Ricci

10 hours ago, jay michael said:

Ok... report after 3 full days of Skram use. 

And a pic of the set up https://i.imgur.com/IGh2BDp.jpg

 

Thanks for sharing your feedback Jay! Looks like a great time. 

What amps are you using to power the Skram's and SH60's?

5 hours ago, Alexlel said:

Wood and B&C 21DS115-4 on their way !

2 Skrams should be up in France before the end of the month

Excellent. I look forward to hearing your thoughts on it. 

13 hours ago, SME said:

Nice.  Maybe @Ricci can attach that to the first post as well.

Done!

14 hours ago, SME said:

Judging by the multiple out-of-context posts, I'm guessing it's some kind of AI spam-bot.  Maybe it's some university student's pet project?

I like to think of this as a preview of our robots/AI future.  AI generally struggles to cope with "understanding" context, so in the future, we'll just do away with context entirely.  Problem solved!

Yeah I noticed these posts yesterday. At first I thought someone who is not a native English speaker using a junky translator because some of the posts seemed "real". Now I'm leaning towards spambot AI.

Went through and looked at all of the posts of this member and the latest had a suspicious link =BAN-HAMMERED!

On 8/10/2019 at 5:54 PM, Samps said:

Is the Pi cooling plug effective?   Haven’t seen it used anywhere else which leads me to believe it’s not very effective.  

It may help with long term heat soak effects but it won't help with rapid voice coil heating at tuning or other WCS frequencies. Something like that takes quite a bit of time to remove heat. Voice coils may be extremely close to the pole and top plate steel in the motor but there is still a small air gap. Even very large coils are still relatively small so they can get extremely hot very quickly. 

Inuke 3000DSP or NX3000D. Should be more than enough power and has DSP built in. These are very cost effective amps. 

Nice looking builds. I like the big square slot port on the 21. You don't see those too often. 

On 7/1/2019 at 3:38 PM, 3ll3d00d said:

what does the average refer to in the CEA-2010 graphs? literally the average of all drivers in the site or something else?

Yes...The average of everything. It can be hidden. 

Thanks for reporting that Dave. 

@Kyle

Notes and free-air specs for these gigantic 24" drivers have been posted under the driver page. 

These weigh in at a back straining 115lbs and are capable of 4" peak to peak. 

Beef it's what's for dinner

On 8/8/2019 at 9:02 AM, radulescu_paul_mircea said:

This cabinet is tricky. The sound is absolutely stunning, but the thermal behavior is not best. It is best used in a low bandwidth and techno is to be avoided.

Even though a dual 18TBX100 sub is from -6 to-10 dB in maximum output compared to my dual 221 Ipal Skhorn XL subs, half the dimensions, on techno the are as loud when limiters intervenes. They do not sound nowhere near as good, but they are quite close in output. This is because the impredance minimum from 45 Hz to 85 Hz is dead centered in the band where that kind of music is centered 

 It's not just low impedance. It's low impedance in an area of minimum excursion. The bad news is this is an issue with almost any type of cabinet that can be built. 

Sealed:  the impedance remains relatively high and there is no minimum excursion frequency at all. Unfortunately the driver is trapped in a chamber which can heat up quicker, the driver uses a lot of excursion to produce output increasing distortion, output is lower and so is overall efficiency and sensitivity. Also the drivers are exposed to the elements and direct radiating which carries some sound signature with it. Smaller than vented.

BP4: This type of system has a sealed chamber which controls driver excursion below tune but it does carry a minimum excursion point in the middle of its bandwidth which also corresponds closely to an impedance minimum. Driver still enclosed in a sealed chamber as well. Can have very high sensitivity but only over a very limited bandwidth. Most of the 1 note BP mythology comes from this type of box due to limited bandwidth, vent noise and compression, bad group delay, etc. Driver can be better protected. Can be made about the same size as vented. 

Vented: Vented offers better overall sensitivity and efficiency than sealed over a large bandwidth. Similar to sealed excursion profile through most of the upper bandwidth which means lots of excursion needed for high output. Near vent tune the driver excursion drops to almost nothing and the impedance is at a minimum. The only thing saving the drivers from cooking in most cases is that the tuning is low enough that the content at tune is rare. Tunings at >40Hz could be problematic. Drawbacks are limited upper range output, lowish sensitivity, direct radiating sound, distortion, drivers exposed, vent noises and compression. Good size vs extension.

Passive Radiator: See vented. Add extra cost, completely sealed cabinet, more cones and moving parts to potentially fail or get damaged. No vent noise though. 

TH: Tapped Horns have a series of minimum excursion frequencies with usually at least 2 in the used bandwidth. Both of them will correspond to low impedance areas as well. A positive with TH's is that the driver is not enclosed and there should be some air exchange from the enclosure and past the driver. A negative is that the driver motor is usually partially exposed which gives a "half" direct radiating sound and gives greater chance of environmental damage. Also generally these have a limited bandwidth of about 2 octaves if the design is good. Slightly bigger than vented for the same corner frequency.

BP6: These are similar to TH's. These have at least 2 minimum excursion points in the bandwidth. Both of them will correspond to low impedance areas. One is at the lower port tuning. The other will be mid band corresponding to the upper vent tuning or path length depending on which type of design it is. These can have a reasonable bandwidth and there is some air exchange in the enclosure since the driver is not enclosed on either phase. No direct radiating sounds from driver operation. Drivers are somewhat better protected than with direct radiators. Slightly bigger than vented for the same corner frequency but generally can be made smaller than TH's. Drawbacks of vent compression / noise. Possible group delay or response issues if not designed well. 

BP8: These have at least 3 minimum excursion points. As with every other cab design they correspond to areas of low impedance and 2 if not 3 of them will fall in the primary bandwidth. See BP6 notes as the rest is quite similar. Can have a very wide effective bandwidth. Can be made to sound very clean. Very difficult to design and very sensitive to small changes in driver parameters or port/slot/horn loading or configuration. Issues with shifting of vent or radiator loading at war volume. Much bigger than vented and usually bigger than a TH for the same corner frequency. 

FLH: These have a series of minimum excursion frequencies that correspond to impedance minimums. Usually at least 2 will fall in the primary bandwidth. Additionally the driver motor  is usually enclosed in a very small sealed chamber. Before someone attempts to correct me on this I am not talking about full size bass horns, which for all practical purposes do not exist in pro audio, home, car or really any other audio systems, except in a handful of fixed installs. Yes if you get them near full size the impedance and excursion profile changes drastically but no one uses subs the size of a room for 1 driver.  Almost all of these that people actually use are greatly undersized. In that case they will have pronounce excursion minimums and impedance minimums corresponding closely with them. Anyway...These can have stellar response, efficiency, sensitivity and distortion with no direct radiating sound and no vent noise. The issues are that the drivers can be cooked easily on the undersized variants, these keep getting better the larger you make them but they need to be downright HUGE at which point they can be bettered by stacks of smaller options. 

Compound horns: See BP6...regardless of what exact mutation or spin -off there's at-least 2 excursion minimums and the corresponding impedance minimums, See a trend here? 

Scoops: These have the primary notch at the tuning frequency from the "scoop" and usually a smaller less severe one in the middle of the bandwidth.  As usual the minimum impedances are very near these minimum excursion points. These are sort of between a TH and a vented cab. These can have very high sensitivity and efficiency but only over a relatively narrow bandwidth and the response usually turns quite nasty above that point. Group delay and resonances can be a big problem. Drivers are exposed and these start to have direct radiator sound when pushed. These are generally not known for high SQ due to the response shape and other behaviors. 

I could keep going with TL's etc.... There are a ton of slight variations on the major design types, each trying to have their own special name or reinvention of the wheel. 

The take away of the above is this...Low impedance = more power applied. Low excursion = no cooling going on. Sealed rear chamber = trapped air/heat. So we want high excursion for cooling and low power? From a driver survival standpoint yes. But drivers run out of linear excursion quickly and it greatly increases distortion? That's also true. The 2 are at odds with each other. 

ALL of the cabinets that are not sealed/ free-air / IB are going to have at least 1 "Kryptonite" frequency band where low impedance (BIG POWER!) and low excursion (NO COOLING!) happen simultaneously. 

Bass reflex and BP4 will only have 1 Kryptonite frequency band. Bass reflex will be at tune. 

Every other design you can think of: BP6, BP8, Compound Horn, FLH, Scoops, TH, etc... Will have at least 2 Kryptonite frequency bands in their primary bandwidth. Some will have 3. 

If we look at it as only a function of handling power and self cooling the alignment that will take the most real average power is free-air, followed by sealed most likely. The next tier down is probably vented. Everything else would be a step down from there due to the multiple "Kryptonite" bandwidths. In the real world we have to consider the output vs the power input though. Some of the other alignments are capable of producing equivalent output with far less real power applied. It then becomes a complicated issue of how much power will each cab really handle vs the output that amount of input provides. A large sealed cab might be able to handle 500w broadband long term but a TH with the same driver may only handle 250w due to much less excursion and cooling being developed. However if the TH is 6dB louder on the 250w...

Excellent posts all. 

Thanks for posting some of your limiter findings Paul. 

To reiterate for anyone reading along...The very short version is that the modern long excursion pro woofers in cabs tuned above about 25Hz really shouldn't need to worry too much about short term peak voltages and setting these may not help protect the drivers in most cases. Over excursion isn't nearly as likely as it used to be with older short stroke drivers and that is mainly what this protects from. The enemy of modern drivers is heat and long term buildup in the voice coil. To that end you need to employ a limiter that protects from too much average power over a longer time period and this will need to be set MUCH more conservatively than the driver power ratings. If the limiter is constantly engaged you need "more rig for the gig" or to turn down the volume some. 

Something like 4 Ultimax 12's or 15's would probably do what you are looking for, but I don't know the costs over in Germany. Probably far higher than here in the US. Peerless XLS-12's might be an option as well. With 12's you will need some excursion and the BG's just aren't going to have it. 

B&C 15DS115's? 

21 hours ago, SME said:

I noticed earlier in this thread you discussed making and improving vent block to adjust the tuning frequency.  Can you provide any details of the design and how it attaches to the front-end?  I did look at the pictures and noticed that you don't appear to use any round-overs at the vent exits.  I'm hoping I can find a way to securely block rectangular vents with round-overs.  Good luck, ehh?

Good luck indeed if you do the roundovers. 

The port blocks I have are cut to fit into the ports and screw in on both ends but due to the way that the port dividers are cut the do not overlap the lip of the ports on 2 sides. I put some electrical tape on the edges and wedge in a bit of dense foam behind them then screw them down. It's not perfect by any means but there is very little leaking. I wouldn't say it's perfectly sealed either though. 

I haven't thought about it in a long time but I'd like to see what you come up with. 

It's in the first post. 

The DXF for this will not attach here. 

On ‎7‎/‎30‎/‎2019 at 3:40 PM, peniku8 said:

Another thing that confuses me is the fact that you did use the lossy inductance setting, but did not use the additional parameters you measured, or am I confusing things now?

When I enter values there and turn them on, the Le will light up in green. The SKHorn measurement looks closest to the simulation without these parameters (Le in red), so should I model my design (using the IPALs atm) with Le in red?

I'm trying to understand this setting, am I correct in saying that lossy inductance kinda does what the shorting ring is doing in the driver?

Updated the HR inputs for modeling the Skhorn cab in the first post. I deleted probably 200 HR records related to these cabs and variations. No wonder I had a hard time identifying the correct ones!

On ‎8‎/‎3‎/‎2019 at 9:24 AM, Murmel said:

I'm not overly confident in explaining the differences but my guess is has to do with duty cycle and crest factor. When testing amps and voicecoils many use a test signal that somewhat reassemble music which is 33% duty cycle, where 100% duty cycle has much more power density hence the long term tolerable VC wattage is much lower. If you use VERY conservative calculations you use a very high duty cycle signal to measure tolerable long term limiting but the output will suffer and subs not reach their max potential is my take on it.

I'm not sure under what conditions b&c came up with the 400w figure for the ipal, what I do know is that by simply measuring the output voltage of the amp with a sinewave and dial the limiter accordingly I use four times the wattage probably due to much lower duty cycle signals.

Correct. Duty cycle has everything to do with it. What might be fine with light amp clipping on 3hrs of sporadic kick drum or HT playback, will probably not be with bass test tones which some of the EDM and other similar genres are pretty much using in some cases.

The 400w recommendation is not the B&C rating. That's from the Powersoft Ipal module literature. The list it as the default setting and somewhere else in their literature for it there is a 700w max recommendation for the 21. That rating is way different from AES testing or pretty much any other that companies are using to rate drivers. That is what we would call a WCS rating. Powersoft offers an actual power limiter that is based on the real average power output of the amp in addition to voltage and current limiters. Most other units do not have this type of limiter.  

Most of us probably know this stuff but it bears repeating for anyone reading along. A sine wave has a 3dB crest factor, but music often has a crest factor over time of 12dB or more. If the average power of the sine wave is limited to 400w and the 12dB crest factor music signal is limited to the same average power, the peak output requirement from the amp is 9dB higher for the music signal vs the sine. While you may be clipping a 3200w amplifier on the signal peaks the true average power to the driver could be under 400w at the same time. In fact most of the time this is how things operate and how drivers survive connected to amps capable of thousands of watts of power. It's all about how much time.

The 23 second long measurement sweeps I use do occasionally kill a driver due to excursion or a burnt coil. A 23sec sine wave at the maximum sweep level I use is very tough but at the end of the day it's only 23 seconds and most drivers have no problem with it once or twice and are allowed to cool off immediately afterward. If I were to loop that same measurement signal 13 times in a row it would burn up the drivers in under 5 min. Once we are talking about hours of playback at high volume the drivers have a chance to fully heat soak the motors and coils and all it takes a couple of low crest factor or higher than average level signals to toast the already hot coils.

With all that said I've found most of the modern pro drivers to be quite resilient and durable including the 21DS115, so I'd have to assume the OP's driver was taking quite the beating when it burnt up.

On ‎8‎/‎1‎/‎2019 at 6:10 PM, Jeff L said:

Any word on the street date for this

Last I'd heard there were some delays on the frame delivery and build up of stock.

It was Luke.

The SP amps will run into a 1ohm nominal load better than any other amps I've encountered so far, but I'd expect that the sustained power is cut back quite a bit from the 2ohm or even 4 ohm rating. Othorn's with 21Ipal's would have the majority of the impedance well above 1ohm. Most of it would be above 2ohm. Also the bass bins used for pro audio work generally only operate from 30-100Hz with steep filters in place.  Luke's were the same. It's a different use than something like a sealed cab run for HT with no high pass, which is a lot rougher on the amps due to only 1 impedance peak and lowest impedances at the deepest frequencies.

There is some disagreement on whether horns achieve a lower corner in stacks. Most of the " good" measurement data I've seen presented points to no more gains than with direct radiators. Increasing mouth area doesn't lower extension by itself. In fact it raises tuning unless the horn volume AND length are also increased. There was a big discussion about this on DIYaudio forum years ago with data but I can't remember the name of the thread. I recall another big discussion on Prosoundweb years ago as well.

22 minutes ago, LSC said:

Wow thanks for your thorough reply!

Very eye opening.. 

It gives me something to work with and puts my (can't really blame the dj) abuse into perspective..

I assumed that the RMS rating states how powerful a sine wave can be for 2 hours continually ☹️ 

Silly me.. Oh well there's always a first... and more to learn haha..

Is there any literature on that? 

Also if there's any more input on how to set this combination up for bass heavy content then that'd be very appreciated!

Will go from ricci's recommendations but maybe someone else who has experience in limiting right for low crest factor signals wants to chime in

Also does anyone like the idea of temperature sensors? Apart from being impractical they would allow us to really know how the driver is doing regardless of how sophisticated the limiting works.. 

I don't consider myself an expert on setting limiters and everyone seems to have a little bit of a different take on how to set them. 

With the amount of power you have with the Behringer amp you shouldn't have to worry about short term peaks or excursion except below tuning. You are concerned with long term heat saturation only. 

A few links. Like I said it's a deep hole and I don't claim to be an expert in this field. A lot of it seems to be trial and error depending on the settings available in your amp or DSP. Perhaps some others with hands on experience will chime in.  

https://www.powersoft-audio.com/en/downloads/documentation/application-notes-white-papers/quick-guides/804-how-to-setup-limiters/file

https://www.rane.com/note127.html

https://www.bassboss.com/limiter-subwoofers/

Yes the JL's do have good output for their size especially among commercial products. This is their biggest attribute and selling point. If size is less of an issue they quickly lose the horsepower war with larger subs but for those who really need something small they are a good option. You do have to pay for it though. 

In case there was any doubt yes a lowly Behringer NX amp is capable of smoking a 21DS115 or most any other driver with the right/wrong? circumstances. 

I'm sorry to hear that.

DJ's are notorious for pushing subs as hard as they will go and blowing speakers. This means often pushing the signal DEEP into bass amp clipping and leaving it running like that for hours. What this does is effectively chop the peaks off of the signal and increase the RMS power into the drivers. The drivers are no longer getting "breaks". If the 6K was effectively clipping constantly it possible that the driver received an average power of 1000w or perhaps even more. If that happens at frequencies with little driver excursion it will result in a cooked coil very shortly. 

I wasn't there and there is no way of knowing what the content was, what spectral makeup, or whether the above is true, but I'd bet that something similar to the above happened. The signals used and the duration are big variables. 

Despite having an AES power handling of 1700w in no way will the 21DS115-4 handle that amount of power for any significant amount of time. None of the drivers will. A 100% duty cycle signal with that amount of power will destroy the coil in under a minute. Was a limiter in use? The harder and longer that the subs will be played the more tightly set the limiter will need to be. Also the type of music is a big factor. A sub for HT or sporadic music listening in a home can probably get away with no limiter. The content is very dynamic and the amp/sub isn't constantly pushed to its limits. Live sound with rock type music would be another area where the limiter may not need set very hard as it would mostly just be the kick drum peaks with bass guitar or other bass instruments much lower in level. Once you get into electronically generated bass heavy music with lower crest factor and prolonged maximum output use you have to be much more conservative. 

As an example of how conservative... The 21IPAL driver is rated as a 2500w AES driver with a huge 6" coil, very high efficiency and tons of motor venting etc. In the IPAL amplifier module manual the long term power limiter setting is recommended at 700w maximum for that driver. About 1/4 of the AES rating and that's one of the highest power handling drivers on the market and that's the bleeding edge maximum that they recommend for it. The default setting for it is 400w...

Based on that I'd say that starting with a long term average power limit of 400w maximum with a 3 or 4 second attack and release seems a reasonable start for the 21DS115 and it may need adjusted down a bit from there. Your peak limiter can be set much higher with a much faster attack/release. Some limiters are voltage based, some are current, and others power. If yours is voltage based something like 40 volts rms equates to about 400w into 4ohms. Unfortunately the NX Behringers only seem to have a single "peak" voltage limiter which is really not much to work with in this case. The problem is not peaks but sustained power over long periods. Perhaps someone can confirm the available limiting settings on the Behringers. I don't own or use them. The online information is surprisingly vague

Limiting is a complex subject and there are so many variables involved. If you are letting others "pilot" your system they will invariably bang it as loud as it can go all night no matter how much rig you bring and how loud it gets, they will find the limits. You will have to plan for worst case scenarios if handing the controls over to others. Basically the same as most companies have to do with their active speakers. 

I really need to get a pair of these going. I'm ashamed I haven't even tested or listened to these yet!