Responsible use of amp power

[Robby Sturgis]

New to amp power and speaker cabinet matching, as I’ve used combo amps most of my career.

I asked an Eminence tech if a speaker rated 225 watts was properly paired with an amp designed at 600/300.

His response: “If the cabinet was properly designed and you used the amp power responsibly, yes.”

So what is responsible use - keep it at 7?

 

[basscooker]

It isn't exactly power, although that plays a part. More of being responsible about it has to do with having realistic expectations and understanding what ratings actually mean.

No 1x10, regardless of any power rating is going to rumble stuff off the shelves a block away, for example. Yes, that's an extreme example but you get the point.

A speaker has typically been advertised with an electrical power rating, which does not take into account its physical limitations.

Often a safe route to approaching bass cabs, or speakers being loaded into a properly designed cabinet for it, is to assume they will hit their limits with a real-world musical bass signal of half (ish) of its power rating. There are stars and duds, so exercising discretion with the low end of the eq is being responsible.

Understanding that an amplifier has a knob to turn down if a cab makes bad noises is being responsible.

Learning and seeking more knowledge about the equipment you have or intend to buy is being responsible.

I'll close with one other point, directly to your OP. Knob position rarely if ever indicates power output. E.g. "5" does not mean the amp will only put out half power. Remember that to some degree or another every single knob, switch or button on an electronic device involving the signal chain is a volume control of some sort. Just because the one that actually says "volume" is low does not mean you aren't putting potentially high or near max output into your speaker.

 

[Roland GR 88]

I would bet he means that if you need to run the amp at 10 hoping to get all 300 watts then you might blow the speaker through either a poorly designed cab or sheer volume.
It's a fair answer considering he has no knowledge of what cab you'll use or how you like to run your amp.

 

[pcake]

i wouldn't turn my 600 watt head up to 7 with a 225 watt cab at all, not even a 300 watt head unless i played pretty gently. there are peaks that occur when you play hard, and also there's more to the cab then just watts - how far the cone can travel out (excursion) is something to be aware of and also the coil can overheat.

go by sound, not the number on the dial. when things start sounding wrong - sound distorting, odd noises - that's when to turn down just a little. for years, i played a 1000 watt head with a 118 rated 800 watts with a 2x10 rated 600, and with my volume at 75, i started to hear things change. i play with a lot of attack, so i never turned up over 70. btw, i always played clean - with OD or distortion, i'd have kept things turned down a bit.

but that applies to combos, too.

 

[Downunderwonder]

Responsibly means to take care not to blow it up.

Overexcursion is the result of too much power applied to low end. You hear that as farty flappy nasty sounds. The cone breaks up or disassembles eventually. In extreme cases you can bang the magnet with the voice coil or bust it up there and then.

Overheating happens from too much power in general.

If you turn up and it doesn't fart out you can still overheat. A good sign you are at the limit is turning up doesn't really sound much louder. Turn it down a little from there and you will never blow a speaker.

If it ever gets quieter you are beginning to overheat. That's when you take a break and reset lower volumes all round.

 

[basscooker]

Also of note, OP, simply swapping a speaker in a bass cab more often than not doesn't turn out as a notable improvement. Some research is suggested.

A good approach is to get the cabinet internal dimensions, including the port (if any) diameter and depth measurements. With this information in-hand, your call to Eminence will help find you what you need more effectively.

 

[Wasnex]

New to amp power and speaker cabinet matching, as I’ve used combo amps most of my career.

I asked an Eminence tech if a speaker rated 225 watts was properly paired with an amp designed at 600/300.

His response: “If the cabinet was properly designed and you used the amp power responsibly, yes.”

So what is responsible use - keep it at 7?

The setting of the amp's controls reduce available gain, but they don't limit the amount of power the amp can make. So if you turn up your preamp, you can still destroy your speakers.

Responsible use means operating within the power handling limits of your cab's design. Unfortunately the power handling limits are fairly complex and typically not fully explained by manufacturers. As @basscooker explained you need to know your cab's mechanical power handling limits, which are determined during the design process. AFAIK, It's fairly common for manufacturers to use the driver's thermal rating instead of the mechanical power handling limits. This makes the cab seems a lot more capable than it actually is.

I will post an Eminence driver data sheet and a matching cab design document that I pulled from Parts Express. If you look through the graphs for each design you will note the low frequency cutoff changes with the design.

Also note the excursion of the driver is related to the port tuning frequency. Excursion decreases as the port become resonant. Below resonance, the output of the design quickly drops off and driver excursion quickly increases. Power handling below port resonance quickly decreases. A good strategy here is to use an HPF to cut off frequencies that are slightly below the tuning of the port.

Note the 3015 datasheet lists the power handling as 450W RMS, 900W Music Program. The power handling specs are the thermal power the driver can handle at higher frequencies, where there is no danger of over excursion. The distance the voice coil can safely move is called Xmax. Xmax for this driver is 5.9mm. Xmax comes into play at lower frequencies (typically a bit under 100hz).

If you look at the first design for the 3015 you will see a note that says: "Displacement Limited to 300 Watts; F3 of 51 Hz. Use a steep High Pass Filter set to 35 Hz or higher to protect woofer from over excursion." Take a look at p. 2 of the document and find the graph labeled "Cone Displacement (mm/Hz) with 300 watts," and the note should make sense. The dark line is where the excursion is within Xmax, and the grayed out line is where the excursion is predicted to exceed Xmax (5.9mm) with 300W. This graph is specific to the design. Take a look at the Cone Displacement graph for the next design and note the difference.

 

[Robby Sturgis]

Thanks to everyone for your explanation of responsible use. I can understand why they don’t put this in the user manual for this novice to read and comprehend. Haha.

 

[seamonkey]

You won't always hear when something is going wrong.
You'll be playing loud in a band. New drivers don't distort much when driven close to their limits.
What distortion is there when pushing the cab may be masked by other loud sounds in the band.
It happens quite a bit these days that people can't believe they burned out a driver because they just didn't hear it straining. Ask the techs.

Trying to limit the amp with the knob may not actually limit it. If the amp has a DSP you may be able to limit the power with the DSP Limiter itself.

 

[iiipopes]

Everyone who has followed my posts know I really get into numbers, specs, etc. As far as this thread, however, "responsible use" is more subjective.

Yes, I used to be in a band that when we got a new piece of equipment that advertised (fill in the blank) capability, we pushed it until it either performed as advertised or broke in the warranty period, because we pushed hard on stage. Is that "responsible use"? Well, maybe. For example, we didn't purposely short out an amp with a two-ohm load, for example, but we would test the limits of its advertised capabilities.

Fast forward to present: 600 watts will fry a 225 watt speaker if pushed. That is because the speaker is being fed more power than its advertised power handling limits. In this particular case, "responsible" may mean are you listening closely to the speaker when it is getting towards its limits, with either heat, cone excursion, or audible raspiness or distortion, or extreme amp settings (bass control dimed out, for example).

 

[spentron]

I've heard that to get maximum power handling from a speaker, the amp needs to be rated 3-4 times what power is actually flowing so the amp stays super clean. But how do you know how much power is flowing? For most people they hear the amp distort, which happens when the amp exceeds its rated power. The maximum power amps can put out, when fully overdriven, is about twice their clean rating. So you can get the most out of a 100 watts speaker with a 300 watt amp, but you can only guarantee the speaker's input stays below 100 watts with a 50 watt amp. And to be very sure the 300W amp stays below 100W, you probably won't be able to exceed 30.

Note that to get full power from the amp, the impedance of the speaker must match the impedance that power is at. If you use an 8 ohm driver with a 4 ohm amp, you'll probably get a 30-50% power reduction. Don't go the other way, a 2 ohm speaker might actually draw more power from the amp until it overheats and shuts down or blows up.

 

[Wasnex]

I've heard that to get maximum power handling from a speaker, the amp needs to be rated 3-4 times what power is actually flowing so the amp stays super clean.

IMHO, this is a good recipe for blowing speakers.

FYI, people normally think of RMS as the speaker's continuous power rating, but I believe it's more accurate to call it an average power rating. Speakers are often given an RMS rating with a 6dB crest factor, so a speaker with a 200W RMS rating would handle short transients up to 800W, basically +6dB and called Peak Power. This is probably where the idea of using amps rated at four times the speakers power rating comes from.

There are two problems I can think of: 1. This relates to the thermal rating and doesn't tell you anything about the mechanical power handling limit of the driver, which is often less than the RMS rating. 2. How do you ensure the average power stays under 200W?

Another thing to consider is the power handling standard used to rate the driver. Some of the standards specify the driver must survive for as little as 2 hours. I think most of us would like our speakers to last a bit longer than 2 hours, so maybe it's not a good idea to push them to their Peak Power limits.

If it's your system and you run it and monitor the amps closely, it may be okay, unless you have an accident. But if you let others run the system, it's likely they will push the power amps into the red and blow drivers.

 

[seamonkey]

I've heard that to get maximum power handling from a speaker, the amp needs to be rated 3-4 times what power is actually flowing so the amp stays super clean...

Depends on where you go, for example read what JBL says:
[Invalid or Expired Link Removed]

Here's the deal - JBL mentions: "Ideally you should pick an amplifier that can deliver power equal to twice the speaker's continuous IEC power rating."

Unfortunately hardly no bass cabinet is going to publich IEC power ratings of the "Cabinet". The cab builders will add up the raw IEC ratings of the drivers and assume it's the same for the drivers in a cabinet. It's not. There are some solid manufacturers who do actually measure to burnout. It's very rare though. Better ask before you buy what the best amp power recommendation is. Get it in writing.

 

[projectapollo]

Back when I was a recording engineer, I was educated by JBL that used to put LOW POWER warnings on their speakers. The idea being that a low power amp driven to distortion can damage a speaker. JBL advises more clean power (more dynamic headroom). Just don't turn it up too loud to cause the speaker to reach its physical limits. But a higher power amp will be more kind to your speaker at a given volume.

 

[Bass_Pounder]

Back when I was a recording engineer, I was educated by JBL that used to put LOW POWER warnings on their speakers. The idea being that a low power amp driven to distortion can damage a speaker. JBL advises more clean power (more dynamic headroom). Just don't turn it up too loud to cause the speaker to reach its physical limits. But a higher power amp will be more kind to your speaker at a given volume.

Distorted amps do not damage speakers.

The white sheet that the info comes from is referring to high frequency drivers being damaged by distortion. This is one of the places that the myth of underpowering a speaker comes from.

If amp distortion killed speakers, please explain guitar amps.

 

[Pilgrim]

Here's my definition of "responsible use" in this context:

- I want to always use a speaker cab rated for the maximum power (wattage) the amp is rated to put out. You may get a number of "angels on the head of a pin" arguments about this, but it's a good place to start.

- If I had to use a cab rated lower than the max power of the amp, I would keep the volume as low as possible and listen to what the speaker is doing. If it started to make any odd noises, I would turn down.

- Remember that you will never damage a speaker by turning down. There is no such thing as under-powering a speaker.

 

[Wasnex]

Back when I was a recording engineer, I was educated by JBL that used to put LOW POWER warnings on their speakers. The idea being that a low power amp driven to distortion can damage a speaker. JBL advises more clean power (more dynamic headroom). Just don't turn it up too loud to cause the speaker to reach its physical limits. But a higher power amp will be more kind to your speaker at a given volume.

The way distortion typically damages speakers is by transferring energy from low frequencies to high frequencies, so basically you exceed the power rating of the mid range or tweeter.

Another factor is if you have a square wave and sine wave at the same voltage level, the square wave will carry more energy. A sine wave increases to it's max voltae and then immediately starts to decrease. A square wave stays at the max voltage for longer period of time. So basically the square wave is actually carrying more power. The damage occurs anytime the voice coil exceeds it's RMS power handling limits. It doesn't really matter whether the signal is dirty of clean.

To my understanding the power handling of voice coils would need to be derated for DC versus what they can handle at AC. But when an amp is clipped, I believe the square shape actually comes from the abundant production of high frequency harmonics rather than DC.

Here's a couple of threads you might enjoy.
Distorted sound
Distorted sound

 

[Downunderwonder]

I've heard that to get maximum power handling from a speaker, the amp needs to be rated 3-4 times what power is actually flowing so the amp stays super clean. But how do you know how much power is flowing? For most people they hear the amp distort, which happens when the amp exceeds its rated power. The maximum power amps can put out, when fully overdriven, is about twice their clean rating. So you can get the most out of a 100 watts speaker with a 300 watt amp, but you can only guarantee the speaker's input stays below 100 watts with a 50 watt amp. And to be very sure the 300W amp stays below 100W, you probably won't be able to exceed 30.

Note that to get full power from the amp, the impedance of the speaker must match the impedance that power is at. If you use an 8 ohm driver with a 4 ohm amp, you'll probably get a 30-50% power reduction. Don't go the other way, a 2 ohm speaker might actually draw more power from the amp until it overheats and shuts down or blows up.

You heard wrong.

Nobody cranks up a SS amp to 100% distortion, not even close.

Yes 2ohm lods on 4 ohm SS amps is a bad idea.

 

[Wasnex]

Here's my definition of "responsible use" in this context:

- I want to always use a speaker cab rated for the maximum power (wattage) the amp is rated to put out. You may get a number of "angels on the head of a pin" arguments about this, but it's a good place to start.

- If I had to use a cab rated lower than the max power of the amp, I would keep the volume as low as possible and listen to what the speaker is doing. If it started to make any odd noises, I would turn down.

- Remember that you will never damage a speaker by turning down. There is no such thing as under-powering a speaker.

Using speakers rated to play at a higher SPL than you would ever need is a good strategy. Then you don't have to worry about too much power.

 

[Pilgrim]

Using speakers rated to play at a higher SPL than you would ever need is a good strategy. Then you don't have to worry about too much power.

Good point. I probably should have said "rated at least as much as the maximum power the amp is rated to put out."