fini Posted December 3, 2002 Share Posted December 3, 2002 John, If I come back here at bedtime, will you tell me the story of The Salami and The Sofa again? fini Quote Link to comment Share on other sites More sharing options...
Clipped and Shorn Posted December 3, 2002 Author Share Posted December 3, 2002 "C&S, if you slot load it next to the floor, you can tune it by adjusting the heitght off of the floor." Jim, How would you do that? Is this something that can be calculated? Does the slot require something equivalent to the short length of tube behind the port? -c7s Quote Link to comment Share on other sites More sharing options...
Clipped and Shorn Posted December 3, 2002 Author Share Posted December 3, 2002 "but your neglecting the downside, yes the rear output is projected fwd but it is time delayed relative to the signal that excited it. For large *theater woofer* type enclosures the time delay can be ~100 milliseconds which is more than enough to result in boomy bass output (remember the story of the salami and the sofa?). You never get something for nothing. " John, Is this something which can be tweaked with the "time delay" adjustment available on the electronic (active) crossover unit? C&S Quote Link to comment Share on other sites More sharing options...
jnorv Posted December 3, 2002 Share Posted December 3, 2002 It is the same as a ducted port, just retangular. Most people only rely on the calculated port length to get close to the final value. Dickerson's book explains how to do the final adjustment with a signal generator. Jim Quote Link to comment Share on other sites More sharing options...
Clipped and Shorn Posted December 3, 2002 Author Share Posted December 3, 2002 Dickerson reference please. c7s Quote Link to comment Share on other sites More sharing options...
jnorv Posted December 3, 2002 Share Posted December 3, 2002 Bad spelling. Vance Dickason, Loudspeader Design Cookbook. Parts Express has them. http://www.partsexpress.com/pe/showdetl.cfm?&User_ID=9829610&St=2451&St2=-39091299&St3=35511662&DS_ID=3&Product_ID=15363&DID=7 Jim Quote Link to comment Share on other sites More sharing options...
WMcD Posted December 3, 2002 Share Posted December 3, 2002 Dear John Warren, I'd like to read more about the 100 mS delay. I can imagine that if the box is a type of filter, which is theory behind T-S designs, then perhaps there is a group delay in the filter. Gee, that 100 mS seems like a lot. Roughly, it would take a path length of 100 feet to do that. Any suggestions for further reading? I like the description of the salami hitting the sofa. The sound of poorly functioning woofers are difficult to describe. Makes you wonder what they sound like if the original recording is actually that of a salami hitting a sofa. Smile. Gil Quote Link to comment Share on other sites More sharing options...
John Warren Posted December 3, 2002 Share Posted December 3, 2002 ---------------- On 12/3/2002 8:00:04 PM William F. Gil McDermott wrote: Dear John Warren, I'd like to read more about the 100 mS delay. I can imagine that if the box is a type of filter, which is theory behind T-S designs, then perhaps there is a group delay in the filter. >>This is what I am getting at. The vented box as a high pass filter with group delay at the lower end of the pass band. Gets the salami whacking at the vent frequency. Gee, that 100 mS seems like a lot.; Roughly, it would take a path length of 100 feet to do that. >>T/S alignments for large boxes with ports tuned to low frequencies (<30Hz) show predicted group delay figures in this range. The audibility threshold is 20-30ms. Any suggestions for further reading? >>"The Differential Time-Delay Distortion and Differential Phase-Shift Distortion as Measures of Phase Linearity" M. Leach JAES, V 37, Sept 1989 I like the description of the salami hitting the sofa. The sound of poorly functioning woofers are difficult to describe. Makes you wonder what they sound like if the original recording is actually that of a salami hitting a sofa. Smile Gil ---------------- Quote Link to comment Share on other sites More sharing options...
Clipped and Shorn Posted December 3, 2002 Author Share Posted December 3, 2002 I guess I know my next reading assignment: W. Marshall Leach, Jr., "The Differential Time-Delay Distortion and Differential Phase-Shift Distortion as Measures of Phase Linearity", Journal of the Audio Engineering Society, Vol 37, No 9, September 1989. C&S Quote Link to comment Share on other sites More sharing options...
fini Posted December 3, 2002 Share Posted December 3, 2002 I'm hittin' the books, myself: http://dogbert.abebooks.com/servlet/BookDetailsPL?bi=175042730 and http://dogbert.abebooks.com/servlet/BookDetailsPL?bi=141550852 Sorry about not making these active links. fini Quote Link to comment Share on other sites More sharing options...
Clipped and Shorn Posted December 4, 2002 Author Share Posted December 4, 2002 John Warren stated: "This is what I am getting at. The vented box as a high pass filter with group delay at the lower end of the pass band. Gets the salami whacking at the vent frequency." ah haa...... uh hmm..... c7s Quote Link to comment Share on other sites More sharing options...
Clipped and Shorn Posted December 4, 2002 Author Share Posted December 4, 2002 still very acceptable if designed properly some quick definitions good overview Good info from someone named Stig c&s Quote Link to comment Share on other sites More sharing options...
jnorv Posted December 4, 2002 Share Posted December 4, 2002 MOre on delay: http://www.trueaudio.com/post_011.htm C&S, I am headed over to SJSU to see if I can find the JAES paper. It may or may not be readable to mere mortals. Jim N Quote Link to comment Share on other sites More sharing options...
Clipped and Shorn Posted December 4, 2002 Author Share Posted December 4, 2002 Jim, Let me know what you find out. There does not seem to be a reprint of the article online that I could find. There seems to be some varying opinions about what threshold is actually audible, some say 10ms others 20ms others higher. Obviously there are a few vented boxes out there that people enjoy and I am sure my little diy project will be just fine. I never said I was trying to put together some cutting edge improvement on the latest state of the art. Mdeneen's diy livingroom cabinets, which mine are essentially duplicating, sounded quite fine to his ears, mine , and fini's, and at volumes many times greater than what is tolerable with our Cornwalls. The project is also do-able by me and that means I can make it a realitly before the Christmas lights are taken down. Nevertheless, the theory, theoretically, is interesting. Fortunately, searching the web has lots of helpful hints and helpful down-to- earth diy-ers enthusiastic to share practical knowledge. -c7s Quote Link to comment Share on other sites More sharing options...
fini Posted December 4, 2002 Share Posted December 4, 2002 c7s, Did you mean, "before the Christmas lights burn out?" fini Quote Link to comment Share on other sites More sharing options...
John Warren Posted December 4, 2002 Share Posted December 4, 2002 Nevertheless, the theory, theoretically, is interesting. c ---------------- Quote Link to comment Share on other sites More sharing options...
Clipped and Shorn Posted December 4, 2002 Author Share Posted December 4, 2002 "If you plan on using *literature* T/S parameters for a large format bass-reflex dedign the risk of getting less than optimum results are significant. Best they be measured directly and then the alignments made." What is the practical method for measuring the relavant T/S parameters for the particular Altec 416B speakers which will be employed? Eg. the fastest method of determining cabinet volume/ port length for a given particular driver. Whereas the risk of getting less than optimum results are significant, that does not say anything about the significance of how much less than optimum is significant. Either mdeneen got lucky using the Altec standard published T/S parameters, or the range of significant acceptability is wider (more forgiving) than the range of significant optimumness, meaning that it is "close enough for jazz". PS. How come all of the Corwall cabinets I have seen have basically the same dimensions ? If every particular driver, as you say, has unique parameters which are best measured individually in order to determine the "alignments" and cabinet design details, how do they work it out so all the cabinets have the same dimensions? I guess, if one is in the market for say Cornwalls or other units, it is best to audition a few dozen or more in order to find a couple of good ones that coincidentally got lucky in transcending the significant risks of less than optimum results during the crap shoot of the mass production process which most likely utilized standard manufacturer's published parameters. -c7s Quote Link to comment Share on other sites More sharing options...
Clipped and Shorn Posted December 5, 2002 Author Share Posted December 5, 2002 >>To judge these they need to be compared to other systems. Not necessarily if all one is after is something that sounds great to one's ears and is as satisfying as one can imagine while listening to the music of choice and is something that has pragmatic reality, that is to say, can be obtained realistically within ones practical reach. Sure, the grass is always greener, but sometimes you just want to smell the roses instead of starting a new corporation. Nevertheless, the theory, theoretically, is interesting. >>It's not a theory, group delay and phase linearity are as real as the air you breathe. The theory of relativity is as real as the air you breathe also, as is the theory of evolution. Only the gods can make trees, at least according to Enrico Murphy's laws of thermodynamically given axioms, principles, and paradigms of antinomy, and only the poets can dance circles around the rules of slip and slide. A purple cow is a confirming instance of the hypothesis that all crows are black. -c7s Quote Link to comment Share on other sites More sharing options...
Clipped and Shorn Posted December 5, 2002 Author Share Posted December 5, 2002 What happens if you plug the port. Same box, same driver, what is the immediate sonic difference? -c7s Quote Link to comment Share on other sites More sharing options...
John Warren Posted December 5, 2002 Share Posted December 5, 2002 ---------------- x Quote Link to comment Share on other sites More sharing options...
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