what is "driving"

[vivisimonvi]

I've heard this term too often but don't quite understand what it "really" means in audiophile terms... What makes a speaker "hard" to drive? Just low impedence? Not enough volume from them? Low sensitivity? Is it really the amp that matters?

What struck me to understand this is a particular scenario... I borrowed my dad's KLH Dolby Digital receiver to compare against my Sony DD receiver to drive a pair of Bose 401's (rated at 4 ohms) in 2-channel mode (Both are pretty much the same in wattage figures)... The KLH seems to 'drive' them fine in the living room without a power amp, the living room fills up with enough sound... We don't have to turn the volume up much to get good sound...

I took the 401's to my room and hooked them up to my Sony... and what a difference between the two! I nearly put the volume at max and the 401's barely put out much output (the protection circuitry tripped the 1st time I hooked them up driving them fairly low volume, was fine after that).

What gives? Btw, the KLH is a R5000 model and the Sony is a STRDE695... For some reason I can't seem to find any reviews or info on the KLH model, as a matter of fact this websites doesn't even have a receiver section for KLH receivers... this receiver being less than half the price (even 2 years ago) compared my current Sony...

Are these receivers underrated?

[skeptic]

Driving is the force that impels action. In the case of a loudspeaker, it is the force of an electrical power supply under the control of a signal voltage which drives a linear electrical motor back and forth, your speakers. That is right, your speakers are linear motion electrical motors. The voice coil is the armature and the permanent magnet is the stator. The power comes for the power supply in your amplifier whose voltage is DC and the input signal is amplified and is used to control the back and forth motion of the motor.

How efficiently this happens depends on many factors and some power supplies are more suitable to drive some speaker motors than others. Efficiency is one consideration. Efficiency refers to the amount of electrical power needed to move the motors back and forth a given distance. We generally look at this from the point of view of "sensitivity" but they are merely different ways of explaining the same concept. Less efficient speakers require more power to achieve a given volume. And of course, there is a maximum amount of power each speaker can absorb before it is damaged. This depends on the frequency and the length of time that power is applied for.

Another is impedence, the resistance to the flow of electricity. Loudspeakers are inherently low impedence devices. This means relatively low voltages and high currents. Impedence is a complicated subject which depends on frequency and the elements of the crossover network. One of the complexities is that unlike a lightbulb which is a purely resistive electrical load, loudspeaker systems have storage elements called capacitors and inductors which briefly store and release energy not in synchrony with the voltage applied by the amplifier. This can create difficulties. Even worse, a loudspekar is not merely a passive device like a light bulb which only converts electrical energy into another form but a loudspeaker can act like a small electrical generator where some of its mechanical motion will kick back at the amplifier. This is especially true for large woofers.

The suitability of an amplifier or receiver for use with a particular loudspeaker is a complex problem and despite the tendency to try to make it possible to drive any loudspeaker with any amplifier, this is not the case and there are many possible poor matches and some matches are better than others. The heart of any amplifier or receiver is its power supply and a good one is invariably heavy due to a large transformer and large filter capacitors. Because audio solid state audio amplifiers were found early on to be easily damaged if abused and because repair was expensive and to avoid the inevitable fights with customers who would claim that they did not subject their new under warrantee amplifier to abuse, the electronics industry came to install may protective devices to shut the amplifier down in one way or another before damage would occur. Overheating of output transistors, overcurrent to the speakers, are just some of the measures these protective devices try to prevent.

Don't confuse amplifier sensitivity with power output. The volume control of an amplifier is like the gas pedal in a car. A car with a small engine and a lightly sprung gas pedal or one that advances the throttle almost fully with just a small travel of the pedal may feel powerful because it seems to lurch forward at the slightest touch while a car with an enormous engine may seem sluggish because you have to depress the gas pedal almost all the way before the throttle advances very far or because the spring under the pedal is very hard to push. My car uses an electronic potentiometer controlled throttle and originally the design was a poor match requiring the driver to nearly floor the pedal to get much power out of the engine at which point it went like a bat out of hell. It was redesigned for better control but the engine itself hasn't changed. Having to advance the volume control fully to get an amplifier to deliver enough power to play speakers loudly means that not enough input signal is available. This is unfortunate but doesn't tell you any more about the amplifier's maximum power capability than the gas pedal action tells you about the engine's power. I hope this improves your understanding. BTW, I have no idea why your Sony receiver shut down on the first try.

[topspeed]

Hehehe...in case you couldn't tell viv, Skeptic is an engineer.

Good lord Skep, talk about using a slege hammer for a thumb tack!

"Drive" is yet another in a long list of euphemisms that audio people use to describe something in place of the correct, if long winded, description that Skeptic gave. The reader's digest version is that "drive" relates to an amps ability to correctly power a speaker. And yes, efficiency and in particular impedence play into it. If a speaker presents low impedence dips, like say a Quad ESL, an amp not rated for it will either clip or not sound very good trying to handle the load. For example, you wouldn't want to try to "drive" said Quad with an 8 watt SET. Bottom line is you won't receive all that the speaker has to offer. Make sense?

there are many possible poor matches and some matches are better than others.

Exactly.

I think a big reason the sound was so different was the room change. Does your bedroom have a lot of sound absorbing things? Curtains, furniture, carpet, book cases, blankets? Is the living room more lively? Glass, tile or hardwood, lots of reflective surfaces? That could be it or it could be that the Sony just wasn't designed to handle 4 ohm loads and a protective circuit shut it down before catastrophic failure (i.e. it ends up in the circular file)

[vivisimonvi]

Thanks for the responses guys!! I'm sure Skep also speaks on behalf for those more knowledgable in this area who simply never asked and are curious of such information. I read a lot of such posts here and have seen none to explain what driving really means.

About the room change thing, I did take the KLH to my room for a bit and speakers sounded rather loud and full at low volume levels. I'm not used to the menu, buttons, and features the KLH had so I took my Sony back. The first time I hooked up the speakers and turned on the receiver, I played a song, as soon as a big bass line hit, the circuit protection kicked on... I double checked the wires and everything seemed fine (there MIGHT have been a single strand touching another wire, that's what probably happened).

I use my computer as a preamp for my music to boost the low level signals to my receiver and they seem to better just a bit from that now...

Now that I look at the two units in terms of size... The KLH is rather large compared to the Sony... about 4 inches larger in depth and about maybe 5 lbs heavier (probably less than 5 I'm estimating).

I've made another post in the past comparing an 80's Pioneer 120 wpc integrated amp vs. a 70's 25 wpc Sansui... To me the Sansui clearly beat out the Pioneer driving these cheap 8' speakers with fullness and depth (with the exception of "loudness"). The Pioneer just pushed out loud, dull, and bassless noise through these speakers (the highs were there that's about it). Upon visual comparison, both are relatively the same in weight (probably over 40 lbs for both units). The Sansui being a LARGER reciever in width, depth, and probably a few lbs heavier. We gave it away long ago which is a sad scenario, it just took up too much room... I should have sacrified some other crap I own and kept the Sansui.

[vivisimonvi]

Skep, I have an important question for you...

Since the Sony doesn't have preouts and seems rather weak in output, I wire the speaker output directly in the input of a seperate power amplifier, that gives me great control over the system entirely... What are potential dangers in doing this?... feeding a "high-level" signal into an amplifiers input section.

I've been doing this for years to drive my CV speakers which handle fine... and the amplifier seems to work fine for years (despite a problem it still has from over a decade ago even before it was given to me)... it's in the speaker forum under Crackling Speaker, btw.

The only problem I see is others actually doing this who don't know when to stop turning up the volume knob.

[skeptic]

"Since the Sony doesn't have preouts and seems rather weak in output, I wire the speaker output directly in the input of a seperate power amplifier, that gives me great control over the system entirely.."

As long as you don't short circuit the hot speaker connections together, I don't see anything wrong with this. Had you gotten it backwards, you would already know you had done something wrong possibly sustaining a lot of damage to the output of the Sony receiver. The speaker output terminals can supply far more voltage than necessary to drive the input of the other amplifier. Just be sure not to turn the volume up too far so you don't overload the other amplifier. As for loading, there is absolutely nothing to be concerned about. The input impedence of the other amplfier is very high compared to a loudspeaker so current draw is nill. As a load, it's a piece of cake.

[vivisimonvi]

I greatly appreciate your response on this issue Skep, for someone whose amongst the smartest people on this board.

Now that I think about it, while my Pioneer has the power potential but lacks the type of output tailored to my taste... I think I'll experiment with some low powered receivers that I like that can output a good signal for the amp to drive my CV's (Based on people's experiences, they seem to have good results with low powered equipment)... I seem to have really good results with this tube preamp from my PC and Sony receiver alone (even with the 401's that don't seem to like much change with standard equalization IMO, they sound considerably different and more "alive" with this tube preamp). Well I only have these speakers for another week or so, I let my dad borrow my CV's and amp... he can't wait to get the 401's back...

I wish I still had the Sansui to experiment with... I really liked the output this thing put out, maybe putting this together with the Pioneer amp would give the type of sound I like, but with more power maybe!