Adding subwoofer, do I need an AMP with MOSFET built in

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Ignoramus13024 - 20 Feb 2004 15:02 GMT

Presently, I have a Pioneer DEH-7500MP cd player in my pickup.

It supposedly has a mosfet amplifier, 50 watts, I think. I have no
idea what does mosfet mean.

I am thinking about adding a subwoofer. Do I need to buy a separate
amp for it? I am not looking to get car shattering performance, I just
want to hear nice distortion free bass at reasonable volume level.

i

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MZ - 20 Feb 2004 15:07 GMT

> Presently, I have a Pioneer DEH-7500MP cd player in my pickup.
>
> It supposedly has a mosfet amplifier, 50 watts, I think. I have no
> idea what does mosfet mean.

"MOSFET" doesn't mean anything important. Don't worry if the amp has a
MOSFET design or not. Most amps don't even advertise that they have MOSFET
output stages, and it's not an inherent advantage anyway. It's a marketing
ploy.

> I am thinking about adding a subwoofer. Do I need to buy a separate
> amp for it? I am not looking to get car shattering performance, I just
> want to hear nice distortion free bass at reasonable volume level.

Yes, you need an amp.

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Peter Klein - 23 Feb 2004 01:16 GMT

Subwoofers draw all the wattage. Speakers don't blow from too many watts,
they blow from not enough. A speaker is an acoustic motor which runs on a
fuel called "watts". The motor only draws what it needs to put out the
musical signal. If there isn't enough you'll have a condition called
"clipping", where the entire musical signal cannot be played. When adding a
subwoofer, you would be well advised to use a dedicated amplifier in mono
mode (4 ohms) of at least 100 watts rms. Almost all Asian made amplifiers
have mosfet outputs. They are cheap, always available, and fairly bullet
proof. American made amplifiers, (Fosgate, Earthquake, JL, Kicker, etc.) use
Bi-polar outputs( not F.E.T.-field effect transistors) which handle more
power, cost much more, require novel circuits to eliminate the distortion,
but make much more accurate sound. Even if you will only listen at realistic
levels, 200 watts would be about right for a single 12" sub in a real
enclosure-not generic. P.

> Presently, I have a Pioneer DEH-7500MP cd player in my pickup.
>
[quoted text clipped - 6 lines]
>
> i

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MZ - 23 Feb 2004 02:09 GMT

> Subwoofers draw all the wattage. Speakers don't blow from too many watts,
> they blow from not enough.

That would defy the laws of physics, so I'm guessing no.

> A speaker is an acoustic motor which runs on a
> fuel called "watts". The motor only draws what it needs to put out the
> musical signal. If there isn't enough you'll have a condition called
> "clipping", where the entire musical signal cannot be played.

Not only is the entire signal played, but more signal to boot (ie.
distortion)!

> When adding a
> subwoofer, you would be well advised to use a dedicated amplifier in mono
> mode (4 ohms) of at least 100 watts rms.

Doesn't need to be a dedicated amp, and it doesn't necessarily have to be
mono.

> Almost all Asian made amplifiers
> have mosfet outputs. They are cheap, always available, and fairly bullet
> proof. American made amplifiers, (Fosgate, Earthquake, JL, Kicker, etc.) use
> Bi-polar outputs( not F.E.T.-field effect transistors) which handle more
> power, cost much more, require novel circuits to eliminate the distortion,
> but make much more accurate sound.

No, they don't "make much more accurate sound." Why do you think that?

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thelizman - 23 Feb 2004 04:36 GMT

> Subwoofers draw all the wattage.

Subwoofers - or any load - doesn't "draw wattage".

> Speakers don't blow from too many watts,
> they blow from not enough.

They teach you that in amp selling class?

Speakers blow from too many watts. Thats the only thing other than
mechanical failure that will cause a speaker to fail. If you use too
small of an amp, you risk causing transient distortin which contain
peaks of more power than the amp was designed to put out. This has an
equal chance of blowing the amp, but usually the speaker takes a dump first.

> A speaker is an acoustic motor which runs on a
> fuel called "watts".

You're hurting my brain. You're making everyone in this group stupid
with your very presence. Please stop.

> The motor only draws what it needs to put out the
> musical signal.

The amp puts out the signal. The amp puts out the signal at a given
voltage, which is determined by the input voltage. When this voltage is
applied across the speakers impedance, a current flows. Voltage *
Current = Wattage.

> If there isn't enough you'll have a condition called
> "clipping", where the entire musical signal cannot be played. When adding a
> subwoofer, you would be well advised to use a dedicated amplifier in mono
> mode (4 ohms) of at least 100 watts rms.

Is that because 100 watts RMS is where the amplifier price-points begin
to pay you more money?

> Almost all Asian made amplifiers
> have mosfet outputs.

Damn those squinty eyed asians!

> They are cheap, always available, and fairly bullet
> proof. American made amplifiers, (Fosgate, Earthquake, JL, Kicker, etc.) use
[quoted text clipped - 3 lines]
> levels, 200 watts would be about right for a single 12" sub in a real
> enclosure-not generic. P.

You are clueless. You are clearly a newb.

http://www.teamrocs.com/crap/newbie.htm

Please stop giving advice from sales-literature.

>>Presently, I have a Pioneer DEH-7500MP cd player in my pickup.
>>
>>It supposedly has a mosfet amplifier, 50 watts, I think. I have no
>>idea what does mosfet mean.

"Metal Oxide Semiconductor Field Effect Transistor". It's a type of
transistor.

>>I am thinking about adding a subwoofer. Do I need to buy a separate
>>amp for it? I am not looking to get car shattering performance, I just
>>want to hear nice distortion free bass at reasonable volume level.

Bass requires as much as 60% (generalization here) of your total system
power, even if you're not trying to rock it. You should almost certainly
get an amplifier, especially if you don't want distortion (you'll never
be distortion free sorry). How much power is up to you - I'm happy with
80 watts RMS of power. Make sure it says "RMS" when comparing watts of
one amp to another.

Signature

thelizman
hammerattack@teamrocs.com
teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

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Nousaine - 23 Feb 2004 06:20 GMT

>Subwoofers draw all the wattage.

Subwoofer frequencies require more acoustical displacement which does require
more power.

Speakers don't blow from too many watts,

>they blow from not enough.

This is the common Urban Legend Myth. It's simply not true. If it were then I
should be able to destroy a woofer with the signal from a Walkman ..... talk
about underpowering :-)

This myth comes about because people can burn-out tweeters (which may have
10-15 watts power handling in a system rated at several hundred watts power
handling) and while they're having them repaired a clever salesman sells them a
new amplifier too.

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