[Lotus99]

So I've been researching things for quite a while and Technic has been a great help so far, but I thought I'd stop bugging him via PM, and ask here, in case others can chime in and I'll post up all my findings also in one place, if it can help others, especially anyone with E93 (convertible) specific needs. There’s lots of posts I found on how to install the subs, but they didn’t talk about amp selection.

I’ll start off by saying that I’m not an audiophile, so keep that in mind when suggests think things for me - I don’t need super high-end stuff. :-) I’m sure quite a few of these questions have been answered here and there, so I hope you’ll bear with me as I post them all in one spot. My plan is to collect all the parts I need, and have a shop install it all for me.

I’ve got a 2008 335 with the Logic 7 system in it (S677A HiFi System Professional DSP option code). I’ve already bought a pair of the 4 ohm SWS 8x subs, and will be buying a Technic harness for the amp connection, as well as his woofer connectors for the sub connections. I've also purchased the spacers from JTSherri.

So what’s left is the amp! And I’m trying to figure out what the key minimum requirements are for the amp to select.

For convenience sake, here are the specs of the subs:

http://www.earthquakesound.eu/car-au...rs/sws-8x.aspx

• Max Power: 300W
• RMS Power: 150W
• Impedance: 4Ω
• Sensitivity: 86.7dB
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AMP LOCATION - With respect to the amp selection, one thing I am limited by as far as I can tell, is SPACE for the amp in the trunk. The three spots I had considered are the two underneath the trunk floor panel, and the little compartment on the left side (which is my least favorite). All three have only about 2 inches high of clearance, which limits me to what amplifiers I can buy. Correct? Or is there anywhere else I should be considering?

I have a ski pass thru, so can't install it on the back of the rear seats in the trunk.




WATTS OF POWER – When I asked Technic what to buy, one amp he suggested was the Arc Audio KS 125.2 Mini which retails for $360. Its specs are 2 Channels @ 4 ohms: 70 Watts | 1 Channel @ 4 ohms (bridged): 250 Watts | 2 Channels @ 2 ohms 125 Watts

First of all, I have no idea how my speakers will be installed (parallel?) and which of those 3 specs numbers is the one that counts…

I’d read somewhere someone saying you can run a mono amp with 4ohm SWS-8's in parallel making a 2ohm load on the amp, which is beyond my understanding…

Its Specs are listed here: http://www.arcaudio.com/p/ks-125-2-bx-mini Its Dimensions are 8.25"(L) x 4.8"(W) x 1.7"(H), so it would fit no problem.

For example, with the Arc Mini amp, which power specs should I be paying attention to? The per channel ones (70 watts) or 1 channel at 4 ohms? (250 watts) Or the 2 ohm loads are what I should look at?

I’ve read as a rule of thumb you should match the amplifier’s per channel RMS power output to the per speaker RMS power handling as closely as possible (+/- 25% per channel RMS power). So wouldn’t that mean in a 2 channel amp I should aim for something around 110 watts to 190 watts per channel (based on 150W RMS per sub)? The Arc Mini at 70W per channel doesn't seem like it would be enough?


CHANNELS – The Arc Mini is a two channel amp. Is that the suggested number of channels for my setup and the types of amps I should look for? When I was chatting with someone at Crutchfield, he was saying to go with a mono amp as that’s the typical setup… But I don’t know if with our cars and the way we’re trying to wire things, that’s not the case


CLASS – should I pay much attention to it? The Arc Mini I think is a class D or G. The Rockford Fosgate PBR300X2 is Class BR (supposedly even more efficient than class D).


AMP SELECTION - I could buy the Arc Mini as I'm sure it would be fine, but if I wanted to spend less than $350 for the amp, how does the Rockford Fosgate PBR300X2 compare? It’s only $150 US on Amazon ($250 list) and has more power than the Arc Mini, but I don’t know if there are other things I should pay attention to. I’m not an audiophile, so unless I can really tell the difference, saving $200 is not too bad… :-)

http://www.rockfordfosgate.com/produ...tails/pbr300x2

100 Watts x 2 @ 4-Ohm | 300 Watts x 1 @ 4-Ohm Bridged | Class BR (supposedly even more efficient than class D) Dimensions (H x W x D): 1.53 x 4.25 x 6.75 (in.)


REMOTE BASS KNOB - Lastly, this one is a “wish” item…

I used to have an Infinity Basslink in my last car, and really liked how there was a remote bass knob that I installed up front. For songs I wanted more bass, it was a quick and easy adjustment, instead of having to go into the EQ settings.

Does it really limit my choices, and I should give up on the idea, for the amps you have in mind?

It would be a bit of a pain running a wire upfront I suppose, seeing right now, I don’t have to run any. Unless the wireless options are reliable… I have heard that JBL amps have a wireless bass knob even that go along with them, the JBL MS-WBC. In case that's something to be considered in your amp suggestions, if their wireless knob works well.

Rockford Fosgate makes one too for theirs, but not wireless AFAIK.

Thanks a lot for any help!!!
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[TRod26]

FYI - There is an Arc Audio 125.2 for sale for in the classifieds section for $130 plus shipping. It is in the Musicar Level 3 for sale thread.

[Lotus99]

Originally Posted by TRod26

FYI - There is an Arc Audio 125.2 for sale for in the classifieds section for $130 plus shipping. It is in the Musicar Level 3 for sale thread.

Thanks for the find!

Any idea on how the wattage of the amp works in the setup I have planned? Which number I should pay attention to? I'm sure it's fine, if Technic suggested it, but I'm trying to learn how this stuff works, so I can make an informed decision.

I just want to make sure he didn't maybe think I have bought 2 ohm SWS speakers, when he made that recommendation, because the Arc Mini puts out 70W per 4 ohm channel, which is less than half the RMS of the subs.

Would that be enough you think? I had read you want to be at least 75% of RMS of the subs for the amp.

So it's not the 2 Channels @ 2 ohms 125 Watts number I'd be running the subs at with that amp? In parallel I thought I read you half the impedence of the sub? Sorry if I sound like I don't know what I'm talking about!

And on the Rockford Fosgate amp vs. the Arc? If I can get the RF amp for the same price as the Arc, but new, it seems like the better way to go, but I don't know if the RF amp is as good or if it's specs are sufficient...
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[TRod26]

See below for my answers. I would recommend Googling and reading about speaker ohms and setups as it seems you want to educate yourself and not just be told what you should do. I am the same way and have spent countless hours trying to learn about this stuff. Thankfully there are people on here that are willing to take their time and share there expertise to help people like us. I will say if someone like Technic or the countless other experts on here say something, I have found it to be absolutely true. Having said that I am pretty new on this forum and I would expect that if anything I have said it not 100% correct it will be corrected. I hope this helps.


Any idea on how the wattage of the amp works in the setup I have planned? Which number I should pay attention to? I'm sure it's fine, if Technic suggested it, but I'm trying to learn how this stuff works, so I can make an informed decision. TRod- You want to look at the RMS output for the ohms that you are running. So for your set up the RMS output per channel is 4 ohms (The amp outputs based on the speaker ohm automatically). For the Fosgate you will get 100 watts per channel at 4 ohms. There are 2 things that can change that. If you run the speakers in a parallel setup which is basically putting both the positive wires and both of the negative wires of both speaker in one channel (2 positive speaker wires twisted together in the positive terminal input and 2 negative speaker wires in the negative terminal input, google this for a better illustration) that changes the ohms. Instead of 4 ohms they will now run at 2 ohms and function as 1 speaker so to speak. If you did that you can then run the 2 twisted positive wires and 2 twisted negative wires to the amp bridged which will double the power output and you will be running them in 2 ohms. But agin you have to look at the amp wattage at the new ohm load (2) and see what you are getting and also if that amp is stable a the new ohm load (2) in bridged mode. From looking online it doesn't show that the Fosgate or Arc are stable bridged at 2 ohm.

I just want to make sure he didn't maybe think I have bought 2 ohm SWS speakers, when he made that recommendation, because the Arc Mini puts out 70W per 4 ohm channel, which is less than half the RMS of the subs. Trod- Correct, the Fosgate on paper puts out more watts than the Arc. Ken at Musicar uses the Arc amps for their level 3 set ups and if Technic also recommended it I don't doubt that it will be just fine. The Fosgate having the option control knob is a big deal and the little extra power (if there actually is a difference in real world) certainly won't hurt.

Would that be enough you think? I had read you want to be at least 75% of RMS of the subs for the amp. TRod- I think either will be enough. I have a 600 watt RMS sub running off of a 300 watt RMS amp and I have the amp turned up about half way and it's more than enough. Obviously there are a lot of varying factors but this has been my experience with much of my set up. Having the extra power is nice but as long as you are in the ball park you should be fine depending on how loud you plan to listen and your expectations

So it's not the 2 Channels @ 2 ohms 125 Watts number I'd be running the subs at with that amp? In parallel I thought I read you half the impedence of the sub? Sorry if I sound like I don't know what I'm talking about!TRod - Correct. It is the 4 ohm RMS number that you are looking at for you set up because you have the 4 ohms speakers. As stated above you could run them in parallel but them you would have to run them bridged on the amp to get the extra power. In that case you would need to purchase an amp that is 2 ohm stable bridged. Then you run into the speaker playing in mono instead of stereo. Some people say it matters, some say it does not. I personally do not know.

And on the Rockford Fosgate amp vs. the Arc? If I can get the RF amp for the same price as the Arc, but new, it seems like the better way to go, but I don't know if the RF amp is as good or if it's specs are sufficient...TRod- I think I have seen Technic recommend the Fosgate for under seats so I an sure it would be fine. With it possibly outputting more power and more importantly giving you a knob control up front I would go with the Fosgate. Also if you buy it from Amazon and you are not happy with it you can return it. You could also run an RCA gain control up front with the Arc amp as well.

[TRod26]

Another option I was just looking at is the JL Audio XD400/4. It is a little more expensive ($250 - $400 on Ebay or Amazon). You can bridge channels 1 and 2 for one speaker and get 200 watts on 4 ohms and bridge channels 3 and 4 to the other speaker for 200 watts on 4 ohms. That would give you 200 watts to each speaker and they would be running in stereo. There is also a remote level knob (HD-RLC) for control upfront.

[Lotus99]

Originally Posted by TRod26

See below for my answers. I would recommend Googling and reading about speaker ohms and setups as it seems you want to educate yourself and not just be told what you should do. I am the same way and have spent countless hours trying to learn about this stuff. Thankfully there are people on here that are willing to take their time and share there expertise to help people like us. I will say if someone like Technic or the countless other experts on here say something, I have found it to be absolutely true. Having said that I am pretty new on this forum and I would expect that if anything I have said it not 100% correct it will be corrected. I hope this helps.

Any idea on how the wattage of the amp works in the setup I have planned? Which number I should pay attention to? I'm sure it's fine, if Technic suggested it, but I'm trying to learn how this stuff works, so I can make an informed decision.

TRod- You want to look at the RMS output for the ohms that you are running. So for your set up the RMS output per channel is 4 ohms (The amp outputs based on the speaker ohm automatically). For the Fosgate you will get 100 watts per channel at 4 ohms. There are 2 things that can change that. If you run the speakers in a parallel setup which is basically putting both the positive wires and both of the negative wires of both speaker in one channel (2 positive speaker wires twisted together in the positive terminal input and 2 negative speaker wires in the negative terminal input, google this for a better illustration) that changes the ohms. Instead of 4 ohms they will now run at 2 ohms and function as 1 speaker so to speak. If you did that you can then run the 2 twisted positive wires and 2 twisted negative wires to the amp bridged which will double the power output and you will be running them in 2 ohms. But agin you have to look at the amp wattage at the new ohm load (2) and see what you are getting and also if that amp is stable a the new ohm load (2) in bridged mode. From looking online it doesn't show that the Fosgate or Arc are stable bridged at 2 ohm.

I now understand how the parallel set up vs. the regular one is. I didn't know how the OEM harness worked (if the subs were powered each on one channel, or if it was a parallel set up), and I assumed by extension, the Technic harness in the trunk Now with your explanation and these diagrams I found, it all makes sense.

This is the setup I will be using:


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This would have required me to do extra wiring I presume to connect each sub together, and I'm not sure how it would've affected the use of the harness either. It's a moot point also because as you say, the amp would need to support a 2 ohms bridged load, which it can't.


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I just want to make sure he didn't maybe think I have bought 2 ohm SWS speakers, when he made that recommendation, because the Arc Mini puts out 70W per 4 ohm channel, which is less than half the RMS of the subs.

Trod- Correct, the Fosgate on paper puts out more watts than the Arc. Ken at Musicar uses the Arc amps for their level 3 set ups and if Technic also recommended it I don't doubt that it will be just fine. The Fosgate having the option control knob is a big deal and the little extra power (if there actually is a difference in real world) certainly won't hurt.

Given that, I would probably have a bit more power with the Rockford amp, and as a bonus, it would be new, as well as have a gain knob, but seeing that the Arc amps are so highly regarded, and Technic in the meantime said to me that the Arc Mini should be fine even for a 4 ohm subs set up, I'll go with the one above. I chatted with someone at Arc also initially, who tells me the amp really puts out about 90W per channel at 4 ohms.

Would that be enough you think? I had read you want to be at least 75% of RMS of the subs for the amp.

TRod- I think either will be enough. I have a 600 watt RMS sub running off of a 300 watt RMS amp and I have the amp turned up about half way and it's more than enough. Obviously there are a lot of varying factors but this has been my experience with much of my set up. Having the extra power is nice but as long as you are in the ball park you should be fine depending on how loud you plan to listen and your expectations

So it's not the 2 Channels @ 2 ohms 125 Watts number I'd be running the subs at with that amp? In parallel I thought I read you half the impedence of the sub? Sorry if I sound like I don't know what I'm talking about!

TRod - Correct. It is the 4 ohm RMS number that you are looking at for you set up because you have the 4 ohms speakers. As stated above you could run them in parallel but them you would have to run them bridged on the amp to get the extra power. In that case you would need to purchase an amp that is 2 ohm stable bridged. Then you run into the speaker playing in mono instead of stereo. Some people say it matters, some say it does not. I personally do not know.

Totally clear on it now!

And on the Rockford Fosgate amp vs. the Arc? If I can get the RF amp for the same price as the Arc, but new, it seems like the better way to go, but I don't know if the RF amp is as good or if it's specs are sufficient...

TRod- I think I have seen Technic recommend the Fosgate for under seats so I an sure it would be fine. With it possibly outputting more power and more importantly giving you a knob control up front I would go with the Fosgate. Also if you buy it from Amazon and you are not happy with it you can return it. You could also run an RCA gain control up front with the Arc amp as well.

Wow, I'll need to look into this RCA gain control thing, as that would be great. Will mention it to my installer!

Thank you TRod for taking all that time to explain it all and use the formatting. Sounds like I'd managed to more or less figure things out, and it's really nice to have someone who actually knows confirm it.

I wrote my responses to yours up above in red to make it easier to follow.