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DrBurrito

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  1. DrBurrito

    Maximum horn compression ratio?

    Yes, this is very educational. Without knowing the equations behind hornresp’s horn frequency response simulation, I can’t say for sure, but I did observe that the key thing in getting a response that wasn’t too peaky was low woofer Q. The woofer needs motor force to drive the horn, but in my simulations I found that a more vented-box-oriented driver like the HST18, despite having fairly high motor force, tended to have sharp peaks in the response unless the box was way too large. The BC 18 iPal has the lowest Q of any woofer I know of, and it seemed to do the best job of getting down to 10 Hz in a somewhat reasonable box without too peaky a low-frequency response. Now I don’t know that Q is really the most important parameter in play, but it does make some intuitive sense that lower Q —> wider bandwidth around Fs —> easier to get less peaky response below Fs.
  2. DrBurrito

    Maximum horn compression ratio?

    Sorry, I’m using the HST (in a vented box) only as a comparison. It’s my baseline. It’s just there so I can convince myself the horn is worth the extra effort over a conventional ported box. The system I’m trying to work out is the horn, which uses a B&C iPal 18”. The HST wouldn’t work for the horn; Qts is too high and motor force is too low. At least per the numbers, 2” is enough clearance for the B&C, since it has a 20mm Xmax and folded surround. It’s not much, but it shouldn’t be hitting the other side of the chamber!
  3. DrBurrito

    Maximum horn compression ratio?

    EDIT: modelling with lossy Le like Ricci suggested makes a big difference. The horn compression ration to achieve an OK response becomes more reasonable, down to about 1:4. The horn flare has to get wider, though, resulting in a shorter and fatter box. I'm re-posting lossy Le results with the HST-18 vented box for comparison. These are presumably more realistic. On the bad side, the box is getting a bit wider than I'd hoped.
  4. DrBurrito

    Maximum horn compression ratio?

    No worries! I have considered the thickness of the main panels but I haven't yet included the bracing. That will cut down the area further, of course (or expand the box). Thanks for the tip on particle velocity. Audio folklore is that velocities should be below 10 m/s, and this gives a good rationale for this horn, I think. I had been struggling to justify all this extra carpentry versus my first design, a Stereo Integrity HST18 low-tuned vented box. Why do all the work and have a larger box if I can get the same SPL at low frequencies just by getting a bigger amp and using a conventional low-Fs, large-Xmax driver? Well, if port velocity is the measure of distortion we care about, the horn wins. I modeled both at the same RMS voltage, and at the voltage where the horn throat is hitting 10 m/s at its peaks at the horn mouth, the vented box is hitting 20 m/s at port tune at the mouth and and is over 10 m/s over most of its range. If we look at SPL, the numbers are less benign. I'm not sure what a bad value threshold is here, but we do see high pressures over more of the range at the horn throat, while the vented box is bad at resonance but much lower overall. Any ideas what SPL limit the throat should be limited to? Maybe a throat adapter could mitigate this? Yes, the fold was key to the design. I did a good bit of math to get the fold sorted. The idea was to use the expanding radius of the accordion fold to create the flare, rather than tilt the wood panels at precise angles and struggle to crumple the fold into the box. This allows a very long horn path to be crammed into a not-completely-insane box in a fairly simple-to-construct way, i.e., via a sort of matroyshka-doll structure. I'm not sure if there's a penalty to pay for the fact that the fold only really flares as it rounds the corners; I was planning on a more detailed Akabak model to capture this if it works out in Hornresp. If this thing goes anywhere, I think it needs to be called the Longhorn. No connection to Texas, but it seems pretty obvious given the length of the fold.
  5. DrBurrito

    Maximum horn compression ratio?

    Here's the hornresp parameters, the frequency response, and a 1/4 cutaway view of the box with the accordion-fold layout I intend to use to get enough path length to get down to 10Hz. The frequency response isn't audiophile flat, but I only intend to run this up to 60 Hz, so I should avoid most of the really choppy stuff. Below that, it doesn't strike me as unreasonable, especially with some room gain and EQ shaping. Feel free to critique! This is my first horn, so if there's any obvious blunders I'm making (besides maybe a too-small compression ratio?), I'd be glad to hear about it.
  6. DrBurrito

    Maximum horn compression ratio?

    I have, and the numbers look good with high compression ratios for sure. That’s why I’m curious if I’m missing anything. I’m more worried about what hornresp doesn’t model than what it does. For instance, it’s not going to model driver failure! It doesn’t know anything about the strength of the cone or the surround glue or whatever. On the other hand, if it does model distortion, I’d be interested to know about it. I haven’t seen that, only frequency response, max SPL, etc. Nothing about distortion.
  7. DrBurrito

    Maximum horn compression ratio?

    Hi, I’m planning to build a tapped horn subwoofer around the BC iPal 18, which models very well in hornresp due to its extremely low q (0.14!) and high motor strength. There’s something magical about this driver; nothing else I’ve modeled manage to get as low with as reasonable a response curve in a not-too-absurdly-huge box. VERY low: I’m planning on scraping 10 Hz if I can! One problem I’ve run into, though, is that the horn compression ratio wants to be quite high, for both response curve smoothness and to keep the box size reasonable. Something in the range of 1:6 all the way up to 1:10 works best. Now this is far outside what is typically quoted for subwoofers, which are supposedly recommended to be held around 1:2, with 1:4 a typically quoted maximum. I’ve read two reasons for this maximum: avoiding excessive horn air velocity and thus distortion, and avoiding simply overstressing and blowing the woofer cone itself. However, I haven’t heard a good *quantitative* reason why the recommended ratios are chosen. If there are any. Since this is databass, I hoped I could get a data-driven discussion on the real limits of horn compression ratios for subwoofers. Is the old 1:2 ratio just based on wimpy older drivers, and is outmoded by the new generation of crazy motor force neodymium magnet woofers, or are there some very good reasons to avoid going too high? How high, exactly, could you go, before you run into problems? Is 1:6 ok? What about 1:10? I’m thinking of something like Ricci’s dual opposed 21 iPal build, which clearly ignored the typical rules of sealed box design and overwhelmed the limits of the tiny air volume with the iPals’ high motor force. If this can be done for sealed boxes, maybe something similar can be done to create mini-horn subs.
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