Adding cones

[Scorpoll]

First off, I know nothing about amps and this may be an obvious question. I have a 10 watt combo amp that I'm rehousing into a vintage bedside cabinet because I think it'll look cool and I've realized that it's a lot bigger than I expected so the one speaker cone is going to look pretty weedy in this big space. Is it possible for me to just split off from the two wires that are connected to the original cone so that they attach to two cones instead? If this isn't possible is there anything I can do to change it which would not require much effort. The cone that's already in there is 4 ohm (this may be irrelevant info but I might as well say) and I plan on adding an identical one.

[eschertron]

If you have a speaker that is 4 Ohms - and assuming this is the original design for the output impedance of the amp - you can replace that speaker with a pair (preferably identical) of 8 Ohms speakers connected in parallel. This parallel wiring arrangement sounds very much like the "split off from two wires" that you mentioned, and two 8 Ohm speakers in parallel will be equal to one larger 4 Ohm speaker. Math courtesy of Ohm's law.

Having said all that, if the amp is transistorized, and not a tube amp, then go nuts with the speakers in terms of impedance and combining them in different wiring arrangements. The only way to kill a transistor output section (well, almost the only way) is to short the speaker wires together. More or fewer speakers tend to not be a serious engineering issue with solid-state amps. Caveat: I may get beat down for making such a blanket statement on this forum

[Jazz P Bass]

To add, what type of an amplifier is it?
Tube or solid state?

2 4 ohm speakers in parallel will drop the dc resistance of the speaker combination , to 2 ohms.

A tube amp will take the mismatch.

Now if it is a solid state amp, the 2 ohm load may 'challenge' that little 10 watt amplifier to the extreme.
At full volume the output section will be tasked with delivering 20 watts to the speakers.
(Again, Ohm's Law: Power Out = Voltage squared divided by the speaker load)

So in the case of a solid state amp, the 'safe' alternative would be a series wiring of the speakers.
(2 4ohm speakers in series= 8 ohms)
Albeit, with a now 5 watt total output.

[Scorpoll]

So I could either use two 8 ohm speakers in parallel and have it work at 10 watt, or I could have two 4 ohm speakers in series and have it work at 5 watt? Could anyone say which would be louder?

[g1]

The two 8ohm speakers in parallel will be louder.

[Chuck H]

So I could either use two 8 ohm speakers in parallel and have it work at 10 watt

Yes. Whether it's tube or transistors.

or I could have two 4 ohm speakers in series and have it work at 5 watt?

Yes. But it will only be at half power if it's a transistor amp. If it's a tube amp it will be more efficient with the mismatch.

And I don't mean to insult, really, but have you never dealt with anything rated in watts before? I would have thought everyone knew watts are power and that 10 is more than 5. Ergo, 10 watts (2x8 ohms parallel) is more power than 5 watts (2x4 ohms series). I'm a little jealous maybe since I remember my fascination at every audio discovery in my life. To start over could be fun

[Scorpoll]

I know that the more watts the louder but I thought maybe the ohms of the speaker had an effect on volume and that 5 watts could be louder in a situation where it was driving different ohm speakers. Needless to say, I have no idea what ohms is in relation to a speaker other that it's something to do with resistance.

[J M Fahey]

Or since you are buying anyway, you might use a single much better 4 ohms speaker instead of 2 small crummy ones.

What size is the original one?

If you have enough space, Jensen MOD speakers are available in 6/8/10/12" , 4 ohms, killer sound, much better than whatever you have there, are not expensive , e anche loro sono paesani
http://www.sica.it/en/company.html

[J M Fahey]

Having said all that, if the amp is transistorized, and not a tube amp, then go nuts with the speakers in terms of impedance and combining them in different wiring arrangements. The only way to kill a transistor output section (well, almost the only way) is to short the speaker wires together. More or fewer speakers tend to not be a serious engineering issue with solid-state amps.

Well, no.

Double the impedance will halve power output.
Bad.

Half the impedance will overheat and burn the amp, will just let you play for some time instead of the instant short circuit death.
Worse.

Caveat: I may get beat down for making such a blanket statement on this forum

See above

[Scorpoll]

The one I've go already is 6". Does the size of the cone have a large effect on the volume?

[Jazz P Bass]

So I could either use two 8 ohm speakers in parallel and have it work at 10 watt, or I could have two 4 ohm speakers in series and have it work at 5 watt? Could anyone say which would be louder?

At either 10 or 5 watts, 'loudness' is not going to be all that much different.

[Chuck H]

At either 10 or 5 watts, 'loudness' is not going to be all that much different.

True dat. Both would be too loud for bedroom practice and not loud enough for a band

[eschertron]

Well, no.

Double the impedance will halve power output.
Bad.

Half the impedance will overheat and burn the amp, will just let you play for some time instead of the instant short circuit death.
Worse.

Consider me spanked

Although I do remember as a beginner, hooking together whatever speakers I could find to whatever (hifi) amp I had, and making it work. It was the initial "bite" of the electronics bug, and I didn't suffer too many negative consequences.

Just thinking out loud:
What is the scope of the project? Do you need to get every last Watt or decibel from the amp? I'm thinking since it's being built into a home (or bedroom) -friendly cabinet, that the answer will be no. If that's the case, there are a lot of envelope-pushing engineering principles under discussion here that are pretty much irrelevant. What you'll want to be aware of is having enough air flow that the amp doesn't overheat (or smell funny in your domestic environment). Also, The quality of the speaker(s) you choose will have a much greater impact on the sound than how big or how many.

A bigger speaker can push more air, and sound bigger/louder; also have a better bass response for more low end. The actual, absolute volume of the speaker (sound pressure level, decibels, Watts) will depend on its efficiency and the impedance of the speaker. All of this matters ONLY if you are cranking the amp to match a drummer, guitarist, or other band instrument.

If the scope of the project is for enjoying a nice piece of furniture, and playing at bedroom levels (with, say, the radio on) then just build it. Scorpoll, As you learn more about amps and electronics you may find that you want to tweak the project. When you decide to push the envelope of the amp's design, then you will need to know about Watts, and Ohms, and how the laws of electronics determine which lines we cannot cross

Ask questions, search the Googleverse, and be safe around high voltage!

[Chuck H]

The one I've go already is 6". Does the size of the cone have a large effect on the volume?

Somewhat, yes. More air moving means more sound. Of course if you move a small cone more and a big cone less... But in general, and within some reasonable limits, a larger cone speaker will at least seem louder if it's not actually louder. For your wattage, more important than actual volume would be the tone. And a bigger speaker will have a tone more suitable for guitar. This assumes you'll be using it with a guitar. The most popular sizes (virtually the only sizes) used for guitar speakers would be 10" and 12". Given the design opportunity I would pick one 10" over two 6". First for the reason already mentioned and second because there are precious few 6" speakers made for guitar with guitar tones as a criteria. In fact I don't know of one but I wouldn't be surprised if someone makes a replacement for the classic Fender Champion 600 model. There are a lot (A LOT!!!) of 10" speakers made just for guitar amps though.