Please Explain: Speaker Efficiency

colourofsound

So, what is Speaker Efficiency and how does it work? I understand that its measured in db and the higher the db the more headroom you get from your amp.

But why is this so? What about a speaker makes it more efficient, and what interaction with the amplifier dictates more headroom?

And, how much headroom are we talking in real world terms? My 68 Custom Deluxe breaks up around 4 on the volume dial - if I install a more efficient speaker, how much further can I crank it before it breaks up?

Thanks in advance to those with the knowledge...

HHwarner

I may be wrong but your amp will still break up at 4 on the dial but 4 on the dial will sound louder with a more efficient speaker. So in theory you wont have to turn your amp up so loud hence, more head room before it breaks up. Thats a very simplistic way I look at it. 
I run different cabs for different scenarios. One has more efficient speakers than the other. I also use a cranked Marshall into an attenuator. A difference of about 3db on the attenuator between cabs to achieve similar volume when comparing both together. Thats what Iv found on the combination I have.

Cirrus

The amp sends power in the form of electric current out down the speaker cable.

Speaker efficiency is about how much of that electrical power turns into volume, and how much of it turns into heat.

thermionic

It's simply power out divided by power in. If all the electrical energy was converted into sound, it would be 100% efficient. Some energy is dissipated as heat from current flowing through the resistance of the voice coil, with lesser losses from friction and others.

Audio power is not as easy to measure as electrical power, and depends on mechanical characteristics of the speaker components so they use the dB as a relative figure. This is shorthand for "loudness in deciBels at 1 m away from the speaker when you send in 1 W of electrical power".

<edited because I had power in/out the wrong way round!>

crunchman

To expand a bit more, the decibel scale is logarithmic so 100dB is not twice as loud as 50dB.  Actually you get a doubling of perceived volume every 3dB.

To use some real examples:  with exactly the same amplifier plugged in at the same volume, a speaker with 100dB sensitivity like a Celestion Blue should sound twice as loud as something with a 97dB rating like a Celestion G12-65, and 4 times as loud as something with a 94dB rating like a Jensen C12R.

It's not quite as simple as that, as different speakers will have different frequency responses, and the human ear is more sensitive to some frequencies than others.  Something like a Vintage 30, which has a peak in the upper mids, may well sound louder and/or cut through a mix better than something with a flatter response.

It's also complicated by the fact that some companies are more conservative with their ratings than others.  An Eminence rated at 100dB is reputed to actually be about the same volume as a Celestion rated at 98dB.

In most respects the frequency response is more important than the efficiency.  That's what gives the speaker its sound.  A Celestion Blue, G12H30 and a Vintage 30 are all rated at 100dB but they sound very different.  

ICBM

Pretty much all covered above, apart from *why* some speakers are more efficient than others.

Essentially it comes down to the strength of the magnet (larger/heavier magnets usually give a more efficient speaker), the size of the voice coil (larger also tends to be more efficient) and the size of the coil gap (smaller is more efficient). Then add the size of the cone (larger is more efficient up to a point, simply because it moves more air) and the stiffness of the suspension and surround (stiffness dampens movement).

These things also affect the sound of the speaker, so you can't just stick a magnet big enough to lift a car onto a huge voice coil and a four foot cone and expect it to produce a good loud tone, Back To The Future style… 

ESBlonde

Why are two 1.9Ltr Diesel engines not equal in there output, one may be better in the mid rev range while another is more suited to low rev lugging. But the fuel used could be different or the same and the torque/rev range will vary. Loudspeakers are a bit like that too. You feed in a set power but the coil/magnet and cone combination deal with it differently. Also how that cone interfaces with the big outside world can make a massive amount of difference (although less so for the restricted frequency range of electric guitar). For loudspeakers power is less of a problem these days because it's relatively cheap and available. Once upon a time 8x12" cone drivers were needed to handle a 100w valve amp giving birth to the famed 4x12" cab stacked. Modern sound reinforcement can have a single 10" cone capable of taking 3-400w with high resolution and efficiency, you wouldn't want that sound from your guitar amp but it shows how the technology has leapt forward in the last 50 years.

Cirrus

Speaker efficiency is very simple to understand. Speaker efficiency is all about how much of an efficiency a speaker has. When speakers have lots of efficiency they can be more efficient than if they had not lots of an efficiency, which is what the speaker efficiency is all about.

When my uncle was a young lad, he was sent to get more efficiencies from the botacethry on the corner. In those days they cost thrupnyha'pence, which was an amount of money no one of the era could comprehend. Scholars later believed that it was an irrational number of pence. My Uncle took 25 years to get to the store, but once he was there and got the efficiencies he decided to use one of them to help get home and it took 13 seconds.

Efficiencies aren't as good these days, because they're a bit more wasteful and environmental legislation means they can't use a lot of the chemicals they used to put in efficiency. Still, thanks to modern CAD technology, things that need efficiency can actually get by with less than they'd have needed in the past.

Hope that helps clear things up?

Voxman

Cirrus said:

Speaker efficiency is very simple to understand. Speaker efficiency is all about how much of an efficiency a speaker has. When speakers have lots of efficiency they can be more efficient than if they had not lots of an efficiency, which is what the speaker efficiency is all about.

When my uncle was a young lad, he was sent to get more efficiencies from the botacethry on the corner. In those days they cost thrupnyha'pence, which was an amount of money no one of the era could comprehend. Scholars later believed that it was an irrational number of pence. My Uncle took 25 years to get to the store, but once he was there and got the efficiencies he decided to use one of them to help get home and it took 13 seconds.

Efficiencies aren't as good these days, because they're a bit more wasteful and environmental legislation means they can't use a lot of the chemicals they used to put in efficiency. Still, thanks to modern CAD technology, things that need efficiency can actually get by with less than they'd have needed in the past.

Hope that helps clear things up?

You're not in politics are you Cirrus? If not, you've missed your vocation mate!  

crunchman

He's probably a lawyer on a break from the supreme court case.  Talking the same amount of unintelligible rubbish.

gordiji

Cirrus said:

Speaker efficiency is very simple to understand. Speaker efficiency is all about how much of an efficiency a speaker has. When speakers have lots of efficiency they can be more efficient than if they had not lots of an efficiency, which is what the speaker efficiency is all about.

LOL. Reminds of how the word unreasonable was defined in a standard law book with regard to litigation. Along the lines of something is only unreasonable if no reasonable person would do it !

ecc83

Being the pedant I am! I am going to say we should not speak of speaker "efficiency" since that is the ratio of power out to power in. It is very difficult to measure the ACOUSTIC power output of a speaker so just the SPL at 1 mtr is measured (in fact it is also next to impossible to define the ACTUAL power into a speaker and makers usually content themselves with a VOLTAGE into a specific impedance)

What is specified is speaker "sensitivity" and, for completeness? SPL = 10Log w+s where "w" is the (apparent!) power input and "S" is the claimed maker's sensitivity. The equation is pretty approximate and only works over a limited bandwidth and power input as thermal compression sets in at about 1/2 rated power. Then, some mnfctrs are, shall we say, "optimistic" about sensitivity figures and power ratings!

Sensitivity (mid band anyway) is dependant on gap flux density, voice coil format and cone mass (a given force causes greater acceleration for a lower mass, Mr N!)

Dave.

Sassafras

If your Deluxe breaks up at 4 on the dial I think it's more than a speaker issue.
Mine used to start getting gritty at about 7 or 8.

ICBM

That depends on how loud the guitar is.

Voxman

ICBM said:

That depends on how loud the guitar is.

And how hard you strum!

Sassafras

True. I only use low output single coils.