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Experts: Amp power & impedance (loud)

Old 06-24-2009, 10:18 PM
  #1  
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Experts: Amp power & impedance (loud)

whats up everybody.....the goal is to get louder mids and high's

here is the senario:

front speakers: alpine type R components
rear speakers: BSA 8 inches 8 omhs (midbass drives only, 200 rms)
Amp: JL audio M4500

how can get the most power out of this amplifier running it at 12.5 volts?

I came up with an Idea but wasnt sure if it woud work..here is...

" parallel wire the front alpine speakers which are 4 ohms to get a total impedance of 2 ohms. Then add a pair of 4 ohms tweeters at the rear and parallel wire this tweeters to get a total impedance of 2 ohms...

but then wire the componet speakers and the newly added tweeters in series to increace the impedance to 2 ohms..which is the minimum that this amp can handel hence incresing the output. "

I suspect this could be good since the rear speakers only give midbass and I have no tweeters at the rear

here are the amp specs, speakers and tweeters:


amp specs:----------------------------------------------------------------------
Rated Power 14.4 V Stereo: 80 W RMS x 4 @ 4 ohm
125 W RMS x 4 @ 2 ohm
Rated Power 14.4 V Bridged : 160 W RMS x 2 @ 8 ohm
250 W RMS x 2 @ 4 ohm
Rated Power 12.5 V Stereo: 60 W RMS x 4 @ 4 ohm
90 W RMS x 4 @ 2 ohm
Rated Power 12.5 V Bridged: 120 W RMS x 2 @ 8 ohm
180 W RMS x 2 @ 4 ohm
THD at Rated Power: <1% THD, 20 Hz - 20 kHz
S/N Ratio: >104 dB referred to rated power (A-weighted, 20 Hz 20 kHz noise bandwidth)
Frequency Response: 10 Hz 25 kHz (+0, -1dB)
Damping Factor: >200 @ 4 ohm per ch. / 50 Hz
>100 @ 2 ohm per ch. / 50 Hz
Slew Rate: 22V / s
Input Range: 200mV 8V RMS

speakers specs-------------------------------------------------------------
Power Handling

* CEA-2031 Power Rating: 110 Watts
* Power Handling Capacity (RMS): 110 Watts
* Power Handling Capacity (Peak): 330 Watts
* Frequency Response: 65Hz - 27kHz
* Impedence: 4 Ohms
* Sensitivity: 87dB / W(1m)

Sellenium Tweeters specs---------------------------------------------------------

couldnt find it but I know they are 4 ohms.

thanks to those brave minds how refuse to have muteless thoughts....but instead retaliate with loud ideas ...--john p--
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Old 07-07-2009, 12:07 AM
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Run 1 channel to each speaker so 80Wx4 = 320W.

Having a 4 Ohm and 8 Ohm speaker sets gives you three options, the one above or:

Speakers in Series:
4+8=12 Ohms (2 Channel Mode: Bridged)
12 Ohms will get you very little power (about 150-200W)

Speakers in Parallel
1/(1/4+1/8) = 2.67 Ohm (2 Channel Mode: Bridged)
Can be dangerous with too low of impedance. Even with impedance rise where heat that builds up in the voicecoil increases the impedance seen by the Amp to somewhere around 3 Ohm's, I would not recommend it.

JL makes great gear and may be able to handle 3 Ohm load but you may also blow up the amp. It may even run for a while before it blows up. Or if your lucky it will just go into protection mode.
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Old 07-07-2009, 09:13 PM
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Originally Posted by compaq View Post
whats up everybody.....the goal is to get louder mids and high's

here is the senario:

front speakers: alpine type R components
rear speakers: BSA 8 inches 8 omhs (midbass drives only, 200 rms)
Amp: JL audio M4500

how can get the most power out of this amplifier running it at 12.5 volts?

I came up with an Idea but wasnt sure if it woud work..here is...

" parallel wire the front alpine speakers which are 4 ohms to get a total impedance of 2 ohms. Then add a pair of 4 ohms tweeters at the rear and parallel wire this tweeters to get a total impedance of 2 ohms...

but then wire the componet speakers and the newly added tweeters in series to increace the impedance to 2 ohms..which is the minimum that this amp can handel hence incresing the output. "

I suspect this could be good since the rear speakers only give midbass and I have no tweeters at the rear

here are the amp specs, speakers and tweeters:


amp specs:----------------------------------------------------------------------
Rated Power 14.4 V Stereo: 80 W RMS x 4 @ 4 ohm
125 W RMS x 4 @ 2 ohm
Rated Power 14.4 V Bridged : 160 W RMS x 2 @ 8 ohm
250 W RMS x 2 @ 4 ohm
Rated Power 12.5 V Stereo: 60 W RMS x 4 @ 4 ohm
90 W RMS x 4 @ 2 ohm
Rated Power 12.5 V Bridged: 120 W RMS x 2 @ 8 ohm
180 W RMS x 2 @ 4 ohm
THD at Rated Power: <1% THD, 20 Hz - 20 kHz
S/N Ratio: >104 dB referred to rated power (A-weighted, 20 Hz 20 kHz noise bandwidth)
Frequency Response: 10 Hz 25 kHz (+0, -1dB)
Damping Factor: >200 @ 4 ohm per ch. / 50 Hz
>100 @ 2 ohm per ch. / 50 Hz
Slew Rate: 22V / s
Input Range: 200mV 8V RMS

speakers specs-------------------------------------------------------------
Power Handling

* CEA-2031 Power Rating: 110 Watts
* Power Handling Capacity (RMS): 110 Watts
* Power Handling Capacity (Peak): 330 Watts
* Frequency Response: 65Hz - 27kHz
* Impedence: 4 Ohms
* Sensitivity: 87dB / W(1m)

Sellenium Tweeters specs---------------------------------------------------------

couldnt find it but I know they are 4 ohms.

thanks to those brave minds how refuse to have muteless thoughts....but instead retaliate with loud ideas ...--john p--
I'm getting a headache trying to wrap my head around this.....you should have mid-bass drivers up front with your comps so all the frequencies that you hear in stereo are where they are supposed to be......adding tweeters and messing with the wiring like that might get you a very small amount louder but it will sound like ***......

If you are going to leave the MB drivers in the rear, parallel them and bridge the rear channels on the amp to run them 4ohm mono.....they will get louder and at least your stereo image will suffer the least amount of damage.

If it is still not loud enough, ditch the 8"s (they are an odd impedance for a car system and large enough they are a pain to install up front) and get a pair of good 6X9s for the rears. They have almost as much cone area as the 8s for MB and your system will sound stronger over-all......

HTH
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Old 07-07-2009, 10:06 PM
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okay, no matter how you wire the amp up you will be getting the same output from it, unless you want to listen to your music in Mono.

Your best bet is to buy an amplifier that makes alot more to begin with. OR get more efficient speakers. Doing anything else really isn't likely to make any improvements
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