changing speaker impedances possible??

[mrjones200x]

Wondered if it was possible to change the value of a speakers resistance?

 

Following on from the vox ac4tv thread on the orange amp forum i tried my Vox AC4TV with an 8 ohm speaker from my 2x12cab and the sound was really nice, more bright more articulate and louder. Anyhow the combo comes with a 16ohm speaker is it possible to switch it down to 8ohms?

 

Ive read on the net that if you have a 8 ohm speaker and you want to run it as 16ohm you can use a resister in series. An 8ohm resister in series rated at 10 watts would be suitable for a 4-9watt amp apparently.

 

If this is right is it possible to do the reverse and run a 16ohm speaker at 8ohms? Id like the option of swapping over by a switch when i fancied to changed the sound and overall volume of the amp. If it means buying an 8ohm speaker then i would do it if it was safe to run it as 16ohms with a resister.

 

Any comments??

[fuse]

Wondered if it was possible to change the value of a speakers resistance?

 

Following on from the vox ac4tv thread on the orange amp forum i tried my Vox AC4TV with an 8 ohm speaker from my 2x12cab and the sound was really nice, more bright more articulate and louder. Anyhow the combo comes with a 16ohm speaker is it possible to switch it down to 8ohms?

 

Ive read on the net that if you have a 8 ohm speaker and you want to run it as 16ohm you can use a resister in series. An 8ohm resister in series rated at 10 watts would be suitable for a 4-9watt amp apparently.

 

If this is right is it possible to do the reverse and run a 16ohm speaker at 8ohms? Id like the option of swapping over by a switch when i fancied to changed the sound and overall volume of the amp. If it means buying an 8ohm speaker then i would do it if it was safe to run it as 16ohms with a resister.

 

Any comments??

This question gets asked so often.....

Yes it is electronically possible.

For many reasons it is not a good idea. One of those reasons is that you will loose half of you amp's power to the resistor. Is it worth it?

Just buy another speaker. A guitar player with just one speaker is like a painter with only one color. It is just something you need to have more than ONE of.

There are lots of EXCELLENT speaker for under 100 dollars.

Just one example..... http://www.bltsound.com/index.php/categories/guitar-speakers

Check out the Patriot and Red Coat line from Eminence.

Good Luck

[mtheory]

Bear in mind that it MIGHT be that the reason the 8 ohm speaker sounded better was because the map was happier with an 8 ohm load than the stock 16. In that case, adding a resistor to create a 16 ohm load might be counter-productive. Generally, an amp will be happiest with whatever load the manufacturer says it likes to see, but that's not always necessarily the case. Sometimes, mismatches work better. The only way to know for certain, however, is to throw the amp on a scope and try different loads to see which it likes best. Otherwise, you could just guess, and run 8, since it's not all that likely that a 100% mismatch is going to kill the amp anyway (though there's really no way of knowing without scoping it, so there is a risk of overheating and melting the output transformer windings that you have to be aware of...if you try it, keep an eye on the transformer for signs of overheating).

[L5Larry]

I'll have to disagree with "mtheory" on this one. ALL amps are designed to run a specific load. Change the impedance of the driver in EITHER direction and you run the LIKELY (and inevitable) risk of blowing the amp. If the speaker impedance is too low, it allows an excessive amount of "feedback" voltage to return to the amp. If the speaker load is too high the amp has to push too hard to get the signal through the speaker. The villain in both cases is HEAT, and heat kills amplifiers.

 

 

If you like the sound of your other (mismatched) speaker, here's what I would do. Get the manufacturer's code numbers and specs off the speaker you like, and find the same speaker in the correct impedance. If you want to post the speaker code here, I can most likely tell you who made it.

[rdsmith3]

I have a similar dilemma that I posted elsewhere. I am using an Epiphone 1x12 cabinet with a Fender VibroChamp XD. I like the sound, but the Fender has a 4 ohm speaker and the cabinet has a 16 ohm Eminence Lady Luck speaker. I contacted Eminence, and the only 12" 4 ohm speaker they make is Patriot Texas Heat, but they said it is very different from the Lady Luck. I think I will still try it because it is supposed to be well suited for the classic rock and blues that I like.

[mtheory]

I'll have to disagree with "mtheory" on this one. ALL amps are designed to run a specific load.

That's correct. However, that specific load that makes the amp most happy isn't necessarily always what the manufacturer SAYS it is. Nor is that magic load necessarily the only load that the amp will run safely at. Many tube amps can safely run 100% mismatches without any detriment whatsoever. The problem is, you would never know that for certain without putting the amp on a scope to see what makes it the most happy, and monitoring the output transformer for excess heat. Heat kills amps, as you said.

 

If the speaker impedance is too low, it allows an excessive amount of "feedback" voltage to return to the amp. If the speaker load is too high the amp has to push too hard to get the signal through the speaker.

The question is, how do you KNOW FOR CERTAIN what sort of load is either too high or too low? You don't, unless you put the amp on a scope and try different options. You can assume that the manufacturer is publishing the best load for a given amp, but that assumption doesn't necessary mean that what they say is the absolute best load for the amp. It just means that this is the load that they feel will work well without causing problems. We can only hope that the design engineers had a clue about what they were doing, but, as is the case with the stock Vjr, for instance, it's clear that this isn't necessarily always the case. They hosed up some pretty basic things in that amp. Given how badly the designers screwed up those very simple things, why would we just assume that they got the output impedance correct, right?

 

Get the manufacturer's code numbers and specs off the speaker you like, and find the same speaker in the correct impedance.

Again, how do we KNOW what the "correct impedance" is, without seeing amp performance on a scope? We really have no way of knowing whether or not the reason he liked the sound of that speaker had more to do with the impedance mismatch than the speaker make/model. I can attest to the fact that swapping output impedance loads, even to an alleged mismatch, can yield quite dramatic results.

 

My point here isn't to be contentious or to suggest that people just march wildly off to try all sorts of load variations that may or may not be detrimental to their amp. My point is to stress that, without actually seeing a sine wave of an amp run through different tap and load options, you really don't know. The only thing you can really do is assume that the designer of the amp knew what he was doing (a pretty bold assumption, imo), and that there is simply no chance whatsoever that he's made an error.

[mtheory]

I have a similar dilemma that I posted elsewhere. I am using an Epiphone 1x12 cabinet with a Fender VibroChamp XD. I like the sound, but the Fender has a 4 ohm speaker and the cabinet has a 16 ohm Eminence Lady Luck speaker. I contacted Eminence, and the only 12" 4 ohm speaker they make is Patriot Texas Heat, but they said it is very different from the Lady Luck. I think I will still try it because it is supposed to be well suited for the classic rock and blues that I like.

 

Eminance isn't the only speaker maker with a 12" 4 ohm speaker. Try Weber and Jensen, for instance.

[rdsmith3]

Eminance isn't the only speaker maker with a 12" 4 ohm speaker. Try Weber and Jensen, for instance.

 

Yes, I was looking at a Jensen C12N. Eminence seems like a better value, though -- it is $12 cheaper.

[jefrs]

Adding a resistor is series with a speaker is possible but not recommended.

 

An 8ohm impedance speaker has a resistance of about 6ohms. Impedance and resistance are not quite the same thing.

 

Even with a high power (power = watts) resistor, they get hot. I've had one such resistor get hot enough to melt the solder connection. All connections need to be made very carefully for low contact resistance, physical strength, and heat dissipation. In this case that means leave long wires on the resistor for stand-off, and solder properly to "massive" metal terminals that can withstand and get rid of the heat.

 

Best method is buy another speaker with the correct impedance. Alternatively run two 8ohm speakers in series (8+8=16ohm impedance), even separate cabs.

[jefrs]

Yes, I was looking at a Jensen C12N. Eminence seems like a better value, though -- it is $12 cheaper.

 

Choose with your ears not your wallet. I'd go with the Jensen.

[jefrs]

I'll have to disagree with "mtheory" on this one. ALL amps are designed to run a specific load. Change the impedance of the driver in EITHER direction and you run the LIKELY (and inevitable) risk of blowing the amp. If the speaker impedance is too low, it allows an excessive amount of "feedback" voltage to return to the amp. If the speaker load is too high the amp has to push too hard to get the signal through the speaker. The villain in both cases is HEAT, and heat kills amplifiers.

 

 

If you like the sound of your other (mismatched) speaker, here's what I would do. Get the manufacturer's code numbers and specs off the speaker you like, and find the same speaker in the correct impedance. If you want to post the speaker code here, I can most likely tell you who made it.

 

Here's the thing, with a bigger amp I would agree that a 100% mis-match is a very bad thing, especially when putting a lower than recommended load onto it.

It is generally accepted that a valve amp will happily take +50% mis-match or even a little more e.g. putting 5.6ohm on a 4ohm outlet.

 

But this is a 4watt amp. So the transformer, which will take most of the punishment, will be over engineered and will not cook. The output valve will have to work harder with a -100% mis-match. What's the worst that can happen: blown valve. That is unlikely to happen unless the amp is thrashed at full volume. The valve should be considered an expendable consumable item anyway.

 

 

The stock speaker in the AC4TV will be the cheapest Celestion 10-in. Replace with the 10-in Celestion G10-30 Greenback of correct 16ohm impedance, this is a superb speaker for any amp wanting a 10-in speaker, it is almost completely different to the G12M-25.

 

Hang on, the OP has a 2x12 cab of excellent 8ohm speakers: reconfigure the box to 16ohm series and ext-cab the Vox - sorted.

[rdsmith3]

Choose with your ears not your wallet. I'd go with the Jensen.

 

How do you choose with your ears? Listening to sound clips on line is limited by the sound qualities of my PC speakers, sound card, etc. which are not exactly high fidelity. Short of buying each speaker and doing a blind AB comparison, I'm not sure how to go about this.

[bolide]

I gotta side more with mtheory than L5Larry on this: Industry standard practice (think lawyerism) is that the rating be based on the amp being able to be used with a 2:1 or a 1:2 mismatch without damage, not on what the optimal impedence is. This protects the manufacturer against slight idiocy causing warrantee claims, as well as accounts for the fact that speaker impedence is by no means exact throughout the range, and can vary considerably even with the same speaker used in different cabinets (the impedence is more than impedence, the speaker does work, and so the impedence will be lower at the cabinets resonant frequencies).

 

This of course only applies to mass produced amps of recent vintage. Older, roll-your-own, and hot-rodded amps had best be used at the recommended load, or suffer the consequences.