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The BBC monitor sound Loudspeakers from Spendor Rogers, Harbeth....
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I have had an interest in these designs since my early Teenage years when I heard a pair of Spendor BC1s I currently own and use Spendor BCIs BCIIIs and currently have Spendor SA3s in place in the main system. Any forum members here have any experience with the LS 5/8 and the passive version the PM510? I may look for a pair of the PM510s or maybe the LS5/8s to simply try them out  Edited by user 15 February 2014 10:20:11(UTC)
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 Rank: HIFI God Joined: 25/11/2008(UTC)
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Originally Posted by: darkmatter  I have had an interest in these designs since my early Teenage years when I heard a pair of Spendor BC1s I currently own and use Spendor BCIs BCIIIs and currently have Spendor SA3s in place in the main system. Any forum members here have any experience with the LS 5/8 and the passive version the PM510? I may look for a pair of the PM510s or maybe the LS5/8s to simply try them out I used to hear them quite regularly at the BBC, but it's a long time ago, and I can't really remember exactly what I thought of them at the time compared with BC1's (like you, I've still got a pair of these, with the super-tweeters). But you do need rather a big room for them.
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Rank: Administrator Joined: 19/09/2008(UTC) Posts: 2,327 Location: UK Thanks: 37 times
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Originally Posted by: frank23 Interesting piece of history an 8" based system
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Rank: Administrator Joined: 19/09/2008(UTC) Posts: 2,327 Location: UK Thanks: 37 times
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Still getting excellent results from my SA3s there is something special about a big two way hence my interest in getting my hands on a pair of LS 5/8s This is an interesting beast the LS5/1 
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Rank: HIFI God Joined: 02/02/2009(UTC)
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I was always interested in behind baffle mounting of bass drivers. I take it this helps with directionality as the frequency goes up? All sorts of, to us, odd tweeters and they still work. Clever.
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Rank: Administrator Joined: 19/09/2008(UTC) Posts: 2,327 Location: UK Thanks: 37 times
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Originally Posted by: ashleym I was always interested in behind baffle mounting of bass drivers. I take it this helps with directionality as the frequency goes up? All sorts of, to us, odd tweeters and they still work. Clever. Yes helps with this with these big two way systems
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Rank: Administrator Joined: 19/09/2008(UTC) Posts: 2,327 Location: UK Thanks: 37 times
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Rank: Moderator Joined: 15/07/2008(UTC)
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Good BBC LS5/1 examples were very good
the problem was the lack of consistency for the Goodmans 12inch paper cones which were never intended for repeatable 2-way use up at this crossover point.
Thus the new project aim was consistency, plus improvement if you could get it.
On balance I preferred the 5/1 to the 5/8 but heard a good dem of an active 5/8 once
Always had a soft spot for the SA3 active, Spencer Hughes on top form
MartinC
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Rank: Administrator Joined: 19/09/2008(UTC) Posts: 2,327 Location: UK Thanks: 37 times
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Originally Posted by: Martin Colloms
Good BBC LS5/1 examples were very good
the problem was the lack of consistency for the Goodmans 12inch paper cones which were never intended for repeatable 2-way use up at this crossover point.
Thus the new project aim was consistency, plus improvement if you could get it.
On balance I preferred the 5/1 to the 5/8 but heard a good dem of an active 5/8 once
Always had a soft spot for the SA3 active, Spencer Hughes on top form
MartinC
Martin, I reckon an 'approximation' but not a new version of the LS 5/1 could be made using this driver or even this? Datasheets and response curves NB the 15" is quite smooth better than many so called hifi drivers, both will need slots to achieve improved diffraction and dispersion. 15"18"Edited by user 30 October 2015 12:28:14(UTC)
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Rank: Moderator Joined: 15/07/2008(UTC)
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the response curves are only on axis , you really need the off axis set to judge them
BTW the 'slot' barely worked and the cavity formed added some coloration
For the LS5/1 the two HF1300 were run in parallel to try and get some more power handling when operated so low in the frequency range, I recall 1.7kHz ?
Those little 19mm paper voice coils weren't up to much , 2W RMS if you were lucky , but with a steep crossover at 3.3k they would take 100W rated on unclipped uncompressed programme
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Rank: Administrator Joined: 19/09/2008(UTC) Posts: 2,327 Location: UK Thanks: 37 times
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Originally Posted by: Martin Colloms the response curves are only on axis , you really need the off axis set to judge them
BTW the 'slot' barely worked and the cavity formed added some coloration
For the LS5/1 the two HF1300 were run in parallel to try and get some more power handling when operated so low in the frequency range, I recall 1.7kHz ?
Those little 19mm paper voice coils weren't up to much , 2W RMS if you were lucky , but with a steep crossover at 3.3k they would take 100W rated on unclipped uncompressed programme Much as I suspected with the slot but will research further and determine the effects of such. I am going to contact PD to see if they have carried out some off axis measurement. Interestingly I have four of the high power Audax 34mm domes which can take the lower crossover frequency anticipated, likely if I did this that would roll one of them off above 5 K or so
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Rank: Administrator Joined: 19/09/2008(UTC) Posts: 2,327 Location: UK Thanks: 37 times
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Questions asked to see if I can have sight of the off axis family indeed I am very interesting to see what they are like off axis Edited by user 18 February 2014 15:05:56(UTC)
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Rank: HIFI God Joined: 25/11/2008(UTC)
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Originally Posted by: ashleym I was always interested in behind baffle mounting of bass drivers. I take it this helps with directionality as the frequency goes up? All sorts of, to us, odd tweeters and they still work. Clever. The slot in front of the speaker in this application is such a small change from the speaker's own diameter that you can pretty well ignore the effect on the speaker's directionality. Usually you'd aim at a slot with width roughly half the speaker's diameter, with the general view to widening the dispersion at right-angles to the slot over the top octave of its useful range. But in general bass speakers of the day were rear mounted because they relied on trapping the cone surround edge between the speaker basket and the baffle, and had gaskets to aid in this. It's only later that bonding techniques developed so that you could rely on them not coming unstuck from the front of the basket.
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Rank: HIFI God Joined: 02/02/2009(UTC)
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Thanks all for the slot info.
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Rank: Administrator Joined: 19/09/2008(UTC) Posts: 2,327 Location: UK Thanks: 37 times
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Rank: Administrator Joined: 19/09/2008(UTC) Posts: 2,327 Location: UK Thanks: 37 times
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Originally Posted by: Martin Colloms
Good BBC LS5/1 examples were very good
the problem was the lack of consistency for the Goodmans 12inch paper cones which were never intended for repeatable 2-way use up at this crossover point.
Thus the new project aim was consistency, plus improvement if you could get it.
On balance I preferred the 5/1 to the 5/8 but heard a good dem of an active 5/8 once
Always had a soft spot for the SA3 active, Spencer Hughes on top form
MartinC
Been searching for an SA3ex the SA3 actives but still cannot find a pair!!
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Rank: Administrator Joined: 19/09/2008(UTC) Posts: 2,327 Location: UK Thanks: 37 times
Was thanked: 10 time(s) in 9 post(s)
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Rank: Administrator Joined: 19/09/2008(UTC) Posts: 2,327 Location: UK Thanks: 37 times
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As an aside I recently located a fine example of the KEF LS5/1AE BBC Monitoring system. I wuill be setting them up before the Carltons in my main system. Bless my Wife our "Bedroom" system will be running a pair on BCIIIs on the end of a Krell S550i and Orelle SA100 Integrated amps :) I will report on the LS5/1AE system once they are set up Simon  Originally Posted by: darkmatter Still getting excellent results from my SA3s there is something special about a big two way hence my interest in getting my hands on a pair of LS 5/8s This is an interesting beast the LS5/1
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 Rank: HIFI Guru Joined: 12/11/2008(UTC)
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The occulsions should help a bit even though they are only slightly narrower than the woofer, they act as secondary point sources which have a wider dispersion pattern than a plane piston or for that matter a cabinet edge.
I've taken accurate polar measurements, and have seen BEM data which shows this effect clearly. These guys new what they wanted to achieve.
Mat.
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