SDA-1C's modified....again

geoff727

Hello all,

I haven't posted anything in a while. Anybody remember these?
http://www.polkaudio.com/forums/showthread.php?t=63110

After several months of listening and comparing to other speakers I have, I uncovered several areas of performance that I was not happy with, or was just concerned about. I'll list them numerically.

1) I felt that the enclosures vibrated and re-radiated sound way too much.

2) I was concerned about internal back waves and reflections from the stereo drivers re-radiating through the SDA drivers, and vice versa. Since the enclosures were all just bare particle board inside, with two rolls of poly-fill at the top, I can't see how this isn't a concern.

3) I had them sitting on the floor, and they were transferring a lot of energy to the floor and walls, which was being re-radiated into the room unnecessarily. This was obvious walking into the bathroom or the bedroom; those rooms contained a low, thuddy soundfield that was coming all the way from the living room floor when the speakers were playing.

4) All the 6510's and 6511's in these are replacement drivers. After looking at them, I felt that the basket structure was very "tinny" in construction, and was probably prone to being set up to magnet-basket (i.e. weight-spring) oscillations. This question entered my mind after doing some reading on the subject by Siegfried Linkwitz. I also wondered if the basket structure was also therefore transferring lots of unnecessary vibrational energy to the enclosure. A flick of the finger on the basket structure gave a ringy 'ping' sound that resonated for a couple of seconds.

5) I hate the wood-screws-into-particle board method of attaching drivers to the enclosure. The last time I tightened the wood screws down (after about 4 months of playing), every single one had worked loose, and one of the tweeter's screw holes stripped when I tightened it- it had been very nearly stripped from a previous owner, and my last turn did it.

6) I was concerned about the rear waves from the stereo and dimensional drivers vibrating the magnet structures of the tweeters, and therefore vibrating the tweeters themselves (especially with all those attachment screws always working loose, and so little absorbant inside the enclosures).

In my listening over the past several months, I came to feel that massed voices and strings were especially muddy; also, certain other voices and instruments had a sort of midrange 'bloom' around them, almost as if being sung or played from inside a very small box. And, there were a couple of piano notes on one Norah Jones album that literally hurt my ears when the keys were struck. So, here is my experiment to try to help out each of the areas of concern, listed in the order of the areas above. Being only about a year into this hobby (at least on a serious basis), I am reading and doing at the same time.

1) I added a series of dowels, side-to-side and front to back, randomly spaced. I was most concerned about the small, thin areas of particle board between the 6510's and 6511's. So, I attached a bit thicker dowels there front-to-back. My main concern in doing this was pushing the resonance of the system into an audibly-sensitive band that would be more objectionable to human hearing than what the speakers started with. However, I think that things worked out fine; the enclosures are actually tighter now, and vibrate far less.

2) I added an inexpensive 1" thick foam to all internal surfaces in an attempt to reduce internal reflections and standing waves. I also added more hot glue on the crossovers to better firm up some of the components.

3) A no-brainer here. I added nice, pretty floor spkies. Now the speakers are very stable also. The bedroom and bathroom low-end 'boominess' is pretty-much absent now.

4) I cut some Dynamat and stuck it to the basket structure of the stereo drivers, dimensional drivers, and passive radiators. It took a long time to do this, because the shapes are complex. A flick of the finger on the basket now yields a low 'thud' instead of a ringy 'ping', and the thud dies off very quickly. I also added another layer of foam between the underside rim of the baskets and the enclosure, in addition to the one that was already there.

5) I drilled out all the mounting holes and installed T-nuts on the stereo drivers, dimensional drivers, and passives. The tweeters now use larger thread brass inserts (visible in one picture). All attach with allen-head metal screws and small lock-washers. Hopefully, the screws will stay tighter a little longer.

6) I built internal enclosures to house the tweeter assemblies. They're heavily braced and are very strong. They're not too large, though. I wanted to avoid large changes to the internal volume of the main enclosures, so I only built them as big as necessary. Also, I cut and applied some felt around the tweeters to try to lessen diffraction on that part of the enclosures.

Now, some quick impressions....

1) Massed voices and strings are still muddy. I think this is one of those "they are what they are" facts about the speakers.

2) The speakers actually disappear into the soundfield better! Whether this is a result of cutting some tweeter diffraction, cleaner signals coming from the stereo/dimensional arrays, less enclosure (and room) resonance...I don't have a clue! But, the speakers are physically separating themselves better now from the music being played.

3) Bass output, as you would expect, is a bit lower in sheer volume level. However, what is there, has really cleaned up a lot. Toady I listened to Reference Recordings' CD of John Rutter's Requiem, a recording with some low organ. And, on the once-again-modified-1C's, it's all still there, every note. Not as bombastic in volume, but cleaner in tonality and pitch.

Overall, I think this was a success. I expected some sacrifice in certain areas to improve performance in others. And, I know that these issues can't be cured, but only helped a little bit. So, I didn't have huge expectations. I had hoped that massed voices and instrumentals would come out just a little better. But, other things certainly did clean up. And the slight extension of the 'SDA effect' was very welcome! Generally speaking, I think the speakers are cleaner sounding and more under control now than they were before I started this.

For those with sharp eyes.... from my previous thread on these -1C's, the TV has been relagated to the floor and replaced by a turntable. Much more enjoyable!

ben62670

I agree with everything you said. Others have applied dynamat to the baskets;) I still need to;( I noticed there is no poly fill behind the MW's. You should have some up there. I prefer the sheet stuff so you can roll it up loosely and it stays put. This should only be behind the MW's. Yes I agree the cabs are flimsy. Nice to see you spent some time fixing some short comings. Nice work.
Ben
Edit.
I just noticed your wall is really to short for SDA's.

F1nut

Thanks for posting what you've been doing.

Massed voices and strings are still muddy.

I can't say that about any of my SDA's. I'm thinking it could be room related in your case.

geoff727

ben62670 wrote: »

I just noticed your wall is really to short for SDA's.

True, but it's all I've got for the moment. A bigger place would be great, but not realistic for now.

geoff727

F1nut wrote: »

I'm thinking it could be room related in your case.

Could be. This room is not that large, and I've done so much experimenting with acoustic treatments that I really don't want to spend time doing any more. I made the sidewalls as non-reflective as I could, just to accommodate the SDA's.

Could also be that I've grown used to listening to the EMIM pseudo-ribbons on the Infinity's, too. They can be pretty resolving.

geoff727

ben62670 wrote: »

I noticed there is no poly fill behind the MW's. You should have some up there.

Maybe after listening for a while, I'll open them up again and try that. There is still some fill at the top of the enclosure, around the bracing for the tweeter boxes.

ben62670

Try hanging some heavy blankets or rugs on the side walls. My SDA's are way to big for my room too:(

MillerLiteScott

I like what you have done with your mods. But I have a question.

Would/Does all that foam inside the cabinet adversely affect the tuning of the cabinet?

Scott

Face

I noticed a subtle difference in tuning when adding foam to an enclosure. It's when you start playing with poly fill that the tuning can really change.

geoff727

MillerLiteScott wrote: »

I like what you have done with your mods. But I have a question.

Would/Does all that foam inside the cabinet adversely affect the tuning of the cabinet?

Scott

To answer that question, I referred to Vance Dickason's Loudspeaker Design Cookbook. After reading, I decided that it would probably be a positive change.

So far, I am really enjoying the changes in the speakers. The piano passage I referred to earlier no longer hurts my ears. And, solo piano actually sounds a little more like a piano. I think the speakers are better balanced top-to-bottom. I haven't uncovered any 'negative' changes yet.

awe-d-o-file

Nice work. I too must agree with Ben about the room. If you want stuff far on the left and right use the long wall and listen nearfield. I have always found SDA's sound better this way. Michael Percy audio has deflex pads to fit the magnet structures. See page 20 of his catalog. Your results may vary etc.

geoff727

Some more impressions...

I haven't changed anything on the speakers themselves or the room placement. My room has been treated on both sides with heavy rugs, heavy curtains, framed silk pictures with sound absorbant backing. I don't know what else to do with this place, short of moving (I wish!). But thanks, all, for your recommendations. I'm sure I'll keep looking and brainstorming.

Anyway, I am very glad that I lessened the resonance and random vibrations within these speakers. The decay of musical information is, without a doubt, cleaner. That alone adds to the realism of the presentation. I still feel that the speakers are a bit less box and a bit more musical soundfield now.

On to the next adventure....