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DIY Digital Crossovers Neil Davis July 18, 2009 Approaches Analog DSP separates Works well, but hard to achieve flexibility Stopped doing this ~2004 DCX-2496 (or equivalent) + amps Difficult to integrate with loudspeaker measurement tools Big, expensive & not DIY Integrated: amps with embedded DSP Uses amps developed for home theater systems (multi-channel) or for LCD TV’s Can be designed as a plate amps for making active speakers DIY: lots of flexibility and more fun Focus Area: Integrated DSP Audiodevelopers product range: Amps with DSP--Example Lots of Class D amps have digital biquads! Some Amps with Biquads Plate Designator amp? # Biquads Coeff per chan size spdif Delay analog in biquads DAC power amps Watts per chan power supply channels sub out sub amp BCPA-1 yes 7 24 none none TAS3004 TAS3004 TAS3004 LM3886 40 on-board 2 analog BCPA-2 yes 7 24 none none TAS3004 TAS3004 TAS3004 AD1994 20 trans or wallwart 2 no BCPA-3 yes 7 28 CS42526 AD1953 AD1953 AD1994 20 trans or wallwart 2.1 analog TDA8920 BA-4 maybe 5 24 CS4525 CS4525 CS4525 CS4525 20 wall-wart 2.1 PWM H-Bridge + PS BA-5 yes 7 26 CS42526 TPA5050 CS42526 TAS5706 --- TAS5706 20 trans or wallwart 2.1 PWM H-Bridge + PS PPA-2 yes 4 24 CS42526 STA328 --- STA328 x 2 30 ? 4 no STA328 SA-1 no 7 26 CS42526 TPA5050 CS42526 TAS5518 --- TAS5518 50 switchers 8 SA-2 maybe 10 24 CS42526 TPA5050 CS42526 --- STA5XX 40 switchers 4 or 8 CS42526 AD1953 optional TPA5050 none CS42526 STA308 What’s a Biquad? …a second-order recursive linear filter, containing two poles and two zeros: Implementation: OK, So What’s a Biquad? One biquad can be configured as: 2-pole low-pass filter (or one pole) 2-pole high-pass filter 2-pole shelving filter, low or high Peaking filter for EQ—variable F, Q and Gain Notch filter Bandpass filter All-pass filter Phase inverter Cascading Biquads Cascading filters allows making higher order filters or crossovers It takes 8 biquads to make a 4-pole 3-way L-R crossover: HFP Q=.7 F=3000 LFP Q=.7 F=3000 HFP Q=.7 F=3000 LFP Q=.7 F=3000 LFP Q=.7 F=300 HFP Q=.7 F=300 LFP Q=.7 F=300 HFP Q=.7 F=300 Unusual value Apogee DDX-8001: $5 8 processing channels , with drivers for class D output stages (30-100W ea) Each channel has 10 biquads Commonly used in many HT amps Similar chip: TI TAS5518, (Panasonic SA-XR series) TAS3103: $8 3 processing channels, each with 12 high-resolution biquads, plus digital delay TAS5706: $6 2.1 amplifier, 20W/channel; 7 biquads/channel + 2 highres biquads for sub channel How Do You Use These Things? Need to calculate the biquad coefficients (b0, b1, etc) Need to program the biquads Most are controlled by I2C bus, so need a microprocessor Need to model the response to build loudspeakers Requires math--trig and complex variables Combine driver response with filter transfer functions to view system response Manage on-chip resources: volume, channel mapping, etc Software/HW Overview Unavoidable feature: microprocessor to control the amplifier Microprocessor stores amp data, so PC only needed for designing the speaker Load Driver Data Calculate Coefficients Audio Interface USB (Analog, USB, SPDIF) Microprocessor Amps Crossover Designer PC Amplifier Amps Early version—2005 or so LM3886 SPKR ±12V LM3886 SPKR Low Voltage Power Supply Power Supply Sub Out Analog In L R TAS3004 Analog LPF & HPF (Sub) EEPROM PC Intfc I2C 3.3V Connectors Modules Power Budget Computer Plate Amp Version 1 BCPA-2 Digital amps run cooler and use smaller transformers Easier to install into a speaker cabinet, and lower cost Small: can still use small low-cost prototyping PCB’s Frustrating: both TAS3004 and AD1994 are now obsolete (*sigh*) Tweeter TAS3004 Mid or Woofer AD1994 SPKR Analog In SPKR Connectors Modules I2C EEPROM Microcontroller MC9S08 (QG8) Low Voltage USB Intfc USB I2C (out) 18V Power Supply Power Budget Computer Plate Amp Version 2 STA328 (DDXi2161) “Analog-free”: all-digital signal path 2-channel for active speakers; USB version for computer speakers Connectors Modules SPDIF SPKR DDXi2161 Filter Connectors Modules Filter Low Voltage PCM2707 DDXi2161 Filter SPKR MC9S08 (QG8) USB In Microcontroller SPKR SPKR SPDIF In Filter USB Intfc USB I2C (out) MC9S08 (QG8) SPDIF 2-Channel Low Voltage USB Intfc USB I2C (out) Power USB 2.1 (40/15/15W) Sub Filter Power Microcontroller Multichannel Amps (DDX8001) Working on a 4+2 board—should be done soon 50/50/15/15/15/15 with DSP: good for 3-way’s Has digital delay (each channel) for making steerable line arrays Picture shows a different version (eval board + control board) Works in stand-alone mode or with PC-based software Software Two Versions, maybe 3 Biquad Crossover Designer (BCD) Smaller amps: 2-channel or 2.1 BCD Multichannel 3-ways to 5-way systems with flexible channel routing AudioDevelopers # Biquads Product per channel BCPA-1 7 Digital Delay no Audio Processor Power amps TAS3004 LM3886 Watts per channel Channels 40 2 BCPA-2 7 no TAS3004 AD1994 20 2 BCPA-3 7 yes AD1953 AD1994 20 2.1 BA-4 5 yes CS4525 CS4525 20 2.1 BA-5 7 yes TAS5706 TAS5706 20 2.1 PPA-2 4 no STA328 STA328 x 2 30 4 SA-1 7 yes TAS5518 TAS5518 50 8 SA-2 10 yes STA308 STA5XX 40 EQ-1 12 yes TAS3013 --- --- Design Software BCD BCD4 to 8 multichannel 3 BCD-EQ Driver Response charts System Response SystemAmp() = Sys_amp_Data SystemPhase() = Sys_phase_Data If biquad windows not opened Response File Biquad charts Plotdata2() = SumTarget System_complex() Plotdata() = Biquad_Data Volume Updates If biquad windows opened Systemresponse() Biquadresponse() Offset and Phase Driver_with_offset() Driver_complex() Driver_data() Biquad Updates Tweeter Mid Graphs FRD_data() Inputs Woofer Bold indicates Complex BCD (2-2.1 Amps) Now in 3rd major revision, (…but none complete) Designed to support multiple amp chips Code for TAS3004 and STA328—others are “placeholders” “Hardwired” for a maximum of 3 channels Current version uses XML structure for saving state Driver Input Reads FRD or CLIO text files for driver response Allows adjustment of acoustic center offset Still working on Min phase algorithm… System Response graph updated when biquads are programmed Biquads (one per channel) Easy to tweak response and hear effect in real time Data gets calculated and sent to the amp for any change Has equations for many “textbook” filter types Other Features Includes screens to control registers in the chips Allows saving settings in EEPROM Controls what the amp loads at power-on Allows rapidly switching loads without re-calculating BCD Multichannel Uses logical channels rather than physical channels DDX-8001 Example Prototypes (currently free) Send email via PE Techtalk for ExpressPCB files Be ready for the “SMD challenge” (actually fairly easy with decent soldering tools) Need to program microprocessor—I will do that for cost of postage Download latest posted SW version: http://www.audiodevelopers.com/Software/BCD.zip http://www.audiodevelopers.com/Software/BCD-Multichannel.zip Need Microsoft .NET framework version 3.5, SP1 Need to download the mschart controls: http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyI D=130f7986-bf49-4fe5-9ca8-910ae6ea442c Need FTDI D2XX drivers: http://www.ftdichip.com/FTDrivers.htm Crippled Marthas Rushed into Service… Uses Spherex Xbox360 amp, not fully modded Still need to isolate digital audio lines…CPU on the board is partially in control Amp is 6-channel DDX-8001 circuit, but is configured “funny”: bridged sub & single-ended surrounds Software to control the amp isn’t complete “Hardwired” (assembly code) as 5-way with 4-pole LR crossovers at 100, 500, 3000 and 7000Hz All drivers arbitrarily set at same volume level No programmable delay control yet (circuitry done) No omni/dipole switching control yet (relays inside) Probably 2-3 weeks away from being done Unusual Features “Ring arrays” with no comb filtering due to crossover frequencies Super-tweeter uses 8cm headphone elements Approx 600 Lumens of light output Also designed to accommodate a circular Heil Total of 28 1W LED’s in each cabinet, but still needs proper resistors for higher output 3-channel color organ feature not enabled yet (but it works…) Fully programmable channel mapping, crossover frequencies, delays, slopes and volume levels Could be an all-day event in itself Proposed Follow-Up “Biquad class” at our cabin in Western MD Plenty of PC’s to design speakers (at least 4) I can bring lots of speakers and amps to play with, or bring your own speakers MarthaFest Compare topologies (2-way to 5-way) Compare crossover frequencies and slopes Compare omni to dipole Listen to effect of time delay compensation Drink beer, experiment, drink beer, etc