KvH: Klipsch loudspeakers

[Umfriend]

Jammrock, just to be sure, that does not contradict the little bit I wrote or does it? Not really into this stuff. On RMS, there is one problem with it AFAIK: it is typically measured without phase shifts and at a continuous load (or impedance). The impedance of a speaker however varies with frequency and the current an Amp can provide may vary with the phase of the signal.

In some mags therefore, they show the voltage (or power, not sure) an Amp can supply at various impedance levels and phase shifts. The flatter that curve the better.

There are more things to the equation though (e.g. damping factor), but your own ear is the best judgement. Having said that, absence of a good P/S with loads of capcitators does not bode well...

There used to be a pretty good article on this on Rotel's website, but I can't find it anymore

[Umfriend]

http://europe.rotel.com/products/pdfs/rotelbrochure_may2001.pdf

Not the one I wanted which was larger and on the topic only, but page 18 shows a bit of it.

Damping factor has nothing to do with current or power that is, if you require too much power, a high DF won't help you.

Do you need a high current Amp? What are you going to drive with the Amp? Graphs like on page 18 say a lot, but especially if the speakers are demanding on the Amp, yer ears should do it as well.

Price won't do all mind you, one can pay hefty prices for valve-Amps that deliver little power.

Having said all this, I have alway wondered whether I ever use more than, say, 5W peak.......

[Jammrock]

The power rating of a speaker is based of the nominal impedence of the speakers, i.e. 8 ohms, 6 ohms, 4 ohms, etc. Nominal impedence I believe the average of the minimim resistance each driver can operate at. Or something like that ... I'm sure Greebe of KvH can correct me if I'm too off target.

Umfriend: yes, the load changes over the course of the music, depending on what frequencies are being used and at what level. Another example from an online AV mag called SoundStage can be seen here:

http://www.soundstagemagazine.com/measurements/odyssey_khartago/

If you look at amp specs they should always tell you what frequencies they used to measure their average RMS. Like my RB-1080 spec sheet:

http://www.rotel.com/products/specs/rb1080.htm

"Power Configurations
Watts/Channel all channels driven, unbridged, 8 ohm load, 20 to 20k Hz, 0.03% THD"

Showing that they to an average power rating from the full audio spectrum.

A good definition of dampenig factor is here:

http://www.kellyindustries.com/articles/glossary.html

You'd only need a really good high-amp amp if you are driving good 3-way speakers, i.e. with a stiff mid driver and/or a good built in sub-woofer system.

But that' sjust my opinion.

Jammrock

[KvHagedorn]

TX: for the layman, and this usually works, btw.. pick the thing up. If it's heavier than you would have imagined, it's probably high current. Technically, if you look inside the thing, and it has a large transformer and large filter caps (this is what makes it heavy) and a discrete transistor assembly as an output stage, you're on the right track. A cheap receiver will crank up voltage to mask the lack of current and give a high wattage figure, and their output section will be through a cheap circuit board (yeah all the power goes through traces on the board) rather than using the "fat pipe" method of discrete transistors.

Just stick with Yamaha, Denon, Rotel, NAD, Onkyo, Marantz, or Harmon Kardon if you are doing a receiver. Get one of the pricier ones (over $1000) if you want REAL high current. Otherwise, try a separate amplifier. That's almost always a better solution anyhow.

[TransformX]

Thanks for all the tips guys

One last question: What's the difference between class A and class B power amplifiers ?

[Umfriend]

One is Class A, the other Class B....

Seriously, in a class A, the transistor or Op-amp is always being fed current and amplifies both positive as negaive signals (or something close).

With Class B, there is one op-amp doing the positive and one doing the negaive side. The main problem with this is how to switch accurately from one to the other.

There are good explanations to be found via google, or do we have to do all the research for you? (could not resist, sry )

[Umfriend]

Oh, and what KVH said about lifting the Amp to check the weight? That is one hell of an advice

[KvHagedorn]

Originally posted by Jammrock
The power rating of a speaker is based of the nominal impedence of the speakers, i.e. 8 ohms, 6 ohms, 4 ohms, etc. Nominal impedence I believe the average of the minimim resistance each driver can operate at. Or something like that ... I'm sure Greebe of KvH can correct me if I'm too off target.

Nominal impedance is a tricky thing.. if you graph the impedance of any speaker, you will see that it varies greatly from one frequency to another. Any amplifier can drive into high impedances fairly easily, but it takes a real high current amp to hold steady and not crap out on the low ones (say below 4 ohms.) Some higher end speakers dip very low at certain frequencies, even to one ohm or below. This is fine if you are using an amp that is also high end, but a cheesy receiver will sound even worse when it is trying to drive these loads, and might even shut itself off.

The B&W 700 and 800 series, especially the floorstanders, need to be fed with a real amplifier. Impedance on these speakers can fall quite low at some points, so they really don't come alive unless they are being fed massive current. They still rate them as nominally 8 ohms, and for most of the range they are, but those low dips are the exception that requires a hefty amp.

A good way to imagine the impedance curve of a speaker is to imagine a guy holding a child who is dangling off the side of a cliff by a rope. The child weighs 70 lbs at normal Earth gravity, but imagine that gravity is not constant.. sometimes it becomes like the gravity on Jupiter (low impedance.) Most people could hold the child up at normal gravity, but when that 70 lb child suddenly becomes 200 lbs, the rope slips from weak hands, just as a weak amplifier craps out when impedance becomes low. It takes a hefty guy to hold on at all times without flinching, and this is why you buy a big beefy amplifier.. not because you want to blast the neighborhood, but because you want the music to sound as effortless at frequencies where the impedance dips as it does where it does not.

[Jammrock]

what he said

Class A amps are big, expensive and sound fantastic

Technically though, it's the method used to amplify the signal that determines the class. The common ones are A (highest end), AB (high-end), B (middle level), and D (low-end and sub-woofers, with the rare exception of Linn class D amps and a few knock-offs ... but mostly low-end). Without getting technical, Class A will give you the most pure sound and raw power, but they are highly inefficient. Class A amps lose more power to internal heat than they send to the speaker to use. Some of the highest end ones will weigh 57 kg (125 lbs.) for a 1 channel 250 W amp.

Class AB is where you will see the best comprimise equipment. They have some elements of the Class A amps, but are not nearly as inefficient. Thus you don't have to have huge heatsinks on everything and you still get a good clean sound. My Rotel RB-1080 is a Class AB amp I beleive, and weighs in at 16 kg (37 lbs) for a 2 channel x 200 W amp.

Class B is very efficient, but doesn't exactly give you the best sound.

Class D = Digital amplifier ... which basicaly means your standard push-pull amp/power supply used in your desktop PC. They are super cheap to make because they require no massive transformer like A/AB/B require, yet can still produce large chunks of power and current. But most Class D designs are made super cheap and don't sound good, except in sub-woofers. The exception to the rule is Linn, but you're going to spend $2k-$40k per amp for a good Linn Class D amp.

[Fluff]

If i ever have enough money to get those B&W 800, or any other large speakers. I think I'd go for this power amp.

http://www.crownaudio.com/amp_htm/studref.htm

But it apparently needs a 30A fuse !!!

The Studio Reference II is 2500 + VAT and weighs a ton.

[KvHagedorn]

Try these:

http://www.stereophile.com/amplificationreviews/878/

http://www.classeaudio.com/Omega.html

Those are currently my dream amps for when I win the lotto.

[Jammrock]

If you're going to win the lotto and buy a big expensive amp, try these out:

http://www.stereophile.com/amplificationreviews/683/

http://www.halcro.com/productsDM58.asp

Jammrock

[Umfriend]

Hmmmm the best I've ever heard so far wqs a Sonic Frontiers Line-3 pre amp and two Monarchy Audio SM-70 Pros.....How much more expensive are these above?

[Greebe]

Amplifiers are grouped as follows

Class A : Transistors always on, through the positive and negative signal swing

Class AB : Transistors on 51%-99%, with a crossover between either half where both ourput rails operate at the same time

Class B : Transistors operate 50%, with a crossover point midway between the two

Of these three, Class A is the best sonically but generates the greastest amount of heat and is the least effecient electrically. Class B being the most effecient electrically, but with a audible notch regardless of power level, but are more pronounced when listening at low levels.
Most amplifiers are Class AB

[Greebe]

Best way to check if an amplifier is high current is partly how Chuck explains, but better is how much power is produced at ever decreasing impedence loads... Example: Amp has a nomimnal power rating of 100w/ch @8ohms

8@100w
4@200w
2@400w
1@800w
0.5@1600w

The closer an amplifier can follow this and the lower it can go the better. The neccessity is very easy to wrap you mind around. When bass "thump" or similar is reproduced in the low frequency range a woofer reacts with an ever decreasing impedence, some designs more of an issue than others (e.g. the Driver itself and the box design albiet acoustic suspension or one of the many bass reflex types or infinite (or otherwise known as the) air suspension types) resulting in a impedence lower than one ohm for that instant.

Personally I think dampening factor is a bit overrated