Cubic ft for sealed box and other questions

beat · « **on:** 30 Jul 2004, 06:28 pm »

Hey all,
I dont really understand why cubic footage would be very impt if the box is sealed anyway. Could someone help me on that? Also, if a box is only to do midrange well and the bass is coming from another box and another amp, is there any reason to port the mid box? I guess basically I am wondering how to decide when to port, passively radiate, infinitely baffle, or seal. My understanding is you port to get more bass and a passive radiator is kinda the same, infinitely baffle to alleviate distortion, and sealing will also reduce distortion but you'd lose some SPL?? These are just educated guesses but whether right or wrong I still dont know which way to go for a given application.
thanks for your input

mgalusha · « **Reply #1 on:** 30 Jul 2004, 07:16 pm »

beat,

A few questions with about a thousand answers.

.

Here is a link to UniBox - a free loudspeaker box modeling program. It's actually an Excel spreadsheet, so obviously Microsoft Excel is required but it's quite nice especially given the price. - http://home20.inet.tele.dk/kou/ubmodel.html

With it you can try different types of alignments and get an idea of how they change things. Ported, IB, sealed etc. All of them are a trade off and of course you will find proponets of each. I don't think UniBox has anything for transmission lines tho.

To attempt to answer the first question - and I'm not a speaker designer by any means. A sealed design uses the compression of the air in the enclosure as a spring and this affects the performance of the driver. A change in volume will change the resonance point, system Q, f3 and other things. I'm sure some of our resident speaker guru's can give you a much better answer.

mike

ooheadsoo · « **Reply #2 on:** 30 Jul 2004, 08:02 pm »

Volume of a sealed box tends to affect f3 by very little. The bigger the box, the lower the q, the lower the f3. But it tends to be relatively insensitive to volume compared to ported/other designs, ime.

beat · « **Reply #3 on:** 30 Jul 2004, 10:16 pm »

Cool,
Well unibox looks like a pretty handy tool. I have a couple of real simple box calculators but nothing like that. Looking at graphs is helpful to get an idea of how things change with box type. Actually, come to think of it, I think I have that program on my old harddrive but a very much older version. Anyhow I downloaded it, thanks for the link Mike and for the low down on f vs q, ooheadsoo. I wonder still if there will be any other audible differences such as tightness, realness, etc with changing box type. I suppose too that the only real way of knowing for sure is by doing test boxes and actually listening. In this case though, I will go with sealed for this project's bass box as that is what is suggested from the manufacturer of the woofer I'm using. Any other talk of box type is still welcome, I would really like to get a better grasp on this subject.

thanks,
beat

ooheadsoo · « **Reply #4 on:** 30 Jul 2004, 10:35 pm »

I prefer sealed boxes for the low q high damping properties and also low phase angle and group delay, which should provide a "tighter" sound. I think group delay is the delay between the front wave and back wave created by the woofer? Something like that...