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New DIY Mid High (90deg) - AKA PM90
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<blockquote data-quote="Peter Morris" data-source="post: 137298" data-attributes="member: 652"><p>Re: New DIY Mid High</p><p></p><p></p><p></p><p><a href="http://www.aes.org/technical/documentDownloads.cfm?docID=391" target="_blank">http://www.aes.org/technical/documentDownloads.cfm?docID=391</a></p><p></p><p></p><p>"<u>Background to the X Curve</u></p><p><u></u></p><p>The cinema reproduction chain is regarded as having two sections; the A and B chains. The B</p><p>chain comprises the elements of interest for this paper: those that follow the switching of signal</p><p>sources including equalisers, power amplifiers, loudspeakers, screen, and modifications to the</p><p>sound caused by auditorium acoustics and distance to listeners.</p><p></p><p>The X Curve (X stands for Experimental) represents the target shape for the steady state</p><p>frequency response of cinema sound systems when measured with pink noise at a reference</p><p>position. The X curve, originally promulgated as ISO2969 and subsequently adopted by the</p><p>SMPTE as S202, has been specified for many years and relates only to the B Chain and</p><p><strong>therefore has no role in pre-emphasis or other signal corrections.</strong></p><p><strong></strong></p><p>Allen1 describes the history of the X Curve equalisation and presents an explanation of the</p><p>factors that are thought to be addressed by it. Figure 1 reproduced from Allen1 shows the</p><p>steady-state frequency response of the B Chain as specified by the X Curve.</p><p></p><p>Allen notes that in listening tests, an equalisation slope of around -3 dB per octave from about 2</p><p>kHz seemed to give the best aural results, along with a slight limitation to low-frequency</p><p>bandwidth. The low-frequency limitation is easy to explain - more low-frequency energy would</p><p>probably overload the loudspeaker and generate distortion components. <strong><em>Allen suggests that the</em></strong></p><p><strong><em>reason for the apparently desirable HF droop is not easy to explain, but offers three possibilities,</em></strong></p><p><strong><em>singly or in combination:</em></strong></p><p><strong><em></em></strong></p><p><strong><em>• Some psychoacoustic phenomena involving the integration of faraway sound and picture.</em></strong></p><p><strong><em></em></strong></p><p><strong><em>• Some distortion components in the loudspeaker, making HF objectionable.</em></strong></p><p><strong><em></em></strong></p><p><strong><em>• The result of reverberation build-up, as described below.</em></strong></p><p><strong><em></em></strong></p><p><strong><em>The bulk of the Allen’s explanation concerns the effect of reverberation, and it is this issue that</em></strong></p><p><strong><em>this paper discusses."</em></strong></p></blockquote><p></p>
[QUOTE="Peter Morris, post: 137298, member: 652"] Re: New DIY Mid High [URL]http://www.aes.org/technical/documentDownloads.cfm?docID=391[/URL] "[U]Background to the X Curve [/U] The cinema reproduction chain is regarded as having two sections; the A and B chains. The B chain comprises the elements of interest for this paper: those that follow the switching of signal sources including equalisers, power amplifiers, loudspeakers, screen, and modifications to the sound caused by auditorium acoustics and distance to listeners. The X Curve (X stands for Experimental) represents the target shape for the steady state frequency response of cinema sound systems when measured with pink noise at a reference position. The X curve, originally promulgated as ISO2969 and subsequently adopted by the SMPTE as S202, has been specified for many years and relates only to the B Chain and [B]therefore has no role in pre-emphasis or other signal corrections. [/B] Allen1 describes the history of the X Curve equalisation and presents an explanation of the factors that are thought to be addressed by it. Figure 1 reproduced from Allen1 shows the steady-state frequency response of the B Chain as specified by the X Curve. Allen notes that in listening tests, an equalisation slope of around -3 dB per octave from about 2 kHz seemed to give the best aural results, along with a slight limitation to low-frequency bandwidth. The low-frequency limitation is easy to explain - more low-frequency energy would probably overload the loudspeaker and generate distortion components. [B][I]Allen suggests that the reason for the apparently desirable HF droop is not easy to explain, but offers three possibilities, singly or in combination: • Some psychoacoustic phenomena involving the integration of faraway sound and picture. • Some distortion components in the loudspeaker, making HF objectionable. • The result of reverberation build-up, as described below. The bulk of the Allen’s explanation concerns the effect of reverberation, and it is this issue that this paper discusses."[/I][/B] [/QUOTE]
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