Didn’t want to highjack the thread “Budget Bass = Response?” which was going into impedance calculations.

This is my train of thought on the subject.

The signal to a speaker is AC right?
The speaker is a coil, an inductor right?
This means the impedance (inductive reactance XC) would vary with frequency as per the equation XC=2*Pi*F*L where Pi = 3.14 F = frequency L = inductance measured in Henries.

Yet all speakers give a fixed impedance value, maybe nominal would be better, always intrigued me. :nuts:

What about the other different types of impedance? ie. resistive or capacitive.
Where a combination of types are used in a circuit they’re calculated using vectors due to lead and lag factors, using: series Total = R+R+R, parallel Total = 1/R+1/R+1/R is not really valid.
Capacitors are often used in filtering/crossovers which if fitted directly to speaker will effect the impedance.

Where the same impedance type is used: series Total = R=R=R, parallel Total = 1/R+1/R+1/R is fine to use.

Does anyone go to this level when calculating impedance to ensure the best match to the Amp so that frequency response is delivered at the speakers.


Thoughts anyone.
Flame me anyone. :D

Very good question.

Here you go:

http://www.members.shaw.ca/loudspeakerpage/impedance.html

i got a D in yr10 physics



:D

but you must realise the molecular structure of the coil allows current to pass through the bi-mass inihibitor port where the neutron gravity feild stabiliser is used to calculate impedence to one millionth of an ome ;)

Yeah Phil, you're right on all accounts, but the difference in impedance across the frequency spectrum is negligible for most intents and purposes.

When I was looking into passive filters for my rear speakers I did take the calculations to the nth degree, but trying to get an impedance curve from car audio manufacturers is not an easy task.

BLKMAG - you had me going until you spelt Ohm wrong, hahaha!

Righto... we do all realise that IMPEDANCE is RESISTANCE + any INDUCTIVE or CAPACITIVE REACTANCE? For example, a coil, when measured might have a resistance/impedance of 3.4ohm? When power is applied, the inductive reactance created will actually ADD to the resistance of the coil, causeing the IMPEDANCE of the coil to rise to say 3.8ohm. This can be shown useing a power factor diagram, which I really couldn't be bothered drawing up, cause it's SO long since I did it at tech. :confused:

The couple of speaker specs I've looked at online for higher quality gear, DO quote NOMINAL IMPEDANCE ie. for all intents & purposes throughout the freq. range, when trying to work anything out, THAT is the value to use.
Most manufacturers probaly leave the word nominal out, cause for 80% of the population, who are about as electrically minded as your average wooden spoon, they'll recognise IMPEDANCE, but throwing in the word Nominal will confuse the hell outta them! :cry: If you start trhowing in values like 3.85ohm, they'll be like "WHAT? How do I add these together?" And I'd say that it'd be beyond MOST of us to create a crossover/filter that can change to account for the MINUTE differences that freq. will incur. That & most of the electrical components that are widely available are acurately valued enuff to recreate your calcs exactly.

But in so saying, when the man****urer quotes impedance, for 99% of cases, it will simply be used to do basic speaker/amp matching.. eg. "I have a DVC 2x 4ohm sub, & therfore, I need a 2 or 8ohm stable amp.. yay!" While the actually impedance may REALLY be 3.85ohm, they will usually quote 4ohm in basic specs, but when you find the nitty gritty specs it'll give you the real value. For matching the amp to a sub though, that wouldn't mater squat. If anything, the way you're putting it, you need to match the SUB to the AMP. You'll want to pick the sub with the lowest impedance, to allow the most current to flow ie. higher watts.

From what I can work out, manufacturers pretty much do that for you giving their drivers an "Efficiency" or "Sensitivity" rating. This is seen as 1Watt/1m? & is expressed as a DB value. For eg. a db meter at 1m SHOULD in theory, hear a driver with a rating of 87db to be twice as "loud" as one with a 84db rating when both recieve an identical 1watt input. (being that for every increase of 3db, sound pressure level has actually doubled)

I'd say this would vary between drivers because of many factors, like the number of turns & layers & wire CSA in the coil, & the "floating cone weight" of the driver.. all of which will affect the amount of work a given amount of power can perform.
If anyone has a more clear idea on how the effeciency thing actually works, fill us in.. I've only looked into a little.. I think I understand what it does, but not fully HOW it works. :confused: Heres how it was explained to me when I asked on the Car Audio Australia Forums http://www.caraudioaustralia.com/forums/viewtopic.php?t=40000

In the end, just take the impedance values they give you. Unless you're an engineer, I wreckon delving toooo far into it is a waste of time :nuts:
Thats my 2c worth (probly getting close to $2 actually :redface: ) Sorry for the LOOONG post & if I'm a bit off the mark, feel free to correct me.

I was pretty sure that the reason for "matching" the output impedance of the amp to the input impedance of the sub(or speakers) is to allow the maximum transfer of power between the amp and the speaker, i cant remember the exact theory behind it at the moment :confused:

Also as the output of the amp can also be modelled as an impedance, wouldnt this impedance also change as the signal frequency changes?? So if the amp and speaker are "matched" then the impedance change of both, with a change of signal frequency, would be the same, and hence still allow max transfer of power :nuts:

(Hmmm what a dodgy answer from someone who's studying Electrical Engineering :redface: )

A BIG Thanks for the feedback, it helps to put it into perpective and those links were great thanks.

The reason I posted the question at a high level was to get in depth information, which you guys provided. :D

As an electronics tech in the RAAF I didn't work in the audio field and I'm amazed at what is available.

Any more links or info (high level) about this stuff would be appreciated.

I realise a lot of people probably aren't interested in this area or level or think i'm a little :nuts: lol , however I am so anyone with knowlege can you please share it.

edit: nearly forgot, that is an interesting theory BLKMAG I'll be sure and pass that on :bowrofl: . I did ask for it.

phil

BLKMAG - you had me going until you spelt Ohm wrong, hahaha!

hehehe :doh: :doh: :doh:

As an electronics tech in the RAAF I didn't work in the audio field and I'm amazed at what is available.
phil
Sheesh... a techy & student Engineer... makin this oh-so-close-to-tradesman 4th year Lecky feel a liiiiitle intimidated :redface: ... oh.. cept the student... they're fun to get a hold of when they're with us on co-op! :badgrin:

:pray: :chainsaw:

Anyways Dim, considering the amounts of power your dealing with.. the MINUTE variations due to frequency will be exactly that.. too minute to consider. Even if you accept the amp as having an impedance, all it does is add to the total impedance of the circuit.. matching the impedance of the amp to the speaker would do nothing more then neatly double the total impedance. And besides, I can't imagin the output impedance to be anywhere near that of a speaker.. from wot I can remember it should be huge in comparison (somewhere in the K or M Ohms?)

In the end, to answer the original question: "Does anyone go to this level when calculating impedance to ensure the best match to the Amp so that frequency response is delivered at the speakers.", I wouldn't imagin so, no... simply because that effect will always be there, no mater what the amp/speaker, & it's too TINY to worry about. You'll probly get more variation from the components of 2 "IDENTICAL" amps then from the freq. lol

but you must realise the molecular structure of the coil allows current to pass through the bi-mass inihibitor port where the neutron gravity feild stabiliser is used to calculate impedence to one millionth of an ome ;)

LOL! that sounded exactly like something Doc from Back to the Future would say about the Flux Capacitor in the Deloreon!!!

lol lol lol lol

Haha, I thought exactly the same thing after I read it a few times.

1.21 GigaWatts!!!!

oh.. cept the student... they're fun to get a hold of when they're with us on co-op! :badgrin:

:cool:




output impedance to be anywhere near that of a speaker.. from wot I can remember it should be huge in comparison (somewhere in the K or M Ohms?)


Shouldnt the output impedance of an amp be really small?? (Based on an ideal op-amp having an input impedance of infinity and output impedance of zero) :confused: