Zaphaudio SR71 with 4 ohm ER18RNX

[bcrazy]

Going to build this speaker
I have gotten hold of 2 Seas ER18RNX, but in 4 ohm version

Can i just half the inductor and double the capacitor for the woofer crossover?
Or is it more complicated?

 

[YSDR]

It's a little more complicated if you want the same rresponse as with the 8 Ohm version, mainly because the 4 Ohm driver's impedance is probably not half of the 8 Ohm driver, and you need to set the tweeter level too to the more sensitive driver.

 

[AllenB]

Can you provide a link to the datasheet for the 4 ohm version?

8 ohm version.

 

[bcrazy]

No unfortunately not, i can email Seas and ask.
I can measure the impedance curve.
If it then turns out to be roughly the half of the 8 ohm, then adapting the crossover, should be straight forward?

 

[Ugg10]

From what I understand just matching the impedance is only the start. It will have a different sensitivity (fairly easy fix) but the TS parameters will be different so box size and tuning will be different.

Example - using the mh-audio bass reflex calculator as a quick estimate with a similar driver -

Satori MW16p-4 = 13.3l box, f3 of 50hz with 5cm diam x 22cm long port and spl 88dB (flat response)

Satori MW16p-8 = 24.7l box, f3 of 39hz with 5cm diam x 15cm long port and spl 87.5dB (flat response)

 

[AllenB]

There is also the response around the crossover to compensate for. This is why putting two manufacturer plots side by side shows the differences well. So would you measuring the response of each type in the same baffle.

 

[bcrazy]

Measured the impedance curve. Seems to pretty much be about halv the impedance of the 8 ohm version, apart from peaking at a higher fs

 

[TMM]

T/S parameters look way different to the 8ohm version. You're probably going to get a peaking midbass and a lack of lower bass in the enclosure designed for the 8ohm version. It'll probably want a sealed enclosure that is 20-50% larger. Vented enclosure will need a total redesign.

Aside from that, make all inductors and resistors in the woofer section half the value, make caps in the woofer section twice the value.

Adjust R0 to between 1-3ohm to set tweeter level to match.

 

[bcrazy]

yes i see the t/s are different, but forgot to mention that i plan to use it in a sealed enclosure, and i will pair it with 2x8" vifa woofers below 100 Hz

 

[bcrazy]

How dos this look?
Do i need to put a high pass section before the mid-woofer? It will be in a sealed box of 5 liters.