# Tech Tip: Wattage, Speaker Efficiency, and Amplifier "Loudness"

When it comes to volume, wattage is only part of the equation

There seems to be some confusion when it comes to how "loud" an amplifier can get. When it comes to "volume," many musicians only consider the amplifier's power or wattage rating, and in general, more watts does mean "louder." But while wattage is an important consideration, the efficiency of the speaker(s) that are connected to the amplifier are also an important factor in the loudness equation.

## Decibels and levels

Decibels (abbreviated "dB") are a logarithmic unit of measurement that pertain to a ratio between two numbers. Okay, I can see eyes rolling and glazing over, so I'll simplify things, and attempt to keep the "math" to an absolute minimum. With a logarithmic scale, you can't just add numbers in the usual way—a doubled number isn't "twice as much," but rather, many times more. For example, 100dB is many times greater than 50dB, not just "twice as much." When it comes to "loudness," which is measured in Sound Pressure Level, (or SPL), a 10dB increase in level is roughly equivalent to a "doubling" of perceived loudness. In other words, if one amp is generating 90dB SPL and another amp is hitting 100dB SPL, the second amp will generally be perceived to sound about twice as "loud" to the typical listener.

## Wattage, power, and SPL

So how many watts does it take to get twice as loud? Let's imagine two amps—one 10 watts, and a second 20 watts. The 20-watt amp is double the power of the 10-watt amp, but doubling the power only translates to an increase of 3dB SPL. Remember, in order to sound "twice as loud," you need an increase of 10dB, so while a 20W amplifier will sound noticeably louder than a 10W amp, it will not sound twice as loud. The same thing holds true at higher wattages—a 100W amp is not going to sound twice as loud as a 50W amp; assuming identical speakers, it will only be 3dB louder, which is noticeable, but definitely not a doubling of perceived loudness.

## Speaker sensitivity ratings

Speakers have specifications in terms of their sensitivity and efficiency— their ability to convert the incoming electrical energy into acoustical energy. Dynamic, moving coil speakers (the type found in most guitar and bass amps) are notoriously inefficient, and most of the incoming power is actual-ly converted into heat, not sound. Normally, speaker sensitivity is measured in an anechoic chamber (non-reflective, soundproof room) and expressed something like this: 90dB @ 1W/1m.

Translated into English, that means "90 decibels (SPL) with one watt of power, and measured at a distance of one meter from the speaker." A more efficient speaker will have a higher number, and a less efficient speaker will have a lower number.

## Putting it all together

So let's assume we have a speaker with a sensitivity of 90dB @ 1W/1m and a power handling capacity of up to 100W. If we power that speaker with 1W of power, it will generate 90dB when measured at a distance of 1 meter. If we double that power to 2W, the SPL measurement will increase to 93dB. If we increase the power to 10W, then the SPL measurement will increase to 100dB, which is "twice the perceived loudness" when compared to 1W. So it actually takes 10 times more power to give us a perceived doubling of volume level. Since this imaginary speaker is rated to safely handle up to 100W, we could double that volume level yet again, and in theory, hit up to 110dB SPL by increasing the power all the way up to 100W. One watt=90dB. One hundred watts, or 100X more power=110dB. That's a huge increase in power but only a "doubled double" (4X) increase in terms of perceived volume levels!

As you can see, it takes considerable increases in power—in the wattage of the amplifier—to "double" the perceived "volume." This is where speaker sensitivity/efficiency comes into the equation. If we replace that 90dB @ 1W/1m speaker with a model that has a sensitivity of 100dB @ 1W/1m, the numbers change dramatically. For starters, 1W of input power will give us 100dB SPL. Remember, the first speaker required 10W to achieve that same volume level! So by installing a more efficient speaker, we can get the same perceived volume level from a 1W amp as we could from a 10W amp that is coupled to a less efficient speaker. Again, this applies all the way up to the maximum power handling capacity of the speaker. Assuming our 100dB @ 1W/1m speaker can also handle up to 100W, it can give us up to 120dB SPL; again, that's double the perceived "volume level" of the 90dB @ 1W/1m 100W speaker's maximum level of 110dB SPL.

Tags: Amplifiers Speakers

Comments

I am confused in buying between 2 2.1 Sound bars

Phillips HTL 3140B specs speaker with 60W (30W x 2) at 8 ohms + 2 Tweeter at 6 ohms + Sub 140W all 3 ohms with input sensitivity of Aux as 900mV and Audio In as 500mV and S?N ratio 65dB

whereas

Samsung HW-F450 specs Speakers 160W (80W x 2) + Sub 140W all at 4 ohms with input sensitivity 570mV S/N ratio 70dB

My Question is

Is Phillips better than Samsung since it has 8 ohms impedance and lesser output wattage than compared to Samsung with higher wattage but at 4 ohms impedance?

Price-wise both are same rate. Which one should I buy which will give me better sound?

For the record, speaker wattage is what they are supposed to safely handle. Better speakers underrate this figure by as much 25%. Higher-end subs fall into this category where it might be rated at 400w but can safely handle 500w. That's the max it can handle. If it has a decent SPL rating, like say 91db, then running off a 100w amp should still get it loud enough. If it has a 83db SPL, then 100w won't be enough to get it very loud. Will probably find you need to crank the volume pot nearly all the way to get loud. This is because they designed the speaker with a lot of wattage in mind and opted for a low SPL design. You can put a 1000w rated speaker on a 130w amp channel, it doesn't matter. But if it has a really low SPL, you'll need more wattage to get it louder.

Wanting a classic radio look, I installed a RetroSound Model Two radio in my 1970 Chevelle SS. Output power is shown to be 25X4w RMS 45X4 Max Power. 4ohm.

2 Kenwood KFC-X173 speakers. 4 ohm.87db.Power range of 2-80 W RMS (240 watts peak power) Rated input power: 80 W. 2 Kenwood KFC-X 693 speakers. 4 ohm. 89 db. 2-130 W. Peak power 300W.

It is not very loud, and I would like more volume.

What is max amplifier wattage I can install, and what increase in db (and volume) would result? Is it worth it? Or, being long in the tooth, should I just invest in a pair of hearing aids?

Thanks for any help you can give me.

I am looking at making a 2x12 guitar cabinet for my 50 watt combo amp. Would it be to safe to use 2 30 watt speakers? I understand about matching the ohms but not the wattage. With so many options out there I want to make sure I buy the right thing

Thanks

Had a look last night and my amp has 8ohms & 16ohms options.

The speakers are both 8ohms so was thinking of wiring them up in series to make them 16ohms.

Would that also work if i was to use 2 types of speakers that are not the same wattage? i.e. have 1 speaker at 30 watt and the other at 25 watts?

Thanks

RMX 2450 specs:

Continuous Power Output Wattage:

- 8 Ohms: 500 W

- 4 Ohms: 750 W

- 2 Ohms: 1200 W

- 8 Ohms Bridged Mono: 1500 W

- 4 Ohms Bridged Mono: 2400 W

- Current Consumption: 10 Amps

JBL PRX425:

Frequency Range: 55 Hz - 19 kHz

- Frequency Response: 75 Hz - 16 kHz

- Coverage Pattern: 90 degree x 50 degree nominal

- System Sensitivity: 100 dB SPL (1w@1m)

- Power Rating, Pink Noise: 600 W / 1200 W / 2400 W (Continuous/Program/Peak)

- Rated Maximum SPL: 134 dB SPL peak

- Nominal Impedance: 4 ohms

Ulm 30-watt speakers. Would it be acceptable to replace those with higher wattage speakers? If so what would be the outcome

And sorry, to answer your question, higher wattage won't change anything. If you want to experiment with different sounds, look at paper, polypropylene, or other materials. I find paper makes for louder mids and somewhat louder full range, whereas polypropylene makes cleaner bass in the lower freq. range, especially when driving high wattage. Although I used to run some Radio Shack Realistic 50 watt polypropylene woofers in the early 90's and they made really good bass when matched to a capable amp. Most car audio subs are polypropylene or some other synthetic. Just experiment if you can afford it, or ask around about specific speakers on appropriate forums to narrow down your selection and go from there. Good luck.

claim 1000watts continuous and the DXR15 claims 700watts continuous if that helps

Can anyone who knows, advice on the wattage I need and the type of speakers than can harmoniously work with it without much of a headache? What I need is far from a home theater....this is for commercial purposes! Grateful for any help!!!

Thanks.

My biggest concern is clarity and a smooth response at all freqs I can generate. I guess my amp is loud enough and I don't have to buy a heavier one.