Edumacation needed for speaker cabinets

Discussion in 'Amp Central Station' started by Nahtabot, Sep 25, 2020.

  1. Nahtabot

    Nahtabot Tele-Meister

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    Fellow Twanger's, I have 2 questions so far.

    1. When using a mini tube head (5W), is there any need to match wattage with the cab? The head has individual outputs for both 8 and 16 ohm speakers.
    2. Is there a preferred enclosure type (open / closed back) that would be better matched to a low wattage amp head?
    Thanks for reading!


    -Mike
     
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  2. PhredE

    PhredE Tele-Holic

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    Others will chime in soon enough, but meanwhile..

    1. Speaker power ratings ('wattage') need not match the output power of the amp -- in your case.
    Just about every speaker imaginable can handle 5W (RMS) of power with no problem. In general, and in practical terms, just make sure you use a speaker that is rated to the same output power of an amp -- preferably about 50% higher is ideal (for safety). Do make sure your speaker impedance matches the output impedance of your amp (extremely important with tube-based amp).

    2. The type of enclosure to use is really a personal preference on your part. Some prefer the 'open'/'airy' sound of an open back; others prefer the 'tightness' of a sealed box. The choice really isn't directly tied to the power rating of the amp. One thing to definitely consider is the type of driver and it's efficiency (aka 'sensitivity') rating of the same. A more efficient speaker is louder than an inefficient one.

    Choosing speakers some players liken to 'going down the rabbit hole'. It can be a nebulous process. But, take some time to research and look at suitable options. Unfortunately with speakers, the buying process doesn't lend itself to 'try before you buy' -- so, you do have to research your 'short list' much more than in buying other musical equipment.
     
  3. Nahtabot

    Nahtabot Tele-Meister

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    Would an old Jensen from a Thomas organ be suitable?

    My neighbors kid can build an enclosure from MDF board.

    Jensen.JPG
     
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  4. PhredE

    PhredE Tele-Holic

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    I don't have experience with old Jensen speakers, but there are plenty here that do... so, stay tuned and let them chime in. That's a cool find for sure! It could make a great speaker for what you are trying to do.

    FYI -- The Model # is stamped on the lower right on the outer edge (C12R -- I think).
     
  5. nojazzhere

    nojazzhere Doctor of Teleocity

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    Your only real concern is ohmage or impedance. You want the speaker to be equal to, or EXCEED the out put impedance of your amp. So, if your speaker is 16 ohms or higher, use the 16 ohm tap on the amp. You could try the 8 ohm tap, which with a 16 ohm speaker shouldn't damage the amp, but may not sound good. I would suggest NOT using a 4 ohm speaker at all....you could damage your amp. Most amps have a margin of error on this, but you can't always count on that. Do you know the impedance of that speaker you show?
     
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  6. PhredE

    PhredE Tele-Holic

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    It might help us help you if you identify the amp head in question.. :)

    Unless someone jumps in and says something like 'the impedance of that speaker is...[X ohms]',
    it might be useful to stick your DMM (digital multi-meter) on the terminals of the speaker and get a resistance reading. I'm guessing it's an 8ohm unit, but I am not familiar with Jensens much at all.
     
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  7. Dacious

    Dacious Poster Extraordinaire

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    Yep. Probably sound great if it's a Tweed style amp.
     
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  8. Nahtabot

    Nahtabot Tele-Meister

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    The head unit is a Wangs Mini 5.

    I will dig out the meter and take a look see. This is all new to me!
     
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  9. Nahtabot

    Nahtabot Tele-Meister

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    Ok, I found my multi meter and after multiple tests and with the display jumping wildly, it seemed to settle on 6 ohms.
     
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  10. PhredE

    PhredE Tele-Holic

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    Comments, in rough order:

    1. It's new to me too (well, this particular speaker and the amp)
    2. I looked up the amp, interesting. I was tempted to buy one of those once. Never did it though. I like the user-selectable rectifier option too.
    3. Sticking my neck out a little bit here, but IMO a 6 ohm resistance reading should put it in the 'ok' to use with an 8ohm output.

    Make a nice speaker cabinet for that vintage Jensen and then hook 'em up and listen to some tube tones through an old Jensen speaker.. could be very interesting. Hope you got a good deal on the amp head.

    Have you tested the speaker yet? Does the cone appear to be intact?
     
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  11. nojazzhere

    nojazzhere Doctor of Teleocity

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    You should be good using the 8 ohm tap.
     
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  12. Nahtabot

    Nahtabot Tele-Meister

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    I got some noise though it from the multi meter. Yes, the paper cone is in good shape.

    You know, I felt dumb gutting that old organ but no one plays those transistor units anymore and I also snagged the Leslie and it had a tube power amp in there as well!
     
  13. PhredE

    PhredE Tele-Holic

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    Sounds like you're on the right path. I'll pipe down and let progress happen.

    Post back when you're up and running with it and let us know how it sounds..
    Good luck!
     
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  14. powerwagonjohn

    powerwagonjohn Tele-Meister

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    IMG_0874.JPG IMG_0880.JPG I have a original Jensen C12R in my Gretsch/Valco 6152 and you should be fine. It is a single ended 5W amp and sounds great!
    Thanks John
    I had to add a couple photos. I know we all enjoy them around here!
     
    Last edited: Sep 26, 2020
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  15. Rockhead

    Rockhead Tele-Meister

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    Personally I wouldn't make the enclosure out of MDF. The cab for a 12" speaker would be heavy. I would use pine which is fairly cheap at the big box stores. I say this because I recently made one from 1/2" MDF and it is pretty heavy and I don't think it sounds good at all.
     
  16. Musekatcher

    Musekatcher Friend of Leo's

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    For older speakers that were designed for lower power ranges, probably not. But later as amps got bigger, speaker design changed to keep up, and in fact you will see ratings of minimum wattage. I seem to recall this was done for two reasons. One, the speaker may not play very flat, or may not produce the frequency range as intended or advertised, not too big a deal. Another reason for a minimum, is to protect the speaker from lowest wattage distortion. Amps can distort at maximum overload operation, but also at the lowest ranges. I did in fact burn up a tweeter once by leaving a speaker on for more than a day at really low levels, did some research and read about low output distortion.
     
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  17. spellcaster

    spellcaster Tele-Holic

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    I can't vouch for this as scientific fact, but in my experience, unless you're planning a large enclosure, sealed boxes produce less output than open or semi-open backed cabinets. And unless the speaker you're using has an unusually long excursion, a sealed cabinet isn't needed.

    MDF is a great material for car-stereo sub boxes, but not the best for music enclosures. MDF's heavy, moisture sensitive and dead-sounding. Rockhead's suggestion of using pine is excellent. It'll be lighter and more likely to produce a warm, resonant tone.
     
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  18. rangercaster

    rangercaster Poster Extraordinaire

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    When using a low wattage amp, you need a very efficient speaker, or you won't achieve sufficient volume...
     
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  19. PhredE

    PhredE Tele-Holic

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    I agree with the previous posters here --

    A modestly efficient speaker powered by 5W is probably enough for bedroom/noodling, but not enough for playing out. I checked the newer C12Rs, they are rated at 95db. Yours is probably close to that. If you want more overall output at some point, you may need to invest in a more efficient ('louder') speaker. Most guitar speakers range from about 93db up to about 103db. An increase of a few db's is noticeable to most ears. Handy chart for reference (no affiliation, do not know person/ business..: http://www.colomar.com/Shavano/spl.html

    Another vote for pine. Also, (as you can see in the pic over << there) I also opted for pine in building my own boxes. Those are the small ones in the pic (a 1x8, and 2x6.5). I used pine boards from a box store. 1x12s nominally, actual is usually about .75" x 11.5". Screwed and glued; not finger-jointed with furring strips along edges/joints of course. Sanded and clear-coated.. nothing fancy (I'm a functionalist at heart).
    If you go to one of the box stores for boards, go through the stack and check for warp, cracks, etc. Pick the best one(s). Some folks like the narrower (1x10s or even 1x8s) instead -- which is fine. When I make a box for a smaller speaker(s), I seal the back and port the front (tuned to about 80Hz; low E) to compensate for relatively timid low-end. For a larger speaker (eg; 12") , I make a two part back so I can remove one panel. I stick the jack/jackplate on the other one (that isn't normally removed).
     
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  20. schmee

    schmee Doctor of Teleocity Silver Supporter

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    That C12R may be great with a little amp like that.
     
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