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Old 7th July 2008, 20:43   #16
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Originally Posted by greenhorn View Post
IIRC, you could Low pass the output of the rears in the 7950. that should improve the bass further
I guess thats what the Rear output: S/W control means. Yes I have set it to ON!

What I dont gather is that I use only a 15A source and there is no amplification apart from that of the HU. How can I fry the HU.

Well, if i use a 100A one, then Yes, else I wonder how

I have undone the rear channel bridging that i had done earlier. Now only one rear channel powers the Sub.
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Old 7th July 2008, 22:14   #17
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Hi people...!!!
Few days back I had a thread called surround sound and our friend HEADERS seem to have done the same thing with a band pass to derive a SUB.

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Originally Posted by greenhorn View Post
let me try to explain. in a 2 channel amp, the outputs are shown as +, - , +, -

say at a particular instant , the output is 1V. if you measure the voltages , they will be +1 V, 0V, 0V, -1V. when you set the amp to bridged mode, the two 0V terminals are shorted together , and the speaker is connected to the +1 V and -1V terminals , so you get 2V total.

amplifier which have one output at 0V are referred to as Single ended output amps. one terminal has constant ( 0 ) voltage , while the other varies. this is what a single channel of a 2 or 4 channel amp looks like . because you have two terminals which are at the same voltage, they can be shorted together.

in a car HU, the outputs are already bridged to get the maximum output from the 12V supply voltage limitation (amps dont have this limitation, since they have SMPS circuits which boost the voltage ) , are at +1 and -1.

if you short the +'s together, and connect the speakers to the -'s nothing much will happen, If you connect the + and - together, you'll short those two halves of the bridged amp(which will end up damaging them, since they are at +1 and -1V ) , while the other 2 halves will drive your speaker. Still your output will be between the +1 and -1V terminals , so you'll get only 2V , which is the same as using one channel of the HU.

Hope I didnt confuse you

Try connecting the sub to just one channel. It SHOULD still sound the same , but without the clipping
Thanks for the info...very useful.

I had done the same thing (connecting to +1v,-1v) without a band pass and I get the rear channel by doing this (confirmed by watching movie in 5.1 and in this set-up).

I have theory explaining how does this give the rear channel...
The difference in the +ve and -ve terminals of the right channel is responsible for the up and down motion of the speaker to produce the frequencies that has to come from right and vice versa for the left.

When the +ve of the right and the -ve of the left is connected to a speaker, it vibrates the differences between the channels

(i.e it plays only the differences between the channels and the sounds common to both the channels are cancelled as both the channels produce the same sound in opposite directions making the driver insensitive for these sounds).

This was how a surround sound was encoded when dolby was in its nascent form and this was how it was decoded from VCD's which has only 2-channels recorded in it.

I had connected the speakers in series to the source (+1v and -1v) and have insulated the other source terminals (the 0 volt terminals).
Does this by any means fry the IC's of my HU...?
If it does wat is a way out for this...?
(I dont want those decoder equipments)

I just need the mid's and hi's in the rear channel so, can I connect the 0 volt terminal to the serialised speakers using a filter (to cut the lo's which contribute a major voltage or wattage or ...???)
(senior BHPians and experts can have all their ridicules played here) or any other sensible solution...?
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Old 7th July 2008, 22:19   #18
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All the best. Been a interesting thread hope your HU survives the test in long run. Its like you are trying to run pull train boggie using a Padmini 137D.

Why fry?

V=IR, P=R*I*I

Wher's Navin and Der!

Last edited by jkdas : 7th July 2008 at 22:20.
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Old 7th July 2008, 22:32   #19
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Quote:
Originally Posted by BaCkSeAtDrIVeR View Post
...
Is a glossary of the terms available anywhere?
...
We have an excellent glossary of ICE Lingo right here on the forum: http://www.team-bhp.com/forum/ask-gu...rminology.html

Enjoy!
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Old 8th July 2008, 07:44   #20
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Quote:
Originally Posted by raajsree View Post
When the +ve of the right and the -ve of the left is connected to a speaker, it vibrates the differences between the channels

(i.e it plays only the differences between the channels and the sounds common to both the channels are cancelled as both the channels produce the same sound in opposite directions making the driver insensitive for these sounds).

This was how a surround sound was encoded when dolby was in its nascent form and this was how it was decoded from VCD's which has only 2-channels recorded in it.

I had connected the speakers in series to the source (+1v and -1v) and have insulated the other source terminals (the 0 volt terminals).
Does this by any means fry the IC's of my HU...?
If it does wat is a way out for this...?
(I dont want those decoder equipments)

I just need the mid's and hi's in the rear channel so, can I connect the 0 volt terminal to the serialised speakers using a filter (to cut the lo's which contribute a major voltage or wattage or ...???)
(senior BHPians and experts can have all their ridicules played here) or any other sensible solution...?
yup, that was one way to get surround out of a 2 channel amp in the ye olde days. however , to get the difference signal, you need to connect the + and - of the speakers to either both the +'s of the amp, or both the -'s.

a good idea would be to connect the Right surround speakers + to the left channel +, and the speakers - to the right channel +
the Left surround's + can be connected to the left channel's - , and the speakers - to the right channel's minus ( I'm not entirely sure about the polarities, but i think this should work) And since equal currents will be drawn from all terminals , it should balance everything out .

in a car HU, the amp's ground (0V) terminals are not acessible , only the + and - are ....

Connecting a speakers to both the +'s or both the -'s should not be an issue , since there wont be a lot of current flowing , only the difference.

I only objected to shorting the + and - of the HU. everything else is fine
PS: I didnt get the ridicule bit. Have we ridiculed anyone ?
Quote:
Originally Posted by headers
What I dont gather is that I use only a 15A source and there is no amplification apart from that of the HU. How can I fry the HU.

Well, if i use a 100A one, then Yes, else I wonder how
a bad automotive analogy would be to claim that if you drive around with your handbrake on , the tyres wont be damaged because you are driving slowly or because the engine is underpowered.

no matter how little current you supply, a shorted output is a shorted output ,and will eventually fry your IC's

Last edited by greenhorn : 8th July 2008 at 07:50.
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Old 8th July 2008, 08:19   #21
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Quote:
Originally Posted by greenhorn View Post
Connecting a speakers to both the +'s or both the -'s should not be an issue , since there wont be a lot of current flowing , only the difference.

I only objected to shorting the + and - of the HU. everything else is fine

no matter how little current you supply, a shorted output is a shorted output ,and will eventually fry your IC's
Sir, Thats what i did earlier, when i was told that one should not connect both the + and both - together.

Also, as there is no amplifier in the setup i just connected both rear + of HU and joined with + of sub and both - to - of the sub.

How does this ruin the setup?

I never shorted the + and - of the HU. That i know will short the system.
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Old 8th July 2008, 09:36   #22
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hmm, what you've done is put both the amps in parallel. Though in theory this should give more current , In practice , amps , unless specifically designed to do this , dont like being placed in parallel. Again to use a bad car analogy, it would be like using two engines controlled by the same throttle to drive the front and rear wheels. Though Ideally it will seem to work, practically each amp will end up trying to drive the other (because instead of the current going to the 4 ohm speaker, it will go to the output of the other amplifier which will be much lower) , and in the end , fry each other

One of the first things they teach you in circuit theory is that you DO NOT put two voltage source in parallel....

Thats why i said , if you want to use both channels, use a DVC sub. since it has two voice coils which are isolated , the outputs will be isolated from each other , and no damage will occur

Last edited by greenhorn : 8th July 2008 at 09:40.
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Old 8th July 2008, 11:50   #23
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Originally Posted by greenhorn View Post
hmm, what you've done is put both the amps in parallel.
Sir, where are the 2 amps. The Hu is the only amp.


BTW, your analogies are great, they make it much simpler to understand! Thanks
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Old 8th July 2008, 12:04   #24
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actually, an HU can be described to be having 8 small amps internally bridged to make 4 channels and each channel can be described as a bridged amp. so the rear right and rear left terminals of the HU are outputs of seperate bridged amps, and you had connected them in parallel.

Last edited by greenhorn : 8th July 2008 at 12:06.
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Old 8th July 2008, 12:06   #25
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Sir, where are the 2 amps. The Hu is the only amp.
Left and right channel. In car amps where it is bridgable, it is designed to run in parallel. But I don't think HUs will support this unless designed for it.
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Old 8th July 2008, 12:07   #26
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Quote:
Originally Posted by greenhorn View Post
actually, an HU can be described to be having 8 small amps internally bridged to make 4 channels. so each channel can be described as a bridged amp. so the rear right and rear left terminals of the HU are outputs of seperate bridged amps, and you had connected them in parallel.
Ok, thats great info.

Now that i have diconnected the bridge and connected only 1 rear channel to the sub. can we run this setup?
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Old 8th July 2008, 12:15   #27
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Originally Posted by jkdas View Post
Wher's Navin and Der!
I've been reading.

I tend to agree wth greenorn on this. The amps in an HU are bridged amps. bridging 2 bridged amps will fry the amps or the power supply that feeds them (both the amps and the power supply are part of the HU's circutry so Ggod 'lone knows what else you can blow up).

HUs are protected against this but still that does not mean one should do it. Besides you are not going to double the wattage since the protection will limit the current to that of one amp.
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Old 8th July 2008, 12:16   #28
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Hehe . I think you have got enough answers from the gurus on this. What is the RMS rating of your sub? I think it will be 250W minimum. The HU will be 18-20W RMS max. Now, try to increase the volume to max/80% "accidentally" by rotating the knob in a flick.
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Old 8th July 2008, 12:27   #29
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Originally Posted by navin View Post
I've been reading.

I tend to agree wth greenorn on this. The amps in an HU are bridged amps. bridging 2 bridged amps will fry the amps or the power supply that feeds them (both the amps and the power supply are part of the HU's circutry so Ggod 'lone knows what else you can blow up).

HUs are protected against this but still that does not mean one should do it. Besides you are not going to double the wattage since the protection will limit the current to that of one amp.
Ok sir, agreed. But if only one channel is connected to drive the sub as advised. I should not theoretically fry the HU! Maybe the HU may not have as much power as an amp to explore the sub to its full potential, but nevertheless, it should work without any issue - right?


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Originally Posted by redfire View Post
Hehe . I think you have got enough answers from the gurus on this. What is the RMS rating of your sub? I think it will be 250W minimum. The HU will be 18-20W RMS max. Now, try to increase the volume to max/80% "accidentally" by rotating the knob in a flick.
Why accidentally boss, i have done it and there was clipping at a point. Hence played with the HU settings to ensure it plays clean at a decent volume!
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Old 8th July 2008, 12:51   #30
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Personally, I've never had issues driving speakers with underpowered amps , but the gurus here feel that this will cause the amp to clip, and result in damage to the amp. Also, subwoofers have very strong back EMF's as well, and a smaller amp may not be able to withstand them.
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