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Old 3rd January 2009, 09:01   #1
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Default Bi Amping using HU and Amp: Feasible ?

was just wondering, if you have an HU with a high quality internal amp, why let it go to waste when you get your system amped ?

Advantages:
1. higher output possible, possibly higher than the sum of each because the amp can play with a bit higher , since the higher harmonics wont reach teh tweeter , and the tweeter doesnt sip a lot of power from the HU
2. the internal amp enjoys a direct path to the source, and the HU is closer to the tweeter than the amp from most install locations, so lesser chance of noise
3. Everybody would love to have an active bi amped setup

Problems
1. HU will still lose power amplifying frequencies that wont be used by the tweeter
2. All comps cant be bi amped
3. when I was discussing this with hydra, he pointed out that the volume change curve may not be the same for the internal amp and pre outs
4. need to have a good HU



Anything else ?
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Old 3rd January 2009, 11:29   #2
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I did something like this and blew the HU.
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Old 3rd January 2009, 11:43   #3
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very adventurous! but looks like a bummer, simply because the maximum power you can harness from the best HU in the market will be about 18-22 RMS. i mean, it makes sense to have a more powerful amp than to compromise on the longevity of the head unit that will be continuously running at its full potential and theres a chance of it blowing!
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Old 3rd January 2009, 11:57   #4
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Quote:
Originally Posted by nitrous View Post
I did something like this and blew the HU.
how come ? if the HU can drive the entire comp, why not the tweeter alone?

note that this works only for speakers which are bi ampable - ie the crossovers have separate tweeter and woofer inputs or seperate crossovers for each

Quote:
Originally Posted by frankmehta View Post
very adventurous! but looks like a bummer, simply because the maximum power you can harness from the best HU in the market will be about 18-22 RMS. i mean, it makes sense to have a more powerful amp than to compromise on the longevity of the head unit that will be continuously running at its full potential and theres a chance of it blowing!
Usually the power dissipation in a tweeter is a fraction( not sure about this , but 10~20%?) of the power dissipated by the woofer. for systems with upto 100WPC, i think the HU should provide enough drive to the tweeter.

The HU will actually be running at a much lesser load than it would be if it were driving the whole comp

Last edited by greenhorn : 3rd January 2009 at 11:58.
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Old 3rd January 2009, 12:32   #5
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Quote:
Originally Posted by greenhorn View Post
The HU will actually be running at a much lesser load than it would be if it were driving the whole comp
WRT bi-amping, think this is what you're referring to:

http://www.team-bhp.com/forum/sound-...e-install.html

About reducing the load on the HU amp, I think the frequency division needs to happen BEFORE the amplifier stage. In case of passive bi-amping i.e. frequency division at speaker out level, each (HU) amp channel would amplify the ENTIRE full range signal and hence run at "full load" (not the correct technical term I know), its just that the power/energy corresponding to lower frequencies would be dissipated by the tweeter filter/crossover....gurus please correct me if my understanding is wrong.

Last edited by Flying Bong : 3rd January 2009 at 12:33.
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Old 3rd January 2009, 12:38   #6
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Quote:
Originally Posted by greenhorn View Post
was just wondering, if you have an HU with a high quality internal amp
I think you are suggesting using the HU with a passive HPF to drive the tweeter and then using an amp connected to the RCA out to drive the woofer.

It is bit adventurous. The likelyhood of engine whine (ground loop) will be higher. This only makes sense if your HU's amp is much better than the power amp. Remember of teh 10-15W the HU is producing you will be wasting 80-90% and only 1-2 watts will be used by the tweeter.
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Old 3rd January 2009, 13:29   #7
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Quote:
Originally Posted by Flying Bong View Post
in that install, One channel of the HU drove the tweeters, one channel drove the woofer. This is about using the HU to drive the tweeters and an amp to drive the woofer

Quote:
About reducing the load on the HU amp, I think the frequency division needs to happen BEFORE the amplifier stage. In case of passive bi-amping i.e. frequency division at speaker out level, each (HU) amp channel would amplify the ENTIRE full range signal and hence run at "full load" (not the correct technical term I know), its just that the power/energy corresponding to lower frequencies would be dissipated by the tweeter filter/crossover....gurus please correct me if my understanding is wrong.
Ideally that would be the best idea, but the problem is that , you cant control the RCA and speaker outputs independently in most HU's. if you HPF the fronts, the RCA output also gets HPF'd . so yes, the whole frequency range will be amplified by the HU. if the bass dominates , the HU will clip the treble - that is an issue.
Quote:
Originally Posted by navin View Post
I think you are suggesting using the HU with a passive HPF to drive the tweeter and then using an amp connected to the RCA out to drive the woofer.
exactly
Quote:
It is bit adventurous. The likelyhood of engine whine (ground loop) will be higher.
if the crossover is a single unit and shares a common ground. if there are seperate crossovers for the woofer and tweeter , like in my hertz dieci, dont think that can happen, since there is no point of two seperate ground wires meeting
Quote:
This only makes sense if your HU's amp is much better than the power amp. Remember of teh 10-15W the HU is producing you will be wasting 80-90% and only 1-2 watts will be used by the tweeter.
yup, thought of this for improving the quality in medium budget installs where 60~100WPC channel amps are used. And its far better to waste the HU's power - its going to be wasted anyway, than using an entire amp channel ( not feasible anyway)

Last edited by greenhorn : 3rd January 2009 at 13:39.
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Old 3rd January 2009, 14:30   #8
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isnt this turning out to be a case of much ado about nothing????
i mean HOW much power are we talking about here guys?
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Old 3rd January 2009, 15:18   #9
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not much, but if we can get a small increase in SQ and SPL for free, why not do it
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Old 3rd January 2009, 19:29   #10
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1. No, the HU will not be wasting any power on the frequencies below the XO's lower cut off point for the tweeter, where the XO presents a high impedance to the amp
2. Ditto for the external amp when you use bandpass filter (the amp's HPF in conjunction with the XO's woofer section, or the XO is BPF itself for the woofer in your case)
3. BUT, the main issue is level-setting for tuning - as hydranup rightly said, the gain profiles for the HU and amp would be different, which might do more harm to your cause than good. Forget SQ / SPL, you might land up spending more time balancing the setup (4 variables now instead of 2) for fidelity than listening to music - perfect example of law of diminishing returns
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