Question for Planet 10

[Ioan]

Hi Dave,

It seems you know about everything about old fullrange drivers, so you may want to give me a hand.

I have a pair of oval 6x9 RFT drivers, more precisely L 2659 PBO, 6W, 6Ohm. Originally they were housed in a tube radio,
sort of open box.

Now they are hooked to a SI T-amp, on improvised open baffles, and the sound seems to me even better than in their original box.
Except being shy on bass, when compared to the Jordans in horns, hooked to the same SI, they are ahead of Jordans in efficiency
so a better mach for the tiny amp in my opinion.

Now, my question. Do you have TS parameters for these guys? Or, do you have any hints regarding a suitable enclosure for them?
I was recommended so far by some guys from German forums:
_ closed box as big as I can live with
_open baffle
_auditorium 23 rondo

I would try a backloaded horn, but I would like some advice before committing to blind horn design and plywood cutting.

Thanks for your patience,

Ioan

[planet10]

The more vintage drivers i find, the more i realize i'm just scratching the surface, but with over 500 pairs thru here i've gained at least a bit of info.

Similar to the attached (2559)?

No T/S, but they are decidedly open baffle candidates... to get bass you need a pretty big baffle -- hence the suggestion of as big a box as you can live with (ie takeb to extremes the box is the next room )

These don't show up too often in North America, being made in East Germany (and before T/S were common) so getting T/S means someone has recently measured some -- and then with age & unit-to-unit variation whether those numbers are close to what your drivers are is a shot in the dark

I should have convienient T.S capability soon, and then i'll be measuring every driver thru here

dave

[Ioan]

Hi Dave,

Thanks for your reply.

500 pairs, that's quite impressive.

Yes, mine are identical to those from your picture, except the label...and the "dammar" cone treatment contour.
I assume that was done by hand, so it would be hard to find two identical patterns.

Indeed, they were made in the former DDR (1959-1962), and used on several models of tube radios of quite good quality.
Here is a link to an interesting site http://www.del-service.de/stern_radio_rochlitz.htm with plenty of old German radios.

As far as I remember, these drivers had very good lows in their original carcass, as opposite to now. Was that related to the tube amp, I don't know, but I really need to do something to get that bass back.

Unfortunately I cannot afford, space wise, large open baffles, so the remaining options would be sealed, the Rondo thing, or a horn.
Based on your experience, would be a waste of time an effort to try a horn for these drivers?

Since you have these drivers and an idle SI T-amp why don't you give them a try. Even in the stock version, I think the SI produced a very good sound with these old drivers. I would be very happy to hear the opinion of a more experienced DIY-er regarding this combination.

Thanks again,

Ioan

[planet10]

Originally posted by Ioan
500 pairs, that's quite impressive.

It may well be more thinking about it... i've probably got that many downstairs... and for everyone downstairs have solf 3 or 4 or more...

Yes, mine are identical to those from your picture, except the label...and the "dammar" cone treatment contour.
I assume that was done by hand, so it would be hard to find two identical patterns.

That is natural -- surround doping that migrated onto the cone over time.

I really need to do something to get that bass back.

Unfortunately I cannot afford, space wise, large open baffles, so the remaining options would be sealed, the Rondo thing, or a horn.
Based on your experience, would be a waste of time an effort to try a horn for these drivers?

Being high Q they aren't really suited to a horn... fortunstely the likely best box is much much easier than that... an aperiodic box. thoe still need some tuning but can be easily described.

Build as big a sealed box as you can live with (if it has a tall aspect ratio that is better). Driver near one end and at the other put some holes (after experimenting i find long narrow slots easier to work with). Then resisitively load the slots with compressed fiberglass insulation (Dynaco gave us the trick of squashing it between 2 pieces of plastic gutter cover ... they used about 2" squashed down to 3/8"). Tuning is done with the size of the vent & how much resistance is in it.

Since you have these drivers and an idle SI T-amp why don't you give them a try. Even in the stock version, I think the SI produced a very good sound with these old drivers. I would be very happy to hear the opinion of a more experienced DIY-er regarding this combination.

Those drivers were thru here about 2 years ago (i don't get to keep the best drivers)

dave

[Ioan]

Thanks Dave,

The aperiodic box seems reasonable and I'll give it a try.

I'm sorry you don't have those RFT drivers anymore, but you can try instead some Saba Greencones with the SI, they were in the same league with the RFT ones. Bottom line, the SI is so good, that makes almost any driver a keeper.

Ioan

[planet10]

Originally posted by Ioan
I'm sorry you don't have those RFT drivers anymore, but you can try instead some Saba Greencones with the SI, they were in the same league with the RFT ones. Bottom line, the SI is so good, that makes almost any driver a keeper.

I've no shortage of drivers.... really enjoying my $7 CAD open baffles... looking forward to how much better they should get as i tweak the heck out of them.

dave