Ricci

Their Reynolds Number study leaves a lot to be desired.  For one thing, the Moody Diagram from which they base their argument that the output hits a wall when the flow goes turbulent, really only applies to so-called fully-developed pipe flow that is several pipe diameters away from any entrance, exit, bend, constriction, expansion or any other flow disturbance.  Only some subwoofer ports will be long enough to have a region of fully-developed flow.  The losses that grow non-linearly with output (and thus cause compression) can occur in the middle of the pipe or in part of the flare or even outside of the port.  Other experiments of their demonstrated that even a slight round-over at the entrance and exit yielded a dramatic performance improvement.  Therefore it is a shame that their Reynolds Number experiments were done on systems with hard transitions between pipe and entrance/exit.  If instead, those experiments used optimal flares at the entrance and exit, we could have gained more insight into the nature of losses in the middle of the pipe vs. elsewhere.

 

Another thing is that their Re data suggest that port velocities need to stay very low to avoid hitting a wall.  They argue on the basis of their data that there is a wall for Re somewhere between 50-100k.  Keeping Re under 50k is not easy.  For 4" tube ports, that's 7.5 m/s; 6" tubes is 5 m/s;  2" or a 1" thick slot is 15 m/s.  The Reynolds number increases with pipe diameter, so the implication if Re is in fact important is that multiple smaller tubes or slots may be better.  But let's do a reality check here, OK?  The trend in their data is that compression sets in for even lower Re with lower frequencies.  So let's look at Josh Ricci's M.A.U.L.  It's got a big honkin 12" port.  Fully-developed flow, if it exists somewhere in there will definitely be turbulent (Re >= 100000) with a port velocity of only 5 m/s, and according to the conclusion reached by looking at that data, his M.A.U.L. should hit an output wall by that point.  Correct me if I'm wrong, but I'm pretty sure 12" was pretty undersized by the usual rule-of-thumb standards.  I bet he's pushing 50 m/s or more through that thing at high drive levels.  And while there is definitely some compression, we're definitely not seeing a wall at only 5 m/s.  Right?

It's almost as if there is some factor they are missing or forgetting to include in the Reynolds number or it is not describing what we think it is. It seems to indicate that larger vent areas start to have major issues at lower velocities than smaller ones. However measurements seem to suggest that the useful core velocity limit (an output wall so to speak) is actually higher for larger vent areas not lower.

Correct. The M.A.U.L. design uses a roughly 12" by 40" vent and it is undersized. That's near the size of a decent subwoofer like an SVS 12" cylinder for just the vent. It's huge. Something like an 18" vent would be much better at managing the output but it just doesn't fit with the tuning involved. Almost every vented system has greatly under sized port area. The vent for the M.A.U.L.  simulated to have port velocity of almost 100m/s at maximum with a K20. Of course compression prevented it from ever reaching that type of velocities but it surely got up near 50m/s. That's not ideal by any means but the space dictated what the compromises needed to be and worked out ok. Seems to me that the larger vent area with less wall friction supports higher velocity before totally limiting but perhaps non linearity sets in earlier as compared to multiple smaller vents totaling the same area. This would be something like a 12" (730cm area) vent compared against 730, individual 1cm area vents packed into the same form as the single 12". I'm doubtful that the 1cm vents will be able to support 40-50m/s airspeeds at all and would likely be at their core limit way before that point.

Don't horns have their share of response non-itineraries as well?  I guess they aren't as bad, or maybe it's just that you get so much output from a horn that you're less likely to hit non-linear output levels.  The same may apply for the M.A.U.L. in practice, even though it certainly doesn't quit at 5 m/s port velocity. 

Yes they do. I believe you are fully correct that most of the time they are simply used well below their capability limitations and that is what allows them to not exhibit these things as much. Horns can and do exhibit large air velocities not to mention extremely high pressures in some cases.

came across this paper recently which goes into this area in some more detail -> http://koti.kapsi.fi/jahonen/Audio/Papers/AES_PortPaper.pdf

Yes...That old study is the best read I've seen on vents but it leaves a lot of questions which SME pointed out.

Looks like it's probably a 4th order bandpass with a bit of shaping and flaring to the front vent unless there's entry from a secondary somewhere into the mouth behind that grill.

Interesting that there were reports of subs having thermal protection issues. Those drivers are seriously low impedance. The average is much higher than normal due to the extremely large impedance peak but near the minimums like in a vented cab it will still be very low and that has to be difficult for an amp to dump current into a 0.5 ohm load especially if the content has a repeating note near a minimum.

Damn...Was hoping the movie was at least decent because this looks like a solid bass movie. Simply turn up the subs a bit and you're there.

Aggressive surround mix. Meh bass.

Did you apply the official Data-Bass +36dB bass boost?

November 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.

SOLD!!!!

2 RE AudioXXX 18d2's (These are currently on Ebay)

Two left. Both are the overhung version 2 which has much higher motor force and the RE logo. $475ea shipped or $375 each local pickup. I will drive a bit to meet. $700 takes both of them with a local pickup!  

SOLD!!!!

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.

Hey Ricci... thought you might like to know I may soon be in possession of that Chane SB-113 box and use it for a dual Ultimax 18 build......

 

 

But I'm not sure how much interior space there is once you account for the difference in box thickness and bracing....

It should be close enough to not matter. Not sure if the bracing or driver cut-out will work without modification though.

Where do you see the PB16U driver is an underhung design? The manual says overhung.

Regardless of that. It's underhung. The SB16 is overhung.

Kudos for the edgewound coil but that 8" coil can handle four or five of the amplifiers they are pairing a single unit with.

 

Maybe not. The SB16U probably since it is an overhung design and a claimed 32mm xmax so that's probably a lot of coil there. The PB16 is an underhung though so it may not actually have that much wire mass. Doesn't look like it in the exploded view. Should be plenty for what they've paired it with though.

I was wondering what the frame diameter is on that driver. Could be actually 16" or could be 17". I read some people discussing the 16" size choice like it didn't make sense to them cause it wasn't "standard". There have been oversized and odd size drivers on the market for years. Orion HCCA 15's are really 16's, RE XXX's are oversized, JL drivers have been odd sizes for years, square subs, pentagons, 11's, 13's, 22's, etc...SVS doesn't sell these except as part of a finished powered system anyway.

But anyway as far as audio is concerned, cinemas have offered little to no improvement in sound quality since the early 90s when digital audio came into being.  Atmos is the clear exception to this, but Atmos is still only as good as the system its played on.  I suspect a fundamental issue is that cinemas do a poor job of configuring and maintain their audio systems.  People don't expect much in return.  A system might sound "really good" one night and poor the next night, so most people just don't pay attention.

Most of the cinemas close to me are Cinemark and we go a couple times a year still. The sound is usually kinda bad. The bass is pathetic. I've heard blown sounds before and or it's M.I.A. altogether. If you're lucky you'll get a few gratifying 35-60Hz booms. The surrounds and main channels are often extremely loud and shouty/harsh (especially the center channel dialog). Not very pleasant. The general impression is of 300-6Khz being hotter than everything else and the system being not quite in its comfort zone anymore, or perhaps just old and worn out.

Here's the thing, a whole lot of people out there really have no reference point for what a good system can sound like. To them the same system I've described above sounds amazing compared to their TV speakers, their soundbar, their factory car stereo, their ear bud headphones, or their Z-logic computer speakers. They go in the same theater I do and are thrilled with the overall volume, dynamics and BIG presentation. Matters of perspective.

Agreed.

The driver is "only" 64lbs which is kinda surprising to me. I'd have guessed more. I find the driver to be the most interesting part of the new SVS's and it seems like so does everyone else, but they are just one part of a finished turn key system and not sold separately. The whole sum of the parts is what matters and how they will be reviewed by a dozen or so publications I'm sure.

Not sure what other claims or marketing blurbs there are to take issue with other than listing peak to peak xmax? Sure there's a lot of rather splashy buzz words and marketing hype going on there but that's par for the course. It's maybe a little thick but pretty similar to that seen a lot of other places IMO.

I have often wondered whether some of the post production and mixing stages are perhaps using transducers to help monitor the bass range, but I've never seen anything confirming it. It would make sense.

I believe they list peak to peak in the literature but yes for people not as informed they will not understand that it should be divided in half for comparison to most xmax specs. Not sure if they actually call it xmax either. Haven't read the owners manuals. The specs on the website appear to be referencing the peak to peak xmech.

Also the cutaway pics of the PB16U seem to show a very large spider. Looks like possibly 13" if I had to guess maybe even slightly larger. Could even be a 14".

Knowing the gap geometry can give a much clearer idea of what type of useful stroke a driver may have. For example you may have 2 drivers both rated at 20mm xmax. Without knowing the gap geometry and going off of just the spec it might be assumed that both offer similar excursion behavior but that may not be true.

Driver 1 could be a 43.5mm coil wind height with a 10mm gap height. 

Driver 2 could be a 65mm coil wind height with a 25mm gap height.

Both could claim 20mm xmax quite easily. Driver 1 could use the common mathematical coil overhang + 1/3rd of the gap depth for the rating. 43.5-10= 33.5/2=16.75mm physical coil overhang. 1/3rd of the gap would add an additional 3.33mm resulting in a rounding to 20mm. Driver 2 could just be using the physical coil overhang method, with no adders, of 20mm. If it did add in 1/3rd of the gap it would be closer to 28.3mm. Another consideration is that the shorter magnetic gap in driver #1 will mean that the coil physically leaves the gap at 26.75mm displacement from center. In all likelihood no matter how much power you put into the driver it will not be able to travel further if even that far. Driver 2 has a much larger gap height plus a longer coil. The coil doesn't leave the gap of driver 2 until 45mm from center. Despite having similar basic xmax ratings the 2 drivers differ quite a bit and driver #2 should have much higher effective displacement. This is very simplified and ignores a ton of other factors like fringe field and suspension performance of course.

Actual coil and gap specs are much more useful than an xmax figure in many cases.

My ball park guess is that these will put up about 4dB on the 13.5" Ultras perhaps with a bit better extension to boot.

About the 8" coil. Kyle is right the first concern is getting a spider system that will support large excursion in a linear manner with so much of the area taken up by the huge 8" former. It's not impossible though. Why use an 8" coil? Well it does provide better centering with the spiders to prevent a long former from cantilevering during large excursions. Also you can get higher motor force with that much coil in the gap and larger heat dissipation surface area. Both can help improve power handling and reduce thermal compression and parameter drift at high power. Some downsides typically would be increased moving mass, cost and perhaps higher inductance. Just because the coil is a larger diameter doesn't necessarily mean that the coil is more massive though. For all we know it could be a relatively short winding height with a single layer edge-wind. Something like a 3" diameter, 3" tall winding height, 8 layer coil, could have more wire mass even though the diameter is much smaller. Those are fairly common in big car audio subs. We don't have enough info to tell for sure. I would assume that SVS's engineering team used the large diameter for centering, improved thermal dissipation, marketing purposes (hey why not?) and higher BL and weighed the tradeoffs versus more normal coil sizes. Their engineering has been quite good so I assume there are solid reasons for it that make sense as per their design goals.

These do look like they'll be solid performers. I don't think the pricing is too bad either considering what you are getting. Sure they aren't cheap compared to DIY or the bang for the buck ID leaders but I also think they offer something a bit more upscale looking from the typical stuff as well.

The driver is certainly the highlight on these. Apparently one of them uses an underhung topology and the other uses an overhung arrangement so the two motors and coils are different between the SB and PB versions. I thought the same about the spiders. That is a big landing on those frames. Probably fit an 11" or maybe even a 12" spider. One of the few things they make no mention of is the spider system. I'd imagine they custom tooled something for them like everything else on them, but that was one of my first thoughts as well. The motors are not neo. Typical ferrite slugs internal inside the pole, which really is surprising to me. They have got to be heavy as hell. The old 13" was 55lbs so these have to be pushing 70 to 80lbs I'd imagine. The PB model is 175lbs and really not very big at 25x21.7x30.9". It's a chunk.

 It'll be interesting to see how they perform.

If we had MUCH better efficiency we wouldn't need exotic cooling methods.

 

Explanation of sensitivity measurements - SP2-12000 wins on the low end

I don't see how this could have anything to do with the amplifers themselves. I think this is solely due to loosened compliance.

 

Explanation of sensitivity measurements - peaks and troughs seem switched between tests

Same with this anomaly. I don't see how going from one flat-response amplifier to another could cause any change here. I think the breakup modes have shifted. On both of these drivers, breakup modes are very mild, exhibiting well damped resonances that create soft lumps in the FR instead of sharp peaks. It doesn't look to me like the peaks have become troughs and vice-versa, it looks to me like all but one or two of the resonances have shifted lower in frequency. The one that I can't really explain is the blip around 150Hz. This can be seen in all your measurements of similarly sized boxes, which is sure to be a rear chamber resonance. I don't see how this could have moved if the enclosure is the same size. Maybe the damping material has settled, affecting speed of sound and therefore perceived depth of the rear chamber to the acoustic waves?

Changed compliance surely plays a part. The impedance results indicate that the peak has shifted down some. I guess it could be possible that some of the breakup nodes have shifted as well. You can see a baffle step in all of the results as well. Nothing in the enclosures has changed.

I'll be revisiting this at some point so I can do a comparison back to back on the same day. Might be interesting to check that same RF driver every year and see how much it changes over the next few years of use. Makes me wonder how far the suspension will soften and what the original brand new driver will look like compared to 3 or 4 years of use later.

I'm planning to go ahead and do the tests again using the SP amp and the K20 both on the same day to reduce the margin of error. Really the only cabs I have that will somewhat handle those amps are the dual 21Ipal and the RF T3. The RF T3 is a bit sketchy on the 6000 during the long term sweeps. It was taking a LOT of power. Not sure how many of those it can take. I'll need to allow a cool down period in between to get the temps down and allow the sensitivity to settle back into the starting point.

I'd like to do more of this type of testing of amps for fun but I need a good 4ohm nominal load and multiple drivers with a lot of excursion. Problem with the RF and Ipal drivers is they are single coil only and the impedance is so low. I really don't want to buy yet another 2 ohm T3 just for a 4ohm load for this type of testing. For example an Inuke 6K isn't even rated for 2 ohms nominal. It would be best to have multiple smaller drivers with dual voice coils to keep the size down and allow more wiring flexibility. Perhaps a whole boatload of low cost 10" or 12" drivers.

I simply mean that one amp is reversed signal polarity from the other. It shouldn't affect anything.

Here are some graphs including the max burst for both.Note that while there are some differences in the 21Ipal FR they aren't anywhere near the RF differences. I've never seen anything like that. It almost looks like there is some kind of oscillation as the two measurements seem to flip flop back and forth. I'm stumped.  

FWIW, the spec sheet on the SP1-6k and SP2-12k call out the max voltage (no current) as 126V.  Where impedance drops low enough, this maximum will droop a bit.  At 2 ohm, rated power of 6 kW is achieved with 109.5 V.  I think the long-term output compression magnitude plot illustrates current limiting in the SP2-12k.

 

Any idea why the "Basic Response" measurements for the T3S2-19 are about 1.5 dB higher across the board using the SP1-6k vs. the K20?  Is this just due to variation in environmental parameters or other random variation?  It would be good to know this because many of the results have the SP1-6k beating the K20 by about 1.5-2 dB.  If it's a margin of error thing, than we can't really say that the SP1-6k is really winning anywhere in these measurements.  Not that tying the K20 for low frequency performance at a fraction of the price is somehow a failure for the SP1-6k.

That sounds right for the SP2-12K voltages. I see that the specs say 126v maximum with no load but 2000w rating into 8 ohms requires 126.5v. I thought that it may be a bit higher than this something around 135-150v short term. Guess not.

Good question. I've been scratching my head over this. There is some margin for error for sure in the atmospheric conditions, calibrator  and actual voltage applied. I'd say +/-0.5dB sounds realistic. The weather was different on the test days. I had thought that perhaps the older test was on a hotter day but I looked at it and the opposite was true. The impedance curve suggests that the suspension of the driver has loosened up and broken in significantly. That's unsurprising due to the first test being on a fresh basically unused driver. I'd only done a free air break in at Fs to check for excursion noise, proper functioning etc and then pulled parameters and impedance prior to testing it. It has spent the last 11 months or so in the back of my Jeep run off a PDX.1000 after the first high power test so it has been used a lot more by now. A loosening of the suspension could account for some increase in the bass sensitivity of possibly 1dB down at 10Hz. That's part of it and the rest is likely 0.5db of voltage or calibration error and atmospheric conditions.

Another thing I remembered is that the K20 and SP-12000 I have on hand have differing polarities. Look at the notch in the original measurement up near 180Hz which has now turned into a hump in response on the SP amp measurement. I find that even more baffling than the sensitivity increase and it is related to the differing polarity I think.

If you look at the 21-Ipal retest the sensitivity there is almost bang on but we still see some odd reversals of notches and humps in the response.

As far as the amp comparison made...I would definitely not go so far as to equate a concrete SPL difference to it but I think the general trend still shows through especially when considering the older same day tests in my room conducted before. The 6000 module produces more sustained LF power into low impedances and the K20 does better with brief dynamic signals and higher impedances. I think that general statement holds from looking at the max long term, CEA-2010 and max output bursts. The maximum burst output (not the passing distortion limited results) is pretty telling in that regard. The shifting down of the impedance peak increases the LF efficiency and we appear to see an increase in CEA-2010 burst output below 25Hz for both systems due to reduced distortion but no increase or less of an increase in the case of the T3 in the maximum burst output in the deep bass.

I need to retest with both amps on the same day to eliminate some of this error potential but that poses issues of its own.

Back on this topic...I'm resurrecting this thread as there is some new data. I recently tested the RF T3S2-19 driver in the 4.5ft sealed cab and also the 24" cube dual 21-Ipal sealed cab both with half of the SP2-12000, so effectively the 6000w SP1-6000 Torpedo plate into 2ohm nominal. I thought it would be good to see what type of headroom and performance these could provide as an "active" type system with one of the most powerful plate amplifiers on the market similar to what could be sold as a high end consumer turn key sealed system. Both can be compared to the tests last year with the K20.

The short of it is that a SP-6000 produces more sustained power into impedances roughly 2 to 3 ohms or lower than the bridged K20. The K20 isn't really rated into bridged loadings lower than 4ohms of course but it operates decently just with reduced power limitations. The max long term testing shows the difference in the sustained power well. The 6000 amp was run all of the way until the clip light was heavily illuminated throughout the sweep into both systems. The burst testing also showed some differences. The K20 did not start to show advantage over the single 6000 amp into these loads until the shorter duration bursts higher in frequency or in the areas where the impedance was high. As previously shown the Speakerpower / Torpedo amps produce much more sustained power into low impedance loads. They can also short term burst a similar amount or more into low frequencies and low impedances than the K series. The K10/K20 amps have a ton of voltage potential and will operate into low impedances but they really perform their best into 4ohm stereo/8ohm bridged or higher where they can use the high voltage rails to their potential and not be current limited as much.

What do you mean? Dual drivers with 1680cm Sd and 15mm coil overhang vs single 1472cm driver with 34mm coil overhang is pretty close in overall displacement.21's win by a bit on displacement and decisively in the areas not limited by excursion.

Useless in the workshop? Draw it in Solidworks or SketchUp and send that bitch to a 3D printer. You can brace it within an inch of its life for no extra work or money. Put gussets on top of gussets inside your gussets. You only pay per gram in 3D printing. You'll probably be using ABS or something. Fiber reinforced plastics can be stronger than many metals, but I don't know if they're printable.

You could 3d print them but the cheaper FDM machines, which produce the cheap parts don't finish that well on parts that big. The materials aren't all that strong without some thickness either. any more than 30% fill can cause huge issues with parts warping / pulling on bigger pieces. SLS or SLA would be a LOT better but the money goes way up too.

 

The devil's advocate side of me is saying no, at ~$2500, this silly speaker is already stupid expensive and way more expensive than expected.

 

   That's one expensive micro speaker!

Since the budget is blown out already, was there any thought to using exotic materials like perhaps aluminum plate for the enclosure?

Ok so practically speaking we are back to rules of thumb (aka experience) as it doesn't seem amenable to modelling without being a fluid dynamics expert.

I am way behind on the PVL / TR discussion you guys have over at AVS but it does seem like the consensus now is that particle velocity should be as high as possible. However a 1" port will always have higher velocity than a 6" vent which will have higher velocities than a 16" square horn mouth. This is opposed to the age old problem of trying to get enough vent or mouth area to avoid severe compression and noise. Also is there any thought being given to other considerations such as the total area of the high speed particles? For example a 4" port firing into the back of a couch versus a 21" driver surface area. One is a higher intensity but much more localized effect versus a more diffuse effect over a larger area.