[ooheadsoo]

I don't have the money to invest in thousands of dollars of room treatment.  I went primitive brute force absorption by employing roughly 4 batts of r-13 fiberglass and 4 standard sized 3lb pcf rigid fiberglass panels in the corners of my highly absorptive room.  And some foam, to boot (really a rolled up foam mattress that I stuck in the dark corner behind the door out of the way.)  And back in my curiousity phase, I picked up 4 eight nerve corners, if that means anything to anyone...  The room can't handle much more treatment.  I have toyed with the idea of getting some Gik traps, but it's too large a portion of my income, and even Brian (of Gik) says that my current stacks of fiberglass are marginally more effective than maybe one or two of his tri traps (of course, his trap is much smaller and actually looks nice.)

Frankly, I'm tired of absorption because of how much space it is taking and am looking to brute force the problem with the multiple sub concept, except that my speaker choice is now getting in the way.  I will see, when the speakers arrive.  Meanwhile, I just acquired a second subwoofer.  I hope I didn't just throw that money away.  The price wasn't even that good.  I guess I'll think of it as spending my economic stimulus check.

[Duke]

To Michael Anderson, I'm not sure what Earl is doing.  I would expect that he isn't using a sub up to 150 Hz in a location that will be audibly distracting.  Whatever he's doing, it probably arises from his "way outside the box" thinking, and it probably works very well.

To ooheadsoo, let me see if I understand you correctly.  You have two problems:  Bass roughness above 30 Hz in the region that your main speakers cover, and lack of bass extension south of 30 Hz.  Is that correct?

If so, here are my suggestions:  If practical, you might want to introduce some assymetry into your main speaker setup.  Like, if you can rotate the whole speaker/listening position triangle by maybe 10 or 15 degrees either clockwise or counter-clockwise, that might help.

I gather that you either now have, or soon will have, two subwoofers.  If they have fourth-order filters, that will give you a bit more flexibility - but this might work either way.  Okay I've never tried this, so it's just a thought exercise at this point (though it becomes a physical one if you decide to try it):

Run both subs up fairly high, maybe 80 Hz ballpark, but not necessarily both to the same frequency.  Place them both in reverse polarity with respect to the main speakers, and start them out fairly close to the main speakers.  Don't turn them up too loud.  I'm hoping that they will tend to "zig" where the main speakers "zag", and you can control how much of an effect they have with their volume controls.  You won't get total cancellation; you'll get some cancellation and some reinforcement.  In the region below 30 Hz hopefully you won't get any significant cancellation, so hopefully they'll reinforce this region adequately.  It probably won't work perfectly your first try, and may never work perfectly - this is me just winging it here - but if you're going to be armed with two subs anyway it might be worth a try.

Best of luck to you,

Duke

[jtwrace]

To Michael Anderson, I'm not sure what Earl is doing.  I would expect that he isn't using a sub up to 150 Hz in a location that will be audibly distracting.  Whatever he's doing, it probably arises from his "way outside the box" thinking, and it probably works very well.

To ooheadsoo, let me see if I understand you correctly.  You have two problems:  Bass roughness above 30 Hz in the region that your main speakers cover, and lack of bass extension south of 30 Hz.  Is that correct?

If so, here are my suggestions:  If practical, you might want to introduce some assymetry into your main speaker setup.  Like, if you can rotate the whole speaker/listening position triangle by maybe 10 or 15 degrees either clockwise or counter-clockwise, that might help.

I gather that you either now have, or soon will have, two subwoofers.  If they have fourth-order filters, that will give you a bit more flexibility - but this might work either way.  Okay I've never tried this, so it's just a thought exercise at this point (though it becomes a physical one if you decide to try it):

Run both subs up fairly high, maybe 80 Hz ballpark, but not necessarily both to the same frequency.  Place them both in reverse polarity with respect to the main speakers, and start them out fairly close to the main speakers.  Don't turn them up too loud.  I'm hoping that they will tend to "zig" where the main speakers "zag", and you can control how much of an effect they have with their volume controls.  You won't get total cancellation; you'll get some cancellation and some reinforcement.  In the region below 30 Hz hopefully you won't get any significant cancellation, so hopefully they'll reinforce this region adequately.  It probably won't work perfectly your first try, and may never work perfectly - this is me just winging it here - but if you're going to be armed with two subs anyway it might be worth a try.

Best of luck to you,

Duke

Great advice from the "DreamMaker"

[ooheadsoo]

To Michael Anderson, I'm not sure what Earl is doing.  I would expect that he isn't using a sub up to 150 Hz in a location that will be audibly distracting.  Whatever he's doing, it probably arises from his "way outside the box" thinking, and it probably works very well.

To ooheadsoo, let me see if I understand you correctly.  You have two problems:  Bass roughness above 30 Hz in the region that your main speakers cover, and lack of bass extension south of 30 Hz.  Is that correct?

If so, here are my suggestions:  If practical, you might want to introduce some assymetry into your main speaker setup.  Like, if you can rotate the whole speaker/listening position triangle by maybe 10 or 15 degrees either clockwise or counter-clockwise, that might help.

I gather that you either now have, or soon will have, two subwoofers.  If they have fourth-order filters, that will give you a bit more flexibility - but this might work either way.  Okay I've never tried this, so it's just a thought exercise at this point (though it becomes a physical one if you decide to try it):

Run both subs up fairly high, maybe 80 Hz ballpark, but not necessarily both to the same frequency.  Place them both in reverse polarity with respect to the main speakers, and start them out fairly close to the main speakers.  Don't turn them up too loud.  I'm hoping that they will tend to "zig" where the main speakers "zag", and you can control how much of an effect they have with their volume controls.  You won't get total cancellation; you'll get some cancellation and some reinforcement.  In the region below 30 Hz hopefully you won't get any significant cancellation, so hopefully they'll reinforce this region adequately.  It probably won't work perfectly your first try, and may never work perfectly - this is me just winging it here - but if you're going to be armed with two subs anyway it might be worth a try.

Best of luck to you,

Duke

I appreciate the reply.  To be more specific, I have SP Tech Timepieces incoming, a speaker I suspect you are aware of, if you haven't actually heard it.  I haven't heard it, myself.  I have extreme cancellation around 80-110hz and a general dip in the 140-200hz regions.  There is also little to no energy below 40hz.  The room is roughly 14.5x16'.  The wall that I face when listening to the speakers actually has a slightly asymmetrical opening to a sink, bathroom, and closet, but other than that, the room is essentially rectangular.  I have had no luck moving my current sub, which is something like 80+lbs of mdf and wedged against the wall behind a bed, a 300lb steel desk, and my old defunct subwoofer cabinet turned amp stand (probably another 120lb.+ with the amp on top.)  So it's not going anywhere.  The driver is roughly at the 1/3 point from the back of the room.  I will try to flip the sub around so that the driver is closer to the 1/2 way point - then place the new sub across the way along side the other other wall.  This should roughly simulate the Harmon white paper 2 sub optimized setup, except that Welti only tests front and back walls and not left and right walls.  I figure it should be the same (am I wrong?  it's just math...  )  If that doesn't work, I'll try to put the new sub as close to a corner as possible.  Unfortunately, I can't get all that close, since all corners of my room are occupied.  If I'm forced into that situation, I'll probably have to put it directly under a batt or two of r-13 fiberglass.

Wish I could try your reverse polarity suggestion.  It sounds like it's worth a shot.  The room is small enough, and the subs are big enough that it either would work or it wouldn't - there's no real room to play with sub positioning.  Perhaps one day when I get into the mood to move a few hundred pounds of furniture, I'll give it a shot.

Just for anyone wondering:
Defunct sub = Madisound 2 x 10" Peerless driver passive subwoofer slapdash modified with cabinet wall reinforcement and stuffed with fiberglass
Old sub = GR Research 12" sub with passive radiator
New sub = Hsu Research VTF-2 mkII (wish I had a mkIII.)

[Duke]

OoheasoO, the Timepiece really does go way down deep, and I think very highly of the design.  If I wasn't bullding something conceptually similar, I'd be a dealer for Bob.  I think you will be very, very happy with them.

Left and right wall placement of your subwoofers will probably work fine, but now you want to cross them over at the same frequency.   In fact, there's even an argument in favor of running one in normal polarity and the other in reverse polarity - namely, the ear interprets an interaural phase difference at low frequencies as "big-hall ambience", and the ear is most likely to detect this if the subwoofers are at the extreme left and right of the listening position.   I'm assuming both subwoofers have the same-slope lowpass filter; if they have different slopes, it gets a bit more complicated. 

My next suggestion is to try different listening positions.  Try closer to the back wall, if you're not already up against it.  Often it's easier to move your chair than to move your speakers and subwoofer.  Try to find where in the room the bass is - and listen from there.  I had a friend with Lowthers and they were positively anemic in his big room - unless you sat up against the back wall, and then the tonal balance was very nice.

You can also try this with subs both in reverse polarity relative to the main speakers, and run up fairly high, as this may help.  Assuming you can position the subs symmetrically with respect to the main speakers and your listening position, you can run them up to 110 Hz and see if that helps with the dip you have up there.

With the addition of that second sub, you'll have more options than you have right now.

Duke

[Duke]

One other thing I probably should have mentioned earlier on - while the plate amp Jake has can be crossed over no lower than 40 Hz, the rack-mount amp that will be standard can be crossed over as low as 30 Hz, 4th order.  When crossed that low, the subs are -3 dB at about 23 Hz.

Duke

[ooheadsoo]

That is really good performance from such a small package.  I hope many enthusiasts will read of it and try it out.  23hz@-3db is really excellent, and having multiple small subs that can perform that low is certainly more WAF appealing than multiple behemoths.  Even if they don't understand the theory behind it all, having 4 subwoofers is just cool.

I wonder if there's an easy way to reverse polarity on a line level input like I'll be using on the Hsu.  My GR sub has an outboard amp, so that's not a problem.

[Duke]

Ooheadsoo, (ooheadhsu?) you're in luck:  The VTF-2 mk2 has a 0/180 degree polarity switch:

http://www.hsuresearch.com/products/vtf-2.html

[ooheadsoo]

D'oh, I knew that 

[youngho]

Ooheadsoo, I assume that you mounted the fiberglass panels across the corners with an air space behind them (and, of course, with the facing paper left intact) and that the batts were left in their bags, which unfortunately doesn't have an internal air space that something like a Tube Trap would. You may still consider diaphragmatic absorbers disguised as panelled walls. Extensive soffit trapping along the edges of the ceiling might be less visually obtrusive. I don't know how much the SP Tech speaker cost, and it sounds like the room is intensely problematic in ways that cannot be addressed with multiple subwoofers, but you're the best judge of how to spend your own money and time. The Welti paper depends on mode cancellation, so I assume that your room is symmetric and rectangular. A lot of the results also depend on parametric equalization, since a single unequalized subwoofer placed in the corner did surprisingly well relative to multiple unequalized ones. In case you're interested, we discussed it a little bit here: http://www.audiocircle.com/index.php?topic=50847.0

Duke, were you thinking of David Greisinger's work? The subwoofers should not be set 180 out of phase but rather something more like 90 to maximize the velocity vector, which is what Lexicon apparently does. For anyone who is interested, there's more information on it here: http://world.std.com/~griesngr/asa05.pdf

[Duke]

Yes, youngho, I was indeed thinking of Griesinger's work.  Good call!

It's been a while since I read it, and I don't remember the exact reason he gave for the 90 degree phase shift (probably skimmed over the velocity vector discussion as the math would have intimidated me), but I did try his setup not too long ago. 

You see, I was thinking of using two plate amps, one for each channel, specifically so that I could get that 90 degree phase difference that he recommended.  Unfortunately for me, at that time there were exactly zero plate amps on the market that combined a 4th order crossover with a continuously-adjustable phase control.  I was on the verge of contracting a production run of custom plate amps that incorporated both features - a considerable investment, but it would have given me a product that was unique, at least until someone else invested in a similar custom plate amp.

Anyway, before making the commitment, I figured I better find out just how important this 90 degree shift was.  I borrowed two plate amps with continuous phase controls, along with 2nd order lowpass filters, but with symmetrical placement to either side of the listening position that would be okay at least for the purposes of my test.

Now my test wasn't a blind controlled test - it was just me.  I wanted to see if I could hear the difference between in-phase, 90 degrees shift, and 180 degrees shift (left channel relative to right channel, in the deep bass only).  I could hear a difference between in-phase and not, but I couldn't hear a difference between 90 and 180 degrees.  So I concluded that the investment to replicate Griesinger's recommended setup wasn't necessary.

The rack-mount amplifier that I recently came across combines a 4th order lowpass filter with a continuously-adjustable phase control, so for the price of a second amp Griesinger's recommended phasing can be duplicated in a Swarm.  Maybe one day I'll revisit that, and this time have someone else do the listening without knowing what changes I was making so that I could eliminate listener bias (although at the time, my hope was that the 90 degrees difference would be an audible improvement over 180 degrees because I thought it would be cool to offer such a unique product).

Duke

[rasmussen]

Hello, I just wandered by on the way from another circle and happen to be looking at re doing the bass in my system. I've had subs in my system for 20+ years now and just discovered that what you appear to be saying about phase settings perhaps being optimized in an out of phase set up is really true. In most all the set up instructions I've come across the standard is to set the phase by sitting in the listening position and selecting the setting that sounds louder. However I have a Velodyne SMS-1 equalizer which I just use for set up, not equalization. It projects a graph of the bass response up to 200Hz on the TV. It has really been a great learning tool which has gotten my much better aquainted with my room.

Last time I set up a sub was at an 80Hz cross but I was noting some irregularity at somewhere around 110Hz or so- a fairly strong peak. The beauty of having the picture on the TV for me is that I can move the mains and or sub around watching the graph and get fast idea about a particular parameter compared to another. This sub only had a phase switch so I flipped it. Lo and behold the spike settled down considerably without much change in overall volume. There was a perceived lower volume though at the new setting with better graph. I just kind of shook my head and wondered how many times I set my sub up so the phase setting exacerbated a room spike based on following conventional wisdom for set up.
 
Ok so a comment/question. My first sub was a big box home made isobaric 15" in the attic, flush mounted firing down between the mains. Lately I'm not so energetic but have been inclined to try out one of the many in wall set ups. Haven't really come across one with the right price/performance. It does occur to me that adding maybe one ceiling and/or one in wall sub to two others might meet the swarm requirement recommended for scattering the subs vertically as well as free up floor space.

Question
> Does it make sense to use a swarm or clone with two boxes on floor then two inwall or ceiling? Or three floor one wall or ceiling? Would the typical repsonse parameters of commericial products tend to fit in with a swarm package? I believe you said some stray subs could be used but didn't get a sense of what the leeway is.

Thanks,
Larry R,
Seattle

[Carl V]

nice discussion so far.

Doesn't or didn't Mr Geddes use Bandpass subs?

Many, many moons ago I had 4+ subs in my room.  I enlisted
the help of a Pro sound guy...his company did churches,
Nightclubs, Hotel conference rooms, Ball parks etc.,

I ended up with an ULD-18 mounted up near the ceiling
towards a corner (ostensibly for Floor space conservation)
2 M&Ks along the side walls on the floor & 2 smaller Snell 550THX
subs mounted on the wall next to the wall mounted Surrounds(Snells as well)
It was very nice.  Later on he came back with Rane PE17 to dial
things in.  Sweet.

Next home I had the DIY bug.  Triad THX in wall speakers but now
I built different sized & tuned Sonosubs.  Russ Herschmann (sp) in Napa
advised an asymmetric placement as well.  Since the sub driver (s) were
at different locations & differing heights.  XO were easily done with Snell
boxes or Paradigm X-30 (not 4th order but 3rd order) or marchand Basis.
Again a very good effect.  BFD was then used to dial things in...sweet.

Over the years friends have done 4 Adire Rava with their Hypex-200 (LR4 XO)
Another guy used 4 Adire 10"XBL subs.  Another did 4 PE kits with outboard
amps & Marchand XO.  Another had a mix-n-match of differing subs of various
qualities...to good effect.  I see now Mr Geddes recommends going to Costco for
the subs or construct simple bandpass ones.

Take home lessons for myself....multi-subs, no corner placements & use EQ.

Present home, I'm still afflicted with DIY.  Larger displacement drivers.

[youngho]

Duke, you can read about the 90 degree phase shift here: http://world.std.com/~griesngr/sfaes.pdf. Two subwoofers run 180 out of phase located directly on either side of the listener will reinforce each other for the width modes (as opposed to mode cancellation) and partially cancel out the height mode and some of the even order length ones, so I'm not surprised that it sounded quite different quite from 0 degrees difference. Depending on the width of your room, it's possible that the width-related modal frequencies were higher than the warble tones you were listening?

Rasmussen, you're right, usually one sets the phase control to the loudest-sounding setting because this is where positive interference occurs between the subwoofer and mains. However, just as you found, sometimes phase can be adjusted to reduce the effects of problematic modal frequencies within the crossover frequency range, and so measurement should be an essential part of the audiophile toolkit. If you have a rectangular and symmetric room, you might consider two in-wall or infinite baffle subwoofers, each located at the midpoint (both horizontally and vertically) of the side walls. Add parametric equalization and a 90 degree phase shift, and kick ass. A very cost-effective option would be consider a small subwoofer located very close to the listening position (a la the Hsu MBM) crossed over to a larger subwoofer near the lowest modal frequency (and here is where setting the phase properly would be quite helpful), which would significantly reduce modal issues and also allow corner placement of the bigger subwoofer for maximal gain.

By the way, anyone interested in seeing a sophisticated but expensive approach to the use of multiple subwoofers to smooth out the bass response should Google "Double Bass Array."

[Duke]

Hello rasmussen, thanks for stopping by and joining in!

Your ability to mount one sub in the ceiling sounds like a good thing to me, as that allows you to significantly spread out your low frequency sources in three dimensions instead of just two.  I see nothing wrong with mixing different types of subwoofers, but haven't done much of it so can't give you any guidelines beyond what I already have (mainly about low-pass filter slope and frequency).

Carl V, looks like you've been doing this for years before someone came along and put a label on it!  I like your approach of using big woofers - I like big woofers too.  But, four big boxes is a really tough sell, so my commercial product uses little boxes. 

I think Geddes' subwoofer designs are indeed bandpass subs, and I think that has some definite advantages.  I couldn't shoe-horn the port lengths needed into a compact bandpass box, and besides I want wider bandwidth so that my system can be used with a wider variety of satellite speakers.  I have my reservations about Costco subs, unless they have a steep-slope low pass filter (which is unlikely in a cheap sub).

Youngho, thanks for the link.  David Griesinger's website ( http://world.std.com/~griesngr/ ) seems to be down at the moment but I'll try back later.

Duke

[Duke]

Seeing that Jake had to turn his Swarm modules sideways to get good integration has gotten my wheels a-turning.   I'm thinking about doing a make-over on the Swarm, and going with boxes that would be square as seen from above.  That means I'd have to run the port vertically to get sufficient port length, so the port would be down-firing.  That means I'd need feet, and while I'm at it might as well put the input terminals on the bottom (no room for the driver on the bottom).  I think the square tower format would better meet one of the goals of the Swarm: namely, that it be as visually unobtrusive as is practical - something Jake is not getting right now.

Duke

[ooheadsoo]

If the bottom of the cabinet becomes part of the port exit, does that mean you will shorten its length?

[Duke]

Ooheadsoo, good question - and I don't know the answer yet.  I'll have to build a prototype and do some measuring to see what effect the nearby floor has on the tuning (adjusting as necessary), and I'll also do some side-by-side listening comparisons.

Running the port in the vertical dimension does give me the option of tuning the enclosure a bit lower, as I'll be able to use a longer port. 

Duke

[JakeJ]

Duke and All,

Please don't take that photo literally, meaning that is not where the subs ended up that was just one of hundreds of angles and placements I have tried thus far. And I haven't turned the stereo on for three days! Dammit! (A sordid tale in it's own right.)

Actually today the subs are parked I took some time to go back to the quads and fine tune the "Triangle of Love"



I wanted to get the speakers front plane ahead of the front of the rack for imaging purposes so I moved the seated position back 8" from 3' 11" to 3' 3", shrank the triangle from 9' 3" on a side to 9' even, this moved the speakers forward about 12" closer together by 8". Today I listen and tweak, then re-introduce the Swarm back into the system. Patience, gentlemen, I do have the next two nights off and the plan is to work with the subs intensely. I'll post my notes and more pics with them.

Thanks
Jake

[JakeJ]

Hey Gang,

I know it's been too long but didn't think it necessary to start a new thread.

I am trying the subs in a new arrangement that I saw pictured in this circle plus discussions in Dr. Geddes thread in the Industry Talk & Events circle. Nice thing about this setup is that they are all out of the way. Below is a photo, one of the sub cabinets is obscured by the left channel Quad.



Bass is just there meaning that I can't locate a sub driver by ear from the listening position. I have to get up and get within about a foot or two to get any directional information. Next I'll try placing the Quads on top of the sub cabs in a somewhat dipole arrangement.

Jake