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PostPosted: May 23rd, 2023, 1:13 am 
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When buying or building passive crossovers, how do you figure out at what crossover point you choose?

What is the deciding factor in choosing (example) 2.5k, 3k, or 3.5k? Woofer size? Horn or tweeter? Etc?

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PostPosted: May 23rd, 2023, 8:26 am 
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There is no simple answer. Everything depends on the specific drivers you are using, their characteristics and limitations. Also depends on the physical arrangement of the drivers on the speaker baffle and the desired acoustical response of the system. The most important factors to select is the crossover point are:

1 Operate the drivers within their bandwidth and above their low frequency resonance frequency (except for the woofer, where the enclosure performs that function) to protect the drivers from being physically or thermally over driven. Tweeters do not take much power to blow them. Usually you want to cross over the tweeter at least an octave above this resonance (i.e., for a tweeter whose LF resonance is 1000Hz, the lowest crossover point should be 2000Hz). Often you need a steep crossover to protect the tweeter. If you are using a simple first order crossover, you will need to crossover the tweeter at a higher frequency (i.e. two octaves or more) provide enough attenuation, at the penalty of needing to operate the woofer too high for clean response.

2. Cutoff the low frequency drivers below cone breakup and response roll-off. (with a few well behaved wide band drivers, may not be necessary, i.e., the classic Dynaco A25 where the 10" woofer is operated full range). Generally, with simple two way speakers, a smaller woofer is better since the cone breakup is high enough in frequency to better match where the tweeter needs to be crossed over.

Obviously, you need response data on the drivers you are using to select the best crossover point. Either published data supplied with the drivers OR measured data.

The actual crossover point is a compromise. Using higher order crossover will help you operate the tweeter lower and the attenuate the ragged woofer response at the top, but increases the complexity of the network and introduces phase and lobing effects. The actual design of the crossover needs to account for driver impedance and efficiency to both match the driver levels and select the component values for the network.

This is just the general concept.

David


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PostPosted: May 23rd, 2023, 2:00 pm 
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Great advice David. I would add that it is important to know the true impedance of the drivers at the crossover point because the stated impedance is usually an average across the frequency band. For example, one of the 12" drivers I use has a stated impedance of 8 ohms but at the desired crossover frequency of 200 Hz, it was actually 13 ohms. That will totally alter the calculation of component values.

Here is a site I use for calculations:

https://www.v-cap.com/speaker-crossover ... Calculator


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PostPosted: May 24th, 2023, 2:32 pm 
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On the cheap side of things: does it matter if you use a pre-made two-way crossover or use a pre-made high pass crossover plus a pre- made low pass crossover in parallel (assuming crossover point is the same)?

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PostPosted: June 5th, 2023, 3:33 pm 
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If you have a 6 ohm driver, is it better to use a 8 ohm or 4 ohm passive crossover in a pinch?

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PostPosted: June 6th, 2023, 12:59 pm 
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Usually, a 6 ohm driver (DCR) is considered a nominally 8 ohm driver.

David


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PostPosted: June 6th, 2023, 2:59 pm 
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The electrical load a speaker in a cabinet presents (or not even in a cabinet) is a lot more complicated than a circuit containing a resistor, inductor, and capacitor

https://testhifi.com/2019/02/11/acousti ... impedance/

If you forget about the radiation impedance (which you need to calculate the speaker efficiency) and the cabinet, the driver is an electro-mechanical transducer so in addition to the resistance of the voice coil and the stopped inductance (when the coil is not moving) of the voice coil their is the moving mass of the speaker which looks like an inductance and the spring constant of the speaker suspension that looks like a capacitance. The cabinet, ports, and damping material would introduce additional capacitive, inductive, and resistive circuit elements.

https://audiojudgement.com/speaker-equivalent-circuit/

Since you are not limited anymore to paper, pencil, and a slide rule like the old days there are many free circuit analysis programs available that you could do a very good circuit representation of your speaker driver, cabinet, and crossover.

To do better you would have to get into programs that can do finite element analysis.


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