Value of subwoofer amplifier power ratings?

Mr Wolf

Well-known Member
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
My ring circuits all have 30A breakers on them at the CU.
 

vm1451

Active Member
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.
You are of course correct, I didn't explain as I should have!
 

Dobbyisfree

Well-known Member

Mr Wolf

Well-known Member
"It's not un-use-ual to have 30 amp breakers, mner mner mner"

[Sorry Dad joke alert]
Thanks Tom! :smashin:

Back to the issue, subs cannot break the fundamental laws of physics. The only way they could ever output more than they're drawing in electricity would be due to energy stored in power reservoir capacitors and this could only be used for very short transient peaks.

Let's not forget they're also at best only 90% energy efficient electrically so 4.5kW RMS output for the Sub 2 would need at least 5kW going into it. That ain't pushing past a 13A fuse.

I'm starting to think these sub amplifier ratings are a joke and probably accurate to +/-50% at best.
 

Dobbyisfree

Well-known Member
Unfortunately subs are in that world that amplifiers used to be years ago.
I remember when I were a lad, I had a NAD 3030 amplifier, it was my pride and joy.
Mates would have their midi systems or ghetto blasters and say "my system is 150w per channel and your NAD is only 30w".
They used to use those PMPO figures (Peak Music Power Output), which were horrendous and they were normally at something like 10% THD.
I gave up trying to explain that the NAD was 20-20000Hz, less than 1% THD, at 8 Ohms... and even that was conservative for the NAD as they always tended to be more capable than their figures in those days.
I helped explain it to them by putting music on. Because the NAD had meters. So, it was loud when the meters were peaking around 60w. Proper loud. And they didn't really understand!
What we could do, if we wanted to be really sad, is put a power meter/gauge on the mains input to our subs and see what it consumes?
 

Mr Wolf

Well-known Member
True, but they're all claiming RMS, not PMPO. And these are big boy hi-fi products, not 80s ghetto blasters - they really shouldn't be playing that game...but then maybe they are.

The RMS vs Peak figure differentials are also interesting. Many manufacturers are simply stating the "Peak" power as being exactly 2x the RMS figure which suggests they're measuring the exact same thing.

SVS on the other hand are claiming way more than 2x the RMS for their "Peak" outputs (e.g. PB-3000s are 800W RMS / 2500W+ Peak). This suggests their RMS figures are taken at either lower distortion levels, more difficult frequency/ranges and/or over longer periods.

What's also curious is how incredibly round every power figure is e.g. 500W, 800W, 1000W. Sounds more like a power supply rating than an amp rating.
 

MemX

Well-known Member
Thanks Tom! :smashin:

Back to the issue, subs cannot break the fundamental laws of physics. The only way they could ever output more than they're drawing in electricity would be due to energy stored in power reservoir capacitors and this could only be used for very short transient peaks.

Let's not forget they're also at best only 90% energy efficient electrically so 4.5kW RMS output for the Sub 2 would need at least 5kW going into it. That ain't pushing past a 13A fuse.

I'm starting to think these sub amplifier ratings are a joke and probably accurate to +/-50% at best.
I think some (most?) amplifiers will have at least some capacitors in them - presumably they need to ensure 'smooth' power supply, so pumping power into capacitors, to then be released, would 'smooth' any small changes in direct power supply.

I think?

My amp is 5000w RMS :D but I don't think I've ever run it at that volume - because that would be insane in a house, lol.

Most high output demands in a home setting are very transient - i.e. bass beats in music, a crash in a film, etc.

IIRC the fuses in most houses are 'slow break' so it's possible to exceed their rated power for at least a short time, which is why it should be possible to get monster power for the peak outputs without tripping things out.

If you're playing sine waves at 0dB, of course, all bets are off :D
 

D1gita1

Active Member
Although room gain wouldn't explain why the smaller/less powerful sealed sub would beat the larger ported sub across the frquency range like Mr. Wolf is measuring.
Room gain sort of does explain this, and it's often a consideration when designing a sealed sub, and why sealed subwoofers aren't as weak against ported subs as many like to suggest.

A sealed subwoofer typically has a 12db per octave roll-off from around 40Hz or so (depending on the design, the room, and the sub's placement) which is fairly gradual, and assuming no filtering at the low end this will continue to as low a frequency as the amp can deliver, which can be into single digits, which is why you see some subs rated to frequencies like 11Hz. Sure the sub driver may be able to cycle at 11Hz, so technically this is true, but the level of output will be so insignificant its all but useless while adding in lots of distortion for no benefit when trying to play this frequency, but you know, marketing!

Room gain will give you roughly an amount of gain that almost exactly matches this roll-off profile, leading many high quality sealed subwoofers to have a naturally flat response in room to very low frequencies. This is why the anechoic response of sealed subwoofers often shows a roll-off from 40Hz or so, like the MK sealed subwoofers for example, but this is entirely intentional by design and doesn't necessarily mean the subwoofer cant perform against large ported alternatives that have greater overall output. On balance, my personal preference has always been for sealed subwoofers and this has never changed.

A port on a subwoofer will boost output around the ports resonant frequency, but below that you get nothing. If you look at just the frequency range output, it's not uncommon for sealed subwoofers to cover more of the frequency range, which can be subjectively perceived as 'more sound', where 'more sound' isn't defined in pure max spl terms.
 
Last edited:

D1gita1

Active Member
I think some (most?) amplifiers will have at least some capacitors in them - presumably they need to ensure 'smooth' power supply, so pumping power into capacitors, to then be released, would 'smooth' any small changes in direct power supply.

I think?

My amp is 5000w RMS :D but I don't think I've ever run it at that volume - because that would be insane in a house, lol.

Most high output demands in a home setting are very transient - i.e. bass beats in music, a crash in a film, etc.

IIRC the fuses in most houses are 'slow break' so it's possible to exceed their rated power for at least a short time, which is why it should be possible to get monster power for the peak outputs without tripping things out.

If you're playing sine waves at 0dB, of course, all bets are off :D
I'd say pretty much all subwoofers have capacitors in them. I'd also guess that the more they have the bigger difference you will see between rms power and peak power. Capacitors drain very fast, so are only good for short bursts, but they also charge very fast as well. A subwoofer power profile will often be very different from what an amp rating might imply. An 800 watt rated subwoofer for example will almost never be putting out that kind of power and it would be quite reasonable to suggest for the most part it's only ever using about 10% of that.

Audio signals are dynamic, and so is the power output of the amplifier driving a subwoofer driver. A subs design influences the power required for any given spl at any given frequency. A more efficient driver needs less power and runs cooler leading to a naturally cleaner sound at the expense of overall spl. If you want to take another subwoofer of the same design and boost output, you typically have to add more power but this leads to diminishing returns. You need a larger, typically less efficient voice coil, that will heat up more (heat resists the flow of power being sent to the voice coil), so you need to engineer in more cooling. You need more excursion for more spl, so your driver needs to be stiffer which usually means a heavier cone, which lowers the resonant frequency of the driver (generally good for subwoofers) but can make it less suitable at higher frequencies as efficiency higher up the range (above 40hz or so) is reduced. By the time you've finished redesigning your 200 watt sealed sub for higher performance, you can very quickly be looking at 1000 watt requirement for max output, by which we mean pushing the driver to max excursion. All that said, your 1000 watt rated subwoofer will still only really be using 10% or so of that rated power for most of the time. All that time it's only using a marginal amount of its power consumption capacity, it's keeping those capacitors fed ready for that instant peak, and as quick as that crazy sound effect is over, the capacitors discharge and recharge again.

I would recommend playing with something like WinISD as this can simulate amplifier load and predicted power usage of a subwoofer across its frequency range. I've attached 2 images below of the power usage profile of a 15-inch driver I once used in a subwoofer build. The max power handling of the driver is 1000 watts and this is with the driver in a cabinet optimally sized to allow xmax (not xmech) at 10Hz with the full 1000 watts used. You will note here that at max SPL the predicted power required is not 1000 watts at all frequencies. You can also see how the power required is greater on either side of the drivers resonant frequency at both ends of the frequency range. The last thing to note of course is that the SPL levels indicated on the graph does not represent anything like real-world use, its a model of the maximum output capability only.
 

Attachments

  • S15 Power.JPG
    S15 Power.JPG
    108 KB · Views: 16
  • S15 SPL.JPG
    S15 SPL.JPG
    97.7 KB · Views: 17
Last edited:

David Alexander

Active Member
Room gain sort of does explain this, and it's often a consideration when designing a sealed sub, and why sealed subwoofers aren't as weak against ported subs as many like to suggest.

A sealed subwoofer typically has a 12db per octave roll-off from around 40Hz or so (depending on the design, the room, and the sub's placement) which is fairly gradual, and assuming no filtering at the low end this will continue to as low a frequency as the amp can deliver, which can be into single digits, which is why you see some subs rated to frequencies like 11Hz. Sure the sub driver may be able to cycle at 11Hz, so technically this is true, but the level of output will be so insignificant its all but useless while adding in lots of distortion for no benefit when trying to play this frequency, but you know, marketing!
Yes, I can (kind of) get my head around the 'sub 40Hz' room gain response, although if someone wants to explain in as simple terms as possible - feel free :) . However Mr Wolf measured the smaller, sealed sub as giving more output against it's bigger ported adversary across the freqency range. Which is odd? Unless the room size which is working in favour of the sealed sub <40Hz is actually working against the ported sub >40Hz.
When I tested a 10" sealed vs. 12" ported in my room the 12" ported had more output than the 10" with volume/gain set similarly. It's just that the sealed sub rolled off a lot lower than the 24Hz that it was quoted at (room gain).
 

D1gita1

Active Member
Yes, I can (kind of) get my head around the 'sub 40Hz' room gain response, although if someone wants to explain in as simple terms as possible - feel free :) . However Mr Wolf measured the smaller, sealed sub as giving more output against it's bigger ported adversary across the freqency range. Which is odd? Unless the room size which is working in favour of the sealed sub <40Hz is actually working against the ported sub >40Hz.
When I tested a 10" sealed vs. 12" ported in my room the 12" ported had more output than the 10" with volume/gain set similarly. It's just that the sealed sub rolled off a lot lower than the 24Hz that it was quoted at (room gain).
Ultimately, it really depends on the design of each subwoofer. Unless you are comparing 2 subwoofers using the same drivers and amplifiers, just in different cabinets, you can never really do an apples to apples comparison. Amplifier wattage ratings tell you nothing about the load they can comfortably drive. An amp that is rated to 500 watts but is limited to 8 ohms will potentially deliver less real-world performance than a 300-watt amp that is happy to drop below 4 ohms. Similarly, you might have one driver that's very efficient, while another may not be, or one driver might use the available load better than another. Inductance building up in a driver will mean it fights the incoming current more, so driver design matters. Ports are often used to make up the difference between cheaper drive units vs more expensive ones.

In the initial post, the comparison of 500 watts vs 750 watts is potentially more or less meaningless. Look at the image attached, this shows the difference between 500 watts vs 750 when using the same driver in the same cabinet, in this case, a sealed cabinet. The difference isn't much more than 1dB, which is virtually imperceptible. You only need one driver to be 3db less efficient and you have less overall output. When comparing amplifier power between subs as well, you need to factor in that every 3db more SPL output requires twice the power (3dB being the generally accepted increase that is obvious), so if you can assume all things as being equal (and they almost never are), 300 watts vs 600 watts, in theory, gives you 3dB more max SPL, while the difference between 1200 and 1500 will give a bit more amplifier headroom, but basically nothing in terms or additional usable SPL. When you have different amplifier topology, different driver technology, and different cabinets, you cant really make any sort of fair comparison based of basic marketing specs.
 

Attachments

  • 500v750.JPG
    500v750.JPG
    113.7 KB · Views: 17
Last edited:

Mr Wolf

Well-known Member
In the initial post, the comparison of 500 watts vs 750 watts is potentially more or less meaningless.
I agree which is the whole point of this thread.

Here's a bit more info as I just found a chart I recorded from the test which was about 3 months ago - thought I had deleted it otherwise I would have included in the first post.

sub contest.jpg


The green line is the 500W 12" sealed SVS SB-2000, the blue line the Velodyne 750W 15" ported sub. Each line represents the maximum SPL output before compression set in somewhere along the FR line. I can't remember but I think I had the 80Hz crossover enabled in the AVR.

Room size is 5.68m x 5.34m x 2.38m. Both subs were in the same corner location with the UMIK-1 at the MLP. All EQ was disabled although both subs have DSP, the Velodyne manual stating that it has a 15Hz HPF.
 

Dobbyisfree

Well-known Member
Room size is 5.68m x 5.34m x 2.38m. Both subs were in the same corner location with the UMIK-1 at the MLP. All EQ was disabled although both subs have DSP, the Velodyne manual stating that it has a 15Hz HPF.

Just to ask and check other variables, "coupling method" to the floor was the same and they were the same orientation?
 

Mr Wolf

Well-known Member
Just to ask and check other variables, "coupling method" to the floor was the same and they were the same orientation?
All identical.

That said, I guess the SB-2000, having a smaller cabinet, may have had the front of its driver positioned a bit closer to the corner point of the room.

The Velodyne has a forward facing slotted port below its driver.
 

Dobbyisfree

Well-known Member
The only reason I asked that is to further prove at these power differences potentially mean nowt. On the basis that if you, with each sub in that test, also measured each:
Rotated 5 degrees clockwise or anti-clockwise around its vertical axis. Or
Positioned 50mm differently forward or sideways. Or
Used spikes or a platform (with different materials).
That it would give considerably different curves for each.
So how relevant does that make the 250w (apparent) Watts, even when we're not talking about the subwoofer design anymore but how you install it.
I mean, even how many people and dogs are sat in the room will affect it. How horribly inconvenient to Sub EQ these can be! :)
Not to mention how much better the sub will sound after a couple of beers!
Sorry I'm just having a laugh :)
 

Conrad

Moderator
The only reason I asked that is to further prove at these power differences potentially mean nowt. On the basis that if you, with each sub in that test, also measured each:
Rotated 5 degrees clockwise or anti-clockwise around its vertical axis. Or
Positioned 50mm differently forward or sideways. Or
Used spikes or a platform (with different materials).
That it would give considerably different curves for each.
Considerably? I'm sceptical of that. You have to remember that the waves we're dealing with are very long. Would a 5 degree shift or a 5cm variation make that much difference when the wave is 10-20 meters long?

So how relevant does that make the 250w (apparent) Watts, even when we're not talking about the subwoofer design anymore but how you install it.
I mean, even how many people and dogs are sat in the room will affect it. How horribly inconvenient to Sub EQ these can be! :)
I don't get materially different measurements whether I'm in the room or not, so I don't know about that either. Maybe it changes with output, or room size?

I'm not sure bags of meat are particularly reflective - acoustically speaking.
 

Dobbyisfree

Well-known Member
Yes, I should have elaborated with the first points, I mean if it's a "real lounge" so it depends on your setup. In many cases, these would make more of a difference because that 5 degrees or 50mm makes more a difference because it is half behind a sofa, a table or a floorstanding speaker relative to the MLP.
Back about 15ish years, when I just had a Paradigm PDR10, it was right next to a hefty cabinet that was deeper than the subwoofer, it made quite a difference moving it forwards or backwards only slight amounts. I'd move it forward when ready to watch a new DVD!
But sorry agree that in a more empty room or a home cinema room this would make barely a difference.
And yes I can't quantify humans and dogs but I would predict (particularly for the clothed ones) they would be more absorbent than reflective. For measurements, you may have one human. For watching a film, there then may be 6 humans and 2 dogs.
I don't include the dogs making noises! That's mostly higher frequency :)
Materials, I was talking about whether on carpet, wooden floor, tile. Or on a plinth, granite or wood etc. - I guess that's probably more for downward facing woofers, radiators or ports though.
 

Mr Wolf

Well-known Member
I'd only just got my UMIK-1 and was in full testing mode that day and measured the subs' FR in all locations and orientations. As predicted by REW's RoomSIM, the rear corner locations gave by far the flattest response across all seats and I measured the subs rotated at every possible angle in these corners and found this made virtually no difference to the FR at the MLP.

This is a dedicated home cinema room with not a lot in it and the layout is perfectly symmetrical, much like the model Dolby layout diagrams.

Anyway, based on the results of the measurements, I replaced the single Velodyne sub in that system with two new PB-3000s. The SB-2000 was borrowed from my living room system for testing purposes but I was really quite surprised/impressed with its performance in a 2,600CuFt space. Two of them would certainly have given a very nice result.
 
Last edited:

Dobbyisfree

Well-known Member
Apologies @Conrad and @Mr Wolf in my comments my mind is thinking of a typical lounge, which is all I have. So, I have various speakers placed around large wooden furniture, large sofas, all obscuring things. Rug on the floor, MLP on a sofa on a back wall (noooooo), walls with random features hanging, pictures, a mirror, surround speakers in a corner. Etc etc.
I can only dream of a dedicated cinema room!
Before I do setup and EQ the subs though, I was going to put each on an approx. half inch granite plinth, thinking better than carpet and old 1970 bouncy floorboards if you agree!
 

vm1451

Active Member
My sub was on carpet and 1958 bouncy floorboards. I bought the SVS soundpath feet and Gaia carpet spikes and I was surprised by the result. It wasn't what was promised by either manufacturer, (surprise!), but it definitely made a difference for the better, (to my ears). I then coupled that with an Antimode that I got second hand and that was also an improvement. I may get around to getting a UMIK-1 and have a play with REW at some point but I suspect that will bring up all sorts of inadequacies which will need cavernous amounts of cash to sort out!!
 

The latest video from AVForums

Podcast: Anthem AVM 70 Review, EQing Your Home Cinema Sound System and More...
Subscribe to our YouTube channel

Latest News

Sky bringing Apple TV+ to Sky Glass and Sky Q customers
  • By Andy Bassett
  • Published
AVForums Podcast: 27th October 2021
  • By Phil Hinton
  • Published
Linn unveils latest Klimax LP12 flagship turntable
  • By Andy Bassett
  • Published
Samsung Tizen plans include cloud gaming for smart TVs
  • By Andy Bassett
  • Published
Freeview Play racks up 10 million users
  • By Andy Bassett
  • Published

Full fat HDMI teeshirts

Support AVForums with Patreon

Top Bottom