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I just bought an older car (1982 BMW 528e) and I was looking to upgrade the car audio system. It currently has an aftermarket 2011 era Sony stereo in it. The car can only run 4x6 speakers and to run larger speakers, I would need to do some metal cutting which I do not want to do. My plan is to replace the stereo with the Sony MEX-XB120BT which has a built in class D amp outputting 45W RMS x4, which is sufficient for my goals of just getting good sound out of four 4x6 speakers. I do not plan to have any sub and would prefer not adding the complexity, wiring, and cost of a standalone amp. The speakers I was considering (all around) were either the Infinity REF-6432cfx 4x6 or the Polk db461p 4x6. The Inifinity is rated at 45w RMS and the Polk at 50w RMS. Is there anything I'm missing, or any critiques or suggestions I should be considering?

Thanks!
 

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First off the stereo isn’t 45watts rms... more like 15wrms per channel, you’d be better off putting a small amp in 👍🏼

your choice of speakers are going to limit any bass you will get. It will sound piss poor, very thin and lack any form of midbass or bass if using the headunit alone...

sorry but you are not going to get many replies on here not suggesting things you’ve said you don't want to do, adding a subwoofer will add some bass at least...
 

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Why is it only 12w rms per channel? Crutchfield explicitly states its 45w rms per channel here. I am open to a small amp, it just seemed my problem was solved with this stereo and it’s built in amp
 

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Why is it only 12w rms per channel? Crutchfield explicitly states its 45w rms per channel here. I am open to a small amp, it just seemed my problem was solved with this stereo and it’s built in amp
If you believe it’s 45watts rms then that’s all good... go and look how big lump of aluminium a 4x45w rms amp is and how hot it gets... then wrap it in a dashboard with no massive heat sink and then get back to me... put bluntly they claim big power to fool people... but I’d put money on it it’s less power than they claim 👍🏼
 

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45 watts is the max power output per channel. That means for like a split second it can amplify some frequency that much. Probably about 12-14 wrms per channel.
 

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Discussion Starter #7
It does explicitly say 45w rms per channel / 100w peak per channel.
It seems like the consensus is although it says 45 rms x 4, that’s just BS advertising
 

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It does explicitly say 45w rms per channel / 100w peak per channel.
It seems like the consensus is although it says 45 rms x 4, that’s just BS advertising
Well I tend to like specification sheets.
If it says 45W x4, then it is the same as other higher end HUs that also put out 45W RMS.

At 2W RMS you should have 93dB(A) and with a crest-factor of 13dB, the 2W RMS would be happening with a 45W peak power... (That is usually loud enough for most long term listening.)
And a proper 100W amp may give 100W RMs, but you can only get ~4W before clipping... (but maybe 10W with clipping sounds OK?

If your speakers are 90dB/W, then maybe hook them up and see how it sounds... we can debate truth in advertising, but it gets harder to claim it sounds bad, if it actually sounds good when you hook it up.
 

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Sony has a few head units that have a class d amp built in that’s good for 45w rms. It even has to have its own fused power wire ran.

Some of the posters jumped the gun to discount the OPs post without researching Sony’s head units with built in amp line.

OP, if you are dead set on not running an amplifier, then this a good way to get better performance from your speakers. Also look into sound treatment. Give your speakers every chance to sound their best.


Sent from my iPhone using Tapatalk
 

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Some of the posters jumped the gun to discount the OPs post without researching Sony’s head units with built in amp line.
...
I suspect that we both trust Sony more than posters on a forum?

Nakamichi also makes/made HUs with 45W/ch, so I think it must be a common IC that does it?
 

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Sony has a few head units that have a class d amp built in that’s good for 45w rms. It even has to have its own fused power wire ran.

Some of the posters jumped the gun to discount the OPs post without researching Sony’s head units with built in amp line.

OP, if you are dead set on not running an amplifier, then this a good way to get better performance from your speakers. Also look into sound treatment. Give your speakers every chance to sound their best.


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OK. Show us links to these 45 watts per channel RMS headunits.
 

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What is the internal fusing on these ?
Looks like the Sony being talked about here has a 15amp fuse in the back - which is the same size fuse that is in the Alpine KTP-445U "micro" class-D amp, which is also 45Wx4 RMS...

Seems like these 45W x 4 RMS head-units are real....
 

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The previous model, the 100BT, was rated at 40W rms and was tested on an D’More amp dyno by Sonic years ago. Ended up putting out rated power; video also shows the power harness and fuse block.

 

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Sony has a double DIN XAV-AX7000 that puts out 45 x 4 RMS. It even has a 2 ohm mode and you can configure the rear to run a subwoofer (yeah I know 45 watts to a sub). I just learned about these a couple weeks ago.

Actually now that I think about it, didn't someone here link to a sonicelectronix Dyno test of a Sony head unit and F150Man made some kind of comment?
 

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Discussion Starter #18
Thanks for all the replies!

Sony has a few head units that have a class d amp built in that’s good for 45w rms. It even has to have its own fused power wire ran.

Some of the posters jumped the gun to discount the OPs post without researching Sony’s head units with built in amp line.

OP, if you are dead set on not running an amplifier, then this a good way to get better performance from your speakers. Also look into sound treatment. Give your speakers every chance to sound their best.


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I would much prefer not to get an amp. It seems a bit unnecessary to just run 4x6 speakers all around, and a sub is not really an option as my trunk is sealed sheet metal, and I really don't want to do any metal cutting. It seems like this is a solid way to get much more power than a standard head unit, and avoid the amp.

Any opinion on the speakers? Or it doesn't really matter that much?
 
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