Adventures In Transmission Line Loudspeakers

If you can imagine shading in on a plan of the room the area around the edges, such that the shading-in toward the middle gets fainter, and the distance this shading is from the edges is about 80 cm (2 ft 6 ins), that will tell you where the bass boom, or reinforcement, is.

The density of the part E plasterboard is high, and if you tap it, the sound you get is very similar to the sound from a plastered masonry wall (pre-plasterboard era).

As such construction should be common to older solidly built houses, then a successful implementation of the speakers should suit such premises too.

Basically the absorption is very poor, unlike common plasterboard to stud walling, which many new builds over the last 20 - 30 years could be.

Therefore, it would seem, there has to be two variants of loudspeaker design, as far as the bass end is concerned.

The "clap test" reveals the bass resonance, with a low pitch in the low hundreds, and no high frequencies are audible. Repeating the "clap test" in a household room gave the opposite. This suggests the acoustic plasterboards are quite absorbent at upper frequencies. The feel is they "suck-out" the upper mids and highs.

Having used studio construction on previous installations, and there the LS35A performs admirably, it would tend to suggest their design is aimed at that use.

Fortunately, the boxes supplied by Stefan, along with the Pluvia 7 (Alpair 7 still to fully appraise) lend themselves better to this room, once they are pulled out of that shaded area.

This dictates placement along the long axis of the room, such that the drivers are firing across the room instead of lengthways.

Taking away the 2 ft 6 ins the speakers are away from the wall, from the 8 ft 6 ins width of the room gives a driver to opposite wall dimension of 6 ft (1.8m).

It is just possible to get a hearing position some 16 ins (40 cm) in from the "rear wall" using  equilateral triangle positioning, where the sides of the triangle are approx. 4 ft 7 ins.

This dictates that the speakers must perform as near-field monitors.

Reverting to the cabinet dimensions as provided by Stefan for the Pluvia 7, and with all the 8 drilled 10mm holes open, I find I get reinforcement at 125Hz, due to the room assisting (one octave up from the room resonance at 63 Hz).

I also get "cancellation" at 100Hz. And therefore I can try the 6 hole porting which centres on roughly 90 Hz.

This is something I shall do shortly and report back.

Interesting stuff to come back to. I've had similar fun with my room acoustics having 1930's brick walls with plaster on top. My 4m x 4m room models worse than it measures because I have the door open into the adjoining kitchen and a gap under the other door. Once I started to think of them like large coupled chambers I realised that leakages and losses explained things.

Fatmangolf wrote: ... is there any news?

Quarterly accounts, end of year books to do, WEEE (EU) reporting, EC (EU) sales lists. Red tape as usual...

I have ordered a range of speaker inductors however. I intend to make a notch filter to subdue the upper mids where full range drivers will always intermodulate, no matter how well made by such an experienced chap (Mark Fenlon reportedly worked for Jordan... wow!)

Why do I stick at it? Because I'm sure there is mileage in using full range drivers, but the current state is not right for me. I hope I can get it to work and it will be of benefit to all.

Sounds like someone needs to purchase protective grilles... Luckily this model isn't too expensive. I'd be gutted if I did that to a 12P driver. The Pluvia 7 only come in pairs? I'd sell the single if I were you, to recoup some of your spend.