Baffle Boards

Discussion in 'Shock Brother's DIY Amps' started by marshman, Feb 19, 2009.

  1. marshman

    marshman Friend of Leo's

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    So, I was foolin' around with some graph paper and a compass tonight, and it looks like maybe a new baffle board for a tweed bassman (obvioulsy an RI--I would NEVER do that to a real vintage tweed) could be cut to hold 2 12"s...am I imagining that?
     
  2. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    If it has a 29"+ diagonal, it might work! ;)

    - Scott
     
  3. marshman

    marshman Friend of Leo's

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    Thanks. I guess I really got to wonderin' how difficult it would be for a cab builder to make multiple baffles for a cab. So, If I got, say, a Bassman RI or HRDv, what else might I be able to install for change of pace.

    Mind, this is idle curiousity more than anything, I've got more projects than I can shake a stick at as it is. The Modular Approach To Cabinet Building, or something to that effect.
     
  4. Natstrat79

    Natstrat79 Tele-Meister

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    Tweed Bassman wants to see 2ohms so you'd be running an impedence mis-match by using 2 12's.
     
  5. sjhusting

    sjhusting Tele-Afflicted

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    or just get a couple of 4-ohm 12s from Weber

    steven
     
  6. marshman

    marshman Friend of Leo's

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    I'm thinking purely hypothetically here, no need to panic....

    Yet.

    My problem is pretty much the opposite. I have a couple luscious sounding 15"ers that are 16 ohm, so that's my problem. I would probably have to get an aftermarket OT to install one of them in just about any amp, though I did have to foresight to build my 18 watter with a multi-tap OT. Of course, the cab for that one's not quite large enough, but I was thinkin' ahead to some extent.

    Though, since the topic has come up, is there any advantage to using the different taps with an amp (assuming you had 4-8-16 available), would there be any pros/cons...I'd read online somewhere that going with (in this hypothetical case) the 16 ohm tap gives a little more bottom end due to "all" the windings being used, but given the disparity among speakers, it's probably pretty tough to guage.

    So, let's say, same head, same cab with 2-8 ohm speakers--would the amp sound about the same with the cab wired for 4 ohm or 16 and plugged into the appropriate tap?
     
  7. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    That's the neat thing about some of the Hammond output transformers -- you connect different output taps together, so you can make use of all the secondary windings and still get the impedance you want. Problem with running the wrong impedance is that your tubes are being operated differently (load line changes), so you may end up with a lot less headroom even if you're using all of the windings on the transformer! Putting too high of an impedance load on the tubes can result in arcing in some amps because the voltage can now swing way higher.

    - Scott
     
  8. celeste

    celeste Friend of Leo's

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    Marshman,

    The differences in using different taps is usually swamped by the difference in speakers with different impedance's. The bass does not get better because you are "using all the windings". If you have Negative Feed Back, it is usualy taken from the 16 ohm tap, so the feed back better matches what is being sent to the speaker. Also there is more inductance in the 16 ohm tap, and a 16 ohm voice coil is likely to have more inductance, so the highs can get rolled off from the extra inductance. That makes the bass sound bigger.

    I buy all my speakers as 16 ohm. All my cabinets have parallel jacks. If I need 8 ohms, I parallel two cabinets. No one ever complains and I lend stuff out a lot.
     
  9. marshman

    marshman Friend of Leo's

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    One of the few things I loved about the science classes I did take was contemplating the process of getting a reliable comparison--how does a guy make a fair comparo of two different things, so that as many factors as possible are unchanged.

    Switching from a 4 ohm speaker to a 16 ohm speaker will taint the results, but using a pair of 8 ohms swapped from 4 ohms to 16 ohms, using the same cab, and the same amp with the same tubes and the same bias blahblahblah seemed the only reasonable way to get a proper comparison.

    I guess when it comes to choosing speakers, I understand (note I didn't use the word KNOW) that plugging an 8 ohm output into a 4 ohm load will possibly damage something, but plugging an 8 ohm load into a 16 ohm cab will probably only dull your tone. Probably.

    It's kind of a moot point, as I am unlikely to have the materials to test this thought process anytime soon. But I love to listen to folks what knows more than me.
     
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