Audio crossovers and variable resistors

Thread Starter

WickedCircuitz

Joined Oct 27, 2020
1
Would it be practical to connect potentiometers to 1 or all of the out puts of a 3-way crossover? Reason being, for example; 1 on the low output to control how much power is sent to the subwoofer, to decrease/increase bass. If so, I am assuming linear? And 10k ohms? Question 2: what would be ideal for volume pots? 5-10k ohms? Logorithmic of course. And would this be the same for low-power as well as home theater systems (5 watt vs 1k watts)? Last question: is there a name for the type of transistor I need for ... Let's call it a frequency activated transistor; something that would open a 4v circuit to LEDs at a set 150 hz frequency (LEDs that light to the beat)? Any help is appreciated
 

Ian0

Joined Aug 7, 2020
1,861
Is it an active crossover? (Most of them have level controls)
or a passive crossover inside the speaker cabinet?
 

Dodgydave

Joined Jun 22, 2012
9,936
Cross overs usually use Capacitors and Inductors to tune the frequency response crossing of each speaker,
Best to give the model number of the unit you have or better still post pictures of the inside.
 

KeithWalker

Joined Jul 10, 2017
1,667
The description of your requirements is rather difficult to understand.
1. Do you want to control the sound output from each speaker connected to the crossover unit?
2. Or do you want an adjustable signal output from each to use with an external device like a color organ?
If it is #1, it is an odd way of going about a simple task that can be achieved by adjusting the tone controls of your sound system.
If it is #2, there are lots of free designs for color organs of all types on the internet.
Or, maybe I misinterpreted your requirements from your vague description.
Regards,
Keith
 
Last edited:

Tonyr1084

Joined Sep 24, 2015
5,856
1 on the low output to control how much power is sent to the subwoofer, to decrease/increase bass. If so, I am assuming linear? And 10k ohms?
Search "L-Pad". It's an 8 ohm variable resistor. You don't want linear and you don't want more than 16 ohms (I believe). This should answer your second question as well.
Question 2: what would be ideal for volume pots? 5-10k ohms?
https://www.amazon.com/Parts-Express-Speaker-L-Pad-Attenuator/dp/B0002KR1EQ/ref=sr_1_5
 

Ian0

Joined Aug 7, 2020
1,861
Another L-pad
https://cpc.farnell.com/monacor/lp-...aMNFAVs2czGQEooUfJ7vhzWVXxWUD7UhoCc48QAvD_BwE
You need an L-pad because it keeps the impedance constant as the level is varied. The crossover will be designed for one specific impedance, and won't operate properly if the loudspeaker impedance is changed.
Generally, the midrange and treble transducer are more efficient than the bass, so only two L-pads will be required, and they will be in the midrange and treble.
If it is #1, it is an odd way of going about a simple task that can be achieved by adjusting the tone controls of your sound system.
Tone controls are first-order filters. Crossovers are generally 2nd-order or higher. A tone control can't correct the error due to mismatching of the levels between individual drivers in a loudspeaker. A graphic equaliser might.
 

MisterBill2

Joined Jan 23, 2018
8,408
There are articles spelling out exactly how to create passive L-C crossovers. The articles go back to the 1960's era, so there are a whole lot of them. And there is more math involved in some of the determinations than you can imagine. And creating a linear sound level versus frequency output is a big deal, really. It really requires an output versus frequency versus efficiency and impedance plot, or equation for each speaker.
 

KeithWalker

Joined Jul 10, 2017
1,667
Tone controls are first-order filters. Crossovers are generally 2nd-order or higher. A tone control can't correct the error due to mismatching of the levels between individual drivers in a loudspeaker. A graphic equaliser might.
Maybe you should have included this information in your original posting. It would have got much more useful responses.
Mister Bill is correct. If you don't do a thorough frequency and phase response for each speaker with it's associated crossover network, you are blindly applying band-aids and have very little chance of finishing up with a really good sound system.
Regards,
Keith
 

MisterBill2

Joined Jan 23, 2018
8,408
An excellent reference is the "Radiotron Designer's Handbook", which includes a large amount of information and thousands of references. It does date back to the sixties, so it includes mostly tube circuits, but passive L-C crossovers for speakers are the same no matter what the driving source.
 
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