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Cab designers: help me out here!

Discussion in 'Amps and Cabs [BG]' started by Lo-E, Jul 6, 2012.


  1. Lo-E

    Lo-E

    Dec 19, 2009
    Brooklyn, NY
    I was recently given an old single 15 cab from the early 70s.
    It's a 'Riviera' cab from Canada - a low-rent knockoff of a Showman cabinet, and it sounds better than I expected it to.

    It's currently loaded with a 'GB Professional' 15", 100W speaker (Korea) that looks to be your basic, no-name, general purpose replacement speaker and even with this obvious handicap, the cab sounds better than it has any right to, to my ears.

    It currently has no back panel bracing or batting, but that's going to change!

    My intention is to pair this up with a low wattage tube amp for recording, practice or little coffee house gigs.

    The interior dimensions are:
    10" depth
    27.5" width
    20" height
    3.17 cubic' volume - excluding the speaker cone volume

    There is currently a slot port (literally, just a slot cut in the baffle board) that is 1" wide and 14.5" long running vertically along one side, 3" from the edge of the baffle board.

    So, with the background info in place, here's what I want to know:

    A)I have an EV EVM-15L that's not in use and just collecting dust. Should I put it in there?

    B)What freq is my cab tuned to?

    C)If I stuff the EV in there, should I re-tune the port? Replace the baffle? Leave it alone?

    D)Is this project not even worthwhile?

    This cab is never going to get pushed hard - I have plenty of modern equipment for that - It's going to be used for old-school, thumpy, low/medium volume tones. It doesn't need to be tuned super-low for a five-string or be loud enough to compete with loud guitars or drums. This is lo-fi all the way!

    Any thoughts you speaker folks have would be greatly appreciated.

    Thanks-
    E
     
  2. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Far from a speaker expert, but I'll try to help as good as I can...

    A. YES!

    B. No clue.

    C. Stuff it in there first, listen, and make your decisions accordingly.

    D. For your purposes, I think it's very worthwhile.
     
  3. rpsands

    rpsands

    Jul 6, 2007
    Phoenix, AZ
    Are you including the slot port in the internal dimensions?
     
  4. Lo-E

    Lo-E

    Dec 19, 2009
    Brooklyn, NY
    No. I'm not even sure how to do that.

    The port is two-dimensional - it has no depth. Actually, I guess it does, doesn't it? The thickness of the baffle board would add the third dimension to the port.

    With that settled, I still don't know how to do that! :eyebrow:
     
  5. Lo-E

    Lo-E

    Dec 19, 2009
    Brooklyn, NY
    My thinking was along these lines as well. I know I could just throw it in, add some bracing and batting and I'm sure it would sound just dandy, but I love throwing this stuff past the people who really know what they're doing because, invariably, one of them will say "Here's something you could try...." and I always - always - learn something!
     
  6. will33

    will33

    May 22, 2006
    austin,tx
    Your EV is a great speaker for low watt tube amps....use it. There, just saved you $$.;)

    Run WinISd to figure out what the box is tuned to and what to adjust. Or just do it by ear seeing as you already have the speaker there. Likely have to install a "shelf" to make the port go longer into the cab. Longer port = lower tuning. Can also lower tuning by blocking off some of the current port but it's most likely gonna have to be modded so the port has some depth going back into the cab.
     
  7. Lo-E

    Lo-E

    Dec 19, 2009
    Brooklyn, NY
    Wow, man, how can I ever repay you? ;)

    I have a mac. I tried using the online version, but it doesn't seem to want to talk to me unless I have round ports. I'm probably just doing something wrong. That's why I post these questions to the folks who know how to do it right!
     
  8. will33

    will33

    May 22, 2006
    austin,tx
    I'm not enough of a "designer" yet to charge much anyway.:p

    That cab size is pretty close to EV's old TL-606 size. It's tuning options were adjustable via a port cover and were set at 40 and 55hz. Anything between those 2 would work and just adjust it according to what your ear likes to hear. I can mess with it tonight if I can get my PC to start up. Is it "f10" you push to get to the screen where you can make it start in "safe mode"? Dumb question for you more tech guys, I know.

    For now, seeing as you're using low power, it won't hurt to install the speaker, see how it sounds, and block maybe 1/2 the port to see how it changes the sound. Could get you in a ballpark as far as what you'd like to hear.

    How low is "low power"? If it's up around 100 watts, keep the volume down for testing until you figure out where the line is as far as speaker distortion/stress, etc.
     
  9. will33

    will33

    May 22, 2006
    austin,tx
    Should be able to select a square port. Enter your 1x14-1/2 as length and width. The depth is how far it sticks into the cab. In your case, the depth would be however thick the baffle is....prolly 3/4".
     
  10. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    All this time yakkin' about it and you could have already been enjoying sweet tones...go swap it already...

    :D
     
  11. majortoby

    majortoby

    Jul 2, 2009
    Tampa, Fl USA
    I <3 cab design threads :cool:
     
  12. will33

    will33

    May 22, 2006
    austin,tx
    Yep.

    I have a testbox I used to use for random speakers I come across with no specs. Just put them in there, try different pipe lengths for different tunings. Throw chunks of styrofoam in there to "shrink" the box, or take some out to make it bigger. Tune it by ear, or sometimes by eye, meaning whatever calmed the cones down most on the low notes so you can play louder. Then measure where everything ended up after it sounded the best I could get it, and build a fresh box to that size and tuning. Can plug all the holes and make a sealed box too.
     
  13. Lo-E

    Lo-E

    Dec 19, 2009
    Brooklyn, NY
    The EV is in the dark, scary basement and I'm lazy. That's why it isn't in there already, Jimmy. :)

    This is all academic, anyway. I'm just curious about these things.

    I tried getting WinISD to do something - anything - for me online. I can't figure it out at all. It almost seems like it's missing some of it's features. The help menu mentions tabs that don't seem to exist. Harumph....
     
  14. will33

    will33

    May 22, 2006
    austin,tx
    Try this.

    http://www.carstereo.com/help/Articles.cfm?id=31

    Yeah, it's for car audio stuff, but tuning a box is tuning a box. The box doesn't know what speaker is in it and that one is said to be a little more accurate with regards to thin shelf ports like that. Just use your size and port dimensions and ignore the speaker for now. Shoot for something in the high 40's/50 hz. 55hz would usually be considered a bit too high but with a 4 string bass and low power it would be OK too.


    Can't link you straight to the pdf from the phone, but the top choice in this search http://www.google.com/search?hl=en&....2592.0j10j1j1j1.13.0...0.0.BGJjxuSO4l8&mvs=0 is the tl-606 plans. The response curves in there are pretty much what yoirs will sound like in your cab (almost the same internal size) at the 40 and 55hz tunings. Higher tuning gives more lowend response at the expense of taking less power before fartout. Low tuning more mimicks a sealed cab. Really low can also start to lose powerhandling. Anything between 40 and 55 should sound good, just depends on how much lows you want before adjusting the bass knob on the amp. If you have to mod the port anyway, could come up with a cover system like that to give yourself a couple of different options for lowend flavor.
     
  15. rpsands

    rpsands

    Jul 6, 2007
    Phoenix, AZ
    I am showing that port as around 35hz if it gets shelf reinforcement and the upper 50s if it does not get shelf reinforcement. I don't know how corner loaded square ports that don't use the entire wall behave.

    Either way you're going to want to raise or lower the tuning for that box to be ideal for bass, unless you use a driver that wants a very low tuning.

    I'd recommend using a sine test on a woofer in that box to determine its actual tuning frequency. Put the EVM 15L in there and do the salt test (put some salt on the cone, lay it on its back, and run a sine wave, looking for the point of minimal excursion). Start at 35hz and go up.
     
  16. Lo-E

    Lo-E

    Dec 19, 2009
    Brooklyn, NY
    @will33: Cool site. It wouldn't let me enter my port because it didn't like the width:height ratio being more than 8:1. Fussy little sucker, isn't it?

    @rpsands: Thanks for doing the math! There is no shelf reinforcement, which will make sense in my next comment.

    @ all: JimmyM lit a fire under my butt so I went to the scary basement and got the EV, dug through assorted mounting hardware and put the thing in. I also upgraded the mounting of the back panel to increase rigidity as much as I could and added foam weatherstripping around the back panel to reduce vibrations as much as possible.
    The verdict: it sounds much better than it did with the el-cheapo driver. A vast improvement, actually. The bottom end fattened up quite a bit and the whole sound has more girth.
    I was using the head from my B-15, which is about as much power as I would ever be likely to use with this. Maybe a little more, but 50-100W tops, and I wouldn't be cranking it.

    As far as tuning goes, I'm pretty certain this was meant to be a "guitar or bass" cabinet when it was made and it's tone certainly reflects that. It sounds like a guitar cabinet. By rpsands' math, upper 50s would probably be about right. That said, I don't mind the high tuning at all. There's lots of detail and still sufficient booty for my purposes.

    The only further plans I have are to add some batting and some braces for the back panel, both of which are going to wait until I reorganize my workshop; a herculean task that I've been putting off. At that time, I'll also track down a little rattle that only appears when I play a B (on the A string). I suspect it's the Riviera logo rattling against the baffle board. I'll re-mount it with a layer of velcro fuzz underneath while I have the thing apart.

    Thanks everybody for the help! The cab's a keeper!
     
  17. Lo-E

    Lo-E

    Dec 19, 2009
    Brooklyn, NY
    Oh, yeah, rpsands: I might try the salt test down the road (once again, gotta finish the durn workshop), but the fact that it rattles on the B would further support your math.
    B = just under 62 Hz. Since I'm sure my measurements weren't 100% precise, that would be a strong argument in your math's favor.
     
  18. rpsands

    rpsands

    Jul 6, 2007
    Phoenix, AZ
    If you extend that port about 1.5" it should drop the tuning to ~50hz, which would probably give you a little more margin of safety. Pretty easy to test out just screwing the section in.
     
  19. will33

    will33

    May 22, 2006
    austin,tx
    Cool stuff. Rspands method for finding the actual tuning is likely the best to use here. There's all kinds of free tone generators you can search and download. The port tuning calms down the cone. Whatever sinewave frequency the salt dances the least is the real tuning frequency.

    Of course, ears are good too.;). Running low power like you are, you're not in any real danger. Although, the 100watt amp turned up will send a 15L past xmax (clean bass, up to 10% distortion) and on it's way to xlim (actual physical damage).
     
  20. rpsands

    rpsands

    Jul 6, 2007
    Phoenix, AZ
    It's actually Bill who told me about that :) Works really well.
     

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