Here is an example of a fairly typical crossover.
The woofer impedance is in yellow and the tweeter impedance is in blue. This is the way they are seen individually from before the crossover, i.e. from the amps point of view. The combined impedance is shown in red.
In this case the impedance is higher around the crossover point and the individual drivers virtually leave the circuit out of their range so the three will not really be in parallel.
The woofer impedance is in yellow and the tweeter impedance is in blue. This is the way they are seen individually from before the crossover, i.e. from the amps point of view. The combined impedance is shown in red.
In this case the impedance is higher around the crossover point and the individual drivers virtually leave the circuit out of their range so the three will not really be in parallel.
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In one word is 8 ohms. But minimum impedance can be lower, look at the impedance curve of drivers. Usually 6 ohm or similar in this case. Final min. impedance dependent of the crossover design and drivers. Plus cables.
thanks Allen. that solves my doubt. is it always impedance more at xover point? any solution to reduce it? thats why i believe its bad to cross between 300hz and 3000hz as at xover point sound gets attenuated. is my understanding correct?
also which software you are using to generate the impedance curves
will this theory holds good even when i apply impedance equalization for mids and tweeters? i mean the impedance seen by amplifier will remain 8 ohms after adding a zobel network to mid and a paralle LCR network to tweeter. on adding these impedance correction circuits the equalized impedance will become equal to Re of the driver (correct me if i am wrong here) right?
thanks
No, you have it back to front.
The power amplifier has a finite output impedance.
The speaker has a finite impedance.
The voltage at the speaker is Vout * (Rload / (Rload+Rout))
let's put some numbers in to that equation.
Vout = 10Vac
Rout = 0r5
Rload = 8r0
The speaker voltage = 10*8/(8+0.5) = 9.41Vac.
The power available at the speaker terminals is V^2 / Rload = 9.41^2/8 = 11.07W
Let the impedance at the crossover rise to 10ohms. Rload becomes 10r0.
The power available at the speaker terminals is 9.07W. Gee whiz we have lost 2W !!
But, the speaker manufacturer designs the speaker to have a flat sounding frequency response, when fed with a flat Voltage response.
The speaker instead of reading 9W vs 11 W reads 9.5Vac instead of 9.4Vac.
This is an increase of 0.1dB. Almost certainly not audible.
As the Power Amplifier output impedance (and all the other impedances of the cables and connectors) gets lower than slight increase of 0.1dB in the example gets even less.
At the limit, if the output impedance is zero the gain/loss as speaker impedance changes is 0dB.
The impedance is normally higher, but you can cross any way you like so it really depends. If you stick to the normal ways of crossing it should be reasonably predictable.
If you want to flatten this kind of peak you might add a tuned circuit (RCL) across the amp.
The impedance is higher, but then there is energy storage around the crossover region. I'm not sure I understand your question about attenuation. You can set the levels where you want them. Some crossovers have a flat response on axis but a reduced power response. For what it's worth, I use a crossover just below 1kHz.
The software is xoversim. The curves were measured and the crossover simmed onto them.
If you want to flatten this kind of peak you might add a tuned circuit (RCL) across the amp.
The impedance is higher, but then there is energy storage around the crossover region. I'm not sure I understand your question about attenuation. You can set the levels where you want them. Some crossovers have a flat response on axis but a reduced power response. For what it's worth, I use a crossover just below 1kHz.
The software is xoversim. The curves were measured and the crossover simmed onto them.
if an impedance equalization network (such as zobel) is applied then Rload will remain same across the frequency band. in that case power available at speaker will remain same. is this what u meant by flat sounding frequency response?
can you point me where i can find calculators or formulae to find out the values of RCL components.
No,
if the speaker designer designed the driver and crossover combination to give an apparent flat sounding frequency response, without using a Zobel across one and/or other driver, when fed a flat electrical signal (i.e. flat with respect to voltage), then adding a Zobel does two things.
It reduces the efficiency of the speaker. Not at all popular nowadays. The Zobel also reduces the voltage seen by the driver at the Zobel's frequency. This creates a dip in the frequency response.
i am following the method as explained in below link to design passive crossover.
Passive Crossover Network Design
this article strongly suggests addition of zobel network.
Speakers are often/normally expected to get an even handed drive voltage at all frequencies. It doesn't mean their response will be flat.
If an amp has zero output impedance then the impedance variations will not change the drive voltage and so there should be no effect in adding a zobel across the amp.
If there is a finite output impedance then adding a zobel may increase the total current but the speaker itself will not accept any more than without it, in fact due to the reduced drive voltage it will pass less current.
There would be a couple of preferrable options if you're interested, one is to measure the drivers' impedance then simulate the values, the other is to simply measure the total impedance while you try different values.
the Zobel in a speaker is normally between the crossover and the driver.
The effect of the Zobel is to reduce the impedance seen by the crossover to below what the driver alone would show. The Zobel only does this over a narrow band of frequency. That's why it is used for EQ and similar corrections.
When the Zobel is used as an EQ style correction it must by definition reduce the voltage delivered to the driver over that small range of frequency.
i.e. it reduces the efficiency of the speaker.
If the speaker can be made to sound flat, without an efficiency reducing Zobel, then adding a Zobel will reduce the output over that narrow range of frequency, i.e. introduce a dip in the voltage frequency response.
you are not understanding the text or the text is badly written and causing that confusion.
I have not read it, so I can't know which of those alternatives apply.
I have quickly scanned through the first few paragraphs and this jumped out at me.
That confirms what I am saying. Zobels reduce efficiency.
It also confirms what I also alluded to. Zobels reduce the effective impedance.
Taking those two together, they are generally not used in modern designs at the cheaper end of the market.
They reduce the apparent sensitivity compared to competitors.
They increase the cost compared to competitors.
I will tentatively suggest that Zobels will only be introduced as a last resort to cure a response peak that cannot otherwise be overcome (and thus improve sound quality), or to flatten the impedance so that the crossover can better share out the frequencies (and thus improve sound quality) or to flatten the speaker impedance to make the speaker more suitable for use with amplifiers that have a high output impedance, i.e. with tube and valve output stages, particularly if they are of low or zero global NFB (and thus improve sound quality).
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i would like to go with the first option as i dont have to experiment with different component values.
Yes indeed.
The crossover deliberately increases the impedance outside the wanted passband.
This reduces the power/current fed to the driver outside the passband. Importantly this applies little load on the amplifier when another part of the crossover is within it's passband. That can be said another way. Each driver and its part of the crossover, only draw significant current in their own passband.
The crossover deliberately increases the impedance outside the wanted passband.
This reduces the power/current fed to the driver outside the passband. Importantly this applies little load on the amplifier when another part of the crossover is within it's passband. That can be said another way. Each driver and its part of the crossover, only draw significant current in their own passband.
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