From Wikipedia: "The acoustic-suspension woofer uses the elastic cushion of air within a sealed enclosure to provide the restoring force for the woofer diaphragm. The cushion of air acts like a spring or rubber band. Because the air in the cabinet serves to control the woofer's excursion, the physical stiffness of the driver can be reduced. Unlike the stiff physical suspension built into the driver of conventional speakers, the trapped air inside the sealed-loudspeaker enclosure provides a more linear restoring force for the woofer's diaphragm, enabling it to oscillate a greater distance (excursion) in a linear fashion. This is a requirement for clean and loud reproduction of deep bass by drivers with relatively small cones.... Acoustic suspension woofers were once very popular in hi-fi systems due to their low distortion. Compared to bass reflex cabinets, acoustic suspension has a flatter frequency response and slower rolloff below their resonant frequency. Bass reflex cabinets are generally more efficient, however, and the use of a vent or port in the cabinet provides improved low-frequency response."
I don't guess there are too many fans of acoustic suspension speakers anymore, but I still have and love my Boston Acoustics T-830s from the 1990s. They claim 90 db efficiency; but they take more amp power to drive than my big 90 db bass reflex Cantons with 2 more woofers.
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Everyone is sort of missing the real cause & effect..... It's not impossible to make drivers and speaker systems that are 97dB efficiency, but they will have far from flat frequency response or tight transient response. (though they can still sound musical). Very light drivers with large magnets, and/or horn loading will have peaks & valleys in their frequency response due to undamped resonances. In a magical world, you would raise those dips UP to meet the peaks, and have a high sensitivity speaker with a smooth response. But that's not reality. All we humans can do is damp those peaks down by adding mass, stiffness, damping, whatever, etc. By the time you are done tapping down all those nasty peaks, you are down to 90, 88, maybe 86 dB.... all depending on about a million variables and design choices. Then you put it out into the world, and see if people like what you did. Nobody sets out to make a low sensitivity speaker as a goal.
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Low efgicience speakers can make your amp woek put to stay strong. Actually, most such speakers gave power sucking, elaborate crossovers to get a flat frequency response. Newer designs use better parts and of course designs. |
Thanks everyone! These are really good explanations. |
Like most things it is a trade off. Lower sensitivity speakers are generally more linear, have greater bandwidth and are generally more accurate (less distortion). It is easy to make a high power amplifier that is extremely accurate (just expensive) it is also easy to make a giant speaker box to get great accurate low end efficiency (again only expensive to build and ship). It is extremely hard to make a light weight diaphragm or cone with a small drive motor and drive it with next to no power and still get anything approaching high fidelity. Just think about it - all of the friction, resonances and other issues of the mechanical cone are relatively much larger compared to the relatively weak but highly accurate drive electrical signal in a high efficiency design.
High end Studios (million $ facilities) have gone gone away from horns for this reason - lower efficiency speakers tend be more accurate and horns tend to have a shouty character due to directivity and non-linear air compression at higher SPL. |
This is meant not as a right or wrong thing but more of an observation
as a recipe for success or consistancy.
It
is not that speaker designers deliberately design low sensitivity
loudspeakers but in order to seem natural or flat all drivers need to be padded to
the one driver that is lowest as mentioned above.
With cost effective
means to look at breakup behavior of cones and domes available today one
reason some designers end up with lower sensitivity is that speakers
end up that way when using drivers that are breakup free in their
passbands or range of operation.
In most loudspeakers especially high sensitivity ones some
of the apparent sensitivity is output from the random ringing of the
cones.
This definitely will smear the music fed to the speaker.
Low wattage single ended tube amps definitely have a sonic signature
and if that is preferred one has no choice.
But for most of us higher
power good sounding amplifiers are available for reasonable money.
Best
JohnnyR
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I forgot, unsound is right. :)
Very high sensitivity speakers (100dB+) often need very quiet amps to prevent the idle amp noise from becoming noticeable.
However I don't know if a single speaker designer who says "Oh, I'm going to hear too much noise, better lower the sensitivity...." :) That's not usually a concern.
Best,
E
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A lower sensitivity speaker will block more noise contamination than a higher sensitivity speaker.
Often times a speaker designer will sacrifice some sensitivity for other considerations.
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how much live unamplified music is in your listening diet ?
and then with a good mic or two before the tape heads or after ?
try that a bit
but yes we all have our opinions
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Mmm, duplication of 'live' is such a 'moving target'. Since one is listening to a recording of a live performance (for example) that's gone through myriad equipment and processes in the interval. It seems to me (IMHO time) that the only way one could really make the comparison properly is to have been at that performance. And even then there's the contrast of where one was sitting, one's state of mind, and the influence of memory.
*Sigh* We're left with attempting to recreate as best as one can our opinion of what it sounded like, or should sound like...in an entirely different space.
Studio work boils down to the artist(s) working with the engineer(s) to make the work sound like what's in the artist(s) mind. There's a certain simplicity in that...
We can either approach that reproduction with either 'bare bones' or a more complex combination of items.
Either way, it comes down to what sounds good to you. And the guy next to you will think it sounds like dreck and you're brain damaged or have a hearing malfunction.
*L* And we're right back to 'what sounds good/right to you, and the enjoyment of that. And 'twas always thus, and will always will be.
MHO and yours....;) May not or never be the same, but many things are like that... |
i think ( and I know the origin of the J Cash comment - seeking to FIRST replicate a live unamplified reference one is VERY familiar with) there are two camps here:
1.) build a full range speaker that comes as close to the reference as possible with manageable efficiency as an outcome.
or
2.) add efficiency target value into the important parameters list. For all kinds of reasons: small amps tend to be affordable, some customers like hearing damage, the 300 B ...First Watt....fill in the blank)
what i find more interesting is all the in and out of phase junk that gets counted as output.....
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I wish I got 18wpc out of my SET 300b. Gosh. 8wch lol
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For a lower wattage tube amp you want both more efficient and easy load speakers for best results. For comparable bass extension those would need to be larger and probably more expensive as a result.
Very fundamental for top notch results to match speakers to amps capable of driving them well and to the max. |
Ok extended bass. I knew these dali ms4's were suppose to sound best away from the wall and now I know why. My only concern would be if I wanted to pair with a lower wattage tube amp in the future. With that said, Johnny Cash sounds unbelievable on these speakers. The extension shows up in a big natural way. |
@audioconnection I make loudspeakers.
I don't think it's an unfair question to ask why some speakers tend to have low efficiency, or how equipment may make some trade offs.
I also don't think efficiency is necessarily a quality standard. You should use your own tastes for that.
Best,
E
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A lot of meter readers types trying to figure it out end up chasing their tail
If your concerned with fidelity why not ask your self
Which speaker makes Johnny Cash sound most like
Johnny Cash.?
Best
JohnnyR
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Hi Puff, It’s not really desirable, but a speaker designer may end up getting there in order to get enough bass. It’s a little complicated to explain in text, but we can often sacrifice sensitivity for the sake of bass extension. Another way to look at it is not sacrificing but balancing one vs. the other. This is how Magico’s S1 Mk II behaves, with an 83 dB sensitivity they manage to push out around 50-60 Hz as a lower cut-off. http://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=1564:nrc-measu...While I am not a particular fan of this speaker’s tonal balance, and overall cost of ownership, the overall idea is sound, meaning it’s not a cheat so much as run of the mill speaker design choice. In my own 2-way speaker with a 6.5" driver I have to sacrifice 6 dB of sensitivity in order to get flat down to the 30-40Hz range, but I end up a little better, around 87 dB sensitivity overall. This is quite typical for speakers designed to be away from room boundaries. I could have sacrificed even more to get more of a bass rise/bump in the lower end, but for my listening I chose not to. Best, E |
In general the main reason to design a less efficient speaker is to enable more extended bass out of a smaller speaker. This has been the popular trend for the most part ever since higher power SS amps started to make their mark. |
There is none only if you like 300b 18watt amps its all personal taste and a well matched system. |
I would be surprised to learn that designer would, keeping all things equal, purposefully forgo efficiency to arrive at an 87 db or lower sensitivity. In other words, designing a speaker that has 90 db efficiency and then padding it down strikes me as bizarre.
This reminds me.....there are lots of anecdotes of 70s/80s era IBM mainframe customers seeking more processing speed, and IBM sending techs out to *remove* a board from the system. Still makes me laugh.
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