SME

2 hours ago, jay michael said:

I did not calibrate my mic with a db meter. Looking at the REW website they mention this.

Calibrating the SPL Reading

Calibrating the SPL reading gives REW an absolute SPL reference by entering a reading from your SPL meter while a speaker or subwoofer calibration signal is playing. Alternatively an SPL calibrator may be used. This step is not required if you are using a USB mic with a cal file that contains a sensitivity figure.

If I am reading this correctly my mic should already be calibrated?? I am using the minidsp umik1 which came with a calibration file. 

I bought my UMIK-1 several years ago, directly from Cross Spectrum Labs.  The cal file did not contain an absolute SPL reference.  I had to calibrate the absolute SPL using the procedure described above.  Your situation may be different.

2 hours ago, jay michael said:

Thanks for explaining the calculations, its what makes this place really special,  I have been learning a ton!    If I do need to calibrate the spl, ill try and get that done and remeasure asap.  Regardless,  I can say that I have a huge freaking smile on my face now!  That was a tremendous amount of work getting those 4 cabs completed on my own and now I am feeling the rewards   You guys rock!   

Fedex is showing my SH-46's arriving tomorrow, its like Christmas over here!  Can't wait to get some music through the new rig, should be a potent little system.  

This calibration doesn't affect the shape of the curves, only the absolute number.  There's no need to remeasure as long as you can figure out what the SPL difference before and after calibration is.  You can add or subtract dB to a curve in REW on the "all SPL" tab.  Under controls, look at "Measurement Offsets".  Enter the number of dB to add and click "add offset to data" to apply the change.  Don't forget to save.

The SH-46s ought to be very good as tops.  My only concern would be that they are a bit narrow in coverage at "40 x 60 degrees".  Maybe that's typical for PA, and if they can be turned onto their sides to get 60 degrees in the horizontal, that'd be helpful.  A dance floor is not necessarily "long and skinny" like a concert venue.  Though larger events can be like that.  A lot depends on the details of the setup.

I once went to a multi-day outdoor festival with a huge system in the absolute middle of nowhere (rural Zambia to be precise).  A huge array was flown like 15-20m up (rough guesses on dimensions) on temporary scaffolding.  I think it took a sizable crew a week to build it, even with help from a crane.  The whole dance floor was something like 200m deep x 100m wide.  The camping areas were probably 0.5 km behind the stage, and the bass still thumped clearly in our tents all day and all night.

3 hours ago, jay michael said:

Thanks for the explanation, I don't understand most of it but super appreciate the people who do!  Thanks a ton for putting another great design out into the public for people to build!  I do have a question, if my measurement was taken at 1 volt @ 1 meter, what is the assumed power shown in the predictions?

I forgot to ask, did you calibrate the absolute level of the mic using an SPL meter?  Your numbers look a bit high compared to the sim @Ricci posted.  Note that the sim is for response with 2 volt at 1 meter instead of 2 volt at 2 meter (or the equivalent, 1 volt at 1 meter).  I'd expect your numbers to come in ~6 dB lower, but I could also be missing some detail.

Anyway, assuming the absolute levels of your mic and multimeter are calibrated reasonably accurately, your data shows "1 watt nominal" response at *2 meters*.  Because you were measuring at 1 meter, I had you set the output to 1 volt instead of 2 so that your numbers could be directly compared to those made with reference at 2 meter.  Note that manufacturers (and Hornresp) usually report output at 1 meter rather than 2, so if you want to compare to typical manufacturer specs, add 6 dB to your numbers.

Also note that by "nominal" the "1 watt" assumes that the impedance is 4 ohms for all frequencies.  Then, 2 Vrms (as used when measuring at 2 meters) will consume 2^2 / 4 = 1 watt on average (formula is V^2/Z).  In reality, impedance varies a lot with frequency and actual power consumed will depend a lot on frequency content.

So to translate your figures to manufacturer's specs sensitivity, again assuming your levels are accurate, your cabs are about 104 dB/1W/1m sensitive in the deep bass, from 30-50 Hz!  Of course, a manufacturer would look at the average over the bandwidth or even the peak value and publish that, so maybe 110 dB/1W/1 meter if quoting things generously.

In practice, if you stack the 4 all together, the stack  will gain close to 6 dB, giving you 110 dB/1W/1m at 40 Hz.  With a bridged K10 amp on those that's like 150 dB SPL max output at 1 meter, 130 dB at 10 meters, 110 dB at 100 meters.  Even if your numbers are off by 6 dB, these are impressive numbers.

Clearly your next task will be to preemptively make peace with your neighbors. 

13 hours ago, Ricci said:

The response shape looks good to me. Looks a little bit different above 130Hz than I expected. More rolled off above 130Hz. Do you have a low pass filter engaged? Low frequency corner seems a little lower than expected too. That could be closer proximity to the port than the horn section.

I think proximity of measurement to the port would affect the balance between upper and lower frequencies, not the low frequency corner.  It looks like the rear wall may be effectively lengthening the port more than anticipated.  The tuning looks to be around 26 or 27 Hz maybe?  I'm curious what the simulation looks like.  How much extra length do you add to the port in the sim to account for the rear wall?

6 hours ago, jay michael said:

Hey man, I’ll have to do some research on the impedance thing. I did play with the mic distance a bit, and it seemed the response was flatter the closer I was to the mouth. With the mic further away from the mount the response had more of a rising profile to it.  I stuck with 1 meter as that was what josh mentioned in his testing article, but I could easily redo it if he suggests otherwise when he gets a chance to chime in.

i do have a quality multimeter. Are you suggesting running pink or white noise through the amp and literally measuring across pos and neg at the Speakon?  

Does your multimeter have "True RMS" capability or something similar?  The best test signal may be a 50-60 Hz sine wave as that's likely what the meter handles best.  Play it at the same level that you use for a sine sweep measurement and measure the voltage.  You might want to do this while the amp is connected to a load, as I've heard rumors that even some solid state amps don't like running disconnected.  Most are probably fine though.

Whatever voltage you read, you can either adjust the test signal level until you get to 1.0 V (if measuring at 1 meter) or adjust the data afterwards based on the actual voltage and distance used.  Assuming the measurements are accurate, this tells us how the sub(s) respond in an absolute sense.  If you also know the max voltage your amplifier can output, then you have an optimistic estimate of max output using that amp.  The estimate is very optimistic though because the driver and/or other aspects of the system may overload or sound bad before you max out the amp.  The amp itself may not be able to maintain the max voltage if the current/power demand is too high.  Still the information is very useful to be able to understand the performance and capability.

Edit: I have cable with SpeakOn on one end and bare wires on the other.  I also have a paralleling SpeakOns Y-adapter.  This let's me measure voltage even when connected to a sub.

Impedance can be measured using REW using a custom electrical jig, but I believe that can be a pain to get to work well.  I use a "Woofer Tester 2" to measure impedance.  There may be other methods or products, but I don't know enough about them to recommend any of them.

It's hard to say for sure without seeing impedance measurements, but the frequency response measurements suggest the tune came in a bit lower than 30 Hz.  I also expected to see more output above ~60 Hz, but maybe that has to do with the SW152 vs. DS115?  Or maybe it has to do with measuring at 1 meter instead of farther away.  I'm curious as to @Ricci 's thoughts on these things.

Anyway, those looks like amazing cabs, and tuning a tad lower than 30 Hz is probably not bad for psy-trance which can sometimes have a lot going on at 30 Hz and below.  By chance, do you have a multimeter to use to measure AC voltage?  If you can measure the voltage from the amp, then your measurements will be more meaningful in an absolute sense.  For your cabs using one 4 ohm (nominal) driver each, a good "standard" voltage to measure with is 2 V @ 2 meter or 1 V at 1 meter.

It's funny, but you posted this about the same time I was exploring horn-loaded "mid-bass" designs with good HF extension as well, and was frustrated to see that OB mounting of a 15" dropped like a rock just a bit too soon for a good XO to the CD+horn combo I was looking at.

I'm glad you figured this out and moved to 12".  And then you probably encountered the fact that 12" pro woofers seem to be either very sensitive with roll-off in the 100s Hz or they are "subwoofers" which are not very good for a mid-bass horn.  There seems to be no middle ground.  Perhaps that's why I don't see many mid-bass horn designs that cover above ~300 Hz?

Anyway, to your question about subs.  I wouldn't worry at all about a 100 Hz crossover.  Bass localization is a weird thing that, IMO depends on a lot more than crossover choice.  If your sub makes a lot of noise or distortion in the HFs, it will cause localization.  If your sub has problematic HF resonances in the cabinet and/or vent system (e.g. organ pipe resonance) , lower XO may help but that won't fix distortion harmonics exciting these resonances.  Another thing is that listeners can perceive extreme pressure differences between ears, and if one is sitting "in a bass null" where pressure vs. location changes very rapidly, the bass can seem directional, making it sound like it may be coming from one sub or another.  This may be accentuated if there is a resonance there also.  And finally, the sound quality of the tops is important.  If the tops are clean, especially in the same frequency range as unwanted harmonics from the subs, you'll be less likely to hear the subs because you'll be paying attention to the music from the speakers.  :)

Assuming this is all in a smaller room, I think XO frequency may be even less critical.  In such a room, you're hearing the sound in a  "well mixed" state.  Localization information may not be useful for those frequencies.  I wouldn't be surprised if a well-optimized small room system could get away with bass management (i.e. using multiple in-room sources) for frequencies as high as 250 Hz.

Now I have to ask again, do you really need 130 dB SPL @ 100 Hz for home listening, with just one of the two channels?  At the seats or at 1 or 2 meter?  That's real loud ya know!  If you want that kind of SPL capability *and* want to enjoy some bass extension, you're gonna need some crazy subs.  You might damage something with that kind of setup.  That said, I think a Skram could probably do it depending on the distance, driver and amp choice, etc.  But will it have enough at lower frequencies?  Hmm, maybe you should build a pair of Skhorn instead.  I wouldn't bother with anything less than one of these if you are serious about that 130 dB SPL @ 100 Hz spec.

If you're looking for a vented cabinet with 30 Hz tune and same driver(s), you can build the cabinet quite a bit smaller and get almost as much performance at the tune.  Above 30 Hz however the Skram will still have at least a few dB edge and the benefit of acoustic low pass filtering.  Larger cabinets don't seem to gain much more, at least with the 21DS115.  The motor is crazy strong.

What is/are the intended application(s)?  Home vs. PA; indoor vs. outdoor; 4 pi vs. 2 pi vs 1 pi vs 1/2 pi?

I think a XO at 700 Hz may be too high because of the rapid roll-off of the woofers, which will tend to make phase shift very fast.  It may be do-able if the DSP capability is very strong, but even then it may be tricky.  Alternatively, use smaller drivers and give up some bass extension which isn't really horn loaded anyway.  If you really want subs that can keep up in a PA scenario, you'll want at least a Skhorn for each I think.  The Skhorn can likely cross higher than the Skram can too.

Of course much of this thinking depends on application.  Are you really going to hit 135 dB RMS @ 1 meter at home?

Parts Express?

Compared to the B&C, I believe the suspension doesn't tighten up as fast, so it has a bit more travel beyond Xmax.  I'm not sure I'd want to run it like that though.

2 hours ago, Ricci said:

Might break the cabinet joints on em if pushed too much further. LOTS of pressure developing. 4 K20's is theoretically only 6dB more and that's not factoring in compression of which there surely would be a large amount. So maybe another 3-4dB? Not worth it. If one of the biggest touring amps isn't enough it's time to add more cabinet/subs. 

I haven't looked much into the mechanical side of things, so I'm curious and rather fascinated that this issue exists.

Are you more concerned about the effects of pressure inside the cabinet or the reactionary forces from the drivers?  I may be missing something, but I doubt the pressure inside the cabinet (alone) is likely to get high enough to threaten anything structurally.  Though I expect that if pressures get high enough, new forms of non-linearity come into play which could increase distortion substantially.

On the other hand, I can see how reactionary forces from the drivers could be a real issue.

6 hours ago, Ricci said:

There are many good ideas out there for improving moving coil speakers linearity and efficiency. A lot of the time there are easy ways to improve drivers that don't involve exotic new technologies, or materials. Very good, relatively inexpensive devices could be made with standard materials and construction, but usually they aren't or have what I would consider to be an Achilles heel. A big part of it seems to be that driver designers simply do not design woofers with their priorities in the same places that I would. I think a lot of that stems from fixation on certain goals or ideas rather than looking at the whole picture from a birds eye view. Some of it is due to thinking that is to some extent crystalized around old school design philosophy.

This makes a lot of sense.  Related to this is classification of drivers by application like "home", "car", and "pro" and design toward ideals within those categories.  The trouble is that the distinction is rather artificial.  The best drivers tend to have useful application in all three categories.  Thinking of the RF T3-19, it's a "car audio" driver that you are using for both home (8 sealed cabinets) and pro (2 M.A.U.L.s).  Likewise, many pro-style 21" "super subs" are finding application in vented cabinets for home theater and are probably quite capable in cars too.

6 hours ago, Ricci said:

A 12" sub with a legit 25mm xmax,  3" voice coil, neo motor, shorting rings, Fs around 25Hz and a Qts in the neighborhood of 0.200. Weight <30lbs. No one makes this type of 12" woofer that I'm aware of. It wouldn't be a cheap $150 woofer but there's no reason it would be an $800 woofer either. The closest thing I've found from any of the major brands is one of the old Peerless XLS 12's and it has half the xmax and not much in the way of power handling. It's also overpriced for what it is. I have designs for these non existent drivers.

I noticed in the pro world, no one really makes good subs in 12" size.  At 12", you're basically looking at a mid-woofer/woofer.  You need to go to 15" or (usually) 18" before you get a real pro sub.  And while 12" is a popular size for car/home subs, such offerings typically come with much higher Qts.

6 hours ago, Ricci said:

As far as a big pro woofer goes...Something like the RF-19 concept is a good start. Basically the in between of it and the 21NTLW5000 would be a good start. For pro audio the RF-19 needs a serious diet. The 1000g mms and super tight suspension squelch the efficiency. We don't need the 34mm coil overhang and 80mm long coil winds. That's twice as much overhang as the highest xmax pro woofers currently on the market. For tunings at 25Hz and above that much excursion just isn't needed. Cut the coil length back to something more appropriate for the app like 60mm long winds which would still leave something like a 24mm overhang with A 12mm gap, which is still quite a bit beyond any of the pro woofers on the market and would remove 40mm of the total coil length and 25% of it's mass. The former would be shortened by 40mm too. The huge, heavy surround could be switched out for a lighter cloth style one. Due to the big reductions in moving mass and less excursion potential the huge 12.5" spiders could be downsized to 10 or 11" spiders with higher compliance and less weight. There are probably some weight savings in the aluminum dust-cap and cone to be had as well. Even the leads are way overkill and probably add a few grams extra. I'm pretty sure you could drop 300 or even 400g off of that driver fairly easily which would do worlds of good for its efficiency. A much lighter and shallower frame and 60mm shorter motor would greatly reduce weight and depth.

What you describe sounds a lot like the Funk TSADv2 and UH-21v1.  Specs I have for the latter: Fs 21.6 Hz; Mms 620g; Qts 0.23.  They don't use a cloth surround though.  The obvious downside is they are expensive.

On 5/27/2019 at 3:13 AM, m_ms said:

Have you done any comparisons between the two Skrams and the single SKhorn, I mean simply by listening to them? 

I wouldn't expect such comparison to be meaningful because the sound will depend a lot on each sub's location in that (presumably) small room.

2 hours ago, radulescu_paul_mircea said:

Good work guys! Attacking the subject from so many angles. 

Regarding a piston in a sealed enclosure. It will never be a good Idea. The efficiency of a piston in an infinite baffle is dependent on the force^2* SD^2/ MMS^2*Re and some constants in the fraction like speed of sound and density. This means that any increase in force squared/mass squared will give an increase in efficiency. But also having bigger radiation surface. Also, there is a relationship between mass and reactance which will change the behavior quite a lot and will make the system non linear. So a hugely powerful piston would be very good only if attached to a huge light weight surface and an amp made for constant current instead of constant voltage to be able to properly work with huge reactance.

I beg to differ!  Realize that the I.B. efficiency you describe is only really applicable for HFs, where practically realizable output depends a lot on inductance too.  For sufficiently LFs where an I.B. or sealed system can be approximated as an air pump, Mms becomes unimportant and Cms/Kms plus the air spring become very important because they provide the dominant forces opposing the motor.

What's particularly fascinating is that increasing Sd alone actually harms LF efficiency.  The pressure difference in a particular enclosure is proportional to air displaced, which in turn is proportional to output at a fixed frequency.  However, the motor force required to overcome the air spring from pressure difference (i.e. ignoring suspension Kms) is proportional to the cone area in addition to pressure (motor force = pressure * area).  So a hypothetical cone with very small diameter but enormous excursion can potentially play low in a sealed box much more efficiently than a cone with very large diameter but equal displacement capability.

For an example of a highly efficient small diameter "piston" in a sealed enclosure, consider the rotary woofer which operates using an impeller to drive an air piston.  It would be interesting to see this concept developed and improved further as that might eventually allow for very efficient operation of ULF in relatively small cabinets.

I can also see potential in novel methods of passive radiator design or maybe vented / PR hybrids.  One crazy (not necessarily practical) idea that comes to mind is to use a liquid like mineral oil as a mass element, which might allow lower tunes with much shorter ports while hopefully avoiding the air pipe resonance.  If the problems of vent length and pipe resonance can be gotten around, then drivers with more mass and stronger motors would enable substantial improvements in output density in these types of systems.

10 hours ago, Ricci said:

Good points made SME.

Thanks for your elaboration.   I generally agree, and I'd like to add a bit more.

There is the issue of particular application, which concerns home vs. pro sound as well as content and desired extension.  I suspect under-porting works quite well for home theater subs because: (1) most of the heavy content is well above the tuning frequency, especially with music; (2) for home theater the big hits at or around tune are likely to involve brief effects that are probably heavily processed and "artificial" sounding anyway.  Will vent overload problems be noticed under such circumstances?  Either way, an under-ported low tune sub is a pretty good compromise if the sound is reasonably accurate 99% of the time.

In contrast consider electronic music with heavy deep bass reproduced in a large scale pro environment.  Here, the tune will almost certainly be high enough to substantially interact with the music.  The music itself may demand high level continuous output and may be of a character that makes problems at certain frequencies stand out a lot more than they would with typical movie content.  While a good HT system is essentially running with "small "signals 99% of the time, the pro system is likely to be running with "large" signals most of the time.  Or there may be alternating periods of "large" and "small" signals.  These are much more challenging conditions.

I suspect with the M.A.U.L. the tune is low enough that it doesn't interfere with content much.  This is a situation where under-porting may be entirely OK, but there's no free lunch here because with the lower tune, the vent contributes a lot less output at higher frequencies than it would.  This is not really a "fault" of the M.A.U.L. though with its 4 x 19" RF TS3 drivers.  With the Skhorn, the design is a good compromise, which I imagine works well with "most" content.  OTOH, If one wishes to flawlessly play electronic music with high level continuous tones centered at 30 Hz, then "extra" cabinets  might be called for.  Orbone can build twice as many Skrams instead!

11 hours ago, Ricci said:

So if the driver is already able to overload the port badly what good is an even more powerful driver, more excursion, more power handling, more amp power? In theory more maximum output potential, less compression, less response shifting, lower distortion. In effect the envelope of acceptably linear operation is pushed a little higher. This has measurable effects even when the system is not being pushed beyond where the lesser driver is comfortable. At some point it is debatable whether these improvements are audible or worth it. Despite the fact that the vent might severely limit the extra performance near the tuning there should still be some performance gains even if they are miniscule at the vent tune itself. There is a lot going on above vent tuning which includes the area of maximum driver excursion and most of the audible bass bandwidth. The improvement may not be as large as what would be seen in a sealed system but it can still show an improvement overall. You may see little improvement near vent tune though if the vent cannot cope with the demands.

As you point out, more excursion, power, and power handling, are pluses, *all else the same*.  But in reality, greater excursion and/or power handling almost always come with a price, both literally and in terms of design compromise.  More excursion and power handling almost always add mass, which impacts high frequency efficiency.  And of course, spending a lot of extra money to expand the linear envelope by say 1 dB may or may not be worth it if that same money could instead be put into building more cabs.  :)

It's interesting that the "horn-loading" in the hybrid BP6 designs essentially compensates for the loss in mid bass efficiency that comes with the heavier, high displacement drivers.  In some ways, the hBP6 designs bring out the best in these drivers.

With that perspective in mind, I expect that the "perfect" driver would enable a design that offers higher output density and/or lower extension than is available now.  What that might look like, I cannot say, which makes it hard to figure out what capabilities the driver should have.  And indeed, the "perfect" driver may not be a driver at all.  Getting down to 30-40 Hz doesn't seem too hard, so some device that can take over and make lots of sound below 30-40 Hz might just be "perfect".

I would guess that graphene will be of greater benefit for high frequency drivers.  We can hope that graphene based composites will allow for large format compression drivers that don't break up until well above 20 kHz.  For subwoofer drivers, break-up is not usually a problem.  The issue is trade-off between loss through the cone material and unwanted mass, but sub drivers also usually have heavy coils making cone mass relatively less important.  I guess it may still make a marginal difference in "no expense spared" designs.

===

On the subject of drivers for pro use and for deep bass (tunes less than ~35-40 Hz), I have to wonder:  Is there a point of major diminishing returns, where better drivers don't help much more?  Certainly for use in sealed boxes in home theaters, more linear excursion is always welcome if accompanied by sufficient motor force and power handling capability, but for pro use, larger resonant cabinets are almost always a must.  Output within these cabinets is often constrained by other factors like port flow area, unless the cabinet is enormous.

Part of this discussion involves the somewhat philosophical question of how to define "useful headroom".  In a vented cabinet, substantial compression is likely to set in well before audible distortion/chuffing sets in, yet this compression is not necessarily innocuous.  It alters the "large signal level" frequency response.  So supposing the subs were setup using "-20 dBFS" (relative to amp clipping) test signals before the show, but then the subs get run closer to "-6 dBFS" where the amps and drivers might still have "headroom" but the ports may already be down 1 dB+  relative to the mid bass.  It's probably similar to (but not the same as) the frequency balance changes that occur with small vs. large signal effects in drivers with poor inductance control.  It's likely to have a substantial effect on perceived transient response.

In my "semi-PA" design I mentioned in an earlier post, the port velocity hits 25-30 m/s @ 53V where the pair of 15" 15NDL76 drivers (as simulated) are just reaching their Xmax/Xvar.  With a 21" 21DS115, I have almost twice as much Xmax and could conceivably put twice the voltage to it, but even at 25-30 m/s, the port is probably compressing a lot.  I doubt I'd see any of that "+6 dB" in deep bass output without making the port area and cabinet twice as big, which is not acceptable for my intended use.  (I want to be able to move it by myself.)

I imagine the situation is similar with the Skhorn.  A pair of IPAL-21s can easily overload the ports, so what is a more capable driver going to offer without making the cabinet even larger?  I imagine anything larger than a Skhorn is going to be a much bigger pain to transport and setup.  Even the IPAL-21 (vs. one of the much cheaper cousins) may be "overkill" in the Skhorn for a lot of people in that it may not be contributing much additional "useful" output at all.

10 hours ago, timcat4843 said:

Why do the studios find it necessary to filter the bass on Blu-ray releases? Are they totally unaware of the capabilities of the Blu-ray format?

No.  They just aren't aware of the impact filtering has on the sound.  That's very unfortunate.

It has occurred to me though that filtering may very often happen by accident.  For example, an "audio enhancement" plugin like a subharmonic synthesizer may be used to try to add *more* bottom end content, but the synthesizer plug-in may itself employ a filter, something that may be at least configurable but is likely enabled by default.  If that's what happened to Hellboy2, that would be quite sad being that it had plenty of bottom already (according to measurements here; I haven't heard the track myself).

FWIW, I believe subharmonic synthesis is being applied to a lot of tracks these days and can sound really good if used judiciously and if a high-pass filter is not present or is reversed (to the extent this is possible).  Sometimes it can be over the top, either a bit or a whole lot.  Even without BEQ to flatten the 30 Hz hump, "Aquaman" was just nuts with ULF content everywhere, including lots of stuff where it probably didn't belong.  I wonder if the mixers would have done things differently if they had experienced all that ULF?

Wow!  I'm glad someone replied because this very interesting but is definitely not an area I know much about.    My inclination is rather to think about the system as a whole, and I don't expect there to be any single "perfect" pro audio sub drivers.

8 hours ago, Kyle said:

Gonna scribble down a few notes, I like your effort here and enthusiasm. Here is what I can comment on really quick...I think the first thing here is to throw size out the window and just set up ratio's that make sense for scale. You can always scale up a driver or use 2 smaller ones that are equivalent to a single larger one. In that sense size does not matter too much. For practical purposes (lifting up the subwoofer) a 21 seems to be about the limit (give or take). At the end of a day, if you make a 24" can it really beat two top tier 18's? I think its important to keep that in mind because otherwise, why scale vertical when you scale horizontal -- to use a software term.

I think the 24"s I know of do beat a pair of 18s, in their own class at least.  Compare Stereo Integrity's 24s with its 18s.  Or look at Funk Audio.  I guess I haven't seen verification, but the specs on Funk's 24" look outrageous.  Despite this, I think larger drivers have a lot of disadvantages compared to smaller ones.  The reason they "win" for big subs is often simply a matter of economy.  Chances are a single 24" will cost less to manufacture than two 18s even with all the expensive upgrades.

At the same time, "other" concerns often become important.  In my own room I couldn't fit any cabinet taller than about 23" in my room, so a 24" driver was out.  The 21" size hit the spot in that regard.  Design flexibility/convenience, perhaps more than other factors, may be why super subs won't get much larger than 21".  At some point, the cabinets they require just get too big for anything other than permanent installation.

On a related note, I am designing a one-off "demo speaker" / semi-PA for myself and will probably opt for 2 x 15" B&C 15NDL76 instead of 1 x 21" B&C 21DS115 to drive a 32 Hz tuned vented cabinet.  Without question, the 21 smokes the 2 x 15s for deep bass   However, given that I have 700 W to throw at the sub(s) in each speaker and the fact that the speakers will still need big boy sub (Othorn/Skhorn class) augmentation in an outdoor setting, it makes more sense to go for the crazy mid-bass efficiency.  And I do expect I'll use it indoors a lot, often with half the ports stuffed to push the tune down to ~25 Hz, when I know I have plenty of spare headroom.  I'm sure my situation is pretty unique though.

8 hours ago, Kyle said:

When you make the former into a conductive material you allow current to be introduced there when pushing it through the gap.

Is this true for all conductive materials?  Or only for those that interact magnetically, which does I think cover a lot of the common conductors.  I don't think copper is very magnetic, but I don't think I've ever heard of a copper former.

Hey, is anyone aware of someone building a bunch of these, for like a big touring rig or something?

I was at a Red Rocks Ampitheater concert recently that had some decently loud bass (though nothing like I've heard some acts bring), just guessing here but maybe high one-teens at 50 m outdoors. (?)  Unfortunately, only one frequency was real loud, right at 40 Hz where the vented cabs were almost certainly tuned.  It was a bit obnoxious, but I don't doubt they were designed that way for loudness.  There were eight of them arranged in two vertical arrays.  They were supplemented by kick bins, but those weren't arrayed and didn't reach back as well as the subs.

That got me to thinking about how many Skhorn's I'd need for similar or higher SPL and realized the numbers are pretty staggering.  I'd probably start with 4 on each side, and a total of 16 would likely not be wasted for heavy "bass music".  I may be discounting some benefits from the acoustics, including a tall (probably tall enough to amplify a lot of bass) wall of rock behind the stage and large rock formations that cradle the space.  It seemed that the loudest 40 Hz continuous notes took several seconds to build to full intensity.

9 hours ago, Ricci said:

Rather than linearizing the suspension stiffness small air volumes may tend towards making the overall compliance worse in certain cases. The air inside an enclosure is a little harder to compress than expand. It gets worse as the enclosure volume gets smaller and the cone displacement gets higher. IOW higher compression and expansion and a larger differential. This asymmetry causes additional even order distortion. It may be enough to wipe out any gain in symmetry over the free air suspension stiffness. In some cases it may worsen it.

Thanks for this clarification, and I agree that a small box can make overall compliance linearity better or worse.  It depends.

You mention that the suspension compliance is not likely very linear because the former is so large compared to the spider.  Whether or not that's the case, it's interesting to note that compliance linearity is not very important if the driver is mounted in a tiny sealed box.  In that case, the stiffness of the air spring dominates and effectively helps linearize the restoring force.  I'm not certain, but I think this would be the case for most vented alignments too, at least at or above tune.

One "flaw" with Klippel measurements is that it's only testing in free air.  The Kms adds to whatever force is provided by the back pressure in the box, so "real world Xmax" with regard to overall compliance is likely higher than Klippel reports, depending on usage.  Similar considerations arise with regard to BL.  For example in a high Qtc sealed alignment operating at Fs, motor force is quite weak compared to the innate mechanical resonance,  isn't very strong  which in a high Qtc sealed alignment has much less influence on frequencies at Fs than at frequencies far from Fs.

Klippel also fails to account for how distortion products are reproduced by the acoustic characteristics of a system.  In a sealed box, BL non-linearity is imparted to the cone motion in form of a distorted motor force, but acoustic output vs. motor force drops dramatically below Fs in the sealed box system, which results in the sudden rise in distortion below Fs in sweeps.  For large room / outdoor applications where room gain may be weak, a driver may produce very offensive distortion at frequencies below Fs at Xmax well below the "70% BL threshold".  OTOH, the same driver in I.B. or a much larger cabinet may not roll-off nearly as rapidly at its bottom and may have much less distortion for the same Xmax.

My point with Klippel is that Xmax derived from arbitrary cut-offs (e.g. 70% BL) can't really be used as a simple "yard stick" to compare drivers to one another.  The plotted data of parameter variation vs. excursion is very useful but should be interpreted in the context of the overall system and intended use.  I haven't seen the Klippel data for this driver, so I'm only guessing here.  But if the testing suggests a low Xmax based on Cms (at 50% or whatever), that may not be all that important for the systems that use this driver.

39 minutes ago, maxmercy said:

The blu-ray I hope has the infrasonic content.  I will buy this title if it does.

At least if it doesn't, you'll know it got dropped in the home mix.

Aquaman: Total bass insanity.  I just can't believe how much bass is in this movie.  I'm not sure even "The Incredible Hulk" in on this level of madness.  And even though the track humps around 20-30 Hz there ULF is everywhere.  I might have noticed stuff below 5 Hz even.  I didn't get to finish the movie because about 25 minutes before the end, my AVR went into protection mode from what I believe was excess low single digit / DC content on one or more  channels.  (I've tripped it before like this using test signals but never with actual content.)  Our movie watching schedule was tight, so by the time I got all the equipment reset it was too late to finish.  I also figured the neighbors were likely getting pissed.  Yeesh!

What makes the bass on this mix particularly powerful IMO is that it is has a lot of content across a wide band and is hot well up into the 100s Hz where much tactile sensation lives.  This is crucial to allow one to "feel" the deep bass and ULF in and on the body.  And I was feeling it like crazy, for pretty much the entire movie.

Indeed, I think the bass was maybe too much.  A lot of content including a lot of the music was just way too heavy-handed for no good reason.  It sounds like subharmonic synths were used heavily on the track, for better or worse.  Also, I think a lot of issue lies in the pacing of the film itself.  I felt like WB was screaming at the top of their lungs that their DC comics were bigger, flashier, CGIier, and louder than Marvel's.  Furthermore the other track elements including the dialog were also *really hot* in the bass, and I struggled with intelligibility at times.  (I'm not sure hearing the dialog was all that important for this movie anyway.  )  I would have liked more mids and treble in everything, which is pretty much the same as saying I would have liked less bass.  Hopefully soon I'll have an adjustable "bass level" control I can use that maintains neutrality but pulls things back from insanity, which is fun for demoing but a bit fatiguing for a full 2.5 hour movie.

Does this suggest that WB's Atmos / home monitoring stages are weak in the low frequencies?  (A common problem with using a variety of room EQ options, in my experience.)  Or maybe it's a Hans Zimmer thing.   He shows up to the mix stages and screams MOAR BASS!

7 hours ago, Ricci said:

Im a 50min drive from them and they are production samples. Full production is a ways off still. Results are very encouraging so far.

That's awesome!  That's a factory I think it'd be a lot of fun to visit.

So I finally watched "John Wick".  Wow!  Excellent bass soundtrack and a fairly decent movie too.  My wife likes it enough to buy it, so I'll have it handy for demoing.

I have to agree that the shootout at the club scene is superb.  It's not what I expected.  It's fairly long and rather relaxed in pace rather than an all-out massacre.  I love the scene in the bathroom in which the bass from the music in the main room leaks through.  I thought the sound in there was very realistic and believable.  The bassline in the music has a pretty strong fundamental traversing the 20-30s Hz range.  Of course there're plenty of gun shots, and lots of very physical bass from them.  The gun shots in the movie had a lot of weight but I did not notice ringing.  They were very tight.

Some heavier effects in the movie did ring a bit in the low 20s, but it was mild and not unreasonable for what was being depicted.  All bass effects in the movie had ample amounts of mid and upper bass.  This was not a 30 Hz boomer.  Would more ULF have added something to the movie?  Maybe, a little.  But for the most part, it sounded good without it.

On 3/14/2019 at 5:33 PM, AmerCa said:

BEQs for Atomic Blonde and First Man possibly the ones that are said to most drastically improve the mix. In the first page of the BEQ thread there are actually a a few demo clips that you can download and toggle the audio to see a direct comparison between the BEQ and non-BEQ version.

Thanks for the suggestions.  I don't own either of those but may rent "Atomic Blonde".  It'd probably be best for me to test a movie that I own with a soundtrack I'm already familiar with.

On 3/14/2019 at 5:33 PM, AmerCa said:

Very interesting thoughts. I agree wholeheartedly with you in that balance in a mix should be the priority over extension or levels. It would help that the majority of mixes were done with the same level of detail and craftsmanship that than Ready Player One, but that's not always the case, ;-). But of course, there's also the question of personal preferences and system configuration and capabilities.

System configuration and capabilities is probably the major factor.  Mixer skill is probably a minor factor.  If the director and mixers are able to hear the bass accurately, a lot bad mixing decisions are likely to be avoided.  However it's also possible for a skilled mixer to know their own system and to know that if ya can't monitor it, then *don't touch it*.  Don't filter it unless it's causing obvious problems with headroom, in which case maybe consider other options like making things less loud.  Indeed, a lot would be fixed just by throwing X-curve in the heap and monitoring bass with a natural in-room rise, as preferred by blinded audiences far-and-wide.

On 3/14/2019 at 5:33 PM, AmerCa said:

I find quite ironic that once you upgrade to more capable subs, you find out you need more of them, as they're not giving enough SPL in the most audible regions. It's not the first time I've read such situation. The pains of being a bass head, I guess, lol.

Thankfully I don't need more of these subs.  When I designed the subs, aiming for passable ULF performance in my open living room, I was worried about the "excess capacity" I'd have above 20 Hz, but now I'm glad I have it.  I'm not really a bass-head in terms of wanting it really loud, but it seems that good quality in the sub bass region needs lots of SPL plus headroom.  Overkill is absolutely possible, but a lot harder than most people probably realize.

I spoke with someone recently who is getting a home theater set up and is not (*ahem*) quite the enthusiast that we are here.  He was debating whether he "really needed a 10" sub" or not.  I told him I had 4 x 21", and he looked at me like I was from a different planet.  I don't even want to try to explain it to him until he's actually been over here for a demo.  Most people would assume it's loud as hell, but for the most part it's just really clean.  It's what I expect reference quality sound should be like.  Clean, powerful, yet still family friendly.