I have heard the term "effeciency" used several times when refering to speakers. Most specifically on the website, the "about" section of the 7100 states "Smaller rooms, efficient speakers and problematic neighbors (or spouses) sometimes dictate the need for smaller amps. The Model 7100 is the ultimate elegant solution."

If I'm not mistaken the efficiency of a speaker is sometimes also refered to as the sensitivity and is measured in dB. But that's about all I know. I was hoping someone could help me to understand this a bit more. As some of you know (from my post on the 950 board) I am still in search of some nice in-walls/bookshelfs for the new HT in the house. What (if any) specific efficiency/sensitivity dB level(?) should I be looking for. I will be using the 950/7100 to power the speakers. Thanks in advance for the help.

Mike

Efficiency and sensitivity are the same thing.

Almost all typical HT speakers fall into a relatively narrow range of sensitivities, usually around 90db/watt. This is not a specification that you need to be concerned with when shopping for speakers, as it has no real impact on a typical system.

There are unusual circumstances of very high efficiency speakers like mine which are 106db/watt, but these are large horn speakers that are not at all typical. Also, there are very low efficiency speakers, but these tend to be either older deisngs from around the 1980s, or exotic types that cost a lot.

I would simply listen for speakers that sound the best to you, and not worry about this specification, since nearly all current HT speakers fall into a ballpark range that is compatible with most current amplifiers for HT use.

You are correct about the efficiency/sensitivity values being measured in dB. The way I think about it is that you provide a measured signal to any speaker, the efficiency is the sound power level produced from that signal.

My main speakers are Paradigm Reference Studio/60's, which have a sensitivity rated at 90dB room and 87dB anechoic (the center and surrounds have the same sensitivity). I originally drove them using the Outlaw Model 1050's built-in 65W/channel amps, although I did benefit some from upgrading to the Model 750 (165W/channel). With the 7100, I would think anything with a sensitivity at or above 87dB or so could be driven pretty comfortably, but that's just sort of a guess on my part. Others may have some better ideas for you.

EDIT: Like I said, better ideas. I think soundhound sums it up well when he says that you shouldn't have any trouble with most speakers on the market today.

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gonk -- Saloon Links | Pre/Pro Comparison Chart | 950 Review

[This message has been edited by gonk (edited November 04, 2003).]

Basically the rule of thumb I picked up states for every 3db increase in volume (for set room size/speaker sensitivity) you will require double the power. For a 10db increase you need 10 times the power.
This is why speaker sensitivity mated to power can be so much of an issue under certain circumstances, but: as SH and Gonk point out with modern amps and modern S range, you don’t often need to be concerned. The setup your looking for wall/bookshelf will often be in the 86 something and up speaker sensitivity range. With the 950/7100 unless you’re filling a concert hall, you should not have any issues.

If I have all the following down vaguely, since you asked the why behind it. Here goes my messy version.
Speaker sensitivity is measured by sending 1 W power into a speaker and subsequently measuring its output or SPL from 1 meter (about 3 ft)

Therefore if you have a speaker rated at 85-dB sensitivity. It takes one watt to reach that level at 1 meter.
Do you want to hear 88 dB at 1 meter then you need 2 watts (per 3-dB increase desired start doubling power)? For 95 dB at 1 meter you need a little over 13 watts.

Start with a 91 dB sensitivity on a speaker and that number becomes 1 watt = 91. 94 dB at 1 meter = 2 watts.

So for the first speaker to listen at 1 meter at 95db (very loud) you need a little over 13 watts.
For the second speaker with higher sensitivity rating of 91db you only need a little over 2 watts for 95 dB listening levels.

You see amps rated at 60w/ 100w/ 200w etc. Seems like overkill. But factor with the above speaker sensitivity your room size, (you don’t really listen at 3 feet to all your music). And then factor dynamic range of the recordings your listening to.

If it takes 3 watts to run your 91-dB speakers in your particular space at your preferred listening levels, with the average dynamic range SPL of the recording you’re listening to averaging 80db; then you have a short burst or transient of a +20 dB increase (this would be huge) in dynamic range in the recording. Your amp suddenly needs (if I have this right) approx. 300 watts.

I know I’m off in applying the 3db-increase math to dynamic range of the recording. But this should give you idea of the factors involved. Speaker sensitivity, Room size, your preferred listening SPL, dynamic range of recording.

Basically 30 watts runs a lot - at average speaker sensitivity, average listening levels. But short bursts or transients of recordings is one reason why you hear the term (I believe) headroom.

If you get farther than me down the learning curve, you can factor how that amp (design, power supply) provides the power. My prior experience has been the Outlaw range of amps breeze through what is demanded.

great teachers around here, they will slap me silly and get all above corrected - if I'm too far off in my description

[This message has been edited by Smart Little Lena (edited November 04, 2003).]

Um... okay... hmmm... I uh, think I understand... sort of.

The main reason I ask is that the speakers I am looking at are either 86dB or 89dB depending on which line I decide on. The speaker that has an efficiency of 86dB has an impedence of 6 ohms, while the one with 89dB has an impedence of 8 ohms. Now let me say this... I don't want to give the impression that I have even the slightest idea of what I just said... 'cause I don't. But if I purchase the 86dB speakers for the fronts which are 6 ohms and the rest of the speakers are 8 ohms, would I run into a problem there?

I just wasn't sure if there would be an issue running either "efficiency" or "ohm" rating with the 950/7100 combo.

Thanks again gang!

Mike

Edit: spelling



[This message has been edited by Arizona Mike (edited November 04, 2003).]

There should not be a problem mixing 6ohm and 8ohm speakers with the 7100, either from a performance standpoint or from a power standpoint.

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gonk -- Saloon Links | Pre/Pro Comparison Chart | 950 Review

If you'll note in the 7100 specs, as the impedence of the load drops from eight ohms toward four, the power delivered increases. (See Ohm's law and variants elsewhere.) For various real world amplifier reasons you would find that an impedence vs. power graph would not be strictly linear, but the principle still applies. As a result your less efficient speakers will be recieving more power, all settings being equal. If you were in a perfectly ideal environment with all speakers equidistant from your position, I imagine that a +/- one db tweak here or there would bring all levels to the same point. You are likely to find that the variables of your listening environment will have as great or greater impact on balancing levels at your listening position(s) than the impedence/sensitivity issue.

So do I understand that to mean that if used the speaker setup below, then the fronts would actually be using more power and pushing more watts than the rest of the system?

Front L/R: 100W (200W peak) @ 6 ohms (86dB sensitivity)
Center: 100W (handling) 15W-150W (operating) @ 8 ohms (89dB sensitivity)
Surrounds: 60W (100W peak) @ 8 ohms (89dB sensitivity)

Mike

PS. Does the 7100 allow me to adjust this balacing of level like Buck suggested?

[This message has been edited by Arizona Mike (edited November 04, 2003).]

6 ohms will draw more power than 8 ohms, but impedance ratings are at best a general guide. The actual impdeance of a speaker varies drastically across the speakers operating range. The impedance specification can only be used as a very rough guide to how much power a speaker will draw. The impedance rating is more useful as a guide to matching the load of the speaker to the amplifier - some amplifiers are not happy with 4 ohm speakers for example.

I wouldn't worry about this aspect, as you can go crazy with all the variables and different ways of presenting specifications. The important thing is that most HT speakers and amplifiers are compatable with each other - manufacturers have seen to that.

There are individual channel trim levels in the 950 before the signal goes to the 7100. The 7100 does not have user level adjustment in each channel.

I agree with SH, regarding the impedance/power/sensitivity issue.

If some part of your brain just "needs to know," then yes, for an identical signal, if speaker A exhibits an actual impedance to that exact signal that is slightly less than speaker B's impedance to that exact signal, then the amp will deliver slightly more power to speaker A than it does to speaker B. This is no problem for the 7100 or for you.

My earlier point was that: one, you are well within normal operating standards; two, you will be making adjustments to the level of each channel to take care of a variety of factors in sound reproduction and listening environment. Any overall signal level inequities that are introduced by impedance/sensitivity issues will be averaged in with the other factors as you adjust. Impedance/sensitivity issues of this type are some of the "small stuff" for which the words, "don't sweat" apply.

Some people use identical speakers all around, but that is more for differences in factors that have a much greater effect than impedence/sensitivity. If you're happy about the way the speakers sound together ...

Relax. Enjoy.

most people tend to stick with the same impedance for all of their speakers, as it puts less strain on the amp. the 7100 is a particular amp that does not struggle with different impedances from the speakers. however if the speakers have different impedances they are probably different brands; mixing brands of speakers is not usually advised either as echoing can occur due to the nature of different tweeters being in the speakers. so if you are going to mix brands be sure to listen and make sure that they sound good together. the sub, being low frequency, can be a different brand w/o any side effects. as far as efficiency/sensitivity, higher dbs are more efficient and therefore require less power to produce the same spl. that is taking into account that they are both rated exactly the same, and if they are different brands they most probably are not. with a pre/pro that has channel gains, etc. its not a big issue because you can get equal sound out of your speakers by making adjustments to the gains. youre not going to find the answers to all your audio questions in a forum though. sound needs to be heard. hopefully this reaffirmed/cleared up the previous posts and you understand a little more. im sure soundhound will disagree with me as he is prone to do. :-)

it looks like youre going to be listening to mostly music??? the power handling is pretty low for your rears, and would not be the best for the 7100 which is 100w channel, it seems like. center and sub are most important for ht, fronts (sub could be) are most important for music so keep that in mind with buying. from what you have been posting it seems like you havent gone into any stores to demo products, you may want to try that, albeit a place with competent salesmen. take in a couple of demo cds so you can see what you like about particular products.

I have Klipsch Speakers and they are very efficient. Those speakers also sound great.

In general, efficiency is defined as desired output divided by required input. In the case of speakers, the desird output is acoustic power (sound) and the required input is electrical power (from the amplifier). So speaker efficiency is defined as acoustic power out of the speaker divided by the electrical power into the speaker.

A typical speaker has an efficiency of about 1%. So for 100 watts of electrical power into the speaker, it is putting out 1 acoustic watt. 1 acoustic watt does not sound like much, but in a typical home environment, is is quite loud.

As I said, the speaker puts out acoustic power. Speaker specifictions usually give specs on sensitivity, efficiency, or whatever term they use, as XY dB with 1 watt of input power (electrical) at, typically, 1 meter (and, technically, an acoustic environment should be specified, such as an anechoic chamber, "typical" living room, or whatever, but often the environment is not specified).

One needs to know the acoustic environment in order to translate from acoustic power (watts) to sound intensity level (dB).

My electrostatic speakers are probably on the order of 1/2% efficeint. Large horn type speakers can be vastly more efficent. I have read that large Klipsch corner horns are about 40% efficent. The horn acts sort of like an mechanical-acoustic transformer, matching the mechanical impedance of the moving driver cone, dome or whatever to the mechanical impedance presented by the air the speaker is trying to move (vibrate).

Paul


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the 1derful1