[JWCoffman]

After watching Dune on my MTM + X-CS setup, I am finally pulling the trigger on a couple sealed servo subs to replace my flabby legacy sub.  The movie sounded great except for anything below 40hz (where Hans Zimmer loves to play).
I'm ordering 2 servo subs, and I hope to build them during an upcoming much-needed vacation from work in a couple weeks.
I have a couple questions for the fine folks here:
- Is it worth doing the sand-filled sub box?  I don't mind the extra work and weight, but not if it's going to yield minimal results.
- Poking around I noticed that Rythmik has a down-firing version rather than a front firing version that is shown on the GR Research site.  Any experience or insight into which might be preferred?  I like the idea of a stealthy down-firing box even though it needs to have some significant space under the driver, but I have a feeling room placement might be more critical in that case.

The possibility here is a modified down-firing sand-filled box, which would require some reworking of the plans.
Also, I really wish I had done this 6-months ago as prices have skyrocketed since then for both the components and building materials.  Oh well, it's still cheaper and more fun than getting one "off the shelf".

[Chops]

As far as front firing vs down firing, there's really no difference at all as long as you keep the crossover point low enough (80 Hz or lower). If you plan on running the subs any higher than that, then front firing is definitely the optimal way to go.

[I.Greyhound Fan]

I  have 2 Martin Logan subs that can be oriented forward or down.  The bass is slightly better downward firing on hard floors but its sounds better forward firing on carpet.  I have wood floors and if the subs are down it affects my Turntable, so I have them facing front.

My son has a Rythmik F12se and it sounds great.  I don't think it hits you hard in the chest like an SVS 3000 or 4000 though, so if you want that, go with a different sub.  Otherwise, it is very musical and has excellent controlled bass with no boom or muddiness.

[mgalusha]

I have three GR/Rhthmik servo subs. My original cabinets were rough plywood. I had a guy build me some beautiful cabs with very thick MDF. Much to my surprise they didn't sound as good. The plywood ones were really well braced. I ended up adding some hard maple bracing to the new cabinets, took care of the problem. I can't say how well the sand filled works but having them stiff made even the very heavy and dense MDF boxes sound much better.

[mlundy57]

It's a matter of preference. I have two servo subs. One is the regular well braced cabinet and the other is a sandbox. Both are very good cabs. The sandbox is a royal pain to move around though.

[JWCoffman]

As far as front firing vs down firing, there's really no difference at all as long as you keep the crossover point low enough (80 Hz or lower). If you plan on running the subs any higher than that, then front firing is definitely the optimal way to go.

Good point.  This would be crossing over in the +/-40hz range, perhaps as high as 50hz depending on how measurements go.  Directionality shouldn't be an issue.

I  have 2 Martin Logan subs that can be oriented forward or down.  The bass is slightly better downward firing on hard floors but its sounds better forward firing on carpet.  I have wood floors and if the subs are down it affects my Turntable, so I have them facing front.

My son has a Rythmik F12se and it sounds great.  I don't think it hits you hard in the chest like an SVS 3000 or 4000 though, so if you want that, go with a different sub.  Otherwise, it is very musical and has excellent controlled bass with no boom or muddiness.

This is very helpful.  This will be on a laminate floor on top of a concrete slab, so it sounds like downward might be preferable in this case.  Or at the very least not a detraction.  I'm finding I really appreciate the texture and immediacy of tighter bass as I get older, and that I listen to music much more on these speakers than I anticipated.  I'm not as interested in "hit you in the chest" bass, even with movies.  The issue I had with Dune was not the lack of "thump" but that it didn't blend well with the precision of the front 3 speakers and just sounded muddy.  I never noticed that issue with the old Klipsch's I had, but I really notice it now.  I'm also hoping that two well placed subs with some more room treatment will help tame the room mode I have at ~44hz.

It's a matter of preference. I have two servo subs. One is the regular well braced cabinet and the other is a sandbox. Both are very good cabs. The sandbox is a royal pain to move around though.

Thanks Mike, I'm inferring here that you don't really notice a big difference between the two?  If so, keeping it simpler, cheaper, and lighter is perhaps a good plan.

[mlundy57]

For myself, I wouldn’t go to the trouble of the sandbox but I’m sure there are others who would disagree.

[Tyson]

I'd go with an MDF box braced internally with something very stiff like oak.  MDF resonates at 1 frequency and the oak at another.  This will give you a much better, more inert cabinet than if you only used one type of material.

[Vince in TX]

I have a pair of OB Servo Sub 4s, and Dune was absolutely phenomenal in the low frequencies.   Combine that with the Soundshakers in the seats, and those worms were IN my theater room.  Amazing.

[Rikard Ekval]

I'd go with an MDF box braced internally with something very stiff like oak.  MDF resonates at 1 frequency and the oak at another.  This will give you a much better, more inert cabinet than if you only used one type of material.

Yes Tyson. More info if possible. In what range does the different resonate? In general. I do understand there are different versions of MDF and how dense and old the oak is, but can you enlighten us a bit more?

[dinoadventures]

I have tried to make a pair of the sandboxes but apparently my skills with a table saw are inadequately precise since if you are off even a little on the inner box it all has to be corrected before building the outer box. Even if there were a CNC'd flatpack for it I don't think it would be an especially simple build.

I have built two of the flatpack sealed subs and that went super great. They build up easily and mega solid (not even in the same league as Dayton flatpack subs, these are DRAMATICALLY better) and I lined them with NoRez between the supports and used Acousta-stuff inside. I am very pleased with the results and, quite honestly, am not curious about any improvements potentially offered by the flat packs.

[JWCoffman]

So I landed on a plan and started the build yesterday.
Screenshot of the Sketchup below.  I'm going with a downfiring version adapted from Danny's plans with a compartment on the rear to house the amp.  This is not a sand-filled box as it sounds like it's probably not worth the hassle.  It will match the X-MTM's and X-CS I built 6 months ago with most of it in walnut with a strip of acrylic backpainted in matte black with a copper channel.  I'm a little concerned about having a thinner wall where the acrylic goes, but I think if I line it up with one of the braces and add a couple mitered strips above and below it, I should be OK.
It's all in trying to keep with the 1970's sci-fi theme of our other speakers.  It actually looks a little like a droid and adding feet will probably only increase that.

The only question is what to do about the feet.  I need at least 2.5" between the bottom baffle and the floor.  I'm tempted just to do some 2"x2" walnut at each corner to keep it sturdy and coupled to the floor, but I'm open to other ideas.
I don't think I'll be logging it like my MTM & X-CS build, but I'll have a few pics to share when I'm done.
Thanks for everyone's input.