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In the Forum: Horn-Loaded Speakers
In the Thread: Tractrix Bass horn vs Spherical Wave Horn - Bass loading
Post Subject: It is about nuances, as usually.Posted by Romy the Cat on: 7/4/2015
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 Blaukopf wrote:
First, Romy describes his horns as spherical. Later he names them tractrix. Are some of the profiles of the spherical wave profile?  

Yes, they are spherical, wish means not rectangular. Everything but midbass are Tratrix. I do not know what is the “spherical wave profile.”
 Blaukopf wrote:
Bruce Edgar wrote : You will be very  disappointed  in the bass response with a  Tractrix  horn. The bass response near the flare  frequency  cutoff  is limited by the throat reactance, which peaks at the flare  frequency . The horn is loaded for the most part by the throat resistance. Any reactance loading will reduce the output. In  exponential  and hyperbolic- exponential  bass  horns  you can cancel out the throat reactance with the back chamber, but with a  tractrix horn it is too short and the back chamber doesn't cancel out the throat reactance.  Tractrix  is great for mid bass and midrange but a terrible choice for bass. Where does the bass frequency start ?  
Well, Bruce Edgar is right but to understand him literally as some kind of firm postulation would make Bruce Edgar wrong. You need to understand that Bruce Edgar customers are generally idiots and whatever he does and say is targeted for semi-idiotic perception and presume that a person is lacking of any personal practicing and thinking. Yes, the bass response limited by the throat reactance and in long horns you can “cancel” throat reactance with the back chamber. In reality you do not cancel anything but you just balanced it out. Do you think the very same does not take place in short (Tratrix and alike) horns? Absolutely the same process. The effectiveness of the “cancelation” of throat reactance by back chamber is less with Tratrix but at the same time Tratrix is shorter then exponential, the mass of air on the horn is lower and consequentially the amount of the throat reactance per the same cut off is substantially lower. Again, it is not the rule but different degree how throat reactance impact different profiles. The different profiles do have own sounds but it has not so much to do with throat reactance but rather deepens from very many reasons: location of horns, how room modes used, cut off and slope, type of crossover, type of driver, type of loading, exit profile, and so on and so on. I would still do not use Tractrix for bass but where bass frequency start in this context is a subject of debates and specific condition of a given installation. Bruce would say that “you will be disappointed  in the bass response with a  Tractrix  horn” but I would retort it that Tractrix  would lose in amplitude response but clearly will in quality of bass. Exponential and Tractrix bass are different if they properly implemented with respect to own topology. Yes the long horn would have “more bass” but it is very much not the final destination.
 Blaukopf wrote:
My sims with hornresp show a good loading for a tractrix profile even at 80 Hz cutoff frequency - horn is huge of course. same for a spherical wave profile. How are they different soundwise ?
Again, you are looking for answer of your general question but the question is formulated faulty. I do not care what hornresp shows – trash this piece of crap or talk about it with the Morons from DIYaudio sites. If you appreciate what is done in Macondo and ask about the tractrix profile of 80Hz then I would ask what the hell you doing to use 80Hz tractrix? The 80Hz tractrix my nature of being too long and too large exclude any time alignment. Are you building horns or Sound? With my experience I see absolutely no use of 80Hz tractrix unless it is some kind of super exotic installation, something that you most likely do not plan.

 Blaukopf wrote:
My dilemma : Exponential horns may load better but in a setup I prefer to have the same profile for all horns.  Could you give some insight into this thorny question ? PS there were some excellent statements by JLH on push-pull TH ( am building one myself) but the images have unfortunately disappeared.

Marc, I do not think that to have the same profile for all horns is proper objective. You do not integrate profile but sound. Trust me if one know what he is doing you can with any profile get good results. I do not know what you are doing and you did not explained in details your ideas in order to solicit any sensible and practical advice. Your debate about short horn vs. long for bass is valid but lacking context. If you are taking about Macondo then it would not be possible to use a long horn for uperbass and it would be a good 2 feet longer and I would not be able to time-align the horns.

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