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What Magico aren't saying is under what conditions that was measured or simulated. I looked but not exhaustively. The sub might do it in a car or a closet. 

4000w = 36dBw 

Average sensitivity of sealed 18's I've measured is about 79-82dB at 20Hz. With 2 drivers in double the airspace it's maybe 85dB tops. It will increase a little with a much larger cabinet, but theirs isn't that large. 

They look to be using Aura based 15's and 18's judging by the pics. They may be modified but those are definitely Aura based drivers at minimum. Decent drivers for sure but no way in hell they maintain 1% distortion with any sort of real excursion being used. Even with active feedback. No way a sealed cab can make loud 20Hz noises without tons of excursion because physics. Unless...they are in a tiny confined space like a closet or measured extremely close to the cone, or both. 

When I measured the Aura 18 it would burst about 107.5dB maxed out at 20Hz with horrendous distortion. This is basically everything it has before something breaks. Add 6dB for a second identical unit on double the power. Call it 114dB rounded up. Subtract a couple dB to clean the output up and pass CEA-2010 thresholds and my estimate for Magico's Q Sub at 20Hz under DB style ground plane testing (2m groundplane, rms) is in the neighborhood of 112dB. Assuming the amp can push it that far. Definitely not with 1% distortion. 

Add 3dB for peak SPL. Add another 6dB for 1 meter results. The remaining 15dB must be from the particulars in the way the sub is measured. 

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14 hours ago, Ricci said:

What Magico aren't saying is under what conditions that was measured or simulated. I looked but not exhaustively. The sub might do it in a car or a closet. 

4000w = 36dBw 

Average sensitivity of sealed 18's I've measured is about 79-82dB at 20Hz. With 2 drivers in double the airspace it's maybe 85dB tops. It will increase a little with a much larger cabinet, but theirs isn't that large. 

They look to be using Aura based 15's and 18's judging by the pics. They may be modified but those are definitely Aura based drivers at minimum. Decent drivers for sure but no way in hell they maintain 1% distortion with any sort of real excursion being used. Even with active feedback. No way a sealed cab can make loud 20Hz noises without tons of excursion because physics. Unless...they are in a tiny confined space like a closet or measured extremely close to the cone, or both. 

When I measured the Aura 18 it would burst about 107.5dB maxed out at 20Hz with horrendous distortion. This is basically everything it has before something breaks. Add 6dB for a second identical unit on double the power. Call it 114dB rounded up. Subtract a couple dB to clean the output up and pass CEA-2010 thresholds and my estimate for Magico's Q Sub at 20Hz under DB style ground plane testing (2m groundplane, rms) is in the neighborhood of 112dB. Assuming the amp can push it that far. Definitely not with 1% distortion. 

Add 3dB for peak SPL. Add another 6dB for 1 meter results. The remaining 15dB must be from the particulars in the way the sub is measured. 

Thanks for your take on this. It would seem the creativity needed to imagine such "particulars" in measurement approach by Magico makes for a scenario that is wholly disconnected from anything real-world. It's telling they'd venture forth with such claims (or simply outright disinformation?) seeing they believe they can get away with it, but I guess it goes to show the general lack of knowledge in this area among audiophiles and how difficult it is to justify prices of (at least) $22k and $36k respectively - that is, for a single item - without flaunting some über-impressive SPL and distortion numbers, at 20Hz no less. 

Sorry to be ranting, but isn't it rather typical of audiophilia to prioritize inertness of construction, finding no doubt its apex with these Magico subs for mega $$, than higher sensitivity, more displacement and bigger size? How important do you find rigidity of construction with subwoofers and the aspect of the enclosure itself - apart from the driver/port/other - as another source of distortion? Is it any real issue as a distortive source with subs like the Skram, Othorn, Skhorn etc. at anything but what approaches war volume, not to mention in domestic environments with lesser SPL requirements? I'm not saying rigidity and inertness of construction isn't important, but I'm asking to which degree. 

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I believe I can hit about 130 dB at 20 Hz on my system of four sealed Funk 21" + SP2-12k...  and help from a partial wall behind the listening area and strong room mode at 20 Hz!

I poked around on the site long enough to notice the stated figure had a footnote "[1]" that appeared to be dangling.   I could not find "[1]" anywhere else.  The figure sounds pretty realistic ... for listening in a closet maybe.

I'm just waiting for audio product NFTs to hit the market.  Just imagine the future in which you'll be able to buy a 30 second subwoofer excursion test video (slow motion) on The Blockchain, for the most authentic digital bass experience: "*yours* for only $59,990!"  (while supplies last)

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4 hours ago, SME said:

I poked around on the site long enough to notice the stated figure had a footnote "[1]" that appeared to be dangling.   I could not find "[1]" anywhere else.

Was looking for that too, but could not find anything...

 

At least Klipsch is transparent about this, here is their top of the line consumer product (single 12" the size of a potato):

grafik.thumb.png.e108c72ee2d0b07985f1f1315d1258b7.png

 

And this is from Klipsch's top of the line actual cinema subs (single 18" the size of two-three Skhorns):

grafik.png.06daf42f4cb0dd70d37fd586b15a757e.png

grafik.png.6a6c68b83f77a0a11a3974f7916f0afd.png

which is fair enough I guess.

But sadly there will be people bragging about how their 12" sub can do 130db, manipulated by "false" information. 122db at 20Hz is what the Skhorn did in my room. And that was on an amp as powerful as probably 20 of the amps they use in their 12" potato. 120db+ at 20Hz is no joke, it's the point where stuff in your house starts coming down from the walls!

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I searched a bit for the notes accompanying note "1" but couldn't find it either. 

Needless to say context matters. The details behind the 1% distortion claim accompanying the 136dB at 20Hz is what really would be of interest. I'm assuming they have active feedback in the subs but even still...Having measured a number of Velodyne, Rhythmik and other subs with feedback, it helps, but it can't clean up things at near maximum output by that much. 

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Sorry for bringing up another sub into this discussion, but I just found this one randomly on youtube and it´s really interesting, yet pretty old:
https://www.youtube.com/watch?v=E7Bkrypxzs4
http://www.eminent-tech.com/main.html

https://www.youtube.com/watch?v=uQfDazQ9Rkg&t=52s


Completely "new" (seems to be already 15 years old now) design compared to any cone woofer, looks and is actualy just a fan looking through a hole into a big closed(?) box to compress the air inside. The complete rotor assembly makes the classic back and forth movements to produce the sound waves.
The motor/ airblade sound is annoying for sure, but why have I never heard about (or felt) something like this?
Anyone here who know´s why this type of sub isn´t already in every cinema? If it´s as good as they claim?

 

edit:

found a good video about those subs, but I still don't know why the arent use in cinemas or big clubs, at least I have never heard of those ratary subs before

Also I learned that not the rotor assembly itself are moving but just the blades, similar to those of RC-helicopters I gues

 

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I'm not a huge fan of PS audio, as Paul tends to spread misinformation to sell snake oil, but the video was alright I guess, bar the fact that he called infrasound "sub sonic" (which is a speed category). I think the rotary sub is similar to an infinite baffle arrangement in the sense that you need a lot of air volume behind the "driver" (essentially a separate room) and the SPL in that room/rear chamber will be the same as in the cinema. Typically it's easier and cheaper to integrate even a dozen subwoofers into your cinema than to basically build a cinema around one device.

Theres also the guy from Sweden(?) who turned his floor into a subwoofer (housing 16 18" drivers iirc in a large horn made out of bricks). I'm sure it's amazing, but I think it's obvious why we don't all have something like that..

Put 4 dual opposed sealed 21" cabs into your HT and you're gonna be pretty happy with the ULF, I'm sure. Want more? Buy/build more subs. Not enough space? Buy higher end drivers.

Personally, I'm not a fan of ULF. I prefer to keep sub 15-20Hz purely tactical through non acoustic devices, like Crowsons or a BOSS platform. Going that route means I can go with something like the Skhorn, plug a port and get good output to about that region, add my tactile device and not be missing much.

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The rotary has been around a long time. Old news. Some guys have tried to DIY it with varying success. The main reasons it isn't more popular is it's expensive as hell, It requires some sort of isolation because the operation is a little noisy, it requires a large airspace / IB for the back wave and it really only operates well below 30Hz. 

With that said I've heard from industry vets that it sounds amazing when done right. 

Anyway...A little off topic for the Skram thread. Unless you are planning to install 2 to operate under Skram's?

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Hello everyone! A few days ago we pulled the speakers into town and enjoyed a little bit (some yes some no) :) 
unfortunately I didn't have time to do the measurements, but the only thing missing were two more boxes :
The difference between these two sounds is in the years. Tms4 are 35 years old and still work impressively, far from being loud for "today's standard", but during that time, respect 🙏 The kicks were modified BPH with 18Sound and Skram with RCF. Other sound are scoop from Rog 21 'loaded w B&C , Kickbin C2D-15' w B&C  and the top box is not finished and loaded w 18Sound.
A comparison between these two box. Scooper have more SPLs and up cut off i higher than in Skram, but for my ear Skram is much more tonal and works better overall, for some people scoop is better, they don't have the depth that Skram have and these days I'll switch them to DSP from K10 and make my cut off freq. and do comparison again hopefully outside w measurement, because now are connected to Ligwa Preamp (only Skram).

skram in city.jpg

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6 hours ago, peniku8 said:

Wow, dedicated MBMs with Skrams and horn loaded tops! Do you even need those? That's a lot of upper bass.

Since it is a soundsystem culture and bass music is played the most (DUB / DNB) it is necessary, especially when you have tms4 over 30 years old :) I made measurements before in the room where we keep the sound and this is how it would look like ... Someone will say no you are crazy, someone that Skram can do range these boxes above them etc ... I agree but I put less strain on him like this and gave him more power for the range that works (29 - 55/60) bph works from (60 - 100) ) and 18 from tms works (100-240) low mid which is otherwise harder to get to sound right and not wonky..
Measurements were made in the room and this is so you can imagine what I think..smoothing 1/24

3 way.PNG

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Hello Chiko,

Interesting comparison...I'm not surprised that the scoops sound totally different. Scoops are really efficient over a narrow bandwidth. The trade off for the efficiency is peaky response, limited bandwidth, limited low frequency output and BIG size. Most of them are huge cabs but really only have LF extension to 40-45Hz. What 's the dimensions for those scoops? Those look BIG. I've never seen any in depth measurements of a good scoop design. 

Did you try listening to music that has deep bass <40Hz? You should hear a huge difference. 

Everyone has their preferences for sound but personally I'm not a fan of running a 4 or 5 way rig with the bandwidth split up into tiny segments in the bass range. When I see the picture of the stack with the Skrams you posted...I think that 1 or 2 more Skrams sitting in place of the MBM's and running the whole bandwidth would be better. That's just me though. 

 

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Last I checked, the vast majority of DnB and Dub Step music go below 40 Hz.  Plenty gets down to 30 Hz if not lower.  A sub synth processor can also add more bottom.  If done well, I believe adding extension is often impressive enough (in perceived intensity) to justify the SPL that was sacrificed.  The biggest issue is that too much content is filtered too high.

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4 hours ago, SME said:

Last I checked, the vast majority of DnB and Dub Step music go below 40 Hz.  Plenty gets down to 30 Hz if not lower.  A sub synth processor can also add more bottom.  If done well, I believe adding extension is often impressive enough (in perceived intensity) to justify the SPL that was sacrificed.  The biggest issue is that too much content is filtered too high.

Random example of SubHarmonic Synthesis, which illustrates this point well, since he switches it on and off and also plays it solo later on:

This is used on a low string section now, but the same thing works with basically any source. I have something like that as effects channel on my live mixing console to fatten up the kick drum/low toms if needed. Or to turn a Cajon sound into a bass drum sound (which is amazing!).

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I mostly play DnB and Dubstep on mine too and the Skrams really shine below 40hz where a lot of other systems lack for this music, did a few measurements of my system before our beach party last weekend.

The measurements were in a 700m2 warehouse with 6m ceilings so the room noise shouldn't be too bad but i'm new to measuring stuff this big. Each cab was measured seperately 1m in front of the port for the subs, and 1m in front of the midbass for the tops (midbass and mid/high are amped seperately) I missed 1 of the tops for some reason. I think these graphs were psychoactive(sp?) smoothing whatever that means.

After these measurements I bumped the gain on the highs up a notch to smooth it out but at the party I ended up bumping it back down to this level as it was a bit too sharp at war volume.

1020894164_monostacktesting.JPG.7a517a79f89ef7d1a3b4b7011afd0604.JPG

267472007_4954248031262156_1399052955521860001_n.thumb.jpg.ce64d37ad2554550cb6fc3d04abe8921.jpg

 

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If you measure the tops at one meter and in front of the mid-woofer, then you are probably at a pretty steep vertical angle, which will have diminished output compared to a measurement directly in front of the top.  So when you boosted to compensate, you were likely running the tops too hot.  Be sure to measure the top from directly in front if you want to use this data to match the different sections.

Also, if that bump at 4-5 kHz shows up at other measured angles, you might want to try knocking it down with some PEQ (if you have it) because that resonance is likely to be a real ear-grinder, not to mention stealing a lot of attention away from the rest of the good stuff.

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Happy new year fellow bassheads,

I would like to introduce myself and announce that I am going to join the race for clean and low bass and decided to build myself a soundsystem that is going to include pair of Skrams (might double up later...). I am Domme from Germany, a DJ of Dub(step)/DnB/Jungle aka heavy bass music and very spoiled from my premium hifi sub (SVS PB12+/2), which hits the 20Hz mark cleanly and also quite loudly but of course lacks capacity for extended SPL-sessions in larger venues with its "only" 750W and 2*12" setup. It still is one of the cleanest bass I have ever heard so far, even at pretty high output levels, and I do miss the low frequencies a lot when I hear familiar tunes in commercial venues/festivals apart from a very few good DIY soundsystems. I love the culture and looks of the more traditional sound systems with their huge scoops and stuff but I don't think it is the cleanest and deepest bass, it's mostly loud. But I do want to deliver a clean and deep bass and not just loud one, at leas there is no war volume required right now. I am also very restricted with weight and dimensions since I only have a small crew, rather small vehicle and so on, especially because I don't exactly register my events in the current situation if you know what I mean so I have to hide in the woods where the floors are uneven and I would sometimes need to haul above roots and stuff... my initial plan was a pair of Othorns but when I worked through this thread and read about the Skram's benefits regarding weight and dimensions plans were changed quickly. Imagine someone building a Skram because he calls it "more mobile". I also prefer the driver to be hidden and protected from external sources of hazard like the audience, weather etc. Now I still have some questions on driver and amplifier. The Skrams might even replace the SVS in my home setup, where I would really like to have a pair and not just a single sub for increased tuning options and overall better room control.

Driver questions
I already ordered a pair of 21SW152-4s for the Othorns and at first I was glad that they can be used in the Skram as well. Then I read about Riccis recommendation to use the NSW6021-6. Could someone please explain to me why the NSW6021-6 is supposed to be easier to drive? Wouldn't it require a much stronger amp (wattage-wise) because of the higher impedance? The thing is that due to xmas/nye I can still return the 21SW152-4 because they have not been delivered yet (14 days return policy in Germany). Now I am very tempted to use the NSW6021-6 instead. Main reason is because I trust Ricci and the good reputation he has on several forums. More headroom sounds good to me so I would rather spend 50% more per driver than having to build and haul more cabinets. And ~45% increased driver cost is still better than having to buy a bigger van.

Amp questions
Closely related to the driver question is the amp question. For example, SME said that the NSW6021-6 is supposed to be easier to drive with common amps. Do you just mean easier because the load is lower? Because I would still need a bigger amp to deliver the power at 6 Ohms, right? And this is most likely not compensated by its 1dB increased sensitivity. Anyway, I am planning to use a Lab Gruppen FP10000Q for 2 subs and 2 tops. Do you think it's fine for them? In the (distant!!!) future I would probably upgrade to 4 Skrams and run all of them on a separate FP14000 and use the spare 2 channels on the FP10000 for kicks so the Skrams can fully concentrate on the frequencies below 80Hz. But as I said this is most likely not going to happen this year anyway.

Any advice would be greatly appreciated 🙂

Kind regards,
Domme

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@Dommewelcome to the forums, nice to see a fellow German here ;)

I can imagine that a single 2x12" sub sounds a bit light on its feet in larger venues. I frequently do shows with only a pair of 12" subs (12BG100) when budget is tight and often wish for more, especially when it's outside. Two Skrams would be a night and day difference for sure. They're similar to the other pair of subs I own and the difference in output to even regular 18" subs is incredible. The Skrams are a fantastic choice, but remember to put big casters (100mm or bigger) on them if you have to roll them through uneven terrain.

About the Eminence, I think Ricci meant they're easier to drive compared to the 1Ohm Ipals (since that's its direct competitor, disregarding the whole IPAL system itself and disregarding the 2Ohm IPAL driver). Impedance wise, the SW152 is the highest. Efficiency wise, the DS115 is the best, by a small bit. The Eminence has a bit more excursion and slightly higher power handling, about two thirds of the way between DS/SW and IPAL. It's like +2db from them to the Emimence and +1 from the Eminence to the IPAL.

Amp wise, I currently run two 21DS115-4 off a 10kQ like you're planning on doing. It's damn loud. For the FP14k idea you'd be better off running two 8R cabs in parallel per channel. I would personally avoid running two 4R cabs in parallel, unless the cables are like max 10m and pretty thick (4mm² at least), or damping factor will come bite your ass.

For driver selection, I don't know what you paid for the SWs, but here are the cheapest prices I could find in Germany:

2 21DS115-8: 1074€ (my personal choice - I have 4 of them)

2 21SW152-8: 1194€ (not much of a difference to the DS)

2 NSW6021-6: 1958€ (~2dB more headroom)

2 21IPAL-1: 2072€ (~3dB more headroom, basically limited to plate amps or extremely short wire runs)

That makes the Eminence ~80% more expensive than the 21DS115.
If the 2dB higher headroom is worth that for you, then go for it.

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24 minutes ago, peniku8 said:

@Dommewelcome to the forums, nice to see a fellow German here ;)

I can imagine that a single 2x12" sub sounds a bit light on its feet in larger venues. I frequently do shows with only a pair of 12" subs (12BG100) when budget is tight and often wish for more, especially when it's outside. Two Skrams would be a night and day difference for sure. They're similar to the other pair of subs I own and the difference in output to even regular 18" subs is incredible. The Skrams are a fantastic choice, but remember to put big casters (100mm or bigger) on them if you have to roll them through uneven terrain.

About the Eminence, I think Ricci meant they're easier to drive compared to the 1Ohm Ipals (since that's its direct competitor, disregarding the whole IPAL system itself and disregarding the 2Ohm IPAL driver). Impedance wise, the SW152 is the highest. Efficiency wise, the DS115 is the best, by a small bit. The Eminence has a bit more excursion and slightly higher power handling, about two thirds of the way between DS/SW and IPAL. It's like +2db from them to the Emimence and +1 from the Eminence to the IPAL.

Amp wise, I currently run two 21DS115-4 off a 10kQ like you're planning on doing. It's damn loud. For the FP14k idea you'd be better off running two 8R cabs in parallel per channel. I would personally avoid running two 4R cabs in parallel, unless the cables are like max 10m and pretty thick (4mm² at least), or damping factor will come bite your ass.

For driver selection, I don't know what you paid for the SWs, but here are the cheapest prices I could find in Germany:

2 21DS115-8: 1074€ (my personal choice - I have 4 of them)

2 21SW152-8: 1194€ (not much of a difference to the DS)

2 NSW6021-6: 1958€ (~2dB more headroom)

2 21IPAL-1: 2072€ (~3dB more headroom, basically limited to plate amps or extremely short wire runs)

That makes the Eminence ~80% more expensive than the 21DS115.
If the 2dB higher headroom is worth that for you, then go for it.

@peniku8Thanks for your reply and summary of the drivers. I already cancelled the order earlier today because I decided to do additional research and get some input from more experienced people. Unfortunately, I will not be able to start working on the cabinets until somewhen in February anyway.

However, one thing confuses me: you are speaking about the 4R DS first, but in your comparison you listed the SW and DS in their 8R version, which the FP10k could not fully support, at least not in 4-channel mode. Did you recommend them because of my plans to maybe upgrade to 4 Skrams later with the damping factor in mind or was there another reason? Until now, I never noticed that there is no impedance recommendation on the SW/DS in the initial post. I must have thought it was 4R because it was still in my head from all the Othorn stuff I read earlier. And then I picked the FP10k to match it.

I can't wait to finally get started with building 🙂

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14 hours ago, Domme said:

@peniku8Thanks for your reply and summary of the drivers. I already cancelled the order earlier today because I decided to do additional research and get some input from more experienced people. Unfortunately, I will not be able to start working on the cabinets until somewhen in February anyway.

However, one thing confuses me: you are speaking about the 4R DS first, but in your comparison you listed the SW and DS in their 8R version, which the FP10k could not fully support, at least not in 4-channel mode. Did you recommend them because of my plans to maybe upgrade to 4 Skrams later with the damping factor in mind or was there another reason? Until now, I never noticed that there is no impedance recommendation on the SW/DS in the initial post. I must have thought it was 4R because it was still in my head from all the Othorn stuff I read earlier. And then I picked the FP10k to match it.

I can't wait to finally get started with building 🙂

Prices are identical between 4 and 8R versions and performance is very similar too. You're right that I recommended the 8R versions because of your upgrade plans in the future and the fact that 2R doesn't like long cable runs. You could also build one pair of 4R Skrams, put them on the 10kQ and then build another 4 with 8R when you get the FP14k and run 6 when needed.

Running 20m of 4mm² cables (typical length I bring to a medium sized gig) you end up with a damping factor of 12 into 2R, which isn't exactly great. To increase it to twice the value (over 20 is decent), you'll need to double the cable thickness (could run a 4x4mm² cable with two wires in parallel each to essentially get a 2x8mm² cable), halve the cable length (will you never need more than 10m?) or double the impedance. If your amps are always close to the subs go for it I guess. If you're not so sure about that, be aware of the issues running low impedance might cause.

The FP14k will pump out the most power into dual 2R, but more power is meaningless if your system sounds bad because the damping factor is nearing single digits.

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6 hours ago, peniku8 said:

Prices are identical between 4 and 8R versions and performance is very similar too. You're right that I recommended the 8R versions because of your upgrade plans in the future and the fact that 2R doesn't like long cable runs. You could also build one pair of 4R Skrams, put them on the 10kQ and then build another 4 with 8R when you get the FP14k and run 6 when needed.

Running 20m of 4mm² cables (typical length I bring to a medium sized gig) you end up with a damping factor of 12 into 2R, which isn't exactly great. To increase it to twice the value (over 20 is decent), you'll need to double the cable thickness (could run a 4x4mm² cable with two wires in parallel each to essentially get a 2x8mm² cable), halve the cable length (will you never need more than 10m?) or double the impedance. If your amps are always close to the subs go for it I guess. If you're not so sure about that, be aware of the issues running low impedance might cause.

The FP14k will pump out the most power into dual 2R, but more power is meaningless if your system sounds bad because the damping factor is nearing single digits.

I never considered the damping factor before, but did some research on it and tried to reproduce your numbers. I succeeded when using the following formula:

DF_cable.png.a55fc6b26a19b03a2e04c8671b43d51f.png

Is this the approach you took? If so, you most likely have forgotten to include the output resistance of the amplifier and much more important the voice coil. If we only consider these, we get the maximum possible damping factor (Re taken from 21DS115-4 TSP and halved because of parallel wiring):

DF_amp_coil.png.136cef4d83aa993c95c40703c11b6628.png

If this model is correct then the damping factor can never get below this value. Even in 16R operation and with perfect cables we only get a DF of ~14. So it looks like cables only have a small impact on the damping factor unless they are extremely long or thin. Anyway, I was planning to use 4mm² cables. Not because of the damping factor but for current density and voltage drop reasons. Still, I see the benefits of using higher impedance drivers.

Sorry if I got a bit off-topic here. I promise to make up for it later by taking a lot of pictures 😘

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2 hours ago, Domme said:

I never considered the damping factor before, but did some research on it and tried to reproduce your numbers. I succeeded when using the following formula:

DF_cable.png.a55fc6b26a19b03a2e04c8671b43d51f.png

Is this the approach you took? If so, you most likely have forgotten to include the output resistance of the amplifier and much more important the voice coil. If we only consider these, we get the maximum possible damping factor (Re taken from 21DS115-4 TSP and halved because of parallel wiring):

DF_amp_coil.png.136cef4d83aa993c95c40703c11b6628.png

If this model is correct then the damping factor can never get below this value. Even in 16R operation and with perfect cables we only get a DF of ~14. So it looks like cables only have a small impact on the damping factor unless they are extremely long or thin. Anyway, I was planning to use 4mm² cables. Not because of the damping factor but for current density and voltage drop reasons. Still, I see the benefits of using higher impedance drivers.

Sorry if I got a bit off-topic here. I promise to make up for it later by taking a lot of pictures 😘

Not sure what you're doing with Re there, but it's not supposed to be there.

You're correct that amp impedance is part of the unwanted impedance, but I left it out on purpose, since its impact is vanishingly insignificant compared to cable resistance (in this scenario and in typical PA applications in general).

Here is a table of the impact of cable resistance on the outlined setup above (2 21DS115 in parallel with 15m of 4mm² cable), calculator provided by Benchmarkaudio, modified by me for a better overview:

D8Sa05q.png

You can see that the amp's output impedance (nominal damping factor) hardly plays a role here (10kQ (250) and 14k (500) are marked in green), since the cables bring it down from 250/500 to 12. Total response error through your operation range is about 1dB, which is about your maximum loss, depending on the frequency. This also causes phase issues, which means even more reduction at the crossover frequency.

You also see ~1dB/10% energy loss in the cable. That's 1,4KW of the FP14k at full tilt. And that's with a beefy 2x4mm² cable.

I attached the calculator to this message for anyone who wants to play around with it.

 

Further reading:

https://benchmarkmedia.com/blogs/application_notes/audio-myth-damping-factor-isnt-much-of-a-factor

https://bennettprescott.com/downloads/dampingfactor.pdf

http://www.cartchunk.org/audiotopics/DampingFactor.pdf

DampingFactorCalculator.xlsx

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Line resistance is basically a linear effect, and when it's small, its impact will probably not be more than that from normal T/S parameter variation in the driver one's using.  One can even input the linear resistance directly as a parameter in Hornresp, to see what happens!  This also means that the effect can be compensated for relatively easily using minimum phase EQ.  Of course, the wasted power can't be recovered, which limits max output.

An important question to ask in the above example is whether it's acceptable to be dissipating "1200W of power" (see below) into those lines.  That depends on how much wire length the dissipation is spread over.  The more general problem concerns how much *current* an electric wire can handle for long periods of time without overheating.  This dictates electric building codes that require a minimum diameter wire for a given current rating.

Now, no one's going to run their sub amps at full blast forever.  Few if any amps will even do that, and the music program rarely requires that kind of power for the long-term.  What your average power looks like, assuming you're not running hard into clipping, depends on the music.  A nominal value of -9 dB ratio of long-term average vs. short-term average is a kind of industry standard.  This -9 dB is equal to 1/8 power.  For dub-step and other music with long, sustained bass, it's possible the average power could get higher, maybe 1/4 power?  I don't know, but I just checked a few tracks I own that have loud sustained bass and, after applying a low-pass filter at 100 Hz and normalizing, the loudest one came in right at 1/4th power!

So take 14400/4 = 3600W long-term average into 2 ohm => I = sqrt(3600/2.0) = 42.4 A

A conductor ratings chart indicates that a 4 mm wire is rated for only 37 A.  So if this system is going to be doing "pedal to the metal" for hours on end, a second 4 mm run (or a single larger diameter run) is best so that the wires won't overheat.  This will also cut power waste in half, which in the above example means getting 0.5 dB back.  Not much, but cables are cheap compared to drivers and amps.

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If I may suggest you consider amps other than the FP14400, keeping in mind that amp power ratings are often based on some unspecified "burst" capability, which doesn't even last long enough to be meaningful for subs.  The other thing to keep in mind that is that most Class D amps need to be run in a "full bridge" or "full bridge tied load" configuration in order to not become unstable when driving subs at high levels.  Some amps like (e.g.) Speakerpower and some ICE products are full bridge on each output channel.  These are essentially already bridged internally.  Other amps like Powersoft and probably the FP14400 are half-bridge on each channel.  These amps typically provide optional bridging functionality, which I strongly recommend when running subs off of them.

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5 hours ago, SME said:

If I may suggest you consider amps other than the FP14400, keeping in mind that amp power ratings are often based on some unspecified "burst" capability, which doesn't even last long enough to be meaningful for subs.  The other thing to keep in mind that is that most Class D amps need to be run in a "full bridge" or "full bridge tied load" configuration in order to not become unstable when driving subs at high levels.  Some amps like (e.g.) Speakerpower and some ICE products are full bridge on each output channel.  These are essentially already bridged internally.  Other amps like Powersoft and probably the FP14400 are half-bridge on each channel.  These amps typically provide optional bridging functionality, which I strongly recommend when running subs off of them.

According to my tests, the Sanway FP13k should be able to burst its rated power for ~130ms, which should be plenty for typical kick hits (sustained notes at max will fry the drivers anyways, so why bother). I'd expect the og amps to perform similarly or better (I sure hope that's the case).

The instability when running unbridged amps only occurs when running the amp asymmentrically to my knowledge. The FP14k is running in 'half-bridged' mode as you say (onec channel's input and output polarity reversed to run mirrored symmetrical loads on the channels), which is a bit easier on the power supply. I've run both my 10kQ and my 13k asymmetrically; full tilt on one channel and much lower power on the other and never ran into issues.

As for the power ratings, Bennett recommended to set a long term average limiter at 1/10th of the rated program power, which would be ~350W, so 700W for two, which gives us 19A. That sounds a bit more reasonable, but the drivers will be fed a lot more juice temporarily of course, like you showed in your example.

Looking at the DIN VDE 0298-4, 2x4mm² is certified for exactly 40A in section 'E', which essentially means free wire outside. That norm targets a 70°C (158°F!) operational temperature. Yikes!

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