diff Lectures/Lec9 - Sound Reproduction/Lec9 - Sound Reproduction.tex @ 15:d780cb4fa37f

Final commit

--- a/Lectures/Lec9 - Sound Reproduction/Lec9 - Sound Reproduction.tex	Mon Oct 07 09:14:16 2013 +0100
+++ b/Lectures/Lec9 - Sound Reproduction/Lec9 - Sound Reproduction.tex	Thu May 15 13:28:25 2014 +0100
@@ -48,6 +48,16 @@
 	\end{itemize}
 \end{frame}
 
+\begin{frame}
+	\frametitle{Diffraction}
+	\begin{itemize}\itemsep10pt
+		\item Diffraction describes how sound waves bend around obstacles, and spread out beyond openings.
+		\item How the wave behaves depends upon the relative size of its wavelength compared to the obstacle (or opening).
+		\item \href{http://hyperphysics.phy-astr.gsu.edu/hbase/sound/diffrac.html}{{\em Diffraction Diagram.}}
+		\item \href{http://www.falstad.com/ripple/}{{\em Ripple Tank Animation}}
+	\end{itemize}
+\end{frame}
+
 \separator{Loudspeakers}
 
 \begin{frame}
@@ -73,16 +83,37 @@
 \end{frame}
 
 \begin{frame}
-	\frametitle{Loudspeaker directivity}
+	\frametitle{Dipole Source}
 	\begin{itemize}\itemsep10pt
-		\item The polar directivity pattern of a loudspeaker is analogous to the polar response pattern of a microphone.
-		\item It describes how the sound is radiated by the loudspeaker as a function of angle and frequency.
-		\item The angle of dispersion is often referred to as the Q-factor (like an EQ filter). A high Q means a narrow angle.
-		\item Loudspeakers are either variable Q, or constant Q (most studio speakers are variable Q).
+		\item A moving coil loudspeaker compresses the air on one side, and expands it the other.
+		\item This is referred to as a dipole source, and it has the same (ideal) polar directivity (response) as the figure of eight microphone.
+		\item A real loudspeaker has a finite width, so how does this affect directivity?
 	\end{itemize}
 \end{frame}
 
 \begin{frame}
+\frametitle{Idealised Directivity Pattern}
+\begin{columns}[t]
+\column{2.1in}
+\begin{center}
+\vspace{-0.6cm}
+		\includegraphics[height=.65\textheight]{Figures/infiniteBaffle.png}
+\end{center}
+
+\column{2.5in}
+{\small
+\vspace{-0.5cm}
+\begin{itemize}\itemsep8pt
+		\item A loudspeaker may be modelled as a circular piston in an infinite baffle.
+		\item The baffle is a box of infinite size that separates the backward reflections for the forward reflections.
+		\item The directivity is dependent on the relationship between the size of the piston, and the wavelength of the sound.
+\end{itemize}
+}
+\end{columns}
+\end{frame}
+
+
+\begin{frame}
 \frametitle{Idealised directivity pattern (a single radiating piston mounted in an infinite baffle)}
 	\begin{itemize}
 	\item Directivity is dependent upon frequency; high frequency is more directional.
@@ -92,6 +123,17 @@
 	\end{center}
 \end{frame}
 
+
+\begin{frame}
+	\frametitle{Loudspeaker directivity}
+	\begin{itemize}\itemsep10pt
+		\item The polar directivity pattern of a loudspeaker is analogous to the polar response pattern of a microphone.
+		\item It describes how the sound is radiated by the loudspeaker as a function of angle and frequency.
+		\item The angle of dispersion is often referred to as the Q-factor (like an EQ filter). A high Q means a narrow angle.
+		\item Loudspeakers are either variable Q, or constant Q (most studio speakers are variable Q).
+	\end{itemize}
+\end{frame}
+
 \begin{frame}
 \frametitle{Directivity Pattern of a real loudspeaker}
 	 \begin{center}
@@ -107,19 +149,41 @@
 \end{frame}
 
 \begin{frame}
-\frametitle{Moving Coil Design Considerations 1}
+\frametitle{Moving Coil Design Considerations}
 {\small
 \begin{itemize}\itemsep10pt
-	\item {\bf HF limit}: a small diaphragm radius increases the HF limit, but is inefficient and has poor sensitivity.
-	\item {\bf LF limit}: a heavy diaphragm and soft suspension decreases the LF limit, but a heavy diaphragm is inefficient with poor sensitivity, and soft suspension is mechanically fragile.
-	\item {\bf Efficiency}: a large and light diaphragm improves efficiency, but it is hard to have both large and light.
+	\item {\bf LF limit}
+	\begin{itemize}\itemsep8pt
+		\item The size of the diaphragm determines how well low frequency sounds can be generated.
+		\item Small diaphragms cannot generate low frequency sounds in the same way that small obstacles can't obstruct low frequency sounds.
+		\item Soft suspension (in spring) is preferable to control low frequency oscillations.
+	\end{itemize}
 	
 \end{itemize}
 }
 \end{frame}
 
 \begin{frame}
-\frametitle{Moving Coil Design Considerations 2}
+\frametitle{Moving Coil Design Considerations}
+{\small
+\begin{itemize}\itemsep10pt
+	\item {\bf HF limit}
+	\begin{itemize}\itemsep8pt
+		\item A small diaphragm can generate high frequency sounds.
+		\item It is easier to generate high frequency oscillations in a lighter structure, i.e. smaller diaphragm. 
+		\item Stiffer suspension is preferable to control high frequency oscillations.
+	\end{itemize}
+	\item {\bf Efficiency}
+	\begin{itemize}
+		\item Large and light diaphragm improves efficiency, but it is hard to have both large and light.
+	\end{itemize}
+	
+\end{itemize}
+}
+\end{frame}
+
+\begin{frame}
+\frametitle{Moving Coil Design Considerations}
 {\small
 \begin{itemize}\itemsep10pt
 	\item {\bf Linearity}: we want the frequency response to be the same at any signal level.
@@ -295,6 +359,23 @@
 	\includegraphics[width = \textwidth]{Figures/responseAlpha1.pdf}
 \end{frame}
 
+\begin{frame}
+	\frametitle{Loudspeaker Arrays}
+	\begin{itemize}\itemsep10pt
+		\item In large concerts the sound system must be able to cover a large audience area with sound.
+		\item It is not practical to use one or two enormous loudspeakers, so multiple loudspeakers are used, and are typically arranged in line arrays.
+		\item Their interactions are controlled and optimised to provide the best possible coverage, and to satisfy other requirements, e.g. leakage onto stage.
+	\end{itemize}
+\end{frame}
+
+\begin{frame}
+	\frametitle{Loudspeaker Arrays}
+	\begin{itemize}\itemsep10pt
+		\item Line array loudspeakers generally contain more than two individual transducers, e.g. 4-way is typical.
+		\item Each loudspeaker can be controlled by its position, and by individual processors to apply gain, delay, equalisation and delay.
+		\item All of these controls are used to manage and optimise the loudspeaker interactions.
+	\end{itemize}
+\end{frame} 
 
 \separator{Room Acoustics}
 
@@ -376,6 +457,41 @@
 \end{frame}
 
 \begin{frame}
+\frametitle{Room Resonance: Source and Receiver Position}
+\begin{columns}[c]
+\column{1.8in}
+	 \begin{center}
+		\includegraphics[width=\textwidth]{Figures/StandingWave.png}
+	\end{center}
+
+\column{2.6in}
+{\footnotesize
+\begin{itemize}\itemsep10pt
+	\item If a source is placed at the anti-node (A) the reflection will sum, and hence it will excite the standing wave.
+	\item If a source is placed at the node (N) the reflection will cancel, and hence sound energy at the frequency of the standing wave will be lost.
+	\item If a receiver is at a node (N) it will not detect sound energy at the the standing wave frequency.
+\end{itemize}}
+\end{columns}
+\end{frame}
+
+\begin{frame}
+\frametitle{Room Resonance: Source and Receiver Position}
+\begin{columns}[c]
+\column{1.8in}
+	 \begin{center}
+		\includegraphics[width=\textwidth]{Figures/RoomLoading.png}
+	\end{center}
+
+\column{2.6in}
+{\footnotesize
+\begin{itemize}\itemsep10pt
+	\item If I place my source and receiver on an anti-node I can deliberately use the room resonance to boost certain frequencies. 
+	\item This can be very useful for acoustic recordings of bass instruments, e.g. kick drum.
+\end{itemize}}
+\end{columns}
+\end{frame}
+
+\begin{frame}
 	\frametitle{Shroeder Frequency}
 	\begin{itemize}\itemsep10pt
 		\item What happens to the room modes as the frequency is increased?
@@ -598,16 +714,6 @@
 	\end{itemize}
 \end{frame}
 
-
-\begin{frame}
-	\frametitle{Frequency Response}
-	\begin{itemize}\itemsep10pt
-		\item The room {\bf impulse response} tells us how reflections affect our source sound as a function of time.
-		\item The room {\bf frequency response} tells us how reflections affect our source sound as a function of frequency.
-		\item These terms are used for any system, not just for rooms.
-\end{itemize}
-\end{frame}
-
 \begin{frame}
 	\frametitle{(Loudspeaker Pair + Room) Response}
 	\begin{center}