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Master_Scythe

Old 3 way speakers

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I wont be pushing it, the amp is 125W per channel. and its a 5.1 amp, is that what you were asking?

 

as i said, staying below 1/4, once they're loud enough to fill a room thats all im asking from them.

 

the rears im using with the amp are only rated max 50 i believe....

 

Im not working this hack-and-slash system hard. its a make do untill i get funds for propper gear.

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Impedance matching is very important.

 

If they read 8ohms at the speaker terminals that's what the amp will be seeing also, so like Logic said - go for it :)

 

Edit:yeah, those caps inbetween the drivers... is the cross over, in It's most basic form o.0

 

More power the better, It's worse with a low powered amp as you then drive your amp into clipping and damage shit, this way you might just pop a few drivers :P Most recievers aren't as powerful as the specs leed us to think, often the max they tout is for stereo.

 

Late edit: I said speakers into clipping instead of amp :P

Edited by datafast69

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Ok this is how I would tackle this.

 

A 220 Ohm cap in series with an 8 Ohm driver = 226 Ohms

A 160 Ohm cap in series with an 8 Ohm driver = 168 Ohms

And a solo 8 Ohm driver.

 

These three "groups" are wired in parallel

 

Some math a got from the web

 

R total = 1/(1/R1 + 1/R2 + 1/R3 + ....)

 

for this to work we need common denominators and this is where I may fuck up

I picked 37968

 

So

R total = 1/(168/37968 + 226/37968 + 4746/37968)

= 1/(5140/37968)

=37968/5140

= 7.386 Ohms

 

Please keep in mind I am not an expert here just an interested party

 

Luck

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A 220 Ohm cap in series with an 8 Ohm driver = 226 Ohms

A 160 Ohm cap in series with an 8 Ohm driver = 168 Ohms

And a solo 8 Ohm driver.

Err, that's just a mess.

 

For starters, capacitors are measured in farads, not in ohms.

 

Rob.

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anywho, trusting my multimeter I connected them up.

 

They work VERY well, they NEED a low pass filter on the woofer as it makes the clarity of the tweeters sound 'muddy'

 

Other than that im very happy.

 

And yes, it seems the multimeter was right.

 

As we figured, a DC multimeter on a set of speakers always reads low. My amp is a 6Ohm.

 

the speakers read 8.5 (8.5X1.3= 11.5\12Ohm). As such the amp is currently on 50 out of 70 and they're not that loud at all, not even close to 'working the speakers' yet.

 

Knowing how damaging it can be, I tried putting the volume on 1 and switching the pos and neg terminals and seeing if the speakers were wired wrong (white stripe goes to black normally yes?)

 

But it seems my amp is far too smart for that, as it didnt care, and the speaker certainly wasnt 'sucking' instead of 'pushing' the cone. Damn new technology, lol.\

 

ok time to keep experimenting.

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Knowing how damaging it can be, I tried putting the volume on 1 and switching the pos and neg terminals and seeing if the speakers were wired wrong (white stripe goes to black normally yes?)

 

But it seems my amp is far too smart for that, as it didnt care, and the speaker certainly wasnt 'sucking' instead of 'pushing' the cone. Damn new technology, lol.

That isn't a new technology thing. There's no such thing as 'sucking' instead of 'pushing'. You can connect a speaker up either way and it will work.

 

Rob.

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wait.... really?

 

OH of course, its an AC signal.... stupid me.

 

Either way, once i filter the highs out of the woofer this is gonna be amazing, the clarity is already 5X what im used to.

 

EDIT:

 

and just got it sounding better again, realising the AMP had a crossover enabled (it expects a sub) so disabling that just improved things again.

Edited by Master_Scythe

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Hi, just reading the OP, I figure the boxes are 8ohms each.

 

The best way to measure is not with a dc meter, but with an ac meter (aka impedence meter)

 

It's very different.

 

but if it says 8ohms, it is ac rated at 8 ohms.

 

dc might show 13 or 7.5. which is wrong, because speakers systems run on ac. (alternating Current)

 

regards Glenn

 

oops, double post. (fixed)

 

<edit>

It's very different. because the re-active load will depend on the signal being sent, whereas a static load (dc) doese not take into account the frequencies being tested.

</edit>

Edited by GlennsPref

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sorry to but in but the polarity is important for the speaker to be "in phase"

you can check by using a small battery and if you have the terminals the right way round the speaker will push out

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The caps used in a speaker box are normally non-polarised , But you can check them with a battery and discharge them with load.

 

a resistor connected || (in parallel) to a volt meter.

 

if it charges up it's working, it's not a measure of how well it works for the specified frequency range.

 

One way to check

Actually this can be disastrous for some tweeters, too much power when the lows are not blocked, pfffftt!!!

, remove one side of the cap connection leg/wire, listen for the difference.

 

Record it with your phone for easy playback and comparison with the test of when the cap is in circuit (connected).

 

Cheers, Glenn

Edited by GlennsPref

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A 220 Ohm cap in series with an 8 Ohm driver = 226 Ohms

A 160 Ohm cap in series with an 8 Ohm driver = 168 Ohms

And a solo 8 Ohm driver.

Err, that's just a mess.

 

For starters, capacitors are measured in farads, not in ohms.

 

Rob.

 

........and this is only the start of it.............

 

http://wiki.xtronics.com/index.php/Capacitors_and_ESR

 

Err, I can't tell if you are having a dig at me as well LogicprObe.

 

A capacitors capacitance is indeed measured in Farads, but they do introduce resistance into a circuit and resistance is measured in Ohms.

In fact it is this property of Capacitors that makes them work as high-pass filters.

 

The phenomenon is called "capacitive reactance".

 

The resistance of a Capacitor will change with frequency. It will behave like a frequency controlled variable resistor.

 

WHAT, holy fuck like a resistor measured in Ohms

 

It is very simple to calculate the reactance, and plot a nice graph with a sweet curve.

Xc=1/2πfC

Where;

Xc=Capacitive reactance

f=frequency in Hertz

C=Capacitance in Farads

 

capacitors pass AC but block DC because at zero frequency (like DC) the resistance is infinite.

 

So while I can't be certain that the figures I used in my first "messy" calculation were correct, I am certain that capacitors do add resistance to a loud speakers circuit.

All I attempted to do was answer one of the OPs questions seeking an explanation for the higher than expected resistance reading for 3 drivers connected in parallel. The OP provided the resistance readings of the Caps.

While not a measure of impedance it did show that caps have an effect on resistance and offered an explanation to the OP for the readings taken on the speaker terminals.

 

Impedance is just resistance with capacitance and inductance factored in. It is the capacitance and inductance that interact with frequency to change the resistance.

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Hi, although a moving coil speaker has a dc resistance, We usually measure the impedance with an ac signal and meter.

 

The reading from the back of the box with a dc meter may give you an indication, but

 

If there is a crossover (of any type) or a pizio tweeter, you only get an indication of the dc resistance,

 

not a definitive reading of the true/actual impedance of the box.

 

This becomes important when building your own boxes and replacing drivers in old boxes.

 

There are far more factors to be aware of, compliance and stiffness (sensitivity), Q (resonance factor, Frequency responce & damping),

 

If you'd like to read up on this stuff, a book I have used,

 

Designing, Building and Testing Your Own Speaker System

with projects

David B Weems 3rd edition 1990

1990 Tab Books

paperback isbn: 0-8306-3374-X

I got mine from Jay Car a life time ago.$37.95

 

It includes all the maths you need to know, and the projects are very good, if not a bit dated, examples of High Definition Audio reproduction.

 

There are many other good books on these topics.

 

Another one of my favourites talks about the different distortions and quallity of caps, resistors and inductors in different applications.

it is...

Valve Amplifiers

Morgan Jones

Reprinted 1997

isbn 0-7506-2337-3

 

hth, Glenn

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Err, I can't tell if you are having a dig at me as well LogicprObe.

 

A capacitors capacitance is indeed measured in Farads, but they do introduce resistance into a circuit and resistance is measured in Ohms.

In fact it is this property of Capacitors that makes them work as high-pass filters.

 

The phenomenon is called "capacitive reactance".

 

The resistance of a Capacitor will change with frequency. It will behave like a frequency controlled variable resistor.

 

WHAT, holy fuck like a resistor measured in Ohms

 

It is very simple to calculate the reactance, and plot a nice graph with a sweet curve.

Xc=1/2πfC

Where;

Xc=Capacitive reactance

f=frequency in Hertz

C=Capacitance in Farads

 

capacitors pass AC but block DC because at zero frequency (like DC) the resistance is infinite.

 

So while I can't be certain that the figures I used in my first "messy" calculation were correct, I am certain that capacitors do add resistance to a loud speakers circuit.

All I attempted to do was answer one of the OPs questions seeking an explanation for the higher than expected resistance reading for 3 drivers connected in parallel. The OP provided the resistance readings of the Caps.

While not a measure of impedance it did show that caps have an effect on resistance and offered an explanation to the OP for the readings taken on the speaker terminals.

 

Impedance is just resistance with capacitance and inductance factored in. It is the capacitance and inductance that interact with frequency to change the resistance.

While that certainly is less of a mess, I still don't think it's correct.

 

The crossovers in the speakers are not using the effects of a lone capacitor. Certainly not in such a simplistic way that you just add the ESR to the speaker coil's impedance.

 

Rob.

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Err, I can't tell if you are having a dig at me as well LogicprObe.

Nah...............I'm trying to tell Rob that no component is perfect and therefore the mathematics are always only an approximation...........especially since they all change with frequency when reactive components are involved.

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Correct, and the 2 books I have mentioned may clear that up for anyone who goes to the trouble of finding them.

 

ie, google books(?)

 

Blah! My 2c

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How's that brick wall going, Glenn?

 

;)

 

Personally I need to get into reading about this stuff more, rather than just feeding myself little bits here and there to get by :P

 

I still have those PDF's that you linked, I should get into them again, think I'm on page 2 of 1 :(

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I'm glad glenn has already sorted this out... saves me from trying to explain it to teh nubs.

 

 

;)

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I'm glad glenn has already sorted this out... saves me from trying to explain it to teh nubs.

 

 

;)

Explain it to me then!

 

I consider myself a noob in this field and I take it that you do as well.

So what if the OP has sorted their concern, the debate, the sharing of ideas is still active, it cannot hurt to have more information on the subject.

 

Drivers are complex and speaker systems get even more complex, the best most of us can do is break it up into chunks that we can understand, if you can bring it all together for us noobs then I beg you do so. So far I have not found a single www article that can bring the entire concept together for me. If you can pull this off you may just get your 5 minutes of fame.

 

Come on! Impress me!

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Err, I can't tell if you are having a dig at me as well LogicprObe.

 

A capacitors capacitance is indeed measured in Farads, but they do introduce resistance into a circuit and resistance is measured in Ohms.

In fact it is this property of Capacitors that makes them work as high-pass filters.

 

The phenomenon is called "capacitive reactance".

 

The resistance of a Capacitor will change with frequency. It will behave like a frequency controlled variable resistor.

 

WHAT, holy fuck like a resistor measured in Ohms

 

It is very simple to calculate the reactance, and plot a nice graph with a sweet curve.

Xc=1/2πfC

Where;

Xc=Capacitive reactance

f=frequency in Hertz

C=Capacitance in Farads

 

capacitors pass AC but block DC because at zero frequency (like DC) the resistance is infinite.

 

So while I can't be certain that the figures I used in my first "messy" calculation were correct, I am certain that capacitors do add resistance to a loud speakers circuit.

All I attempted to do was answer one of the OPs questions seeking an explanation for the higher than expected resistance reading for 3 drivers connected in parallel. The OP provided the resistance readings of the Caps.

While not a measure of impedance it did show that caps have an effect on resistance and offered an explanation to the OP for the readings taken on the speaker terminals.

 

Impedance is just resistance with capacitance and inductance factored in. It is the capacitance and inductance that interact with frequency to change the resistance.

While that certainly is less of a mess, I still don't think it's correct.

 

The crossovers in the speakers are not using the effects of a lone capacitor. Certainly not in such a simplistic way that you just add the ESR to the speaker coil's impedance.

 

Rob.

 

I am not sure what ESR mean? I hope I have not missed a point here but I will rave about crossovers anyway :)

 

It can be just that simple(as a single capacitor), ask many DIY audio enthusiasts, and they will tell you that a 1st order crossover is the best option.

 

In reality they are rare, this is (as far as I can tell) due to the slow roll off of the 1st order crossover, at 6dB/octave it leaves a big section of the frequency spectrum to both drivers and blending is harder than a more "codified" approach, where a driver only works with the frequencies that it is good at.

 

A 2nd order crossover rolls off at 12dB/octave, 3rd order at 18dB/octave etc.

 

I don't use any crossovers (as in a circuit, there is another concept, the acoustic crossover in effect)but that is because I have a unique set up, not one many people would be familiar with.

 

Each increase in order makes for a more complex crossover circuit, phase becomes a consideration at some point but that is beyond my understanding.

 

often there will be addition component s added to the crossover circuit to manage impedance.

 

As an example I will use my loud speaker system

I have rear loaded horns using a fostex full range driver, this is an uncommon config.

The driver is good from 50Hz to 21KHz but it suffers in the low end because it is small , in this case the horn is designed to amplify the bass, the highs tend to not be so great when measured off axis (this is not an issue for me) so I could add a super tweeter to this config to get better highs.

 

A capacitor would be the total extant of crossover needed , say I wanted to cross over at 13kHz, a 1.55uF capacitor should do the job.

One octave is down is 1/2 the frequency so at 6.5kHz the signal will be -6dB from the tweeter, maybe a bit too high, crossing over at a higher frequency might be better.

 

A sharper roll off can be made by using the same cap but adding an inductor in parallel to the tweeter after the capacitor (the cap is in series)this has the effect of shunting low frequencies (an inductor is a low pass filter) to bypass the tweeter leaving only highs.

this is a 2nd order crossover, so at 1 octave down the signal is now attenuated by -12dB. ( I tried to draw this but I failed :()

 

more complex and more issues with impedance I would guess.

 

it would seem that you can make a crossover as complex as you want there is no limit to an nth order crossover but more components do reduce the efficiency of a system and that stuff about phase but I can't get my head around that atm.

 

In conclusion;

I would say it can be as simple as reactive cap in series but more often it will be more complex due to the limits of drivers and the need to control total circuit impedance

Edited by yogsogoth

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I am not sure what ESR mean?

Lower ESR is nearly always better, especially in audio.

In computers, the ESR is very important and always considered.

This is why if you are replacing caps on a motherboard, you not only have to find a cap of the same capacitive value but it has to be the same ESR!

You might think that using higher quality caps as replacements would be a good thing but because the ESR is different, the motherboard is unlikely to work.

 

From the link......... http://wiki.xtronics.com/index.php/Capacitors_and_ESR

 

ESR Equivalent Series Resistance

 

The ESR rating of a capacitor is a rating of quality. A theoretically perfect capacitor would be lossless and have an ESR of zero. It would have no in-phase AC resistance. We live in the real world and all capacitors have some amount of ESR. To understand why let us review what a capacitor is and what they are made of and how we rate them.

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Hi,

 

datafast69, How about linking the source for those pdf's, I lost them, and would have linked them here if I could.

 

Please.

 

I'm putting together a reply off line, and should have it ready by lunchtime. ;)

Edited by GlennsPref

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