Ricci

The best advice I can give is to use a simulation program and use it to look at the way the system design changes the impedance curve. Start by settling on a tuning. Change the enclosure volume while keeping tuning the same and watch how the response and impedance change. Then look at how the tuning will change the impedance curve while keeping the rest constant. Lastly you can look at various drivers in the same alignment and see how that changes the curve. This is the best way to learn the tradeoffs and how the impedance curve reflects the performance.

IPAL system is powerful but it still has the limitations of any other setup. The amplifier voltage and current limits, the driver excursion limits and thermal handling etc. The driver simulation circuit can only work up to the point that some limitation is met. In that way you want the highest power handling most efficient driver possible. True efficiency of the system cannot be changed. In that way the driver modeling is interesting to me but I would concentrate more on using a very high performance driver and match the cab to the driver as much as possible so as to use very limited signal shaping. To me the DPC feedback system is the real item of note with the system.

Checked out the Kv2 website. Looks like a well established company with a full lineup of products. Can't believe I'm just now hearing about them. Amplifiers seem to be big,heavy and slightly underpowered. I am a little suspect of some of their claims in their technology segments. There are a lot of claims but very little measurements, explanation of the conditions, or data to back any of it up. I'm sure they make good products but the claims of "pulse" response and the like being so much better than other products is not passing the initial sniff test. Minor rant here... Actually this is a trend I've been noticing with the pro companies in the last few years. It seems that less concrete data is being offered for their speakers. It is becoming rare to see an impedance, or response measurement for a cabinet anymore. Now it is mostly a basic FR spec of +/-3dB and +/10dB, a max peak output, usually calculated and often with no qualification of what frequency it occurs at. Same thing for sensitivity. Sensitivity sometimes gets fudged by putting 2.83v into a 2ohm minimum impedance and then quoted at the single peak frequency. The FR flatness claims often involve either DSP for active systems and/or significant smoothing of the measurement, which is then not shown in any case. Hmmm. I don't see that anywhere in the literature. Is that from the replacement parts list? Would be odd for them to use 8ohm drivers when the IPAL module is being used and it is designed to work with a pair of the 18's wired parallel at 1 ohm. Martin is a big enough company to have it done if they want though. Could be??? Interesting sub. Looks like a number of people seem to have hit upon the same idea for bass cabs around the same time.

Hey Paul, Vents will compress but so do horns believe it or not. Pressures and air speeds get very high inside horns as well. The vent sizes that you have are gigantic and larger than many horn segments near the throat, so they should be quite capable of supporting high airspeeds. The DPC circuit may try to combat vent non-linearity but I'm not sure how effective that would be at the extremes when the vent is heavily compressed. Looked at your HR sims. Yes those cabs do have a very high efficiency. Higher than the Othorn for sure. They are around twice the size though and the corner is a little higher on them. I've attached the HR inputs for a dual Othorn cab with the 21 Ipal drivers for your comparison. I designed the Othorn quite a few years ago now. One thing you have to remember is that it had to be exactly 36x36x24 due to restrictions I had on size, prior to any design work, while also having high output all of the way down to 25Hz. It isn't the loudest cab on the block. The real trick was the package of extension, size, clean sound and output. IMHO of course. I will send you a pm shortly to discuss a few things.

If you feel like posting the HR inputs I could take a look. You said that one system is close to 1000L? Othorn is about 420L so the bigger cab likely would be much more efficient.

Hey Paul it is impossible to tell much of anything from your graphs without the inputs used. We would have no idea the comparative sizes used, tunings, what loading, etc...One very easy way to increase efficiency is tune higher and/or allow a bigger airspace. It makes a HUGE difference that cannot be understated. Also I would never compare multiple cabs versus multiple cabs. I know that HR has the tools for it but I just don't quite trust it because I've never seen sufficiently detailed measurements of adding additional cabs of the various types of alignments. Just my personal preferences but I always use either half or full space loading and compare the minimum amount of cabs. If it would be 4 of one versus 8 of another I'd reduce it to 1 vs 2. I'm not remembering the datasheets where they suggest the M-force be used with the K10 or K20? They may say that but here's the thing. The IPAL and M-Force systems are designed for maximum efficiency/higher order loadings (BP, TH, FLH or vented at minimum) and are made for relatively narrow band response. The drivers are so efficient that the average impedance is much higher than "normal" or what the Re would suggest. Once they are loaded in a band pass or horn there are multiple peaks of impedance in the bandwidth and then the intended bandwidth is restricted to something like 30-90Hz. This keeps the actual impedance seen by the amps much higher than you would think. something like a full bandwidth sealed or IB system would cause serious limitations. The amps will not like that I assure you. It's heavily APP dependent. I certainly haven't seen optimal performance from the PS digam series into impedances that low.

Now you're getting somewhere...WT2 and actual impedance curve FTW. Torpedo amps are high current beasts...Are you going to repeat the tests on your other amps on hand?

I agree. They seem to work for a lot of people but the 2 units I tried a few years back I had a number of issues with. They just weren't for me.

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.

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.

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.

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.

Have your tried moving the LP closer to the speakers so that the angle of coverage between yourself and the 2 speakers is larger? This can work sometimes as well but isn't practical in many cases or causes other problems.

I hate to say it but you may need a wider room and a greater spacing of the speakers for that effect.

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.

He had everything on hand by Saturday night. Some serious team work on that sale, with 4 parties involved. Went super smooth.

Thanks for helping with the sale EndersShadow.

Yes the moving mass of the drivers does matter. A lot of the modern big bass drivers are 400 to 600g of mass in the moving assembly. Once you start to think about the acceleration and velocity forces involved with high output from them and coupling those rigidly to a cabinet it's no surprise. A 15 with 200g mass isn't going to vibrate the entire enclosure as much as one with 400g. This can have an effect on tactile response at the LP as well. The heavier vibrations from the more massive driver can be directly transmitted through the floor to the furniture and listener. I believe this may be part of why many like downfiring drivers. The RF 19 causes a lot of reactionary force with 1Kg of mass. Good luck running it solo in a cab and not vibrating the whole assembly. It may as well be an oversized tactile transducer.I was running the first one free air sitting vertically on my floor with a channel from an SP2-12000 on it. I decided to see how much excursion it would produce before sounding stressed. The driver vibrated so hard that its 70lb mass was literally jumping off of the floor and started jack hammering itself. This is on carpet at about 2.5" peak to peak at 25Hz.

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.

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.

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

Yeah mine served faithfully for many years on an amplifier with about 3x the rms rating of the driver. Still works fine. Not a bad driver at all. It just isn't worth much. I'm trying to find homes for all of this equipment I've got collecting dust.

Enclosure bracing and damping is a deep topic. On the surface it's easy. Make the walls 6" thick concrete with re-bar cross bracing every 8", no parallel walls and make the whole thing weigh 3000lbs. Add a liberal amount of poly fill strategically. Of course none of that is really practical. The trick is getting to a good compromise point of complexity/weight/cost that starts to run up against diminishing returns if pushed any further. Subwoofers are generally easy. Brace the hell out of it and push the resonances up above band. The bigger issue with them is vibration of the entire cabinet mass. Dual opposed takes care of that of course. If that isn't an option it can become an issue with powerful subs though. I've seen well braced Othorn systems bouncing off of and vibrating across the floor. Midrange is much tougher IMO. The response issues and resonances are in band and more difficult to push out of band or squelch satisfactorily.

MAY 2016 Updated for sale list... I'm in the Louisville KY metro area. No international shipping. All equipment is used and may have a few cosmetic blemishes, etc... but is otherwise in correct functional shape. Aurasound NS18-994-A Bought last year. Tested. Needs a good home. Good condition. $450 shipped or $400 local pickup. I will drive a bit to meet. SOLD!!! JL Audio 10W3v2 SOLD !!!! Pulled out of my stealthbox in my Jeep WJ. Needs a good home. Good condition. $40 + shipping or $40 local pickup. 2 RE AudioXXX 18d2's Two left. Both are the overhung version 2 which has much higher motor force and the RE logo. $475ea shipped or $400 each local pickup. I will drive a bit to meet. SOLD!!! Chane Audio SBE-118 and a Chane VBE-118. SOLD!!! Both are passive cabs with a single Eminence built 18" driver. SBE-118 is sealed (Roughly 22" cube) the other VBE-118 is slot vented and tuned to the 17Hz range (Roughly 23x23x36"). Local pickup preferred. $100 each! I will drive a bit to meet provided gas is covered. Someone PLEASE take these! I'll ship these if someone pays the shipping! Does anyone know a broke, young or otherwise financially strapped person who can't afford much? This is basically charity at this point. Anyone know of a struggling audio enthusiast in need? BMS 18n862 18's. 1 pair. Low distortion with excellent all around performance. Little bit of oxidation on the motors. $450 each shipped. $400 each local pickup. B&C 21 IPAL's. 1 pair. Barely used at all. $850 each shipped. $750 each local pickup. Will drive to meet. RF T3S2-19 No longer for sale. I'm keeping my baby.

A custom acoustic table? You sir are either a genius or a madman.