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B&C 21DS115


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#1 Ricci

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Posted 24 February 2017 - 10:04 PM

I had a chance to pull the specs from these after a bit of mild 20Hz break in. I have the 4ohm versions. This is about as close as I've seen to matching factory specs. This driver is encouraging so far. It's light and $100 cheaper than the 21SW152. The only thing I was disappointed with so far is they used a smaller diameter spider than on the Ipal and 152. It has a smaller coil diameter so the bigger 6" formers need a bigger spider but the large one would've improved suspension linearity most likely. I assume they did it for mechanical protection where the smaller spiders increased stiffness will keep things under control if hit with too much power. More later.

 

21DS115-4 SEALED VS FREE AIR IMP.jpg

 

Specs I pulled. Like I said this is really really close. They've got a pretty low DCR on this driver but it is so efficient that the impedance peak is huge so it'll likely be at or above 3 ohms min between 10-125Hz.

 

 

Parameter  Value  Dim    

Fs 31.51  Hz    

Re 2.2  ohms[dc]

Qt 0.2  -    

Qes 0.2  -    

Qms 6.86  -    

Mms 379.75  grams    

Rms 10.95386  kg/s    

Cms 0.000067  m/N    

Vas 266.34  liters    

Sd 1680.02  cm^2    

Bl 28.52571  Tm    

ETA 3.94  %    

Lp(2.83V/1m) 103.67  dB              

Le 821.03  uH

L2 1930.6  uH  

R2 57.1  ohms    

L3 0  uH     R3 0  ohms    

1kHz Le 2.62mH


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#2 radulescu_paul_mircea

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Posted 24 February 2017 - 11:16 PM

Cool. How does it behave at high excursions?

#3 Ricci

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Posted 25 February 2017 - 03:28 PM

Similar to the other B&C drivers. Clean and quiet up till 20mm peak to peak. Takes on a bit of mechanical noise but otherwise still quite useful at 30ish mm p2p which is rated xmax. It'll go further but it's diminishing returns past that point. Distortion and noise grows quite a bit. I'd estimate I pushed it to 40mm peak to peak. Takes a lot more power to get there. Like the others it'd take some work to mechanically damage it.

#4 NiToNi

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Posted 01 March 2017 - 02:24 PM

This new generation of B&C subwoofers look very interesting. I like the stronger motors compared to the previous generation for brute-force operation in small sealed boxes. e.g:

 

102jfb8.jpg

 

 

This is with a LTW of F0=79Hz, Q0=0.45, Fp=20Hz, Qp=0.85. The gray line is max SPL at Xvar of 16.5mm. Four of those on 3400W each should do 122dB at 1m  :P

 

To go louder down deep, a vented 135L enclosure tuned to 15Hz (Dv=8", Lv=120" which may be a deal killer of course) seem to be able to do this with a bit of flattening EQ (HP LR4=15Hz; PEQ Fc=15Hz, 5.5dB, Q=1; LTW F0=50Hz, Q0=0.286, Fp=13Hz, Qp=0.44... LTW because Jeff Bagby's WBCD5 doesn't have a built-in shelf filter):

 

2nqa9lv.gif

 

 

Only two of those on 3400W each would be enough for 122dB at 1m :lol:

 

How come though that your measured Re of 2.2 ohms is so far off factory spec of 5.1 ohms? That's less than half and would rule out some amplifiers not happy driving less than 4 ohm loads (e.g. bridged Class D). I mean this is nominally an 8 ohm driver with a rated minimum impedance of 6.5 ohm.

 

On the same note, nominal power handling of 1700W is based on rated minimum impedance. Ohms law yields 105V @ 16A. Based on your own measurements, what peak voltage (Vp) would push your driver to Xvar of 16.5mm at 15Hz? Around 75V? 



#5 Ricci

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Posted 01 March 2017 - 02:55 PM

How come though that your measured Re of 2.2 ohms is so far off factory spec of 5.1 ohms? That's less than half and would rule out some amplifiers not happy driving less than 4 ohm loads (e.g. bridged Class D). I mean this is nominally an 8 ohm driver with a rated minimum impedance of 6.5 ohm.

 

On the same note, nominal power handling of 1700W is based on rated minimum impedance. Ohms law yields 105V @ 16A. Based on your own measurements, what peak voltage (Vp) would push your driver to Xvar of 16.5mm at 15Hz? Around 75V? 

 

Hello Nitoni,

 

I measured the 21DS115-4 not the 21DS115-8. See the PDF and compare with the parameters I pulled. ;)

 

Attached File  21DS115-4.pdf   76.87KB   16 downloads

 

Parameter  Value  Dim    

Fs 31.51  Hz    

Re 2.2  ohms[dc]

Qt 0.2  -    

Qes 0.2  -    

Qms 6.86  -    

Mms 379.75  grams    

Rms 10.95386  kg/s    

Cms 0.000067  m/N    

Vas 266.34  liters    

Sd 1680.02  cm^2    

Bl 28.52571  Tm    

ETA 3.94  %    

Lp(2.83V/1m) 103.67  dB              

Le 821.03  uH

L2 1930.6  uH  

R2 57.1  ohms    

L3 0  uH     R3 0  ohms    

1kHz Le 2.62mH


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#6 NiToNi

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Posted 01 March 2017 - 04:12 PM

Ah... that explains it!  :P    Sorry, I missed that part completely. There's no mentioning of a 4 ohm version on B&C's website so I hastily concluded there's only one model available...

 

So what sort of peak voltage (burst) could you safely put through the nominal 4 ohm VC from a thermal perspective you reckon and what sort of compression could one expect at that level?



#7 Ricci

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Posted 01 March 2017 - 04:51 PM

Ah... that explains it!  :P    Sorry, I missed that part completely. There's no mentioning of a 4 ohm version on B&C's website so I hastily concluded there's only one model available...

 

So what sort of peak voltage (burst) could you safely put through the nominal 4 ohm VC from a thermal perspective you reckon and what sort of compression could one expect at that level?

 

 

You'll have to wait for the ground plane measurements to answer that. I could guess but the workup will answer that much better.



#8 NiToNi

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Posted 01 March 2017 - 06:02 PM

Gotcha :)

#9 Kyle

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Posted 03 March 2017 - 06:06 PM

Displacement can be leveraged from cone area so while the xmax is average, overall displacement is still pretty damn decent at 5 liters. Josh, what is the SPL@1 watt? 100dB? To put this into perspective, a 12" high excursion woofer needs an xmax of 50mm to match this, and it won't have anything close to 100dB @ 1 watt.



#10 NiToNi

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Posted 03 March 2017 - 09:14 PM

Ricci referred to sensitivity above as  103.67dB/2.83V/m. However as you can see from the graph below, you will only get that sort of sensitivity above a bit over 500 Hz. 

 

kp007.gif

 

From 130Hz and below, sensitivity will be in the double digits only.

 

2u41x0z.gif

 

Flatting the curve with EQ, targeting an F3 of 20Hz and a Q=0.707 rolloff, the "useful" sensitivity is more like 88.45dB/2,83V/m.

 

160v510.gif

 

 

That's in free air. Any smaller sealed box than that will gradually reduce sensitivity down low where it counts.

 

2.83V is 3.65W in the case of this driver (TSP as per DB) and is the better way of referring to a driver's sensitivity IMHO but if you insist on 1W/m (1.48V), sensitivity is 98.12dB and the graph looks like this:

 

346am2a.gif



#11 Ricci

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Posted 04 March 2017 - 03:14 AM

Nitoni,
Driver or even cabinet sensitivity specs are still important but efficiency is much more important to me. Once the efficiency starts to get very high as it is with this driver base voltage sensitivity starts to drop. Despite this the driver requires less power despite the lower sensitivity.

Equalization is a manipulation of the signal being sent to the amplification stage it does not change the voltage sensitivity of the cabinet and driver system.

I expect this driver will be around 100dB at 100Hz with 2 volts in the 4.5ft sealed cab in the GP test.
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#12 Seek

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Posted 04 March 2017 - 06:44 AM

Subscribed. This will be interesting ;) So you mentioned you have a large ported cabinet you plan to try it in after the sealed enclosure testing. Is the ported cab' you mentioned by chance the 25 hz tuned one you used SW152 in?

 

Thought I would attach a pic of the 792 liter, 22hz tune tapped horn I have a DS115-8 in, shown before finishing up the last of the bracing and stitching the front on. It's a roomful, alright, and sure moves the house. I have everything I need to get some nearfield sweeps done, everything except time this weekend. I'll try to get that done next Fri or Sat.

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  • 20170126_152935.jpg


#13 NiToNi

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Posted 04 March 2017 - 11:15 AM

I expect this driver will be around 100dB at 100Hz with 2 volts in the 4.5ft sealed cab in the GP test.

 

Seems like that could be a bit on optimistic side...

 

29vl3de.gif

 

...at least in simulated theory  :P

 

Seems like you will be able take the 21DS115-4 up to about 61V in that 4.5 gross cu ft enclosure while staying within reasonable excursion...

 

2zisb9d.gif

 

208hatv.gif

 

 

Equalization is a manipulation of the signal being sent to the amplification stage it does not change the voltage sensitivity of the cabinet and driver system.

 

 

 
True of course but it's only after response shaping of the cabinet & driver system's passband that it becomes truly useful, especially a strong pro driver in a sealed cabinet. This is the same as above after  LTW F0=58Hz, Q0=0.35, Fp=20Hz, Qp=0.707:
 
2yp0q52.gif
 
Max SPL 112dB, F3=20Hz, F6=15Hz and F10=12Hz. The borderline excursion at around 10Hz should be mitigated by electronic roll-off elsewhere in the signal chain:
 
35jgo6h.gif
 
Again, only theoretical anechoic response in the simulated world of course. In-room response will of course require further ("different") EQ to flatten the response. Nevertheless, if you stick to only reducing gain (without any boosting) during the EQ process, the SPL capability at the low end of the passband (e.g. ~20Hz), in-room net after adding room gain and deducting compression, will ultimately dictate the performance throughout the whole passband (e.g. ~20-100Hz).
 
Also subscribed and looking forward to your test results, Ricci! A couple of these drivers are potential candidates for my own system - unless the bigger brother 6" VC is expected to follow soon...  ^_^
 
EDIT: Simulation file (WBCD5 Excel XLS file) attached for anyone interested in playing around.

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#14 chrapladm

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Posted 04 March 2017 - 01:13 PM

Seems like 100db is a good guess at 100hz. I dont expect Ricci to be perfect but 98 roughly at 100hz is pretty close.

 

Screen%20Shot%2003-04-17%20at%2011.29%20

 

 

Both 4ohm versions in 127 liters. This new DS115 is the best value subwoofer for me to use in a HT. I do enjoy the 18IPAL better for its smaller size the DS115 is $100 cheaper than that driver. I have too many other projects taking my money so these new 21's will have to wait. :D


"Music is not in the notes, but in the silence between."


#15 SME

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Posted 04 March 2017 - 11:31 PM

Here's the thing about efficiency vs. sensitivity.  As long as the efficiency is very high over the bandwidth of interest, you can run more subs in parallel to overcome sensitivity limitations.  For example, a driver may have a DCR of 3 ohm for a 4 ohm "nominal" impedance, but with a high efficiency driver in the right cabinet design, the frequency-dependent impedance might be 8 ohm or 12 ohm over the bandwidth of interest.  So in theory, you could run 4 in parallel from a 2 ohm amp instead only 2.

 

Of course, there are legitimate concerns that low impedance minimum may cause the amp to perform sub-optimally over those frequencies, but modern class D designs are becoming more robust against very low impedances.  And if you one is willing to operate the subs within a more limited bandwidth this problem can likely be avoided entirely.


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