand or model) but it was 500wpc and the only thing that came close to the SRS's were a set of Infinity RS monsters. I do not recall the exact model. Most preferred the sound of the SRS for vocals, midrange and imaging, but the Infinity's had a slightly better bass "punch" for rock. Otherwise they were nearly identical. Except the Infinities had a price more than double the SRS's.

After testing every set of speakers we had to the SRS's I took a pair of SDA CRS and A/B'd them to the SRS's. Everyone was shocked at how close they sounded, but of course the volume and low end was not the same. So I added a 2nd pair on top of the first and once again, everyone was wow'd at how little difference there was. We then tried 4 pair of CRS being compared to a single set of SRS. (skipped 3 pair due to the problem with how to wire them, 3 ohms or 12 ohms?) The only difference at this point was a slight advantage to the SRS at the very lowest bass notes. But on volume, imaging, quality of sound, there was really no difference.

At the time, the price of 4 pair of CRS was about that of a pair of SRS so you gained nothing there. However, the space taken up by 4 CRS was almost half of what the SRS use. And that you could build this system one pair at a time instead of spending all your money at once.

So I bought 2 pair of CRS+ with the intention of one day building my QUAD SDA CRS+ system.

Well that day is now. They are a bit hard to find, but I think I can find 2 more pair of CRS in good condition.

My question is this: How much will I lose if I run them all off one amp? I bought a Yamaha P5000S (500w/c at 4 ohms) and if I took 4 pair and series two pair and then paralleled them that would be a 4 ohm load. I know this will work, (we did it back in 86 with 80's technology amplification) but I'm wondering how this will compare to running a dedicated P5000S for each pair of CRS. Of course it'll save a lot of money using just one 500wpc amp, but what will I gain by using 4 amps to run 4 pairs of CRS? I seem to recall something about dampening factor and a single amp trying to control 8 voice coils (ignoring the tweeters) per channel being a challenge.

Just to answer the questions because I'm sure some one will ask (no offense):

Why? Because I want to.
Why do you need...? Because our space is pretty large. 27x37 with 16' ceilings. It's a very large space. To get a full "concert effect" is going to take a lot of speaker/power.
Why don't you just buy ...? Because I like the way the Polk drivers sound and the SDA effect. Also I already own 2 pair and for the price of 2 more pair of used CRS, I could never equal the sound of what I believe I will get when I'm done with the QUAD CRS+ project.
Why don't you go with new high efficiency speakers? Because newer is not always better and high efficiency does not generally translate to high quality.

Anyway, I'm interested in the amplification issue and if newer amps might be able to do this with no problem, or will I need multiple amps. And if I've overlooked something, or you want to make a comment, feel free to let me know.

DarqueKnight

I have two identical pairs of CRS+'s and a pair of SRS's as shown in figure 19 of this thread. I have done comparisons of the CRS+ to the SRS and the SRS 1.2TL, but I have never considered stacking them.

Since you have a large room, one of the larger SRS models such as the original SRS, SRS 2.3TL, SRS 1.2 or SRS 1.2TL would be a better match. However, I know this project has been on your back burner for a long time and you are anxious to try it. Here are some performance issues you may want to consider:

1. Cabinet resonance - CRS+ cabinets are particle board rather than the denser and less resonant MDF. Stacking cabinets could introduce resonance issues. I would not think that having one or two vibrating masses in contact with a speaker cabinet would be a good thing.

2. Coherence - four stacked CRS+'s provides the same number of drivers and tweeters as the SRS, but the SRS drivers and tweeters are time aligned and under the control of a single crossover network. You may want to do some careful studies noting the placement, clarity and weight of images with one pair and then stacked pairs of CRS+'s. I expect that comb filtering effects from four, or even just two, adjacent pairs of CRS+'s would diminish imaging accuracy.

3. Impedance - Using one amp, and connecting two pairs in series and two pairs in parallel will mean that the series and parallel connected pairs are receiving different signal levels. This will affect coherence. I expect that the bass performance of the higher impedance series-connected pair would suffer due to lower current delivery. You could use two identical amps, with each amp running a series connected pair of CRS+'s, but I expect that clarity and detail would be diminished by the unnaturally high impedance.

4. Cabinet volume and bass performance - four CRS+ cabinets equates to 9500 cubic inches (12.5" x 20" x 9.5" x 4) compared to 17,335.5 cubic inches (63.5" x 21" x 13") for the SRS. As you mentioned, the four stacked CRS+'s take up roughly half the space of the SRS's. If things like bass articulation and tactile sensation are important to you, you may want to pay careful attention to differences in bass performance (clarity, detail, tactile sensation) between a single pair and stacked pairs of CRS+'s.

5. Placement issues - four rear firing passive radiators might present some placement issues with respect to the rear wall.

VR3

I honestly can see nothing good coming out of doing what you are describing...

All it could accomplish is a big wall of sound that is so disorganized it would give you a head ache

evhudsons

I was wondering a similar question, what if you had 1c's and set the crs+ above it without being resonance connected. If I ever found a deal on 1c's locally I would have to get them, but I won't ever get rid of my crs+. Plus the imaging is so superb that they will always remain my main fronts.

Whether these things work, I love the well thought out reasons not to do it.

network23

DarqueKnight wrote: »

I have two identical pairs of CRS+'s and a pair of SRS's as shown in figure 19 of this thread. I have done comparisons of the CRS+ to the SRS and the SRS 1.2TL, but I have never considered stacking them.

Since you have a large room, one of the larger SRS models such as the original SRS, SRS 2.3TL, SRS 1.2 or SRS 1.2TL would be a better match. However, I know this project has been on your back burner for a long time and you are anxious to try it. Here are some performance issues you may want to consider:

1. Cabinet resonance - CRS+ cabinets are particle board rather than the denser and less resonant MDF. Stacking cabinets could introduce resonance issues. I would not think that having one or two vibrating masses in contact with a speaker cabinet would be a good thing.

It could be a problem, but it's one I can deal with. Also the forces are going to be "front to back" not in any direction. So there should be no more than what a regular pair of CRS would see. And the bottom CRS will be held solid by the mass of those above it.

2. Coherence - four stacked CRS+'s provides the same number of drivers and tweeters as the SRS, but the SRS drivers and tweeters are time aligned and under the control of a single crossover network. You may want to do some careful studies noting the placement, clarity and weight of images with one pair and then stacked pairs of CRS+'s. I expect that comb filtering effects from four, or even just two, adjacent pairs of CRS+'s would diminish imaging accuracy.

the only time alignement is in the horizontal plane. I'm unaware of any time compensation on the vertical drivers on an SRS. I'm I missing some info?

3. Impedance - Using one amp, and connecting two pairs in series and two pairs in parallel will mean that the series and parallel connected pairs are receiving different signal levels. This will affect coherence. I expect that the bass performance of the higher impedance series-connected pair would suffer due to lower current delivery. You could use two identical amps, with each amp running a series connected pair of CRS+'s, but I expect that clarity and detail would be diminished by the unnaturally high impedance.

Yes, the biggest concern I have is this. I will have to compare buying 3 more amps with being something like a set of Mag 12s or other good speaker.

4. Cabinet volume and bass performance - four CRS+ cabinets equates to 9500 cubic inches (12.5" x 20" x 9.5" x 4) compared to 17,335.5 cubic inches (63.5" x 21" x 13") for the SRS. As you mentioned, the four stacked CRS+'s take up roughly half the space of the SRS's. If things like bass articulation and tactile sensation are important to you, you may want to pay careful attention to differences in bass performance (clarity, detail, tactile sensation) between a single pair and stacked pairs of CRS+'s.

yes, that monster radiator of the SRS depends on the cavity of the cabinet to work. And I expect not the same bass as a pair of SRS. But we have subs now, something we didn't have back in the day.

5. Placement issues - four rear firing passive radiators might present some placement issues with respect to the rear wall.

I've taken that into account. Should be no problem.

Thanks for the input!

heiney9

Buy SRS's and don't **** around stacking like speakers. It won't work as intended and rarely is a good idea for coherence and good sound. That said, it's your money and your fantasy. But if are asking advice, then you will get it.

H9

heiney9

network23 wrote: »

It could be a problem, but it's one I can deal with. Also the forces are going to be "front to back" not in any direction. So there should be no more than what a regular pair of CRS would see. And the bottom CRS will be held solid by the mass of those above it.



the only time alignement is in the horizontal plane. I'm unaware of any time compensation on the vertical drivers on an SRS. I'm I missing some info?


Yes, the biggest concern I have is this. I will have to compare buying 3 more amps with being something like a set of Mag 12s or other good speaker.




yes, that monster radiator of the SRS depends on the cavity of the cabinet to work. And I expect not the same bass as a pair of SRS. But we have subs now, something we didn't have back in the day.



I've taken that into account. Should be no problem.

Thanks for the input!

Sounds like you have convinced yourself you have everything "handled" so why are you asking for advice, if you are just going to say "no problem, I have that handled"? It won't work as intended and is a bad idea all the issues and more that Darqueknight has raised will be there in spades, so I for one want to know why you think you can make them a non-issue? But better yet how about a detailed explanation about how these very real phenomenon in speaker design will magically not be an issue for you?

H9

DarqueKnight

network23 wrote: »

It could be a problem, but it's one I can deal with. Also the forces are going to be "front to back" not in any direction. So there should be no more than what a regular pair of CRS would see. And the bottom CRS will be held solid by the mass of those above it.

What will the top CRS be held by?

network23 wrote: »

the only time alignement is in the horizontal plane. I'm unaware of any time compensation on the vertical drivers on an SRS. I'm I missing some info?

Here is a link to the 1985 Stereo Review article on the SDA SRS: SDA SRS Review. The last two paragraphs on page 86 and the first two paragraphs on page 87 discuss the time alignment characteristics of the drivers and the tweeters:

"In the frequency range from 200 to 1,000 Hz, these drivers act in many respects as a uniformly driven line source with limited vertical dispersion, thus minimizing any interfering reflections from the floor and ceiling."

Of particular interest is the "progressive point source" arrangement of the vertically oriented tweeters which cannot be achieved with four separate crossover networks per channel.

The caption for figure 3 on page 89 further discusses phase compensation. Since you will be attempting to align eight drivers and four tweeters, with four different crossover networks, in four different cabinets, you may encounter some objectionable imaging degradation. However, it is also possible that you will like what you hear.

network23 wrote: »

yes, that monster radiator of the SRS depends on the cavity of the cabinet to work. And I expect not the same bass as a pair of SRS. But we have subs now, something we didn't have back in the day.

Trying to blend a sub with eight speaker cabinets and eight acoustically isolated passive radiators will be a challenging task.

evhudsons

After hearing some 1c's, I see that a subwoofer is either needed in a bass volume deficient system, or for home theater for the lowest of low bass frequencies. The crs+ does give beautiful bass but not as much as a bigger volume speaker even if multilple crs's are used. I am not as educated on SDA but it seems logical that 4 crs's would not equal the srs, but how many crs's would it take to start to rival the volume, and even if so I'm certain the imaging and finer details would be lost. I am curious still however what multiple sda's will do to each other. The crs+ has the ear to ear distance that is lacking in the bigger sda's? For me the greatest thing about sda is the imaging and sound stage. On the 1c's the volume was much greater, the bass powerful and deep, but the crs+ beat everything I've ever heard into the dirt when it comes to imaging and stereoscopic audio music (and sound).

I bet if you put a wall of sound, a wall of thousands of crs+'s with enough power to drive them, you could perform a mini concert. When I was at the U2 concert they had hundreds of smaller speakers angled on the frame of the stage to give a big 360 sound stage. But that is not compatible with sda or home stereo. I'm hard pressed to find that many crs's to put in my home. Plus, the optimal listening spot is the sweet one, right where the Stereo Dimensional Array was designed to be located in the vicinity of the listening zone.

network23

DarqueKnight wrote: »

What will the top CRS be held by?

Friction and the mass of the cabinet. There is no inertia to move the first or last cabinet other than the drivers moving. The weight of the system compared to the weight of the cones moving is infinite as far as it matters. If not, every speaker in the world would be "rocking off the bookshelf."

Here is a link to the 1985 Stereo Review article on the SDA SRS: SDA SRS Review. The last two paragraphs on page 86 and the first two paragraphs on page 87 discuss the time alignment characteristics of the drivers and the tweeters:



Of particular interest is the "progressive point source" arrangement of the vertically oriented tweeters which cannot be achieved with four separate crossover networks per channel.

The caption for figure 3 on page 89 further discusses phase compensation. Since you will be attempting to align eight drivers and four tweeters, with four different crossover networks, in four different cabinets, you may encounter some objectionable imaging degradation. However, it is also possible that you will like what you hear.

This is exactly the type of information I was looking for. I need to get my mind back into the technology. Thank you for the link.

Obviously what I'm trying to do is create a "line source" not a "point source."

Close to the speakers, yes, there would be problems, but once I get 4' or so away, I think I'll be okay. There will be zones of reinforcement and zones of cancellation. However as long as I stay in the range (from the bottom to the top) I think I'll be good. My bottom speaker will be about 40" off the floor, the top will be at about 80". So as long as my ears are in between that range, I should be okay. There may be some strange effects when going from standing to sitting, but once my ears are at a height, I think the brain will automatically adjust.

As far as the progressive rolling off of tweeters, I have anticipated that. I plan to do the polyswitch modification and I can use varying degrees of the resisters I put in place of the switch. I might leave the top one "wide open" and then work my way down with larger and larger resisters. Or I might end up reversing it. I don't know what will sound better, max tweets at the top or max tweets at the bottom. Or I might not even need to do that because of the greater vertical distances of the tweeters (as compared to the SRS).

Trying to blend a sub with eight speaker cabinets and eight acoustically isolated passive radiators will be a challenging task.

Yes, this is true. But I have the phase switch of course and I think I can use sub location to reduce the problem. I have considerable leeway with sub location.

Really I consider this as much an adventure as I do science. It might work out, it might not. But I think it's worth a shot.

Thanks.

network23

heiney9 wrote: »

Buy SRS's and don't **** around stacking like speakers. It won't work as intended and rarely is a good idea for coherence and good sound. That said, it's your money and your fantasy. But if are asking advice, then you will get it.

H9

I have no room for the SRS in my setup. Like I said, this is not entirely a crap shoot. I did this 2 decades ago and it was almost identical to an SRS. Yes, there were minor differnces, but 5 experienced audio people all listened to it and everyone had nothing but good things to say about the setup. Yes, the imaging was not as "spot on" as the SRS, but we are talking 93% compared to99%. The only real complaints were the lack of the bass. But I have a plan to address that issue. When we did our experiment, we had the CRS 3' off the back walls because we didn't want to move all the other speakers in the room. The SRS are not near as critical to location to the back wall as CRS's are. My setup has them at 3" or so from the back wall. With the 2 pair it already has pretty decent bass.

DarqueKnight

network23 wrote: »

Friction and the mass of the cabinet. There is no inertia to move the first or last cabinet other than the drivers moving. The weight of the system compared to the weight of the cones moving is infinite as far as it matters. If not, every speaker in the world would be "rocking off the bookshelf."

If this were true, Polk would not have offered the bass brace for coupling the tallest SRS's (SRS, SRS 1.2, SRS 1.2TL, SRS 2.3, SRS 2.3TL) to the rear wall. If the mass of a 2.3 or 1.2 cabinet is not enough to stabilize against forward and backward cabinet movement due to driver motion, what hope does a stacked group of much smaller CRS cabinet have without any rigid coupling or reinforcement?

Bracing my 1.2TL's against the rear wall resulted in audible and measurable improvements. See posts 32-41 of this thread for details.

network23 wrote: »

Really I consider this as much an adventure as I do science. It might work out, it might not. But I think it's worth a shot.

Of course. All that matters is that you like what you hear. I am not trying to be discouraging. You asked for discussion and suggestions and I am only complying with your request.

network23 wrote: »

I did this 2 decades ago and it was almost identical to an SRS. Yes, there were minor differnces, but 5 experienced audio people all listened to it and everyone had nothing but good things to say about the setup. Yes, the imaging was not as "spot on" as the SRS, but we are talking 93% compared to99%. The only real complaints were the lack of the bass.

You are doing very well if you can remember quantitative details of an audio evaluation done two decades ago. I often forget sonic details from an audio session done minutes ago, which is why I take detailed listening evaluation notes.

network23

While I agree holding the cabinets rigid will improve bass response and accuracy, I believe the effect you experience is a combination of things. I believe the increase in the bass felt would be due to the coupling of the cabinet to the wall. Basically what you did was turn your drywall into a super passive radiator. It would not take much at all to notice an improvement in felt bass when you have an 11,000 square inch radiator added to your system. (just a WAG on your wall size, it could easily be more.) Most speakers with radiators are "air coupled" but your system is "all-thread coupled." But it's the same principle. You can easily test this by going to the adjoining room and feeling the vibrations on that wall with your speakers coupled and with them uncoupled. I will bet it's a pronounced effect.

I think the increase in accuracy is due to the cabinet vibrations being transmitted to the wall, thereby acting as a damper to the cabinet to keep the woofer basket from resonating, thereby reducing distortion.

I am not saying the effect isn't real or isn't worth the effort. However in my case the bass will be produced by a separate sub. (maybe 2). In fact I have the CRS crossed over right now at 60hz and let the sub handle from there down.

Will I loose some bass response? Maybe. If I feel it's worth it, I can do just the same thing you did with your speakers.

Regarding my memory from 20 years ago. I can't recall the details of the sonics. But I can easily remember the reactions and general comments of the people in the room, and the general consensus. I remember at least some of the music: Pink Floyd DSM. :cool:

However, I'm still working this system out and I'll consider your comments.

Thank you.