Question about hooking a 2 subs to a box (Car Audio)

[zumbo]

WRONG!
The amp must be stable to 2 ohms MONO. Tell me how the amp changes 2 ohms to 1. It is NOT possible. All you are doing is internally summing the voltage from the left and right channels.

Of course his amp cannot drive both speakers in parallel. The amp is only stable to 4 ohms mono not 2 ohms mono.

An amplifier that is stable to 2 ohms stereo (if bridgeable) is almost always only stable to 4 ohms mono.
An amplifier stable to 1 ohm stereo (which is very rare) is again, almost always stable to 2 ohms mono.
I think we are on the same track just looking at it from different angles. If using a bridgeable amplifier he would nned to look for one stable to 1 ohm stereo. If using a mono amplifier he would need one stable to 2 ohms.

What he really needs is a 500 watt rms class D mono amplifier stable to 2 ohms (which most if not all are).

Yes. I have stated that you are much more learned than I. But, we are saying the same thing. I am ONLY talking about bridging the amp with his 2ohm load. When bridged, I am calling it 1ohm. That might be an incorrect term, but it HAS to be 1ohm stable to do that.

 

[RecLodossWar]

Punch 120a2 - 30x2 @ 4 ohm, 60x2 @ 2 ohm, 120x1 @ 4 ohm

If I hook both of them up it will give me 60 watts each according to this, not 30. And if this amp can't handle 2ohms, how come it shows a spec for 2ohm setup?

 

[zumbo]

Wrong on that too!
A good mono amplifier will typically double (or nearly double) it's output from 4 to 2 to 1 ohm (if it is 1 ohm stable).

Unless, the amplifier has impedance regulation circuitry built in, like JL Audios "Slash" series amps.

Mono block means 1 channel. Not 1 wattage.

I understood mono to be one, and block to mean block impedence drop. Pardon the terminology.

 

[annunaki]

Yes. I have stated that you are much more learned than I. But, we are saying the same thing. I am ONLY talking about bridging the amp with his 2ohm load. When bridged, I am calling it 1ohm. That might be an incorrect term, but it HAS to be 1ohm stable to do that.

Zumbo,
I am not trying to state that I am more learned than you. i am only trying to help.
The amp would need to be 1 ohm stable but only in stereo. In mono it would have to be 2 ohm stable. Saying that the amp actually sees 1 ohm when in fact one is running a 2 ohm mono (bridged) load is incorrect. By saying the amplifier switches the impedance internally to half is not what is actually happening. Like I stated before, it is just a sum of the left and right + voltages and left and right - voltages.

 

[annunaki]

If I hook both of them up it will give me 60 watts each according to this, not 30. And if this amp can't handle 2ohms, how come it shows a spec for 2ohm setup?

Because it is stable to 2 ohms STEREO only not 2 ohms stable in MONO.

 

[zumbo]

If I hook both of them up it will give me 60 watts each according to this, not 30. And if this amp can't handle 2ohms, how come it shows a spec for 2ohm setup?

Each of your subs is 4ohm. If you run it in stereo, that is 30x2 @ 4ohm.

If you series them, and then bridge it, that works out the same way.

 

[annunaki]

Quite right Zumbo.
Except they will play in mono instead of stereo. Series wiring is not usually recommended with separate woofers.

 

[zumbo]

http://www.crutchfieldadvisor.com/S-wsD5WPbIjvk/learningcenter/car/amplifiers_faq.html#13

 

[zumbo]

Because it is stable to 2 ohms STEREO only not 2 ohms stable in MONO.

This is what I have been trying to say. He has two 4ohm subs. You can't run them parallel and bridged on a 2ohm stable amp.

Oh, stereo is the key word here. I know what I am trying to say, I am just having trouble saying it.

 

[zumbo]

First off, when bridging two channels of a stereo amp, it "sees" the impedance of the speaker load as one half of what it is rated at.

In an ideal situation, the bridged amp will see one 8 ohm speaker as four ohms.

It would see one 4 ohm speaker as two ohms.

Two 4 ohm speakers connected in parallel would producr an effective impedance of two ohms on a non-bridged amp, and this is pushing any amp, believe me.

This is what I was tought also.

 

[mulester7]

.....this thread has turned into purest gold....outstanding....Professors Annunaki and Zumbo are in the building....I have done little thinking inside the terminal posts up until this thread....what Bob said about cutting the damping factor in half strapping two sides of a stereo amp hath settled it, though....I shall go for "clean" from now on no matter if it be mains, mids, rears, or subs....great job, Gentlemen....Rec, I still say you'd be surprised what 30 watts can do even on subs....

 

[zumbo]

Annunaki, can you link me an amp that states it is 2ohm stable mono. I bet if you find one, it will also say it is 1ohm stable.

 

[annunaki]

This is what I have been trying to say. He has two 4ohm subs. You can't run them parallel and bridged on a 2ohm stable amp.

Oh, stereo is the key word here. I know what I am trying to say, I am just having trouble saying it.

Any time one talks of stability it sould be stated as "# ohms mono" or "# ohms stereo" It aleviates much confusion.

 

[zumbo]

What about post #70?

 

[annunaki]

Annunaki, can you link me an amp that states it is 2ohm stable mono. I bet if you find one, it will also say it is 1ohm stable.

True. I will not argue that. The way I understood it, since we were dealing with a bridged amplifier, was that you were insinuating a 1 ohm mono stable amplifier.

 

[annunaki]

What about post #70?

 

[zumbo]

True. I will not argue that. The way I understood it, since we were dealing with a bridged amplifier, was that you were insinuating a 1 ohm mono amplifier.

Yes. Yes. Yes.

Don't you always bridge subs?

 

[annunaki]

.....this thread has turned into purest gold....outstanding....Professors Annunaki and Zumbo are in the building....I have done little thinking inside the terminal posts up until this thread....what Bob said about cutting the damping factor in half strapping two sides of a stereo amp hath settled it, though....I shall go for "clean" from now on no matter if it be mains, mids, rears, or subs....great job, Gentlemen....Rec, I still say you'd be surprised what 30 watts can do even on subs....

Professor...I do not think that is applicable to me.

 

[zumbo]

What about post #70?

Agree, or disagree? You said the amp doesn't lower the impedence. I have been trying to say that when "bridged" it does.

 

[annunaki]

I disagree. How is it possible? It does not add to the load. The load is still 2 ohms. The load the speakers present to the amp cannot just cut in half by bridging it. Some people have stated this over the years as a way to describe what is happening , but it just is not true.

ask Dan Banquer