Single stack / Dual stack

DodgeTheViper

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I know this has been discussed a few times already but just thought I'd ask for any other thoughts.

Lets say Subs are along the front wall and 1/4 distance in from the side walls. And assuming a single stack will fit and even a dual stack will also fit.

Thoughts ?
 
It depends on why you’ve got two subs. If it’s for a smoother response then you need separation. If you need the headroom/volume and have a good response then stack them.

By single stack do you mean two subs and dual stack is four subs?

If it’s four you could have the best of both worlds with two single stacks?
 
Two stacks spaced apart then would be my guess. Depending on what you're trying to achieve.
Which subs?
 
I'm not looking to increase the lower end of the range. More a case of output above 20hz or so.
 
I guessed that.

EDIT: are you hitting the limits, can you not just turn the subs up or run a house curve that rises from 80-20?
 
No, not reaching any limits at all. It's just a musing thats crossing my mind.
 
Do you realise you can simulate stacked subs in REW's Room Simulator? I'd have s play with this if you haven't already.

I'd be surprised if four subs aporopriately distributed around the room wasn't a better way to go though in terms of generating an even frequency response.
 
I'm not looking to increase the lower end of the range. More a case of output above 20hz or so.
If your specifically looking for more upper bass output, what your really talking about it changing the response of your subs to give more of that frequency range. Add in more subs, or stacking or whatever, if they're the same sub they won't give you more 20Hz and up specifically, you'll just get more of the same, or the same as you have now with lower cone excursion.

The caveat to this is that what I say above doesn't account for any change to the in room response.

Stacks in the height axis will reduce and eventually effectively illiminate the height modes of the room and improve overall response, including in the time domain. You don't stack to boost upper frequencies.
 
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We are running 2 x dual stacked X12’s. Front L&R
This increases the headroom of our system.
The X12 has the headroom maximiser circuit. When you start to push a single subwoofer, when the amp and driver start to reach their limit, you will see compression in the frequency response. Compression introduces distortion. The circuit in the X12 resolves this by reducing low end output slightly as you go louder. The affect on the frequency response looks similar to compression (the very low end won't increase as much as the upper bass), but the circuit does this without the actual compression and distortion.

When you add multiples, you're reducing the input signal and the amount of output from each subwoofer for any given spl. This means the maximiser circuit won't kick in as early, so that flat to sub 20Hz frequency response can be maintained to higher spl's. While increasing headroom is a key benefit, with the X12 it also means greater low frequency output at higher spl as the system doesn't need to worry about compression as much, which effectively means it can maintain that flat frequency response for longer as you increase volume.
 
Stacks in the height axis will reduce and eventually effectively illiminate the height modes
But at the expense of less control over longitudinal and width modes compared to distributing the same subs more widely around the room.

Having subs at different heights does make sense but putting the higher sub on top of something other than a load of other subs would be a better option overall I think, in terms of maximising the benefit of a given number of subs.

Last weekend's Bristol HiFi show had a stereo setup with Rel employing stacks of three subs per side. It didn't though employ any EQ or time delay correction and to be honest I found it utterly underwhelming. I'm pretty confident I could have achieved better with a single sub and EQ (which would cost a lot less!)
 
But at the expense of less control over longitudinal and width modes compared to distributing the same subs more widely around the room.

Having subs at different heights does make sense but putting the higher sub on top of something other than a load of other subs would be a better option overall I think, in terms of maximising the benefit of a given number of subs.

Last weekend's Bristol HiFi show had a stereo setup with Rel employing stacks of three subs per side. It didn't though employ any EQ or time delay correction and to be honest I found it utterly underwhelming. I'm pretty confident I could have achieved better with a single sub and EQ (which would cost a lot less!)
You don't get less control, at worst you get the same as you would have had, but typically you should get some slight benefit at least. A full hight stack creates a different type of pressure wave in the room compared to a single sub. A single sub in the bottom corner creates a spherical bubble pressure wave, whereas a stack at full height creates a cylindrical pressure front that pushes through the room in a much more uniform way. This is why the height mode is eliminated. The width modes will largely exist as they were, except you should only really be getting reflections directly from the side in the horizontal plane, none (or much reduced) of the issues associated with reflections at angles off the horizontal plane (hopefully that makes sense). The additional subwoofers will add headroom, reducing overall distortion which in conjunction with the removed height mode leads to an overall cleaner sound that should also be more detailed. Drivers with only 25% of the excursion in play can naturally stop faster for example.

I can't comment on Rel, but they seem to have a very old school Hi-Fi mindset from the dealings I have had with them and your experience wouldn't surprise me. That said, I think trade shows are a terrible way to get to hear any products personally. I see a lot of these types of companies ignoring things like electronic eq (go look on youtube at any video from Acoustic Fields where they talk about bass or subwoofers), but honestly and cost aside, I cant see you taking a single subwoofer with eq and putting it against a dual-stack of Rel 15 inch subwoofers in your same room and the Rel stacks being clearly worse. Obviously you would hope not. FWIW though, Im actually still have a little bit of a soft spot for Rel subs.
 
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You don't get less control, at worst you get the same as you would have had, but typically you should get some slight benefit at least.
I think you misunderstood my point. By distributing subwoofers appropriately around the room you can even out the frequency response caused by room modes. To do so with regard to a longitudinal mode you need subs at different positions along the length of the room, and to do so for width modes you want subs at different positions across the width. My point was that by stacking subs you are trading off the benefits of different heights against the benefits of different length or width positions.

Consider some of Erle Geddes multi-sub arrangements Vs having the same number all in a single stack somewhere.
 
but honestly and cost aside, I cant see you taking a single subwoofer with eq and putting it against a dual-stack of Rel 15 inch subwoofers in your same room and the Rel stacks being clearly worse.
This wasn't my original comparison but actually I would take a single decent sub with EQ vs 6 without EQ in my own lounge. It's not huge (about 4.7 m x 3.5 m) so one sub is loud enough and I have a very pronounced mode at around 36 Hz, the boom of which is horrible when excited. Note my main focus is music so I prioritise quality over all-out volume, although frankly a single PSA S1510 has more headroom even for movies than I'll use.
 
I think you misunderstood my point. By distributing subwoofers appropriately around the room you can even out the frequency response caused by room modes. To do so with regard to a longitudinal mode you need subs at different positions along the length of the room, and to do so for width modes you want subs at different positions across the width. My point was that by stacking subs you are trading off the benefits of different heights against the benefits of different length or width positions.

Consider some of Erle Geddes multi-sub arrangements Vs having the same number all in a single stack somewhere.
Even the Harman white papers and pretty much anything you read anywhere will support the idea of spreading subwoofers out to tackle room modes. All your really doing is trying to fill in any dips in response. Stacking can still help with this, stacking subs is, after all, distributing multiple subwoofers. throughout the room. I know of an employee for a subwoofer manufacturer that uses 4 x dual 8" subwoofers placed throughout his room at the centre points of each of the 4 walls, apparently the results are stunning.

You could line subwoofers across the entirety of the front of your room and achieve the same effect as stacking, you just cancel the width modes instead of the height. The only way to really know which is best is to measure the room but whichever way you line subwoofers, you will always gain benefits, it's just typically more convenient to stack in most rooms, whether you're trying to reduce the number of active modes in your room, trying to increase headroom, or both. All of these goals are positive.
This wasn't my original comparison but actually I would take a single decent sub with EQ vs 6 without EQ in my own lounge. It's not huge (about 4.7 m x 3.5 m) so one sub is loud enough and I have a very pronounced mode at around 36 Hz, the boom of which is horrible when excited. Note my main focus is music so I prioritise quality over all-out volume, although frankly, a single PSA S1510 has more headroom even for movies than I'll use.
The question here is, is that peak caused by a height mode, a longitudinal one, or otherwise. Axial modes are typically the strongest so that would be the safe bet, but Id generally agree with your principles here. The old school way to fix the peak would be to move the subwoofer away from the corner or move your seating away from the boundaries, or a bit of both. The beauty of electronic eq is you don't have to do that (suffering the potential negative side effects of doing this like loss of boundary gain or the introduction of more modes), and like yourself, I'm a big advocate of room correction used in the right way to improve in-room response with the goal of ultimate accuracy.
 
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Even the Harman white papers and pretty much anything you read anywhere will support the idea of spreading subwoofers out to tackle room modes. All your really doing is trying to fill in any dips in response. Stacking can still help with this, stacking subs is, after all, distributing multiple subwoofers. throughout the room. I know of an employee for a subwoofer manufacturer that uses 4 x dual 8" subwoofers placed throughout his room at the centre points of each of the 4 walls, apparently the results are stunning.

You could line subwoofers across the entirety of the front of your room and achieve the same effect as stacking, you just cancel the width modes instead of the height. The only way to really know which is best is to measure the room but whichever way you line subwoofers, you will always gain benefits, it's just typically more convenient to stack in most rooms, whether you're trying to reduce the number of active modes in your room, trying to increase headroom, or both. All of these goals are positive.
My point is that I think it's likely that an approach that addresses all directions will virtually always be better than just focusing on one, which is why I think generally stacking will be worse than a more distributed approach. The main point though is that there are potential trade-offs and so different options should be compared.

The question here is, is that peak caused by a height mode, a longitudinal one, or otherwise.
It's the lowest longitudinal axial mode. There are other modes too of course although I've reduced their effect significantly with corner bass traps.

@DodgeTheViper will I'm certain be using EQ though so we're straying off-topic. Here's a photo of the REL stacks I mentioned to get us back on track :). The subs in question were the S/510 model.

REL array.jpg
 
Pursuit Perfect System just released a two part video showing the REL S/510 line array demonstration from Bristol HiFi. The first part primarily talks about the technology behind these subs, while the second part goes into more detail regarding the benefits that we find with stacking subwoofers.

Part One:
Part Two:
 

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