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Dual opposed vs line array

post #1 of 67
12/30/12 at 3:59pm
Thread Starter 
As we see a lot more DO builds popping up, I'm curious as to the principles behind these and if they are really superior to line array builds.

We know that DO have a cancellation effect, but is this something that's going to translate into real world benefit? My last few subs all employed dual drivers, and none of them seemed to transfer any forces into the surrounding area.

Is there any other reason to build them in lieu of conventional stacked woofer designs?
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post #2 of 67
12/30/12 at 5:15pm
I assume you're referring to subs, as that's the only genre where dual opposed is used. Line array subs are seldom used, as there's no major benefit to a line array unless it's at least 3 wavelengths high. At 40 Hz that's 84 feet
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post #3 of 67
12/30/12 at 5:24pm
Bill,
Why do you cross fire woofers in your bass cabs?
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post #4 of 67
12/30/12 at 5:30pm
I think the OP was referring to just having dual front firing, as opposed to a true line-array, vs dual opposed smile.gif But correct me if I am wrong!
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post #5 of 67
12/30/12 at 6:18pm
The bigger effect from opposed firing woofers is that you can turn the rear one around without having to look at an ugly basket. Yes opposed firing cancels out vibrations, but if you don't turn one around, there's not a huge benefit. However, the more linear a woofer operates, the less the benefit with turning a woofer around.
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post #6 of 67
12/30/12 at 6:48pm
Quote:
Originally Posted by Looneybomber View Post

The bigger effect from opposed firing woofers is that you can turn the rear one around without having to look at an ugly basket. Yes opposed firing cancels out vibrations, but if you don't turn one around, there's not a huge benefit. However, the more linear a woofer operates, the less the benefit with turning a woofer around.

What do you mean by turning woofer around? Making it fire inside the cabinet?
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post #7 of 67
12/30/12 at 7:40pm
Thread Starter 
Quote:
Originally Posted by beastaudio View Post

I think the OP was referring to just having dual front firing, as opposed to a true line-array, vs dual opposed smile.gif But correct me if I am wrong!

That is correct. I sometimes don't word things perfectly. smile.gif

In my upcoming build I have a few options, and am curious about the benefits or drawbacks to each.

I have a few different options I'm weighing. Based on room size and wanting to keep everything behind the screen, I am waffling between a few different setups.

1) 6 woofers - 3 per cab aligned vertically firing forward. I like this setup, but am concerned about vibrations transferring to stage. (Stage is heavily damped and filled with sand so maybe not a huge deal, but a concern never the less.)

2) 6 woofers - This one is a little interesting. One woofer on each side and one firing forward. I'd get some effects from dual opposed, while also having a nice frequency dispersion which might help with evening the FR.

3) 4 woofers - Opposed setup with each driver firing to the sides. I'd save the other two for backups. smile.gif

The 4 and 6 driver setup both produce almost the exact same SPL. The 6 driver setup has more surface area but will only get 2500 watts. The 4 driver setup will get about 1300 more watts. The 6 driver does benefit from less excursion, but I don't know if that would translate into real world noticeable differences.
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post #8 of 67
12/30/12 at 7:52pm
I think the only advantages of dual opposed are less cabinet material and its more inert.

I'm Making two DO's now and I might add a couple singles around the room later.
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post #9 of 67
12/30/12 at 7:57pm
Thread Starter 
Quote:
Originally Posted by brian6751 View Post

I think the only advantages of dual opposed are less cabinet material and its more inert.
I'm Making two DO's now and I might add a couple singles around the room later.

It's not really that much less material.

Inert, like the gas? smile.gif
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post #10 of 67
12/30/12 at 8:04pm
Quote:
Originally Posted by bass addict View Post

It's not really that much less material.
Inert, like the gas? smile.gif

Inert- In English, to be inert is to be in a state of doing little or nothing. As in, not shaking.

Its not much material but depending on your design it could mean needing another sheet. also, its easier to build two DO cabs than it is four singles.
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post #11 of 67
12/30/12 at 8:31pm
Thread Starter 
Quote:
Originally Posted by brian6751 View Post

Inert- In English, to be inert is to be in a state of doing little or nothing. As in, not shaking.
Its not much material but depending on your design it could mean needing another sheet. also, its easier to build two DO cabs than it is four singles.

I was just messing with you, but thanks for the wikipedia discourse. biggrin.gif

Where in my post did I make mention of single cabs?
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post #12 of 67
12/30/12 at 8:38pm
I know. I was just being a smart ass. smile.gif

You didn't mention singles. I just mentioned them as a plus for DO but I would think they would still be easier to build than two drivers in the same cab firing the same way.
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post #13 of 67
12/31/12 at 6:19am
Quote:
Originally Posted by zheka View Post

Bill,
Why do you cross fire woofers in your bass cabs?
I don't.
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Yes opposed firing cancels out vibrations
Opposed firing would cancel vibrations if the drivers were wired out of polarity. As that would also cancel their output it's not recommended. The advantages to opposed is the halving of the baffle size required compared to having both drivers on the same baffle, and the cancellation of vector forces that otherwise might cause the speaker to 'dance'.
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post #14 of 67
12/31/12 at 6:37am
Vector force cancelation. There BA. Is that better than inert gas? Lol!
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post #15 of 67
12/31/12 at 6:56am
Quote:
Originally Posted by zheka View Post

What do you mean by turning woofer around? Making it fire inside the cabinet?
Yes. It's a tactic for reducing even order harmonics invoked by driver non-linearities.
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post #16 of 67
12/31/12 at 7:41am
Quote:
Originally Posted by Looneybomber View Post

Yes. It's a tactic for reducing even order harmonics invoked by driver non-linearities.
That's the official line, but if it's driver non-linearity that causes harmonic distortion then cancelling it would require that the two drivers be identically non-linear. As the harmonics in question have relatively short wavelengths the drivers would have to be mounted on the same baffle, tightly spaced and precisely time aligned. That doesn't mean there's no validity to the theory, but in practice it's a lot of effort invested for minimal gain.
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post #17 of 67
12/31/12 at 8:01am
Thread Starter 
Quote:
Originally Posted by Bill Fitzmaurice View Post

I don't.
Opposed firing would cancel vibrations if the drivers were wired out of polarity. As that would also cancel their output it's not recommended. The advantages to opposed is the halving of the baffle size required compared to having both drivers on the same baffle, and the cancellation of vector forces that otherwise might cause the speaker to 'dance'.

And that's the question of the day. In real world scenarios, is there going to be a noticeable difference between opposed and vertically aligned?
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post #18 of 67
12/31/12 at 8:05am
Bill,

it's your guitar cabs, not bass cabs, that use dual cross-firing woofers. my bad.

http://www.billfitzmaurice.com/XFCabs.html

is there any benefit from something like this when it comes to LF transducers?
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post #19 of 67
12/31/12 at 10:20am
Quote:
Originally Posted by zheka View Post

Bill,
it's your guitar cabs, not bass cabs, that use dual cross-firing woofers. my bad.
http://www.billfitzmaurice.com/XFCabs.html
is there any benefit from something like this when it comes to LF transducers?
No, it's purely a midrange and high frequency dispersion tool.
Quote:
Originally Posted by bass addict View Post

And that's the question of the day. In real world scenarios, is there going to be a noticeable difference between opposed and vertically aligned?
Maybe. If I was going to do a dual driver direct radiator I'd probably go dual opposed, if only because they potentially might work better than a single driver cab. I wouldn't do a dual driver vertically aligned as it offers no benefit over a pair of single driver boxes.
Edited by Bill Fitzmaurice - 12/31/12 at 10:26am
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post #20 of 67
12/31/12 at 10:30am
I would think one of the main benefits of a line array like the op is talking about (6 driver) would be exciting multiple room modes from a single sub location. It should have superior in-room performance vs a 6 driver cube sitting in the corner.
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post #21 of 67
12/31/12 at 10:33am
Thread Starter 
Quote:
Originally Posted by Jay1 View Post

I would think one of the main benefits of a line array like the op is talking about (6 driver) would be exciting multiple room modes from a single sub location. It should have superior in-room performance vs a 6 driver cube sitting in the corner.

Yup, but that's also the quandry.

If I do vertical it would be 3 per cab, arranged vertically. Total of 2 cabs.

The opposed would be the same setup, 2 per cab, total of 2 cabs. I've heard the opposed has better dispersion, so it might be splitting hairs between the opposed and vertical with one extra driver.

My main concern still comes back to forward firing vs side firing and how much resonance will be introduced into the stage from front firing vs opposed.
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post #22 of 67
12/31/12 at 11:04am
I know this is outside of the two ideas you are comparing, but I think you should also consider an arrangement like bosso has built.. This may not be an option for you, however he has posted rather positive results using his DO arrays. I wanted to go this route myself but lack the space to do it in vertically. I have not seen any results from anyone comparing a line array vs DO. I think it would be a very cool experiment.
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post #23 of 67
12/31/12 at 12:39pm
Quote:
Originally Posted by Jay1 View Post

I would think one of the main benefits of a line array like the op is talking about (6 driver) would be exciting multiple room modes from a single sub location. It should have superior in-room performance vs a 6 driver cube sitting in the corner.
Where adjacent drivers are within 1/4 wavelength of each other they'll couple to create a single source. Even six drivers would still couple to a single source. If taming room modes was that simple that's how we'd do it.
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My main concern still comes back to forward firing vs side firing and how much resonance will be introduced into the stage from front firing vs opposed.
The results would be identical.
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I've heard the opposed has better dispersion, so it might be splitting hairs between the opposed and vertical with one extra driver.
Within the subwoofer passband dispersion would also be identical.
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post #24 of 67
12/31/12 at 12:55pm
Thread Starter 
Quote:
Originally Posted by Bill Fitzmaurice View Post

Where adjacent drivers are within 1/4 wavelength of each other they'll couple to create a single source. Even six drivers would still couple to a single source. If taming room modes was that simple that's how we'd do it.
The results would be identical.
Within the subwoofer passband dispersion would also be identical.

So other than aesthetics, there should be no difference between stacked and opposed (in regards to dispersion, transferred energy, etc).

If that's the case I'll probably go with forward firing just because. Now I just need to decide if I want more drivers with less power, or less drivers with more power.
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post #25 of 67
12/31/12 at 1:05pm
Quote:
Originally Posted by Bill Fitzmaurice View Post

Where adjacent drivers are within 1/4 wavelength of each other they'll couple to create a single source. Even six drivers would still couple to a single source.

do subwoofer arrays truly act as point source across the passband?
40 Hz 1/4 wavelength is approx 7 feet. It seems like many wall to wall arrays we are seeing around here may not sum perfectly above this frequency, at least where the drivers most distant from each other are concerned. Am I wrong about this?
Edited by zheka - 12/31/12 at 1:16pm
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post #26 of 67
12/31/12 at 1:17pm
Quote:
Originally Posted by zheka View Post

do multidriver subwoofer arrays truly act as point source across the passband?
40 Hz 1/4 wavelength is approx 7 feet. It seems like many wall to wall arrays we are seeing around here may not sum perfectly above this frequency, at least where the drivers most distant from each other are concerned. Am I wrong about this?
All sources act as both point and line sources, depending on the frequency. Where the source is at least 3 wavelengths in dimension it has line source characteristics, where it's shorter it has point source characteristics.
Don't confuse this with mutual coupling. That occurs where sources are less than 1/4 wavelength apart. Where they're further apart they act as individual sources. With subs it would be difficult for any array not to fully couple. The distance from one end of the array to the other need not be less than 1/4 wavelength, only the distance between each element.
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post #27 of 67
12/31/12 at 1:38pm
i think i understand the source of my confusion now. thank you.
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post #28 of 67
12/31/12 at 1:45pm
Thread Starter 
Quote:
Originally Posted by zheka View Post

i think i understand the source of my confusion now. thank you.

No pun intended lol.
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post #29 of 67
12/31/12 at 2:49pm
Quote:
Originally Posted by zheka View Post

i think i understand the source of my confusion now. thank you.
It's very confusing, when you consider that one cab can be both a line array and a point source, and the individual drivers within can be fully mutually coupled at some frequencies and not at others, while if the listening distance is sufficient all speakers or arrays are point sources, and all drivers or speakers are fully mutually coupled. With large concert sound arrays that scenario takes place at about 300 feet out, give or take.
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post #30 of 67
12/31/12 at 2:50pm
Thread Starter 
Quote:
Originally Posted by Bill Fitzmaurice View Post

It's very confusing, when you consider that one cab can be both a line array and a point source, and the individual drivers within can be fully mutually coupled at some frequencies and not at others, while if the listening distance is sufficient all speakers or arrays are point sources, and all drivers or speakers are fully mutually coupled. With large concert sound arrays that scenario takes place at about 300 feet out, give or take.

If this is the case, why do so many claim design superiority with opposed builds. Few different sites I've searched people mention the opposed due to better performance.
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