What makes a speaker efficiency

In order to retain the same sound pressure level SPL, meaured in dB's , though, this requires both a very large amplifier and a driver that can handle a lot of power and move a lot of air requiring high excursions. Furthermore, it must be able to do so with minimal distortion. This is exacerbated by power compression, a phenomenon where the power heating of the driver's voice coil results in a non-linear relationship read "distortion" between the electrical power in and the acoustical power out.

You can provide the perception of violating Hoffman's Iron Law by using a bandpass design, which can provide a lot of bass primarily across a very limited bandwidth. In all too many bandpass designs, the impressive bass is produced around a single frequency.

This is often referred to as "one-note bass". It can rattle the furniture and impress your friends, and may even be OK for sound effects in action movies, but don't expect too much accuracy when listening to music with a lot of low bass content. All other bass under about hz is extremely variable. A few Zu fans have tried to discredit these independent measurements, but I don't buy that for a second.

They were performed at the National Research Council of Canada, a serious government lab, in a proper standardized anechoic chamber. And they actually show precisely what any designer would predict from a similar vented design. To increase any of the three, you HAVE to give up something from the other two, with box size being the most sensitive. You put the tone on, and read the dB meter, or your ears, and think, "my but that's loud and efficient". Then you check it out with a real time analyzer, and notice that the 40HZ tone is actually the same, or sometimes many dB down from the 80 and HZ harmonic that the speaker is creating, rather than reproducing, making for the high spl level.

If a speaker happens to produce even order harmonics distortion it will still tend to sound musical, even though it is grossly innacurate. The Zu's may hit db at certain freq. The fact that various "glowing" reviewers don't trust basic design theory enough to at least intelligently question the claims - or are ready to believe it's all been changed by back venting through a motorcycle muffler because an enthusiastic 30 year old tells them so - is well, typical.

Clearly, it's been a slow day at work. Eldartford- Is that because of the much larger radiating area? Not that that would necessarily change their appetite for lots of current, but amp matching might be a little easier than some of us have suppossed.

An exception to this would be highly directional Low bandwidth horns These must be well over dB. Swampwalker - thanks for your kind words! Regarding line source loudspeakers, maybe I can offer a few thoughts. From a point source, radiation intensity falls off at 6 dB for every doubling of distance, and from a line source radiation intensity falls off by 3 dB for every doubling of distance.

With a point source the radiation is expanding in all three dimensions, but with a true line source which would extend infinitely in one dimension the radiation is only expanding in two dimensions - hence the more gradual falloff with distance. In practice how well a speaker approximates a true line source depends on the height of the radiating line or line array, the height of the room, the wavelength being reproduced, and the distance from the line-source-approximating speaker to the listener.

As a general rule of thumb, line source characteristics will hold up quite well out to about four times the height of the line-source-approximating radiating element s , then begin transitioning to point-source characteristics. There is yet another type of source - a planar source. With a true planar source infinite extension in two dimensions , there is NO falloff in SPL with distance! Up close to a large elecctrostatic panel, planar source characteristics dominate - but we're talking distances of only a few feet at the most.

Getting back to line sources, I once measured a point source speaker and a line source speaker at 1 meter and again back at 8 meters practical limit in my room. Anechoic theory predicts the point source speaker's radiation would fall off by 18 dB over that distance, and it fell off by 11 dB. That extra 7 dB came from the reverberant sound field. Anechoic theory predicts that the line source speaker's radiation would fall off by 9 dB over that distance, and it fell off by 4 dB, with the reverberant field contribution making up the difference.

As you can see in a real-world room the line source speaker's radiation fell off by 7 dB less over that distance 1 meter to 8 meters than the point source speaker's did. That's a significant difference. But in this case the point source speaker was still more efficient than the line source speaker even measured back at 8 meters. Opalchip - very good explanation of Hoffman's Iron Law.

Having scratched my head about the Druids quite a bit, I think that they are exploiting undamped pipe resonance to extend the bass deeper than it would normally go, but the tradeoff is the deep hz notch revealed in the SoundStage measurements indicative of a roughly 90 inch long pipe.

Having built undamped pipe speakers myself I'll say that they measure worse than they sound - the ear is surprisingly forgiving of that deep notch.

Let's look a little bit more closely at the Zu specs though, and give 'em the benefit of the doubt just for kicks.

The Druid is a 12 ohm speaker, so what if when they claimed dB "sensitivity" implying 2. If so, then translating that to 2. That's pretty close, especially if we let Zu use an "in-room" rather than "anechoic" or "simulated anechoic" measurement.

Next let's look at the claimed bass extension. Zu claims a "bandwidth" of 38 Hz to 25 kHz. We're used to thinking of the bandwidth as the -3 dB points or maybe -6 dB points, but that might be a mistake on our part. In prosound use, the dB point are often given as the limits of a speaker's bandwidth. Now let's go back and look at the SoundStage measurements. See that little response bump at 38 Hz?

Relative to the 97 dB sensitivity determined by SoundStage in a free-air measurement, that 38 Hz bump is 19 dB down. With the reinforcement of three room boundaries, we'd add 9 dB and then we'd be only 10 dB down.

And dB fits the prosound definition of bandwidth. I don't know if this is how Zu arrived at their specifications, but it might be. I welcome correction from anyone who knows the real story. One final comment on the perceived loudness of the Druid's bass. If indeed the Druid's enclosure is an undamped or minimally damped resonant pipe, then it will sound louder in the bass than it measures.

This has to do with human hearing - if two fairly short-duration sounds are exactly the same frequency and sound pressure level, but one lasts longer than the other, the longer-lasting sound will be perceived as louder. So if we have relatively slowly-decaying bass resonances in the Druid's enclosure, the bass will sound louder than it measures.

As to why the Druids don't sound resonant and boomy, I think it's because the shape of the frequency response curve keeps us from perceiving it that way. If so, then the Druid's bass loading system based on a patented automotive muffler design would not work well with a speaker that measures "flatter" in the bass region.

The height-off-the-floor tuning, which apparently is critical to getting the bass to sound right, mght be adjusting the decay of the muffler-like pipe resonances. The specifications you see may say the loudspeaker sensitivity was measured using 2. If you are going to compare two different speakers, they need to be measured into the same impedance.

Otherwise, they cannot be compared. Some manufacturers will use a lower impedance to make it appear their speakers are more efficient. The whole point of having a good amplifier and speaker system is so we can hear the best sound possible and make the best use of the technology. Although all speakers will waste most of the power they receive — so this is a relative thing. More efficient speakers will sound louder as they are able to use more of the power they receive to create sound.

As I have already said, a less efficient speaker will create less noise. So the lower the dB level — the lower the sensitivity. Therefore, 84 dB speakers are less efficient and require more power to get the same volume as more efficient 95 dB speakers. Changing your speakers from 87 dB efficiency to 90 dB will result in an increase in volume that is the equivalent of doubling the power from your amplifier.

More efficient speakers will generally be more expensive to buy than less efficient ones. So, your decision may come down to what you can afford to buy.

Also, bear in mind that the size of speakers will affect the sensitivity. Log in or Sign up. What makes a speaker efficient or inefficient? Messages: 10, Location: Southern Colo. I am just tooling around with a first DIY project. Its an older 60's drivers but wanted to use a 80's AR crossover. I know most AR's are known as inefficient so how will it work with these older supposedly efficient drivers?

Is it the driver or the crossover that makes a speaker inefficient? Messages: 15, Location: Seattle, WA. It has a bit of both.

There are other major factors though, such as cabinet size. Byrd , Nov 7, Messages: 8, Location: Gainesville, FL. Type of enclosure has some effect as well. Sealed designs are usually less efficient and require more power since the drivers especially the woofers must alternately work against negative and then positive pressure inside the cabinet as they move out and in. Tedrick , Nov 7, Ampire , Nov 7, Messages: 3, Location: RIP How the drivers are constructed also has a big effect.

A woofer with thick, heavy paper and a small motor will be much less efficient than the same woofer with either a larger motor or lighter paper. Some drivers are intentionally damped to suppress harmonic resonances due to the material used, or change the tuning of the driver. Bextrene drivers were commonly damped with thick paint.