[TrollSelektor]

I have been doing a bit of research and I think I have found a setup that will work but I just wanted to check with some other people to make sure I wasn't missing/overlooking anything.
 
I have a lap top without any line out so I will be using a Fiio E7 that I already have (http://www.fiio.com.cn/product/index.aspx?ID=28&MenuID=020301) as my DAC/Preamp (its plugs into the laptop via usb). Now for what I haven't bought.
I will take the output from my E7 and run it into the actual amp/crossover (http://www.parts-express.com/pe/showdetl.cfm?PartNumber=300-803) mids/highs will be sent to a pair of book shelf speakers (http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=300-652&scqty=1) while lows will be sent to this driver (http://www.mcmelectronics.com/product/55-2421&scode=GS401&CAWELAID=220564908?cagpspn=pla&gclid=CJ_T-qeyiLICFUhN4AodglgAcA) which will be in a subwoofer cab that I am building.
 
Is this a workable setup?
Should I go with a lower power amp and still get the driver to really move?
How do I make sure that my bookshelf speakers which are lower power don't get too much wattage?
 
Thanks

 

[mtkversion]

Couple problems.
 
That subwoofer is a 120w RMS (240w max) and the amp is a 250 watt.  
 
You will still need an amp to power the bookshelf speakers.

 

[TrollSelektor]

So will I need to perform a cross over and THEN have 2 more amplifiers? (One for the bookshelf speakers, one for the subwoofer)
 

 

[ProtegeManiac]

If you're building a sub, get a plate amp that has either

1) a crossover, preferably bit through low- and high-level inputs so you can choose which sounds better in case one does, but yes you'll need another amp for the speakers
 
 
2) a 2.1 channel design - look through PartsExpress or Madisound, they have a high-power plate amp that can make a 6" monitor and 8" sub version of much smaller PC speakers.

 

[TrollSelektor]

So I would need something LIKE this http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-773? except with an output between 40-75 watts and another for between 120-240 watts?
 
Or a plate amp that is between 120-240watts that feeds a low level output into a smaller amp to power the bookshelf speakers?

 

[TrollSelektor]

Also what is wrong with a 250watt amp? From what I've read it is advised do have a amp that can provide 10-20% MORE power than what the speaker's MAX power is.
 

 

[obobskivich]

So I would need something LIKE this http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-773? except with an output between 40-75 watts and another for between 120-240 watts?

Or a plate amp that is between 120-240watts that feeds a low level output into a smaller amp to power the bookshelf speakers?

You need an amp for each speaker (or each driver, depending on how esoteric you want to get) - the plate amp you picked won't do that. It has to go like this:

Analog Line Out -> Crossover -> Amp (speakers) + Amp (sub)

Unless you don't care about properly dialing things in, in which case you can just run dual line out and use the LPF on the plate amp and call it good (this can still sound fine). What I'd probably do, because I'm lazy, is get an AV receiver that has a crossover and sub output plus speaker amplifiers, hook the speakers and sub up to that, and configure on the AV receiver (if you spend enough you can probably get one that will even do that for you - just place a measurement mic and let it do it's "thing").

Also what is wrong with a 250watt amp? From what I've read it is advised do have a amp that can provide 10-20% MORE power than what the speaker's MAX power is.

 

It doesn't really matter either way. That amp can kill that driver, but I doubt you'll ever run it that loud for that long. You should have an amplifier that is appropriate for the input max and output (acoustic) needs of the system you're designing - that's the only thing that matters. Any other "rule of thumb" is probably just sales hash.

 

[ProtegeManiac]

Quote:

Also what is wrong with a 250watt amp? From what I've read it is advised do have a amp that can provide 10-20% MORE power than what the speaker's MAX power is.
 

 
Generally, you need clean power more than just absolutely just a lot of power. For subs it's the other way around - harmonic distortion may be too high but as long as it supplies enough current and has high enough damping factor you won't hear the harmonic distortion in bass frequencies. But of course in a 2.1 system you have to get more power for your 2ch speakers to be able to play with the sub - which means 2w flea amps (and maybe even 8w T-amps...maybe) are out, but generally what you have to be able to match the gain structure in both amplifiers.
 
 
Quote:

So I would need something LIKE this http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-773? except with an output between 40-75 watts and another for between 120-240 watts?
 
Or a plate amp that is between 120-240watts that feeds a low level output into a smaller amp to power the bookshelf speakers?

 
Here's the thing, even if you have separate amps - even full-range, maybe even bi-amp plate amps for the 2ch, like active monitors - you'll need at least two sound-tuning features to make a 2.1 system work: 
 
1) crossover - to distribute the freqs to the appropriate amp/speakers
2) a master preamp for gain-matching

Note obobskovich's suggestion above - while such features are normal for the more discerning car audio enthusiast equipment (since you have, for starters, non-center seating unless you convert a McLaren F1 into a Grand Tourer with a nice audio system) - it's not for most 2ch home audio equipment. Even those (pre)amps with a dedicated subwoofer output, like NuForce Icons, are only one feature removed from, say, a NAD integrated amp. The NAD has only a loop out so you can use it as a dedicated preamp or power amp, and you hook up the sub to the tape (record) output, which isn't affected by the preamp - so everytime you move the volume knob on the integrated amp you have to reach down to the sub to adjust that. The NuForce, I think, wires the dedicated sub output so it can be controlled by the preamp, but the sub still needs to have its own amplifier with a crossover.
 
You have two choices now - either the 2.1 plate amp or as suggested by obobskovich a home theater receiver. Both have pro's and cons:
 
1) Plate amp
Pro : self-contained system, easier mounting on sub, wherever it's mounted its smaller than an HT receiver
Cons : if mounted on sub, depending on sub placement it might be hard to reach
Possible Fix : 
i. mount the sub where it's easy to reach ; might require you use compact 6.5" and smaller subwoofers, depending on your desk
ii. wire a potentiometer to it and mount that on a chassis, and put it where its easy to reach (might be too complex a project, depends) ; same thing computer speaker manufacturers do except they mount it on one of the satellites
iii. don't mount the plate amp on the sub ; try mounting it on an MDF panel and secure that where its easy to reach
 
2) HT receiver
Pro : self-contained features, including a good multi-channel DSP system (ie, DAC), but check to make sure you get one with a compatible USB input ; some are already cheap nowadays, depending on where you are (Fry's has good deals on Onkyo and HK) ; you might just go ahead and make more satellites (now or later) and you can get surround for movies and games
Cons : you already have the E7 (but you can sell that) ; still lacks amplification for the subwoofer ; HUGE chassis ; you're paying for 5channels of amps and only need two, but then again...(see Pros)
Fix :  you can just run longer wires and use the remote, or just make/get a new desk and have it within reach and you can also see the display

 

[cel4145]

Quote:

 you're paying for 5channels of amps and only need two, but then again...(see Pros)

 
This may be more than the OP wants to spend, but something like the Denon 1612 can put out 120 watts at 8 ohms with 1% distortion into 2 channels. 2 channel receivers and integrated amps in this price range aren't going to do significantly better. Also, I'd suggest the Denon 1612 because it comes with Audyssey MultiEQ room correction software which will EQ the subwoofer and the speakers by running the software with the included microphone. Can't get that from any other receiver at this price (other entry level receivers that have room correction software don't EQ the sub), and subs can typically really use the help in most rooms. 

 

[whitefero]

I would have thought they'd work OK.. but I don't really know that much