2-Way 24dB/oct Linkwitz-Riley Crossover (part 2)
The pcbs finally arrived. The photo above is with it fully populated. I laid out the the components exactly like in the schematic. This will make it easier to understand the circuit.
On the left is the Balanced Input. If you are using unbalanced, jump a wire from the -ve to the 0V and connect your RCA to the +ve input. That’s how you convert a balanced input to single ended.
Immediately after the balanced input is the Gain Adjustment. That’s the 1st potentiometer. It is basically a Volume Control with a gain of 1. From here on, the signal takes two paths.
The op amp at the top is for the High Pass network while the bottom is for the Low Pass. The component values are very easy, all resistors are the same values as are the capacitors. This will help builders as I will not be supplying the components, only the pcb. With these values, the result will be a 24dB/oct Linkwitz-Riley High and Low Pass.
The output of the High Pass is fed to a Delay network. This is to delay the tweeter for time alignment. The 2nd potentiometer is used to adjust the delay. After the delay is a volume control to adjust the volume of the tweeter. This is done with the 3rd potentiometer.
Testing Out the Crossover
Out of convenience, I used the Soliloquy-IIb for a test speaker. This speaker is based on a 5″ Tang Band W5-1685 woofer mated with a Seas 27TBFC (H1212) tweeter.
I could have used another speaker, just that this one has the woofer and tweeter mounted and the passive crossover had already been dismantled.
This is a Biamp setup, so one channel is used for the tweeter while the other is for the woofer. I selected the resistor and capacitor values for a crossover of 2,400Hz because it’s a comfortable crossover point for most 1″ dome tweeters. The Seas 27TBFC will not sound stressed at this frequency.
Fig 1 – Sum of Tang Band W5-1685 with Seas 27TBFC at 2,400Hz (24dB/oct Linkwitz-Riley)
The Blue plot in Fig 1 is with the tweeter wired in normal phase. The Black plot is when I flipped the tweeter wires around. What this indicates is that there’s more cancellation when the tweeter is wired in phase.
Fig 2 – Tang Band W5-1685 Low Pass and Seas 27TBFC High Pass
The plots in Fig 2 are of the woofer low pass and the tweeter high pass. No passive components are attached to the drivers. The power amplifier outputs are directly connected to the woofer and tweeter. From here, we can see the ease of achieving a 24dB/oct slope when it’s done actively. It would have taken a lot of passive components and many hours of my time to get this.
Fig 3 – Null response
The Violet plot in Fig 3 was achieved with the tweeter wired in phase and the delay adjusted for the deepest null. It took me only a few minutes to dial in the alignment. I can assure readers that it’s not so simple with a passive network.
Fig 4 – Time-Aligned Soliloquy-IIb
For correct summing, I flipped the tweeter wires around, that is the Seas 27TDFC is now wired in reversed phase. Fig 4 shows the final time-aligned frequency response of the Soliloquy-IIb.
Auditioning the Crossover
I’ve been listening to the Soliloquy-IIb with this electronic crossover for a few days and it’s totally transparent. There’s no veil. No loss in dynamics. The music is as pure as can be. I don’t think it can get better than this.
I will be placing an order for 50 pcs of this crossover pcb soon. Price is $24.90 per pcb plus shipping. You will need 2 pcbs for stereo. If you are interested, let me know and I’ll reserve the pcbs for you. I will contact you when the pcbs are in stock.