Cabinet Building and Speaker Ohms

[Wesley]

I'm going to be building a speaker cabinet and was hoping you guys could give me some tips. It will be a somewhat low budget deal. Just wondering what I should look out for when building it and if there is anything I should do beyond building a simple box? The cabinet will house a 12" speaker and what would be some reasonable dimensions? I plan on making it within the stylings of the older fender tweed amps.


Also, what spawned the project was an extra speaker I had kicking around from an amp purchase. I bought a 70's Traynor Guitarmate and took out the original speaker which has been just sitting around. (I believe its Marsland 8ohms but correct me if im wrong) Anyways, I plan on using the new cabinet with my Fender Champion 600 ri and was wondering if the ohms of the speaker would work with that amp. I couldnt find any markings on the amp suggesting the ohms output and I dont have the manual.

Sorry for the longwinded thread, but one last question. Are there any stores in Toronto that carry the jackplates and wires for such a project or is it something I'll have to order online?

Thanks

[RIFF WRATH]

there is a us site, Shivano, that has all sorts of speaker and cabinet info.
as for the jacks..most Home Hardware will have the regular jack for a few $.
if you have a multimeter you should be able to test your speaker. will read close to the ohms.
cheers
RIFF

[Wheeman]

The best bet for jacks and wires would be Crappyshack (gah, The Source nowadays), although the employees are usually worthless if you need help with matters.

As for the ohms rating, I don't know much regarding speakers. Try checking the manufactures website for more info or looking at the speakers in it/previously used.

[Wesley]

got some specs.

The Champion 600 runs a 4ohm speaker. The guitarmate has an 8ohm speaker jack (im assuming thats what the original speaker is rated at).

So can i use the 8ohm speaker with the Champion 600?

[Wild Bill]

got some specs.

The Champion 600 runs a 4ohm speaker. The guitarmate has an 8ohm speaker jack (im assuming thats what the original speaker is rated at).

So can i use the 8ohm speaker with the Champion 600?

Yes, and no, Wesley!:smile:

First off, you can measure speaker ohms with a multimeter as long as you understand you're not really measuring speaker ohms!:eek:

Confusing? Here's the scoop. Multimeters measure DC resistance, like the small resistance in a coil of wire. When we say a speaker has an 8 ohm load we're talking about an AC impedance reading. This is something that needs expensive lab equipment to measure. A multimeter can't do it.

However, there's an old tech trick that works "good 'nuff". If you DO use a multimeter to measure the DC resistance of the wire that makes up the speaker voice coil you will get a reading that will be somewhat lower than the AC impedance figure but not so much lower that you can't make a good guess.

Speakers are normally sold in 4,8 and 16 ohm increments. The DC ohms of an 8 ohm speaker might read 6 or 7 ohms but it won't likely be less than 4. So you can safely assume that reading indicates an 8 ohm speaker. If you read 3 and a bit ohms then assume it's 4 ohms and if you get maybe 12 or 13 ohms then you've likely got a 16 ohm speaker.

This trick works great for guitar speakers. You will notice after doing it a few times that higher power speakers have DC readings even lower than low power speakers. That's because for higher power you need thicker wire in the voice coil to keep from burning out and thicker wire has a lower DC resistance.

Now, as to running an 8 ohm speaker in your 600. Tube amps will tolerate a mismatch but you're not talking about just to use a new cab at a single gig. You're talking wiring in an 8 ohm speaker permanently!

Will that blow anything up? Not very likely. The tone might be a little bit different. One thing is sure, you won't get as good tube life as with the right speaker load. How much less? Can't say for sure. I would say we're talking months less and not weeks, against several years of normal life.

So now you know. It's up to you. Maybe you've got a girl friend who works in a tube store and can score you replacements for free...:smile:

:food-smiley-004:

[Wesley]

thanks for all the info. have always been lost on understanding ohms (never really took the time to learn). The speaker I am planning on using isnt the greatest, but i just wanted to screw around with a little speaker cabinet making project. So ill probably be replacing the speaker in the near future anyways. Good to know that i can start building and can use that older speaker until then.

[Wesley]

another quick couple questions and hopefully that will be it for this project. I bought the input jack and was wondering which prong is negative and which is positive. Also, do I have to use shielded wire or will normal speaker wire do?

Thanks again

[bcmatt]

I find that it's harder to find a good speaker cabinet than I thought, so your cabinet will probably be worth more to you in the end than the original speaker you are making it for. The time to build it and the parts you'll need add up, so make sure you build something you like. It will still be cheaper and possibly much nicer than one you might find to buy.

another quick couple questions and hopefully that will be it for this project. I bought the input jack and was wondering which prong is negative and which is positive. Also, do I have to use shielded wire or will normal speaker wire do?


I'm not sure which style of jack you are using, but whatever tab connects to the tip of your plug will be the positive one that you will connect to the positive tab of your speaker with your wire.
Normal speaker wire is all you need. 18 gauge is easily heavy duty enough for such a short distance that you would be using in a 1x12 cab (or basically inside any cabinet IMO).

[Wesley]

awesome thanks. yeah its taking quite a bit of work to build and I am pretty happy with the results so far.

[bRian]

Post some pics when you are done. I have a Jensen P12N kicking around I'll be building a cab while I'm off during midterm. I found a useful site with a good tutorial on making box joints.


http://www.lowes.com/lowes/lkn?action=howTo&p=Build/boxjnt.html