Subs 3 or 4?

[speakerman39]

I agree.

I use the equivalent of three subs in my system (because I run the mains full-range, and they can produce impressive output at 20Hz), and I've been able to attain some rather impressive bass smoothness at my listening seat (measured and auditioned with test tones). Of course you know this, but others may not, running the mains full-range means you're willing to use multi-range parametric equalization on the subs, otherwise you'll get exaggerated bass, though it might be somewhat less ragged.

If it turns out that (3) suffices, then I will use the 4th with my JBL 305's that I use when on my desktop. If on the other hand, I can fully integrate all (4) of my SB12-NSD's then I will do something different for my 305's. I do listen to a lot of music when on my desktop. Will run my mains X-overed between 80-90 Hz. Of course, that may all change once measurements are taken.

Cheers,

Phil

 

[TheWarrior]

Very nice write-up! Thanks for the info! But, I am still trying to determine which approach would work best for my needs in my room. I have already calculated the axial modes for my room. But, how do I apply that info to my room? That is another place that I am stuck.

Right now not too worried about the miniDSP as that will come later. SVS recommends the miniDSP HD. That will be the last piece to the puzzle. I know that going from a single sub to duals helps smooth out the frequency response a lot. But, how much more so going with (3) or even (4) subs do that. Is it even audible?

Cheers,

Phil

Predicting room modes IS the first step simply because it requires nothing more than a tape measure and some basic algebra. It also defines any 'no-go' locations (if there are any in YOUR room - every room is different) for subwoofers.

Floyd Toole wrote the formula on page 5 of his white paper - Getting the bass right p3.

One sub can work great for a single listener. But assuming you're not asocial, you want to entertain more people. In many rooms, two is still not sufficient (unless you're lucky.) Yet, from what it sounds, you have not yet fully utilized the two you have, so I recommend more math and more measuring before spending more money.

 

[speakerman39]

Predicting room modes IS the first step simply because it requires nothing more than a tape measure and some basic algebra. It also defines any 'no-go' locations (if there are any in YOUR room - every room is different) for subwoofers.

Floyd Toole wrote the formula on page 5 of his white paper - Getting the bass right p3.

One sub can work great for a single listener. But assuming you're not asocial, you want to entertain more people. In many rooms, two is still not sufficient (unless you're lucky.) Yet, from what it sounds, you have not yet fully utilized the two you have, so I recommend more math and more measuring before spending more money.

I have already calculated the modes for each dimension just as Dr. Toole instructed. But, what do I do from there? How do I calculate the wavelengths for said modes? I already have (2) of the SB12-NSD's here and (2) more are on their way as we speak. Tomorrow, I will order a CSL UMiK 1 and already have REW downloaded. So, there will be about 9-12 axial modes that I need to be concerned about right? That is, 3-4 axial modes for each dimensions, no?

Cheers,

Phil

 

[TheWarrior]

I have already calculated the modes for each dimension just as Dr. Toole instructed. But, what do I do from there? How do I calculate the wavelengths for said modes? I already have (2) of the SB12-NSD's here and (2) more are on their way as we speak. Tomorrow, I will order a CSL UMiK 1 and already have REW downloaded. So, there will be about 9-12 axial modes that I need to be concerned about right? That is, 3-4 axial modes for each dimensions, no?

Cheers,

Phil

1130 (speed of sound - feet per second) divided by the frequency (hz) gives you wavelength.

example: 1130fps/20hz = 56.5 ft diameter

Recommend listing your calculations in the format that Floyd did, that way you can more easily see which frequencies suffer from multiple modes. Due to rooms having windows/doors etc, the walls can flex more easily, so measured modes are typically lower in frequency than predicted.

The number of axial modes in a room depends on the room. Mine for example is an open living room, so I've got a lot of work to do still and of course I'm sick today, so my custom sub isn't quite finished. Just running dual SVS PC12s currently.

Your measurements should yield a steady rise in bass from 20 hz, a smooth horizontal line across from there, until around 15khz +/- it tapers off as a result of propagation loss - wavelengths at those frequencies are measured in millimeters, and as most listening is done in the far field (beyond 2-3m) they run out of energy more quickly.

If you are doing all of this, Do NOT run audyssey or any room correction. If you already have, you will need to reset your receiver/preamp. An omni mic in an unknown room, with unknown speakers cannot possibly know what the speaker sent out, and how the room influenced it. (Floyd has written about this in multiple places) This is the controversial part as so many have been bought and sold by the idea of auto setup. The truth is, a good loudspeaker (smooth on axis, off axis, directivity) will sound fine all on it's own just from listening and adjusting the distance from the wall behind, as well as adjusting the distance between and toe in. The trick is getting the bass right below transition frequency of the room (typically 200 hz) and that is why you are doing all of this math. The room is in control, so if you want the best sound, you can mathematically predict ideal locations for subs.

A subwoofer is a pressure source, so you can therefore measure where you have pressure minimums/maximums all around the room (apply a grid 3ft /1m for starters) and that will give you a clear picture of how all these standing waves are influencing your listening position. The subs can be positioned in pressure minimums to boost pressure and vice versa.

Oh, and measure 20hz - 20khz sweep around 80 dB. I've seen people confusing room measurements with max output tests. Cheers!

 

[speakerman39]

1130 (speed of sound - feet per second) divided by the frequency (hz) gives you wavelength.

example: 1130fps/20hz = 56.5 ft diameter

Recommend listing your calculations in the format that Floyd did, that way you can more easily see which frequencies suffer from multiple modes. Due to rooms having windows/doors etc, the walls can flex more easily, so measured modes are typically lower in frequency than predicted.

The number of axial modes in a room depends on the room. Mine for example is an open living room, so I've got a lot of work to do still and of course I'm sick today, so my custom sub isn't quite finished. Just running dual SVS PC12s currently.

Your measurements should yield a steady rise in bass from 20 hz, a smooth horizontal line across from there, until around 15khz +/- it tapers off as a result of propagation loss - wavelengths at those frequencies are measured in millimeters, and as most listening is done in the far field (beyond 2-3m) they run out of energy more quickly.

If you are doing all of this, Do NOT run audyssey or any room correction. If you already have, you will need to reset your receiver/preamp. An omni mic in an unknown room, with unknown speakers cannot possibly know what the speaker sent out, and how the room influenced it. (Floyd has written about this in multiple places) This is the controversial part as so many have been bought and sold by the idea of auto setup. The truth is, a good loudspeaker (smooth on axis, off axis, directivity) will sound fine all on it's own just from listening and adjusting the distance from the wall behind, as well as adjusting the distance between and toe in. The trick is getting the bass right below transition frequency of the room (typically 200 hz) and that is why you are doing all of this math. The room is in control, so if you want the best sound, you can mathematically predict ideal locations for subs.

A subwoofer is a pressure source, so you can therefore measure where you have pressure minimums/maximums all around the room (apply a grid 3ft /1m for starters) and that will give you a clear picture of how all these standing waves are influencing your listening position. The subs can be positioned in pressure minimums to boost pressure and vice versa.

Oh, and measure 20hz - 20khz sweep around 80 dB. I've seen people confusing room measurements with max output tests. Cheers!

Very informative post. Looks like I got my work cut out for me. Going to get started on this today. Have so much to do as well. Time is of the essence! Thanks!

Cheers,

Phil

 

[ATLAudio]

Almost all rooms benefit from two subs, and three to four total subs usually have some benefit. Since like most folks I don't have unlimited locations for placement. I have generous freedom on the front wall, and a few spots on the sides, and two spots behind. A subwoofer might be best in the middle of the room, but domesticated limitations make that a non starter. So I focused on places that will work. I had a dozen plus different measurements.

So, using a umik and REW I measured the sub at the MLP along the front wall in 6" increments, and in all the locations to the side and back. With REW I was able to see where to place my two subs for smoothest response. If I had a third and forth, I'd have a good start to know where they would go too. However, I found that the benefit from one to two subs was substantial, the jump to three and four would be modest.

 

[ATLAudio]

Also, this is Mark Seaton's subwoofer setup guide which I found very useful.

http://www.whatsbestforum.com/showthread.php?15802-A-summary-of-how-I-optimize-subwoofers-in-a-system-Take-1

To summarize some of my thoughts and experience, here's my suggestion for most attacking their system with REW and other measurement systems:

1. Take a subwoofer only measurement in your first subwoofer location while noting signal levels to the subwoofer and volume setting.
2. Do NOT change any signal levels and start moving the subwoofer to any other possible locations saving a measurement at each location. The response should be louder or softer from different locations and you want to see this.
3. Choose the location with the balance of fewest dips and most efficiency across the subwoofer range.
4. If you have more than 1 subwoofer, pick locations that compliment eachother where dips do not overlap.
5. With multiple subwoofers overlay individual responses and then measure both together driven at the same level to see how they sum. Maximum summation of 2 equal sources is +6dB. Unless there is a big peak, the goal is to get the sum to be +0-6dB and not negative. Moving the sub or adding delay to the closer sub is my preferred way to make this adjustment.
6. If manually EQ'ing, now apply EQ to the subwoofer alone while also watching for peaks out to 120-200Hz that go above the target or above flat flat if no HP is in the measurement.
7. Now run any auto-EQ/room correction.
8. Measure the subwoofer alone and center channel alone, then the combination of the two.
9. Make adjustments to the subwoofer distance setting, most often adding to the physically measured distance at 0-8ms.
10. Choose the smoothest interaction and adjust the crossovers up or down if you see room for improvement.
11. If you have separate EQ on the subwoofer you can sometimes improve a lumpy/peaky summation by adding a notch to the subwoofer around the crossover range. The benefit to dialog and music balance far outweighs a small dip to the LFE channel.
12. Next compare the interaction with the left & right speakers making crossover setting and delay adjustments to get a best fit for both.
13. The more you listen to movies & surround concerts, the more you should prioritize the center channel vs. left/right.
14. Now measure what happens when you increase the subwoofer level by 3,6 and 9dB to understand what happens when raising the sub level.
15. Do some listening and adjust the subwoofer level and/or shape to what you are after, and then re-measure subwoofer-center interaction to insure any ramping up in response you add is as smooth as practical.
16. Enjoy!

 

[Dave Blount]

LOL yanking yer chain a bit Phil. Somehow I didn't see your cuft measure, tho Shape of the room counts, too, though as well as positioning of the subs and measured response so really hard to know. I'd think dual subs in a room that size for your own seating would be sufficient....unless you just want to get crazy but spl/headroom wouldn't likely enter into it....

agreed, given room dimensions two properly placed subs should work perfectly

 

[lovinthehd]

agreed, given room dimensions two properly placed subs should work perfectly

At one seat maybe. Perfectly is a big word. Too late in any case, he's got 4 now. Fortunately he's popular with the neighbors and is conscientious.

 

[shadyJ]

You should try toeing in your speakers. Right now you are listening to them off their main axis. Post some measurements when you get the chance.

 

[ATLAudio]

I would definitely want to place a sub in that front left corner and see how that sounds.

Also hang some curtains on that window stat.

 

[ATLAudio]

The fronts on one pre-out, and the rear on the other is likely your best approach. No two subs will measure the same, but at least your distances with be more or less similar with the fronts as a pair and the rears as a pair.

 

[ATLAudio]

Going strictly by the book it's a little too early to run Audyssey, but you might as well since it's basically all you have right now. It'll also give you a good baseline.

This is a very extensive Audyssey How To from Wayne Myers. It explores a lot of the hic ups folks get when using MultEQ, and how to best implement it in your set up.

http://www.hometheatershack.com/forums/audio-processing/68407-audyssey-multeq-faq-setup-guide.html

 

[William Lemmerhirt]

Pretty sure that'll work just fine. So the nsd's have pre outs? If not just use a splitter.


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[William Lemmerhirt]

Yeah I think that's right since the rca connections will not pass anything unless they have power. I used splitters for my rear subs for the same reason.


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[William Lemmerhirt]

Yes indeed. Wait until you start playing with REW. And minidsp! I used a BFD for my eq. It's not beautiful or streamlined and the learning curve is steep but it's effective. Love this stuff.


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[William Lemmerhirt]

You should be in good hands. Plenty of smart guys here.


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[Verdinut]

Three subwoofers are definitely better than two.

Same as Irvrobinson, I use three 15 inch subs for my three identical front channels as part of 3-way system cabinets.
These are actively bi-amplified and, although I haven't as yet done any EQ adjustments on them, I haven't noticed any gross low frequency amplitude deviation below the 200 Hz crossover point.

I mostly listen to classical music including opera and some jazz.

 

[William Lemmerhirt]

Gonna have to dig out the manual. Unless someone else has the same avr and knows off hand.


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[William Lemmerhirt]

Lol. Nope. I won one from home theater shack and minidsp.


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