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  1. #1

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    Default Car amp for home audio

    Ever since i started upgrading my home surround sound system, I have come to the following conclusion: Properly powering 4 ohm speakers is very expensive. When i upgraded from the rti to lsi speakers, i went out and bought the outlaw audio pre amp -amp combo, and have been somewhat disappointed in the outlaw amp. not only hooked up with my lsi speakers but also with my rti ones as well. there was not enough bass output or dynamics. the amp didn't take ahold of the woofer like it should and deliver lifelike sound at low volumes. So anyhoo, back to my post. I have been looking at amps spec that can deliver 200 amps at 4 ohms and 400 amps at 2 ohms for my lsi 9 speakers. since their impedance can drop to 2.4 ohms, i want to make sure my amp can handle it properly that low (at least to 60 hz anyway). So i am looking at two channel amps and the only ones that will double their output when the impedance changes from 4 to 2 ohms are somewhat expensive. So i was wondering what you guys thought about buying a 25 amp power supply from radio shack ($100), a nice rockford fosgate car amp (maybe Rockford Fosgate Power T8004) for around $1000, and one or two 1.0-farad Capacitors ($200). This comes to under $1500 and I have a feeling will sound much better than any $1500 two channel home audio amp that can find. Any ideas?

  2. #2

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    I think you have your amp(ere)s and watts mixed up. Make sure that wherever you buy the equipment has a great return policy as I don't think you'll be pleased with the results.

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    I think that you need to re-evaluate the amps that you are looking at in the $1500 range if you think that a car amp will outperform a home amp. Apples and oranges my friend. There are many home amps for under the $1500 range that will power the LSis more than adequately.
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    Maybe the levels just needed to be adjusted on the Outlaw pre? Did you try to calibrate the setup?

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    Quote Originally Posted by Sami
    I think you have your amp(ere)s and watts mixed up. Make sure that wherever you buy the equipment has a great return policy as I don't think you'll be pleased with the results.
    I might, but it makes since to me. wall power = 120V AC at around 10 amps max. convert that power to 12V DC at 25 amps max. them plug it into a car amp that is rated at 200 watts x2 at 4 ohms. Not sure how this would sound, but i have a rockford amp in my truck and it sounds much better than my current home audio system. Much more dynamic

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    Quote Originally Posted by PolkThug
    Maybe the levels just needed to be adjusted on the Outlaw pre? Did you try to calibrate the setup?
    I did the auto calibration. Though about mabee adding some eq to the system, but figured i would just eventully want a better amp.

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    120v at 10 amps is 1200 watts. 12v at 25 amps is 300 watts.

    Your car system sounds much more powerful because of the 3db per octave rising bass efficiency as you go lower in frequency. This is because of the cabin size. Hum will be an issue also. I'm not saying you can't do it, its just that for the same quality level the car amp/pwr supply is going to cost more than the home system.
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    Quote Originally Posted by madmax
    120v at 10 amps is 1200 watts. 12v at 25 amps is 300 watts.

    Your car system sounds much more powerful because of the 3db per octave rising bass efficiency as you go lower in frequency. This is because of the cabin size. Hum will be an issue also. I'm not saying you can't do it, its just that for the same quality level the car amp/pwr supply is going to cost more than the home system.
    madmax
    the wall can put out only about 12 amps max at 120v. The power supply i was looking at buying at can only transform a small % of the wall power of which it will be 25 amps at 12v DC. the output power of the wall will not equal the output power of the power supply (and thank god). I have to power other things on the same fuse such as my living room lights.

    Yea, the only issue i would have is noise (THD). I havent looking into the car amp specs too detailed yet.

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    Quote Originally Posted by sickicw
    the output power of the wall will not equal the output power of the power supply
    The PS will not equal the power potential of the wall. :)

    That PS is not enough to power 2 * 200W at 4Ohm. Not that it would have to in real life application but you get the idea (in reference to your original post below)

    "So i am looking at two channel amps and the only ones that will double their output when the impedance changes from 4 to 2 ohms are somewhat expensive."
    Last edited by Sami; 10-31-2005 at 12:37 PM.

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    You first problem was switching from RT to Lsi . Since you are a "grab ahold of the woofer kind of guy" you have no business using the laidback LSi line. They weren't designed for impact like the RTi line is. Secondly, car audio bass is mostly 30 hz chest pounding thump. Home theater type bass dips down to 20 hz and below. It just isn't as impactful and teeth rattling as car audio pressurization.

    Noone has asked, what Outlaw amp did you buy and are you using a powered sub?

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    What LSi's & Outlaw amp do you have? If you have any of the 200 watt amps your LSi's are getting plenty of power to drive them. Do you have a subwoofer, and have you calibrated the system?

    Perhaps you are expecting too much bass from the LSi's than they can reasonably deliver.
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    I have the outlaw 755 pushing 2 lsi9s and lsic with a svs PC-plus (fully EQed for a flat response) and crossed over at 60hz. I did a audo calibrate with my outlaw pre, but no EQ. I also had the 755 hooked up to my rti6s, csi5, and fxi3s. Before my upgrade i bought a niles amp and hooked it up to my rti6s. That sounded much better than the outlaw, but unfortunately i returned it to fund my lsi and outlaw upgrade. I never had a chance to demo the niles with the lsi line, but i figure it would sound better than the outlaw. I also used a onkyo as a preamp with the niles using the rtis. I was using the auto eq with the onkyo-niles-rti6 combo, which also makes a comparison hard. I have no regrets with my lsi upgrade, but I think i need a better amp to power em. The only thing i didn't realize when i upgraded was amps for home audio that are designed for 4 ohm loads are very expensive (since 8 ohms is the norm), however most amps for car audio are designed for a 4 ohm load (because 4 ohms is the norm). I have no doubt that the lsi9s are capable of great bass if properly powered.

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    Quote Originally Posted by sickicw
    I have the outlaw 755 pushing 2 lsi9s and lsic with a svs PC-plus (fully EQed for a flat response) and crossed over at 60hz. ... I have no doubt that the lsi9s are capable of great bass if properly powered.
    That 755 should be more than enough for the LSi's, especially with xover at 60Hz. I think Cathy and Dennis have it covered what the real reason for your dissappointment is...

    http://forums.audioholics.com/forums...d.php?p=108732

    "Into a 4ohms load, six channels driven, clipping occurred at 320Wpc at 20Hz and at 347Wpc at 1kHz (396Wpc with two channels driven at 1kHz into 4ohms)."

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    Quote Originally Posted by Sami
    "Into a 4ohms load, six channels driven, clipping occurred at 320Wpc at 20Hz and at 347Wpc at 1kHz (396Wpc with two channels driven at 1kHz into 4ohms)."
    Wow. That's very impressive.
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    Quote Originally Posted by audiobliss
    Wow. That's very impressive.
    Actually, that seems to be for the 770 as the 755 is a 5ch amp... :)

    Not that the 755 should be any worse:

    "The 770 has 2 each transformers that equal 3.7 kVa.
    The 755 has two each transformers that equal 3.2 kVa."
    Last edited by Sami; 10-31-2005 at 03:45 PM.

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    Perhaps the Outlaw and LSi's aren't a match made in heaven. Specs are specs and don't mean crapola when it comes to quality sound. Having said that, watts don't mean that much, current (amps) generally hold more weight.
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    Quote Originally Posted by F1nut
    Having said that, watts don't mean that much, current (amps) generally hold more weight.
    Manufacturers watts don't mean that much, if they are not dependant of the power supplies capabilities (amperes). Since many aren't, what you said becomes true in real life. Then again, many manufacturers don't rate their power supply so watts is the only thing we can compare. That's why measured power is the best thing.

    And yes, SQ isn't dependant of power. I had a 500WPC Samson S1000 that sounded awful with speakers, a 75W HK stereo receiver trumped it easily. Including a pair of Polk RTi150's that certainly could have used that Samson power.

  19. #19
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    Quote Originally Posted by sickicw
    Much more dynamic
    What exactly does this mean?
    Before throwing out the baby with the bath water you need to spend some time looking at a few different things.
    1) Placement is very important with the LSi speakers. WWW.Dolby.com and the Polk Audio Home Theater Handbook are must reads on the subject.
    2) Calibration. Get a Radio Shack SPL meter and calibrate the system the right way. http://www.audiophilia.com/hardware/spl.htm
    3) Source. What are you listening to and how is it connected?

    A home audio system is not going to sound the same as a car audio system. The environments are totally different and each has it's own problems.
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    Quote Originally Posted by Frank Z
    What exactly does this mean?
    Dynamic to me means that every note is powerfull, has presence, and does not get mushed in with the other notes.

    I have a Radio Shack SPL meter and use if for my sub. Dont have a EQ for my fronts, and use auto calibrate from my outlaw pre amp with its mic.

    I have moved my speakers around a bit, but it only helps so much. I think power is the issue here, not placement.

    I listen to tvs, movies, and all types of music. It is conected with blue jeans interconnects and 10 gauge wire.

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    this i very funny i have thought of this but car amps are very curent happy. the efency of the amp is not to big sence you car has alot of curent. now to get a powersuply with 40-60 amps of draw will cost you 500+ bucks. and caps aare a bandaid on most cars and some times the make the car sound worse. the problem with caps and car is if you draw to much the cap wont recharge and make it worse. caps are good on car if you have alot of power and can recharge them.
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    yea, the high current (specifically into low impedances) is kinda why i want to do this. I think i have decided to give this a try, at least for two channels. I was going to buy a good car audio amp anyway. There are some power supplies here...
    http://www.cascadeaudio.com/prod/powersupp.html
    ...that range from $100 (15 amps) to $400 (100 amps). I will probably have to look into investing in a dedicated 15 or 20 amp wall power line directly from the fuse box. Shouldn't have a hard time finding an electrician to do this. Most high end amps (like krell) recommend this anyway....

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    Quote Originally Posted by sickicw
    yea, the high current (specifically into low impedances) is kinda why i want to do this.
    High current in low voltage defeats the purpose, don't you think? Even with a 100A PS you're way below the power levels your amp (755) can deliver.

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    The output of the rockford car amp might be below the 755 (i havent done all the calculations) for power output, but you seem to be talking about input power. The car amp takes a lot of amps and low voltages and the 755 takes high voltage and low amps. Since P(power)=V(volts) I(amps), it doesn't really matter.

    As far as output goes, i want an amp that can push 8ohms and then double the power at 4ohms, and then double it again at 2 ohms. The 755 can't do that (although the 755 might be able to output more power at 8 Ohms).

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    Quote Originally Posted by sickicw
    The output of the rockford car amp might be below the 755 (i havent done all the calculations) for power output, but you seem to be talking about input power. The car amp takes a lot of amps and low voltages and the 755 takes high voltage and low amps. Since P(power)=V(volts) I(amps), it doesn't really matter.
    100A PS at 12V is only 1200W while the PS in 755 can in theory push 3200W (according to the post in audioholics).

    Quote Originally Posted by sickicw
    As far as output goes, i want an amp that can push 8ohms and then double the power at 4ohms, and then double it again at 2 ohms. The 755 can't do that (although the 755 might be able to output more power at 8 Ohms).
    Anyway, it's your system, your money. If you're willing to experiment then go ahead, especially if you can return the equipment for full refund or have other use for them. Numbers point to the 755 being much better for the system however and I would suspect that is also the case in practice.

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    yea, i am only going to try the car amp thing for 2 channels, so i will still be using the 755 for center and surround. If all else fails, then i will be stuck with a good car amp that i can hook up in my truck, and a power supply that I will probably keep incase I need it in the future. I have had my eyes on this rockford amp for a while anyway.

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