Speaker theory: What makes one speaker more efficent than another?

[ihateyouguys]

I'm curious to learn about the hows and whys behind speaker function, so here are some questions for the experts:

 

First question: What will make one speaker more efficient than another speaker of the same size? Is it materials or design or something else?

 

And I guess a related question would be the same thing for speaker sensitivity.

 

Any insight would be appreciated.

[soul-x]

Think of it like any other piston motor assembly. If you're a car guy, this should come easy. Reducing piston stroke will increase revs at the expense of low RPM torque (LF extension in the case of a speaker). Lighter materials may be used, reducing inertial forces, but may result in peaks in power delivery and decreased reliability. Compression ratio (motor strength) may also be played with at the expense of linearity, weight, and reliability.

 

There's a lot that goes into the process, and efficiency is just one design goal. Hopefully someone who is active in transducer design can round out the specifics.

[agedhorse]

Some things that improve speaker efficiency:

 

Magentic strength

Magnetic field shape

Number of turns inside the magnetic gap at any one time

Gap width, clearance

Weight of the moving mass

 

All of these have corresponding tradeoffs, and just making something more efficient may not make it better for a specific application. A less efficient speaker may produce more low frequency though, if it allows for better tuning of the speaker box. It's all about managing tradeoffs and how you choose to measure efficiency. As soon as you define the desired power bandwidth, the problem becomes much easier to define though.

[Ear Abuser]

If you start to think about how these factors interact you can see how there is no free lunch.

For example to make a speaker more efficient you can reduce the moving mass. But this raises the resonant frequency, so low frequency response falls off. Or you can put more turns on the voice coil- but this makes the moving mass increase, which may offset any increase in efficiency. Or you want to increase power handling for more maximum output, so you put in a bigger voice coil, but now it's heavier and the efficiency drops and maximum output may not have increased at all.

[agedhorse]

Exactly. At some point, you reach diminishing returns. This is why it's pretty easy to spot specs that are not "reasonable" and raise the BS flag.

[boseengineer]

Three things make a speaker more efficient:

a) money

b) smart transducer design

c) good system engineering.

 

As Andy has pointed out, there are many design parameters for the transducer. Besides the motor (magnet, gap structure, voice coil, back plate, front plate, tinsel, etc.) there is also cone design & materials, spider design, surround, dust cap, etc.

 

There isn't really a one-size-fits-all approach anyway, because the transducer has to play nice with the acoustic package (sealed box, ported box, wave guide, etc.).

 

For this reason we pretty much do a custom driver for every new product and have hundreds of drivers currently in production.

 

You get the best efficiency through good overall system design.

 

The best way to get high on-axis sensitivity, is to make the speaker really beamy. This way all the acoustic energy is concentrated in a reltaively small area where the SPL is realtively high. That renders the speaker pretty much unusable for many applications but makes for a great spec sheet.

[agedhorse]

I can't emphesize more that it's really a system design approach that yields the most USEABLE acoustic output.

[dboomer]

most USEABLE acoustic output.

 

Not just the most output. And that's not usually in the specs

[agedhorse]

most USEABLE acoustic output. Not just the most output. And that's not usually in the specs

 

Exactly!

[stunningbabe]

This means there is no 'perfect speaker' in the world. It does not exist. All speakers are really trade offs for one thing or another. You cant have everything. Yes?

 

Is there a speaker you'd say is the best balance for efficiency, power handling, sound quality, throw and etc?

[agedhorse]

Depends on which parameter is most important for your application. I do a venuw where the throw is 250 feet to one end (about 1000 people sit there) and there's no way to fly any fills to cover it so obviously long throw directionality is very important to me... fot THAT venue.

[boseengineer]

 

This means there is no 'perfect speaker' in the world. It does not exist. All speakers are really trade offs for one thing or another. You cant have everything. Yes? Is there a speaker you'd say is the best balance for efficiency, power handling, sound quality, throw and etc?

 

 

As Andy said, there is no one size fits all.

This is like asking "What is the best car?". It all depends on what you are planning to do with it.