"Reading (the verb, not the place)"
Week 3 (Friday 12th March)
After last week's supervision with Tony, it was suggested that I continue making good ground into the reading list provided by Andrew Jones. It is hoped that next week we will be able to arrange the first (of hopefully several) skype meetings with Andrew in order to gain a better understanding of exactly how the project will work in practise. The reading list contains a broad range of topics in the area of loudspeaker performance and measurement techniques, and I will discuss them in more detail below.
One of the major topics surrounds baffle diffraction. Baffle diffraction is a long standing issue in loudspeaker design. A loudspeaker driver is typically installed in a cabinet. This cabinet has edges and when sound radiates from the driver, a proportion of the total energy is diffraction around the sides of the speaker cabinet. This is an issue particularly for higher frequencies as sound with a wavelength longer than the size of of the object will pass straight through. This is a very real problem in loudspeaker design however, as it results in something known as a 'baffle step'. When a driver is positioned in half space - in an infinite baffle for example, no energy is lost due to diffraction. In a cabinet however - with finite edges, a 6db drop is measured due to energy being diffracted by the cabinet edges to the back of the loudspeaker. The image to the right is from audio judgement - a great website that so far has been extremely helpful in reading up on areas relevant to my project. The image demonstrates this topic.
In addition to the 6db energy loss from diffraction round the back of the cabinet, this can also result in phase cancellation. If the distance from the centre of the driver to the edge of the baffle is half the wavelength of a certain frequency when it diffracts, it will be 180 degree out of phase with the original wave and non-perfect cancellation will occur resulting in a dip in frequency response at that frequency. This of course results in a colloration to the sound - an undesirable effect for any loudspeaker designer.
Another audio judgement image shown to the right demonstrates this effect - please click here for the original page.
This Week's Supervision Meeting
Tony and I went through the steps outlined by Andrew in more detail, bringing up questions we would like clarification from Andrew in our Skype meeting.
Tony gave me a much clearer sense of the overall aims of the project, however more clarification from Andrew is certainly needed.
Plan for the Coming Week
Thorough reading into electrical impedance to gain much deeper understanding
Continue reading of baffle diffraction
Find more recent research done in the topic area
Organise skype meeting with Andrew Jones (Tony)