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Re: Murphy Corner Line Array (MCLA)
Hi Rich, welcome to the MCLA thread at Techtalk!
I've been thinking about your question because I am reluctant to get very deep into subjective descriptions of the "sound" of the system. Most of my own listening is centered on popular rock/country/jazz recordings where the perception of depth arises primarily from reverb and delay settings applied when the recording was mixed. On these recordings the sense of depth seems to be conveyed properly. In my opinion, the MCLAs provide a full sense of width across the soundstage as well as appropriate perceived depth.
Concerning soundstage depth vs. speaker placement away from the front wall I would just note that as the speaker is moved away from the front wall it becomes progressively more separated in space from its front wall reflection. The speaker moves forward 5' but the reflected image moves back 5'. Moving the speakers off the front wall will change the system impulse response such that the front wall reflection and all of its higher order reflections will all be delayed about 10 ms (for the case of speakers 5' from the front wall) compared to the direct sound and the other reflections. This small rearrangement of the playback system impulse response is likely to be audible but not necessarily better or worse; rather, it seems likely that it would just be randomly "different". In one room it might sound "better" while in another room it sounds "worse". From a "system" point of view we want to optimize the total system impulse response given a direct sound impulse and numerous early arrival image impulses which then repeat with progressively closer spacing and evolve into reverberation before decaying. We cannot make the reflected impulses "go away" (as with anechoic testing) but we do have some freedom in aligning the timing of the reflection impulses. We would achieve the highest listening resolution if we could align all of the impulses at any one time. Where that is not possible the next best thing with the earliest arrivals is to align the impulses so that they are clustered as tightly as possible. If we can squeeze all the impulses into a single "fusion window" (about 20ms or so) our human brains will perceive them as a single acoustic event. In the case of speakers placed along a wide front wall I would probably want to start with the speakers on or near the wall in order to move the reflection as close as possible to the source and tighten the timing between the two impulses. The ideal case would be flush mounting the speaker in the front wall so that the source and the image are not just close but virtually merge into one sound source. This happens again when you move the speaker into the front corner; you then merge the side wall reflected images with the sound source and front wall image. With narrower front walls corner placement works out nicely for either point sources or line arrays.
Getting back to Rich's question about the image sounding "tall"... I wonder if perhaps the notion that line arrays provide a "tall" image does not arise from the fact that the image is always perceived to be exactly at the listeners height such that when the listener stands the image moves upward to track the height of the listener's ears. When you sit, you hear the image track down with you. This is a readily noticeable difference from the way point source speakers behave. In any event, once I am happily seated (or standing) I do not perceive the performers as being "tall". But it is a little unusual at first to hear how the performer seems to sit when you sit and stand when you stand.
Regards,
John
Originally posted by richidoo
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John, I have been reading your speaker design articles on your website for a long time, and recently stumbled onto your new MCLA design. Thanks for sharing it. I tried to find it again a couple days later, not so easy. But I got it bookmarked now. A friend of mine brags about his pipedreams all the time, so I want to give your array a try. I am accustomed to in room speakers which have good imaging and depth, with tweeters spaced 5+ feet from the front wall.
Referencing Curt's post above, can you comment on the soundstage depth of the MCLA? The mirror effect that you describe has me thinking that maybe the front wall kind of disappears due to the reflections, and there might be decent depth perception. I will be using these primarily for stereo music listening. Do the images seem to be natural size, or stretched tall? Pipedream and Maggies claim to have a naturally full size (large) presentation.
Thanks
Rich
my 1st post on PE forum
Referencing Curt's post above, can you comment on the soundstage depth of the MCLA? The mirror effect that you describe has me thinking that maybe the front wall kind of disappears due to the reflections, and there might be decent depth perception. I will be using these primarily for stereo music listening. Do the images seem to be natural size, or stretched tall? Pipedream and Maggies claim to have a naturally full size (large) presentation.
Thanks
Rich
my 1st post on PE forum
Hi Rich, welcome to the MCLA thread at Techtalk!
I've been thinking about your question because I am reluctant to get very deep into subjective descriptions of the "sound" of the system. Most of my own listening is centered on popular rock/country/jazz recordings where the perception of depth arises primarily from reverb and delay settings applied when the recording was mixed. On these recordings the sense of depth seems to be conveyed properly. In my opinion, the MCLAs provide a full sense of width across the soundstage as well as appropriate perceived depth.
Concerning soundstage depth vs. speaker placement away from the front wall I would just note that as the speaker is moved away from the front wall it becomes progressively more separated in space from its front wall reflection. The speaker moves forward 5' but the reflected image moves back 5'. Moving the speakers off the front wall will change the system impulse response such that the front wall reflection and all of its higher order reflections will all be delayed about 10 ms (for the case of speakers 5' from the front wall) compared to the direct sound and the other reflections. This small rearrangement of the playback system impulse response is likely to be audible but not necessarily better or worse; rather, it seems likely that it would just be randomly "different". In one room it might sound "better" while in another room it sounds "worse". From a "system" point of view we want to optimize the total system impulse response given a direct sound impulse and numerous early arrival image impulses which then repeat with progressively closer spacing and evolve into reverberation before decaying. We cannot make the reflected impulses "go away" (as with anechoic testing) but we do have some freedom in aligning the timing of the reflection impulses. We would achieve the highest listening resolution if we could align all of the impulses at any one time. Where that is not possible the next best thing with the earliest arrivals is to align the impulses so that they are clustered as tightly as possible. If we can squeeze all the impulses into a single "fusion window" (about 20ms or so) our human brains will perceive them as a single acoustic event. In the case of speakers placed along a wide front wall I would probably want to start with the speakers on or near the wall in order to move the reflection as close as possible to the source and tighten the timing between the two impulses. The ideal case would be flush mounting the speaker in the front wall so that the source and the image are not just close but virtually merge into one sound source. This happens again when you move the speaker into the front corner; you then merge the side wall reflected images with the sound source and front wall image. With narrower front walls corner placement works out nicely for either point sources or line arrays.
Getting back to Rich's question about the image sounding "tall"... I wonder if perhaps the notion that line arrays provide a "tall" image does not arise from the fact that the image is always perceived to be exactly at the listeners height such that when the listener stands the image moves upward to track the height of the listener's ears. When you sit, you hear the image track down with you. This is a readily noticeable difference from the way point source speakers behave. In any event, once I am happily seated (or standing) I do not perceive the performers as being "tall". But it is a little unusual at first to hear how the performer seems to sit when you sit and stand when you stand.
Regards,
John
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