An electronics text book of mine says,
"Increasing the gain of an amplification stage reduces feedback and therefore reduces linearity".
This means overall distortion is increased.

To increase power output (without adding extra stages of amplification) and avoiding this problem a manufacturer would have to make their higher powered amps completely different to the lower powered ones. Any amplifier I have looked at internally(admittedly only cheaper ones, too scared to play with expensive ones) has just beefed up power supplies and added more amplification stages.

So I still think if you need no more than 100 watts you would be better off with an amp that produces 120 watts than an amp that produces 200 watts.

The problem with purchasing an amplifier that is on the border line of the required power is that ur probably on the limits of all the output components - like where the Vgs vs Id curve starts to flatten out (in fet outputs.. ie moves from triode to saturation) - this is more likely to cause distortion than the fact that you have more stages cascaded together (as you prev stated reduces feedback and linearity..)

[ February 19, 2003, 18:03: Message edited by: STIK79 ]

Yeah good point about the linearity of the MOSFETs. I still think(at least hope)decent quality amps would reach their rated power while still in the triode region because the gate/source voltage levels out pretty quickly once it reaches the end of this region. I'm guessing thats what causes the rapid increase in distortion when an amp reaces its limits.

So before this rapid distortion the MOSFETs are still operating in the triode region and should be just as linear at about 90% of their maximum as they are at 10%.

Clipping is the result of pushing the FET into the saturation region - so this is what's happening when the low power amp runs out of steam - you're 100WRms amplifier only has the voltage rails to produce 100WRms (cbf working the value out for it ) (unless underrated in which case it's really a mroe powerful amp anyway ) so if you ask it to produce more you push the FET into saturation. Thus I think it's wise to use a slightly over powered amplifier and carefully adjust the gains to the power you want (using scope etc) this way you can be sure you're avoiding the triode/saturation junction and any repercusions associated with it...

but ur right below about 90% of that junction it should be "perfectly" linear...

[ February 19, 2003, 18:36: Message edited by: STIK79 ]

Totally agree. I Still think that double the required power is not desirable. However the difference is surely outweighed by the possibility of upgrading speakers one day and keeping the same amps because they can produce more power than was previously required.

I think that if the signal is not clipping, then the movement of the cone will cool the coil, which is better than having it dissipate a lot of power while remaining still
Whereas if you pushed your speakers too hard, the cooling action of the cone offsets the heat created by the coil
then again I could be just lost

Well I have a real world example for ya'll

Initially hooked up to my Alpine F#1 2 ways I had hooked up an MRV-T320, this sounded very nice. The amp wasnt driven very hard at all but was still at about 75% of capacity, I'm guessing their was still about 25wrms free.

I then had the opportunity to upgrade to an MRV-T420 (double the power of the 320) and the sound quality increased dramatically, the change was simply a plug in change over, nothing else was changed. This amp puts out 120wrms and the quality increase was certainly audiable.

Sure, higher powered amps may have a higher thd as a base point than a lower powered amp (if built the same) but in the end, you can drive the larger amp alot harder before the thd increases, which is great for transient peaks.
ofcourse if we play sine waves all day it wont be a worry in the world. but music has alot of peaks and the extrta headroom makes the sound much more controlled, which is alot better for your speakers and your ears
thats just my 2cents

trouble though with having a larger amp, is u get stuck in the position i am inw here i really wanna utiliise my 120wrms on the splits when they can only handle 70wrms *so depressing*

i am a firm beleiver in running large amps for front stage running lower gains as it allows "headroom" for peaks and troughs in music ... however ...

one important point left out is the actually passive crossover for the speakers which can only take a certain amount of power before components start to run into dramas as well ... from my experience with my own car i found you hit a point where simply more power does not make a difference compared to say, running a fully active front stage ??? i dont know if everyone will agree on that one however removing that passive crossover from a split system and running active from an amp gave me a far better control over my front stage while still allowing for the headroom for music ...

Yes passive crossovers are the killer in a system with large headroom. Once the cores of the inductors saturate thats it, large amounts of distortion are encountered.
The same occurs with any driver. The only way you can truely setup a proper SQ system is to perform a Dumax test (or Klippel testing) to determine your drivers linear power output and max power output. After this you know what amp power to use or if your drivers will/won't perform the function you want.
I have never seen anybody design an SQ system in Australia or heard of anybody in car audio who knows how to do it! Its a bit sad really when you have all these so called SQ cars being built and they have already decided on their drivers and amps, its completely the wrong way to go about building the system. This is only half of the testing you need to do and I have never even heard anybody hint that they know how to do the other parts.

How is Klippel testing performed??

I am considering going active instead of passive and want to know if there are any limitations with either the crossovers or drivers.

mj

With a lot of test equipment and the knowledge to interpret the results.
Basically you are testing for the various forms of distortion that occur with the drivers. Such things as the BL lineratiy vs power, compliance of the suspension vs power, distortion due to the electrical properties of the speaker, all this this is done at various frequencies and power levels.

A Dumax test would be suficient as this will give you most of the important information about your drivers.

Simply buying high end gear and installing it perfectly isn't going to give you an SQ system like people would have you believe. There are too many other variables which need to be determined before you install or decide on drivers.
Your amp power and your drivers are more than likely to be your limiting factors rather than the active xover.

Oh yeay I forgot to add - you can never have too much amplifier power.

well i might make the suggestion that its because nobody (ok not 'nobody' rather very few) know how to. can you elaborate on what it is a little more, obviously testing limits of drivers with those things you mentioned, but (without trying to sound like too much of a novice to the idea ) how would anyone go about doing that? performing those tests? its it feasable for any normal (ie everyday person with a nice system) to contemplate the concpet? or does it involve specialised equipment most people wouldn't or can't get access to?
just curious if you wouldn't mind letting on a little more about it

Kippel also tests for inductance nonlinearities..

This is definitely true, although in a high end component set, usually the crossovers would be matched to the components, so when the inductors saturate, the speakers would already be producing a significant amount of distortion..

But for true LOUD sound quality system, active crossovers certainly have an advantage..

As far as the kippel/dumax testing goes, that would only be neccesary if you want to know how much you can push them.. IMO not all people designing SQ systems really need to know that information..

That's usually not the case. Lets take a set of components that has an average power handling of 100watts. If this component set was designed properly it should be able to handle dynamic peaks of 10dB or 1Kwatt. The inductors in your passive xover are going to saturate way before this power level is reached. This is why you need to do testing as described by the dumax/klippel tests so that you know your speakers limits. Any 100 watt speaker that can't handle a 1KW burst is not what I would call a 100watt speaker. If your speaker could only handle say 500watts peak (without significant THD) then I would only classify it as a 50watt speaker. This average level may not be enough to overcome the noise floor in your system across the frequency range. This is basic info which ALL people who are designing an SQ system need to consider. Once you know what SPL/acceptable distortion you can reach you can work out if this driver will be able to reach your dynamic range whilst not creating undue distortion.

GMHVNS,
The best way to elaborate is to read the inventors AES papers. But basically they measure the different forms of distortion at various power levels. They can be found here for Dumax testing and here for Klippel's papers.
The best way to go about getting it done is to get someone else to do it! The dumax machine costs a fortune and the to set up the Klippel system costs about the same. Either way you need to have the knowledge of what you are doing. Maybe send DLCdesigns an email and ask them which drivers they have tested or what it would cost to have your speakers tested. I have used the Klippel method to test a few drivers. Ask around the US and find out who has had testing done. Also be aware that just because one driver outperforms another it may still not be the better driver for you. Especially since your amps are most likely to be way smaller than the amps used for testing. So the two speakers may match each other at the lower power levels in which case you may opt for the cheaper or more efficient driver.

[ March 07, 2003, 08:46: Message edited by: KDog ]

so is all this audibly relevant? i mean, would the 'perfectly matched system' be audibly better?

i think most people are quite happy with their own results, so i'm not sure what place, if any, such tests have in our hobby.

still, i'm always interested to hear of means to improve on what i have. however, pardon my ignorance, but i don't see it as good value for money, or a worthwhile investment of time and effort. that fact that no one does it may be telling us something?

thanks for the info KDog, i'll have a read for interests sake

Actually, i'm very interested now!! lol, i have 2x200wrms running into splits that require ~100wrms, and like kdog said, i can make my amp distort well before my splits do. Which makes me wonder, is that due to exactly what you say? that the speaker can handle a ~1kw peak before distortion? It is making me wonder because i was considering at one stage going active (ONE DAY!) but, after reading this, i'm not 100% sure it'll make any difference!
Aaron

blah blah blah

i have a friend with a home audio amplifier that has a meter displaying the watts being output in real time, with it turned up to a respectably loud level, the thing only outputs around 5 watts. - yes, 5 watts. and it is capable of much more, yet it doesnt get used with real music - unless of course you play sine waves or push your system to clipping.

i really think most people over estimate how much power is needed to get speakers moving

t-bro, i too have a meter for home that display's wrms, and 20wrms from my old nad used to push my home speakers really well, however, for the "200w" in my car, it's so much louder it's not funny, i used to think my home setup was loud, car setup is just silly! But, i do agree with you, not 'much' power is needed to make efficent speakers move!

i do agree that a Dumax testing and other such testing can make a difference ... but i think this debate has changed a bit from where it started ... firstly we were talking about amp head room ... i mean, sure, the actually amount of power a speaker can take as to distortion etc is important, but in the real world in 99% of "sq" systems its not really that important !!!

im not doubting that in a perfect world, such testing does have its place, but how many cars around the world that win a great deal of sq comps actually use data like that in making system choices ??? not a great deal ... they take it into account, but do not base sq speaker and amp decisions upon this ... but more upon how amps and speakers sound to your ears ...

look at cars such as alpine f#1 status cars which actually perform quite well in sound quality comps ... the drivers in these cars where not picked to because of such tests in reality ... i mean, sure the data from such tests may have been taken into account, but would not have been the deciding factor for all such systems, otherwise every alpine dealer around the world would build f#1 status system using exactly the same amps to match drivers etc ... like i said i am not doubting you in the terms that it can be important, its just not as important as a great deal of other factors ...

say for instance you performed all this testing at large costs, and then did not do little things like sound deaden doors etc ...

and the drivers themselves are only half the story ... you talk about limiting factors in x-overs ... take 3 way split systems such as the dynaudio system 340 or 360 and alpine expert series 3 way splits ... the drivers only work as well as how you set the x-overs up ... you talk about such testing as Dumax testing but how many people actually take the time to perform phase testing in cars while tuning the alpine x-overs, in which phase correction is built in, but then again, there is only a finite level of adjustment in them, what about if you were 0.5 degrees out ... and how many people take the time to check that dynaudio 3 way x-overs where designed to suit two differnt tweeters of completely differnt impedance ...

little stuff like this is more real world important then Dumax test as it is more relevant to people who own the gear ... cause more importantly Dumax testing cannot tell your ears which drivers sound better ... again, not saying it is not important, maybe for that very very very fine nth degree of sound quality, but then again out of reach of most people unfortunatly

and just quickly while i remember such testing has its limits in car audio as in car we can never get a perfect location or install on speakers anyways ... we cannot really practically change the volume of a door enclosure to be ideal or get the perfect level dampening from an enclosure ... as anyone who has looked at car dynaudio vs home dynaudio ... while there are slight mechanical differences between divers in the testing phases of the speakers, the price difference is huge !!! most of that money would surely go into creating the enclosures as some car audio dynaudios even carry the "authenic fadelity" badge of the home dynaudio not the "mobile fadelity" badge of the car drivers