Low-sensitivity speakers — What's special about them?

When designing a driver, its a choice you make: efficiency or bandwidth.  This choice doesn't change if the driver will be used in a horn or infinite baffle,   

    

Johnk:

"Low-sensitivity some design for such have complex networks or need a small size. But in general, it means cheap low-powered magnets undersized transducers, and cabinets. It means the loudspeaker and owner of such has to purchase a massive power amplifier thus putting that speaker's cost savings back on the owner since now his amp costs more is larger and uses more energy. It also means thermal compression in most designs since amps heating VC."

I have to address this very confusing post. 

Low sensitivity has little to do with the complexity of the crossover.  A horn loaded design could use a simple 6dB per octave crossover and be very efficient; a sealed box design could be lower sensitivity and also have a 6dB/octave simple crossover, or a more complex 3rd of 4th order design for steeper slopes.
   
Low sensitivity is not a by product of reducing cost.  A manufacturer could decide to build a cheap system with low or high sensitivity.  A high quality company, like the one I work for (ATC), chooses lower sensitivity to improve bass response in a smaller speaker.   Most high end companies with lower sensitivity speaker systems do it for the same "better performance" reason.  Sensitivity is simply a measure of how efficient the complete system is, which is dictated by a whole series of choices like drivers, box, porting, etc.

Implying low sensitivity is a purely low cost choice/cheap system option is a not correct.  Lower sensitivity speakers do not have overly complex networks by nature, or require massive power amplifiers.  A 86/87dB 1w/1m speaker referred to often as "low sensitivity" is only 3dB away from a 90dB 1w/1m - referred to as a "high sensitivity speaker".  This 3dB difference represents twice the power, so  100w/ch instead of 50w/ch or  200w/ch instead of 100w/ch.  In this modern era where very good amplification is available at relatively low cost, a large power amp is inexpensive compared to their predecessors of even 10 years ago.    Our own 150W channel P1 is roughly 3500 and the double the power (gaining +3dB) is only 4500.  This $1000 is a far lower cost difference than many speaker upgrades. 

Your comment that low powered magnets (I assume you really mean "smaller motors")  are always related to low sensitivity is also not true.  Small motors can be found in very expensive high efficiency loudspeakers.  I remember my old Klipsch La Scalas (mid 70s era) used EV OEM components that had tiny motors, yet were very efficient.   Small motors are usually a choice made by an engineer for price or some other reason, not efficiency.    The massive motor in our 7 inch SL woofer in an ATC SCM19 with 86/87dB 1w/1m sensitivity is larger than most 15 inch LF drivers used in other consumer speakers.  This larger motor gives us more control for lower distortion, not less control and higher distortion.  No massive power amplifiers are needed to make up for the 3dB lower sensitivity issue and the benefits in clarity are measurable and very audible.
  
The thermal compression you speak of is purely a function of the driver's ability to dissipate heat, not the amplifier, as all voice coils get hot when "powered up" by any size amplifier.  Its the inability to cool the driver that causes thermal compression and reduces driver performance.  Thermal compression happens to high and low sensitivity speakers at all price points.  Listeners will wonder why their speakers "sound different" when played loud for periods of time, this is a voice coil heating up and reducing its dynamic range.  Since its impossible to see this in action, its within the driver itself, we cannot assess this externally or by any spec.    

Brad
ATC importer to the US
Lone Mountain Consumer
TransAudio Group Pro

Focusing on efficiency as a measure of speaker technology or quality is like judging a passenger car based on miles per gallon.  MPG does not measure or reflect the quality of seating, the quality of materials in the car, the car's performance, its reliability or safety.   There have been many terrible high MPG cars that are uncomfortable, don't handle well, don't look good, are unreliable and unsafe.  

Brad

There are decades of scientific research, testing and effort on this subject. Old ideas about horn loading have not been disproven or debunked; rather the audio community, led by science and research, now understands better where horns pay off and where they don’t. Live sound could not exist without horns. In home audio, they are your friend if all you have is a 20W tube amp and you want to recreate the experience of a live orchestra. In home audio, they are not your friend when it comes to dispersion and low distortion. Personal anecdotes do not overcome the extent of verified research done on the subject by audio’s superstars such as Raymond Cooke (KEF), Floyd Toole (JBL), Billy Woodman (ATC) and all the unknowns from companies that got us here, such as Advent, EV, James B Lansing’s brother Altec, on and on.......

Talk about old technology, I have a 1929 Stromberg Carlson radio with a 15 inch 2 way coax (discrete hand made coax, not an acoustic coax "whizzer cone") sitting on what I think might be the worlds first home use transmission line. It was the beginning of high end audio.
Brad
Lone Mountain

There are newer generations of horns that are much better no doubt.  But well known to have lower distortion?  That gem is not in my physics text book!  Maybe I should qualify my comments to apply to normal SPLs in  nearfield applications (home audio)?  Maybe that's what you mean, that at higher SPL horns can measure better?  Over long distances or high SPL I would think could be true, but I'm not sure.  But nearfield?   I very much doubt that horns beat direct radiators in the low distortion game.  Certainly isn't my direct experience in my years in the audio business.   One only needs look to what the best of the best speaker designers of the industry are using for their best nearfield designs- and only in very rare cases (the JBL M1 comes to mind) are horns used.  

Does this mean there aren't horn based systems that sound good?   I've heard some that were very impressive.  But if you want Tom Petty's guitar to sound exactly like the real thing in the studio or at home, off axis and on axis, at listening SPLs we'd really use at home or the studio, Tom's engineer and Tom himself chose direct radiators.  Most of the great records over the past 30 years used direct radiators for monitoring AND mastering.  

Controlled directivity- In a nearfield setting, highly controlled directivity can be a negative for audio quality as off axis reflections are now significantly different from on axis speaker output.  This is a big no-no for authentic reproduction.  In real life a trumpet or a guitar don't create a limited dispersion sound.  Reflections are a natural part of real life music and are needed for authentic imaging.  So authentic imaging needs its off axis output to look very similar to the on axis output, only lower in SPL (level).   Like a guitar playing in your living room, the guitar radiation pattern bounces energy off side walls that recombines with the direct sound at your ear.  This is one big reason why some rooms sound different.  .

A room with highly reflective surfaces (lets say glass sidewalls and tile floors to illustrate the point), doesn't sound good by nature.  A wide dispersion speaker does not sound good there.  These super reflective rooms can benefit by  avoiding sending energy to these highly reflective walls.  This is the time where a highly controlled dispersion loudspeaker (such as a horn) at home pays off.  It could also be controlled by acoustic control, such as drapes or absorption on the sides and rugs on the floor.  .            

Brad  

Yes JBL M2- Sorry!.

This efficiency issue is one "spec" out of many that a designer must balance. All these performance parameters are evidence of the enormous number of trade offs in creating a complete driver/box/electronics design. So designers make their own choice ("I want a horn, that’s what I like") and balance everything to favor their choice ( it will have limited dispersion, HF narrowing, but that’s okay I’ll try and minimize it, etc). This is the way speaker design is, balancing hundreds of issues that represent hundreds of choices and all of them have resulting tradeoffs. You may want a low distortion driver but its too expensive, or the OEM manufacturer can’t build it till next year and you’ll be out of business by then. Or, the horn you want to use wont fit the box you already bought or built, or you don’t care about efficiency as amps are cheap so you want the widest bandwidth possible, ..on and on.

There is a practical science at play here, with product development controlled by economics, engineering principles, sales, marketing and a whole bunch of other factors we’ll never know about at the factory that drive those choices. In the end, the company "sells what they have" as ALL speakers are a sum of trade offs. Many of the issues debated are really arguments over someone’s clever marketing points and we as consumers take these marketing issues as gospel, as facts. Since everything is choices, it may be these performance features are important only in THIS type of design. To another design, they don’t matter. Like wide dispersion is not desirable when you are trying to throw sound over a long distance (think football stadium). But to home audio, and wide dispersion means I get to sit on both ends of the couch and hear it properly, that matters a whole lot to me.

The company I work with makes perhaps the best cone and dome drivers on the planet but their speaker cabinets are plain rectangular boxes. Some say the box is everything but in this design 2 of the 3 drivers have their own chamber and the box is not involved in the driver at all. The baffle is more or less "a holder" for position and improves output as there is acoustic gain by sealing drivers to a surface. Some say the box looks old fashioned- so to balance that we use some exotic woods and make them look like beautiful furniture. The best you can do is find a way to make some happy and others will just not see it/hear it the way you do.

These are trade offs made all the time by speaker builders and then we as purchasers and users get to choose if we agree and make the same choices. The funny part is how people, who aren’t acoustics scientists, want to insist their isn’t a choice, there is only one way to do it, and this is it! I know, I read the entire brochure! Or, I saw this demo once that showed XYZ and THAT was the truth let me tell you!   "Their" speaker maker’s choices are the only right ones, they understood it and no one else does.   A comment like this company is the only one "that really understands cabinets" is a very simple view of a very very complex business. Speaker engineering and building is HARD and because its physics, many of the choices are not flexible or open to interpretation. There is a large body of science behind all this that is available to everyone to draw on. I certainly don’t think the brand I work with has the only solution. There IS more than one way to do it and many good sounding speakers out there. Each has its own application set that it excels at and other applications that it doesn’t do well with. We have not arrived at a universal solution.

Brad

Oceanway is a relatively new player to studio monitors, Alan Sides always "built his own" when he owned Ocean Way.  He was from the old school days of large format horn loaded 2 ways soffit mounted, a type of speaker most studio people call "bigs".  Now's he's entered the consumer speaker building business and he has Phil Hendrickson, who is a really great guy BTW, talented as heck, working for him.  Phil is a highly experienced transducer designer who's developed several new ideas like vented gap technology in EV's early "DL" woofers.  I first met him at Electro Voice in the 80s.  He later went to Bose, now working for Alan.  I think Alan has something going and is getting some studio sales but is really targeting the international market for consumer.    Oceanway has significant brand recognition.    

Does your comment Sounds_Real_ Audio mean you think a passive crossover is different in a horn vs a direct radiator?

Brad