Introduction to designing crossovers without measurement

[jimk04]

Hello forum

Having read the main elements of this thread, I am readying myself to try this method on my first 2 way speaker build.
Before I go further here with the details...what is the number we use to determine tweeter attenuation level down -9db.? I have a hot tweeter and may well use BSC of -3db on the woofer.
The numbers stop at 6db.
Thanks

[picowallspeaker]

Go to Level Calculator
Strassacker: speaker - kits - tools
(it is comprised also in CRossover Calculator )

[jimk04]

Thanks for that.....good link. If I use a zobel to flatten impedance do I still use the tweeter nominal Z or the new Z?

[AllenB]

Does your Zobel cover the whole tweeter range, or just the upper rise or lower peak? Is it after the L-pad or before? Or, if you haven't decided yet, what do you want to achieve with this Zobel?

[jimk04]

I am not really sure. Following your example and my tweeter is 6ohm...adding a 10R for example gives me 3.75ohm.....as in your example. So would I put 6 or 3.75 into the calculator linked above.

My tweeter has an Fs of 720Hz with a peak of 18/19ohms at this point.

[AllenB]

It sounds as though you are putting the resistor in parallel then wanting to add the L-pad. Can I suggest instead, just use 6 ohms in the L-pad calculator and don't worry about any of the other resistors. Ie: just the two that the calculator suggests.

Doing this will have the same effect of reducing impedance variation around tweeter resonance.

[AllenB]

The word Zobel is often used differently by speaker builders. In electronics it has a common meaning ie: compensating for impedance variations so that a load (eg the whole load) looks like a simple resistor.

Often with speakers it is used to describe an RC circuit, like the one used on the woofer in this thread. This is only a part of what Zobel is intended to mean, and I ask for clarification. An RC circuit does little for a tweeter the way they are normally crossed.

More important for a tweeter is the impedance variation at the lower frequencies around resonance. The ultimate conjugate (makes it flat) is a series RLC circuit (bandstop, notch) across the tweeter, providing a simple platform for future tweaking. However the combination of a parallel resistor and second order filter, especially when tweaked, can bring the correct response.

[Piersma]

Hi,

Could the following assumption make sense?

A 10" woofer with a sensitivity of 90dB
A 5,5” midwoofer with a sensitivity of 86dB
Mounted on a 12” (30 cm) baffle
Baffle step frequency : 115/.3 = ca. 380 Hz

If the woofer and midwoofer are crossed at ca. 400Hz, and the bafflestep Is taken into account, would the SPL of the midwoofer roughly match the woofer?

[AllenB]

Thinking 'outside the box' this way saves you from attenuating the mid.

Each of the two drivers is affected by the baffle, each in more or less the same way. When you filter each you would be best to consider the effect this is already having, to subtract this from the filter you are adding.

To make this easier to visualise I ran a sim.

[I used 6dB difference to keep things ideal, you chose 4dB which is more practical. The difference is not clear cut which is why I avoided using 4dB for the sim.]

What this shows is what each driver response should look like (darker trace), vs the amount of filter effect required to achieve it considering the baffle effect. Eg: The first (woofer) plot shows that you need to cut more to compensate for the rising response. This can mean using a larger inductor, aiming for a lower cutoff frequency than first expected.

[Piersma]

hi Allen,

Thanks for your response and clear explanation.