When I was R&D tea-boy at Wharfedale, I spent time trailing around the country with Barry Fox our Promotions Manager, putting on lectures/demos & shows.
Part of the stuff we carted around was the Wharfedale Ambi rig which was - 12 x TSR110 speakers http://www.gramophone.net/Issue/Page/October%201980/126/792093/Wharfedale+Laser+200+and+TSR+110+Loudspeakers - A souped up Integrex decoder optimised to run a hex system using only 4 channels of decode and amps - Calrec Soundfield Mk3a controller - Rotel RB5000 amp. 100W/channel and still my all time favourite. - ANOther high powered amp which I can't remember. - Teac 3440 + stack of Dolby Bs all to play my Soundfield recordings and some UHJ stuff. Horizontal only. The speakers were arranged as top & bottom units with the top sitting upside down on the bottom; each precarious pair mounted on quite a tall stand to get the speakers above the seated audience. The idea was to create a line source, short at HF where the treble units were close to each other while the 4 bass units spanned nearly 1.4m vertically. Our biggest crowd was more than 150 in Guildford (IIRC), a foreign city South of Watford. The huge amp was to implement the system MAG described in the Integrex article to use 4 amps to drive 6 speakers in a regular hex. 'W' needs to be nearly 4x the power of the other Amps. I describe a low level version for multichannel soundcards at http://ambisonic.info/info/ricardo/decoder.html at the end of the section on Classic Ambisonic Decoders. MAG told me (to my surprise) that it was the first practical trial of this method. The most successful part of the demo was making the soundstage revolve round the audience with the Mk3a controller. Oh. And the whole she-bang sounded good too especially the stuff recorded in Bradford's St. Georges Hall; Sir Thomas Beecham's favourite venue. The biggest problem was making sure all speakers were connected up properly and in phase. The supa dupa Ambisonic Surround Decoder MUST have built in facilities to facilitate this. _______________________ The idea behind line sources was to increase the "sweet spot". To some extent, the Wharfedale rig achieved this; good sound and "localisation" even on the fringe of the large audience area. A line source avoids (?) the 1/r attenuation you get with a point source. But we also put the speakers as far from the audience as possible which might have been a bigger affect. Conclusions - I don't think you can get proper line sources unless they span from floor to ceiling. - Even then, all you are doing is putting most of the audience in the "near field". In BLaH2, we used tall Revel Studio Monitors (2 x 8" units arranged vertically like the TSR110s) and spent some time trying to determine if we had 1/r with them in the listening room. In most rooms, at frequencies where ceiling & floor reflections might help lengthen the "line source", you are well into the area of "reflections" so how do you measure 1/r? In fact measuring 1/r is a standard technique to determine how "anechoic" a chamber is. I don't think we had anything approaching a line source for BLaH2 - However I do think even the above poor approximations help with a large audience. - I think standard Classic Ambi Decoder with NFC at the correct frequency for the size of the array is appropriate even with these "line sources". - Probably good to move the "transition from rV to rE" lower down. ________________________ The York decoders for large area work are either rE with no Shelfs or the Furse "Controlled Opposites" which guarantee no sound from speakers opposite the source direction. I should point out that Controlled Opposites require a fairly even distribution of speakers. If the array is at all wonky, you get some really strange decoders. If anyone else has experience with "line sources" in a horizontal Ambi rig, please show & tell. Or even pseudo pontificating ... _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
