bushroot Posted March 17, 2014 Report Share Posted March 17, 2014 The smoothest low end you'll ever hear. At 17hz, my power meter slaps the side of the house! Sounds perfect for a Home theatre design . put a nice looking lid on that box and you have the pimpest coffee table in the neighborhood It sits behind the sofa. I think it's something like 30x38x18 and weighs whatever nearly 3 sheets of 3/4" red oak plywood weighs. The 18 is going to be much bigger. The port area must be equivalent to the cone surface area, meaning if you have the FI 18, you need 187.5 square inches of port. This is the profile of the port straight through the cabinet. The length determines tuning frequency. You start with the frequency you want to hit. The 15 is tuned for 22 Hz if I remember. The 18 will be tuned for 20, which means you find the wavelength of sound at 20 Hz, which is 676 inches or 56 feet. You multiply that by 1/4 to get the quarter wavelength, which would be about 14 feet. You need to 45 the corners to keep the port profile consistent, but that's the math behind it. It's really not that complicated. If you decide to build one, hit me up. I'll give you a hand. Link to comment Share on other sites More sharing options...
Smoove Posted March 17, 2014 Report Share Posted March 17, 2014 I will definitely let you know if I try it. I am now following this thread so I can refer to it later. Thanks for the info. I would probably do a 12 or 15. 2 Team Fi 15's v1 2 DD M5's 970amps of Alt 6th order blowthroughThe truck Blowthrough build : http://www.stevemeadedesigns.com/board/topic/155555-smooves-1996-chevy-ext-cab-c1500-slow-build/The 350z build : http://www.stevemeadedesigns.com/board/topic/170694-smooves-2003-nissan-350z/ My FB page https://www.facebook.com/pages/Smooves-Car-Audio-and-performance/719746144805343 Team Fi Audio http://www.ficaraudio.com/ Link to comment Share on other sites More sharing options...
bkolfo4 Posted March 17, 2014 Report Share Posted March 17, 2014 The smoothest low end you'll ever hear. At 17hz, my power meter slaps the side of the house! How does it compare to IB? Current system: 1997 Blazer - (4) Customer Fi NEO subs with (8) American Bass Elite 2800.1s Previous systems: 2000 Suburban - (4) BTL 15's and (4) IA 40.1's = 157.7 dB at 37 Hz. 1992 Astro Van - (6) BTL 15's and (6) IA 40.1's = 159.7 dB at 43 Hz. Link to comment Share on other sites More sharing options...
gr8handogoatness Posted March 17, 2014 Report Share Posted March 17, 2014 I have seen many reputable people suggest a port velocity of 10m/s to even 5m/s. But seeing as how an infinite baffle is supposed to isolate the front and back waves while reducing the acoustic suspension. I don't see how a port that is too large can create one. No you're right. I mean free air not infinite baffle. That's my bad. I was too tired to be posting. Apologies. But you can make a big port. Like 5m/s rear port air velocity, I personally wouldn't but you can i guess. But if you start getting bigger there is no loading and the sub will free air. Link to comment Share on other sites More sharing options...
gr8handogoatness Posted March 17, 2014 Report Share Posted March 17, 2014 Like as in port area? Yes it can. The woofer will act as though it is in an infinite baffle arangment if the port is too big.Does that mean that the port acts like a hole in the box more than a port, or does that mean the sub can bottom out much easier?Yes that, forgive me, I was too tired to be posting anything intelligent. Link to comment Share on other sites More sharing options...
Krakin Posted March 17, 2014 Report Share Posted March 17, 2014 I still don't understand how it could be free-airing if it is still in an enclosure and still has a first and second resonance. Krakin's Home Dipole Project http://www.stevemeadedesigns.com/board/topic/186153-krakins-dipole-project-new-reciever-in-rockford-science/#entry2772370 Krakin, are you some sort of mad scientist? I would have replied earlier, but I was measuring the output of my amp with a yardstick . . . What you hear is not the air pressure variation in itself but what has drawn your attention in the two streams of superimposed air pressure variations at your eardrums An acoustic event has dimensions of Time, Tone, Loudness and Space Everyone learns to render the 3-dimensional localization of sound based on the individual shape of their ears, thus no formula can achieve a definite effect for every listener. Link to comment Share on other sites More sharing options...
gr8handogoatness Posted March 17, 2014 Report Share Posted March 17, 2014 I still don't understand how it could be free-airing if it is still in an enclosure and still has a first and second resonance. You're right it will still resonate. There will be gain from the box itself but if the port is too big, like massively too big, the amount of loading will be negligible causing the woofer hit mechanical limits sooner greatly reducing power handling, or acting like it is "free air". Just looking strictly at an over-sized port, will still work just be hard to build and make fit. I think this is where we are seeing things differently. I'm talking about a huge port, like put an 8 in place of 4 15s in a wall huge. The woofer will act as though it is "free air". Now I don't know what the cutoff is for any given woofer as to when it becomes an open baffle, but all woofers will at some point. Link to comment Share on other sites More sharing options...
Krakin Posted March 17, 2014 Report Share Posted March 17, 2014 That could very well be where we were getting off. I guess that I also kind of have a problem saying it is free-airing when if you took measurements it wouldn't be the same, you know? I can see how an enclosure that has an 8 in sub and, just a random number, a port area of 400 sq inches could have adverse affects. I however don't want to definitively say this as I haven't seen it tested. Krakin's Home Dipole Project http://www.stevemeadedesigns.com/board/topic/186153-krakins-dipole-project-new-reciever-in-rockford-science/#entry2772370 Krakin, are you some sort of mad scientist? I would have replied earlier, but I was measuring the output of my amp with a yardstick . . . What you hear is not the air pressure variation in itself but what has drawn your attention in the two streams of superimposed air pressure variations at your eardrums An acoustic event has dimensions of Time, Tone, Loudness and Space Everyone learns to render the 3-dimensional localization of sound based on the individual shape of their ears, thus no formula can achieve a definite effect for every listener. Link to comment Share on other sites More sharing options...
gr8handogoatness Posted March 17, 2014 Report Share Posted March 17, 2014 I put a 4 inch in a box for my 15 (built for the 15 so the chamber was way too big not to mention port) and it would bottom out on like 10 watts of low frequency tones. About the same point as free air ( the large chamber had a lot to do with this too). I was impressed by the sound of it though before it bottomed out. In the little box it came in it would play those same frequencies well (for a 4) on its little 30 watt built in amp without bottoming. Now you got me wanting to try to build a box with a small chamber and huge port just to see. Disclaimer: the internal amp says it did 30 RMS and the other amp does like 15 RMS so my 10 was just a guess, but the volume knob was in the same spot for both free air and in the big box, I know because I marked it. Basically I didn't really do a test I was just messing around. Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted March 17, 2014 Report Share Posted March 17, 2014 I put a 4 inch in a box for my 15 (built for the 15 so the chamber was way too big not to mention port) and it would bottom out on like 10 watts of low frequency tones.... Thanks for posting about your experience. I wonder how much of what you saw was due to the enclosure being too big vs the port being too big. One of these days I'd like to do a test with port sizing just to see. Just off the top of my head I bet you could get away with a port up to about the same size as the subs radiating area before you ran into significant issues. I could be wrong of course, but it would be an interesting test. The biggest issue with car audio and port size is always fitting the darn things into the space you have. It would be interesting to see what could be accomplished when space wasn't an issue. "Nothing prevents people from knowing the truth more than the belief they already know it.""Making bass is easy, making music is the hard part."Builds: Link to comment Share on other sites More sharing options...
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