Im not derailing your thread, but try to explain you something, so you can use this knowledge in your situation. Maybe you don't like Germans, but thats international physics.
You got to learn to calculate using Volt, Ampere, Watt and Ohm. Mostly called Ohms laws.
Maybe just with some lamps or resistors. That way you understand bridge amps much better.
Because mainly of D-amps and mostly the high tollerance of our Chinese friends to correct termination, there is some confusion now about bridged amps.
(remeber: Chinese = tollerant, Germans = intollerant with physics)
When amps are only feed by a single voltage, like 12 Volt+ and ground, they have very little power and need a capacitor at the output. That doesn't sound good, is weak and expensive. So we take two of them in a bridge configuration. Which gives us 4 times the power and eliminates the capacitor. Good, strong and cheaper.
Such an amp CAN NOT be bridged any more.
They have about 18 Watt rms /4 Ohm in a car, but are mostly called 2x25W as you can read on many car radios. Some call them 2x50W and that is just the same...
Now, if you double the output devices of such amps, you may drive a 2 Ohm load. Even some car radios have the option to use two channels combined to give real 36Watt rms. Often called 50 or even 100 Watt. (The best lie wins in marketing.) You trade two amps for one with double the current.
Volt x Ampere = Watt
Many D-amps like the TDA3255 to name a popular D-amp chip, have the option to use two amps in parallel, so you got a stereo amp consisting of two amps each. A single TDA3255 in fact always is 4 amps, bridged in almost any case, so we get two channels.
Now comes the catch: such an amp may have a switch labeled "BRIDGE" and our Chinese seller claims it to have 600W instead of 2x300W if you use the magic option. Which is not a real lie, but not true either.
In fact you now only parallel these two bridged amps! So because of higher current (ampere) you now can use them with 2 Ohm without cutting off, instead of 4 Ohm. At a 4 Ohm load such a "double bridged" amp has no extra power!
So to make it clear, using something in parallel is NOT bridging.
I hope that helps and you will now understand why Perry asks the same question I did a few posts before.
You got to learn to calculate using Volt, Ampere, Watt and Ohm. Mostly called Ohms laws.
Maybe just with some lamps or resistors. That way you understand bridge amps much better.
Because mainly of D-amps and mostly the high tollerance of our Chinese friends to correct termination, there is some confusion now about bridged amps.
(remeber: Chinese = tollerant, Germans = intollerant with physics)
When amps are only feed by a single voltage, like 12 Volt+ and ground, they have very little power and need a capacitor at the output. That doesn't sound good, is weak and expensive. So we take two of them in a bridge configuration. Which gives us 4 times the power and eliminates the capacitor. Good, strong and cheaper.
Such an amp CAN NOT be bridged any more.
They have about 18 Watt rms /4 Ohm in a car, but are mostly called 2x25W as you can read on many car radios. Some call them 2x50W and that is just the same...
Now, if you double the output devices of such amps, you may drive a 2 Ohm load. Even some car radios have the option to use two channels combined to give real 36Watt rms. Often called 50 or even 100 Watt. (The best lie wins in marketing.) You trade two amps for one with double the current.
Volt x Ampere = Watt
Many D-amps like the TDA3255 to name a popular D-amp chip, have the option to use two amps in parallel, so you got a stereo amp consisting of two amps each. A single TDA3255 in fact always is 4 amps, bridged in almost any case, so we get two channels.
Now comes the catch: such an amp may have a switch labeled "BRIDGE" and our Chinese seller claims it to have 600W instead of 2x300W if you use the magic option. Which is not a real lie, but not true either.
In fact you now only parallel these two bridged amps! So because of higher current (ampere) you now can use them with 2 Ohm without cutting off, instead of 4 Ohm. At a 4 Ohm load such a "double bridged" amp has no extra power!
So to make it clear, using something in parallel is NOT bridging.
I hope that helps and you will now understand why Perry asks the same question I did a few posts before.
Hi!
Just a little bit about that impedance halving.
Say you have an amplifier that puts out 12Vrms over a 4 ohm load. The amplifier has to supply 3A and so it is producing 36W.
If the load was 2ohms, the amplifier would have to supply 6A and so it would be producing 72W.
When you bridge two of these amplifiers you double the voltage over the load. So now you have two amplifiers giving 12Vrms each and 180° out of phase, so you wil get 24Vrms over your 4 ohm load. The amplifier has to deliver 6A to the load and so it is producing 144W.
So you see that each amplifier is putting out 12Vrms but is delivering 6A. This is the same as with the 2ohm load.
So the load doesn't actually halve, it's just the amplifier putting out twice the current.
The power is quadrupled but of course the power supply of the amplifier has to be built to be able to deliver this power.
Just a little bit about that impedance halving.
Say you have an amplifier that puts out 12Vrms over a 4 ohm load. The amplifier has to supply 3A and so it is producing 36W.
If the load was 2ohms, the amplifier would have to supply 6A and so it would be producing 72W.
When you bridge two of these amplifiers you double the voltage over the load. So now you have two amplifiers giving 12Vrms each and 180° out of phase, so you wil get 24Vrms over your 4 ohm load. The amplifier has to deliver 6A to the load and so it is producing 144W.
So you see that each amplifier is putting out 12Vrms but is delivering 6A. This is the same as with the 2ohm load.
So the load doesn't actually halve, it's just the amplifier putting out twice the current.
The power is quadrupled but of course the power supply of the amplifier has to be built to be able to deliver this power.
"Maybe you don't like Germans"
- I have no such problems. Quite an assumption to make based off of nothing, shame.
Hi xa488!
This is already much more clear to me, thanks! I've got another question. In your example, you start your calculation with 12Vrms, and 4Ohm as a load.
The 4Ohm I understand, as that is the load I'm trying to drive. But where does the 12V come from? Is this just an arbitrary number for illustration purposes? In other words, I'm trying to figure out where one 'starts' these calculations if you will.
For instance, can't I start out with the speaker's power rating, and work back from there? Or is this number set by how 'loud' the user sets the volume? I feel like I'm hung up on whether the amplifier 'pushes' the power to the speaker, or whether the speaker 'pulls' the necessary power from the amp. Does this make any sense?
This is already much more clear to me, thanks! I've got another question. In your example, you start your calculation with 12Vrms, and 4Ohm as a load.
The 4Ohm I understand, as that is the load I'm trying to drive. But where does the 12V come from? Is this just an arbitrary number for illustration purposes? In other words, I'm trying to figure out where one 'starts' these calculations if you will.
For instance, can't I start out with the speaker's power rating, and work back from there? Or is this number set by how 'loud' the user sets the volume? I feel like I'm hung up on whether the amplifier 'pushes' the power to the speaker, or whether the speaker 'pulls' the necessary power from the amp. Does this make any sense?
I'm still somewhat unfamiliar with the details of how all this works, so bear with me. Just sharing some thoughts here. I'm not 100% sure, but I feel xa488's calculation just made clear to me how this works.
First off: I take it that the volume setting on the radio actually controls the output voltage, right?
Next: It seems to me that no-matter-what, the amplifier will -or perhaps should- never exceed the rated power of the speaker. From here, I gather that using this rating is appropriate, as there are no desirable use cases above that level. The sound will distort, or the speaker might be damaged. In either case, going above this rating is a no-no.
Taking this into account, I arrive at the following when it comes to the dual coil sub I intend to use:
In short: From xa488's reply, I gather that it's the doubling of the power-per-channel that's the problem for the amplifier. But as long as I stay below half the maximum voltage, I never actually double the power, I'm just leveraging two channels to drive one voice coil instead of a single channel
Furthermore, couldn't I just halve the input voltage, thereby protecting the amp from going over the aforementioned 160W? This is still well over the 125W I need.
First off: I take it that the volume setting on the radio actually controls the output voltage, right?
Next: It seems to me that no-matter-what, the amplifier will -or perhaps should- never exceed the rated power of the speaker. From here, I gather that using this rating is appropriate, as there are no desirable use cases above that level. The sound will distort, or the speaker might be damaged. In either case, going above this rating is a no-no.
Taking this into account, I arrive at the following when it comes to the dual coil sub I intend to use:
- Having only 80W @ 4Ohm per channel is insufficient for powering a sub with a rating of 125W/4Ohm per coil. This is why I wanted to look into bridging in the first place.
- Bridging the amp to make use of 2 channels per voice coil puts the max supply at 4x that level (4x80W=320W), as explained by xa488. Problem is, the amp might not be able to deliver that without being damaged.
- I understand this is not a problem if you double the impedance, as this limits the current going to the load. Doing so limits the current to the 'original' level -so to speak- while still leveraging the higher voltage swing to put out more power. Only now, the power is merely doubles, not quadrupled.
In short: From xa488's reply, I gather that it's the doubling of the power-per-channel that's the problem for the amplifier. But as long as I stay below half the maximum voltage, I never actually double the power, I'm just leveraging two channels to drive one voice coil instead of a single channel
Furthermore, couldn't I just halve the input voltage, thereby protecting the amp from going over the aforementioned 160W? This is still well over the 125W I need.
The input (from the head unit) determines the voltage at the speaker terminals. The actual voltage gain is determined by multiple stages in the amp, the gain stage in the preamp stage has the most variation on the overall gain.
A person with a working brain can have an amplifier that's rated for more than 10x the speaker and never damage the speaker. It's all about self control and paying attention.
The power ratings for speakers is as close to useless as they can possibly be. Some are exaggerated to fantasy land status.
Insufficient power? Not really. It depends on what you require. For some it would be plenty. For others, they will never have enough.
When you bridge two 4 ohm coils in series, it's the same as connecting one coil per channel. There is no doubling of voltage, as far as each coil is concerned.
The problem for the amplifier (one with poorly designed protection) is from connecting a load that will allow too much current to flow through the output transistors.
What you don't do (shouldn't do) is to connect a load to the amplifier that's lower than the rated lowest impedance. The amplifier is designed so that the maximum voltage is can produce won't cause too much current to flow through the output transistors with the lowest rated load connected.
A person with a working brain can have an amplifier that's rated for more than 10x the speaker and never damage the speaker. It's all about self control and paying attention.
The power ratings for speakers is as close to useless as they can possibly be. Some are exaggerated to fantasy land status.
Insufficient power? Not really. It depends on what you require. For some it would be plenty. For others, they will never have enough.
When you bridge two 4 ohm coils in series, it's the same as connecting one coil per channel. There is no doubling of voltage, as far as each coil is concerned.
The problem for the amplifier (one with poorly designed protection) is from connecting a load that will allow too much current to flow through the output transistors.
What you don't do (shouldn't do) is to connect a load to the amplifier that's lower than the rated lowest impedance. The amplifier is designed so that the maximum voltage is can produce won't cause too much current to flow through the output transistors with the lowest rated load connected.
Hi, forgive me for saying this, but you are making the situation more difficult than expected.
If the speaker has a double coil and you have four channels available from the amplifier, you can safely connect two channels for each coil.
Why bridge the amplifier?
To get more power?
What makes you think you need more power?
If i understand correctly, you have not yet done any practical tests on this, so you could do a lot of calculations uselessly.
I would rather pay more attention to the filtering of the frequencies which is essential for a good sub section.
For your questions, the power correlation between amplifier and speaker has no practical value but only indicative.
If a speaker supports 125W, you can drive it with 15W or with 300W, the important thing is an adequate regulation of the input signal with its potentiometer, this to avoid the introduction of distortion, which is the real killer for speakers.
Once this is done, you will be able to understand if the applied power is sufficient or not.
But in any case, driving the two speaker coils with the four channels of the amplifier is equivalent to driving the two speaker coils in series (at 8 ohms) with two channels of the bridge amplifier.
I hope this helps.
Hi JP,
Somethings to consider:
To bridge an amplifier you have to invert one of the two channels by 180° degrees. So you need access to the amplifiers input.
Doubling the output power only raises the spl level with 3dB. So a 160W amp is only 3dB louder than a 80W amp driving the same load. 3dB isn't very noticeable. You can more easily increase the SPL by choosing a more sensitive speaker with a higher efficiency.
When a class B amplifier has an output of half it's supply voltage (for 24V supply an output of 12V peak) the output transistors dissipation is worst case. So the amplifiers output transistors have been chosen and are being cooled for this worst case scenario plus a little extra usually. With a doubling of current (like when you bridge or half the impedance of the speaker) the worst case dissipation doubles. It might not be made for this.
Somethings to consider:
To bridge an amplifier you have to invert one of the two channels by 180° degrees. So you need access to the amplifiers input.
Doubling the output power only raises the spl level with 3dB. So a 160W amp is only 3dB louder than a 80W amp driving the same load. 3dB isn't very noticeable. You can more easily increase the SPL by choosing a more sensitive speaker with a higher efficiency.
When a class B amplifier has an output of half it's supply voltage (for 24V supply an output of 12V peak) the output transistors dissipation is worst case. So the amplifiers output transistors have been chosen and are being cooled for this worst case scenario plus a little extra usually. With a doubling of current (like when you bridge or half the impedance of the speaker) the worst case dissipation doubles. It might not be made for this.
Found some pictures on the internet:
https://www.proxyparts.com/car-part.../6560j1/part/radio-amplifier/partid/21002805/
If the amp is really from around 2000 (as stated in the page above) I suspect it's not (yet) a class D amp. And guessing from the heat sink, the size and the connectors 4 × 80 W seems tremendously overrated.
Just my 2 cents.
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Apologies, but please understand that I'm not just trying to answer the question of what I'm trying to do in practice is feasible. I'm trying to prevent getting people on here to tell me me whether it is or isn't, getting some numbers thrown at me, coming out not understanding what any of it means and not having learned anything. I'm more interested in how the topology works, and what the limiting factors are so I can make my own decisions. Your comments and those of xa488 have been massively helpful in that manner. Thank you!
I'm stuck on how I would do this without bridging the amp. Earlier on, I was told I can't just tie two outputs together. How would this work?
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Maybe not. In fact, there's 8 channels on there, so that would make it only less likely I suppose.
That being said, I've looked at some wiring diagrams, and it seems the amp is fused at 15A. While it's pulling from the alternator with the engine running (14,5V), that would only be a little over 200W, thus at most 25W per channel. Am I going about this correctly?
You can do that, but it's not as straightforward as it may seem.
The problem is that you may get two outputs "fighting" eachother - have a look at the neurochrome page "parallel" section:
https://neurochrome.com/pages/output-power#parallelBridgeBoth
That would be roughly 2 A per channel, thus only 16 W per channel with 4 Ohm loads (disregarding peak/rms difference for now).
I guess your amp has bridged outputs already and supply is simply the alternator/battery voltage (no dc/dc converter).
I think there is a misunderstanding.
You are probably referring to the bridge again, but i think this cannot be done because:
Which should be the thought previously expressed by Perry and Turbowatch2.
In fact, for an 8-channel amplifier, the amplifier seems to be undersized, in the sense that it should not have the voltage booster => therefore the output channels are already bridged => and the output channels cannot be bridged further (two by two as you say).
These are guesses because we don't know much about this amplifier, but they are very close to reality.
What i suggest instead, is to connect each of the four output channels to each of the four speaker terminals.
Two coils = four terminals.
Coil 1:
- two terminals (terminal + and terminal - connected to the channel + and channel - of the amplifier)
Coil 2:
- two terminals (terminal + and terminal - connected to the channel + and channel - of the amplifier).
Four amplifier channels for four speaker terminals.
Right, thanks for clearing that up, I understand now. I'd already read possibility of multiple channels 'fighting' each other, so it didn't make sense to me so far.
This is still a bit vague to me. How do you come out at 4 channels? Only way I would know how this can work is:
Terminal + of coil 1 goes to channel 1 +
Terminal - of coil 1 goes to channel 2 -
Terminal + of coil 2 goes to channel 3 +
Terminal - of coil 2 goes to channel 4 -
If this is the case, what's the benefit of doing so?
If not, how do you arrive at 4 channels?
OR
I would need to connect the channels in parallel, but as stv & the website he links suggest, this is easier said than done. Probably not something I can just do without the necessary precautions, making the setup too complex to justify. At that point, it would indeed be easier to just get a new amp...
I would need to connect the channels in parallel, but as stv & the website he links suggest, this is easier said than done. Probably not something I can just do without the necessary precautions, making the setup too complex to justify. At that point, it would indeed be easier to just get a new amp...
So now we are there where the thread started: You want more power, get another amp. Hope you understood just a little of all that theoretical stuff.
I may add something: Nothing is more practical than good theory. It is making your life simpler by erasing impractical ideas without wasting time and money on them.
I may add something: Nothing is more practical than good theory. It is making your life simpler by erasing impractical ideas without wasting time and money on them.
Yes, exactly.
It's not correct to speak of advantage, because it's the ONLY way to proceed with the connection.
This, because:
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In my opinion this is the most sensible final consideration.
This is because the parallel of the channels, as rightly observed, would be very complicated, for this reason i explained before that the 4 out of 4 connection is the only possible one.
Furthermore, an additional amplifier allows you to choose a power dedicated to the sub speaker and a correct filtering for the useful frequency range.
To do this, however, you will need a dedicated output from the car radio.
I hope my 2 cents are not wrong.