Speaker sensitivity question

robert bartsch · 05-15-2008, 02:43 PM

Long ago, I had a pair of Altec voice of the theater speakers with 15 inch drivers and cast horns. Their sensativity rating was 98DB with 1 watt at 3 feet. A smallish amp of 80 watts or so was sufficent to raise the roof.

Anyway, I have since bought a set of Klipcsh home speakers which I enjoy. They take up less space and still produce clean sound with the modern multi-channel receivers of today. These are rated at 92DB.

Although I never compared the two speakers side-by-side, my recollection is that it the Altecs produce a much higher sound level than the Klipsch's - given the same input power.

So my question is this; there must be a very noticable difference in speaker effeciency rating 92 Vs. 98; right? Why don't they build home speakers with higher sensitivity ratings?

On a hunch, I recently looked at some JBL professional series drivers and many are rated at over 110 DB. Wow, these must crank at low to moderate power levels.

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JohnRice · 05-15-2008, 02:58 PM

Because speakers are complex electronic/mechanical systems and sensitivity isn't the only important factor for them.

robert bartsch · 05-15-2008, 03:40 PM

Hey John:
Is it fair to say that speaker sensitivity ratings are a measure, in part, of the strenght of the electro-magnetic field within the voice coil gap?

Isn't this rating indicative of the mechanical efficency of the driver?

Some of the professional series speakers have some monster magnets, super high sensitivity ratings (+100 DB), and can make high sound pressure levels with moderate power. Therefore, isn't a high sensitivity rating beneficial; if not, why are these ratings provided?

JohnRice · 05-15-2008, 11:58 PM

There is certainly a benefit to high sensitivity, but it also has nothing to do with the quality of sound the speaker produces. If your only priority is playing high volume with little power, then sensitivity is all that matters. Most people are also concerned with the sound quality of a speaker.

Robert_J · 05-16-2008, 09:22 AM

Quote:

Originally Posted by robert bartsch

Is it fair to say that speaker sensitivity ratings are a measure, in part, of the strenght of the electro-magnetic field within the voice coil gap?

Isn't this rating indicative of the mechanical efficency of the driver?

The measure of strength you are describing is called BL. Eminence has a very good definition.

Quote:

Originally Posted by robert bartsch

Some of the professional series speakers have some monster magnets, super high sensitivity ratings (+100 DB), and can make high sound pressure levels with moderate power. Therefore, isn't a high sensitivity rating beneficial; if not, why are these ratings provided?

Magnet size is not an indication of high BL though. You have to know the size of the magnetic gap, the strength of the magnets, the type of steel used in the motor and the size, windings, layers of wire in the voice coil. All of that combines to determine the BL. Normal cermic magnets are cheap and pretty powerful. Neodymium magnets are MUCH stronger size for size when compared to ceramic magnets. I have a 45 pound sub motor with ceramic magnets and a 20 pound sub motor with neo magnets and they are basically the same.

Moving mass of the cone or dome (mms specification) is a better indication of sensitivity. Also, the frequency range that the driver is designed to play over is a huge factor. A driver can't play a 20hz tone at 100db with 1 watt of power. The current technology isn't there.

Hoffman's Iron Law is also in effect here. It basically says that you trade sensitivity for lower frequency response. Like all of speaker design, everything is a tradeoff when you are trying to reach your goals.

-Robert

robert bartsch · 05-18-2008, 12:05 PM

Well I got a new receiver w/ 130 watts per channel and cranked it up with the 92Db Klipsch towers (4) and center.

The sound level was no where near that of the old Altecs. I always thought the Altecs did an excellent job of reproducing low passages, music, voices, etc.

JohnRice · 05-18-2008, 01:05 PM

I'll be blunt. It is clear your priority is sensitivity and maximum output, so, I suggest getting a set of PA speakers. They are outrageously sensitive (typically well over 100dB) and have almost limitless maximum output. Look at partsexpress.com for numerous options. Your old Altecs were really just borderline PA speakers in less industrial cabinets. You'll be in hog heaven.

robert bartsch · 05-18-2008, 03:52 PM

I suppose speakers are a subjective thing.

It is a fair statement that the Klipsch floors are quality untis but IMO they can't produce the quality sound that a professional cinema speakers.

I'm considering these, which seem like a steel:

JBL Professional 3677 at Performance Audio

JohnRice · 05-18-2008, 06:50 PM

Robert, "quality" is a subjective thing. The more common spelling for your use of the word would be "L-O-U-D", which is not the same as what most people would consider to be the defining characteristic of "Q-U-A-L-I-T-Y".

For your priorities, I would say the JBLs you linked would do the trick, though I expect you can find even more sensitive models.

robert bartsch · 05-19-2008, 01:37 PM

I'm not a fan of loud music.

I think if you listened to some professional studio monitors with compression drivers in a home setting you would agree that home speakers do not compare.

I can say this because I owned the studios for about 30 years! My comparision is based my current system with 4 Klipsch floor tower monitors and a Klipsch center and powered sub through Denon and Onkyo receivers with 105 and 130 watts @ each with THD of .05%, respectively.

I'm assuming some of this relates to the fact that Klipsch's require a moderate amount of power to produce normal listening levels whereas the studios require very little. The other beef I have is the need for a sub in my current system which is not necessary for accuarate reproduction with the studios. The sub is an interesting concept but my complaint is that the lower frequency sound is localized to a single spot in the room.

Oh well, since my Denon has now returned from the repair shop once more, I'm planning to buy a pair of these:

http://www.performanceaudio.com/medi...100/1254_s.pdf

At <$600 a pair, they seem like a bargin compared to the Klipsch towers which are more expensive.

Rich Allen · 05-19-2008, 02:22 PM

A properly setup sub isn't localized to a single spot as many here can tell you.

chuckg · 05-19-2008, 02:43 PM

Howdy!

jsut dropping my twenty millidollars here.

Speakers are less efficient these days because it is easy and cheap to build powerful amplifiers. Back in the 60s no audiophile would be caught dead with icky transistors. Tube amps of limited power were the rage, and speakers had to be big to make the sound loud enough to drown out the neighbors tea party. There are still such audiophiles around today, though tubes are a tad harder to come by.

Ten decibels of loudness difference should be twice as loud (or quiet), and therefore a speaker that is ten dB more efficient ought to produce about twice the loudness at the same amplifier output power.

As others have said, efficiency is just one measure. Having a flat response, and maintaining quality over a wide power range are more important than sheer efficiency.

I would tend to disagree, though, with the poster who compared the Altec VOTT speakers to borderline PA. In my experience, PA speakers are harsh nasty things intended only to make the human voice loud enough to cut through the general hubbub. VOTT is way nicer than that...