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#292747 - 02/17/10 08:37 PM Car Amps, For Johnk
fredk Offline
axiomite

Registered: 12/06/07
Posts: 7786
Loc: Canada
So, are car audio devices also covered by the FCC/FTC (never can remember which it is) regs.?

A perusal of car deck specifications for a basic unit with 4 channels gives me 40w x 4 rms. No mention of how many channels driven. Something tells me it is not all 4.

FWIW, a couple of weeks of reading in a car audio site and a few visits to bb tells me that the quality of a speaker is determined by its overall diameter and its power handling.

If I start posting about how cables make a difference, I need an 'intervention'.
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#292794 - 02/17/10 10:59 PM Re: Car Amps, For Johnk [Re: fredk]
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10631
Fred, the FTC regs specifically apply to units sold for "home entertainment purposes" and therefore don't regulate automotive equipment. In 1998 the Commission took some evidence relating to expanding the coverage to include mobile units, but determined that there wasn't sufficient evidence presented to support the proposal.

There are no regulations which have the force of law, such as those which should make us confident of the accuracy of home audio amplification equipment power ratings , which would give similar assurance as to automotive equipment. There is a voluntary regulation(CEA-2006-B)for mobile equipment proposed by the Consumer Electronics Association which some manufacturers follow, but of course this isn't law. A brief discussion of this can be found here .
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#292806 - 02/18/10 12:12 AM Re: Car Amps, For Johnk [Re: JohnK]
fredk Offline
axiomite

Registered: 12/06/07
Posts: 7786
Loc: Canada
Thanks John. As always you seem to have the answer. Wow, so they can pretty much put whatever they want. 20w x 4 could mean one channel driven. Sigh.

Looking at a power calculator, an average of 3-7w should drive a set of speakers sufficiently, but how the heck do I know if a deck will deliver that? I guess 20w one channel will translate to roughly 10wpc 2 channels driven?
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Blujays1: Spending Fred's money one bottle at a time, no two... Oh crap!

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#292842 - 02/18/10 08:00 AM Re: Car Amps, For Johnk [Re: fredk]
terzaghi Offline
connoisseur

Registered: 04/04/07
Posts: 4870
Loc: Tulsa, Oklahoma
My car audio guy told me that a typical deck rated at 50wpc might actually deliver 15 wpc. I have no idea what lead him to say that (experience, just a guess, who knows.)
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#293410 - 02/22/10 05:04 PM Re: Car Amps, For Johnk [Re: fredk]
alan Offline

connoisseur

Registered: 01/29/02
Posts: 3265
Loc: Toronto/New York/parry Sound
Hi fredk,

Yes, car audio "specs" are wildly misleading and inaccurate, especially for the in-dash head units. Power output is often quoted at 10% distortion levels in order to get bigger output numbers.

If you go to separate power amplifiers and more expensive head units that have pre-outs, you'll generally get much more complete and accurate specifications.

I'd agree with the figure of about 3.5 to perhaps 7 watts per channel maximum at a reasonable level of distortion (1% or less).

To get lots of clean power output in a car, you have to go to separate power amplifiers. With off-shore manufacturing, those are much less expensive now than they used to be.

Regards,
Alan
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#293893 - 02/25/10 09:54 PM Re: Car Amps, For Johnk [Re: alan]
fredk Offline
axiomite

Registered: 12/06/07
Posts: 7786
Loc: Canada
 Originally Posted By: alan
Hi fredk,

Yes, car audio "specs" are wildly misleading and inaccurate, especially for the in-dash head units. Power output is often quoted at 10% distortion levels in order to get bigger output numbers.

Thanks Alan. I hadn't even thought about distortion. Hmm... looks like I'm going to be doing this by the seat of my pants.

Looking at head units, its not going to be too expensive to get something with pre-outs.
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Fred

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Blujays1: Spending Fred's money one bottle at a time, no two... Oh crap!

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#294490 - 03/01/10 12:32 AM Re: Car Amps, For Johnk [Re: fredk]
darcman Offline
old hand

Registered: 02/22/10
Posts: 74
Loc: The Wack, British Columbia
The Alpine PDX amps are pretty kick a$$. I have a few of them and they come with birth sheets. They are all underated. My Alpine PDX-4.100 is rated at 4x100 watts and its actual measurement was 4x125 watts 2 0hms or 4 ohms doesnt matter. They are a class D, run super cool, super small, and super sweet.

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#294537 - 03/01/10 08:49 AM Re: Car Amps, For Johnk [Re: darcman]
Wid Offline
axiomite

Registered: 06/22/03
Posts: 6789
Loc: The Peoples Republic of Il.
MTX does the same thing. My amp (MTX Thunder 282) came with a test sheet with the actual wattage on it.
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"A fear of weapons is a sign of retarded sexual and emotional maturity." Sigmund Freud


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#294588 - 03/01/10 01:54 PM Re: Car Amps, For Johnk [Re: Wid]
fredk Offline
axiomite

Registered: 12/06/07
Posts: 7786
Loc: Canada
The question is which 'actual' wattage? I have yet to see a spec for a car amp the tells me how many channels were driven for that 4 X xxx watts.
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Fred

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Blujays1: Spending Fred's money one bottle at a time, no two... Oh crap!

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#294593 - 03/01/10 02:16 PM Re: Car Amps, For Johnk [Re: fredk]
Ya_basta Offline
connoisseur

Registered: 06/23/07
Posts: 4299
Loc: Sitting down somewhere
Fred, did you pick out a head unit yet?
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