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Author Topic: RCF 21" Sub Build Pics and Impressions  (Read 22529 times)

Josh Ricci

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Re: RCF 21--Designer comments
« Reply #50 on: November 05, 2010, 10:33:22 pm »

[quote title=Phillip Graham wrote on Fri, 05 November 2010 13:34]
Quote:

I am curious which way the tuning shifted.  If I had to guess, based on the state port area of 500 cm^2 (per driver?) is that it first went up, and then back down slightly at very high power levels?

The Le(x) curve variation for these high power professional drivers is usually so small that the impedance data, even at large excursions, will give you more information about the port Q and tuning frequency than almost any other measurement.


This latest generation of drivers is really starting to hit on all cylinders...

That's 500 cm of port per driver. Tuning I believe did as you suggested and dropped a little at higher outputs as the port compressed. About 700-750cm per driver seems to be what would be ideal but pesky issues like port length, volume, and resonance get problematic.

Quote:

Oh, my mistake, I was under the impression that the 6" VC 21 did not have the variable "split" vc winding, but it appears that it does.  Thus it should should have the excellent Bl(x) behavior of the SW115 with more power handling.  Oops!  Apparently there was a discontinued 21" driver that did not have the split coil.

That would now make the 21SW152 the top dog Smile


Yes the 21sw150.

I'd say that overall I'm quite happy with the drivers and the measured performance even with the lower than intended tune. As far as what people might expect something like this to be able to do based on manufacturer's marketing specs they might be underwhelmed, but real world output will almost never live up to those inflated specs.

Quote:

The test in VC is how I became aware of the split winding drives.  Fantastically even and symmetrical Bl(x) and kms(x).  Good Le(x), too.


Yes. I already had the drivers when I saw that test which made me very happy (assuming some family attributes will rub off). The NW100 also did very well.  Very Happy
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Jeff Wheeler

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Re: RCF 21--Designer comments - Quick side question-2268H
« Reply #51 on: November 06, 2010, 12:05:07 am »

Steve Hurt wrote on Thu, 04 November 2010 20:39

I do believe the SRX's were rated in full space, however, some of the other lines like the PRX subs for instance, must have been rated in "Outer Space" to get their output ratings!

This must be what inspired Jeff to name his new subwoofer product the Orbit Shifter. Wink
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Steve Hurt

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Re: RCF 21--Designer comments - Quick side question-2268H
« Reply #52 on: November 06, 2010, 12:16:19 am »

LOL!  If you turn the Orbit shifters all the way up in a club I work, the owner will kick you into orbit before the 1st verse is sung.

Speaking of PRX...

Here's something from the PRX518 spec sheet:

Maximum Peak output measured with IEC pink noise at 1 meter in front of speaker baffle under free space
conditions. Measurement instrument set to peak hold. Speaker muted and released at full power, recording maximum
peak level.


Free space = full space isn't it?

Sounds like they wind it up and let it hit one note before the speaker can heat up.  (and then add 6-10 db)
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Peter Morris

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Re: RCF 21--Designer comments
« Reply #53 on: November 06, 2010, 02:27:58 am »


"That would now make the 21SW152 the top dog :)"


Hi Phil,

Sort of ...  but the 115 and the 152 appears to be designed for slightly different applications. The 152 will go very very low, but if you want a more general purpose sub that does not go quite as low, the 115 is more efficient and will probably give you better results.(from what I can remember when I did all the sims)

In terms of output per cubic foot this new generation of speakers from B&C and RCF (and 18sound) has raised the bar quite a bit.

Peter

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Phil Lewandowski

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Re: RCF 21--Designer comments - Quick side question-2268H
« Reply #54 on: November 06, 2010, 10:15:32 am »

Steve Hurt wrote on Sat, 06 November 2010 00:16

LOL!  If you turn the Orbit shifters all the way up in a club I work, the owner will kick you into orbit before the 1st verse is sung.

Speaking of PRX...

Here's something from the PRX518 spec sheet:

Maximum Peak output measured with IEC pink noise at 1 meter in front of speaker baffle under free space
conditions. Measurement instrument set to peak hold. Speaker muted and released at full power, recording maximum
peak level.


Free space = full space isn't it?



Yeah, I noticed that too a while back with several of JBL's subs.  So either JBL is making up those full-space responses or they are actually measuring subs in full-space which still doesn't make sense to publish and advertise full-space responses, but who knows.

Actually the VRX918-SP says "free field conditions":

http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3 &docid=581

Looks like both the MRX subs are measured in full as well:

http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3 &docid=599

http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3 &docid=600



Why can't you just measure all the subs in half-space JBL and make it much easier...?



~Phil
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Phillip_Graham

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Re: RCF 21--Designer comments - Quick side question-2268H
« Reply #55 on: November 06, 2010, 10:29:41 am »

Phil,

I think it is a stretch to assume that free field is Full space.  Free field is a non standard term, and potentially chosen to obfuscate.

Go back to the 2268H datasheet linked above, where the driver was measure on the roof of one of the jbl/harman buildings.  Id wager that this is SOP for all the lf devices here.

Manus generally don't provde detailed info about their test methodologies, otherwise it would be harder to juice the numbers.
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Steve Hurt

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Re: RCF 21--Designer comments - Quick side question-2268H
« Reply #56 on: November 06, 2010, 11:06:49 am »

Phillip Graham wrote on Sat, 06 November 2010 10:29

Phil,
 Free field is a non standard term, and potentially chosen to obfuscate.



On the PRX series, I would choose to obfuscate as well!
The crank em up, hit the on switch, and measure the first note thing, says "chosen to obfuscate" to me.


Be great if someone would measure the SRX subs
The numbers seem low if they're half space, but my "measurements" have been with my ears (and my ears have been known to tell big fat lies)

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Phillip_Graham

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Re: RCF 21--Designer comments
« Reply #57 on: November 06, 2010, 01:40:35 pm »

So the B&C website was down this morning when I went to look up the T/S parameters of the 21 SW152.  So I went to "the Google" and quickly found a thread by Josh Ricci, who is contributing to this thread, on building his 21 SW152 speakers:

 http://www.avsforum.com/avs-vb/showthread.php?t=1240709& page=1

Quickly skimming the thread, it appears that one of the papers on port behavior in my AES library (that I paid good money for!) is available for free on the Harman website:

 http://www.harman.com/EN-US/OurCompany/Technologyleadership/ Documents/Scientific%20Publications/11094.pdf

If you try to access the root directory, though, it appears to be password protected.  It appears Harman is perhaps better at building speakers than playing administrator on Apache...

Regardless, this a long (27 page) paper on ports.  JBL/Harman typically has excellent technical papers, and this is no exception.

Cliff Hendrickson, Doug Button, Mark Ureda, and Don Keele--all JBL/Harman guys--have collectively authored a great library of AES papers on all things loudspeaker design.

As a PS in appreciation of the LAB community, I could not believe how unruly the thread on that "AVS" forum appeared to be.  Thanks for being civil everyone!
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Josh Ricci

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Re: RCF 21--Designer comments
« Reply #58 on: November 06, 2010, 06:47:10 pm »

Yes...That JBL paper on porting is a great read if you are interested in porting and overload effects and how ports of varying geometries behave under various power levels. Can't remember where i first saw that years ago.

Sorry about all of the off topic banter and forks in the road on the AVS thread if anyone attempts to read through it. (8 pages of bickering over the ultimate port design Mad ) It was a long journey. There is some good stuff in there though. Rolling Eyes
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Art Welter

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Re: RCF 21/SRX 728 comparisons
« Reply #59 on: December 21, 2010, 02:30:34 pm »

Loren Jones wrote on Mon, 01 November 2010 17:52


I currently have a borrowed SRX-728 and the aforementioned CE4000 amps both loaned to me by another exceedingly kind LABster, Mark Phillips.  Hopefully we will be able to get at least some meaningful comparisons to the 728 taken under the same conditions.  The tests won't be lab quality but hopefully it will give some idea of how this design compares to what is generally regarded as the default standard mid-level dual 18" vented sub.  Hopefully we can get those comparisons done this weekend perhaps.

I will do all I can to get the box either up to Evan or down to Phillip for proper measurements.  I want to do this out of curiosity to see what the real performance is of "my baby".  Also I think that if good measurements help refine the design so that a really professionally designed and documented reflex loaded sub can be made available for the DIY types, then that is a good thing.

Thanks again for Phillip in kindly providing me with this design and lots of handholding along the way.  Thanks also to Jeff for the good deal on the drivers and to Mark Phillips for loaning me some gear to compare them to.



Loren,

Wondering if you got a chance to do any comparisons or measuring of the RCF 21 cabinet ?

If not, any simple dB meter readings, or subjective descriptions?

Art Welter
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