Woofer wattage?

Thread Starter

Daan Lageschaar

Joined Jul 8, 2019
45
Hi,

So a friend of mine has a woofer which says 500w on the back, now I'm wondering if that'd be 500w RMS or 500 peak.
Unfortunately there doesn't seem to be any information about it online, that's why I'm asking it here.
So would it most likely be 500w RMS or peak?

Thanks in advance :)
-Daanwoofah.jpeg
 

Delta Prime

Joined Nov 15, 2019
1,311
Hello there. :) RMS and “peak power.” Both are similar in concept, but when you really begin to break them down there are a number of important distinctions.
RMS is an acronym that stands for “root mean square.” This number refers to how much power a particular subwoofer can handle on a continuous basis.


Peak poweris exactly what its name suggests – the total amount of power a subwoofer can manage in short bursts for a limited period of time. Both numbers are important to know, as if you push your subwoofer beyond these levels you could end up accidentally damaging it.
Think about it like this – because RMS measures the amount of power your subwoofer can handle without damage on an ongoing basis, it’s actually a lot more relevant to your current interests than peak power. This is true even though the RMS rating will likely be LOWER than that of peak power. If you’re talking in terms of straight performance, RMS is going to be reflective of the experience you’ll get the vast majority of the time. Peak power may give you the confidence to know that the short helicopter crash in the third act of your favorite movie is going to sound fantastic… but what about the other 98 minutes of screen time? RMS is going to tell you a lot about how THAT is going to sound, too.
specifications of a subwoofer, thinking that neither RMS or peak power values are very high. This is because you’re forgetting about the most important component of all: efficiency.
you don’t necessarily need to pay as much attention to wattage as you might think you do. With RMS power handling, an efficient subwoofer can deliver an exceptionally strong bass performance – even if the wattage doesn’t seem to be very high at first glance. Remember that many manufacturers specifically exaggerate power and focus on peak power LEVELS for this reason – it looks great on a spec sheet, but it’s not a true representation of the overall type of performance you can expect from a subwoofer
 

Audioguru again

Joined Oct 21, 2019
5,183
Name brand speakers are rated in RMS continuous power. Cheap speakers have any big number that sells more.
I have a pair of Radio Shack 2-way speakers rated at 40W. When one woofer died I looked inside and it was stamped Realistic 5W Korea. I ordered a pair of replacement woofers that looked a little different and were stamped 10W. I complained and the store manager gave them to me at no charge.
 

dendad

Joined Feb 20, 2016
4,219
Go with RMS as the "Peak" power usually has a multiplication factor determined by the advertising department, and how many chrome knobs and LEDs the amplifier has.
I have seen many stereos that have something like "200W" power rating but the power supply running them is 15W.
They are amazing devices! Capable of outputting more power than the input!!!
Generally, just ignore peak power altogether. It is an artificial number more to do with marketing than performance.
My 15" Tanoys are rated at 85W RMS. I never drove then anywhere near that as they were plenty loud on 10W.
Efficiency is what you need.

And your "500W" subwoofer is rated at "Imagination Power".
 

Audioguru again

Joined Oct 21, 2019
5,183
I have a Sylvania "150W" sound system that is used for my TV and computer. It sounds great. Inside is a power transformer rated at 10W. The little power amplifier ICs have a small heatsink glued in top. It is class-AB so is about 50% efficient then the total power is 5W RMS.
 

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KeithWalker

Joined Jul 10, 2017
2,522
As the others have stated above, loudspeaker ratings are usually pure marketing fairy tales. The output of a speaker is dependent on many factors including speaker sensitivity, the inductance of the voice coil, The limit of travel of the cone, The temperature of the coil which increases during prolonged high power levels, the characteristics of the enclosure, etc. There have been cases of marketers advertising speaker power using pk/pk power which is 2.8 times higher than the rms power.
I am curious to know why anyone would want to buy a 500 watt speaker unless they were equipping a concert in a very large arena. 1 watt of audio power is quite loud in the average home. 500 watts is enough to permanently deafen the whole street.
Regards,
Keith
 

nsaspook

Joined Aug 27, 2009
10,426
As the others have stated above, loudspeaker ratings are usually pure marketing fairy tales. The output of a speaker is dependent on many factors including speaker sensitivity, the inductance of the voice coil, The limit of travel of the cone, The temperature of the coil which increases during prolonged high power levels, the characteristics of the enclosure, etc. There have been cases of marketers advertising speaker power using pk/pk power which is 2.8 times higher than the rms power.
I am curious to know why anyone would want to buy a 500 watt speaker unless they were equipping a concert in a very large arena. 1 watt of audio power is quite loud in the average home. 500 watts is enough to permanently deafen the whole street.
Regards,
Keith
I need high power speakers and amps because my HT media room is highly damped at low frequencies to help eliminate room modes. I need the acoustic power to maintain a dynamic range that matches the uncompressed source material at normal
theater listener levels.

Damping traps for walls and corner room modes.
The classic RS NOVA speakers have all been rebuilt (PARTS EXPRESS) with new professional drivers and crossovers.
 
Last edited:

Berzerker

Joined Jul 29, 2018
621
I'll point out again "I'm no expert" but doesn't the speakers Ohm's fit in here somewhere?
The 2, 4 and 8 Ohm is on that speaker for a reason.....isn't it? Doesn't it take more power/wattage the lower/higher (Can't remember) the Ohm's number to get the same results?
Brzrkr
 

nsaspook

Joined Aug 27, 2009
10,426
I'll point out again "I'm no expert" but doesn't the speakers Ohm's fit in here somewhere?
The 2, 4 and 8 Ohm is on that speaker for a reason.....isn't it? Doesn't it take more power/wattage the lower/higher the Ohm's number to get the same results?
Brzrkr
Not usually if the speaker driver is designed with that in mind. You can buy the same basic type of professional speaker with different speaker coil combinations for the impedance needed for a specific speaker array wiring connection.
https://www.parts-express.com/cat/p...earchable","1")]&PortalID=1&showMoreIds=10014
 

Audioguru again

Joined Oct 21, 2019
5,183
The antique Radio Shack speaker uses a 10" woofer. The most expensive Parts Express "professional" Faital 10" woofer has a maximum rated power of 300W RMS for 2 hours and has 96dB sensitivity at 1W/1m. Then its output is 84dB at 1W/4M or is 108dB (pretty darn loud) at 256W/4m. If 2 woofers are playing 256W then the sound level at a distance of 4m is 111dB.

Years ago I measured 120dB in a disco when I was 2m away from one 18" woofer and many metres away from other woofers. Each one had a 900W amplifier but were not playing at maximum output power.
 

Audioguru again

Joined Oct 21, 2019
5,183
I'll point out again "I'm no expert" but doesn't the speakers Ohm's fit in here somewhere?
The 2, 4 and 8 Ohm is on that speaker for a reason.....isn't it? Doesn't it take more power/wattage the lower/higher (Can't remember) the Ohm's number to get the same results?
Brzrkr
Ohm's Law says that a 2 ohms speaker uses double the current of a 4 ohms speaker or 4 times the current of an 8 ohms speaker.
An audio amplifier is a voltage source where its output voltage swing is not changed by the speaker ohms. If the amplifier is designed to drive a 2 ohm speaker then the current is 4 times higher than with an 8 ohms speaker but the power is the current squared times the ohms. The amplifier and the speaker must be designed to survive the power.
 

nsaspook

Joined Aug 27, 2009
10,426
The antique Radio Shack speaker uses a 10" woofer. The most expensive Parts Express "professional" Faital 10" woofer has a maximum rated power of 300W RMS for 2 hours and has 96dB sensitivity at 1W/1m. Then its output is 84dB at 1W/4M or is 108dB (pretty darn loud) at 256W/4m. If 2 woofers are playing 256W then the sound level at a distance of 4m is 111dB.

Years ago I measured 120dB in a disco when I was 2m away from one 18" woofer and many metres away from other woofers. Each one had a 900W amplifier but were not playing at maximum output power.
Nova 8's, Optimus-5B's and several other antique Radio Shack speakers have 12" woofers.
https://worldradiohistory.com/Archive-Catalogs/Consumer/Radio-Shack-1977.pdf page 19
Top stack Nova 10 with 10", bottom stack Nova 8 with 12", side stack two Optimus-5B with 12". That's the left side. The right side only has the Nova stack.

The center speaker array has the mid/tweeter array on the projector screen cover with the woofer on the equipment cabinet.
Then there are the middle and rear speaker pairs for surround sound not shown here.

I don't run the average power super high but I do want chest crushing bass for when it's needed.
 
Last edited:

Berzerker

Joined Jul 29, 2018
621
nsaspook said:
Not usually if the speaker driver is designed with that in mind.
My reason for asking was what if someone where looking to replace a speaker. It would matter then...right?

AG again said:
Ohm's Law says that a 2 ohms speaker uses double the current of a 4 ohms speaker or 4 times the current of an 8 ohms speaker. An audio amplifier is a voltage source where its output voltage swing is not changed by the speaker ohms. If the amplifier is designed to drive a 2 ohm speaker then the current is 4 times higher than with an 8 ohms speaker but the power is the current squared times the ohms. The amplifier and the speaker must be designed to survive the power.
power/current same thing. Isn't a 2 Ohm speaker louder than a 4 Ohm speaker with the same current going through it?

@Audioguru again
What happened to your name? I mean what is the "again" about?
Brzrkr
 

nsaspook

Joined Aug 27, 2009
10,426
Sure, for a direct replacement it matters because of the existing system amplifier drive requirements, crossover design, etc ...
 

Audioguru again

Joined Oct 21, 2019
5,183
An amplifier produces a constant voltage, not a constant current.
With the amplifier producing a certain voltage output (example 20V RMS):
1) An 8ohm speaker produces (20V x 20V)/8 ohms= 50W. The current is 20V/8 ohms= 2.5A.
2) A 4 ohm speaker produces (20V x 20V)/4 ohms= 100W. the current is 20v/4 ohms= 5A.
3) A 2 ohm speaker produces (20V x 20V)/2 ohms= 200W. the current is 20/2 ohms= 10A.

If you adjust the volume so that the current is always 5A:
1) An 8 ohm speaker produces 5A x 5A x 8 ohms= 200W.
2) A 4 ohm speaker produces 5A x 5A x 4 ohms= 100W.
3) A 2 ohm speaker produces 5A x 5A x 2 ohms= 50W.

I changed my email address but this website and many others do not allow that. Then I needed to register again. Audioguru was already used and could not be used again so I added "again" and now I am "Audioguru again".
 

dendad

Joined Feb 20, 2016
4,219
If, for example, you have an amplifier designed to drive a 16 ohm speaker, then put a 2 ohm speaker on it, you run the risk of damaging the speaker or the amplifier.
For a given drive level, that is the amp output voltage, a 2 ohm speaker will give more output power than a 16 ohm one as long as the amp can drive it, assuming nothing pops.
Some applications run high impedance speakers, like PA systems installed in buildings may be 600 ohms or higher, as there is less current involved so the speaker wires can be a lot longer without loss.
If you wanted to run a speaker 100 meters away from the amplifier, a 2 ohm speaker is not suitable as a large percent of the power would be lost in the cable.
So, yes, the impedance does effect the power out, but if the amp and speaker are matched, it does not matter.
It is best tho' to run the correct impedance speakers, and not lower than the design requirements.
 

Audioguru again

Joined Oct 21, 2019
5,183
So, yes, the impedance does effect the power out, but if the amp and speaker are matched, it does not matter.
The impedance of a modern amplifier Never matches a speaker's impedance. The output impedance of an amplifier is much much less than the impedance of a speaker so it can damp resonances of a speaker. It is called the Damping Factor. Many amplifiers have an output impedance of 0.04 ohm and some even lower.
Of course the amplifier must be designed to supply enough current into its lowest rated speaker impedance.
 

Delta Prime

Joined Nov 15, 2019
1,311
Unfortunately there doesn't seem to be any information about it online, that's why I'm asking it here.
Now you know! In fact through their chatter amugst themselves
They have given you answers to future questions whenever you want to upgrade or replace audio components.& They didn't try to sell you anything!
Once you get these guys started
You can't shut them up.;)
I love this place!!
 
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