stigg
Quarternote
Posts: 19
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Post by stigg on Jan 27, 2021 17:38:37 GMT -5
I have a new Fender rumble 40. It is fully enclosed and the tone is ok but I remember some small bass cabs with ports that sounded better so I'd like some info on how to figure the size of the ports. The details: 40 watts, 1-12" speaker, cab depth 12", cab width 16.5" bottom to top 16.5". I don't know the formula to find cubic inches, in order to find the right or close to right size of the ports. Thanks. s:0)
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Post by Jim D. on Jan 29, 2021 9:43:54 GMT -5
Much to be said here. First, the cabinet volume in cubic feet (or inches) and the speaker you have was carefully designed as a system. This is so the the frequency output (what you hear) is predictable and controlled (shaped) as to not overly favor or disfavor certain frequencies or notes on the bass. What you have now is an acoustic suspension design where the air in the cabinet is sealed and acts as shock absorber, controlling and damping the speaker cone movement. It is entirely possible the speaker is not designed for a free air cabinet where the air in the cabinet has access to outside air. A ported cabinet design uses the port as access to outside air and is a form of a free air design. The port dimensions are absolutely critical and are based on the natural frequency data of the speaker and the cabinet dimensions. There are many design calculators for ported cabinets. Here is one of them: www.diyaudioandvideo.com/Calculator/SpeakerBoxEnclosure/Notice all the data you need to design this. If a ported design can be done with your speaker, you probably do not have sufficient volume (cubic feet) with your cabinet to do this. If you just choose a port inside diameter and length and install it you could end up with booming bass on certain frequencies (bass notes) and other frequencies or notes will be tuned out, non resonating, or essentially dead sounding. I would not suggest adding a port. If you want to proceed anyway, many companies sell plastic ports in various inside diameters and you would cut the length to the exact dimensions given by such speaker box calculator configurators as the one above. |
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Post by Jim D. on Jan 29, 2021 9:52:48 GMT -5
Volume is W x H x D, so 12" x 16.5" x 16.5" = 3,267 cubic inches. In cubic feet this is 1.891 cubic feet.
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Post by Peegoo 🏁 on Jan 29, 2021 11:29:23 GMT -5
Without the TS specs for the speaker you're using, adding a port is guesswork. It's more than just cutting a hole in the baffle; there's usually a tube in the cabinet attached to the port that must be cut to a specific length ("tuned") to create a balanced sound.
One thing you could do, in the event the TS numbers are unavailable for your current speaker, is get a replacement that has published specs.
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Post by roly on Jan 31, 2021 17:44:44 GMT -5
Is speaker displacement included in the TS specs?
I think the displacement is a factor to be considered when calculating port size and depth.
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Post by Jim D. on Jan 31, 2021 19:12:17 GMT -5
If you go to the link I provided, there is much speaker data required. The site has a link to ported enclosures. There is so much to consider it is not likely worth the effort. One thing is clear. A ported enclosure must be larger than a non ported with the same speaker. Placing any port in the original poster’s cab would no doubt ruin the sonic quality and output frequency curve.
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