Speaker crossovers

Vaughan

Member
2004-01-04 9:51 am
Hi guys,

I was having a discussion with a guy on another forum where he told me that the crossover in a receiver can interact with the passive crossovers in the speaker.

Now I don't know how this would be possible. So for example, if you chose a 100 Hz crossover in your amplifier, 24 dB/octave low pass (which most low-pass filter slopes are), how would that interact with a speakers internal passive crossovers?

Is this guy clueless, or does he have a point? :confused:
 
yes, you're right and your friend is wrong ;)
Once the signal is being processed, then amplified and delivered to the speakers, what the terminals 'see' is just the output devices, so it's just a matter of damping factor ( internal resistance/ speaker resistance) .

About the crossover point, it depends on the design. A tweeter is asked to
vibrate very fast and to reproduce very short wavelenghts, and it usually
reproduces frequencies above 1K2 Hz or something near
 

Vaughan

Member
2004-01-04 9:51 am
What would a typical small speaker like a bookshelf speaker be crossed over at? The woofer, I mean?

I mean if a speaker had a low-pass filter to the woofer at 500 Hz and the amplifier had a 500 Hz crossover then I imagine in this hypothetical example there would be interaction. Correct?
 
You would hear only bass and mid-bass. You'd have to specify if the slope is rising or descending, i.e. high pass or lowpass.
In the case you mentioned, you'd just preclude to the woofer its abilty to reproduce the mid frequencies, which would result in a very dead sound. That's why a 3 way is the best, because of the right relation between driver's diameter, and the tweeter being asked to reproduce only above 5 KHz, and having a dedicated driver for the 'central' band. Nowadays the crossover point between a woofer and a midrange is put in the 200-400 Hz range, being it about 500-800 Hz for older designs, which is not very good because you'd truncate each driver's emission in a very delicate zone, where/when the ear is very sensitive, being it the vocal range .
 

Vaughan

Member
2004-01-04 9:51 am
Okay I'm just trying to understand this better. If I set a crossover of 100 Hz on my receiver then it can't interact with the crossover in the speaker because the frequencies the drive units are crossed over to are outside the operating bandwidth of the receiver.

Is that it in a nutshell? If a bookshelf has it's woofer low-passed at 200 Hz then if I selected a 150-200 Hz crossover would that not cascade or interact negatively?
 

LJNorth

Member
2011-11-14 2:00 pm
Winch
Any series deployment of crossover networks, active or passive, can and will interact to change phase and amplitude response. The magnitude of the interaction depends on how much overlap in frequency there is and weather you can detect the interaction, this is really a question of specific application.
 

Vaughan

Member
2004-01-04 9:51 am
Are you saying then that the active receiver crossover can interact with the passive crossovers for the drivers in the speaker? How is that possible?

If you choose a 100 Hz crossover in a receiver what speaker arrangement would that affect in terms of its own internal crossover? My understanding is that for crossover slopes to combine/subtract they both need to be operating in the same range.

So if I have a speaker that has a woofer low-passed at 400 Hz and I use a 100 Hz crossover then by the time it reaches 400 Hz the level of the slope would be like over 70 dB and would not affect anything. Correct me if I'm wrong.
 
Last edited:
You say low pass in your first post, why would you low pass bookshelf speakers unless you only want them to play bass or be an inefficient subwoofer? Assuming you mean high pass (i.e. the amplifier connected to your bookshelf speakers has an active hi-pass filter to cut the bass frequencies for power handling reasons) then you may need to consider the interaction of the bookshelf’s natural LF acoustic roll-off and the filter (both are filters one is electronic the other mechanical), the interaction of the active filter and your passive crossover filter is most likely minimal because of their frequency separation.
 
So if I have a speaker that has a woofer low-passed at 400 Hz and I use a 100 Hz crossover then by the time it reaches 400 Hz the level of the slope would be like over 70 dB and would not affect anything.
Correct the interaction is minimal because of the likely frequency separation, mathematically the signal is always there just smaller and smaller and smaller.
 

Vaughan

Member
2004-01-04 9:51 am
Well if you set a crossover of 80 Hz on the AVR and the low-pass is 24 dB octave then if your woofer is low-passed at 300 Hz passively the slopes cannot combine or interact negatively. That's what I'm asking and I think you are agreeing with me.

If the low-pass was 12 dB on the speaker at 300 Hz then the slope of the AVR isn't going to add to 24 dB by the time it eventually gets to 300 Hz.

If you use a high pass at 80 Hz then bass below 80 Hz will be sent to the sub. Understand that. But it still would not cascade or interact with the speakers passive crossover. That is what I'm asking, not the acoustical roll-off.