Value of subwoofer amplifier power ratings?

vm1451

Active Member
I'm not sure if my knowledge is moving forward or if brain is starting to bleed! :D Maybe a bit of both...
 

Conrad

Moderator
I'm not sure if my knowledge is moving forward or if brain is starting to bleed! :D Maybe a bit of both...

If there was only one way to do it there would be a company called The Subwoofer Company and they would make The Subwoofer and everyone would have one.

It’s a complex subject.
 

MemX

Well-known Member
Nicely described.

However, excursion only helps with output, not extension. Only driver size does that, and I don't know why.

If you have a 12" sub in a room and it's capable of outputting down to, say, 20Hz. Adding 10 more 12" drivers will get you loads more output, but won't get you any more extension. With more output you can EQ hard and use the increased low level output to generate extension, but a larger driver is just capable of moving more air at the slow speeds required for low Hz.

To hit 7Hz for example the driver needs to cycle 7 times a second, that's slow enough to be easily visible. If a 12" driver is moving that slowly it's barely moving any air. If an 18" driver does it, it gets windy!

I'm starting to get the limits of my knowledge here so if anyone can clarify or correct it would be really useful.
I think the bit in bold might be verging on the dubious 'large drivers = sloppy, but small drivers = fast' thinking :p lol, but it does also recognise that displacement is key to output ;)

I do get what you're saying - output (displacement) is down to driver design. If, as you note, a driver is crap below 20Hz, it's never going to put out a lot of displacement/output.

But...

That would be because it has limited surface area / Excursion / both.

In theory you might need, say, 20 drivers with 3mm Xmax to hit Reference at 16Hz (e.g. if using 'pro drivers' designed for bass guitar work) - that would be down to their limited displacement each but their large combined displacement.

If you swapped them for a driver designed for Home Cinema with, say, 30mm Xmax, that's 10x the excursion therefore 10x the displacement.

That should mean that you'd have the same output from two of the higher excursion drivers as 20 of the lower excursion drivers.

At least I think that's how it works... :D lol


Would there be differences in the sound? Likely yes, as each would have different characteristics and I'd expect the Pro drivers to have more 'punch', but then the high excursion drivers might have a monster neodymium (spelling? lol) magnet and a shed-load of grunt to stop and start that cone quickly, which could produce the same sort of 'character'.

:)
 

vm1451

Active Member
So lets take two subs from the same manufacturer, SVS.

The SB 3000 and SB4000. The specs of these say a 13.5" driver and a 1200w amp with a frequency response of 19-310 Hz for the latter. The former has a 13" driver with an 800w amp and a frequency response of 18-270Hz.

The larger driver wont go as low as the smaller driver and goes higher than the smaller driver. I guess it requires more power to move the larger driver but that doesn't explain the frequency responses, does it? :confused:
 

Conrad

Moderator
I think the bit in bold might be verging on the dubious 'large drivers = sloppy, but small drivers = fast' thinking :p lol, but it does also recognise that displacement is key to output ;)
How dare you sir!

I posted my thoughts on that here (and apparently killed the thread with it):

TL;DR:
Bigger drivers go lower. Lower notes take longer to decay = big subs are slow.
Nonsense of course, my 6x15" drivers have a lower GD time than most single 13s as they're barely moving to hit 30Hz notes.

I do get what you're saying - output (displacement) is down to driver design. If, as you note, a driver is crap below 20Hz, it's never going to put out a lot of displacement/output.

But...

That would be because it has limited surface area / Excursion / both.

In theory you might need, say, 20 drivers with 3mm Xmax to hit Reference at 16Hz (e.g. if using 'pro drivers' designed for bass guitar work) - that would be down to their limited displacement each but their large combined displacement.

If you swapped them for a driver designed for Home Cinema with, say, 30mm Xmax, that's 10x the excursion therefore 10x the displacement.

That should mean that you'd have the same output from two of the higher excursion drivers as 20 of the lower excursion drivers.

At least I think that's how it works... :D lol


Would there be differences in the sound? Likely yes, as each would have different characteristics and I'd expect the Pro drivers to have more 'punch', but then the high excursion drivers might have a monster neodymium (spelling? lol) magnet and a shed-load of grunt to stop and start that cone quickly, which could produce the same sort of 'character'.

:)
Like I said, I'm reaching my limits.
I guess that's how the Paradigm Sub 2 works though, 6 x 12" drivers in one cabinet with an obscene amount of power (7000w I think) and that'll hit 7Hz in room.
 

MemX

Well-known Member
Six 15s?

I like your style ;)

Headroom is a good thing :D lol
 

Conrad

Moderator
one 15" driver for every 100 cubic foot of space is my motto :D
 

Conrad

Moderator
So lets take two subs from the same manufacturer, SVS.

The SB 3000 and SB4000. The specs of these say a 13.5" driver and a 1200w amp with a frequency response of 19-310 Hz for the latter. The former has a 13" driver with an 800w amp and a frequency response of 18-270Hz.

The larger driver wont go as low as the smaller driver and goes higher than the smaller driver. I guess it requires more power to move the larger driver but that doesn't explain the frequency responses, does it? :confused:
And this is why numbers alone aren't a good way to buy subs.

It might be that the 4000 is at -3.1dB at 18Hz which means it's outside the standard +-3dB parameters, so they have to go up a whole number of Hz. Nobody wants to read that it's 18.8Hz at +-3dB.

The bigger amp means it'll go louder before compression (probably) and with less distortion.

If you compare the two slopes, the 4000 rolls off more slowly which means it'll benefit more from room gain meaning that, in-room (where it counts), you should end up with greater extension.

And that roll-off will likely be shaped by the internal DSP, and once you introduce that all bets are off. It's a black box and whatever the sub manufacturer does with the DSP could completely change the behaviour away from the predictable. I refer you back to the new Kef that can do 11Hz.
 

Dobbyisfree

Well-known Member
Nicely described.

However, excursion only helps with output, not extension. Only driver size does that, and I don't know why.

If you have a 12" sub in a room and it's capable of outputting down to, say, 20Hz. Adding 10 more 12" drivers will get you loads more output, but won't get you any more extension. With more output you can EQ hard and use the increased low level output to generate extension, but a larger driver is just capable of moving more air at the slow speeds required for low Hz.

To hit 7Hz for example the driver needs to cycle 7 times a second, that's slow enough to be easily visible. If a 12" driver is moving that slowly it's barely moving any air. If an 18" driver does it, it gets windy!

I'm starting to get the limits of my knowledge here so if anyone can clarify or correct it would be really useful.

Are you sure about that? I would say, if you have EQ, then multiple subs does help with extension... E.g. you have two subs, each show a curve say -3dB at 23Hz. When you EQ them together, they can attain a higher dB at 23Hz and, as such, a higher dB at all frequencies lower than that. As long as they are EQed, so the EQ device would adjust them so that they are running at lower gain (lol) at higher frequencies.
In the next couple of months, I'll have multiple (what AVForums calls because they are not brand new class D with ten million watts etc) rubbish old subs. Hopefully, when I get the Audyssey app results back, I believe (if it works) it will show the overall lower extension as more capable...
 

Conrad

Moderator
Are you sure about that? I would say, if you have EQ, then multiple subs does help with extension... E.g. you have two subs, each show a curve say -3dB at 23Hz. When you EQ them together, they can attain a higher dB at 23Hz and, as such, a higher dB at all frequencies lower than that. As long as they are EQed, so the EQ device would adjust them so that they are running at lower gain (lol) at higher frequencies.
In the next couple of months, I'll have multiple (what AVForums calls because they are not brand new class D with ten million watts etc) rubbish old subs. Hopefully, when I get the Audyssey app results back, I believe (if it works) it will show the overall lower extension as more capable...

That’s exactly what I meant by EQ hard.
You have to cut everything higher up to reduce the relative difference between <20Hz and >20Hz. This means you’re giving up a lot of output. If you have it to spare then sure, but I’d want to check compression and distortion when doing so.

I’ll be interested to see how you get on.
 

MI55ION

Distinguished Member
Are you sure about that? I would say, if you have EQ, then multiple subs does help with extension... E.g. you have two subs, each show a curve say -3dB at 23Hz. When you EQ them together, they can attain a higher dB at 23Hz and, as such, a higher dB at all frequencies lower than that. As long as they are EQed, so the EQ device would adjust them so that they are running at lower gain (lol) at higher frequencies.
In the next couple of months, I'll have multiple (what AVForums calls because they are not brand new class D with ten million watts etc) rubbish old subs. Hopefully, when I get the Audyssey app results back, I believe (if it works) it will show the overall lower extension as more capable...

He is correct. The low frequency roll off is linear so regardless of how many subs, the response will remain -3db at 23hz. The only caveat as stated by Conrad is if you use a lot of subs and apply massive amounts of EQ to target say flat down to 15Hz. Seems incredibly wasteful and there are much easier ways to get there i.e. larger drivers.
 

Dobbyisfree

Well-known Member
That’s exactly what I meant by EQ hard.
You have to cut everything higher up to reduce the relative difference between <20Hz and >20Hz. This means you’re giving up a lot of output. If you have it to spare then sure, but I’d want to check compression and distortion when doing so.

I’ll be interested to see how you get on.

I will definitely report in once done. Will be a month or two, like I said. At the moment, I have multiple subs all without a plate in. LFE is from the main speakers for a while d'oh!

@MI55ION I don't really see it as "wasted", I don't listen at levels like a lot of AVF members do. Maybe -24dB absolute maximum for a film on Denon with Audyssey. To be honest, it's probably lucky I do have the older, lower powered (possibly low powered as who knows what the quoted figures mean, the subject of this thread) subs... if I had new SVS, Arendal etc etc it really would be a waste as they would probably never run even at a quarter at what they're capable of. I'm pretty convinced that I never run my subs into much distortion.

You will probably all take the mickey but I did once, with two of the subs running in front corners try the scene at the beginning of Ep 5 where the Star Destroyer rumbles past at -10dB and to be honest the pressure just hurt my ears and I did sense some distortion. Which is probably to be expected at that level.

Funnily enough, we were talking about the triangles. One of them is that we don't all have home cinemas, we have a lounge and not everyone can have big 15" subs in them! So, aesthetics ends up quite a major triangle.
 

MI55ION

Distinguished Member
I will definitely report in once done. Will be a month or two, like I said. At the moment, I have multiple subs all without a plate in. LFE is from the main speakers for a while d'oh!

@MI55ION I don't really see it as "wasted", I don't listen at levels like a lot of AVF members do. Maybe -24dB absolute maximum for a film on Denon with Audyssey. To be honest, it's probably lucky I do have the older, lower powered (possibly low powered as who knows what the quoted figures mean, the subject of this thread) subs... if I had new SVS, Arendal etc etc it really would be a waste as they would probably never run even at a quarter at what they're capable of. I'm pretty convinced that I never run my subs into much distortion.

You will probably all take the mickey but I did once, with two of the subs running in front corners try the scene at the beginning of Ep 5 where the Star Destroyer rumbles past at -10dB and to be honest the pressure just hurt my ears and I did sense some distortion. Which is probably to be expected at that level.

Funnily enough, we were talking about the triangles. One of them is that we don't all have home cinemas, we have a lounge and not everyone can have big 15" subs in them! So, aesthetics ends up quite a major triangle.

Sounds like an interesting project to take on. Don't forget to take a few measurements if you can as I'd like to see the difference.

The Paradigm Sub 1, although a ground up design, managed to achieve a respectable 12hz extension using 6 8" drivers and 1700 watts. A single PSA S1812 would probably achieve similar output at that frequency. That's what I mean by "wasteful", not that it can not work or that you should not do it given your very specific personal circumstances.
 

Mr Wolf

Well-known Member
Like I said, I'm reaching my limits.
I guess that's how the Paradigm Sub 2 works though, 6 x 12" drivers in one cabinet with an obscene amount of power (7000w I think) and that'll hit 7Hz in room.

I didn't know that monsters like this existed. The specs for the Signature Sub 2 show 9,000 watts Dynamic Peak / 4,500 watts RMS. That's insane.

Signature SUB 2

What I really don't understand though is how this sort of amplifier power is actually possible from a electrical supply perspective. Obviously it couldn't be used with a 13A plug socket so do you have to have a dedicated power line installed like a cooker or are these "dodgy" watt figures?
 

MI55ION

Distinguished Member
I didn't know that monsters like this existed. The specs for the Signature Sub 2 show 9,000 watts Dynamic Peak / 4,500 watts RMS. That's insane.

Signature SUB 2

What I really don't understand though is how this sort of amplifier power is actually possible from a electrical supply perspective. Obviously it couldn't be used with a 13A plug socket so do you have to have a dedicated power line installed like a cooker or are these "dodgy" watt figures?

Well that's something @maxkolonko123 is currently finding out with his new baby, the JTR RS2. He already blew a 5amp fuse. :D
 

Dobbyisfree

Well-known Member
I've decided to install six SIgnature Sub 2 in my lounge. I have set up two diesel generators behind the sofa. I'm wondering if a MiniDSP will make an anti-noise from the subs to EQ out the diesel engine noise. :)
 

vm1451

Active Member
I guess it depends if the equipment inside the sub is actually running at 240v? Might be stepped down or changed into three phase?

The motor in my F3a competition aeroplane is rated at 3Kw but the batteries are only rated a 5A, (44v). I'm pulling 80A at peak power and with proper throttle management can get around nine minutes of flight time. The magic that allows me to do this is the electronic speed control, (ESC), that changes the battery power to three phase. Don't ask me how as I have absolutely no understanding of what goes on in there!


Notice two power cables on one side and three on the other.
 

Dobbyisfree

Well-known Member
That's cool. I'm a vaper, a lot of the small removable batteries can provide quite incredible peak currents.
Remember back to school time, as far as I am aware, if we talk Watts then we're talking power and there is a limit to the power that 13A at 220-240V can provide before something clicks out or a fuse blows. No matter what you convert it to, the power draw is the power draw. I think!
It also depends on how quick the peaks are though. E.g. if you look at the power consumption on the back of your AVR, again, this is something that doesn't always follow the same rules. Some are quoting an absolute peak, others different.
That great American AVR test site where they actually measure power output to channels simultaneously, it's interesting to look at what some of the AVRs achieve versus what they say is the consumption on the back panel.
 

maxkolonko123

Well-known Member
I didn't know that monsters like this existed. The specs for the Signature Sub 2 show 9,000 watts Dynamic Peak / 4,500 watts RMS. That's insane.

Signature SUB 2

What I really don't understand though is how this sort of amplifier power is actually possible from a electrical supply perspective. Obviously it couldn't be used with a 13A plug socket so do you have to have a dedicated power line installed like a cooker or are these "dodgy" watt figures?
Why you think 13A is not sufficient? Would like to know more about it cause rs2 amp is 6000w RMS
Well that's something @maxkolonko123 is currently finding out with his new baby, the JTR RS2. He already blew a 5amp fuse. :D
O mate tell me about it, just imagine how my heart was pumping when jtr went off and I was "wtf have I done" it was only - 30mv did burn it or what 😂😂

Now running with 10A fuse but won't go crazy and will try to find some solid cable
 

Mr Wolf

Well-known Member
Why you think 13A is not sufficient? Would like to know more about it cause rs2 amp is 6000w RMS
Simply because Volts x Amps = Watts. A 13A fuse x 240V gives a theoretical 3.1KW limit on anything using a regular wall plug socket.

It's why you can't buy a fast boil kettle that higher than 3kW.

Does the sub have two plugs?
 

vm1451

Active Member
Absolutely agree, the limit is 13A at 240V and W=A x V.

If you start using transformers and increase V, you will lose some A. How they convert two phase to three though I have never looked into, if my father was still alive I'd ask him as he was an electrical engineer.

Bottom line is at the socket there is 3.1Kw to play with, which will give you a nice perm if you plug your fingers in!
 

vm1451

Active Member
Simply because Volts x Amps = Watts. A 13A fuse x 240V gives a theoretical 3.1KW limit on anything using a regular wall plug socket.

It's why you can't buy a fast boil kettle that higher than 3kW.

Does the sub have two plugs?
Two plugs won't make a difference as they will be on the same ring if in the same room. The ring will be limited to 15A-16A at the consumer unit unless designed for something else like a cooker or electric shower which will have 30A.

The 13A limiting factor is in the plug, but a "standard" ring will support a total load of around 3.8Kw
 

Dobbyisfree

Well-known Member
I also have the added complication that we live in a maisonette where the master fuse is only 60A. So, when washing machine, dishwasher, oven, shower, boiler, lights etc etc all on how much does the AVR, power amp and subs add to it ;o)
 

Mr Wolf

Well-known Member
I guess it depends if the equipment inside the sub is actually running at 240v? Might be stepped down or changed into three phase?

The motor in my F3a competition aeroplane is rated at 3Kw but the batteries are only rated a 5A, (44v). I'm pulling 80A at peak power and with proper throttle management can get around nine minutes of flight time. The magic that allows me to do this is the electronic speed control, (ESC), that changes the battery power to three phase. Don't ask me how as I have absolutely no understanding of what goes on in there!


Notice two power cables on one side and three on the other.
They won't be 5A output batteries but they may have 5aH capacity though which is fairly typical. Their maximum current output potential will depend on the battery's C-rating (C=numbers of time it can discharge itself per hour). If they were 5aH capacity batteries and rated 50C then their maximum amp output capability would be 250A (5aH x 50C). 44V x 250A = 11kW.

Maximum current draw of a 3kW motor on a 44V battery = 3kW/44V = 68A i.e. 27% of what's available so plenty of headroom which is good.

Three wires going feeding into a brushless motor is the norm due to how they operate. ESCs don't have any current multiplying "magic" unfortunately - I wish they did.

I've raced RC cars on and off for nearly 40 years.
 

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