Sub Question
Registered User
Joined: Oct 2000
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From: Port Angeles
An amplifier will put out more power (50-100%) into a 4 ohm speaker. However, if you are using two 4 ohm subs (depending on how you connect them) the load on the ampflifier could drop below two and some amps don't like that. If you are using a low to medium power amp with one subwoofer 4 ohms is probably the way to go.
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Joined: Nov 2001
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From: Toronto
This is a difficult subject to address in a post, so I will make an quick attempt and cut a few corners just to get the basic idea across.
When speaking about direct current (dc) the direction of the electons is constant so the way electical components act is a little simpler, for example a coil (a wire wrapped in a circle, such as the voice coil in a speaker) will only have a resistive value (i.e. resistance, which is the opposition to the flow of current or electrons). If you take a voltmeter and measure the resistance across the speaker terminals you will measure about 3.2 ohms on a 4 ohm speaker. This is the resistive value of the speaker as the voltmeter is placing DC across the current.
When speaking about alternating current (ac), which is what music is, the way certain electrical components will react is a little more difficult to measure unless you know more information. AC basically means that the current will flow in one direction, then switch and flow in the other direction (like a sine wave for example). Coils will react differently depending on the frequency of the AC signal applied...the opposition to current flow will be dependant of the frequency of the applied signal. For instance, if you place a 100Hz signal on the speaker, the speakers "resistance" will be different than what it would be if you placed a 1000Hz signal on the speaker. This measure of opposition to ac current flow at a particular frequency is impedance.
For coils, the higher the frequency, the higher the impedance you get. For capacitors, the opposite is true, the higher the frequency the lower the impedance.
This is also what makes a crossover work, if you want a crossover point at a certain frequency all you need is the right combination of coils and capacitors and bang, highs go to tweeters and lows go to bass drivers. This is because a capacitor will present a high frequency signal a lower impedance at than the coil, so the current will take the path of least resistance and go to the tweeter. The opposite happens for low frequencies.
So as the frequency applied to the speaker changes so does the impedance of the speaker. At certain frequencies it can be below 4 ohms and at others it could be higher than 8 ohms (as high as 50 or 60 ohms) even if the speaker says it has a 4 ohm impedance. What the 4 ohm impedance means is that the speaker will have an average impedance of 4 ohms over a range of frequencies.
I hope this helped, if you want more info...just post.:
When speaking about direct current (dc) the direction of the electons is constant so the way electical components act is a little simpler, for example a coil (a wire wrapped in a circle, such as the voice coil in a speaker) will only have a resistive value (i.e. resistance, which is the opposition to the flow of current or electrons). If you take a voltmeter and measure the resistance across the speaker terminals you will measure about 3.2 ohms on a 4 ohm speaker. This is the resistive value of the speaker as the voltmeter is placing DC across the current.
When speaking about alternating current (ac), which is what music is, the way certain electrical components will react is a little more difficult to measure unless you know more information. AC basically means that the current will flow in one direction, then switch and flow in the other direction (like a sine wave for example). Coils will react differently depending on the frequency of the AC signal applied...the opposition to current flow will be dependant of the frequency of the applied signal. For instance, if you place a 100Hz signal on the speaker, the speakers "resistance" will be different than what it would be if you placed a 1000Hz signal on the speaker. This measure of opposition to ac current flow at a particular frequency is impedance.
For coils, the higher the frequency, the higher the impedance you get. For capacitors, the opposite is true, the higher the frequency the lower the impedance.
This is also what makes a crossover work, if you want a crossover point at a certain frequency all you need is the right combination of coils and capacitors and bang, highs go to tweeters and lows go to bass drivers. This is because a capacitor will present a high frequency signal a lower impedance at than the coil, so the current will take the path of least resistance and go to the tweeter. The opposite happens for low frequencies.
So as the frequency applied to the speaker changes so does the impedance of the speaker. At certain frequencies it can be below 4 ohms and at others it could be higher than 8 ohms (as high as 50 or 60 ohms) even if the speaker says it has a 4 ohm impedance. What the 4 ohm impedance means is that the speaker will have an average impedance of 4 ohms over a range of frequencies.
I hope this helped, if you want more info...just post.:
Honorary Member
Joined: May 2001
Posts: 2,121
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From: Indian Land SC
Originally posted by Daniel L
Anyone mind explaining the whole impendance thing? I always wondered..
Anyone mind explaining the whole impendance thing? I always wondered..
What I find interesting is that your response is totally different than mine would have been, not that yours is wrong by any means. I thought the guy was asking about how the impedance changes when you put speakers in series or parallel, or how the impedance affects power output. You evidently thought he wanted to understand why impedance is different than resistance. Just goes to show how different people looking at the same thing see it from completely different viewpoints.
I wonder what he was really asking? Probably wanted to know about "impotence" and just spelled it wrong. (j/k Daniel L)
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Registered User
Joined: Mar 2002
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From: LA, CA - Durham, NC
I was asking about impotence but uhh.. I think he gave me the answer to something else I had always been curious about, albeit in more technical terms. I was always curious as to why my home theatre speakers were 8 ohms, why amps were "stable down to two ohms" etc.. etc..
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Joined: Oct 2000
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From: Port Angeles
I believe that home speakers are normally 8 ohms because they offer lower distortion figures (albeit inaudible) than 4 ohm speakers. Also, if you wanted to wire two sets of speakers in parallel off the same amplifier you would have a resistance of about 4 ohms and an amplifier should have no trouble handling that. If you parallel four ohm speakers resistance will drop to two ohms and fuses will begin to blow. I think the formula works something like this - for two 8 ohms speakers in parallel
8 X 8 64 resistance would be 4 ohms.
8 + 8 16
For and eight and a four: 8 x 4 32 resistance would be 2 2/3.
8 + 4 12
The resistance for an 8 ohm speaker may range for 5 to 16 ohms and is just an average. With so many speakers being put into one car, the car stereo people designed amps that were stable to 2 ohms and below. The lower the resistance the more wattage an amplifier will deliver to s speaker
8 X 8 64 resistance would be 4 ohms.
8 + 8 16
For and eight and a four: 8 x 4 32 resistance would be 2 2/3.
8 + 4 12
The resistance for an 8 ohm speaker may range for 5 to 16 ohms and is just an average. With so many speakers being put into one car, the car stereo people designed amps that were stable to 2 ohms and below. The lower the resistance the more wattage an amplifier will deliver to s speaker
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Joined: May 2001
Posts: 2,121
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From: Indian Land SC
Some advantages to 8 ohm speakers:
1. They draw less current for the same power. (they use a higer voltage to compensate). Less current means the amplifier does not work as hard and generates less heat and therefore less "wear" on the components. Heat is the #1 enemy of solid state components. HIgher voltage does not create more heat.
2. Less current means the amp's components cost less. High current electronics is expensive. It's easier to build a higher voltage amp than a higher current one. (unless you're talking about extremely high voltages >1000v, which we're not). And since home systems start with a higher voltage (120 volt AC), it's very easy to build the higher-voltage lower-current amp needed for 8 ohm speakers.
3. Less current means there is less voltage loss (therefore power) in the cabling. A 100 watt 8 ohm system will have half the cable losses of a 100 Watt 4 ohm system, if they both have the same length and gauge of speaker wire. If you halve the impedance, you should use wire 3 gauge sizes larger; example - 8 ohm system with 16 gauge wire, 4 ohm with 13 gauge, 2 ohm with 10 gauge) Home systems usually have longer speaker cables than cars, so this is important.
4. Higher voltage (because we have less current) gives greater signal-to-noise ratios, which again translates to less distortion.
5. Less current means the cross-over parts are smaller and lighter, therefore cheaper. To maintain the same quality, a 4 ohm crossover will cost more.
6. Damping factor is higher on an 8 ohm system. Damping factor is the ratio of the speaker's impedance to the amp's impedance, and it affects how well the amp is able to control unwanted speaker cone movements (distortion). Homes are usually better listening environments, where distortion is more likely to be noticed. (no flaming from those that spent more money on the car stereo than they did on the car, please)
Advantages of 4 ohm speakers:
1. The lower impedance allows more power to be consumed by the speaker, which gives higher audio output, assuming the amplifier is designed to handle the higher current. A 4 ohm speaker will draw twice the current, and 2 ohms 4 times the current of an 8 ohm speaker. Amplifiers not designed for this will not be happy. Ones that are will survive, they just get hotter.
How much louder will 4 ohms be than 8 ohms? Electrically speaking, twice as loud. Aurally speaking (how your ears interpret it), a little bit. You'll be surprised how little.
To see how loud "twice the power" is, just adjust your left-right stereo control to full left (or right). You are listening to half your speakers, and so it's running on half power output. Then turn it to mid-way (listening to both speakers). That's twice the power.
1. They draw less current for the same power. (they use a higer voltage to compensate). Less current means the amplifier does not work as hard and generates less heat and therefore less "wear" on the components. Heat is the #1 enemy of solid state components. HIgher voltage does not create more heat.
2. Less current means the amp's components cost less. High current electronics is expensive. It's easier to build a higher voltage amp than a higher current one. (unless you're talking about extremely high voltages >1000v, which we're not). And since home systems start with a higher voltage (120 volt AC), it's very easy to build the higher-voltage lower-current amp needed for 8 ohm speakers.
3. Less current means there is less voltage loss (therefore power) in the cabling. A 100 watt 8 ohm system will have half the cable losses of a 100 Watt 4 ohm system, if they both have the same length and gauge of speaker wire. If you halve the impedance, you should use wire 3 gauge sizes larger; example - 8 ohm system with 16 gauge wire, 4 ohm with 13 gauge, 2 ohm with 10 gauge) Home systems usually have longer speaker cables than cars, so this is important.
4. Higher voltage (because we have less current) gives greater signal-to-noise ratios, which again translates to less distortion.
5. Less current means the cross-over parts are smaller and lighter, therefore cheaper. To maintain the same quality, a 4 ohm crossover will cost more.
6. Damping factor is higher on an 8 ohm system. Damping factor is the ratio of the speaker's impedance to the amp's impedance, and it affects how well the amp is able to control unwanted speaker cone movements (distortion). Homes are usually better listening environments, where distortion is more likely to be noticed. (no flaming from those that spent more money on the car stereo than they did on the car, please)
Advantages of 4 ohm speakers:
1. The lower impedance allows more power to be consumed by the speaker, which gives higher audio output, assuming the amplifier is designed to handle the higher current. A 4 ohm speaker will draw twice the current, and 2 ohms 4 times the current of an 8 ohm speaker. Amplifiers not designed for this will not be happy. Ones that are will survive, they just get hotter.
How much louder will 4 ohms be than 8 ohms? Electrically speaking, twice as loud. Aurally speaking (how your ears interpret it), a little bit. You'll be surprised how little.
To see how loud "twice the power" is, just adjust your left-right stereo control to full left (or right). You are listening to half your speakers, and so it's running on half power output. Then turn it to mid-way (listening to both speakers). That's twice the power.