1. Neil Davis July 18, 2009 DIY Digital Crossovers

2. Approaches  Analog  Works well, but hard to achieve flexibility  Stopped doing this ~2004  DSP separates  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

3. Focus Area: Integrated DSP  Audiodevelopers product range:

4. Amps with DSP--Example Lots of Class D amps have digital biquads!

5. Some Amps with Biquads Designator Plate amp? # Biquads per chan Coeff sizespdifDelayanalog inbiquadsDAC power amps Watts per chan power supplychannelssub outsub amp BCPA-1yes724none TAS3004 LM388640on-board2analog BCPA-2yes724none TAS3004 AD199420 trans or wall- wart 2no BCPA-3yes728CS42526AD1953CS42526AD1953 AD199420 trans or wall- wart 2.1analogTDA8920 BA-4maybe524optionalTPA5050CS4525 20wall-wart2.1PWM H-Bridge + PS BA-5yes726CS42526TPA5050CS42526TAS5706---TAS570620 trans or wall- wart 2.1PWM H-Bridge + PS PPA-2yes424CS42526noneCS42526STA328--- STA328 x 2 30?4noSTA328 SA-1no726CS42526TPA5050CS42526TAS5518---TAS551850switchers8 SA-2maybe1024CS42526TPA5050CS42526STA308---STA5XX40switchers4 or 8

6. What’s a Biquad?  …a second-order recursive linear filter, containing two poles and two zeros: Implementation:

7. 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

8. 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 HFP Q=.7 F=3000 LFP Q=.7 F=3000 LFP Q=.7 F=3000 HFP Q=.7 F=300 HFP Q=.7 F=300 LFP Q=.7 F=300 LFP Q=.7 F=300

9. 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 high- res biquads for sub channel

10. How Do You Use These Things?  Need to calculate the biquad coefficients (b0, b1, etc)  Requires math--trig and complex variables  Need to program the biquads  Most are controlled by I2C bus, so need a microprocessor  Need to model the response to build loudspeakers  Combine driver response with filter transfer functions to view system response  Manage on-chip resources: volume, channel mapping, etc

11. Software/HW Overview  Unavoidable feature: microprocessor to control the amplifier  Microprocessor stores amp data, so PC only needed for designing the speaker PC Load Driver Data USB Crossover Designer Calculate Coefficients Amplifier Micro- processor Amps Audio Interface (Analog, USB, SPDIF)

12. Amps

13. Early version—2005 or so LM3886 Power Supply SPKR Power Connectors Modules TAS3004 EEPROM Analog In Low Voltage Power Supply Sub Out PC Intfc I2C L R 3.3V ±12V SPKR Analog LPF & HPF (Sub) Budget Computer Plate Amp Version 1

14. 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*) 18V Power Supply SPKR Power Connectors Modules Low Voltage Analog In SPKR AD1994 Tweeter Mid or Woofer EEPROM Microcontroller MC9S08 (QG8) USB Intfc USB I2C (out) TAS3004 I2C Budget Computer Plate Amp Version 2

15. STA328 (DDXi2161)  “Analog-free”: all-digital signal path  2-channel for active speakers; USB version for computer speakers SPDIF 2-Channel USB 2.1 (40/15/15W) SPKR Power Connectors Modules Low Voltage SPDIF In SPKR DDXi2161 Microcontroller MC9S08 (QG8) USB Intfc USB I2C (out) SPDIF Filter SPKR Power Connectors Modules Low Voltage USB In SPKR DDXi2161 Microcontroller MC9S08 (QG8) USB Intfc USB I2C (out) PCM2707 Filter Sub

16. 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

17. Software

18. 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 Product # Biquads per channel Digital DelayAudio ProcessorPower amps Watts per channelChannels Design Software BCPA-17noTAS3004LM3886402 BCD BCPA-27noTAS3004AD1994202 BCPA-37yesAD1953AD1994202.1 BA-45yesCS4525 202.1 BA-57yesTAS5706 202.1 PPA-24noSTA328STA328 x 2304 SA-17yesTAS5518 508 BCD- multichannel SA-210yesSTA308STA5XX404 to 8 EQ-112yesTAS3013--- 3BCD-EQ

19. Tweeter Mid Woofer System Response Response File Offset and Phase Biquad Updates Biquad charts Driver Response charts Plotdata() = Biquad_Data Plotdata2() = SumTarget Biquadresponse() Systemresponse() SystemAmp() = Sys_amp_Data SystemPhase() = Sys_phase_Data Driver_complex() Driver_with_offset() Bold indicates Complex System_complex() If biquad windows not opened FRD_data() Driver_data() If biquad windows opened Volume Updates Graphs Inputs

20. BCD (2-2.1 Amps)  Now in 3 rd 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

21. 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

22. 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

23. 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

24. BCD Multichannel  Uses logical channels rather than physical channels

25. DDX-8001 Example

26. 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.zip  http://www.audiodevelopers.com/Software/BCD-Multichannel.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 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

27. Crippled Marthas

28. 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

29. Unusual Features  “Ring arrays” with no comb filtering due to crossover frequencies  Super-tweeter uses 8cm headphone elements  Also designed to accommodate a circular Heil  Approx 600 Lumens of light output  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

30. 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