2-Way 24dB/octave Linkwitz-Riley Electronic Crossover

2-Way 24dB L/R Crossover

I have about five electronic crossovers from different manufacturers and not one am I completely happy with. The only reason I use an electronic crossover is because it’s a quick way to listen to the drivers before I commit on designing the passive crossover. Now that I’ve mastered passives, I’m turning my attention to electronics. There are things that passives are good at. Where it’s weak, I have no issues using electronics as long as it doesn’t compromise the sound. My Bass EQ project is one of them. This 2-way crossover is another.

First off, this crossover is for one channel only. There are good reasons for doing this. One is it can be installed inside a speaker as in an active bi-amped speaker. Alternatively, two pcbs can be mounted in a standard 19″ case as in a conventional outboard 2-ch crossover.

Coming to the design proper, the line input is balanced. This is mainly for professional applications. Following the balanced amp is the gain control. After this, the signal is directed to the high and low pass networks. The filters are fourth order (24dB/oct) Linkwitz-Riley types. 

It is at this juncture that I departed from the norm. The crossover uses fixed resistors instead of a potentiometer to set the crossover frequencies. I prefer this method because I find the normal potentiometers degrade the sound quality. An exception is stepped potentiometers. But then again. we are back to fixed resistors because that’s what a stepped attenuator is, a series of fixed resistors.

Forgoing the crossover tuneability is a sacrifice I’m prepared to make for better sound. I can still set any crossover frequency I want by selecting the right combination of resistor and capacitor values. Since I have enough 2-way designs, I will select a few popular ones for active conversions. This will circumvent the cost of the passive crossovers.

A very important feature in this crossover is a delay network in the high pass section. In my collection of crossovers, the delay is in the low pass. I can’t blame the manufacturers because those crossovers are meant for pro sound systems. Most of the speakers have horns for the treble. Because of the depth of the horn, the woofer is ahead of the tweeter. So for proper phase alignment, the woofer needs to be delayed.

In hifi speakers, the majority of tweeters are domes. So, the situation is now reversed. It is the treble that reaches the listener first. Therefore, for proper phase alignment, the tweeter must be delayed, not the woofer.

An added advantage of having this delay is that I won’t need to resort to using a step or sloping the front baffle to align the tweeter with the woofer. I can simply dial it in. Once I lock the phase in, I can replace the potentiometer with a resistor. Of course, this is dedicated to one speaker design only. However, if the user has some means of measurement, then the delay can be left tunable. 

At the end of the high and low pass networks are the line amps to interface with power amplifiers. I left the outputs unbalanced for hifi. For the high pass, I made the output adjustable. That’s because the sensitivity of tweeters are often higher than woofers. Moreover, some power amplifiers don’t have any volume controls at the front that one can use to lower the tweeter volume. If there are no means of adjusting the high pass output, that amplifier cannot be used. 

The pcb above is what the crossover looks like. As before, it is double sided. I incorporated ground planes at the top and bottom for better grounding. This crossover uses five dual op amps in total. For stereo, you’ll need two pcbs. The board measures about 8″ by 2.5″. It is quite compact considering the features.

I’ve been meaning to design this crossover for years. It’ll be interesting to see how it performs. I will update this post when my pcbs are delivered.