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RCF 21" Subwoofer

post #1 of 16
1/28/10 at 1:33pm
Thread Starter 
Hi Im new here, I recently aquired a RCF 21" subwoofer and im looking for box ideas.  I already have 4 old denon 12" subs in sealed cabnets, I dont have specs on them right now but if nesicary I can get them. This will be used for 100% home theater no music.

The sub will be located in the connecting room with a vented door as there is not really anywhere else to put it.

Here are the specs, there is some info around the net on it but not much.
Here is the link with some specs from the manufacturer. http://www.rcf.it/web/rcf/products/precision-transducers/neodymium-low-frequency-transducers/lf21n451

4,5 - inch Inside/Outside copper voice coil
-3000 Watt continuous program power handling
-98.5dB Sensitivity
-30Hz - 1kHz Frequency range
-Dual-forced air ventilation for minimum power compression
-Dual spider designed with silicon based damping control
-BL of 33.5 T/m to provide a faster and accurate low frequency
(Fs) : 30 Hz
(Re) : 5,5 ohm
(Qms) : 5,5
(Qes) : 0,25
(Qts) : 0.24
(BL) : 33,5 T.m
(Mms) : 272 gr.
(VAS) : 440 Litres
(1220 cm²)
(Xmax) : 10,2 mm
1kHz (Le1K) : 2,9 mH
(Eff) : 4,50 %

Any help would be greatly appreciated.
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post #2 of 16
1/29/10 at 7:10am
Quote:
Originally Posted by Brandon3212 View Post

This will be used for 100% home theater no music.
You got the wrong sub for the job.  This is a professional sound reinforcement driver used in clubs and live musical performances.  I can try help you design something tuned in the 25hz to 30hz region but you are going to be missing a lot of low bass.  What are you powering this with?
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post #3 of 16
1/29/10 at 7:19am
Thread Starter 

Right now I have got it running in a 17 cubic ft box with a 6" port tuned to about 12 hz, im powering it with on side of a behringer EP1500 at the moment.  I just kind of whiped the box together in an afternoon so its FAR from perfect, and was just looking for some advice on how I can maybe improve.

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post #4 of 16
1/31/10 at 9:37pm
Thread Starter 
also, any ideas as to how much power I should run? the woofer is fairly efficent so it shouldnt need tones
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post #5 of 16
2/1/10 at 7:27am
That sounds like an absolute beast, I would love to hear that in action. I am surprised you actually have room for that anyway.

I wish you good luck in getting it up and running properly
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post #6 of 16
2/1/10 at 8:37am
Thread Starter 
I had to stick it under the work bench in the next room, fits like a glove.  But I think that there is still room for improvment, figured some people here might no more than me about proper box building and tuning.  Anyway heres a couple pics.
plays right out the door
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post #7 of 16
2/4/10 at 5:51am
Thread Starter 
Another question, should I brace this box?  Will it actually make it sound any better, or will it just help reduce box noise from flexing, because its in the other room so I cant really hear any box noise from where Im sitting any way.  The box is 17.2 cubic feet  with 1 6" port stuffed with polyfill and lined with a material kind of like roofing shingles to help dampen it.
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post #8 of 16
3/1/10 at 6:58am
Thread Starter 
Anyone have an answer?
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post #9 of 16
3/2/10 at 4:10am
I'm not a sub woofer builder but I would think bracing beats not bracing anytime. Even if sound quality isn't improved construction quality and reliability would be.
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post #10 of 16
3/2/10 at 5:51am
Just because you can't hear the cabinet vibrating doesn't mean that it isn't.  Bracing is the only thing that stops the vibrations.  The roofing material dampening can't control the vibrations like a good set of braces.
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post #11 of 16
3/2/10 at 6:28am
Thread Starter 

Well from what you guys are saying, I really cant go wrong by bracing it so i will see what I can do.  At least it will be a fairly easy job considering that the box is almost big enough to stand in. I will post some pics of the bracing job when its done.  This woofer is shaping up to be absolutely terrifying. I watched War Of The Worlds last night and it was threatening to rip the house apart.

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post #12 of 16
3/2/10 at 10:36am
If I can find my copy of MS Office, I'll run some sims to compare your sub to others.  But the Maelstrom 21" http://www.diycable.com/main/product_info.php?products_id=692&Cid=c4520a729e47abc0a140c902bce43f29 can move 3 times the air as your RCF driver.  It just needs a LOT more power to do it.  That's the difference between a pro audio driver and a home theater driver.

I'm surprised you haven't destroyed that driver yet since you don't have a subsonic filter.  At least with the low tuning it is protected most of the time.  Don't watch Black Hawk Down since it has massive amounts of bass at 8hz.
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post #13 of 16
3/2/10 at 1:26pm
Thread Starter 
So far this driver has been nothing but awesome even at the very lowest stuff Ive hit it with (haven't tried black hawk down yet) but it has never failed me yet, even with the 1600 RMS I run it on .  Also when i bought this I didn't know the Maelstrom 21 even existed and given a massive enough box this driver rocks.  I also paid over 150$ less with taxes included for mine and no shipping because I bought it local.  I'm sure that the Maelstrom can move more air but I already have 4 12" woofers so how much more do you really need in a room before you kill your self?  The digital theater by my house uses the same RCF woofers and it sounds awesome so I'm really not that opposed to using some of these very large pro drivers but I would think that you would want to stay away from the smaller ones. 
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post #14 of 16
3/2/10 at 1:47pm
Thread Starter 
If your going to model it try modeling it with 17.5 cubic foot box and one 6" port 23" long ran off of a briged Crown XLS 602, that's what its in right now and it seems to work really good, but if you have some other ideas I would really love to know!
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post #15 of 16
6/23/10 at 7:43pm
Thread Starter 

I have tried changing ports, bracing and other things and I still cant get this sub to sound the way I want it.  I am thinking of trying a transmission line enclosure for something different.  I realize this is going to be huge and very complicated, I have approx 52 cubic feet of space that I can use for the box and can use more if necessary.  I have read many of the websites on T-line boxes and have got a basic understanding of them and how they work.  I no they are very difficult to build, but I have two other friends helping me with 20+ years of experience building subwoofer boxes, so hopefully it will turn out well.  Does anyone have any advice, or any reason why I shouldn't use this design for home theater use? 

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post #16 of 16
2/12/12 at 10:04pm
Hi Brandon,
Just read your posts about the RCF 21 subwoofer. Very interesting. I just bought TWO of them and plan to use them in a 9cuft. sealed box with Linkwitz Transform circuit to raise the low end of the frequency spectrum.
The speaker modeling software program WinISD, shows two RCFs to have HUGE power potential below 20Hz and response down to single digits for home use. Maximum SPL is 132dB @100 Hz.
My box is complete except for handles and wheels. It's 48" H X 24" W X 16" D. I made it using 3/4 inch Birch Plywood. There are braces all over the inside of the box. Weight is at 70Lb.
Do you still have your RCF 21" driver?
The RCF 21" inch driver was designed for PRO use BUT it has the same qualities that home theater drivers do except that under normal pro use the source material is limited to about 30Hz. The RCF can easily play that stuff but also has the potential (29mm X-mech) to play the subsonic FQ too. The listed X-max (that's LINEAR excursion) doesn't nearly do the driver justice. I played it out of the box with a Crown Xti-4000. It plays LOUD and the cone MOVES!
I'm anxious to complete my box and do a side by side comparison with my T C Sounds LMS 5400 18" sub in a 6.1 cuft. sealed box. I think the RCFs will do as well or better.
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