Replies to This Discussion

Permalink Reply by Ron "Oily" Sprague on March 10, 2017 at 11:22am

Not necessarily. 1/2 W is plenty to drive car speakers. Check with Wes Carl, Wayfinder, and several others here who build amps using that and similar kits, with all kinds of speakers, including car audio types.

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Permalink Reply by Paul Craig on March 11, 2017 at 9:23am

Most car speakers are 4ohm and most guitar amps are 8 ohm. 

A 4ohm speaker will be damaged quickly hooked up to a 8ohm amp, but you can wire 2 4ohm speakers in series(+ of speaker 1 to amp +, - of speaker 1 to + of speaker 2, - of speaker 2 to amp -) to work with a 8ohm amp.

Car speakers will not last long though with a guitar amp because they aren't made for that kind of use.

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Permalink Reply by Timothy Hunter on March 13, 2017 at 12:40am

if the 4 ohm speaker is of sufficient wattage then it wont suffer any damage. what CAN happen is that a 4 ohm load on the output of an amp can overload the output transistors and burn them out. basically less resistance more current flows , exceeds transistor capacity. dead amp. the only time you will blow speakers is if you are trying to put 100w through a 10 w speaker. then it gonna die!

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Permalink Reply by Timothy Hunter on March 13, 2017 at 11:37pm

yes. amps are usually designed with an output load in mind. that can usually be 4 ohms to 16 ohms. a speaker is a dynamic load. what it is is a coil of wire suspended by a cone in a circular groove  in a permanent magnet. what power the speaker can handle depends on how strong the magnet is. the gauge and number of winds in the coil and the stiffness of the suspension. the part of the speaker that connects to the rim and allows movement. 

assume you have a 5W amp module. the most obvious thing to do is to try to match it to a 5W speaker.If you only have a 10W speaker then you are not going to hurt the speaker or the amp you just wont get full efficiency out of the amp.

Now lets use that 5W amp to drive a 50W speaker. we are now putting only 1/10th of the power that the speaker can handle. you will hear sound but there wont be any punch to the sound. the movement of the speaker cone is called excursion , how far back and forward the speaker cone can move. with only 1/10th of the power the cone wont move much at all.

go to the other extreme and put a 1/2 W speaker on a 5 W amp, you are now putting 10 times the power into the speaker than it was designed to handle. the speaker cone will try to move beyond the limits that it was designed to and the suspension will fail. blow out the speaker. unless the added current and voltage through the coil doesnt burn it out first. 

now that was all assuming the amp and speakers were the same  that is 8 ohm load and 8 ohm output amp.

with load mismatch the amp controls the voltage the only thing that can change is the amount of current . To horribly oversimplify this if you have half the load you get twice the current. by ohms law twice the current is twice the power developed assuming the voltage stays the same. so now your 4 ohm speaker is trying to pull 10 W out of you amp. 

Valve outputs are slightly different because they have a transformer as the load and the speaker is on the secondary.

https://en.wikipedia.org/wiki/Loudspeaker

 

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Permalink Reply by Nathan T. Logsdon on March 14, 2017 at 2:12am

That is very helpful! Thank you!

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Permalink Reply by Nathan T. Logsdon on March 15, 2017 at 2:21am

I know! Right!

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Permalink Reply by Paul Craig on March 13, 2017 at 8:33am

Damage can also occur to the speaker coil from ohm mismatch. One of the parts will be damaged for sure.

But the real damage to speaker coils comes from using a instrument that has a high level output in a small dedicated range of sound that's used with a speaker that's designed for a lower intensity wide range of sound for stereo audio output.

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Permalink Reply by Paul Craig on March 13, 2017 at 8:36am

You can use car stereo speakers, but it will damage them a little at a time and eventually rag them out and make them sound terrible. If you use a guitar speaker, that will not occur.

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Permalink Reply by Paul Craig on March 13, 2017 at 9:10am

Guitar speakers can be expensive, but there's plenty of speakers now that can be purchased for as little as 15 bucks. Mostly 6" and 8", but some 10" speakers can be had for less than 40 bucks that sound ten times better than a little car stereo speaker.

Jensen MOD speakers, Celestion has some 8" and 10" from 30 to 40 bucks, Eminence and WGS have 2 or more that I know of under 40 bucks.

Good  and correct speakers are available for affordable prices these days and they sound so much better. The cost of parts are coming down.

I used a Home Theater Subwoofer in my little 4watt bass amp. Lasted 6 months. Bass speakers are so much more expensive, but Eminence now has a 8" and 10" available for 75 bucks. They used to be in the 200 dollar or more range.

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Permalink Reply by Paul Craig on March 13, 2017 at 9:17am

A lot of those little boards are made for home audio for music playback from cell phones, laptops or tablets.

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Permalink Reply by Nathan T. Logsdon on March 14, 2017 at 2:13am

Are you using these with the CB Gitty amp setup?

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Permalink Reply by Timothy Hunter on March 13, 2017 at 11:39pm

nice wes.... 

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