Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Cabinets-Speakers => Topic started by: firemedic on November 01, 2011, 11:59:42 am
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Okay, I have made a mistake (imagine that).
I bought 2 non-ported 15" speaker cabs (no speakers) today for $60. They are made of particle board.
I am not the sharpest knife in the drawer.
But- they do have crossovers and 8 ohm horns. Plus the handles & metal grills, so at least I have something.
So off I must go to get some real wood, or at least plywood. I have never built a bass cab so what is the process for porting these things? Also, how does the crossover affect the impedance the OT sees? I'd like 8 ohms overall for each cab.
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Correction, I think it is really MDF. Maybe not so bad.
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Hi firemedic,
MDF is Medium Density Fiber board, denser than particle board, heaver too. Machines nice, takes a finish well, but chips easy just like PB. I've cut more than a few sheets of this and the dust is just terrible from it. Very, very fine, you do not want to breath it. Easy to get a sinus infection from it. :w2:
I can't say from experience, but some guy's like the sound of cab's made from it.
Put a speaker in and see how they sound to you, you might like them? :dontknow: Gonna be a PITA to haul them around tho.
Brad :icon_biggrin:
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I'll sand off the really bad parts & just polyurethane the outside for now. They are at least well built & tight.
I'm thinking about closing off the rectangular holes that the horns were in, and mounting some tubular ports instead. Any opinions regarding the use of those horns?
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I'll sand off the really bad parts & just polyurethane the outside for now. They are at least well built & tight.
Sounds like a good plan. Since it's for bass and depending on the speaker you put in it, MDF might sound great. Pine is not the only good sounding cab wood/material.
I'm thinking about closing off the rectangular holes that the horns were in, and mounting some tubular ports instead. Any opinions regarding the use of those horns?
Sorry no, but you know the guys here will help you. Maybe you could leave the horn in and put a switch in on the back to disable it when you want, for different sounds? :icon_biggrin:
Brad :think1:
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Bypass the crossovers, you do NOT want them for an instrument speaker.
Yank and sell the horns. Quick-cut thin plywood to cover the horn holes. Make a lot of screw-holes. Start with the port half-open. Run your scales in your lowest octave, listen. Try port full-open and full-closed, scales again. Watch for cone-flap on the lowest notes. When sound is best, cut nice hole-covers for permanent tuning.
(It is possible to pre-compute an "optimum" but you have to know a LOT of numbers, and you have to have a clue what "optimum" is. Optimum for stage-amps is NOT textbook optimum.)
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I ordered a couple of 4" adjustable-length port tubes already. I figured I could cover the horn-rectangle and install one or both tubes in one of the cabs, then adjust the tube length as needed.
But before using the ports I could try a sealed cab (perhaps just mount the horns unconnected).
I know nothing about bass speakers. I'm about to buy a new-in-box Peavey Black Widow 15" from a guy in town & I intend to build one cab at a time. Ported s. sealed is academic to me at this point, please insert sage advice here.
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> insert sage advice here
The guy who designed the cabinets knew more about speakers than you and I put together. You won't go wrong just using them as-is (minus crossover, and probably with horn removed and hole sealed).
Tuned-box is NOT a simple matter. Duct-length is a very-very minor point. You first find an "optimum" port AREA. Port (duct) length is very secondary.
It might be good to know how big they are inside?
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Since i have 2 boxes, I'm sealing one and using a Black Widow 1508-SPS (got it brand new in box & cheap). It has a very helpful spec sheet, and I'm comfortable using it in this application. Once I run a full signal into it and I'm satisfied it won't disintegrate, I'll pretty it up w/ tolex & corners.
The other box will be ported. Speaker TBD. Suggestions welcome.
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love those pv spec sheets.
if you like the widow and it doesn't destroy the cab, try to find a low rider for the other one...simply monsterous.
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I tried the 40w TOS with a bass guitar, since I haven't built the bass head yet. It really doesn't make much sound so I'm building for 4-6550s now. Stand by for results...