RT-2 Horn sub, the result

[AndrewT]

a Labhorn is 600Litres and you need 6 of them for floor loading down to 27Hz.

[Elbert]

wow.. that was interesting!

Looks like the classic transmission line to me!

Been a while since I've looked in to that by the way..

But heck, this thread is really starting to de-rail now..

Since I've been away from any proper audio-projects for a long time, I've decided that I'll go ahead and see what I can really get out of the horn.. If not for building the greatest subwoofer ever, then at least for the fun of some good old experimentation. I Guess that's where the word "hobby" comes back in..

This also means I'll have to keep within certain economical constraints as I cant justify buying $$$ drivers just for the sake of experimentation...

So where to start?

Light cones.

The gamma driver recommended is certainly very light, and makes for a relatively smooth sim. The Seas is somewhat comparable, that too having a fairly, at least by current standards, ligh cone.

And the drivers origninally recommended were allso very light...

The challenge will be to find some candidate drivers in this category, new or second hand.

Any ideas are of course welcome..

And to tie it all together...

Klason & Strange, folded basshorn, acient design ?

[bjorno]

Looks like the classic transmission line to me!…

Yes, it’s very similar but there are a difference that makes it possible to acoustically filter out some of the speaker driver generated distortions that are not present in the input signal, especially in the upper bass. (80-160 Hz).

I’ve compared TQWT’s with BP-TQWT’s using the same drivers close to x-max and found that the sound is produced/heard differently: TQWT’s sums at far field while BP-TQWT’s always at a point in Nearfield = the port.

Of course there are TQWT’s where the port is very close to the driver entrance and if the driver generated buzz and rattle/ distortion is low its hard to hear any difference, but IME only expensive driver types with very stiff cones (aluminum) and large x-max works satisfactorily.

My surprising experience is that ordinary (inexpensive) stiff paper coned drivers in a BP-TQWT are if designed with care almost behave blameless near x-max but not in other BR type of boxes.

The speaker localization que(s) are IME heavily attenuated if a BP-TQWT equipped with a suitable placed port, if you compare the two types the advantage is easily recognized.

b

[Elbert]

Interesting bjorno..

Had it not been for the fact that I'm "past the concept stage", BP-TQWT would have been something that I'd look more in to...

After some tweaking with the active X-over, EQ, and general levels, the Horn is starting to work really well..

Since its running with the SEAS woofer from the right speaker, tweaking and tuning is not optimal so to speak.

But the sound is now what I would best describe as dry, deep and tight..

Listening to some classic Motown tracks, the fender-bass with flat-wound strings, complete with "live" studio reverberation, it really shines!

So I've decided to try and find a suitable woofer and then perhaps build a sub-EQ to fine tune the horn electronically. With the 10 band parametric I have, there's really only the two, perhaps three lowest controlls of 31, 63, and 126 Hz that's usable.

After a heap of iterative hornresp sims, it is becomming evident that the selection of suitable drivers is very limited.

So far, the sim that gives the most promising result is actually the SEAS 33F-WB!

the gamma LA1231 is very close except for seeming to be a few dB below the seas at 35-45 Hz (not by much though)

The advantage of the gamma is that the response is smoother further up than the SEAS. This is probably due to the very low cone weight, all the sims I have doone seems to show a very strong correlation between cone weight and ripples in the response curve.

Enclosed is the plot for the SEAS driver with the gamma curve superimposed in grey.

The strength of the SEAS is that it has 2mm more of linear excursion over the gamma.

But the biggest drawback of the gamma is that the integrity of the data I have scraped together may be somewhat dubious and the fact that its origins and quality are a bit obscure...

So that leaves me searching for an extra SEAS 13" woofer (hard to come by as they went out of production in the mid 80's), or any modern equivalent....

The characteristics that seem to work is:

Very low moving mass; 20-40g
Very low Fs; around 25 Hz
Moderate BL; around 10 N/M
Xmax; 5-7 mm
Qes around 0.4

relatively high Vas 240 and up..

regrettably, very few modern drivers seem to resemble this...

any suggestions will of course be most welcome..

[tinitus]

SBAcoustic, right under your nose, fits the bill

[Elbert]

Thanks for the suggestion tinitus!

Low frequency extension comes out significantly better than the SEAS 33F-WB.

But unfortunately, the heavy cone (I assume) causes a more ragged response which will probably make integration with the stereo speakers more challenging.. (?)

I've attached the response from this SB Acoustics driver superimposed in gray over the SEAS response..

The perfect driver would probably have the smoother response of the seas driver and the low end extension of the SB driver.

[Elbert]

And following this up..

I modified the moving mass of the SB driver from 99 g to 35 and did a new sim.. And the result from that was in deed excellent looking..

A driver (if it existed or were even possible) with that response would certainly be worht trying.
Enclosed is the response superimposed in grey over the SEAS again.

[tinitus]

The ragged response seems to be related to your design

Last time I suggested the Dayton RS270S, you disapproved because its only a 10"
I suggest you try to sim it anyway, cant hurt, and you might be surpriced

Which reminds me that you could also try the SBAcoustic 10"
Lighter cone than its 12" brother, all else mostly the same

Your design is from a time before Martin Kings software, which is supposed to be the only one to do the calculations correctly, so the design may even not be optimal with a 12", a different size may as well do it

You may also want to take a look at other Daytons

http://www.intertechnik.de/index.htm...2595&suchwort=

[Elbert]

Tried a sim with the last woofer you suggested.. but the result didn't look very promising...

untill I tried simulating with two!

it should be physically possible to cram in two 10" or 8" woofers in tandem by making an adaptor baffle fitting over the original 12" driver cut out.

Tried simularting some drivers in this configuration, and the reults so far look encouraging..

[AKN]

Hi,

Go with 12" driver to the RT-2 horn.
Here's one of several measurements from the original RT article (SEAS 30F):