Conceptualizing and Constructing the Smart Speaker: Designing a power-limiting device for the common 2-way loudspeaker. Presented by Ryan Gwinn. Project Advisor: Professor James Hedrick. Union College Electrical and Computer Engineering Department. October, 2008

Ryan Gwinn Union College What is a ‘Smart’ Speaker and Why Build One? What are loudspeakers up against? Mechanical Failures & Thermal Failures caused by: -User Ignorance. -Overpowering. -Under-powering (amplifier clipping). “If the system is always operated safely within its linear range there is no need for limiting. This could happen in our lifetime, as could world peace.” -Bob McCarthy

Elementary Block Diagram Ryan Gwinn Union College SIGNAL SOURCE 2-way passive crossover Power limiter, specifically designed for connected speaker driver Tweeter Midrange driver or woofer CROSSOVER POWER LIMITER SPEAKER CABINET AMPLIFIER LOUDSPEAKER Three Approaches: 1)A Feedback System. 2)An Active Switch. 3)Entirely Passive.

Marketability Ryan Gwinn Union College Practicality of Cost vs. Benefit HIGHLY BENEFICIAL Limiter as a passive element MODERATELY BENEFICIAL Limiter using an active switch BENEFITS ARE QUESTIONABLE Limiter using a feedback system Market Availability PASSIVE Virtually any loudspeaker system with a sealed enclosure ACTIVE SWITCH High-priced loudspeakers where additional cost and maintenance is worthwhile. FEEDBACK Self-amplified loudspeakers, and shelf systems.

SIGNAL SOURCEAMPLIFIER The 2-way Loudspeaker is a System. Ryan Gwinn Union College Loudspeakers must be carefully designed, with the components balanced based on the needs of the overall system. Consideration must be made when implementing a new device into the system.

SIGNAL SOURCEAMPLIFIER The Enclosure. Ryan Gwinn Union College Enclosure Volume: Vas=(1.4x10 5 )(Sd 2 )(Cms) Vas=cabinet’s volume Sd=piston area of the driver Cms=driver’s compliance. Enclosure Dimension Ratio: (.618) : 1 : (1.618). Enclosure Type: Ported/Bass Reflex? Sealed? Passive Radiator? Internal Dampening: Acoustic Foam? Stuffing/Polyfill?

SIGNAL SOURCEAMPLIFIER The Crossover Ryan Gwinn Union College Passive or Active? 2-way, 3-way? Separate or Combined? What is this speaker being used for?

SIGNAL SOURCEAMPLIFIER The Crossover Ryan Gwinn Union College

SIGNAL SOURCEAMPLIFIER The Crossover Ryan Gwinn Union College nd Order Low Pass Filter. 2 nd Order High Pass Filter. 6 dB Attenuation to Match Tweeter & Woofer Sensitivities (db/watt/meter).

SIGNAL SOURCEAMPLIFIER The Drivers Ryan Gwinn Union College The two driver’s frequency response curves should overlap by at least an octave. The two driver’s sensitivities should be as close as possible.

SIGNAL SOURCEAMPLIFIER The Drivers Ryan Gwinn Union College

Testing Experimental Frequency Response

Ryan Gwinn Union College Testing Experimental Frequency Response Woofer Tweeter Summed

Ryan Gwinn Union College Testing Experimental Frequency Response Woofer Tweeter Summed Ideal

Testing Experimental Frequency Response Ryan Gwinn Union College

Testing Experimental Frequency Response Ryan Gwinn Union College Experimental Ideal Expected

2-way passive crossover Power limiter, specifically designed for connected speaker driver Tweeter Midrange driver or woofer CROSSOVER POWER LIMITER SPEAKER CABINET Altering the Design Ryan Gwinn Union College SIGNAL SOURCEAMPLIFIER Limiting with Negative Feedback

2-way passive crossover Power limiter, specifically designed for connected speaker driver Tweeter Midrange driver or woofer CROSSOVER POWER LIMITER SPEAKER CABINET Altering the Design Ryan Gwinn Union College SIGNAL SOURCEAMPLIFIER Limiting with Negative Feedback Must limit the power reaching the loudspeaker’s drivers regardless of the input signal connected to its exterior terminals. Should react to the input signal within 15 milliseconds. Should function with a changing audio file containing significant dynamic range. When not active, the device must have minimal effect on the loudspeaker’s performance parameters (frequency response etc.).

Ryan Gwinn Union College Negative Feedback Peak Limiting

Problems with Extending Beyond a Feedback System Ryan Gwinn Union College way passive crossover Power limiter, specifically designed for connected speaker driver CROSSOVER POWER LIMITER SIGNAL SOURCE AMPLIFIER Passive limiter with LDR and LED Tweeter Midrange driver or woofer SPEAKER CABINET Unit to dissipate power above threshold. May cause distortion to loudspeaker even when inactive. It is currently unknown how the limiter would dissipate the extra variable AC signal.

What’s Next? Ryan Gwinn Union College Completed: A Control 2-way Loudspeaker. An Experimental 2-way Loudspeaker. MATLAB Frequency Response Program. Design of a Negative Feedback Peak Limiter. In Progress: Implementation of Feedback Limiter. Testing Against Original Performance Specifications. Possible Continuation: More In-Depth Research Towards Understanding Passive Switching and Dissipation of AC Signals.

Ryan Gwinn Union College Questions? Q&A “Speakers are not unlike a typical teenager: they are resistant to change and require a great deal of motivation to be moved from their natural state of rest.” –Bob McCarthy

Basic Procedure. 1)Model a common 2-way loudspeaker by selecting a woofer and driver with closely matched sensitivities, and with combined frequency responses that cover much of the frequency spectrum. 2)Test each driver to find its physical limitations. 3)Design a 2-way passive crossover to function with the chosen drivers. 4)Design separate limiting devices that function between the crossover and the drivers. 5)Test the completed loudspeaker’s performance. Ensure its performance equals that of the system absent of the device, and also that the device functions as intended. That’s Pretty Straight-Forward, But How Can it be Done? Ryan Gwinn Union College

Specifications Review Ryan Gwinn Union College Design Specifications- Must limit the power reaching the loudspeaker’s drivers regardless of the input signal connected to its exterior terminals. Limiting circuit must be implemented in the design process of the loudspeaker. Should ideally be a passive element within the speaker system. When functioning, it must warn the user. Performance Specifications- Should be successfully implemented in a 2-way loudspeaker. Should react to the input signal within 15 milliseconds. Should function with a changing audio file containing significant dynamic range. When not active, the device must have minimal effect on the loudspeaker’s performance parameters (frequency response etc.).

2-way passive crossover Power limiter, specifically designed for connected speaker driver Tweeter Midrange driver or woofer CROSSOVER POWER LIMITER SPEAKER CABINET Creating a Limiter Using an Active Switch Ryan Gwinn Union College SIGNAL SOURCEAMPLIFIER Active switch Switch activates at each driver’s threshold, and dissipates the signal to a safe level, allowing the user time to make necessary changes. An active switch necessitates an additional power supply, independent from the power amplifier.

PERFORMANCE Determining the threshold for the limiter’s activation is difficult because individual drivers will perform differently at different frequencies. PRACTICALITY Implementing a passive switch with a variable AC signal. What may be limiting its success? Ryan Gwinn Union College The two main problems:

Ryan Gwinn Union College Understanding Frequency Response.

Ryan Gwinn Union College Understanding Frequency Response. Measures the response of a speaker in frequency, amplitude and time. Lines closest to you are measurements taken later than the ones in the back. Amplitude (dB) Frequency (Hz) Time (ms) Figure 1 Figure 2

Ryan Gwinn Union College Predictive Feedback

Ryan Gwinn Union College Impedance and Polarity