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Ricci

B&C 21-IPAL Driver and Measurements Discussion

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Ricci    652

I finally got around to groundplane testing these drivers about 4 years after getting them. Results for a pair of them wired in series in the old DO cab are uploaded. K20 still couldn't quite get to the absolute limits. It doesn't like wanging everything it has into 1ohm per channel for some reason.  :rolleyes:

 

Any discussion of the drivers or test results should go here please. 

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Ricci    652

Scott these are 0.7 ohm dcr. Single coil.

 

Luke...I kinda had a different cab idea a few years ago and went down that rabbit hole instead. The initial investigatory units of this different system are nearly done. If it works I've already got a different Othorn replacement drawn up. In other words the PH may never get built. However what I really should do is modify it just slightly to work better with the 21sw152 and give out the plans as a true Othorn update. That foldshould be much better and produce a more solid cab.

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SME    210

Another big wow!

 

I did some Googling to see how much these would set me back.  I'm a bit disturbed to see these sold by indie retailers via places like Amazon and Walmart online.  Are there rip-offs on the market to beware of?  I'm seeing these sold for as little as $1300 or so, but a more realistic price may be $1700.

 

Another question, do the CEA results have anything to do with the amp limits?  It looks like the CEA limits are hit at levels well within the Powersoft's means at 40 Hz and below.

 

In any case, I like the looks of these drivers more than the RF-T3 19s, due to their form factors and apparently lower price.  The low impedance is a nuisance, but I think a SpeakerPower SP2-12000 ought to handle four of them just fine.  The distortion measurements suggest that the suspension linearity is phenomenally good.  I think I'd increase the enclosure size a bit to try to get a bit more deep bass efficiency and to fill the space I actually have.

 

At this point, these are definitely looking like a strong contender for me, but the cost at $1700 still runs a bit high.

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Ricci    652

USSpeaker has them now. They are reputable. If you are in North America and you dig hard enough you can probably better there price by a bit. Nobody here would know anything about that though. ;) Hell I've got two for sale for $850ea right now.

 

40Hz and lower burst output was distortion limited. Drivers have a good 3dB left past that point shown in the red column under static graphs tab,  but the K20 would mute before the drivers would give up completely. Same thing at every bandwidth. Amp could not bottom the drivers. It seemed to be getting close at some bandwidths though. The single driver sealed test should be even more insightful since the cab volume will be 4.5ft instead of 2.75. 2.75ft is tiny for a 21 no matter how you slice it. A lot of 15" subs have bigger air volumes to work with than that so it definitely hampered things a bit. Vented cab testing will be fun no doubt. SP2-12000 on four would be a good match. No need for an MBM that's for sure.

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SME    210

The resonance being so high is weird and makes it easy to pass up this driver, but the efficiency is still insanely high across the range.  The numbers I see in my simulations are actually scary.  Like > 150 dB SPL at the listening position scary.  Alright, maybe I'm just a bass whimp, but with numbers like that (for higher frequencies like 150 Hz), I'm admittedly paranoid about system faults causing hearing damage, or worse?

 

USSpeaker has them now. They are reputable. If you are in North America and you dig hard enough you can probably better there price by a bit. Nobody here would know anything about that though. ;) Hell I've got two for sale for $850ea right now.

 

Thanks for the tip about USSpeaker carrying them, and yeah, being able to pick up two of the four used would definitely sweeten the deal.  But I'm also considering a couple other products, trying to carefully weigh the pros and cons.  One thing I don't like in what I see for the IPAL is the impedance blip at 180 Hz or so.  Do you hear any nasty resonances there?  Either way, I'd probably let these concentrate on the deep bass and use other drivers for mid bass.  The inductance is good but not *that* good.

 

So for now, those IPALs of yours are still up for grabs, but I may change my mind pretty on that pretty soon.  The tricky part about the decision is that both the other options are not immediately available, but this "good deal" on the IPALs surely won't last.  ;)

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SME    210

I've decided to pass on these drivers.  The super powerful motor is somewhat held back by the ultra-tight suspension in all but the smallest enclosures.  The bigger problem is that the impedance is just too low to be useful with typically amps.  I estimate that even an SP2-12k could not bring 4 of these drivers to full excursion in a reasonable sized box, if at all.  While this amp doesn't have a problem operating into the < 2 ohm impedance, its maximum power capability is diminished below its rated when operating as such, especially below 20 Hz.  In fact, I'm aiming for a minimum impedance a bit higher than 2 ohm in hopes of getting just a bit more juice out of some SP amps for ULF.

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Ricci    652

Correct...The main issue is the impedance of these and finding an amp happy with driving them. I disagree a bit about not adequately powering 4 with something like a top touring amp from Speakerpower, Powersoft, Crown, LabGruppen, etc...These make more noise with less power than the majority of drivers. The limits are high but you don't want to actually use any driver at the limits. I try to have +10dB headroom over where I will typically operate at maximum and I want that +10dB of headroom to be at say 3dB under the limits for the drivers.  I greatly prefer being amp limited.  

 

Not sure why the 190Hz blip is there. It's on the factory and my measurements. It has to be a cone resonance or perhaps a resonance under the dust cap in the motor system? I can't say that I hear it at all, but I haven't run these up that high too often either. The surrounds, spiders, and cone are the same on the 21SW152-4 and it does not exhibit that feature with the same amplitude. It's still there just barely but not nearly as prominent. The 21-Ipal does have a reinforcement ring on the cone around the last 2" or so of the edge and I believe an extra spider for added stiffness.

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SME    210

Correct...The main issue is the impedance of these and finding an amp happy with driving them. I disagree a bit about not adequately powering 4 with something like a top touring amp from Speakerpower, Powersoft, Crown, LabGruppen, etc...These make more noise with less power than the majority of drivers. The limits are high but you don't want to actually use any driver at the limits. I try to have +10dB headroom over where I will typically operate at maximum and I want that +10dB of headroom to be at say 3dB under the limits for the drivers.  I greatly prefer being amp limited.  

 

Not sure why the 190Hz blip is there. It's on the factory and my measurements. It has to be a cone resonance or perhaps a resonance under the dust cap in the motor system? I can't say that I hear it at all, but I haven't run these up that high too often either. The surrounds, spiders, and cone are the same on the 21SW152-4 and it does not exhibit that feature with the same amplitude. It's still there just barely but not nearly as prominent. The 21-Ipal does have a reinforcement ring on the cone around the last 2" or so of the edge and I believe an extra spider for added stiffness.

 

What limit do you use for your "3 dB under the limit" rule?  Xmax (or something like CEA score) or Xmech?

 

For pro use, mostly > 40 Hz, these IPALs are undoubtedly awesome.  For ULF sealed sub use, they are very good for getting a lot of output in a small space, but the low minimum impedance holds them back, IMO, compared to other options.  The differences are very close though.  If SP made a 10 kW X 2 channel amp, it would probably work very nicely on 6 of these, wired as triples in series for a minimum impedance of 2.1 ohm.

 

The resonance could be in the surround too.  Glad to know you don't hear it, so it's likely mostly harmless in this case.

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Contrasseur    17

Whooh what a monster of a driver!! I'm so glad you got around to publishing these results!

 

I had no idea these were down to $1300 now! In the pair, this system costs about as much as the T3-19 with more efficiency, displacement, and nearly the same impedance. On one hand, it seems that nothing outside of the purpose built IpalMod will get you the full performance of this driver. On the other hand, you have to admit that the amp-limited performance is still really hard to touch!

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Ricci    652

What limit do you use for your "3 dB under the limit" rule?  Xmax (or something like CEA score) or Xmech?

 

For pro use, mostly > 40 Hz, these IPALs are undoubtedly awesome.  For ULF sealed sub use, they are very good for getting a lot of output in a small space, but the low minimum impedance holds them back, IMO, compared to other options.  The differences are very close though.  If SP made a 10 kW X 2 channel amp, it would probably work very nicely on 6 of these, wired as triples in series for a minimum impedance of 2.1 ohm.

 

The resonance could be in the surround too.  Glad to know you don't hear it, so it's likely mostly harmless in this case.

 

 

All of the above...That's what all of the data for raw drivers here is about is providing useful information on how the drivers behave and where they start to fall apart and using it to make informed decisions on how they can best be utilized in a finished design. What I meant above is I prefer to operate at 50% of capability or under if at all possible. I like to WAY overshoot the headroom requirements in the drivers used whenever possible. The moving coil driver is usually the weakest link in the chain other than the acoustic space. I don't want to plan on using the last 3 to 5dB headroom of any system. In that way, when looking at the measurements here, I use them to judge where that point is and what the results should be in the proposed design.

 

I see people all the time who advise against using a higher performance driver because they don't have enough power on tap to "push it" because they only have a 1500w amp and winisd or whatever says they need 3000w to go past xmax a bit. Then someone will advocate using a cheaper driver because it will "match up" better with the amp and will reach xmax on the 1500w amp in the simulator. They often forget the a 6dB increase requires double the displacement from the driver and a 3dB increase requires 2X the amplifier power. That last 3 to 6dB has the reproduction distorted the most by far. The less capable driver may be operating safely but far less effectively near the edge of its performance envelope at times, while the other more capable driver is loafing along. There's nothing wrong with having enough amp to overpower the drivers by any means of course either as I'm definitely guilty there, but I don't like to be operating at or even near the limit if I can help it.  

 

 

If I could get B&C to make changes to this driver it would be #1 to make it available in either 2 or 4ohm if possible. #2 would be to soften the spiders a little. The Fs up near 40Hz is not really an issue but if it was allowed to be in the 25Hz range that would help get the impedance peak down lower in frequency. The Qts and Qes would drop more as well. Obviously these are about as far from a typical sealed driver as you can get and these are not intended for that in any way shape or form. They do well simply because the xmax is generous as is the power handling and the motor is ridiculous. However with the impedance peak up near 50-60Hz in a sealed cab the amp better be able to dump some current below 30Hz. Just not a sealed driver really. However it can work and is quite fun. Clearly optimized for 30-100Hz range. Now once we get these into vented, BP and horn cabs things get interesting. Due to the motor force the response shapes come out rougher than normal. You have to understand that what you are seeing as peaks in the response is increased efficiency and that these are made to be used with modern signal shaping. For example the peak at vent tuning you'll see in a typical cab size that could support the port and tuning needed for one of these, looks bad on the raw unprocessed graph. However if you add in the HPF and LPF that will be needed at minimum things look much different.

 

Bit of trivia...This driver was developed years ago and is the grandfather of the current line of B&C woofers. The 21sw152-4, SW115's, SW150 and their other high power neo subs were developed after years of work on this one and using the knowledge gained from it. I had thought it was a buildup to producing this design but it was the precursor.

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MemX    97

I finally got round to reading the data on these - that's pretty crazy stuff :blink:

 

They're a remarkable 'pre-loved' steal at $850 each!

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Contrasseur    17

What are everyone's thoughts on the Eighteen Sound 21iD? $300 cheaper, 20lbs lighter, double the impedance.

 

1mm less coil overhang, barely higher normalized inductance, slightly smaller voice coil.

 

Looks like a damn fine woofer.

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Ricci    652

18Sound xmax figures are not coil overhang. It is as below.

 

(9) Linear Mat. Xmax is calculated as; (Hvc-Hg)/2 + Hg/4 where Hvc is the coil depth and Hg is gap

depth.

 

I don't know for sure since they don't give gap or coil specs but I'd imagine the coil overhang is somewhere between 9-11mm. Top plate is probably between 9-12mm. Ipal 21 coil overhang is 15mm. MFG's xmax is 22mm vs 14mm for the 21ID. Ipal also has a deep top plate with an 18mm depth. Coil doesn't leave gap until 33mm. 21ID is likely to leave the gap around 20-23mm.

 

Like I said it's probably a great driver but it doesn't have the amount of stroke the B&C IPAL drives do. I would like to test one at some point.

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Contrasseur    17

Oops, thought they did the Celestion formula.

 

Still though, seeing how favorably the 21LW1400 compared to the 21SW152-4, I think we could still see some usable stroke beyond manufacturer Xmax. Not equal to the IPAL I'm sure, but almost certainly more than 14mm.

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Ricci    652

I've been interested in that amp for a long time. It is expensive (surprise!). I haven't seen any testing on one and very little in the way of user reviews. Looks like a beast but it looks like the minimum impedance it is rated for is 2.6ohm or 5.2 ohm bridged.

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SME    210

Interesting.  That almost sounds like a more "honest" rating.  How many amps with 2 ohm / 4 ohm bridged really double the power output versus 4 ohm / 8 ohm bridged?  I wouldn't be surprised if a lot of 2-ohm rated amps are capable of giving just as much or even more power into 2.6 or 2.8 ohms as into 2 ohm.

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Ricci    652

Interesting.  That almost sounds like a more "honest" rating.  How many amps with 2 ohm / 4 ohm bridged really double the power output versus 4 ohm / 8 ohm bridged?  I wouldn't be surprised if a lot of 2-ohm rated amps are capable of giving just as much or even more power into 2.6 or 2.8 ohms as into 2 ohm.

 

Or it indicates that the amplifier does not do well at all with impedances lower than 2.6ohm and the output is limited greatly. Nothing wrong with that. None of the modern big burst amps really sustain the types of current needed for continuous output into low impedances. I'd love to see detailed testing on this amp and a bunch of others but nobody seems to be doing it any more.

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Hi all,

Trying to develop a very powerful and efficient subwoofer, I noticed something interesting. When comparing the Othorn Ipal with other sub designs like K-Array KS8, KV2 VHD4.21 or martin MLX and ASX, I notice that the bandpass and hybrids works better and more efficient than the Othorn. that seems odd since from what I know, TH are more efficient than Bass reflex and shoud be more efficient than band-pass. but not using the Ipal or M-force drivers. You can see in the pics that when using multiples, the efficiency increases very quick and with 4 large ported BPH  enclosure using 2*21 Ipal the output is huge using less energy than with 8 Othorns.

So whats the catch? Would 2200 sq cm ports avoid compressing at those SPL? 

post-3306-0-26279000-1467655745_thumb.jpg

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post-3306-0-10051000-1467655747_thumb.jpg

post-3306-0-90632400-1467655757_thumb.jpg

post-3306-0-32215300-1467655758_thumb.jpg

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Ricci,if you still have those bass reflex enclosures made for the 21sw152, you could put the Ipal driver inside to see when and how much those ports would compress and how different those drivers behave.

Also, regarding the low impedance stability of the K20, on some of the Powersoft datasheets and white papers they say the M-Force driver can work also with K10 or K20. But that one has a RE of less than 0.26 ohms.

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