Ls3/5a. Why is B110 rear mounted?

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#5
With deference to the mighty ZM I beg to differ. Now realize I say this with every expectation of being wrong but here goes:

I had a pair of these way back when and was initially concerned when I saw how the driver was mounted. One would think that back mounting would cause unwanted reflections?

Even though the baffle board was 13 mm one could easily see that if the driver was front mounted there would be significant blockage of the back wave.

The B110 basket was not deep and those slots in the basket would be facing the baffle board. Just imagine if the baffle was 19 mm.

My guess is that phase would likely be easily handled within the crossover since with either mounting method the center of the B110's woofer would be behind the T27 with rear mounting obviously being 13 mm further behind the tweeter, an even worse proposition which I would assume would require more crossover trickery.

So my guess it was done so the driver could breath easily with no obstruction.

Sure wish I could find a source for that wool felt they used around the tweeters!
 
#10
I am confused by what you are saying.

Are you referring to a KEF kit? What I know is that no one ever duplicated the quality of the licensed LS3/5as.

Chamfering a 13 mm panel would not be a good idea for driver/baffle rigidity.

I am not saying it is not phase related but it would seem just as easy to correct the phase with the driver mounted in front of the baffle as behind. But then I know nothing baout how to correct phase with a crossover!!
 
#11
The first commercial loudspeaker system, that I am aware of, that used a front mounting arrangement , was the Leak Sandwich of circa 1962.The other innovation of this model , is the thin walled bitumen padded enclosure. The woofer mounting included a bracing arrangement by means of a long stud bolt which tensioned the front and back panels of the enclosure. The LS3/5 design, on the other hand , seems to be more of an experimental assembly, in that by means of the screw clamped panels, internal alterations can be readily accomplished if changes are required.
 
#12
easiest way of maintaining linear phase between two drivers is to align their acoustical centres vertically , when looking from side

you're getting that usually by backing HT driver , and for that driver dimensions , that's pretty close to usual front baffle thickness

then , connecting appropriate xover , there is no delay between drivers , in xover region

however , you can do the oposite - mounting HT driver in front of bass driver ( by same amount of mm as in previous case) , then just flipping electrical phase on HT xover

chamfering or not (basket issues) ....... that is an issue per se , but in case of LS3/5 of secondary importance

there is plenty of info around , here is just one - quickie found in my PC

remember that phase with LS3/5 was extremely critical , them being intended for near field use
 

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#13
You know I am not arguing with you (of all people) but was desiring enlightenment.

Did not realize that was how it is done.

I do have many fond memories of those things. I know they were made for nearfield but it was amazing how much of a sound field they could produce when one was sitting back from them.

Brings back memories of hearing E. Costello's THIS YEAR"S MODEL for the first time along with XTC, SIMPLE MINDS, WIRE, TELEVISION, MAGAZINE, PERE UBU, Graham Parker, SKIDS ... among many others whose name's are not coming to mind. Those speakers and that era of rock music are forever entwined in my memory. Good sounding records especially from the British pressings.
 
#15
Hi Rick, I think your original question is a good one. I have wondered for yrs why it was rear mounted. There was a good technical research paper in HFN/RR in the '70's about the effects of obstruction BEHIND the driver cone and it was recognized as affecting a change in the sound.

I have done some rough measurements and reckon that the air gaps in the basket of a B110 are quite a bit smaller in area than the actual cone area. This always made me smile when people produced DIY plans for transmission lines and went to the trouble of calculating cross-sectional areas of pipes and so on when the very first thing a vibration from the rear of a B110 cone saw as it entered the "line" was a very severe restriction about an inch and a half from the cone........

Be good if someone from the design team (if still alive) or a commercial license holder could join the conversation with some first hand info'.
I gather there is a dedicated LS3/5a site and another forum elsewhere on the Web.

Thanks again, Rick.
Cheers, Jonathan
 
#19
Zen Mod. I can only find articles about a Tannoy speaker using that LS3/5 link. Where should I be looking?

Before the "13mm baffle" becomes an accepted fact, on the design specs I have seen, the baffle is 9.5mm 7 layer birch ply. This is a different thickness to the rest of the cabinet.

I am very happy for Rick to get the praise for the question, but it was not him who posed it.
 
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