two amps into one sub to drop it to 20hms... how ?
11-27-2006, 05:46 PM
#12
Strapping and bridging are generally electrically the same thing.
Seems like the term bridging is used when a 2 channel amp is bridged internally, while the word strapping is used when 2 separate amps are used. In theory any pair of normal amps can be bridged as long as they can handle the extra current. An exception is Head Unit amps as they are already Integrated Circuit amps in a bridged configuration to be able to supply the rated 20 or so watts RMS out of 12 volts.
Lets assume that an amp has a +45V and -45 Volt supply and that the output transistors dont have any loss. This is just to make the math easier. The output from that amp would be 50x sqrt2= 32 volts RMS, (rounding)
if we have a 2 ohm sub, that gives a power output of
(32x32)/2 = 500watts RMS. (Power= V^2*R)
The current will now be about 16 amps RMS
if we bridge or strap 2 of these amps, we first need to drive the "negative" amp 180 degrees out of phase. Then we connect the speaker to the positive of both amps.
Now when one amp is at +45v peak, the other is at -45v peak, providing 90 volts peak to peak to the sub, or 64 volts RMS. or 2000watts. However the current has now doubled to 32 amps RMS. So the amps must be well designed in order to handle the extra current thru the output stages and power supply. Sometimes the minimum speaker impedance is increased in order not to draw too much current.
So an amp may be 250W x2 into 4 ohms, 500 watts x2 into 2 ohms, or bridged 1000watts into 4 ohms, but NOT 2000 watts into 2 ohms because that would draw too much current.
On 2 channel amps you sometimes have a "bridge" switch to do the inverting of the second channel as well as feeding the same signal to both, sometimes you simply connect the speaker to the pos of one channel and the neg of the other channel.
When using 2 separate amps sometimes care must be taken to carefully adjust the gains of the 2 amps with a test tone, other times they can do that internally with some sort of master/slave connection.
The important thing is to read the manual.
ONE THING IS CLEAR: the amps are in series in order to double the voltage. NEVER IN PARALLEL. If you put amps in parallel, each amp's very low output impedance will act as the load to the other and will cause overload.
So If you have a 4+4 DVC sub, giving 2 ohms in parallel, you could carefully strap 2 amps according to the manufacturers directions making sure they can drive the current.
Many of the MTX amps can be "strapped" and the owners manual shows how to do that. Check their website to see if the ones you want to use can be strapped.
Seems like the term bridging is used when a 2 channel amp is bridged internally, while the word strapping is used when 2 separate amps are used. In theory any pair of normal amps can be bridged as long as they can handle the extra current. An exception is Head Unit amps as they are already Integrated Circuit amps in a bridged configuration to be able to supply the rated 20 or so watts RMS out of 12 volts.
Lets assume that an amp has a +45V and -45 Volt supply and that the output transistors dont have any loss. This is just to make the math easier. The output from that amp would be 50x sqrt2= 32 volts RMS, (rounding)
if we have a 2 ohm sub, that gives a power output of
(32x32)/2 = 500watts RMS. (Power= V^2*R)
The current will now be about 16 amps RMS
if we bridge or strap 2 of these amps, we first need to drive the "negative" amp 180 degrees out of phase. Then we connect the speaker to the positive of both amps.
Now when one amp is at +45v peak, the other is at -45v peak, providing 90 volts peak to peak to the sub, or 64 volts RMS. or 2000watts. However the current has now doubled to 32 amps RMS. So the amps must be well designed in order to handle the extra current thru the output stages and power supply. Sometimes the minimum speaker impedance is increased in order not to draw too much current.
So an amp may be 250W x2 into 4 ohms, 500 watts x2 into 2 ohms, or bridged 1000watts into 4 ohms, but NOT 2000 watts into 2 ohms because that would draw too much current.
On 2 channel amps you sometimes have a "bridge" switch to do the inverting of the second channel as well as feeding the same signal to both, sometimes you simply connect the speaker to the pos of one channel and the neg of the other channel.
When using 2 separate amps sometimes care must be taken to carefully adjust the gains of the 2 amps with a test tone, other times they can do that internally with some sort of master/slave connection.
The important thing is to read the manual.
ONE THING IS CLEAR: the amps are in series in order to double the voltage. NEVER IN PARALLEL. If you put amps in parallel, each amp's very low output impedance will act as the load to the other and will cause overload.
So If you have a 4+4 DVC sub, giving 2 ohms in parallel, you could carefully strap 2 amps according to the manufacturers directions making sure they can drive the current.
Many of the MTX amps can be "strapped" and the owners manual shows how to do that. Check their website to see if the ones you want to use can be strapped.
Last edited by zoomer; 11-27-2006 at 06:06 PM.
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