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.

------------------
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.

------------------
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.