First Crossover

[Drevlin]

Hi new here. I am trying to come up with my first crossover and for some reason I haven't started small. I am having trouble with figuring out nominal impedance. I want to know from the Xover I have drawn, what I would be looking at for ohms but I dont know how to add this. Here is the xover I threw together (I have a feeling it is poor). first off is this even a good idea for a crossover and any advice to make it better or to work would be greatly appreciated. I have no cap values yet as I have not made a decision on frequency's. I do have drivers picked out.

4 of these Parts-Express.com:Peerless 830656 5-1/4" Paper Cone SDS Woofer | Peerless SDS 830656 5-1/4" Woofer bass mid midbass mtm coated cone 2-way tymphany09
1 of these Parts-Express.comayton DC28FT-8 1-1/8" Truncated Silk Dome Tweeter | tweeter dc28f-8 silk dome tweeter dome tweeter soft dome dayton audio dayton loudspeaker dayton dayton silky daytweet-41108 DT010109 DayAudiTweetWoofMid050109

[PeteMcK]

there may be some helpful pointers for you in this:
design 2 way crossover - diyAudio

[NagysAudio]

Drevlin,

First, read this entire article very carefully: Passive Crossover Network Design
Second, using formulas will only give you an approximate/theoretical crossover and if you were to measure the speaker it's ALWAYS going to be different. This is just an extremely primitive way of building a speaker.

To get the impedance... For example lets say the tweeter is Rvc=6 ohm, since you're using a Zobel (Zobel is mandatory for all drivers), its impedance will remain a constant 6 ohm, more, or less. The best way to guesstimate this is to use an ohm meter and measure the Rvc of the tweeter, then use these formulas to figure out the Zobel:
R=Rvc
C = 1 / ( 2 π f Rvc )
f = Rvc / ( 2 π Lvc )

Do this for all the drivers.

[Drevlin]

so I read through a good amount of the article and see that Zobels will flatten the impedance of a speaker. so an 8 ohm would stay 8 ohm relatively. but in my schematic I have 2 sets of 2 woofers in parallel which would drop them to 4 ohms (correct?) so if I have 2 sets of 4 ohms and and 8 ohm tweeter all with zobels they stay at 4 at 8 respectively?

[PeteMcK]

re:'if I have 2 sets of 4 ohms' - yes, you'd have 4ohms nominal, and you'd use one zobel across both drivers...

But essentially your crossover is a 2.5 way; a better way to connect the bass drivers
is how Zaph's done it here: Zaph|Audio
(you'd put your C1 in series with your mid drivers)
means you can use a lower value inductor for L1, (& tweak it for Baffle step compensation).

[Drevlin]

ok I think I only have one last question. voicecoil inductance: How does this effect desinging a Zobel circut if I have 2 speakers wired in parallel or series?

[PeteMcK]

Inductors sum the same way as resistors, so add values in series (assuming there is no interaction between the coils - need to keep them physically separated),
in parallel, you find the reciprocal of the sum of reciprocals of the individual values -
(1/Lt = 1/L1 + 1/L2 + ...)
if they are the same value, two in parallel come to half the impedance of an individual inductance