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Stereo Sub-Woofers

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Posted on December 29, 2016 at 09:41:28
Bold Eagle
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Posts: 6838
Location: America's Heartland
Joined: May 27, 2001
I wanted a little more deep bass in my den system, so I hatched a plot to build up a pair of sub-woofers using stuff I had lying around. First, I had a pair of old JBL L-110 cabinets. Next, there was a pair of 250 Watt Parts-Express plate amps from maybe 10 years ago. And third, there were a pair of Eclipse W1038R 10" woofers. The woofers had once been installed in the JBL cabinets, so the threaded inserts were still there for mounting the woofers.

The L-110 cabinets were ported, so I closed the ports with wood plugs. Then opened the mid-range sub-enclosures, and capped the midrange opening. The cabinets were 100% filled with Acousti-stuf, as I wanted a true Acoustic Suspension set up.

The plate amps were mounted to 4" deep open back frames and mounted to the back of the cabinets using small angle brackets, and the output leads from the plate amps were terminated in gold banana plugs and plugged into the 5 way binding posts on the back of the cabinet. The plate amp covers the cabinets input jacks.

OK, that gave me a matched pair of sub-woofers. They were placed in the front room corners with the front of the cabinets facing a wall with a 2" spacing. The air trapped between the front of the cabinet and the wall adds mass to the cone and lowers the resonant frequency of the system by a few more Hz. The subs are driven off the output of my Adcom GFA-545 II with a separate set of cables going to the right high level input on each plate amp. The low pass filter on each sub is set to about 50 Hz.

The main speakers are a pair of Advent cabinets on 15" stands and fitted with a SEAS 27TBFC/G tweeter and a SEAS A26RE woofer.

I'm a big fan of using stereo subs rather than a single sub fed with a summed L+R signal. Years ago, I had the opportunity to compare stereo subs vs summed L+R through the same two subs. The summed signal seemed to have less information - something was missing in the summed signal. I think this is due to cancellation of out-of phase data from the L & R channels.

Stereo subs, as opposed to a single mono sub have an advantage in power handling, lower distortion, and no pulling the image to one side or the other. I also find it a lot easier to set up a pair of subs each located near the main speakers than a single mono sub. I also find stereo subs don't need a steep low pas filter. These amps use a second order filter which is easier to blend with the main speakers, which are run full range.

Bottom line - How does it sound? I'm finding deep bass in recordings where I didn't know there was any. Overall balance is better and recordings with room ambience give a more natural sound. It's easy to overdo the level with sub-woofers, so I started with a low level and gradually increased the level. Depending on the recording, I'm now at the point of having a little too much bass on some albums, and a bit too little on others; but most sound well balanced. Deeper male voices don't sound "chesty", thanks to the low setting of the low pass filter.

The project was months in the planning before I decided to pull the trigger on it. Over the next couple of weeks there will be some fine tuning of the plate amp settings (level, phase, and low pass frequency) and some tidying up of details. But mostly, I'm done and pretty happy with the results.

And my "unused" pile of stuff is now considerably smaller.

Jerry

 

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RE: Stereo Sub-Woofers, posted on December 29, 2016 at 17:53:09
airtime
Audiophile

Posts: 8582
Location: Arizona
Joined: February 4, 2003
Same here! Stereo subs.

Just last week tried using stereo subwoofers. Now I would argue the point that you only need one for stereo use.

You go Jerry!!!!

 

RE: Stereo Sub-Woofers, posted on December 30, 2016 at 11:20:17
Eli Duttman
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Posts: 9409
Location: Monroe Township, NJ
Joined: March 31, 2000
Good job!

What you have done with 2 SWs is clearly fine. However, excellent results can be obtained using only 1 SW. A 24 dB./octave Linkwitz/Riley crossover "cornering" low enough and correct enclosure placement get the job done. As has been hinted, spatial cues have to be kept out of the single SW.

BTW, deep bass on LPs is summed to mono, in order to limit stylus excursion in the vertical plane.

Eli D.

 

RE: Stereo Sub-Woofers, posted on December 30, 2016 at 11:26:37
dbphd
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I readily agree that two subs are usually better than one. I'm skeptical about "stereo" for frequencies below 50 Hz, or even the commonly recommended 80 Hz. Try using a meter to set all your speakers at the same SPL with pink noise. Even a single sub shouldn't pull the sound image to one side or the other.

db

 

RE: Stereo Sub-Woofers, posted on December 30, 2016 at 11:31:31
DavidLD
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Posts: 4881
Joined: May 29, 2002
Jerry were you there the time a guy brought a giant sub to the DYI speaker show in Dayton Ohio?...it was in one corner of a big room.He switched it on and it started to play. The funny thing I think is that there was not a hint of directionality to the sound coming out of the giant sub. I shut my eyes and without a visual cue there was no way i could determine where in the room the bass was coming from.And it was purposely way off center.

If you feel a sub is directional, then either the sub is playing frequencies that are high enough to be directional(not uncommon with consumer grade 3-piece systems) OR your eyes are fooling you and you think you are hearing the sub frequencies coming from one side or another of the room because of the visual cue for the sub location.

David


 

RE: Stereo Sub-Woofers, posted on December 30, 2016 at 12:05:44
Bold Eagle
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Posts: 6838
Location: America's Heartland
Joined: May 27, 2001
David et al.,

I believe there's more to the single sub than just directionality. I also think there's an issue with quality from a couple of factors.
First, there's the issue of exciting room modes. Two subs give a different pattern of room modes, and the excitation ought to be smoother.

Second, in a two woofer set up, switching the bass from mono to stereo sounds different. It could be from room modes, or interaction with the main speakers; or the summing when done electrically is not the same as when done acoustically in the room. For one thing, a single sub will not have the effect of Mutual Coupling. For another, if the original bass source is not centered, it will emerge from the two woofers with some phase shift between them. That phase difference gets wiped out in a summed signal.

My best success in a single sub, was a 12" woofer from Speaker Lab in a 3.25 cu. ft. ported enclosure with a third order low pass filter. But it only worked properly when wall loaded and accurately centered. Turned to the wall, the sound is more diffuse from the woofer, including port noise and woofer harmonics.

Another factor, usually overlooked is the production of harmonics by the woofer. While a 4th order low pass will certainly attenuate the fundamentals above its pass band, the harmonics are generated by the woofer itself and are not attenuated. Similarly, port noise is not attenuated. That argues for significantly higher quality woofers in a mono sub than would be needed in a pair of subs, stereo or not. In my case, I chose an Acoustic Suspension design to eliminate port noise.

Jerry

 

Ever listen to subs by themselves?, posted on December 30, 2016 at 16:53:39
E-Stat
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The two powered Eosone 12" subs used in the HT have a 12 db / octave low pass crossover switchable from 50 to 120 hz. Even set to 50 hz, I can faintly make out vocal fundamentals.

I've yet to hear a single sub not call attention to itself.

Edit: Meant to place above this post, but am traveling and editing with phone is difficult. You get it, but I'm not sure that David does.

 

RE: Stereo Sub-Woofers, posted on December 31, 2016 at 13:56:35
Crazy Dave
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Posts: 12584
Location: East Coast
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If I recall correctly, Linkwitz recommends multiple open-baffle subwoofers placed around the room to best deal with room modes. I don't have room for additional subwoofers, so my solution is to let my satellites (Spendor BC-1's) run full range and roll the subwoofer in around 40Hz. My room is paneled, with a carpeted concrete floor and one wall of cinderblocks. There is a lot of base boost so the subwoofer is set very low. It work pretty well. There is more than one way to skin a cat.

Dave

 

RE: Stereo Sub-Woofers, posted on December 31, 2016 at 18:22:03
airtime
Audiophile

Posts: 8582
Location: Arizona
Joined: February 4, 2003
You're usually the last person I would argue with. But going from one sub to two I would argue that two are better. I think the key thing is the mutual coupling that happens between the sub and monitor speaker. It brings in another dimension to the speakers sound.

charles

 

RE: Stereo Sub-Woofers, posted on December 31, 2016 at 20:20:39
Eli Duttman
Audiophile

Posts: 9409
Location: Monroe Township, NJ
Joined: March 31, 2000
I said excellent results can be had using 1 SW. I was definitely not "knocking" 2 SWs.

When you are as space constrained as I've been, for many, many, years, you learn to make things work well using 1 SW.

A 24 dB./octave Linkwitz-Riley crossover is in phase at the "corner" freq. That is very important, given the abrupt transition from "satellites" to SW. Of course, the crossover is electronic and the rig is multi-amped. I was fortunate, in the past, to have enough "folding green" to work around the space issues. Dash it all, there is no escape from TANSTAAFL.

Eli D.

 

RE: Stereo Sub-Woofers, posted on January 1, 2017 at 06:33:56
sony6060
Audiophile

Posts: 696
Location: SE MI
Joined: August 8, 2014
I used two subs 15 years ago using expensive Peerless 10" subwoofers and two Parts Express 120 watt plate amps. It sounded ok, but I suspect the plate amps were not best quality.

Now a days, the newer Parts Express 10" subwoofer is better sounding than my old subwoofer system. The 10" subwoofer is faster responding than the Parts Express 12" subwoofer and sounds better as I owned both. You would have to spend a lot more money (perhaps 5x) to get a better sounding subwoofer.

 

RE: Stereo Sub-Woofers, posted on January 1, 2017 at 06:58:21
airtime
Audiophile

Posts: 8582
Location: Arizona
Joined: February 4, 2003
I just stacked the monitor over the sub simply like an old fashion three way speaker.

The key is to have a decent plate amp. A good plate amp will help integrate the sub/monitor combo much smoother.

When I had the original Paradigm plate amps I never was able to get a good smooth transition. after I bought ONE Keiger from Madisound that sub sounds smooth. The other Paradigm with the original plate amp doesn't work well at all. So I do plan on buying a better plate amp for that one.

The trick with subwoofers is you have to have them do as little as possible. Strange but true.

 

RE: Stereo Sub-Woofers, posted on January 1, 2017 at 18:51:23
Crazy Dave
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Posts: 12584
Location: East Coast
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10" does appear to be a magic number for woofers. Of course there are bigger woofers that sound great, but they tend to be the more expensive ones.

Dave

 

RE: Stereo Sub-Woofers, posted on January 2, 2017 at 07:02:24
airtime
Audiophile

Posts: 8582
Location: Arizona
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I've also found that a powered 10" sub is ample size. That plate amp is busting a nut to crank out a 30Hz tone. Saving your amp and speakers from that nastiness.

 

RE: Stereo Sub-Woofers, posted on January 2, 2017 at 09:45:29
Crazy Dave
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Posts: 12584
Location: East Coast
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Every 10 Hz lower brings a whole new set of problems and a smaller groups of recordings that have any sound down there.

Dave

 

RE: Stereo Sub-Woofers, posted on January 2, 2017 at 14:38:47
BillH
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Interesting--had you ever tried subs facing a wall before this project?

 

RE: Stereo Sub-Woofers, posted on January 2, 2017 at 20:04:43
Bold Eagle
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Posts: 6838
Location: America's Heartland
Joined: May 27, 2001
Bill,

Yes I had, twice before. It was originally inspired by an article in a small magazine full of DIY projects. This one involved use of the Electro-Voice 30" woofer in a 64 cubic foot cabinet. The showed the decrease of the in-box resonant frequency as they moved the cabinet closer to the wall. So I tried it with my 12" and it worked. The second time was helping a friend build up a good system. He had a pair of AR-3's that we drove with a Phase Linear 700. The AR's were on isolators and turned to the sidewalls, about 3' down the wall from the LS3/5a's that were the main speakers. They were placed about 1.75" inches from the wall (measured from the wall to the front molding). The owner then had finish panels made to cover the back of the AR's. Some of the best bass I've heard. The AR woofer is actually closer to an 11" driver.

In my case I'm using the same 1.75" spacing; but in my cabinet, the woofer is not recessed as on the AR, where the front panel is recessed at least and inch behind the from molding. More like an Advent cabinet. My friend's den had hardwood floors with an area rug, so the AR-3's sat on the hardwood. Without the isolators they made everything rattle and vibrate. The isolators were coil springs stuffed with polyurethane foam. We used 5 per speaker to handle the weight and to get the resonance high enough to get it away from the arm cartridge resonance on his Dual turntable. I coveted that turntable - direct drive and a heavy platter. Maybe a 714?

Some of the best low bass I've heard. The owner was an accomplished organist and collected recordings of famous organs, including several he made himself with a Nagra portable recorder. He wanted his own system to match the kind of bass he got out of a large pipe organ - we spent 2 years building and fine tuning the system.

One of the anecdotes about the system came when he hosted a dinner party at his home. He was in the kitchen mixing drink, while the system in the den was playing a Stravinsky number in which there was a very soft flute passage followed by a big crescendo. As he was fixing the drinks, the flute suddenly got a lot louder. Knowing the crescendo was coming he headed for the den - too late! As he got to the den door, there was this tremendous crash - and then silence. Next morning, a Sunday, he called me. Could I come over and see what was wrong? So I grabbed a bunch of stuff and drove the 15 miles. The electronics were all OK; but the woofer cones were stuck full inward, the voice coils jammed in the air gap. I pulled both woofers, got my fingers behind the cone and yanked. The cones popped back out and looked OK with no rubbing of the VC's, and continuity on the VC's. So I put it back together, and we tried the same Stravinsky piece. It worked fine. Those AR's were built tough.

The rest of the system was a Soundcraftsmen 2217 preamp/EQ with an Ortofon transformer for the MC cartridge. A Nakamichi Dragon cassette deck, and a Revox reel to reel. And a tweaked up Fisher FM tuner. Power for the Rogers was a Van Alstine Stereo 120 which matched the Rogers LS3/5a's quite well. Electronic crossover was a Phase Linear Series 20 (Pioneer). Most pieces were bought used or already on hand. Only the LS3/5a's, Van Alstine mods, the Ortofon transformer, the Dual TT and cartridge, and Crossover were bought new. Oh, and there was a huge Stromberg Carlson rim drive transcription TT in a lift top cabinet he used as a record cleaning machine. Boy, did it have torque!

Jerry

 

Maybe the same thing - I've had good luck with downfiring, posted on January 4, 2017 at 12:19:43
ToddM
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Posts: 1523
Location: Atlanta, USA
Joined: May 15, 2001
I wanted to be able to move them around the room, out from corners and walls, so I put them on some adjustable Ikea Capita legs (4", I think). They sound great without booming - I have the 70-watt PE plate amps and Dayton 12" woofers in a ~2 cu ft ported enclosure, and they really round things out with my single-driver/fullrange speakers. Now I'm looking forward to getting them integrated with new-to-me Spicas. I do have concrete floors, carpet + padding may work differently ...

I also have that extra pair of Advent woofers laying around, now that I think of it ...

 

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