[alea35]

I just ordered the E-MU 0404 USB to go with my laptop and I plan on using the headphone out on that or my PPAV2 to drive my Denon AH-D2000's. My question is would the E-MU 0404 USB be powerful enough to drive floorstanding speakers such as these:

FRYS.com*|*Polk

My guess is no, but hey maybe I'll be surprised. If they can't what's a decently cheap amp that could? T-Amp?

 

[sejarzo]

No way.

What one needs to understand is that most headphone amps can only put out a very low amount of current (which effectively translates to limited power) and speakers are much lower impedance devices than Senn HD's (they suck up a lot more power.)

To get some idea of the difference.....

If you are driving Senn HD580's to peaks in the 100 to 105 dB range, they require a signal of about 2.0 volts.

power = voltage squared/impedance

4/300 = 0.0133 watts (13 milliwatts)

Speaker sensitivities tend to be around 90 db at 1 meter at 1 watt for a lot of 8 ohm models--which is exactly what Polk specifies for the RTi8. The Crown Audio web site has a calculator for sizing power amps for sound reinforcement, but the calculation holds for any speaker/amp situation:

Amplifier Power Required Calculator

Let's assume that the listener is 3 meters (~10 ft) away from a speaker that has a 90 dB per 1W at 1 meter sensitivity, and that the listener still wants to listen at a level requiring 100 dB peaks......plugging those values into the calculator, we find it requires 90 watts power to drive that speaker (setting the amplifier headroom in the calculator to 0 dB to find the actual power required, not with a safety factor to prevent clipping.)

So, the speaker will require 90/0.0133 or 6,766 times as much power to achieve the same volume as the headphones.

The other issue is voltage. If an 8 ohm speaker requires 90 watts to reach the peaks, the power amp output stage must be able to supply a 27 volt signal.

The power supply for the 0404 USB is basically a 5 volt, 1 watt supply.

I hope that makes it clear that why a typical headphone amplifier cannot drive speakers.

 

[Ross1]

What it can do is be the source for balanced powered monitors.

But its certainly not a speaker amp.

 

[alea35]

Thanks for the quick replies! So should I pick up the Sonic T-Amp for my purpose?

 

[cyanidebm]

A T-amp would do the trick, I have mine hooked up to my Trends Audio T-amp with some Monster TR 1/4" to RCA.

 

[jilgiljongiljing]

Yeah the T-amp is probably the cheapest and also a compact solution.

 

[alea35]

Alright I think I might go that route. Sell my PPAv2, get the T-Amp, run it from the 0404 USB, to the Polk RTi8's. Then just use the integrated headphone out on the 0404 USB. Thanks!

 

[sejarzo]

If you expect the quality of sound out of those Polks driven by the T-Amp to be anywhere close to that from your HD580's driven by the PPAv2, I think you are in for a huge disappointment.

Bass peaks consume a lot of power on large speakers. Using the Crown calculator, and presuming that your listening distance is 10 feet, a T-amp will clip at a 92 dB peak. A lot of the great reviews of that amp are from reviewers who combined it with hugely efficient horn speakers designed to run on such lower power. Polk says that the minimum power for the RTi8 is 20 w/CH....and I think that such recommendations are like Microsoft saying that you can run XP on a 233 MHz CPU and 64 MB RAM.....it will work, but not work well!!!!

There are more capable power amps available for what you can net from the sale of your PPAv2......check out Audiogon for something like a used Adcom in the $175 to $200 range, and I think you would be much happier in the end. There's even a pair of Parasound HCA-1201A mono block amps for $240 on Audiogon right now--and those would serve you far better than the T-amp.

 

[alea35]

Thanks for that reply! I guess I have some research to do

 

[sejarzo]

Yeah, the nice thing about the 0404 USB is that you don't need a preamp to drive power amps or powered speakers, because it already has the Main Level control for volume--and, like any modern component, the line out voltage is more than adequate to drive consumer-level amps to clipping.