Increase bass in SDA SRS 1.2

[idemo]

Hi,
Years ago I owned a pair of model 1.2s and always loved the midrange clarity and the dimensional array sound, but was always disappointed with the bottom end response. I realize that the specs show the units operating way down in the frequency spectrum, but it's not apparent when actually listening to them.
I even went to the extreme of replacing the passive radiator with active speakers and realized a great improvement in bottom end, but at the expense of natural sound.
For the past 6 or 7 years I've been running with 2 sets of speakers...alternating them occasionally just to have something to do. I have Altec model 19s and Klipsch Cornwalls...both of which sound great and have awesome bass response with no sub needed at all. I run a pair of highly modded McShane Citation 2 power amps and an AR LS25 Mk 2 preamp. The combination has been inspiring. I also have 2 Mac 275s available although the Citations kick the heck out of the Macs.
This week I ran across an extremely well cared for set of SDA SRS 1.2s that are all but flawless and I just had to pick them up. I set them up and again am in love with the soundstage and vocals, but to my dismay have also lost all but a little of the bottom end response I am used to with the Altecs.
I have read several posts of members changing the crossover components and increasing the bass response substantially and would like to do something with these as well.
What, if any, are the ways to increase the low and mid low bass response from these units? I love the looks and the overall sound, but the bass seems to lack terribly compared to the Altecs and yet I want to use these....I just need to help out the bottom end without having to run several subs to make up for the loss.
Is there anything I can do with the crossover components or the passive radiators to make any marked improvements?
I'm sure running a 1000 watt solid state amp might make some difference, but I'm a tube person and I think a good solid 100 watts per channel out of my bridged Citation 2s should be more than enough to really kick these things in. I can barely run them past the 12 O'Clock position on my preamp and still stay in the room. It's not a power problem.
Any advice on crossover component changes or radiator changes to raise the level of the lower frequencies would be greatly appreciated. I know I could again go to active 15s in the system, but it feels like a butcher job and even though it does make a big difference it also has drawbacks in other areas.
Thank you for any suggestion you can offer.
Kind Regards,
Bill

[ben62670]

Bridged amps can not be used without the A1 cable. Also you didn't say how they are physically set up. Adding an active woofer is a big no. If you are missing bass it is do to setup. I am done for the evening, but if you check back later I am sure others will chime in.

[idemo]

Thank you... I hope so. The speakers are now being run by a single Citation2 level 2 plus by McShane. They are not bi amped at this point The speakers are about two feet from the wall...parallel with each other...( not tilted in), but in my room setup they cannot be put against a back wall so they are about 15 feet from the listening area, but are open in the back...(The doors and a fireplace prevent them from being back up against a wall although this made no difference whatsoever with any other quality speaker I've used. That's a factor that I will have to live with since there's no alternative. The living room...( small) has no separation between it and the "family room" except for a waist height open single level waist height bookshelf. It's just one reasonably large room with doors and things on each wall that prevent them from being setup that way. I know this reduces bass response substantially, but never affected the Altecs or the Cornwalls. I also realize that using an active in them is a no-no, but have done unconventional things in the past 50 years of building systems that have proved to be effective. You don't really know until you try. I do special effects in the film industry...pyrotechnics, motion control, etc and have had some very unlikely projects work quite well once actually tried....like moving a 1 million lb pirate ship in Pirates of the Caribbean 8 ft up and down on each and and rocking 30 degrees side to side controlled by a simple laptop....a complex and huge hydraulic motion control setup, but linked with camera movement allowing repeatable motion in sync with camera time after time when needed. I never discount any idea until it has proven to not work. That's how we learn and progress and some very unconventional ideas have proven themselves in the audio industry to be major breakthroughs. I agree with what you've said, but am also willing to experiment to produce the results I'm looking for. Up until reasonably recently the only way to get deep solid bass has been with big high efficiency woofers and large cabinets. That has changed in the past years, so I have no doubts that my goals can be achieved....it's just a matter of how. I sold the Altecs tonight....something I might regret since they did sound beautiful, but getting $2500 for them and paying $1000 for the Polks and still having the Cornwalls as backups I don't feel quite so badly. The Polks are all but flawless looking, are one owner and came with the original cable and owners manual. I think I did OK on the deal.

[Lasareath]

The closer you are to the back wall the more bass you will hear. Mine are 8" from the back wall.

My two amps provide around 600 watts per channel. Click theb bottom link in my signature to see my videos on youtube.

The bass I get out of these things is the hardest hitting bass I have ever felt.

Lasareath

[phocion]

First, welcome to club polk!

So many different topics in this post, I'll address what I have read the most on:

Positioning is important (and cheap!), and the general suggestion is that you place the speakers a foot or less away from the wall. It sounds like you are stuck on this particular problem, so I will leave it for now.

Caps apparently have made a huge difference for SRS and other SDA owners. Rebuilding x-overs is considered the "first" modification step toward a better bottom end, since the caps are old, and much higher quality caps are available.

Air leaks are also an enemy of bass in a sealed cabinet, so you should check the seals and see how the air pressure is holding. If you press in on the passive radiator, the mid cones should move out and slowly (3 sec or so) return to neutral. If they return right away, you are losing air, and air loss is bass loss.

Putting active speakers in a passive design places a lot of stress on the smaller drivers, pushing them beyond their intended excursion due to sound pressure. I know a lot of people will just throw stones at you for modding them, but it sounds like you are a quality over quantity guy and figured it out on your own. Good on you for experimenting.

In line with experimentation, a CP member occasionally makes runs of laser cut rings that sandwich the mids to the speaker, and a quick search of rings will show you many people who describe the bass as tighter after installation.

If you like gobs of bass, and you are handy enough to float a 500 ton ship, you might consider making a Sonotube or two with those 15's and sparing the sealed box an overpressured fate.

[idemo]

Thanks.... 1st for the welcome although I've been a member since 2002...I just don't post. The cabs are absolutely air tight. I can barely press in on the passive and it takes a while for it to resolve to it's original position. I'm not without good subs, but have always felt that a really good speaker can produce great bass without them. I haven't had to run mine for several years using the aforementioned speakers I have.
My active was sealed below the crossover and although I know it affected the ability and size containment of the main speakers, it did produce good results. I had contemplated putting the passives on the back above the active, but didn't want to do anything to the speakers that was irreversible. I did read one one of the past threads about someone doing some really heavy research into crossover mods and am leaning towards that approach if I can get more info on it. I have always used PIO caps for crossovers since they are so much more linear than polys. Motor run caps in older systems are currently being reinstalled in many systems that had changed over to polys ....Solens, etc. thinking that they would be better sounding. Generally they are not, nor are they better sounding in amplifiers as Mundorf and Jensen have finally discovered in the past years. The Russians with their K40s have known it for over 30 years and are one of the better replacement caps in amps that are currently running polys or Orange Drops, Black Cats, Bumble Bees etc. They simply sound more natural and better. In this case I'm wondering if it's not more in the inductors rather than the caps, but need more info to begin anything.
To the prior poster.... I'm sure you can get quite good bass that way...you didn't mention if you used EQ in your system or not. I can take my old 9090BD Sansui and get good bass from these with EQ, but my current system is more of a what you get is what you hear system....no EQ at all and has never needed it with past components.
Anyway.... Thank you both for your help and perhaps others with crossover experimentation experience will see this and can also help. I do appreciate all the good advice though. I toured with Michael Jackson for over a year and it's funny how much bass he was able to get by simply having an array of speakers put around the stage with no walls at all! I know he had EQ available, but I can't completely accept the fact that the only reason these can't get better bottom end is that they are not up against a wall. My Cornwall in the middle of the room can make your bellybutton hit your spine with it's bottom end. There must be another way. I like the speakers too much to scrap the idea and go back to the Cornwalls, even though I love them.... I want to hear these doing what they already do so well, but with the addition of some bottom end. Aside from rebuilding my house and installing a wall down the middle of my living room there has to be a way. Here's hoping some crossover experts can possibly shed some more light on the subject.
Thank you all again!

[phocion]

Well, you have been here longer than I have, but welcome just the same :)

Here is a thread with all the SDA x-over schematics and values:

http://www.polkaudio.com/forums/showthread.php?t=55888

and here is a thread showing a complete redesign of the SRS x-over board, if you are feeling particularly nuts :)

http://www.polkaudio.com/forums/showthread.php?t=109611

You might benefit by taking this conversation over to the Vintage section of the forum, where a lot of guys can offer more insight. The general troubleshooting board < vintage speakers for this stuff.

[HB27]

When I have bass issues it's usually with locked up mid drivers or out of phase wiring. Even wires that have come loose in transport. More often I've had the mid drivers lock up when moving the speakers.
I've never experienced lack of bass in a properly working Polk.
Push in again on the passives and make sure all of your midwoofers are moving. Any not moving I'd press in gently on them to make sure they're not locked up.
The schematics are available on the site for wiring also.
Good Luck finding the issue.
Harry

[phocion]

Good spikes discussion for improving bass on 1.2's over in Vintage, might help since you have placement problems :)

[F1nut]

but I can't completely accept the fact that the only reason these can't get better bottom end is that they are not up against a wall.

It may not be the only reason, but in your case it is the biggest. You can upgrade the crossovers, install the rings and add spikes, but you're still not going to get the bass you want with the room issues you have. Also, you need more power to drive these than your other speakers.

[nooshinjohn]

It may not be the only reason, but in your case it is the biggest. You can upgrade the crossovers, install the rings and add spikes, but you're still not going to get the bass you want with the room issues you have. Also, you need more power to drive these than your other speakers.

Agreed with Jesse on all points. I run my 2.3TL's at 7 inches off the back wall and 6 feet apart. They are spiked and the bass is tight, accurate and deep. I would suggest following the recommendations of Polk and try and set them up 4 to 8 inches off the wall, no toe-in and a minimum of 6 feet apart. You will be suprised by how much different they sound.

[michaeljhsda2]

They could be wired out of phase (from the factory). Make sure the positive (red) upper and lower binding post nuts are on the left, not the right. Almost every pair of 1.2's that I've seen, at least 4 pair, had both red nuts on the right and black nuts on the left and this should never be the case for 1.2's.

[idemo]

I do agree that placement is an issue although it doesn't affect other good speakers nearly as much as these. Power isn't a problem.... Less than 1/3 volume out of the Citation will drive you out of the room. My last pair was driven with a pair of little MAC30s and I was doubtful if they would do it, but they did just fine. My Citation is running Tungsol KT120s at present and probably doing an honest 100 watts per channel and as I'm sure most of you who have run both SS and tube systems know....100 honest watts of tube power per channel can do an awful lot. I've had "500-600" watt SS units that couldn't do nearly what a good tube amp can. I'm neither a lover or hater of any good system....my preference has always been the tube sound, however, since I have never developed "listening fatigue" with a good tube setup. Too many of the SS systems I've run, including some Krell and really nice Nakamichi amps I've owned sounded a bit too "clinical" for me and I tired of listening to them to quickly. It's a personal thing though and of course there have been scores of long discussions back and forth about both. It boils down to what your ears like. I don't think power is an issue here though and if it was I can always throw in another Citation or a pair of Mac 275s to do the job.
I'm fascinated with some of the crossover mods that have been done and although I realize that it's not a complete cure, I appreciate the posting of all the schematics of the crossovers and some of the mods that have been made. It's the kind of tinkering that I enjoy although I dare say I wouldn't go to the extremes of the coil burners and scoping every change I made. A scope can't tell you what your ears can and although it might indicate a fault it won't tell you if you're going to like the sound or not....only you can do that. I did throw my Velodyne back into the system today and did a little more listening. Now the bass level is about where the Altecs were without it, but the improvement was immediate and easy to do.
I do appreciate all the advice and help and hope that I will continue to get more ideas. You guys have all been very kind to help. My main reason for even getting another pair of these was for the pure sound of vocals that they give. Annie Lennox "Bare" has always been one of my favorites and sounds awesome through them....as does Jennifer Warnes "Famous Blue Raincoat" although I do miss some of the bottom end in that album. " The Hunter" is another I like to hear through these.
I've always known that wall placement is important with some speakers...I discovered this in the 50's when I was in my early teens...pointing a speaker into the corner to increase the bass with cheap speakers, but didn't realize that it was seemingly so ultra critical with these particular speakers. I'll keep at it for a while though and all this useful information is of great help. I do appreciate it!

[michaeljhsda2]

I power my 1.2 TL's with a 52 watt EL34 based tube amp and there's enough bass to shake the house down. It's not all about the watts as you know. The room acoustics make up a huge part of the equation IMO.

[ben62670]

They need to be close to the wall. Again 6-8 inches is usually best. Also they should be 3 feet from the side walls with no toe in.

[idemo]

PS... Checked phasing and it's correct. Thanks for the suggestion.

[idemo]

I hate to even open up to this, but basically the general consensus is that Polk dictates to you what size room you need and what type layout is has to be. We don't always have this option. That would seem to make them pretty inflexible to use in all applications....one of my loves for the Altec 19s, La Scallas and Klipschorns....or the Patricians which I had at one point and never should have turned loose of them! Put them almost anywhere and they sound great.
These are wonderful speakers, but would seem to be limited in their "proper" use. I will most definitely find an answer though....especially with all the help you have offered.

[idemo]

And thank you for the "spike" suggestion. I do hear that it can greatly improve on placement problem issues.

[ben62670]

Yes setup is crucial. Just like Carver Amazings, some Vandersteens, planers, and plenty of others. The spikes will not fix placement issues in the least.

[F1nut]

No different than any number of other speakers that are best when placed far into the room, which IMO is a major PITA. One of the reasons I love SDA is because they are best close to the back wall.

Sure 100wpc of tube power will drive them, but in an open area such as yours it isn't enough to wake up the big SDA's.

My last pair was driven with a pair of little MAC30s and I was doubtful if they would do it, but they did just fine.

You mean after you replaced the PR's? That doesn't count.

[nap]

I'd like to throw out an idea here. Has anyone ever used or discussed the Polk Audio bass brace ? If so, please go easy on me I' am only asking. If not I'll explain. Around the time I started at Polk the SDA 2.3 was in development. For reasons that were never made clear to me, the lead engineer (CC) and Mathew Polk tried bolting the rear of the cabinets to the back wall. What they found was that the bass response improved. How much I am not sure, I was never privy to the information. It was just one of those things I kind of just filed away mentally until now. Anyway, long story even longer, they came out with something called the Polk Audio bass brace. Which was an upgrade you could buy in kit form. It consisted of a couple of brackets, some all thread and related hardware. Like I said this may have been tried by some of you guys, so just go easy on me. HTH.

[idemo]

No... A pair of little Mac30s did just fine with the stock setup. They gave more than adequate volume. You say that more power will wake up the bass and 100 watts per channel will more than drive you out of the room even at 1/3 volume.....so I can't understand how you can say that you need more power to get better bass when if you do have it even though it might give better bass the rest of the array is at such an outrageous volume that you cannot be in the same room with it. That makes no logical sense. The idea is to get equal bass volume with the mids and tweeters.Increasing the power input increases the volume on everything....not just the bottom end. Experimentation and modification is a learning process and there are very few items that cannot be improved on....especially ones built 20-40 years ago. I belong to the Citation forum. If people felt that the amplifier could not have been improved on Jim McShane would not have the reputation that he does now. The modded Citation 2 is one of the finest sounding amplifiers ever produced. Even Bob Carver has made a mod or two to them with good success. I have communicated with him on a number of occasions about his mods and he will be the first to tell you that nothing is perfect...even though it might have been of exceptional quality when it first came out. I received a lot of scoffs and laughs and outcries when I installed actives in my first set of SDAs, but the people who came over to listen to them with the thought of purchasing them were amazed at the sound. I had 4 people at one time bidding against each other in my living room to see who would walk away with them.....and they were all prior owners of SDA systems. Don't put anything down until you've either tried it or heard it. At that point you have the right to do so...., but not until then. I mean no malice here.....you guys have been great with advice and suggestions and I do plan on trying each and every one of them to the best of my listening room conditions.....and any more ideas are very welcomed. You're a great bunch of guys and I am honestly appreciative of everything you've suggested.
I can certainly understand where bolting the speaker cab to the wall would make a marked difference. When I worked on the film "Earthquake" years and years ago I walked away with some huge 18" subs that had bolting straps on the back to mount them to the frames of the viewing room as well as several huge Cerwin Vega power amps that would only reproduce sounds from 15hz and below. They were useless for anything else, but if you wanted to shake your house you could surely do it.... I still have them sitting in my garage.

[F1nut]

That's not how it works. Bass notes eat power, so the more power you have, the better the bass at the same volume level.

[idemo]

I agree with that.... that's power in reserve....exactly the reason that McShane increased the power supply ratings from about 80-100mfd to well over 1000mfd and in some cases motor run caps were also installed to provide extra reserve when needed without swamping the power supply. But that only applies when you hit a deep bass note that saps your power supply down to where your amp cannot produce it's rated power. That is not the case in this instance...nor was it with the huge Krells that I had. I don't feel that it's a power issue at all, but will be investigated nevertheless. Thank you.

[idemo]

I would love the opportunity to hear what some of you are saying is excellent bass with these units setup as they should be. Hearing is believing. Is there anyone in the Los Angeles area with a pair producing what they are advertised to do? If so...I'd dearly love to listen to them sometime.....no subs....no EQ....

[inspiredsports]

It may seem counterintuitive that an amp that producing what seem to be adequate db's is underpowered, but as above, the long wavelengths required for low bass require exponentially more power. However, your amps should be adequate for more bass than you are getting.

However, if "doors and a fireplace prevent them from being back up against a wall" you simply will not EVER get decent bass response, even though it "made no difference whatsoever with any other quality speaker (you've) used."

Your join date of 2002 with only 11 post is perplexing and maybe you should be "grand-fathered in" to be able to sell before the obligatory 100 posts now required, but I can already see where this is going.

[nap]

Okay so I had to satisfy my own curiosity. I e-mailed Matthew Polk this morning and inquired about the bass brace. What follows is the body of his e-mail reply. I hope this will stimulate some conversation. Cheers.

The “Bass-Brace” was introduced as a recommended modification for the SRS 1.2 and was available free for the asking. The kit was composed of nothing more than a piece of all-thread, ¼” I think, with a t-nut for the back of the cabinet and an selection of wall anchors. All late production SRS models came with the t-nut already installed in the back of the cabinet plugged with a bolt to seal the hole. (Note: when the all-thread is screwed into the cabinet it will often wind Dacron around it like cotton candy jamming in place and requiring removal of a driver to free-up.)



The “Bass-Brace” did make a noticeable difference in bass performance. Slam and speed were noticeably improved. If you anchored to a masonry wall the difference was really quite dramatic, more than you’d get from improving your speaker cables and even better than spikes.



However, the real reason for the Bass-Brace was not initially to improve performance. Around that time new industry safety guidelines were issued for loudspeakers which included a “tip test”. The tip test specified that with the speaker placed on an inclined plane at 10 deg. (as best I recall) it would not tip over in any orientation. Needless to say, the SRS products did not pass. That was a real problem and with an inventory of product already in the warehouse we needed a solution. The solution was the Bass-Brace which when installed prevents the speaker from tipping over. But, when trying it out we realized it also made a significant performance improvement. So, it became both a performance modification and a safety feature. However, it was very difficult to install and I doubt many SRS owners ever enjoyed the benefits. Over Amy’s objections I did install mine and anchored them to an 18” thick brick and masonry wall. It was very impressive.



Hope that helps



-msp

[idemo]

Thanks for the reply. My lack of posts is simply because after having my first set of SDAs back in 2002 I never tried them again. I began using La Scallas, Altec 19s and such. I had a chance to get a bargain on these, but over all the years forgot what I felt all the shortcomings with them were. I'm listening to them now....with 2 subwoofers running along with them and they're acceptable, but lack the sweetness of a really good horn and the bottom end I'm used to. Rather than screwing with them too much I'll probably sell them and go back to big drivers and horns. As much hack as I might get here for my impressions I'm getting twice as much from three other forums for even considering using them instead of the Altecs! Can't win either way. There are great guys on all forums, but Polk users seem to be more fanatical about the SDAs and most other forums feel just the opposite even though they're not speaker only forums. We run Maggies, Klipschorns, Altecs...all kinds of different systems, but the Polks are generally the last choice of the members there. To each his own and I did feel the need to give them another try. I just don't want to have to run a pair of speakers that dictates so closely the only way they will perform as advertised. I certainly won't be adding walls into a 60 year old house just to see if these will do what I need them to. I feel like it's going out and buying a washing machine and discovering that it will only function if it's facing North with the sun at the 10 o'clock position!
Anyway... They sound nice...nothing spectacular, but acceptable until I put another set of big Altecs or Klipschs in. I figure maybe three or four more days before the Cornwalls come out of the garage!
No offense intended to anyone here....you've all been extremely helpful and generous with your good advice. I guess I'm just not a Polk guy!

[nooshinjohn]

Nap... how can I get in touch with you. I have a couple questions for you that I would like to ask off-forum.

[idemo]

Very interesting note on the wall brace. It might be something to try. Thanks for going to the trouble of checking it out!