Crossover circuit for a hybrid speaker I'm building

[borisxboris]

Hey guys,

I am a second year Sound Engineering student and am bulding a portable speaker for one of my modules.
I am combining a simple electrodynamic tweeter and an electrodynamic vibration transducer and one of the parts I'm struggling with is the crossover. The amp works with 3-8Ω load impedance, and both of my speakers are 4Ω, so they need to be connected in series. The problem is that I initially designed my crossover circuit (Second Order Linkwitz-Riley) to be in parallel and now I don't know how to make in series, and I'm also not sure if it's going to work.

I was wondering if you can take a look at my circuit and tell me what's wrong with it? Is this configuration correct? (needs to be in series) Do I need to change the values of the components now that they are in series?

I did research this, but couldn't find the answers I was looking for so a little help would be very much appreciated!

P.S. I am aiming for a crossover frequency of about 4.7-5 kHz

Thanks
Boris

 

[Fish4Fun]

Hey Boris! Welcome to the forum!

Passive crossovers....at best power sucking heaters....I can remember when....quite a long time ago....I was fascinated with "Hi Fi" (back in the 70's and early 80's)....passive crossovers bothered me then much as they do now....but back in the day, amplifiers were relatively expensive and copper was cheap....even then I chose to solve the "crossover problem" actively rather than passively.....and I would suggest as a "sound engineering student" you consider the benefits of putting the crossover upstream of the amplifiers....this approach has numerous advantages even in low-cost systems....and with the ready availability of "amplifiers on a chip" makes a great deal of sense regardless of system size....In the bad old days high quality speakers frequently shunted 50% or more of the input power in an effort to accurately reproduce the source, and still it was never difficult to find a source + volume that would "make them sound bad".....Properly sized magnetics and reliable, close tolerance capacitors are expensive....more expensive than amplifiers in most cases....combine this fact with the fact that speaker elements rarely behave linearly wrt (With Respect To) each other for more than a fairly narrow power range and "designing the perfect crossover" becomes little more than a an exercise in concessions for any condition not meeting the narrowly defined power range.....With an active crossover upstream of the amplifiers, non-linearity can be accomplished with analog compensation; digitally if precision is required....with active feedback in truly demanding environments....

A common practice in passive crossover design is the use of power resistors to dissipate power and balance impedance in an effort to make the speaker elements "more linear" wrt each-other and satisfy the requirements of generic amplifiers....from my perspective a somewhat draconian approach, but common none-the-less.....as an example: https://www.madisoundspeakerstore.com/xover-design ....certainly NOT linking this page as any sort of endorsement, simply an example of a "conventional passive crossover".....In the real world if you simply place the woofer and tweeter in parallel: the woofer with a series inductor and the tweeter with a series capacitor the speaker will likely sound just as "good" as any other compromise you settle on....I know...I know...in theory the impedance has the potential to damage the amplifier, and the math on of the frequency response will make an ugly graph....but it will still likely "sound as good" as a passive crossover with a more impressive graph....AND while I doubt seriously this approach will actually prove to be damaging to the amplifier, you could add a 2.0 Ohm power resistor in series, ahead of the paralleled-series elements if you wanted to "be safe"...as an added benefit you will add some extra heat to the room....

Sorry to be so negative on passive power crossovers, but I really cannot think of a scenario where they are the best or even the most cost effective approach....At least not in this millennium...

Good Luck!

Fish

 

[BobK]

Why do you think the speakers have to be in series?

When you use a crossover, the impedances will not obey the rules for parallel resistors because the crossover will make them high impedance outside of the range that they are handling. The impedance of two 4Ω speakers with a correct crossover should be still close to 4Ω.

Bob