Subwoofer power ratings, why so diverged?

[timiark]

I am a bit confused that while some subwoofers are only rated like 50w, or 100w, e.g. Genelec's, other subwoofers are rated with much higher RMS power consumption. For example, svs micro 3000 is rated 800w and KEF kc62 is rated 1000w.

Does this has something to do with the subwoofer being sealed, ported? I'd appreciate some recommended reading materials on this, thanks!

 

[DVDdoug]

It's mostly driver construction (voice coil, magnet, etc.). Most of the energy is converted to heat. I've forgotten how efficient speakers are but from what I remember less than 10% of the energy is converted to sound and I think it's closer to 1%. (Horns are more efficient than almost any other design but bass horns are huge and rarely used anymore.)

Low frequencies require lots of energy, and +3dB is twice the power and +10dB is 10 times the power so you can "need" lots of power if you want deep-strong bass.

And then there's a BIG question of honesty and "philosophy". I trust sensitivity ratings more than I trust power ratings... A 100W speaker is supposed to be safe with a 100W amplifier playing regular undistorted program material. But it might burn-up with constant 100W test-tones. And in a multi-way speaker system the tweeter can't handle as much power as the woofer (and there is less energy in the high frequencies with "regular program material").

JBL has a paper on IEC speaker ratings but I never see "IEC" mentioned in speaker specs.

 

[voodooless]

I think it's closer to 1%.

Actually, for subwoofers, it’s probably closer to .1% Especially for the smaller ones. That means you need a lot more power to play louder. Reflex is more efficient than closed (above tuning frequency), so may need less power.

Bigger subs with larger enclosures have more efficiency and will play louder with the same power. Even there, getting above 1% efficiency is not easy for sub frequencies (or 92 dB/1W/1m)

And finally there is the maximum SPL a sub can muster. More SPL equals more needed power.

 

[digitalfrost]

I can only say from personal experience designing subwoofers (just for DIY) that most chassis cannot do huge power levels. Like often times not even what they're electrically rated for, simply because they will reach excursion limits first. I don't know how these companies arrive at their numbers, but when I see 800W or 1kW, it's just a joke to me.

Here is a simulation of the Scan Speak 26W/4558T00 in a 40l box with the passive membrane. The chassis is rated for 350W. As you can see from the graph the maximum that you can put into it is 200W at 32hz.

Okay yes you can reach the electrical limit below and above that, but with a subwoofer we surely have to calculate with the worst case. If there's bass at 20hz there's surely bass at 32hz, and probably at 50hz as well...
And that is already a highend chassis, and this is kind of a best case example. Smaller/cheaper chassis will look much worse than that. So unless these manufacturers found something I don't know I'm really skeptical about these specs.

 

[ryanosaur]

I can't even count the number of conversations I've seen where it is said you can't shop by Amplifier power on an Active Sub. This even from a professional reviewer. It is effectively a meaningless topic.
Finding CEA-2010 burst tests and long term compression sweeps tells a much more informative picture than comparing Amp power ratings.

 

[FeddyLost]

If sub is small and sealed, it's extremely inefficient and needs massive EQ in really sub range, at 50 hz and below.
So, to get decent bass from 2*6,5" even with really long throw, you'll need a lot of power.
Result is: if we take big vented pro sub with 18" and fridge size, it can shake whole house with 100w, if we take small hightech sub with 2*6,5", it will require 500+ w for LFE channel ...

 

[timiark]

If sub is small and sealed, it's extremely inefficient and needs massive EQ in really sub range, at 50 hz and below.
So, to get decent bass from 2*6,5" even with really long throw, you'll need a lot of power.
Result is: if we take big vented pro sub with 18" and fridge size, it can shake whole house with 100w, if we take small hightech sub with 2*6,5", it will require 500+ w for LFE channel ...

Seems like the case now, I got the KC62 shipped and I had tested it. I works well down to 20hz with around 2% THD around 80dB despite it cannot reach high SPL. Its chassis is contantly hot and I think it probably because of this 'massive' EQ.

 

[timiark]

I can't even count the number of conversations I've seen where it is said you can't shop by Amplifier power on an Active Sub. This even from a professional reviewer. It is effectively a meaningless topic.
Finding CEA-2010 burst tests and long term compression sweeps tells a much more informative picture than comparing Amp power ratings.

I mean, I totally understand the number is simply a number here. But, still, it is interesting thinking about how inefficient those small subwoofer can be.

 

[timiark]

Actually, for subwoofers, it’s probably closer to .1% Especially for the smaller ones. That means you need a lot more power to play louder. Reflex is more efficient than closed (above tuning frequency), so may need less power.

Bigger subs with larger enclosures have more efficiency and will play louder with the same power. Even there, getting above 1% efficiency is not easy for sub frequencies (or 92 dB/1W/1m)

And finally there is the maximum SPL a sub can muster. More SPL equals more needed power.

yah.... my KC62 is constantly hot whenever it is playing loud for a whole... I guess it is super inefficient indeed. But it does the job in my small room nevertheless.

 

[FeddyLost]

Its chassis is contantly hot

It depends on what is "hot" for you.
Typically if chassis (also it's the heatsink) is around 40C it's hot to touch, but nothing dangerous for electronics.

 

[timiark]

It depends on what is "hot" for you.
Typically if chassis (also it's the heatsink) is around 40C it's hot to touch, but nothing dangerous for electronics.

Yeah, around 40c. It is not a problem for electronics for sure. Still a bit curious for a sound reproduction gear.

 

[Mnyb]

Never got this “fight against physics” attitude for sub design, let the damn thing be its natural size for the acoustics performance you need , my sub is moonlighting as a lamp/flower table
I mean all speakers design is juggling a bunch compromises and trade off’s against each other , why also impose a very strict size limitation on top of all this ?

I think it’s 600w for this rhythmic 15” bass reflex sub , it’s some kind of high power variant servo controlled .






I know it’s customers that demand this , more education is needed in this space , not more miniature speakers
Acoustics is probably the least understood science of all , just look at speaker placement among non audiophile friends ( if they haven’t ditched the old stereo for some mono bt thing )

 

[timiark]

Never got this “fight against physics” attitude for sub design, let the damn thing be its natural size for the acoustics performance you need , my sub is moonlighting as a lamp/flower table
I mean all speakers design is juggling a bunch compromises and trade off’s against each other , why also impose a very strict size limitation on top of all this ?

I think it’s 600w for this rhythmic 15” bass reflex sub , it’s some kind of high power variant servo controlled .






I know it’s customers that demand this , more education is needed in this space , not more miniature speakers
Acoustics is probably the least understood science of all , just look at speaker placement among non audiophile friends ( if they haven’t ditched the old stereo for some mono bt thing )

Well, personally, I am willing to see some shoe-box designs because it is pretty much what I need. I wish I could have a bigger place to place a somewhat giant 12" sub beside my desk, but I don't.