Wiring new speakers for a cab

Hello,

I'm new to the board, but have lurked here for a while and it's clear this place is filled with people who know what they're on about. I was wondering if somebody could help me out?

I've recently bought a second hand Roadster and a unloaded OS 2x12 Port City cab. I was planning to install a couple of V30's in there.

I'm relatively new to this and could use some advice regarding wiring the speakers...

My question(s) for any experts out there is this:

1. What ohm speakers do I need - 8 or 16ohm? My thinking was this: buy two 8ohm speakers, wire them up in parallel and drop the load to 4ohms, then connect the jack to the 4ohm socket in the Roadster. Correct?

2. Why is there two 4ohm jacks in the Roadster?

3. Is there any difference between running the ohm load at 4, 8 or 16? I've heard that the lower the resistance, the better, is that true?

4. If there's no difference, then is there any difference between running the speakers in series or parallel?

Much appreciated.

Axle said:

My question(s) for any experts out there is this:

1. What ohm speakers do I need - 8 or 16ohm? My thinking was this: buy two 8ohm speakers, wire them up in parallel and drop the load to 4ohms, then connect the jack to the 4ohm socket in the Roadster. Correct?

2. Why is there two 4ohm jacks in the Roadster?

3. Is there any difference between running the ohm load at 4, 8 or 16? I've heard that the lower the resistance, the better, is that true?

4. If there's no difference, then is there any difference between running the speakers in series or parallel?

Much appreciated.

Click to expand...

I will try to answer all of these.

1) You're thinking is correct, but Mesa claims their amps sound the best at 8ohms and to be quite truthful, most amps don't sound that great to me running at 4 ohms, I like 16ohms or 8 ohms.
There are only two rules when it comes to impedance matching - match the head's output with the cab, and if you can't, never use a cab that has a smaller rating than what the head needs to see (so 8ohms into 16ohm cab=OK, 16ohms into 8ohm cab NOT ok). Other than that it's your preference what impedance you need.

2) On the combo, it says "Use with two cabinets" below the two 4 ohm jacks - that's why. They are probably wired in series to give a total impedance of 8ohms (someone correct me if I'm wrong), but with two separate cabs.

3) "The lower resistance the better" usually applies to PA gear because you need as much power as you can and therefore as little resistance as you can. With guitar amps, it is, again, a matter of taste - I don't like running my Marshall with a 2x12 at 8 ohms, I like 16ohms better. It feels better more than sounds, I guess. Likewise I don't like running my Boogie at a mismatch (8ohms into 16ohm cab mono). I like 8ohms stereo better.
If you have the chance, try the running the amp with different loads to see what sounds&feels best to you.

4) There is a difference when it comes to wiring, there always is!

Series means the speakers are one after another (obviously) but the more important thing is that for the total impedance, you just add up the impedance of the speakers you have wired in series using normal addition, so if you had two 8ohm speakers in series the final load would be 16ohms (8+8=16)

So series: R1 + R2 + R3 +...+ RN=R

Parallel means the signal is split between the speakers, and the math is a little more complex. Instead of just simply adding up the impedance, you must calculate with inverted fractions of the impedance of each speaker and then invert the fraction again (technically that's not right* but with these numbers it gives the right result). So if you had two 16ohm speakers in parallel, that means the final load would be 8ohms (1/16 + 1/16 = 2/16; invert that, you get 16/2, which is 8 ).

So parallel: 1/R1 + 1/R2 + 1/R3 +...+ 1/RN=1/R, then you invert 1/R and you get R.

*in reality when you rewrite the formula to get R the formula is R= (R1 x R2 x R3 x...x Rn)/(R1+R2+R3+...+Rn)

Hope the math part didn't turn you off, enjoy your V30s! :mrgreen:

Jackie said:

I will try to answer all of these.

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Thanks!

Since reading your post I've also read that Roadster combos come loaded with 16ohm V30s wired in parallel and plugged into the 8ohm out. I'm assuming recto cabs will be the same?

So, I'm thinking I should do the same and go for two 16ohm speakers, wire in parallel and plug into the 8ohm out. Sound good?

What do you mean about mono vs. stereo?

Cheers.

The 4 ohm taps are wired parallel. They are to be used with either a single 4 ohm speaker load into one jack or two 8 ohm speaker loads, one in each jack (if you have two 8 ohm cabs, plug each one into the 4 ohm jacks).

Mesa amps are pretty tough as far as impedance mis-match, but a general rule is to not use lower than a 4 ohm total speaker load.

Your manual covers this subject.

Mesa guitar cabs are generaly 8 ohms. The 2X12's have two 16 ohm speakers wired paralled for 8 ohms total. the 4X12's have four 8 ohm speakers wired series/parallel for 8 ohms total mono. The left and right pairs are wired parallel to 4 ohms, then those 4 ohm pairs are combined in series for 8 ohms total when run mono. When you use the stereo jacks on the 4X12's it breaks the series connection giving two 4 ohm pairs (left & right)

Hope this helps.

Dom

Thanks for that.

I think I'm going to go for the two 16ohm speakers and wire them in parallel for 8ohms.

A few more questions...

1. Just to clear-up, stereo is when you run all speakers together in unison? What do you mean when you're referring to 'mono' in a cab?

2. The Roadster is 100w. Do I need to match the wattage of the speakers combined to that of the amp? For example, two 65 watt v30's = 130w. Does this mean I'd be unable to use, say, two alnico blues which are 15w each? Do I always have the match the wattage of the amp to the combined speaker output? How does this work when you switch the Roadster to run at 50w?

3. What kind of electrical wire should I be using to wire the speakers? Is there a specific 'top' brand I should be looking out for?


Thanks again.

Axle said:

Thanks for that.

I think I'm going to go for the two 16ohm speakers and wire them in parallel for 8ohms.

A few more questions...

1. Just to clear-up, stereo is when you run all speakers together in unison? What do you mean when you're referring to 'mono' in a cab?

2. The Roadster is 100w. Do I need to match the wattage of the speakers combined to that of the amp? For example, two 65 watt v30's = 130w. Does this mean I'd be unable to use, say, two alnico blues which are 15w each? Do I always have the match the wattage of the amp to the combined speaker output? How does this work when you switch the Roadster to run at 50w?

3. What kind of electrical wire should I be using to wire the speakers? Is there a specific 'top' brand I should be looking out for?


Thanks again.

Click to expand...

1 - Mono is having the same signal in all speakers. Stereo is having different signals coming through different speakers. Unless you're running multiple amps and/or using different effects on each amp, the signal through any given amp will be mono.

2 - Your speakers should be rated higher than the amp. Using 15W speakers with a 100W amp will work if you're playing at low volumes, but if you bump the volume knob accidentally, there goes your speakers. Then again, it's all up to you and how safe you feel running underrated speakers.


3 - Typically, 14-18 gauge wire is used. You can use lamp cord, readily available at any hardware store. I haven't noticed a single difference in brands of speaker cords over lamp cord.

domct203 said:

Mesa amps are pretty tough as far as impedance mis-match

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Any good tube amp can handle a 1 step "down" mismatch, AFAIK at least. You can go two step but I wouldn't expect it to sound great.

Mikey gave you some nice answers there, I just want to add that if you will be mixing speakers, one may be louder than the other so it's effect on the tone might not be as dramatic... what matters here, more than the wattage, is the frequency response of a speaker - for instance, mixing a Celestion G12H30 and Celestion V30 is a good match because the G12H30 has the lows and low mids, whereas the V30 is more high mid oriented - there won't be a big volume difference even though one is half the wattage of the other, because they compliment each other tonally.

BTW I didn't know about the lamp cord thing... thanks mikey!

Thanks.

Even more questions! Sorry about this, I'm a newb.

1. The V30's come with those male spade connections. Can I solder the speaker wire onto them? If so, should I wrap the stripped wire through the hoops and then solder, or just lay it on the connectors and solder?

2. What size screws will I need to fit the speakers into the cab?

3. What make of speaker cable is best, to connect the Roadster to my cab? (My cab should be 8ohm once I get the speakers in).

Thanks again.

Newb schmewb, we all started somewhere, ask away :wink:

1) Either way will do just make sure the solder joint is ROCK solid and that there are no wires touching anything they shouldn't be. I'd wrap it around though, makes soldering easier IMO.

2) Can't answer that one, sorry, I used my existing speaker screws.

3) I don't buy the "this cable sounds better that that one" snake oil BS so I don't care about brands and try to find the most reliable one out there that's not too stiff so I can squeeze it in if I have to. What you gotta watch out for is the gauge - the higher the gauge the more power the cable can handle. This is something you shouldn't take lightly, I have heard stories of cranked amps melting cables that were too thin...
I think Mogami makes some solid cables, also Monster cables are good. I'm a nut for Neutrik connectors though (you'd need a tank to break those) so I try to buy cables that have those (like the Proel esoteric, but I don't think they have speaker wire) or I make my own.
Also, speaker cables are usually UNshielded. Technically there's nothing wrong with using shielded cable as long as the cable is thick enough but I wouldn't recommend it.

Jackie said:

3) I don't buy the "this cable sounds better that that one" snake oil BS so I don't care about brands and try to find the most reliable one out there that's not too stiff so I can squeeze it in if I have to. What you gotta watch out for is the gauge - the higher the gauge the more power the cable can handle. This is something you shouldn't take lightly, I have heard stories of cranked amps melting cables that were too thin...
I think Mogami makes some solid cables, also Monster cables are good. I'm a nut for Neutrik connectors though (you'd need a tank to break those) so I try to buy cables that have those (like the Proel esoteric, but I don't think they have speaker wire) or I make my own.
Also, speaker cables are usually UNshielded. Technically there's nothing wrong with using shielded cable as long as the cable is thick enough but I wouldn't recommend it.

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Thanks.

Would these be a decent speaker cable? http://www.award-session.com/cleartone_cables.html#high-current
They say they're 0.75mm² - thick enough?

These will probably do, yeah.

I live in the Uk and have an export Roadster with a transformer that can deal with our 240v mains.

Any ideas what the output voltage from the amp to my speaker cab would be?

NO, NO, NO. DO NOT USE SHIELDED CABLE FOR SPEAKER USE. NEVER.

Jackie said:

What you gotta watch out for is the gauge - the higher the gauge the more power the cable can handle.

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Actually, it's the Lower the gauge the more current (power) the cable can handle. A 10AWG wire is a lot thicker than an 18AWG. Also, cable length is something to consider. An 18AWG cable would be fine if under 3 feet long. If you wanted say a 25 foot cable for some reason I would recommend no less than 14AWG. I use a 12AWG X 10 foot cable from my head rack to speaker cabinet. The inside of my cabinet uses 16AWG.

And NEVER use an instrument cable, never.

Dom

domct203 said:

Jackie said:

What you gotta watch out for is the gauge - the higher the gauge the more power the cable can handle.

Click to expand...

Actually, it's the Lower the gauge the more current (power) the cable can handle. A 10AWG wire is a lot thicker than an 18AWG. Also, cable length is something to consider. An 18AWG cable would be fine if under 3 feet long. If you wanted say a 25 foot cable for some reason I would recommend no less than 14AWG. I use a 12AWG X 10 foot cable from my head rack to speaker cabinet. The inside of my cabinet uses 16AWG.

And NEVER use an instrument cable, never.

Dom

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The speaker cable would literally be travelling about 40cm from my cab up to my head which sits on top. The speaker cable in the link I posted a few back looks good though, right? It's somewhere between 18 and 19AWG at 0.75mm sq.

Can anybody answer my question above regarding voltage? Thanks.

Axle said:

domct203 said:

Jackie said:

What you gotta watch out for is the gauge - the higher the gauge the more power the cable can handle.

Click to expand...

Actually, it's the Lower the gauge the more current (power) the cable can handle. A 10AWG wire is a lot thicker than an 18AWG. Also, cable length is something to consider. An 18AWG cable would be fine if under 3 feet long. If you wanted say a 25 foot cable for some reason I would recommend no less than 14AWG. I use a 12AWG X 10 foot cable from my head rack to speaker cabinet. The inside of my cabinet uses 16AWG.

And NEVER use an instrument cable, never.

Dom

Click to expand...

The speaker cable would literally be travelling about 40cm from my cab up to my head which sits on top. The speaker cable in the link I posted a few back looks good though, right? It's somewhere between 18 and 19AWG at 0.75mm sq.

Can anybody answer my question above regarding voltage? Thanks.

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It's somewhere around 44 volts if I remember correctly. 18 gauge in the short distance you're talking about shouldn't be a problem.

mikey383 said:

It's somewhere around 44 volts if I remember correctly. 18 gauge in the short distance you're talking about shouldn't be a problem.

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I thought as much. Thank you!

domct203 said:

Jackie said:

What you gotta watch out for is the gauge - the higher the gauge the more power the cable can handle.

Click to expand...

Actually, it's the Lower the gauge the more current (power) the cable can handle.

Click to expand...

Thanks for correcting that