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post #1 of 50 Old 06-26-2014, 10:26 AM - Thread Starter
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Worst case scenario of using two subs that are not identical

I'm about to pull the trigger on a new sub (SVS PB-2000) and I'm planning to move my old sub to the living room. The new one will greatly outclass the old one (at least, it should) but I've been reading a lot about dual subs smoothing out bass and I wonder if it's worth trying them both at the same time (the living room doesn't really need a sub, it's just the only place to put the old one if I don't keep it in the "cave").

I will not be overdriving the subs, so I guess my only concern is whether there is a chance that I could damage my older sub by running it with the new one (if the SQ is no good, that'll make the final decision easy). I currently have a Boston Acoustics PV900 (had it for ten years and it has served me well enough). I usually listen at -20 to -15dB from reference (very occasionally, in an empty house, at -10dB) and my room is about 2200 cubic feet.

If the consensus is that I could damage my PV900, then I won't bother with the experiment (it's in perfect working order at the moment so I don't want to "throw it away" on an experiment).
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post #2 of 50 Old 06-26-2014, 10:51 AM
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Quote:
Originally Posted by Ovation View Post
my only concern is whether there is a chance that I could damage my older sub by running it with the new one
That could only happen if you ran it too loud, which would be revealed by high distortion.
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post #3 of 50 Old 06-26-2014, 10:52 AM
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If you're adding a second more powerful sub, unless your plan includes playing things a lot louder than before, how are you going to damage the sub? If anything, the old sub will have it easier than before.
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post #4 of 50 Old 06-26-2014, 07:59 PM - Thread Starter
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I'm not sure what to expect as I've never run two subs in the same system. However, if there is no danger, I'll try them together and the new one alone and compare. My wife will be happy if I can make them work well together (no need to accommodate a sub in the living room). But I haven't told her that, as I've prepped her to expect the old sub to move upstairs. House will be mine alone for about two weeks. Ideal time to experiment.

Guess my next question is whether my odds of them playing nicely together are poor, fair or good (I'll assume excellent is unlikely as they are quite different)?

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post #5 of 50 Old 06-26-2014, 08:08 PM
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You can get a great result if you take a little time in setting them up.

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post #6 of 50 Old 06-27-2014, 09:55 AM
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You didn't mention how you're driving the subs. If you have something like Audyssey SubEQ, then no prob at all, otherwise a bit more work. I essentially do what you're doing. One sub is a SVS PC13Ultra, the other is a "better" (than the SVS) quality sub you've never heard of lol, but it has much lower amp output and a much less strong driver too. So I had the same thoughts as you. You will of course have to set the sub input levels/gain differently for a start. When set up carefully and the subs decently positioned (you may need to be very flexible here), you should end up with a smoother bass frequency response across a "reasonable" listening area, and less distortion too. Quite a lot more pleasant really, don't be surprised if it sounds less loud/"boomy" than you're used to so you think there's "less" bass, at first.
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post #7 of 50 Old 06-27-2014, 10:31 AM - Thread Starter
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Quote:
Originally Posted by cfraser View Post
You didn't mention how you're driving the subs. If you have something like Audyssey SubEQ, then no prob at all, otherwise a bit more work. I essentially do what you're doing. One sub is a SVS PC13Ultra, the other is a "better" (than the SVS) quality sub you've never heard of lol, but it has much lower amp output and a much less strong driver too. So I had the same thoughts as you. You will of course have to set the sub input levels/gain differently for a start. When set up carefully and the subs decently positioned (you may need to be very flexible here), you should end up with a smoother bass frequency response across a "reasonable" listening area, and less distortion too. Quite a lot more pleasant really, don't be surprised if it sounds less loud/"boomy" than you're used to so you think there's "less" bass, at first.
I have an Anti-Mode 8033 and it is a version with two outputs (so can use with two subs--one is 180 degrees out of phase with the other, so setting the sub's phase to 180 brings it back to proper phase).

I do not have a lot of placement flexibility, so I am prepared to simply stay with the new one and move the old one upstairs if I can't make it work with both subs. I will be using REW to measure sub response (I think I still have my old REW readings for my current sub somewhere, so I'll have a baseline to compare).

With my current sub (I don't run it hot), in the MLP, I get decent LF performance (can feel it as well as hear it--I've been watching the Star Wars movies on Blu-ray with my son and there are some good moments on each disc so far). I placed my sub according to REW measurements for best performance within my limited choices, and the 8033 has made the sub more articulate and smoother overall (main drawback with current setup is a bit of a null around 63hz, but it's not too deep or very wide). While my PV900 was not the best bang for the buck in its day at MSRP, for what I paid, no other sub was better (long story, but short version is the store gave me an excellent price because of a screw up with another piece of gear I was buying--screw up was manufacturer's fault but store owner was excellent about it). It's 10 years old (likely 11 or 12 in design), so of course I expect much better from a modern sub. But it is ported, has a 12 inch driver, a 300 watt BASH amp and has been reliable since day one. The only time it ever seemed to strain was last week, when I decided to experiment with the two "lift" functions on the 8033 and then run the latest Trek movie at -10dB on my receiver. It didn't make an overly alarming noise, but it was clearly working at its limits (especially with the 7dB boost centred on 25hz--the other is centred at 35hz).

Given my usual listening habits, it's probably overkill to even upgrade the sub. But what the heck, it's been 10 years, I can afford it and I'm curious about "the next level".
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post #8 of 50 Old 06-27-2014, 11:41 AM
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Level match each sub, one at a time to 73-75 db at the MLP. With the Antimode, you should be able to get things to work.

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post #9 of 50 Old 06-27-2014, 03:45 PM
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^ Yup, that should work. And I agree about the bottoming-out thing (though you didn't explicitly say it, I think that's where you were heading...). My smaller sub is older too, a bit older than yours, and it was designed mainly for music, in the days when movie soundtrack LFE was less aggressive, so it didn't take kindly to modern LFE when running as the only sub. I use REW too, it will help hugely in setup, don't know how you'd really do it decently without it (or similar), especially with two quite different subs. In my case, the older sub was sealed, and the newer SVS was optionally sealed, which I eventually chose at the expense of (apparently, I didn't test) less output. Greatly smoothed out the response in the listening area, even more so at the MLP. Try and put the subs near opposite walls.
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post #10 of 50 Old 06-27-2014, 06:23 PM - Thread Starter
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Quote:
Originally Posted by cfraser View Post
^ Yup, that should work. And I agree about the bottoming-out thing (though you didn't explicitly say it, I think that's where you were heading...). My smaller sub is older too, a bit older than yours, and it was designed mainly for music, in the days when movie soundtrack LFE was less aggressive, so it didn't take kindly to modern LFE when running as the only sub. I use REW too, it will help hugely in setup, don't know how you'd really do it decently without it (or similar), especially with two quite different subs. In my case, the older sub was sealed, and the newer SVS was optionally sealed, which I eventually chose at the expense of (apparently, I didn't test) less output. Greatly smoothed out the response in the listening area, even more so at the MLP. Try and put the subs near opposite walls.
That will be very likely the layout, though rather unlikely to be symmetrical. Ed Mullen at SVS suggested I might actually get a better result with an asymmetric placement (we were discussion dual SVS options at the time, not different types of subs together, so I don't know if it matters). Hope he is correct (will find out in the next 7-10 days).
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post #11 of 50 Old 06-28-2014, 12:59 AM
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Todd Welti & Allan Devantier of Harman Intl. (AKG, Harman Kardon, Infinity, JBL, Lexicon & Martin Levinson) published the fol. classic study re WHERE to place MULTIPLE sub-woofers:
http://www.harman.com/EN-US/OurCompa...s/multsubs.pdf
http://mkloudspeakers.com/pdf/todd-w...hite-paper.pdf

The fol. explanatory articles were obviously derived from the above work:
http://www.aperionaudio.com/blog/dua...r-home-theater
http://seriousaudioblog.blogspot.com...-multiple.html
http://www.bgcorp.com/PDFs/Better%20...subwoofers.pdf
http://www.audioholics.com/subwoofer...-calibration-1

Due to the SIZE of my Sub-Woofers, I don't have much choice as to WHERE they are located. I bought a pair of Altec Voice-Of-The-Theater Speakers ("smaller" A7-800 vice A7-500 type in fancy cabinet with 15-in Woofers and Large Sectoral Horn Mid/Tweeter) way back in 1971 and after doing the requisite driver MEASUREMENTS, tried some alternative alignments (e.g. closed, partially open vent) after the Nevielle Thiel and Richard B Small series of articles first came out in the 1971-1973 Audio Engineering Society (AES) Journal re Analytical Analysis of Speaker Alignments. I also built a pair of DIY Rear Surround Bass Reflex Speakers using PietzoElectric (and other) Tweeters:
http://en.wikipedia.org/wiki/Thiele/Small

Much later, I upgraded to Cerwin Vega drivers in the Rears and calculated/measured some new alignments. I also built (L/R Bi-Directional) DIY Planar Magnetic Mid-Range, Ribbon Super-Tweeter & Closed Box Speakers for L/R/C with much faster response times than conventional speakers.

So JUST the two Altec 15-inchers became my TWO sub-woofers (3 dB down at about 25 Hz in the room). Their DRIVERS are located just over 3-ft from L and R front walls. They also provide a place to stack 2 Stereo Amps on the Left for L/R Woofers & L/R SW's and 7-Ch AVR for the rest plus D-VCR, BD-Player, Cable Box, etc. Thanks to the sloping "Cathedral" ceiling in the living room, I don't have to worry about any Floor/Roof modes. Recliner/Curtains & Couch breaks up the L/R modes...and there is a passageway to the DR/KIT in L-Rear Corner that somewhat suppresses the Front/Rear modes. Nonetheless, significant narrow-bandwidth correction is needed to reduce two primary room modes and provide a bit of boost for the in-between nulls.

Although my Pioneer AVR has a Room Equalization feature, it doesn't have narrow-band filters for the Sub-Woofer range of frequencies. I use a 1/3-Octave Graphic Equalizer (between the AVR's SW Output and the mid-70's Marantz 125 wpc SW Amp) to adjust for best SW frequency response AT MY SITTING POSITION, using a CD (also DVD-Audio) with Wideband and 1/3-Octave Noise Test Signals. A R-S Digital Signal Level Meter feeds the Audio Input on my Laptop running TrueRTA software to display results. I also used this to find which pictures needed some FOAM behind them and FOAM weatherstripping on the closet door to prevent rattling:
TrueRTA-for-dummies

Narrow Band Equalization, either through 1/3-Octive Graphic Equalizers or the Behringer Parametric Equalizer is needed if you want to get rid of the "Boomy" room modes and actually HEAR each and EVERY note in a Bass Guitar riff, Organ Concert or whatever computerized super-bass sequence grabs your gut.....

Note that Sub-Woofers do NOT need matching frequency responses....indeed, it would actually HELP if one maintained full energy when the other has a dip in it's response....and you'll probably find that L/R settings on the Equalizer don't match....and the ROOM MODE variations will be MUCH LARGER anyway....

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post #12 of 50 Old 06-28-2014, 01:15 AM
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I thought about this too. SBU13 and SB12+. Antimode 8033Cinema. Go from SBU13 input, output then onto SB12+ disabling built in high pass and any other thing onthe line level output. Manually set levels.

av pre-amp--->Antimode---SBU13---SB12+

Switch on both subs, reduce SBU13 volume to minimum. Adjustab SB12+ so test tone results in 75dB. Switch off SB12+. Increase volume on SBU13 until it results in 75dB. Switch on SB12+. Run antimode setup. Then calibrate sub level on av pre-amp sub output.

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post #13 of 50 Old 06-28-2014, 06:55 AM
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Quote:
Originally Posted by Ovation View Post
I'm about to pull the trigger on a new sub (SVS PB-2000) and I'm planning to move my old sub to the living room. The new one will greatly outclass the old one (at least, it should) but I've been reading a lot about dual subs smoothing out bass and I wonder if it's worth trying them both at the same time (the living room doesn't really need a sub, it's just the only place to put the old one if I don't keep it in the "cave").

I will not be overdriving the subs, so I guess my only concern is whether there is a chance that I could damage my older sub by running it with the new one (if the SQ is no good, that'll make the final decision easy). I currently have a Boston Acoustics PV900 (had it for ten years and it has served me well enough). I usually listen at -20 to -15dB from reference (very occasionally, in an empty house, at -10dB) and my room is about 2200 cubic feet.

If the consensus is that I could damage my PV900, then I won't bother with the experiment (it's in perfect working order at the moment so I don't want to "throw it away" on an experiment).
One general key to using dissimilar subs is to systematically position the subs for best individual performance and equalize them independentaly for best possible performance.

I don't know of any AVRs that provide independent equalization for multiple subs, so this means introducing one or more additional equalizers into the system. This can be implemented by the equalization controls of the subwoofers or actual separate equalizers.

The general strategy is to route the heavy lifting to the more capable sub. Put it in charge of lifting up response at the lowest frequencies if needed. Put the less capable sub in charge of filling small holes at high frequencies.

I'm currently implementing this with a mixture of a separate analog parametric eq and controls on the subwoofer itself. My future direction involves a MiniDSP 2x4 balanced for handling up to 4 subs.

Last edited by arnyk; 06-28-2014 at 06:58 AM.
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post #14 of 50 Old 06-28-2014, 08:57 AM - Thread Starter
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Lots of info to consider. Thank you all (and thanks in advance to any other contributions). Just received an email saying it will arrive on Monday (was thinking Thurs. or Fri., so, yay me).
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post #15 of 50 Old 06-28-2014, 10:24 AM
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To follow on from what Arny said, here's what I did with two quite dissimilar subs (dissimilar re amp power and output level). You can see if it's feasible for you, and see if my sub-"logic" makes sense. In the meantime, you will almost certainly need a new fairly long sub cable. If so, depending on length, consider using a coaxial one. I say "long" for experimenting with sub positioning. Also, make sure you have a suitable AC source near where the second sub will be (actually, this was a slight prob for me, so mentioning it JIC for you), or at least a decent extension cord/power bar etc. Hopefully not on a circuit that has any random on/off motors on it (fridge, A/C, etc.: may cause annoying hum). Might as well be ready for action when the sub arrives!

I am going to guess you are the fussiest listener in your house, and you sit at the MLP when possible. So we'll say that any REW measurements will be taken there, for initial configuration at least. And I'm going to guess you're not sitting in the center of the room (generally sonically undesirable, especially for bass), and more toward the rear of the room than the front. Here's my example to contemplate:

You're sitting at the MLP facing forward. Put the new powerful sub in the front left corner. Put the old less-powerful sub in the rear right corner. I don't know if Ed Mullen would call this "assymetric", it kind of is in some ways, but to me it is diagonally symmetric... By "corner" I don't mean the actual corner, but more like 2-3' along the front/rear wall from the corner, and >6" out from the wall too. You might want to start with the weaker sub a little closer to the corner, to reinforce it a tad more, and also note it's going to be (physically) closer to the MLP than the large sub. As Arny said, the big sub provides the oomph, the small sub provides the smoothing. You will possibly be surprised just how much balance/FR smoothing a smallish sub can provide when decently positioned. It worked very well for me. Feel free to swap my right and left obviously. Move the subs along the front/rear walls to taste/fit/best measurement. Yeah, it's a bit time-consuming, but much faster with REW than with SPL meter and spreadsheet...
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post #16 of 50 Old 06-28-2014, 01:24 PM
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Be judicious when using an equalizer to squeeze out the very last few Hz of low frequency response....there is a trade-off of how much very low frequency power can be pumped into the speaker cone before non-linear CONE EXCURSION creates harmonic distortion on the higher frequencies which you CAN hear (rather than just "feel").

Note that common 16-ft (32 Hz, low-C in A440 tuning) organ pipes are a WORTHY GOAL...but with early organ tunings being as low as A392 (18c France), some historical organs are actually putting out 30 Hz, depending on temperature. However, reportedly NONE of the organs Bach played (and composed for) had low-C, with Low-D being the lowest pedal. Huge 32-ft organ pipes (17 Hz) are fairly common, but you're gonna need a BIG ROOM and some SERIOUS SUB-WOOFER(S) that COUPLE to the room (e.g. Klipschorn & other Room Loaded Horns) to make that happen with loud levels....otherwise all you'll hear/feel are the HARMONICS.

FYI: Atlantic City Boardwalk and Sydney Town Center are about the only recorded organs with MONSTER 64-ft organ pipes....and some insane hobbyists have constructed and recorded 128-ft pipes, which apparently are only good for shaking the room (like the old EARTHQUAKE movie Sensurround system, which fortunately? unfortunately? never made it to DVDs):
http://ibsubwoofer.blogspot.com/2010...gan-pipes.html
http://en.wikipedia.org/wiki/Pipe_organ_tuning
http://en.wikipedia.org/wiki/Sensurround

Lowest notes on a Bass Guitar is either 31 or 41 Hz, depending on the number of strings....so the only "natural" source of sub-30-Hz music in most situations will be BIG drums and of course, synthesizers...many of which use a neat trick whereby they only generate the HARMONICS of a (missing) Fundamental waveform (e.g. Square, Triangle, whatever)....your BRAIN also does this trick when the Fundamental signal is missing, such as is typical for 32 and 64-ft organ pipe sound reproduction systems that simply can't generate much power for 17-Hz and lower frequencies.....so there isn't as much NEED to try to generate massive amounts of energy at those frequencies:
http://en.wikipedia.org/wiki/Bass_guitar_tuning
http://en.wikipedia.org/wiki/Missing_fundamental

More info re Klipschorn (my son's father-in-law has a pair of these antiques from the '70's). Note that the Corner of the Room becomes an EXTENSION of the internal Horn structure so that very low frequency energy can actually be COUPLED to the Room:
http://www.klipsch.com/klipschorn-history
http://hornloudspeakermagazine.blogspot.com/2008/11/comprehensive-list-of-klipsch-plans.htm

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post #17 of 50 Old 06-28-2014, 02:09 PM
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I've been looking over my room equalization notes when I was "tweaking" the DIY Crossover Network for the 10" L/R & Planar Magnetic Mid-Ranges & Ribbon Tweeters which reminded me of some other "issues" due to trying to "correctly" match the phase of the various speakers near the Crossover Frequencies to avoid a null in the frequency response. Some (not all) Crossover Network Designs result in a PHASE-REVERSAL, so one speaker may need to have the speaker wires reversed...which would also impact the phasing at the OTHER Crossover frequencies.

A Bass-Reflex Speaker with a front facing port inherently has a PHASE-REVERSAL between the low frequency signals coming out of the Driver and signals coming out of the port (good reason to use Closed Box or "Infinite Baffle" type speakers)....and if the Bass-Reflex Port is located ELSEWHERE, such as rear or bottom of the box, interference patterns will occur making the radiation patterns irregular. So when you adjust the equalizer, flip the leads (or switch) on the Sub-Woofer to see which setting minimizes the null near the Crossover frequency.

ALSO, since you can't really "hear" sub-30-Hz signals, if you crank the amps wide open hoping to "hear" signals at the same levels as higher up, you will soon hear the "buzzzddttttt" of a warped speaker cone....a costly mistake. Don't crank it up any higher than you did for UNDISTORTED higher bass frequencies (painful, use ear plugs)....and with Bass-Reflex speakers that might even be too much as the amount of Cone Excursion INCREASES at and below the 3 dB roll-off point.....where YOU CAN'T HEAR IT:
http://www.silcom.com/~aludwig/Sysde..._excursion.gif

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post #18 of 50 Old 06-28-2014, 02:37 PM
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For what it's worth, I'm using a Def Tech Supercube I as my main sub, located approximately front center, and an older Def Tech ProSub 100TL, fed from the second subwoofer output on my pre/pro, and located about center back between the rear speakers (5.1 setup).

It took quite a bit of trial and error to get the right balance between the subs in this small room (without room eq equipment). I have the rear sub turned almost all the way down, just audible enough to give the rear channels presence and a little punch. The added rear presence really helps with imaging in both music and movie soundtracks. I'm pretty pleased with the results.
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post #19 of 50 Old 06-28-2014, 04:06 PM
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Oh my! Where to begin!


So many misconceptions about subs and bass


Let's start with bass equalization... OP indicates bass boost applied at 2 different frequencies... this almost NEVER does any good. A boost is attempting to fix a dip in response. Most response dips in bass octaves are caused by cancellations that are a function of room dimensions and the locations of the subwoofer and listener. If there is, say, a 15 dB bass deficit at some frequency... let's say 32 Hz just for the heck of it... adding more bass is going to be subject to the same cancellation. You keep adding energy at 32 Hz, but room dimensions and sub and listener placement continue to cancel the added energy. When using equalization for bass, use cuts, to even things out as much as you can. Adding bass boost is almost never helpful. To eliminate a bass suckout, you have to move the subwoofer or listener or both --- OR --- wait for it --- add a second subwoofer.


There is NEVER EVER, NOT EVER, any kind of problem you would likely ever encounter by using 2 subwoofers.


99% (or more) of EVERYBODY out there trying to setup their system does not realize that when you install 2 subs in 1 room, the effect you get is almost identical to placing ONE subwoofer at the midpoint between the 2 subwoofers... THINK about that for a moment, it is a VERY critical concept to understand in order to use 2 subs effectively. You put a subwoofer 10 feet in front of you and another subwoofer 10 feet behind you. What you have done, effectively, is placed a single subwoofer centered on the main listening seat without having to PHYSICALLY have a subwoofer in that location. In most rooms, this sort of placement will produce very very good bass response at the main seat (or at whatever location is half-way between the 2 subs).


You don't really CARE what the bass response is in your room anywhere but pretty close to your main seat (and perhaps a couple of nearby seats). You can find good subwoofer or listening seat locations by "mapping" your room with measurements every 2 feet. When you find a location with good bass response, that would be an ideal location for your main seat or for a subwoofer.


I've never (that is a very strong statement!) heard 2 subs sound worse than 1 sub. Never.


Even if neither sub is all that great in their locations by themselves (measuring 1 sub at a time), when you use both of them at the same time, you almost ALWAYS (leaving a small chance this might not work 100% of the time) get better bass response when the 2 subs are working together.


You will get the best possible results with 2 subs if your surround processor or AVR has two subwoofer outputs that are processed separately. That way, if you have Audyssey or some other room correction in the processor or AVR, each sub has separate measurements and separate corrections applied so that when they are used together, you get the best possible end result. If there are 2 LFE outputs, but they are fed the same signal, Audyssey or other room correction software will only measure 1 subwoofer even though 2 are being used. This is better than nothing and can still provide useful improvements.


If you have NO room correction you have to decide how much "weight" to apply to each of 3 different measurents: Sub1, Sub2 and Sub1&2 together. I would suggest applying 25% weighting to each subwoofer alone and 50% weighting to the measurements of the 2 subs working together.


Using 2 subs will result in both subs running 3-6 dB lower in level than they would if you were using only one sub in the room.


Placing a subwoofer anywhere other than the center of the room (left to right) is likely to cause higher bass frequencies to appear to be coming from off-center in whatever direction the sub is placed. People often say this effect stops at 100 Hz, but in my experience, 80 Hz is a more realistic cut-off point for directionality of bass. BUT (another important concept), placing the subwoofer as little as 6 inches off-center (left to right) will often improve bass response in the room considerably since that 6" difference means the sub-to-left-wall dimension and the sub-to-right-wall dimension are 1 foot different and you will have few cancellations you can't fix.


Measurements don't tell the whole story of bass response.


Listening doesn't tell the whole story of bass response.


Both listening and measurements together can be pretty effective at getting great bass results.


Measurements made with an unsuitable (and uncorrected) microphone will not be helpful.


There aren't many microphones that are linear in their bass measurements below 35 Hz or so. Even SPL meters may not be corrected for accurate bass measurements below 35 Hz. Contrary to what you might think, larger microphone diaphragms tend to be worse at measuring bass, on average, than smaller diaphragms. Microphones intended to be used for measurements, tend to be better for bass measurements than microphones intended to be used with instruments or voice.


I hope at least some of this is useful info.
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post #20 of 50 Old 06-28-2014, 06:26 PM
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Originally Posted by Doug Blackburn View Post
There is NEVER EVER, NOT EVER, any kind of problem you would likely ever encounter by using 2 subwoofers.
I can think of one...

If you have one really powerful sub, with massive output capabilities and deep LF extension, and you try to add a 2nd sub that is much less powerful and has a significantly higher roll-off, AND you level-match the two subs, you could very quickly approach the limits of the "lesser" sub, which would limit the capabilities of the entire system. In that case, adding the 2nd sub could actually reduce the performance of the 2-sub "system" by limiting the "system" response to the capabilities of the "lesser" sub.

Of course, the way to deal with that is to not level-match the two subs. Use the "lesser" sub as a fill-in sub at a lower level. Of course, that approach pretty much requires the use of measurements of the response to optimize the results.


Quote:
Originally Posted by Doug Blackburn View Post
You will get the best possible results with 2 subs if your surround processor or AVR has two subwoofer outputs that are processed separately. That way, if you have Audyssey or some other room correction in the processor or AVR, each sub has separate measurements and separate corrections applied so that when they are used together, you get the best possible end result. If there are 2 LFE outputs, but they are fed the same signal, Audyssey or other room correction software will only measure 1 subwoofer even though 2 are being used. This is better than nothing and can still provide useful improvements.
One point of clarification... Audyssey XT32 with SubEQ HT will set Levels and Distances for 2 subwoofer outputs SEPARATELY. However, when it comes to the Room Correction Equalization, it will "ping" the subs together, measure the subs together, and EQ the COMBINED response of the subs as if they were one sub. It would be much less useful to EQ the subs individually because they will interact with each other and, even though each sub could be EQ'd to flat individually, their combined response will likely be anything but flat. Since you actually listen to the combined response of the subs, you want to EQ their combined response.

You may have known this, but the way you worded your statement above, it wasn't clear.

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post #21 of 50 Old 06-28-2014, 07:36 PM
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I wouldn't worry too much. The worst thing that could happen is 1 good sub with one meh sub won't sound as good as 2 good subs. I still think 1 good sub with 1 meh sub is still better than just 1 good sub. I have a PC12-NSD running with an RW12d on a denon x4000 and it sound really great. The cheaper sub has more output in midbass so I feel I get a great full sound. Especially if your AVR is good at smoothing things out. If they are equalized well a meh sub will enchance your overall performance.

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post #22 of 50 Old 06-28-2014, 08:10 PM
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I use two different boxes with my two 12inch subs (Earthquake Magma X), one is a ported box and the other has a passive radiator. Both are tuned differently and the Antimode 8033 (first version) has no problems tuning them together on the same signal set to 0 degrees.
I also run them both together in series/parallel on the one channel off my Behringer iNuke NU4-6000.

With the Antimode on the flat setting they are all good but on the 25 gain setting I have to be more cautious when playing very loud as the tuning freq of the ported box is not low enough so that sub can have a decent amount of excursion while the PR box sits pretty.

If your antimode can tune two separate subs then once it does its EQ I would set the level of each to 72db for the combined 75db calibration or if you like them hot then set each to 75db and keep an eye on them but I think you will be fine!

I'm about to try four different boxes on the one EQ with the Antimode to see what it's like with the two subs I have mentioned and two more in small 0.6-0.8cuft boxes sealed boxes as It's all fun in my books...
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post #23 of 50 Old 06-29-2014, 12:16 AM
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Microphones need to be CALIBRATED for accurate measurements.....or at least apply a CORRECTION from a known Calibration Curve. Here is an example of one person's COMPARISON of R-S SPL's vs professionally calibrated microphones while measuring the (obviously irregular) room response....and ALWAYS trust your EARS...after all they are what you REALLY need to please...so what if you prefer a bit of BASS BOOST...too bad Amps don't have a simple (5.1-Ch ???) Bass Boost control anymore...now I frequently have to search down the right menu on my Harmony R/C to adjust the SW Level control....and adjusting the Bass Boost on the L/R Woofers is nearly impossible since it's buried in the AVR's Setup Menu and requires switching HDTV to the very rarely used AVR Video Output:
http://www.sasaudiolabs.com/mics_group3.gif
BTW: There is now a NEWER R-S Digital SPL Meter with a foam wind cover on the mike...NOT included in the above chart.

Calibration curves are found in the links at the bottom of the article:
http://www.stereophile.com/content/r...-or-accurate-1
If all we are seeing is a typical low-frequency roll-off, it should be fairly easy to extrapolate to somewhat lower freqs than the lowest 20 Hz calibration point:
http://www.gearslutz.com/board/post-...ion-table.html

It's been awhile since I bought mine, but didn't the R-S Digital SPL Meter COME with a Calibration Chart????

BTW: Microphone technology has come a long way....Surface Mount, ALL Solid State Piezoelectric MEMS type mic's can have a VERY LINEAR Low Frequency Response down to AT LEAST 10 Hz...and for DIYers, only cost 2 bucks plus a simple Op Amp for high input impedance and matched output impedance:
http://www.st.com/web/en/resource/te...DM00074869.pdf
http://www.mouser.com/ProductDetail/...SCEDe4KyaYA%3d
http://electronicdesign.com/componen...ency-responses

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post #24 of 50 Old 06-29-2014, 07:13 AM
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Audyssey XT32 helps with 2 separate subs

ArnyK, The reply below addresses your comment about whether any AVR's have the capability to independently equalize/integrate two separate subwoofers. My Integra 80.3 AVR includes Audyssey XT32 .




One point of clarification... Audyssey XT32 with SubEQ HT will set Levels and Distances for 2 subwoofer outputs SEPARATELY. However, when it comes to the Room Correction Equalization, it will "ping" the subs together, measure the subs together, and EQ the COMBINED response of the subs as if they were one sub. It would be much less useful to EQ the subs individually because they will interact with each other and, even though each sub could be EQ'd to flat individually, their combined response will likely be anything but flat. Since you actually listen to the combined response of the subs, you want to EQ their combined response.

You may have known this, but the way you worded your statement above, it wasn't clear.

Craig[/QUOTE]
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post #25 of 50 Old 06-29-2014, 11:18 AM - Thread Starter
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Wow. A lot of info to absorb. Some of this I'll be able to use right away (I have REW, the calibration file for my trusty Radio Shack analogue SPL and an appropriate sound card), and I'm familiar with the basics of room effects at different frequencies.

At the moment, having just splurged on a new sub, I will forgo adding more EQ (my Anti-Mode 8033C will have to suffice for now) and more mics. At some point, I'll add the mic recommended for use with REW (think it's called a Umik-1) and maybe a miniDSP EQ (hey, have to leave something to add later on :lol: ). I will bookmark this thread, though, to keep it handy for future reference (I'm sure I'll eventually try a lot of the stuff mentioned herein--did the same with similarly appropriate advice back when I was shopping for and setting up other gear).

I did come across something elsewhere where someone combined a PB-2000 (classic corner placement) with a much less powerful PSW110 (Polk?) (in a "near field" placement--though I'm not sure how "near-field") and he posted REW generated graphs (no EQ applied) that looked rather good (he seemed astonished at the result). Is there any chance that such a near field placement would be beneficial if the main goal with the second, smaller sub, was to counteract nulls rather than add output (I'm guessing a near field placement would allow a lower gain setting--less danger of overdriving the smaller sub or limiting the larger one as described above in a post)? I know that trying it out will reveal that, but it would require a degree of effort regarding furniture placement that I might want to avoid if this idea is without merit. Thoughts?
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post #26 of 50 Old 06-29-2014, 01:36 PM
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Quote:
Originally Posted by PrismV View Post
ArnyK, The reply below addresses your comment about whether any AVR's have the capability to independently equalize/integrate two separate subwoofers. My Integra 80.3 AVR includes Audyssey XT32 .

One point of clarification... Audyssey XT32 with SubEQ HT will set Levels and Distances for 2 subwoofer outputs SEPARATELY. However, when it comes to the Room Correction Equalization, it will "ping" the subs together, measure the subs together, and EQ the COMBINED response of the subs as if they were one sub.
That agrees with what I've been told before...


Quote:
Originally Posted by PrismV View Post
It would be much less useful to EQ the subs individually because they will interact with each other and, even though each sub could be EQ'd to flat individually, their combined response will likely be anything but flat. Since you actually listen to the combined response of the subs, you want to EQ their combined response.
IME and looking at extant literature, the above ignores the fact that in every case the various subwoofers will have different effects on the room. Even if they are identical, from the standpoint of any listener at any location, they will have different response and different dynamic range. There are thus potentially any number of different equalization curves for each subwoofer that will produce a given system response. Since real world subwoofers have limited dynamic range, the division of the workload is too important of an issue to be handled arbitrarily.

For example it is likely that each subwoofer will cause peaks and dips in response. In order to optimize dynamic range, only the peaks should be equalized. But, the frequencies of at least some of the peaks are likely to be unique for each subwoofer. Therefore each subwoofer should be equalized individually.

Equalizing each subwoofer individually does not eliminate the need to equalize them as a group. In fact equalizing the subwoofers as a group addresses the problem of interactions, mentioned above.
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post #27 of 50 Old 06-29-2014, 03:45 PM
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Currently working on trying to integrate 2 different subs into a system myself. Found this thread very helpful. Thx.

Notice people experiencing issues if their AVR doesn't have the multiple LFE management. You can obtain total control of your mains and as many subs as you like using the DSP found in pro and semi pro multi channel audio interfaces.

I use this MOTU Ultralite.http://www.motu.com/products/motuaudio/ultralite-mk3

You can send the same signal independently to the mains and both subs. Then use the built in 7 band parametric EQ in Cuemix to effectively design your own crossovers. http://www.motu.com/products/motuaud...-overview.html

It's a $600 unit but you can get ones with fewer channels or a less expensive brand. Won't be everyone's cup of tea but I hope someone finds the information that alternative solution exist is useful.
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post #28 of 50 Old 06-29-2014, 05:03 PM
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I run two subs, each totally different in size, design and response.

The main unit is an 18" JBL infinite enclosure, which covers the range from xover (lets be generous and say 100Hz) to around 16Hz +- 3Db.
The second sub is a DIY folded horn, with a 15" driver, (another big enclosure, but I have the space to fit them), covering from xover to around 20Hz, probably a little lower but I haven't bother to measure it, but has a small soft peak at 45Hz.

The peak was designed in to give that stomach punch from sudden transitions like explosions, and it works really well.
The JBL is at the back of the room and gives solid all-round bottom end without clipping and any bad behaviour. The other DIY unit is at the side towards the rear of the room. My room is 7.5m x 5m.
I tuned them, in conjunction with the rest of array and room, with Audyssey, using the 11.2/2-subs option.
The front array are 3 very large JBL studio monitors, which have a fabulous low response in their own right.
The side and rear surrounds are also JBL studio monitors, but smaller (and full range).
The room sound fabulous, only the rattling trinkets annoy.
I can't wait for the Dolby Atmos processor to hit the Home Theatre market.
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post #29 of 50 Old 06-29-2014, 05:10 PM
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Quote:
Originally Posted by arnyk View Post
IME and looking at extant literature, the above ignores the fact that in every case the various subwoofers will have different effects on the room. Even if they are identical, from the standpoint of any listener at any location, they will have different response and different dynamic range. There are thus potentially any number of different equalization curves for each subwoofer that will produce a given system response. Since real world subwoofers have limited dynamic range, the division of the workload is too important of an issue to be handled arbitrarily.
The "division of workload" is handled by "gain-matching" the subs. If they're gain-matched they all have EXACTLY the same workload, but only if they are also sent EXACTLY the same signal, i.e., if they are all sent EXACTLY the same EQ'd signal. IOW, they NEED to be EQ'd as a combined system in order to have an equal division of workload. You don't accomplish that by EQ'ing them separately.

Quote:
Originally Posted by arnyk View Post
For example it is likely that each subwoofer will cause peaks and dips in response. In order to optimize dynamic range, only the peaks should be equalized. But, the frequencies of at least some of the peaks are likely to be unique for each subwoofer. Therefore each subwoofer should be equalized individually.
What happens when one sub has a peak that offsets a null from the other sub? If you EQ down the peak, you're left with the null... that had already been corrected. What are you going to do then? EQ the combined response by adding a boost to bring up the null? That makes no sense at all. Better to measure the combined response and apply just one offsetting EQ to the combined response.

But hey, you do whatever you want. I've explained this to you twice now, and you still persist. I have no interest in further conversation with you on this topic.

Craig

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post #30 of 50 Old 06-29-2014, 07:32 PM
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I found this article and the articles linked from it very helpful in working with my subs.
http://seriousaudioblog.blogspot.com/2012/05/two-great-articles-on-multiple.html
Basically, Geddes multiple sub recommendations.
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