IMF RTS 1 loudspeaker opinions please

[r100]

Hello to All,
does anybody know these speakers ? I am looking at an advert on a local auction where a pair is going for around 50 quid. They seem to have a good and professional reputation. Thank's.

https://www.dropbox.com/s/6svwx8cq47zl83x/tdl.jpg?raw=1

[walpurgis]

They're TDLs, not IMFs.

Look decent enough though. The drivers look rather similar to items Heybrook used. I'd grab them. Why not make an offer?

[r100]

oops, yep... and the model is RTL not RTS ... :cool:

[YNWaN]

TDL's 'design thing' was transmission line bass loading and the foam filled rectangular ports suggest this is the case here too. The only thing is that this is really too small a speaker to make use of a proper transmission line so it's more likely to be a kind of damped port (aperiodic).

[walpurgis]

this is really too small a speaker to make use of a proper transmission line(aperiodic).

Try telling that to PMC :).

[YNWaN]

Yeah well it's still true, physics is still physics and marketing is still wishful thinking.

[Macca]

RTL stood for reduced transmission line - or something similar to 'reduced' anyway. Same as the RTL1, 2 3 and 4 which are still around on the used market.

Somewhere between a port and a TL but then so is any TL that contributes the rear wave to the sound.

[walpurgis]

Try working out the principles behind the IMF ALS designs. I think I can guess how they work.

http://i63.tinypic.com/2cek7x3.jpg

These were capable of some very fruity, tight and powerful bass.

[Macca]

Thus in the somewhat smaller bookshelf ALS 40 Il an additional bextrene sub-woofer is fitted at the end of the line to enhance low frequency efficiency and extend the bass response below that which is typical of such an enclosure size. This extra bass unit is electrically driven via the crossover network and is of dissimilar but interelated resonance to the upper bass unit and to the length of lirie. As such, the 1 active' transmission line (ALS) is a stage removed from the slave units employed with reflex enclosures

not sure I fully get it but there you go


RTL was Reflex Transmission line

Here is the link to the brochures - Rupert is looking at the RTL1 not the RTS 1 which doesn't exist

http://www.imf-electronics.com/Home/tdl

[r100]

yep, sorry, I got the title horribly wrong. Thank's for the input so far :)

[DSJR]

RTL stood for REFLEX Transmission Line, in other words, a longer than usual port that ran full width on the box helping it to be more rigid. The RTL2 was the star of this particular range we found, but the RTL1, with identical drivers (and possibly crossover?), could be a little fierce without the extra bass extension to balance it. Very 'clean' as I remember and great for jazz. Will work fine very close up to a back wall and should reward a good system as well as tolerate a less than exalted one.

Only thing I can say against this series of RTL's is the cabinet vinyl finish, which was tolerable in black, but bubbly in the rosewood colour they also made these in. I thought at first that £50 is a tenner or more too high, as RTL2's used to go for £75 or so, but as used prices are stupid these days, so I could be way off...

[walpurgis]

RTL stood for REFLEX Transmission Line

A bit of a misnomer I suspect. I doubt the 'reflex' bit had much to do with a true Hemholtz resonance design. More likely 1/8 wavelength line like the B&W DM2 or possibly even 1/16 wavelength on the small models, which would most likely be a selling point than a feature that properly augments bass output via the line.

[YNWaN]

The concept of a transmission line is that the back wave is gradually absorbed by the 'line' and is, in effect a pure infinite baffle. The reality is that for low frequencies you need an extremely long transmission line and even when folded up this makes a very large cabinet. The halfway house is to accept that some output will still exist at the end and this can be used to couple to the room so long as the output phase is correct. The reality is disjointed and badly timed bass - PMC included (quantity doesn't equate to quality).