RT-2 Horn sub, the result - Page 3 - diyAudio
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Old 9th January 2009, 07:33 PM   #21
Elbert is offline Elbert  Norway
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According to the simulation I've done, there's plenty of headroom with regards to max excursion all the way down. Currently I don't even have the amp power available to take me near the damage excursion limit.

And no sir, the rear chamber is 100% tight, the carpentry work was at least one thing I got reasonably right with this project so far!

Now, If I can just get that SEAS woofer in there...
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Old 9th January 2009, 09:08 PM   #22
Elbert is offline Elbert  Norway
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.. And in it went...

Well, that was a remarkable difference, suddenly the basement was back in the music!

Allthough there is probably still some room for improvement with proper equalisation and X-over adjustments (and perhaps an inductor), the Horn now seems to go just as deep as the old BR woofer, so that proves that I screwed up on woofer selection and that the horn has true potential given the right driver.

Too bat in a way, that Eminence driver was just soo sexy looking with that big fat magnet and everything!

Enclosed is a hornresp sim based on the horn profile provided by Bjorno was kind enough to share. The gray curve is the result with the 27 Hz Fs SEAS woofer.

http://www.seas.no/images/stories/vi...-wb_and_dd.pdf

The graph shows a somewhat improved low end response, but the audible result was certainly more dramatic than what the simulation plot suggests.

So, goodbye High Fs PA midwoofer and welcome lo Fs HiFi Sub!

but then there is a new problem, the main speaker will want it's woofer back, and I need to find something equaly, or even better, performing to go in the horn...

there are a number of super-low Fs monster woofers out there (a lot of them with very poor efficiency it must be said).

What worries me a bit is that most of these woofers have very heavy cones.

The original article warned against using woofers with heavy cones just like it advised the use of low Fs drivers..

Hmmm..

but now that I've got an improved hornresp model and have performed some practical experimentation correlating simulations with real life results, this tool might be a bit more usefull for selecting a new woofer.

I must however change my conclusion from "disappointing" to "really promising"
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Old 9th January 2009, 10:21 PM   #23
tinitus is offline tinitus  Europe
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Nice to hear we were on the right track, and you have done good work to prove it, makes it meaningfull to be here

One reason your Seas works subjectively better but really dont measure that much different could, besides the lower Fs, be due to different and higher Qts

A 10" SB Acoustic may be a good choice, but its not the cheapest, 212 EUR from IntertechniK

They also sell the US Dayton, and the 10" RS270S cost only 99 EUR and is said to be real good value

The Dayton has 12mm Xmax which is ok, unless you play exstremely loud
The SB Acoustic is a real performer in terms of Fs and Xmax

I have never heard any of them, just fore inspiration


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Old 9th January 2009, 10:56 PM   #24
Elbert is offline Elbert  Norway
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This thread has certainly been useful so far!

One thing is theorizing and discussing, but the real fun part is to do some practical experiments!

Some of those drivers look interesting, but I'm more on the lookout for a 12" driver as this is what the horn is dimensioned for.

Just did some more hornresp sims, and I the general trend seems to be that low Fs woofers with heavy cones generate very uneven responses.

Having said that, the low end extension seem to be better, so it might be that there is an inevitable inherent compromise there.
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Old 9th January 2009, 11:18 PM   #25
AKN is online now AKN  Sweden
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Hi,

I've built that basshorn back in the eighties and I was very satisfied with it, good performance for it's size being a horn.
Back then I had best result with a Gamma LA-1231 (some rebranded Bulgarian unit), very lightweight cone and large VAS. Gamma driver still available at Hi Fi Kit same cone but ferrite magnet opposed the prior AlNiCo magnet used on earlier units. What the motor change have done to the specs I donít know but I suspect performance has decreased somewhat.
I remember that I the gamma unit had limited power capability, remembering that I fried the coil playing loud at a party.
I did also try a low VAS high Fs driver and the result were almost a disaster as I recall.
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Old 9th January 2009, 11:52 PM   #26
Elbert is offline Elbert  Norway
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Hei Anders!

Well, as a matter of fact, I just did a hornresp sim with the gamma driver you mentioned, and the response curve is by far the best looking so far, so it is very interesting to hear that you had such good results with this driver!

And your disasterous result seems to correlate very well with my own recent experience using the Eminence Delta pro 12".

If the driver had been slightly less expensive (300 NOK in shipping to Norway bumps up the price), I would have concidered buying one just to try it out.

But at the moment I'm having doubts wheteher I should continue to sink more money in to this project as I suspect that even with an optimal driver, I will not get the deep bass I really wish for.

And with a box that size, I really feel that there should be an advantage compared to what one can achieve today with a BR enclosure of the same size..

on the Hifi-kit web page, the Gamma is rated at 150 watts, so perhaps there has been some improvements over the years?
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Old 10th January 2009, 12:39 AM   #27
AKN is online now AKN  Sweden
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Elbert,

Ok, I did put about 300W into the horn when the Gamma VC blew.
How low in frequency did you expect the RT-2 to reach, done any measurements in room?
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Old 10th January 2009, 08:45 AM   #28
AndrewT is online now AndrewT  Scotland
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Quote:
Originally posted by AndrewT
................It is simply too small.

It should make an upper Bass horn...............
quid pro quo.
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Old 10th January 2009, 10:56 AM   #29
Elbert is offline Elbert  Norway
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300 Watts? Small wonder the thing melted, hehe!

Expect and expect... Well.. I was assuming that it could go down to 40 something with reasonable output, but you might say I was perhaps expecting more a certain listening experience than numbers. Like jbell pointed out numbers are one thing...

I guess I was hoping for something that could really set the room in motion without getting pushed in to distortion you might say..

How did the Gamma actually compare with other drivers you tried, what made it better?
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Old 10th January 2009, 11:38 AM   #30
AKN is online now AKN  Sweden
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Quote:
Originally posted by Elbert
300 Watts? Small wonder the thing melted, hehe!

Expect and expect... Well.. I was assuming that it could go down to 40 something with reasonable output, but you might say I was perhaps expecting more a certain listening experience than numbers. Like jbell pointed out numbers are one thing...

I guess I was hoping for something that could really set the room in motion without getting pushed in to distortion you might say..

How did the Gamma actually compare with other drivers you tried, what made it better?
The Gamma had great sensitivity and did go lower in RT-2 compared to other available units. That said, I think that many modern drivers would also perform nicely.
I had certainly no problem reaching down to 40 Hz with good sensitivity and low distortion. I used third order active filter crossing at 100Hz over to main speakers.

I was 15 years young back in 1982 when I did build the RT-2 together with my grandfather, an experience I'll never forget. The RT-2 was then in duty for about 10 years until a heat radiator sprung leak and destroyed the horn.

Back then I did not have any measurement capabilities as of today. It would be higly interresting to see some in room measurements for this bass horn.
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