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WWill my 6 ohm tweeter be 9,3 ohms.


Leo Veto
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You would design for nominal 6 ohm.  The 3.3 ohm resistor you have added,is already part of the crossover network and is adjusting tweeter level to be lower, relative to other loudspeaker(s) you are using.  

 

You need to make yourself a diagram of how you have the 3.3 ohm configured, as there are 3 options, the middle one being the most likely way you have it presently wired. 

Tweeter Question.pdf

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1 hour ago, Leo Veto said:

The resistor is in series with the + terminal and then goes to the cap. in a simple 1st order network.I thought the tweeters 6 ohms would add and sum with the resistor.

No because the tweeter is not a resistor - although it can be measured with resistance, it is principally inductance of the speakers coil, where the term henries or increments of henries could measure its inductance.  But that's way too simplistic, as the speaker also has many other properties when the coil is placed within the flux of a magnet, then exhibiting electromagnetic force to the incoming signal, when it vibrates , so the speaker itself is never included when calculating frequency.  

 

Rather we use resistors inductors and capacitors as passive components to cause  accurate calculation of  low pass and high pass filters that can control the requirements of the speakers ability to reproduce its needed frequency response.  We can see one of the formula's here  https://en.wikipedia.org/wiki/RC_time_constant

 

 

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Thanks a lot.So it seems I must choose a cap which will give me the frequency for 6 ohms and not consider the 3.3 ohm resistor as anything but the volume reducing component.Heve I got it right?. Thanks again.

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Hi, For tweeter attenuation in passive crossovers I usually use an Lpad rather than a series R, though a single series R can be used if you want less attenuation at the very top end response where the tweeter imp increases ( extra sparkle for us oldies ? )

 

https://www.diyaudio.com/forums/multi-way/242206-lpad-single-resistor.html

http://techtalk.parts-express.com/forum/tech-talk-forum/20969-l-pad-vs-series-resistor

 

cheers

 

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On 24/08/2020 at 5:19 PM, Leo Veto said:

Thanks a lot.So it seems I must choose a cap which will give me the frequency for 6 ohms and not consider the 3.3 ohm resistor as anything but the volume reducing component.Heve I got it right?. Thanks again.

The capacitor is chosen for its ability to block lower frequencies, and pass high frequencies. you need to choose the frequency you need, and the rate at which the frequency begins, expressed as decibels per octave.   There is some excellent help here:    https://sound-au.com/lr-passive.htm

 

Regarding your ongoing question about allowing for the speaker, the article reaffirms, as explained in a earlier post  that it is the speakers inductance rarely quoted by manufacturers,  that will be a bonus to know.

 

The requirement is to know the loudspeakers impedance. Impedance is a complex term, different to resistance   https://en.wikipedia.org/wiki/Electrical_impedance   , but wrongly sometimes thought of as the same thing.  Impedance, encompasses magnitude the same as resistance but introduces phase that enables AC analysis, and includes including resistance inductance and capacitance.

 

"3.1   Speaker Impedance

One area where measurement is essential when designing passive crossovers, is the loudspeaker driver itself.  There is usually very little information in the makers' data that will prepare you for the behaviour of a loudspeaker / crossover network combination, and these data are usually derived empirically.  In some cases the voice coil inductance will be quoted, and if so, this may be a bonus, as will be shown shortly."

 

Loudspeakers in audio systems enable vibration of cones, planar diaphragms and other forms in partial sympathy with the voltage amplification afforded by amplifiers. each are signal AC devices, hence relegating loudspeakers in terms of only DC resistance measurement ( like the speaker is 6 ohms ) usually ignores their actual function as processing signal AC.

 

Where it gets confusing is both reactance (AC) and resistance (DC ) are expressed as ohms . What is needed is to always to define the loudspeakers actual impedance.  A graph see image, comparing to frequency reveals the true behavior.

 

It can be seen impedance varies  related to frequency.  Hence knowing the true impedance behavior is far more valuable, as nominal figures such as referring to a speaker as 6 ohms ( and no other figure ) misses essential design information.      

 

 

 

 

 

 

   

 

 

Kef LS50 impedance graph.jpeg

Edited by stereo coffee
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