downsizing from Seaton Submersive to Rythmik

[SeattleDucks]

Hi all,

i am moving cross-country from Seattle to Florida and downsizing our home and the theater room. I had a Seaton Submersive HP that I was pleased with but did not want to risk damaging it in the move and did not want a sub that large in my new small dedicated room in Florida, so I sold the SubM and I have decided on Rythmik for the replacement.

The new home is a villa townhouse style that has one shared wall (a pretty massive firewall separating me and my neighbor, two layers of concrete plus insulation in the middle). The HT room is on the opposite side of the house as that shared wall and is completely enclosed and only 1450c.f., carpet/pad over concrete slab with cinder block exterior wall construction and standard studs with drywall interior. The room has a total of 9 bass/acoustic traps from GIK. Usage is 90% movies and volume is typically not louder than -15db from reference. I plan to try the Rythmik nearfield directly behind or next to the couch so that further reduces the need for a high output sub and keeps the gain lower so bass is less likely to disturb neighbors.

Based on the usage of this small room, do you think an F12 will likely be sufficient? Or is there a compelling reason to spend more money and tolerate the larger size of an F15 or D15SE?

Thanks,
Ross

[FirstReflect]

hmm... This one is a bit tricky because you've got several variables all changing at the same time. You're going to have a new subwoofer producing the bass, a new, smaller room reflecting those bass sound waves, and new placement that will potentially have a large impact on the tactile impact and linearity of the frequency response at the seat.

So one way to think about it is to consider one variable at a time.

If you were to put a Rythmik F12 in your old room, in the spot where your Seaton used to be, you'd likely notice quite a difference! The biggest change is below 40Hz. The F12 has the natural 12dB/octave roll off that you would expect from a sealed subwoofer. And as you crank the volume way up high, the output starts to compress as the distortion goes up.

The F12 is a great sub, with a surprising output capability above 40Hz. But it can't match the headroom and sheer output of the Submersive HP - obviously ;) The 40-50hz range is the fun, "hit-you-in-the-chest" tactile range. And the F12 can rock out there really nicely! But there's a really special tactile effect in the really deep 20-25Hz stuff. That's the "blur your vision" and "rattle your teeth" range. That's a speciality of the huge Seaton! Very few subs can match what the Submersive HP can do in that range.

So you'd be giving that up with the F12. You just can't recreate the "blur your vision" tactile effect from a sealed, compact 12" sub :)

Now, let's consider the effect of the much smaller room. Your use of several bass traps should aid in keeping the worst of the 60-100hz resonance to a minimum. That's the really annoying "boomy", "ringing" bass that usually causes complaints when people don't have any bass trapping in their room. But down low, you're going to have a lot of room gain. Enough that at 85dB, the natural roll off of the F12 combined with the room gain should result in a pretty flat frequency response so long as you're not sitting in a node ;)

The issue is when you start to crank up the volume in order to get that "blur your vision" tactility back way down low. We humans detect really low bass so poorly that those 20-25Hz frequencies need to get up over 95dB before we start to even notice them, really. The F12 compresses and stops getting any louder way, way down low pretty quickly. So if you're after the 115dB peaks that are called for from full Reference Volume, even in the small room with all that room gain, the F12 just isn't playing the 20Hz stuff loud enough to get there.

But you're in a townhouse with a neighbor physically connected to you now. You've pointed out that your theatre should have some decent soundproofing and distance from that neighbor. But bass is exceptionally difficult to contain. STC ratings are based on the A-weighting scale, and even on the larger C-weighting scale, deep bass below 70Hz is all but ignored. Being so long and powerful, a huge percentage of bass sound waves get reflected back into the room by the walls, which is why bass is virtually omnidirectional in any room. The reflections just bounce around in there like crazy! But also because they're so long and powerful, bass waves travel exceptionally easily via the structure of your building vs. airborne transmission. So the real key for soundproofing and containing bass is decoupling and damping. Prevent as much physical vibration transfer as possible! The airborne stuff will do what it will do. Keep the room as close to air tight as you can, and the majority of the airborne bass will reflect within the room, and be contained. Carpet pad over concrete is a good start, but if your subwoofer had "feet" of any kind (or worse yet, spikes), those can compress any carpet pad rather easily, and wind up physically coupling the subwoofer to the floor again. A flat bottom sub (with lots of surface area as a result) should fare well on just the carpet pad as the damping device. It's all about pounds per square inch! But if you really want to be safe, go ahead and build or buy a riser. Get that subwoofer decoupled! And don't for a minute think that concrete is inert. It ain't! Far from it, in fact. Concrete will transmit physical vibrations easily well enough to bother an attached neighbor!

So, I have to assume you had a Seaton Submersive HP because you love bass, love high output, and love tactile bass, both in the "hit you in the chest" AND in the "blur your vision" ranges. It's going to be tough to keep both in your new room without bothering your neighbor. But if you still want to even have the option, I'd caution that the F12 is not a 20-25Hz champ. You'd be losing the "blur your vision" stuff with that choice ;)

Placement has less effect than one might imagine. Where you really notice it is in the upper bass. In the really deep bass, the sound waves are so long that you just can't detect them until they've bounced around the room for a while, anyway!

So that creates a conundrum. You have to turn down the volume overall so that the upper bass (above 60Hz) doesn't sound overblown, boomy, or "chesty". But if you do that (due to a nearfield placement), you further decrease the output in the really deep bass. That means you either need to EQ it like crazy, or you need to use a sub that can play really flat all on its own right down to 20Hz.

So, you straight up do not need the sheer output of a Seaton in a small room :) But if you still want the really deep "blur your vision" tactile effect, you still need some pretty potent output down there, simply because we humans detect that deep stuff so poorly! You'll get more room gain than in a larger room, but you still need solid, natural 20Hz output from the sub itself if you want to hit full Reference Volume.

For placement, you have a choice. If you place the sub really close to your seat, your sub needs to be as linear and extended and flat as possible. If you position the sub farther away, you'll have more of a curved output, with the room gain supplementing the deep bass, and then the mid and upper bass being a little bit louder from the sub itself to compensate for the distance.

So, if you go sealed, IF you want that deep "blur your vision" tactility, put it as far away from your seat as you can, and get one that can still pump out high output way down deep all on its own. That'd be one of the larger sealed Rythmiks, or possibly even a sealed SVS Ultra or Velodyne DD or DD-Plus.

If you want the nearfield placement, I'd suggest going ported for a flatter output right down to 20Hz.

Finally, dual subs are the only way, especially in a small room, to get even frequency response across more than one seat. It seems counterintuitive, because it has nothing to do with playing louder. But two subs are more important in a small room than a big one! It's all about evening out the frequency response throughout the entire seating area using controlled interference between the bass waves. That requires optimal placement, too. So it's complicated. But one sub in a small room can only be EQ'd to be linear at ONE seat. If that's all you really care about - one seat - then a lone sub is fine :)

[SeattleDucks]

Thank you for your thorough reply, it helped me flesh out my priorities in the new home.