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Old 7th January 2011, 18:06   #1
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Default Bridging of HU outputs possible?

Dear Gurus,
I couldn't find any suitable answer to my query in any of the post, hence had to create this new thread.
I'm owning a 2005 mobel Zen and planning to make some little modification/upgrade in ICE. Currently it's having a minimalistic basic set up - One Sony HU and JBL co-axial in the front. Nothing is there on the rear as rear space is much more priority than ICE, at least to my better half.

Planning to change to a better HU and a component speaker. But, as I'm not going to install any seperate amp, I guess only HU power might a little less to drive the compo. So, can I bridge the output like ( FR + RR ) and (FL + LR) to get cumulative higher power?

Also, is Alpine 9870 any good? Given that bridging is possible, is it enough to drive compo like JBL 605 C?

Or any other suggestions?
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Old 7th January 2011, 18:23   #2
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Default Re: Bridging of HU outputs possible?

You'll blow the HU's output signal.
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Old 7th January 2011, 18:27   #3
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Default Re: Bridging of HU outputs possible?

What does it mean? Is the MOSFET on HU going to get damaged, or any other on-board amp circuit?

I guess it is possible to bride in the two channel amps ( I did it earlier too), then why not on the HU?
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Old 8th January 2011, 11:59   #4
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Default Re: Bridging of HU outputs possible?

Not so simple, @bhatmaster. The output device configuration on after-market amps is quite different from that on HUs. HU amps have the output devices already bridged internally (in the IC) to get higher power output from smaller devices. If you try to bridge them further, you will come to grief.
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Old 8th January 2011, 17:27   #5
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Default Re: Bridging of HU outputs possible?

OK, although not very clear technically, I'm considering it ou of scope now. I assume, a higher impedence speaker ( 8 Ohms) should be easier to drive by the amps. So, instead of fitting car components, can I use home audio drivers and tweeters ? Has anybody tried that route so far?

I have already a vifa tweeter left in my house, in that case I'll source another better mid-woofer and will do the cross-over accordingly.

Any suggestion Gurus?
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Old 8th January 2011, 18:17   #6
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Default Re: Bridging of HU outputs possible?

Car speakers mostly have a 4-ohm impedance and all HU amps are engineered to work with 4-ohm speakers.
Some speakers like the JBL GTO series have an impedance of 2.86 ohms.
I've seen some high end components with an impedance of 3 ohms.
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Old 8th January 2011, 19:13   #7
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Default Re: Bridging of HU outputs possible?

Yes, all the HU amps are designed to have the loads 4 ohm or higher. So, giving a speaker rated nominal impedence of 8 Ohms should be even less loads on amp, isn't it?

Provided at a given frequency, the HU voltage rail can supply 12 V ( ignoring the efficiency loss). So, I = 12/8 = 1.5 where the HU is rated to withstand a current flow of 3 Amp ( I = 12/4).
I understand, during driving a home audio speaker the wattage will be less according to the formula

W = V*V / R, i.e in our case 12*12 / 8 = 18 Watt peak and hence 9 watt RMS. But, in a car environment, 8-9 watts should not be a problem , isn't it?
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Old 9th January 2011, 06:24   #8
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Default Re: Bridging of HU outputs possible?

Sorry for my novish questions, what is the driver from home audio stable is most recommneded for cars? Gurus, please help me. MY budget is around 50 USD / driver. I agree that the rubber srrounding may get damaged early as they are not designed for high heat. But, I'm ready to take the risk. Of course I'd want to fit usher 8945P there, but the space in Zen will not permit it.

Also Gurus, who all are expert is desiging the cross-over for car please help me for feeding the parameters. I'm struggling there because it is neither falling 'in-box' nor in infinite baffle category. How to adjust the BSC there?
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Old 9th January 2011, 06:41   #9
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Default Re: Bridging of HU outputs possible?

Quote:
Originally Posted by DerAlte View Post
. The output device configuration on after-market amps is quite different from that on HUs. HU amps have the output devices already bridged internally (in the IC) to get higher power output from smaller devices.
Hi DerAlte, is it possible to explain schematically how that is bridged in HU IC? Sorry, I'm just a newbie here and don't understand many things ( that's why drwaing is always better to understand). I thought if there is a 180 degree phase difference in two channels, they can be bridged to double the power , but with double load which comes from the same formula. And left and right channels are in the two node points of the sine waves at a given point. Please correct me if I'm wrong.
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Old 9th January 2011, 16:40   #10
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Default Re: Bridging of HU outputs possible?

a. You have got your power calculation equations all wrong. We are dealing with AC signal and inductive loads
b. Supply voltage in an amp is not 12V, rather as high as 35V or so (up-converted from 12V)
c. Yes, the average power put out to speakers is about 8-12W RMS (not by your equation), and HU amps are rated 18W RMS. For normal listening this quite adequate. What one misses with the low power of the HU amp is dynamic range - the ability to reproduce well the soft and loud passages in music. For that one has to use an external amp of at least 40W RMS per channel capacity, even though the average power output will still be the same
d. None of the home audio drivers are recommended for use in a car. One can, and a few people have tried in here with not so satisfactory results!
e. Please search for data sheets of single chip amplifiers on the net - they contain the schematic too. The difference will be apparent to you. The issue is not simply that of "bridging possible because channels are 180deg phase-shifted"
f. Left and right channels contain different signals. You perhaps are talking about the upper and lower halves of a Class B amplifier - the classic text-book model
g. Save yourself some headaches and stress, even if you are a die-hard DIY person (albeit an economy-first one). If you are in the US, walk in to the closest Best Buy or Fry's store and audition the many component options they have. You will find many good ones for USD50-60 (JBL, Alpine, etc.). If you are in India, visit a decent car audio dealer and audition some components - one gets good ones (JBL, Bull, Auditor, Blaupunkt, etc.) for about INR6K

Last edited by DerAlte : 9th January 2011 at 16:41.
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Old 9th January 2011, 18:17   #11
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Default Re: Bridging of HU outputs possible?

Quote:
Originally Posted by DerAlte View Post
a. c. Yes, the average power put out to speakers is about 8-12W RMS (not by your equation), and HU amps are rated 18W RMS. For normal listening this quite adequate. What one misses with the low power of the HU amp is dynamic range - the ability to reproduce well the soft and loud passages in music. For that one has to use an external amp of at least 40W RMS per channel capacity, even though the average power output will still be the same
Hi DerAlte,
Thanks for your explations. Can you please explain the above figure with little more calculative way? I'm struggling to get the figures matching. ( Considering the rail voltage 35V as u stated). I guess these HUs are class A/B designs, isn't it?

And, currently I'm neither in US nor in India, but I can get few things shipped from US through my colleagues,
I don't have a skill of doing DIY alone simply because I'm not that knowledgable as people here and just brans new in this area of interest :-)
But, in my personal experience in other car, I used to drive JBL power series ( P650C) with a borrowed JBL amp ( don't ask the model number) and pioneer HU, but I was quite disappointed with the result. They state the frequency range 45 Hz to 10 KHz, but It's nowhere close to 45 Hz (+/- 3 DB) I can say, ( I even tested with sound meter and frequency testing track)
As my Diy in home is very successful ( with lot of help from Jay Kim and Suman jana), I started thinking of following the route here and also normally it proves to be a cost effective option which is important for a poor guy like me.
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Old 10th January 2011, 00:56   #12
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Default Re: Bridging of HU outputs possible?

Quote:
Originally Posted by bhatmaster View Post
I started thinking of following the route here and also normally it proves to be a cost effective option which is important for a poor guy like me.
cost effective option could be to start with a used component set, many of them put up on classifieds when they upgrade, you could get a one year used thingy at approx 50% less.

another option would be to look for bi-amp component sets in which case you can divide the output, the front output goes to the tweeter, the rear to the midbass.

though it's really amusing to see creative minds coming up with creative ideas like using creative speakers through a 12v socket and playing them with their MP3 player, never tried it though!
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