purplesyrup Posted May 10, 2012 Report Share Posted May 10, 2012 (edited) I searched the forum, and the web, on many different occasions trying to get a complete explanation on vent mach. Ive built quite a few SPL/sq boxes over the years, I've always kept the vent mach around .04 to .05, its always worked out and performed how I expected. I am in the progress of a specific design that is throwing me some curves, you will see why in about a month, and Anyways, I have to have about 40 sq inches of port. One port that I have figured out has a vent mach of .04 which I know will work out fine, but then I was also looking at possibly using 2 5" ports which keeps me right at almost 40 SQ inches but reduces the vent mach to .02. My question is, will it be an advantage or a disadvantage to go to .02? how will it affect the performance, will it make the sub capable of more output, or cause less output, will it go from sounding great a .04 to sounding like shit at .02, I have searched and searched the web, I have never found a single source elaborating pro's and con's explaining vent mach. Any help on this subject would be greatly appreciated, I like to experiment, but have to get it right the first time on this project. My Goal with this design is also an SPL/SQ style box, sounds great with music, with the ability to burp a high number tone. Sub is DD9512, will be have 2000w RMS of real amp power. Edited May 11, 2012 by purplesyrup Quote Link to comment Share on other sites More sharing options...
AI James Posted May 10, 2012 Report Share Posted May 10, 2012 never heard of the term vent mach Quote Link to comment Share on other sites More sharing options...
purplesyrup Posted May 10, 2012 Author Report Share Posted May 10, 2012 its the rate of speed that air flows in and out of the box. having too high of a vent mach will create horrible port noise like 16% and up, whch means 16% of the speed of sound from what i've found out, so really the difference between .04 and .02 is only a 2% difference, but small numbers can still have a big impact which is what im trying to find the answer to. Quote Link to comment Share on other sites More sharing options...
OrionStang Posted May 10, 2012 Report Share Posted May 10, 2012 Disregard James' comment. He either "knows it all" or doesn't know shit. Quote SMD Super Seller My Feedback Thread Link to comment Share on other sites More sharing options...
n8ball2013 Posted May 10, 2012 Report Share Posted May 10, 2012 how about the frest of the box specs Quote THERE IS NO BUILD LOG! 1998 Chevy Silverado ext cab Alpine CDA-9887 4 Team Fi 15s 2 Ampere Audio TFE 8.0 2 Ampere Audio 150.4 3 Digital Designs CS6.5 component sets Dual Mechman 370XP Elite alternators inbound! 8 XS Power d3400 6 XS power d680 Second Skin Stinger Tsunami Wiring Sky High A Real Voltmeter not a piece of shit stinger. Link to comment Share on other sites More sharing options...
purplesyrup Posted May 10, 2012 Author Report Share Posted May 10, 2012 (edited) I figured it out. Having a vent mach of 0.02 will slow the subs sound waves to the point that it will be a disadvantage, the first con of the vent mach being that low is the loss of back pressure, the sub looses its ability to load, which can make the sub have a weaker power handling because its getting close to having a free air experience, the next con is that the slowed down sound waves come out so slow that sounds are noticeably delayed to where you are still hearing one sound when the sub has already started playing another blurring the different tones together due to the slow leftover soundwaves murdering the sq quality I was looking for. I'm sure that a one tone burp box that is the perfect size for the sub through trial and error may benefit from such a low vent mach, but for music it would sound sloppy. .04-.05 is ideal for spl/sq, (plays music.accurately while allowing the sub enough back pressure to get very loud. And then up to .10 for sq, having a vent mach this high limits the subs from its ability to release its full SPL potential because the vents airflow is restricted. Hope this helps some one in the future. Edited May 11, 2012 by purplesyrup Quote Link to comment Share on other sites More sharing options...
purplesyrup Posted May 10, 2012 Author Report Share Posted May 10, 2012 I'll show the box specs when its all done, the first fun fact is its not a box. I'll have step by step photos and YouTube videos of what I've been doing as soon as my dd sub is here, i'm at a hold on the project until the sub is in my hands, its 50% done. the 9512 is awaiting they're newly updated parts, but they said it will be shipped out in 4 Weeks. Quote Link to comment Share on other sites More sharing options...
AI James Posted May 10, 2012 Report Share Posted May 10, 2012 Disregard James' comment. He either "knows it all" or doesn't know shit. and how did your comment have anything to do with the topic at hand?i hadnt heard of the term, so i told him i hadnt heard of the term hoping he would elaborate. I always call it port velocity, its the wrong term but its refering to the same thing. But i wouldnt have known that had it not been elaborated. Quote Link to comment Share on other sites More sharing options...
C-Fizzy Posted May 10, 2012 Report Share Posted May 10, 2012 Wouldn't different frequencies cause alternative port velocity? 20hz surely can't travel out of the box as fast as 45hz, can it? I would also like to know how you calculate this. Quote under construction I hate People with crappy primered cars rolling on hubcaps that are louder then me. u hate c-fizzy? Link to comment Share on other sites More sharing options...
purplesyrup Posted May 10, 2012 Author Report Share Posted May 10, 2012 (edited) The vent mach's maximum velocity is at the tuned frequency, Edited May 11, 2012 by purplesyrup Quote Link to comment Share on other sites More sharing options...
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