Active crossover in Linux with the amazing TI chip amps
You’ve probably noticed that many speakers have more than one uh, speaker. These speaker systems are called 2-way, 3-way, 4-way, and so on depending on how many individual speakers, or ‘drivers’, they have.
Multi-way speaker systems usually split the incoming signal into several signals tailored to each driver in the cabinet. The woofer gets low frequencies while the tweeter gets high frequencies. This way, the tweeter doesn’t ineffectually try to produce bass notes (this will produce distortion and could actually damage the tweeter) or vice-versa (woofers “beam” high frequencies unpleasantly).
The component that splits the sound up is called a crossover.
Passive vs active crossovers #
Passive speakers have a passive crossover. This means that they take away unwanted frequencies post-amplification, using passive analog components like resistors and capacitors. Passive crossovers are not only inefficient, but limited by the capabilities of (expensive) high-voltage analog parts since they operate in the post-amplification analog domain.
Passive speakers have plain wire inputs marked + and -.
Active speakers have an active crossover. Each driver in the speaker cabinet is separately amplified, which is more efficient and introduces less distortion. Active speakers also allows for digital crossover implementation. Digital crossovers can create cleaner sounding, steeper filters which reduce the sonic overlap, or crosstalk between drivers. A digital crossover may also compensate for non-linearities in the drivers and perform room correction.
Active speakers have line-level inputs like RCA, XLR, or TRS connectors. Digital crossovers may include coaxial SP/DIF, Toslink, and AES/EBU inputs, to avoid unnecessary DA/AD conversions.
Ingredients for active crossover #
Minimum: #
- multi-way speakers with well-chosen drivers
- 4-8 channels amplification
- fanless PC with SSD running Linux
- 4-8 channels DA on soundcard
- the necessary line-level and speaker cables
Recommended addons: #
- wired network connection
- analog, digital inputs on soundcard
- measurement microphone, preamp
- room correction software
The details of selecting any of these components is beyond the scope of this article, but let me give you an example.
Infinity Kappa 8 active crossover #
Backstory #
In 2008 I purchased some Infinity Kappa 6 (~1989) speakers, to replace the Tannoy System 10 (~1994) I had been using at my recording studio.
Right away, I fell in love with the highly dynamic and fast sound of the 3-way speakers. Tweeters tweet, woofers woof, and mids sing with lower distortion. The larger, sealed cabinet made for a smoother, deeper, and ‘laid back’ low-end response impossible with ported designs.
I wanted to use the Infinity Kappa 6 for mixing and mastering, so I replaced the (very good!) Polydome midrange drivers with Dynaudio D52AF soft-domes. The result was quite good, but I felt that the low-mids were being compromised by the lowish crossover frequency (< 400hz). I restored the Polydomes to the Kappa 6’s and traded up to the Kappa 8 for a few hundred dollars more. (Gotta love craigslist!)
The Kappa 8’s have served me well for the past 5 years. Factory crossover frequencies of 80hz, 800hz and 4500hz integrate the drivers fairly well, provided you’re sitting in the right position. But when moving around, there could be nasty phase issues between the 8 separate drivers.
- broken crossovers removed
- tweeters replaced: hivi rt1c-a
- hi-mids replaced: dynaudio d52af
- TPA3116 * 12 channels = 600W total class-D
- Meanwell 24V DC psu * 2 = 1000W total
- Intel e6600 PC, underclocked w/ passive cooling
- Arch Linux w/ alsa, jack, zita-lrx, zita-njbridge, jconvolver
- ASUS Xonar HMDI1.3 / H6 soundcard
- the $30 Vantec USB 7.1 also works great
- bought several $2-$15 usb soundcards on ebay, will review soon
edit: Upgraded amps:
- 6 channels TPA3116 for the tweeters (50wpc) and hi-mids (bridged for 100wpc)
- 2 channels TAS5613 for the low-mids (150wpc)
- 2 channels TAS5630 for the woofers (300wpc) the best chip amp
- total power is now 1200W @ 10% THD (which I never, ever hit)
- THD much lower (<0.03%) at normal listening volumes