Dual Opposed Subwoofer & Room Acoustics

[win]

If you are willing to put in a bit more work, multi-sub optimizer is amazing software and totally free. It can basically get the frequency response, at an arbitrary number of seats, to an arbitrary degree of flatness.

I am similar to you in that my choice was mostly aesthetic, which is why I went with the sb-1000, it's white and easily blends in. I have 4, but running just two through multi-sub optimizer still produced remarkably flat results. Good to have one in a corner and another somewhere - anywhere - else. Let the software optimize it.

 

[Chrispy]

Damn, that link is very interesting indeed. Seems to support the notion that dual opposed could smooth out room response a bit for a single sub.

You all are about to make me buy a pair of G22s to hedge bets both ways!

I don't read it that way, they're co-located (within a quarter wavelength of each other for most of their range), so room smoothing isn't a particular benefit IMO. By itself it's just a sub IME.

 

[Elk]

Welti's and Devantier's research on subs in square rooms (a worst case) state that the use of two subs at mid points on opposite walls controls the rooms standing waves well and evens out the bass response throughout the room almost as well as 4 subs at mid points on all four walls. The downside is their volume levels have to be higher because the corners of the room are not helping to amplify their outputs. I use the method and wouldn't go back. See section 4 if the whole article is a bit much: https://audioroundtable.com/misc/Welti_Multisub.pdf

 

[syzygetic]

Unfortunately I don’t think it’s that simple.

Are you optimizing for multiple seating locations our just your one seat? If just one seat, I’m reasonably confident you can get one sub with good placement and eq to work.

If you want even bass over 2 or more seats, it’s tougher.

The results you get depend entirely on your room at subwoofer frequencies. You might be lucky have both good and even bass from just one sub. Totally depends in the room, and it’s somewhat of a crap shoot as most real world rooms are hard to model—they are not rectangular boxes.

My room is open on 3 sides in the mid wall to other rooms, and the back wall is a giant bay window, which lets bass right through. I can place a sub anywhere in my room and get giant suck outs in mostly the same frequency ranges. And moving across seats—really inconsistent bass with wide variation in frequency response. Othears get a big bass boost that’s easy to knock down, with more consistent bass response across seats w/ no fancy multi-sub optimization.

In my room, I can only get good results with multiple sub optimization, and even then I still have one consistency problem that I need to work out at around 60hz, where there is a dip on some seats.

Question about glass: you mention that this bay window causes a suck-out. Coincidentally, the room I described is actually a glass cube. It's hardly more than a hard tent, not kidding. If I didn't have a wood stove, winter would be brutal. So... are really large windows, and many of them, a problem for bass? Maybe I just have to measure to find out?

 

[yourmando]

Question about glass: you mention that this bay window causes a suck-out. Coincidentally, the room I described is actually a glass cube. It's hardly more than a hard tent, not kidding. If I didn't have a wood stove, winter would be brutal. So... are really large windows, and many of them, a problem for bass? Maybe I just have to measure to find out?

I’m not sure at all if the giant bay window at my place causes the suck out—it could just be the geometry of the room and the shape of all of the open areas, and the total volume of the room plus adjacent room. Trying to model it is way above my pay grade.

People pay a lot of money for bass traps—you have all of that for free

It could be that at bass frequencies, your room could act more like a 2pi free field space. That would be good for very even bass, but you’d lose some SPL because any off axis bass would essentially go out the window. You might even have short decay times because of that. Paired with a sealed, low Q dual opposed subwoofer, your bass might be very ”tight” and accurate.

But in practice, I‘m sure the bass would model differently than that naive model I just mentioned.

Concrete floors can be challenging for a lot of people, as you tend to need a lot more output for the same in room SPL.

Maybe you’re on to something, though. My walls are very open to rooms, and each room has massive bay windows. Outer walls are really more glass than solid wall Some pros for me though is that my room is very symmetrical, and the side walls open exactly where I would want absorption panels, creating a kind of built in “reflection free zone.” Might not be great for bass though!

Final selling point for multiple sub—if you add 2 or more of the same Rythmik sub to your cart, you will get a discount.

 

[sigbergaudio]

Dual dual opposed is always a good way to go You might find this interesting on the measurement of a dual-opposed sub....I have an Empire myself. https://data-bass.com/#/articles/5cb4eb62079a580004e73249?_k=0ph329

Hm, wonder if the same disadvantage in measurements is present in downfiring subs (where the driver can't be directed at the microphone unless you put it on its side).

 

[yourmando]

Hm, wonder if the same disadvantage in measurements is present in downfiring subs (where the driver can't be directed at the microphone unless you put it on its side).

As you say, down firing shouldn’t be a problem for measurements because it can be positioned on its side for 2pi ground plan measurements, or 4pi free space measurements.

 

[detlev24]

About dual-opposed sealed subwoofers : maybe this helps a bit.

 

[sigbergaudio]

Hm, wonder if the same disadvantage in measurements is present in downfiring subs (where the driver can't be directed at the microphone unless you put it on its side).

For those interested, I actually tested this, and having the subwoofer on its side with the driver facing the microphone gave roughly the same results as measuring in the down-firing position.