[Horacio]

Hello.

I'm in the process of replacing my Rel Storm III in my hi-fi with two DIY 12" Rythmik subs. So far I have settled on the drivers and associated amp, and a sealed design. Of course, I have a million questions, even after reading many threads here.

What's the optimal box volume? Rythmik sells these drivers with 2 cubic feet boxes. Any point in second guessing them?

I'm planning to use 1.25" MDF + 1/2" veneered plywood for the box, heavily braced inside. Good path?

Thanks!
Horacio

 

[pharoah]

i dont think i would second guess them.the box sounds like it will be plenty heavy.

 

[theJman]

I agree; if Rythmik uses that size chances are you can as well. However, bear in mind that they have the ability to program the amps DSP to do anything they want it to, which you won't be able to do. If Rythmik sells "vanilla" amps, where the DSP has no signal shaping, you're no longer able to look at what they sell and assume you can just duplicate that. It might be worth a quick email to Rythmik and ask them what size cabinet they recommend.

 

[Horacio]

However, bear in mind that they have the ability to program the amps DSP to do anything they want it to, which you won't be able to do. If Rythmik sells "vanilla" amps, where the DSP has no signal shaping, you're no longer able to look at what they sell and assume you can just duplicate that.

Jim,

I'm not sure I'm following you here. Could you please elaborate?
I did buy one of their amps, the A370PEQ. I believe the driver and amp are exactly the same as in their F12 subs.

Thanks for the input!
Horacio

 

[Horacio]

I checked the drawings supplied by Rythmik and it's a 1.7 cu.ft box, and asked Rythmik and they say 2 cu.ft is optimal. Plus I checked several DIY projects for 12" Rythmiks here, plus Ikka's measurements and they all were with 2 cu.ft (56 liter) boxes. So 2 cu.ft it will be.

BUT, when we talk 2 cu.ft, than means the volume inside the box net of bracing and driver volume, right? We are talking the actual air volume in the sealed enclosure behind the driver, correct?

Thank you!

 

[theJman]

BUT, when we talk 2 cu.ft, than means the volume inside the box net of bracing and driver volume, right? We are talking the actual air volume in the sealed enclosure behind the driver, correct?

Correct. Net after bracing, driver and amp are subtracted. Most times you have to take a little bit of a guess, because the space each of them displace may not be 100% accurate. If you end up with a little less you can always "fool" the driver into thinking the cabinet is larger with extra damping.

 

[Horacio]

If you end up with a little less you can always "fool" the driver into thinking the cabinet is larger with extra damping.

Ah! That's interesting. Rythmik said there's enough dacron in the DIY kit the shipped to cover the inner walls with 1" layer. So fooling the driver is the purpose of that layer. They said isolation, but it had me wondering.

What's the flip side of having the driver see a larger box than what it really is? What would I gain if I used a larger box and no dacron?

Thanks!

 

[theJman]

You should always use damping material for a sealed sub, so I wouldn't advise going without any at all.

The damping material is mostly to quiet down the cabinet, so it doesn't color the sound by resonating (the back pressure from the driver can be rather intense during deep bass passages, so it's always better to try and muffle it). If you put in an excess quantity of material it can fool the driver into thinking the cabinet is larger, so if you get the interior volume calculation of the physical cabinet wrong extra damping can help mitigate any problems you may encounter.

The damping can help you make a smaller enclosure then the driver ideally calls for. Suppose the driver you select would be perfect in a 2.5 ft^ cabinet, but you have one that's 2.0 ft^3. Unless you can tune the signal using a DSP in the amp -- not likely -- you won't achieve the best possible results. Adding more damping is almost like a "mechanical" change of the drivers characteristics (mechanical being if you physically altered the driver). By limiting it's movement further than normal you essentially trick the driver into believing you have a bigger cabinet.

I probably did a lousy job explaining this, so perhaps someone else will chime in and clarify it better.

 

[Horacio]

Jim,

Thanks for the explanation. It does help. You got me thinking around "back pressure from the driver can be rather intense". I plan to use the plate amp from Rythmik, mounted on the sub box like Rythmik does on their finished subs...but having the amp exposed to those intense waves (a.k.a. vibrations) has me thinking if I shouldn't have the plate amp built into a separate box outside the sub. Yet top manufacturers as REL and JL use plate amps inside the box, so maybe I'm exagerating the impact on sound.

I guess 3/4" MDF + 3/4" plywood for the box, plus heavy internal bracing should keep wall ringing minimized, but since the dacron is included with the DIY kit I might try it both ways and decide.

Thanks for the food for thought!

 

[theJman]

The pressure on the amp wouldn't impact sound, just longevity. However, the better manufacturers -- like Rythmik -- spend a consider amount of time designing their amps to withstand that pressure, so I wouldn't be too concerned.

I thinks it's a good idea for you to experiment with the damping material but I suspect you'll ultimately leave it in, so perhaps you should try that configuration last.

 

[BD55]

...but having the amp exposed to those intense waves (a.k.a. vibrations) has me thinking if I shouldn't have the plate amp built into a separate box outside the sub...

If your enclosure is braced well, the amplifier won't see much vibration except for higher frequencies due to the panel ringing. If your amp is shaking so much that it's getting damaged, you need to add bracing! If you are worried about the amp components themselves vibrating, then the amp wasn't properly designed for plate amp duty. You should see zip ties, epoxy, hot glue, etc. to keep everything tied down and safe.