Tractrix
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Posts posted by Tractrix
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Guys,
I don't think the sidewall obscuring the throat is a problem at all for a simple driver with a single diaphragm used as a mid-range. It just seems to mess things up when the two drivers of a coaxial need to work together. Notice the green plot on the K2 horn goes west right at the 9 KHz crossover. That's where the two drivers are both operating and must sum together cleanly. Earlier tests with the DCM50 driver showed good off axis response all the way to 10 KHz, Dr. Edgar expected his type of horn to be crossed over far lower than that anyhow! I'm not sure what would happen to the off axis response with a wide range driver. I don't have one here to try. For use in the Khorn, it would need to extend all the way down to 400 Hz without distortion too. That's a tall order! That's why PWK couldn't do a 2-way. This is really the reason for doing a coaxial. It's to get as close to a 2-way as possible.
Al K.
The tweeter needs 2 notch filters and the midrange needs a zobel network in order for the passive crossover to function correctly.
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Well, I found that the B&C 12PE32 is an excellent driver for a horn, so I bought 2 of them. I only had Erik's spreadsheet at the time, and saw that a 60Hz tractrix 1/4 size could be only 67cm long. So, I got excited and ordered the drivers. Then I used Hornresp and saw that there was a big difference using that program, where the length was something like 160cm! So, I've been trying to figure out which program is the correct one, double checking my numbers over and over again and scratching my head. I used another program and it said something like 158cm for that horn, so I guess Erik's spreadsheet has an error in it. So, I designed a 100 Hz hyp-ex, 1/4 size, that is 105cm long. It seems like a waste to use this driver for that, since the Fs is 51Hz, but without an accurate way to design a tractrix horn, I'm left with the hyp-ex, which isn't a bad thing really. Most people use hyp-ex for bass horns since they easily extend to the horn's Fc. Tractrix bass horns a known for not really extending to the horn's design Fc. So, I thought I'd ask the horn experts here about this and see what everyone had to say.
I was just told on another message board that Erik made a mistake in his spreadsheet. The formula for the mouth radius has the speed of sound @ 340m/s. That needs to be changed to 344m/s and then it agrees with the other software!
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Having the mouth cut off is less correct, so in that instance Erik's spreadsheet is better as you will get less edge diffraction.
Or something like that...
That sounds right to me, but the folks working with Hornresp seem to think just hacking off the horn is the proper way. Erik's spreadsheet seem to make a miniature horn with the same final 90 degree flare of a typical tractrix. I just can't believe the length since it is so different from everything else I've used. This thread talks about how different people truncate or miniaturize a tractrix horn from full size to something smaller: http://www.diyaudio.com/forums/multi-way/194184-tractrix-1-pi-2-pi.html
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Well, I'm impressed! I tried playing with the speed of sound in Erik's spreadsheet and it didn't change the length of the horn very much. It's the difference in length that has me scratching my head. Erik gives 67cm whereas the others are more like 160cm or so.
I'm thinking of just sticking with a 100Hz hyp-ex that is 105cm long and admitting that I can't live without a direct radiator subwoofer. At least in this case, both Erik's spreadsheet and Hornresp give the same results.
The last time I designed a horn was 20 years ago, when I had a Mac computer with MathCad on it. I used the formula's from Bruce Edgar's Speaker Builder articles.I paid someone to build a 1/4 size 70Hz hyp-ex straight horn using the EVM-15L lead guitar driver. I was happy with it and stopped designing horns. I now think almost 4 feet (including rear chamber) is kind of excessive for horn length in a normal size living room.
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At some point....I'd like to call you. A lot of this stuff is heard to explain in a few paragraphs.
I use online calculators....purely for "calculators". Volvoteer's has a lot of other stuff built into it that I ignore. Another I've used is...
http://fullrangedriver.com/singledriver/tractrixcalc.html
Now.....I've compared these two to each other and they are close if not the same.
Hornresp.....I piddled with it for sometime and currently don't use it. I still draw out everything on paper. I used to do the exp or tractrix calculations by hand but came out very similar to the calculators.
I thought Hornresp was cool when I wanted to take a design/idea and figure out what kinda response change I would get for small changes in throat size or whether I'm gonna stick the design in a corner or not. The last three bass horns I designed and put together (not posted), I never touched the Hornresp program. This isn't a recommendation to you....just the way I do it.
jc
That would be great, after we deal with the hurricane coming through! I appreciate your assistance.
With Volvoteer's spreadsheet, for a 1/4 size 60 Hz tractrix horn using the B&C 12PE32 driver, I get:
throat area: 178.8cm2
mouth area: 6388 cm2
length: 67.1cm
For the single driver website you listed, I get:
(I put in the same throat area)
mouth area: 6145cm2
length: 158cm
for Hornresp, using their system designer, I get:
throat area: 168cm2
mouth area: 6539cm2
length: 161cm
So, I don't know what the heck is going on, something has to be wrong here.
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Also, did you design your tractix from the Hornresp program or from a spreadsheet? I noticed a big difference between this spreadsheet:
http://www.volvotreter.de/dl-section.htm
He didn't respond to my request for clarification on the differences. It seems that the spreadsheet preserves the flare of the tractrix at the mouth when downsizing the horn, but Hornresp does not. It merely chops off the tractrix curve to make it smaller. I'm not sure which way is the proper one. I was very excited when I initially designed a 60 Hz tractrix using the spreadsheet because it wasn't very big. But, when I used Hornresp it was much larger, using the same driver. So, I switched to a 100 Hz Hyp-Ex horn, where both the spreadsheet and Hornresp agree. I just have to accept that I need subwoofers...
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I have been told that the rear chamber calculation in Hornresp follows the Leach (or is it Keele?) formula, which is only appropriate for Hyp-Ex horns. It's not clear if it applies to a tractrix horn. Also, it seems that anything that affects the acoustical impedance of the horn also affects the ideal rear chamber size. Tractrix bass horns are known for not extending down to their cutoff frequency in real life. That's why they are mostly used in midrange and tweeter horns.
I wasn't referring to a Zobel network. I was mistaken about the notch filter.
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I personally use hornresp and adjust the rear volume until the lowest impedance peak flattens out in the simulation...which works well when you start deviating from standard rule of thumb horn size equations. Although I must confess that I've never tried comparing the equations to the hornresp model - I should probably do that.
On my next horn build, I'm going to use the Dayton WT3 woofer tester to measure the impedance and then adjust the rear volume until the impedance flattens.
I see from trying this out in Hornresp that if you adjust the rear volume to make the electrical impedance resonance point become flat, then the SPL response in the lower frequencies goes down. If I increase the chamber volume just a bit above that point, the bass response improves. I suppose there is a compromise in there? What if we used a passive RLC notch filter to cancel the impedance peak instead?
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Hey Craig, I want to run this by you to make sure I'm going in the right direction.
On the Sectoral cap:
Old New
50uf to 100uf
40uf to 100uf
30uf to 50uf
15uf to 50uf
I'll install one on top witht the clamp and one underneath. I thought I would solder the two ground pins to ground circuit first and then work the Pos.
Thanks.
By george I think you got it. The 17 years of fog is lifting
Be careful about making the DC supply capacitors too large since the inrush current may become so high that it strains the power transformer and rectifier too much.
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I would make sure that the following resistors were matched:
R47:R48
R45:R46
R55:R56
R53:R54
R61:R62
Also, because the line voltage has changed since this amp was built, going from 110 to 120VAC, you now have too much voltage on the output tube plates. These tubes are going to run hotter than intended. You may have to adjust R58 to bring the DC voltage down.
Otherwise, without changing the input and driver stages, there's not much to do that has not already been said.
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I ordered a Little Dot DAC:
http://www.littledot.net/forum/viewtopic.php?f=9&t=814&sid=bcdf970ddeb399032b74fe4a83f1aaf1
$259 + $45 shipping from Hong Kong.
"The Little Dot DAC_I is an exceptionally versatile, reference-quality external DAC unit with both single-ended and balanced outputs! Four inputs (Coaxial, BNC, Optical, and USB) allows the Little Dot DAC_I to be used with digital source like a CD Transport or a computer as a standard USB audio device. User functionality customizations include setting the bit-rate, maximum sampling frequency, and how the DAC's digital filter operate (sharp or gentle). At the heart of the Little Dot DAC_I are the Wolfson Micro's high quality 24-bit 192Khz WM8740 DAC chip, WM8805 ultra-low jitter (50ps) digital transceiver chip, and the ultra-low distortion LM4562/LME49720/LME4910. A dual crystallizer re-clock circuit ensures a synchronized and jitter-free signal!
The internal components have been carefully chosen for their quality and precision - tight tolerance resistors, WIMA coupling caps, ELNA and NISSEI filter caps, Toshiba optical and Neutrik XLR connectors."
It does not have a remote control though if that's important to you.
David makes another DAC that has a headphone amp in it, as well as a large variety of headphone only amps.
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This would be very hard for me to describe in words....and lengthy. It you were sitting next to me with my drawing it would be easy.
It is one horn really. 90 sq in throat. You could think of two 45 sq in throats that fire into a intial short horn about 14cm...that have a tractrix flare expansion based on a 90 sq in throat, Fc 100 full space.
The explanation for the full space......that would be lengthy and a bunch of jibberish if I were to explain all that. I could have done 1/2 space and use a smaller Fc.....but can't remember why I talked myself out of that when I drew this up long time ago. One thing though........I like the idea of pulling the speakers away from the wall/corner.
jc
OK, thanks. What made you decide that the initial short horn should have an Fc of 100Hz? Is that a full size expansion? I thought this was an 80 Hz horn over all? I'm confused... sorry.
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There are couple of formulas on this page:
http://www.rocketsciencecanada.com/rocketsciencecanada/Sound/Horns/Info_Design.asp
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I'm curious about this design. It looks to me that you actually have two horns, connected mouth to throat. The first horn(s) are very short, one for each driver, and they are merged to the throat of the larger tractrix horn. Can I ask where you got this idea? How did you design the very short horns? Are they exponential or some other shape?
Thanks for posting all of the photos for the horn. I've been working with an Excel spreadsheet to design a similar horn, but with only one driver.
I've read that tractrix horns generally do not provide good bass response. You say that you designed these as full size because you wanted to be able to put them anywhere, but what if I was committed to placing them against a wall for 1/4 space and designed a 1/4 size tractrix horn. Would the bass response be better or worse than a 1/2 or full size horn?
I'm planning on using the 12PE32 driver since I need extension up to 500 Hz. How do you change the parameters for the horn calculation when you use 2 drivers like you have done?
Klipsch Lascala Plans
in Technical/Restorations
Posted
Does anyone know how to adapt this type of horn for other drivers? If I design a particular horn for a particular driver, how do I fold it up into a La Scala shape? I think have an idea of how to do it, but I'm not sure yet if it works since I've never built one.