question about bass blockers

[MrSwiss 10+ year member]

now i know that a 4 ohm mid and a 4 ohm tweet will not equal a 2 ohm load on a crossover, but it will if using an inline crossover yes? because it is only stopping the tweet from getting low notes, but not stopping the mids from getting high notes.

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[helotaxi 5,000+ posts]

The mid will naturally roll off because of impedance rise cause by the voicecoil inductance. At the overlap between upper rollof of the mids and he lower rolloff of the tweeter, the amp will see somewhere around 4 ohms in a perfect world. It doesn't really end up working that way though.

Simply wiring a cap inline with a tweet is a sure recipe for toasting it. Because there is a spike in the impedance of a driver right at its resonant freq and the crossover function of a capacitor is dependant on driver impedance, the resonance spike creates a spot where the crossover doesn't work as advertised. This is the reason that most purpose built high end crossovers have a Zobel circuit in line with the tweeter. The Zobel circuit resonates opposite the tweter and levels the impedance curve so the crossover filter behaves predictably.

 

[MrSwiss 10+ year member]

X_X

so what u r saying there is no cheap way out of it. im gonna have to buy a crossover. >=/

 

[GordonW 10+ year member]

X_X
so what u r saying there is no cheap way out of it. im gonna have to buy a crossover. >=/

Pretty much.

Though, if you put the crossover point AT LEAST 1.5 octaves ABOVE the resonance of the tweeter (ie, if the tweeter resonates at 1500 Hz, then crossover NO LOWER than 4500 hz) then you can usually ignore the tweeter resonance. That's about the only exception. However, that usually wastes the potential response of the tweeter... it's usually MUCH better to use a second-order (12 dB/oct) highpass on the tweeter, so you can take it lower (and usually blend with the midrange/woofer better), safely...

Regards,

Gordon.

 

[MrSwiss 10+ year member]

well the blockers i ordered....(b4 starting this thread btw).... they are crossed at 5khz.

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=266-190

these are going to be used on my lpg 25nfa's

resonance value is 1800hz for them. so it looks like i am in the safe zone ^_^

 

[MrSwiss 10+ year member]

i have installed them. the tweets sound great so far. im not getting any low notes just as planned.

these little things are pretty nice build quality. these in line xover's.