Why do PA speakers driven with more power deliver clearer and better sound?

Question

I have notices with my own equipment as well as making note of other musician's equipment that there seems to be a direct correlation between the amount of power (in watts) driving a PA speaker, and the quality of the sound.

Take a powered speaker for example. Common sense seems to imply that the reason you would use a 1000 watt powered speaker versus a 500 watt powered speaker - would be if you were in a larger venue covering a larger audience and needed more volume to reach a farther distance.

But I have observed that a 1000 watt speaker compared to a 500 watt speaker (even if both are the same size), will deliver a clearer, crisper, cleaner, more articulate, less mushy, and overall better sound - even if both speakers are reproducing the sound at the exact same LOW volume!

I have a basic idea of how a speaker cone reproduces sound. The signal from the source electrifies the magnet which reacts with the voice coil to produce a vibration that correlates with the source and produces the intended sound waves. But what is it about a greater degree of power in the amplifier that makes the same size speaker cone sound better with more power?

And is this phenomenon equally true whether you are using a powered speaker (with its own internal built in amplifier) or driving passive speakers with a separate power amplifier?

I do know that at higher volumes the extra power is needed to prevent clipping and distortion, but my question is about the sound with volumes well below what the speaker/amplifier combination is capable of producing.

And my question is specifically about PA speakers of they type that would be used in live sound reinforcement, not your home stereo or studio monitors.

And my presuppositions are based on my own personal observations with what I have seen. I suppose it is possible that there might be some exceptions to my opening statement, but if there are I have not found them yet.

Answer 1

Leaving aside questions of build quality, component quality, etc.:

The answer is actually very simple. All audio reproduction systems have what we call an "operational range." This is the softest soft sound, up to the loudest loud sound, that the system can produce.

Within this, there is something called the "linear operational range." This is the area within the full operational range where the system is behaving linearly, i.e. the amplified output is a faithful reproduction of the source input. Outside the linear range, the system goes into "non-linearity" which basically means distortion, of one sort or another.

Now, non-linearity isn't just about volume, per se. Take for example a PA system that is reproducing a snare drum hit at moderate volume. The shape of the snare hit waveform consists of a very sharp, steep leading edge transient, followed by a quick decay. That leading edge transient requires a very large amount of power to reproduce faithfully, as the system has to almost instantaneously go from zero to full power, if only for a brief instant. With an "underpowered" PA, that leading edge transient is smashed down, it is not nearly as "steep" or as "tall" as it was in the input signal, so though the system itself is operating in the middle of its range, the transients (and complex waveforms like square waves, sawtooths, etc.) are not being reproduced linearly. This is perceived by the listener as a "lack of oomph," a "smeary, mushy sound," etc.

In a well-powered system, the linear range is typically much wider than in the under-powered system

Answer 2

Several reasons:

• Size Matters Not: You write, "But I have observed that a 1000 watt speaker compared to a 500 watt speaker of the same size" (emphasis mine). It doesn't matter that the sizes are the same. The enclosure size is not always related to driver size, and driver size is not related to quality.
• Wattage isn't always what you think it is: You write, "Common sense seems to imply that the reason you would use a 1000 watt powered speaker versus a 500 watt powered speaker of the same size - would be if you were in a larger venue covering a larger audience and needed more volume to reach a farther distance." It requires a very large increase in power to make a significant impact on loudness. Doubling the power while keeping the same design only provides a 3 dB increase in level, and about a 10 dB increase in level is usually percieved as twice as loud. So to get twice as loud you need eight times the power. Another, more cost-effective way to increase loudness is to increase the sensitivity of the speakers in use. The immediate benefit of using double the power is more headroom, not more loudness. And headroom is a factor in sound quality.
• More power requires a different design: If the components and design of the 500 Watt system in question could have handled 1000 Watts, it would have been sold as such at the higher price. Even in the same product line from the same manufacturer, a 1000 Watt design likely shares only the enclosure, input stage electronics, and possibly one of the drivers (probably not, though) with the 500 Watt design. Most likely, the power amp(s) and all drivers are different, and even major design elements may be different. For instance, the 500 Watt design might be a single power amplifier connected to two drivers through a passive crossover, while the 1000 Watt design might be bi-amped. That kind of design change would have a significant impact on sound quality.
• All specs tend to scale up together: A customer buying a 500 Watt powered speaker is more likely to be choosing based on price. A customer buying a 4000 Watt powered line array element is more likely to consider sound quality a major decision point. A 1000 Watt powered speaker clearly falls somewhere in between there, but manufacturers tend to make several things better about their products as the price goes up. Sometimes, there is a more or less ideal design that is created, and then the lower cost options are created by compromising more and more on that design as the cost is decreased. That makes more sense than spending the same kind of design time and effort on a product that is meant to appeal to bargain-hunting computers.

Overall, the main point is: Comparing size and power output is not an apples-to-apples comparison. There are too many other factors at play in the sound quality. Imagine comparing a 2015 Les Paul Standard to a vintage '59 Gibson Les Paul Standard and seeing they are the same size, similar design, similar output level, etc., and wondering what about the vintage '59 makes it sound amazing versus the new one. Our ears are amazingly sensitive, and sometimes even the smallest details make a big difference.

Answer 3

It is all about headroom. I will use arbitrary numbers. If I was playing in a club at a volume that is not very impactful with three part harmonies and maybe an acoustic guitar in the system depending on how efficient the speakers were you could get by with 200 watts.

Now lets think a bit differently but now you want a more impactful sound. You decide to start mixing drums and running bass and electric guitar in the system too. Your 200 watts that did vocal fine when you turned it up and decided to put drums in it your 200 watt vocal system that was OK is not doing the job.

The lowest cost way these days to take a step up in performance is to add a powered sub. Depending maybe 1 will do. There are a lot of variables.

Once you get low frequency information out of the vocal range speakers you will pick up a lot of headroom. It is much easier than it was in the old days because many speakers are self powered with crossovers for subs built in as well as processing for the speaker to run at its best. In the days when a 15 and a horn was typical if you took and ran 250 watts or so into the 15 you could run less than a 100 watts into the horn and have a lot of headroom.

Bear this fact in mind too. I could blow a 400 watt speaker out easier with a 100 watt amp than a 600 watt amp. It is the clipping distortion that will take the speaker out.

Also another mistake I have seen made. People I have seen take a control on a power amp and set it at half thinking I will get 1/2 the power. That is not the way it works. Those controls are input sensitivity controls and I can get the full output from the amp with the amp control set at 1/4. I would just have to drive the mixer harder.That makes it easier to get distortion before the signal gets to the amp or speaker.

The end result is get as much power and efficiency as you can afford. A decent system would be a couple 12 horn speakers on sticks when you are more laid back. Add a couple 15 or 18 inch subs if you are going to put drums and bass in the system.

Answer 4

In terms of the two speakers being compared, were they of the same make/series etc? I can't speak for PA speakers as much, but I know from selling near-field studio monitors all day every day that even the smallest Genelec monitor can sound much nicer than a big 8" cone Yamaha monitor or similar. A lot goes into the design of the enclosure etc. as well as the power amplifier.

Answer 5

It's a difficult question to answer as different speakers may have different responses. However, one contribution factor is noise. More power does amplify source noise and music at the same rate, but noise acquired "downstream" from the amplifier will (in general) be less obtrusive. For example if a signal of strength 100 (in whatever units) would get 1 unit of noise, the S/N ratio is 100/1 or 100; if the signal strength were 200 and the same noise showed up, the S/N ration would be 200 which would be better.

As you described the problem, it's the speaker-amplifier combination that you are measuring. (You posted 1000-watt speaker compared to 500-watt speaker, not 1000 vs 500 watts applied to the same speaker.) In this case, the 1000-watt combination may just be of higher quality that the 500 watt system.

Answer 6

A higher rated speaker needs to transfer a larger amount of energy to the air. Doing that may require a larger chassis and stronger magnets and coils. That may make for a more direct/accurate response particularly when you are not maxing the system out.

Answer 7

That will depend on the amplifier used and the speakers. A good pair of speakers will sound almost the same at low and at higher volumes (they will just sound louder but all information will be there no matter the volume). I am talking about Higher End speakers. Some amplifiers may not be very "linear" and "respond" different at higher volumes. But if you have an amplifier with enough "torque" (not to be confused with Torque Amplifier (TA)) , it will drive a good pair of speakers without loosing quality both at low and higher volumes. It doesn't matter if the amplifier is rated at 50W or 250W or even 2500W. What matters is how it "presents" the available power. If an amplifier has a bigger transformer and bigger PSU capacitors so that it can draw more power from the mains and store that inside the circuit ready to deliver to the speakers and can present it accurately from 0 to what ever volume you decide (that will depend a lot on the design of the amp itself), the amp will have more "torque" than an amplifier with a small power supply and a "lower quality" design.