Same Speaker Different Data Loudspeaker design and analysis

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Same Speaker, Different Data? Loudspeaker design and analysis tools Presented at ALMA Asia Symposium 2010 UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Introductions • Prism Sound: – Established 1987 (23 years) – Founders Ian Dennis and Graham Boswell designed world’s first digital audio console at AMS Neve – Ian Dennis co-wrote AES-ABU digital interface standard – Professional audio logging / recording / editing solutions – Audio test and measurement equipment • Simon Woollard: Simon Woollard Prism Sound – BSc (Hons) Audio Technology, University of Salford, UK – Worked as loudspeaker design engineer (NXT, Mission) – Now Applications Engineer for Prism Sound’s Test and Measurement Division UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Agenda • Introduction • Typical Measurement Setup • Discussion: Sources of Inconsistency • Recap • Conclusion UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Part 1 • Introduction • Typical Measurement Setup • Discussion: Sources of Inconsistency • Recap • Conclusion UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Introduction: Measurement Inconsistency • THE PROBLEM - Same Loudspeaker: • Different data! UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Introduction: Measurement Inconsistency • We ship samples & employees across continents to investigate UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Introduction: Measurement Inconsistency • We ship samples & employees across continents to investigate + • Measurement inconsistency costs time & money! UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Part 2 • Introduction • Typical Measurement Setup • Discussion: Sources of Inconsistency • Recap • Conclusion UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Typical Measurement Setup • Typical Loudspeaker Measurements: – – – On-axis frequency response Off-axis frequency response (polar plot) Power response Distortion / non-linearities Impedance Thiele-Small parameters • Today we will discuss on-axis frequency response; Perhaps the most common loudspeaker measurement UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Typical Measurement Setup • Typical Loudspeaker Measurements: – – – On-axis frequency response Off-axis frequency response (polar plot) Power response Distortion / non-linearities Impedance response Thiele-Small parameters • Today we will discuss on-axis frequency response; Perhaps the most common loudspeaker measurement UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Typical Measurement Setup • Typical frequency response measurement setup: UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Typical Measurement Setup • Typical frequency response measurement setup: 1) Test System 1 UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Typical Measurement Setup • Typical frequency response measurement setup: 1) Test System 1 2 2) Amplifier UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Typical Measurement Setup • Typical frequency response measurement setup: 1) Test System 2 1 2) Amplifier 3) EUT 3 UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Typical Measurement Setup • Typical frequency response measurement setup: 1) Test System 2 1 4 2) Amplifier 3) EUT 4) Baffle 3 UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Typical Measurement Setup • Typical frequency response measurement setup: 1) Test System 2 1 4 5 2) Amplifier 3) EUT 4) Baffle 5) Microphone 3 UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Typical Measurement Setup • Typical frequency response measurement setup: 1) Test System 2 1 4 5 2) Amplifier 3) EUT 4) Baffle 5) Microphone 6) Room / Chamber 3 6 UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Typical Measurement Setup • Typical frequency response measurement setup: 1) Test System 2 1 4 5 2) Amplifier 3) EUT 4) Baffle 5) Microphone 6) Room / Chamber 3 6 7) POTENTIAL SOURCES 8) OF MEASUREMENT 9) INCONSISTENCY UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Part 3 • Introduction • Typical Measurement Setup • Discussion: Sources of Inconsistency • Recap • Conclusion UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Test and Measurement System 1) Test System 2 1 2) Amplifier 3) EUT 4 5 4) Baffle 5) Microphone 3 6) Room / Chamber 6 UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Test and Measurement System • Calibration of test system (2 main types): 1) Dedicated Hardware: – Usually calibrated by manufacturer – Typical accuracy ± 0. 05 d. B (absolute), ± 0. 05 d. B flatness – Should include amplitude ranging to ensure maximum noise / distortion performance at low signal amplitude 2) Generic Soundcard: – Requires calibration by operator, or errors could be ~d. Bs! – Noise and distortion of soundcard may affect accuracy at low amplitude (frequency response affected less) UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Test and Measurement System For Today’s Examples d. Scope Software d. Scope Series III Hardware USB IEC Baffle Cyrus III G. R. A. S. 46 AE / 26 CA UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Test and Measurement System • Possible stimuli for frequency response measurement: Stepped sine (sweep) Broad band noise Maximum length sequence (MLS) Continuous sweep (chirp) Multi-tone UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Test and Measurement System • Impulse response (using broad band stimulus) is widely used: UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Test and Measurement System • Impulse response methods require a broad band stimulus • Stepped sine sweep cannot remove room reflections Stepped sine sweep Log swept sine + Impulse response UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Test and Measurement System • Choice of window function affects frequency response: Window Function: Prism 7 Prism 5 Gaussian Blackman-Harris Hamming Hann Blackman Triangular Rectangular UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Test and Measurement System • Length of window function affects LF cut-off: t UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Test and Measurement System • Length of window function affects LF cut-off: Window Length: t = 5 ms t = 10 ms t = 15 ms t = 20 ms t = 25 ms Shorter window t = 30 ms • HF also affected by reflections in non-anechoic measurements UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Test and Measurement System • Low frequency cut-off is given by: f=1/t f = lowest valid frequency in measurement (Hz) t = length of time domain window (seconds) UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Test and Measurement System • Stimulus Amplitude: Excursion @2 V, mm 6. 0 4. 5 3. 0 1. 5 0. 0 • Voice coil driving force is non-linear WRT transducer excursion • At high excursion, efficiency will be lower (e. g. low frequency) UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Test and Measurement System • At high excursion, efficiency will be lower (e. g. low frequency): Stimulus Amplitude: 15 V 7. 5 V 3. 75 V 500 m. V 250 m. V 100 m. V 50 m. V UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Test and Measurement System • Start position of window can affect low frequency response: Correct Window Position UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Test and Measurement System • Start position of window can affect low frequency response: Correct Window Position Window Starts too early • LF attenuation due to early start of window function UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Power Amplifier 1) Test System 2 1 2) Amplifier 3) EUT 4 5 4) Baffle 5) Microphone 3 6) Room / Chamber 6 UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Power Amplifier • Output / cable impedance: • Output impedance and cable impedance should be minimised, and ideally calibrated in the test and measurement system UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Power Amplifier • Assume a loudspeaker impedance as follows: Loudspeaker impedance Frequency Response Measurement Error • Assume amplifier output impedance + cable impedance is 0. 5Ω; • We see error if we measure without calibration UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Baffle 1) Test System 2 1 2) Amplifier 3) EUT 4 5 4) Baffle 5) Microphone 3 6) Room / Chamber 6 UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Why do We need a Baffle? + - Using a baffle restores diaphragm low (positive pressure) Air expands significant pressure cone motion compressesbehind air acoustic in front of diaphragm Acousticvoltagecircuit’ at (negative pressure) Positivein‘short of diaphragm frequency No front > outward radiation UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Baffle Low Frequency High Frequency • If the wavelength is long compared to the baffle dimensions, radiation is omnidirectional (4π) • If the wavelength is short compared to the baffle dimensions, radiation is in the forward direction only (2π) : SPL is 6 d. B greater UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Baffle • IEC / AES standards for baffle size; varies with transducer size IEC / AES standard baffle dimensions for transducers up to 8” diameter UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Baffle • Baffle should be large compared to wavelengths of interest • If baffle is too small, we see low SPL at low frequencies: Baffle Size: 1650 x 1450 mm (IEC) 650 x 550 mm UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Baffle • Ensure a good air seal between transducer and baffle • If air seal is poor, we see errors at low / mid frequencies: Air Seal: Airtight Poor Seal UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Microphone 1) Test System 2 1 2) Amplifier 3) EUT 4 5 4) Baffle 5) Microphone 3 6) Room / Chamber 6 UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Microphone • Use a dedicated test and measurement microphone • Calibrate the microphone using manufacturer’s data Calibration data for G. R. A. S. 46 AF mic S/N 57302 UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Microphone • For highest precision, use a pistonphone or calibrator G. R. A. S. pistonphone type 42 AA G. R. A. S. calibrator type 42 AB UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Microphone • Correct for actual atmospheric pressure UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Microphone • Use the correct microphone capsule! Typically a choice of 2: Pressure microphone: Free-field microphone: For Measuring SPL at a boundary For measuring SPL in free space Mic does not modify pressure field Mic modifies pressure field, so is acoustically equalised to correct error UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Microphone • Free-field response of a ½” pressure mic capsule: Image from Cirrus Research UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Microphone • Using wrong capsule type gives error at high frequency: Free-field measurement: Free-field mic capsule Pressure mic capsule UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Microphone • Use of non-instrument grade mic, and / or generic calibration data will be less accurate: Mic: G. R. A. S. Type 46 CA (calibrated) ‘Brand x’ mic, no calibration data supplied UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Microphone • Be careful if you are not measuring at a distance of 1 m • Response is affected at close mic distances: We can measure at any distance and normalise to the equivalent 1 m sensitivity… x UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Microphone • Be careful if you are not measuring at a distance of 1 m • Response is affected at close mic distances: Microphone Distance: x = 0 mm x = 50 mm x = 100 mm x = 200 mm x = 400 mm x = 800 mm UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Microphone • ‘Comb filtering’ caused by path differences from cone to speaker: • If y – x = n*wavelength: CONSTRUCTIVE interference x • If y – x = (n - 0. 5)*wavelength: DESTRUCTIVE interference y (where n is integer) UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Microphone • ‘Comb filtering’ caused by path differences from cone to speaker: x y • x and y approximately equal in far field; comb filtering is minimised UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Room / Chamber 1) Test System 2 1 2) Amplifier 3) EUT 4 5 4) Baffle 5) Microphone 3 6) Room / Chamber 6 UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Room / Chamber • Reflections from room boundaries cause ‘comb filtering’ UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Room / Chamber • Reflections from room boundaries cause ‘comb filtering’ x UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Room / Chamber • Reflections from room boundaries cause ‘comb filtering’ x y y UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Room / Chamber • Reflections from room boundaries cause ‘comb filtering’ Path difference = 2 y - x • If 2 y – x = n*wavelength: CONSTRUCTIVE interference • If 2 y – x = (n – 0. 5)*wavelength: x y DESTRUCTIVE interference y (where n is integer) UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Room / Chamber • Reflections from room boundaries cause ‘comb filtering’ Early Reflection No Early Reflection UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Room / Chamber • Reflections can be removed from an impulse response • But we lose low frequency information from our measurement UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Room / Chamber • Reflections can be removed from an impulse response • But we lose low frequency information from our measurement Window Length: 5 ms 10 ms 15 ms 20 ms 25 ms 30 ms UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Room / Chamber • Move the microphone & speaker away from room boundaries UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Room / Chamber • Use absorption if possible (anechoic chamber) UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Room / Chamber • Small chambers are very sensitive to mic position and reflections UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Sources of Inconsistency: Room / Chamber • Small chambers are very sensitive to mic position and reflections – – – Make the microphone mounting secure and accurate Use non-simple ratios between chamber x, y, and z dimensions If possible, use non-parallel chamber walls Use high specification acoustic absorption Use high stiffness, high damping, high mass chamber walls to prevent panel resonances and noise transmission – Ensure that multiple chambers are built to identical specifications UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Part 4 • Introduction • Typical Measurement Setup • Discussion: Sources of Inconsistency • Recap • Conclusion UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Recap • Earlier we saw 2 measurements of the same loudspeaker: • We have now identified the major causes of the discrepancies UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Recap • Causes of frequency response measurement inconsistency: – Test System: • • • Calibration Stimulus type / measurement method Stimulus amplitude Window function (for impulse response) Window length Window start time – Power amplifier: • Output impedance / cable impedance • Calibration for output impedance – Baffle: • Baffle size - IEC / AES recommend standard baffle sizes • Air seal between transducer and baffle UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Recap • Causes of frequency response measurement inconsistency: – Microphone: • Use a dedicated T&M mic (omni-directional) • Capsule type: pressure or free-field • Calibration for sensitivity, frequency response and mic pre gain • Correction for atmospheric pressure • Correction for any gain in ear couplers • Distance from mic to loudspeaker – Room / Chamber: • Nearby boundaries • Room dimensions • Windowing (if used) • Position of mic UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Part 5 • Introduction • Typical Measurement Setup • Discussion: Sources of Inconsistency • Recap • Conclusion UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Conclusion – Sources of ERRORS should be MINIMISED / calibrated, e. g. : • Cable and amplifier impedance • Microphone frequency response • Environmental noise – Measurement VARIABLES should be STATED with measurement data, e. g. : • Stimulus type • Stimulus amplitude • Microphone distance • Type of window function • Baffle dimensions • Room dimensions UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Conclusion • Suggested datasheet format: Brand XYZ, model ADCD, S/N 0123456 On-axis frequency response re 2. 83 V, 1 m UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Conclusion • By minimising ERRORS and documenting VARIABLES, we can all save time and money! UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com

Further Considerations • We could also talk about measurement inconsistencies in: – EUT; atmospheric temperature, humidity, voice coil temperature due to test cycle duration etc – Impedance, TSPs, distortion measurements etc – Electrical measurements – power amplifiers, crossovers etc – Headphones / ear couplers / HATSs • But we are out of time! Perhaps a topic for ALMA 2011… UK: +44 (0)1353 648 888 US: +1 973 983 9588 © Copyright Prism Media Products Ltd. 2008 2009 www. prismsound. com