Powered Monitors

Best way to hook them up?

Folks:

I’m hoping to purchase a set of decent powered monitors soon, but I’m confused about the best way to hook them up, especially since many of the monitors I’ve been looking at have only 1/4" or TRS inputs.

Can I hook powered monitors directly to my sound card’s speaker output, like the ordinary computer speakers I use now?

Or do I need to use a mixer of some sort (or something else) in between the sound card and the monitors (eg. connecting the monitors to the “tape out” or “control room” connectors on my UB802 for example)?

I’d like to keep things as simple as possible, but I want to do it properly in any case. Are there important advantages to one method or the other?

In case it matters, my soundcard is a Soundblaster Live! 5.1, with a Live!Drive II front panel interface.

Thanks for any insights you can offer.

PR

Hi PapaRomeo!

As far as I can tell from the specs found at Soundblaster, the outputs of your Soundblaster Live! 5.1 card are line outs - your speakers are probably of the powered type already…

Powered monitors hooked up to a powered output is a no-no.
You’ll blow up the monitors (and probably damage your hearing as well as the soundcard) Use a line-level output instead (your soundcard already has that)

Using a mixer for this is a good idea, since it already cones with decent output connectors. Use the ones marked “control room”, not the “tape out”. It gives other flexibilities as well, such as turning the speakers off when recording.

Good luck with your purchase!

regards, Nils

:D

Thanks, Nils. That’s what I thought, but just wanted to get the expert confirmation.

Now I just have to scrape together the cash for those monitors. I might actually get a second UB802 (~$49 USD) at the same time, just for this purpose, so I can keep the other for live/rehearsal use. More toys! :laugh:

PR

SoundBlasters, at least some of them, are made so that the line out will drive typical headphones directly. They won’t get very loud but it will work and it won’t hurt the soundcard. Anyway many headphones have an impedance of 600 to 1000 ohms, not 4 or 8 ohms. This dual-use line outs are not the same as speaker outs which is available on much older SoundBlasters. Those are intended to drive 4-8 ohm speakers and can get pretty loud, and sound like crap, but that’s another story. If it says line-out your good to go (plug into the powered speakers). If it says speaker-out don’t do it.

Thanks, phoo.
I’m running Logitech powered 5.1 surround speakers now, so it looks like I have line-outs. I figured I could probably run that straight into the powered monitors, but wanted to know what the pros/cons of doing it that way might be.
PR

Having a low output impedance (which is necessary to drive headphones directly) doesn’t automatically rule a source out for connecting an active speaker. What matters is the maximum voltage the source can produce. Since the input impedance of the speakers is probably 1-10 kilohms, it would take a fairly large voltage to fry the inputs (probably above 15 volts if 1/4 watt resistors are used and the input were 1 kilohm). It is unlikely that your sound card can supply that kind of voltage although a real power amp usually can. In any case, the amount of power dissipated in the load is a function of the loaded voltage and the load resistance (in this case the input to your speakers). Since headphones are usually designed to be driven by only a few volts and have good efficiency compared to speakers, few soundcards can source enough power into a high impedance input to do any damage.

Check your specs for the input impedance, if it is over 2k don’t worry about it. If you are particularly cautious turn the souncard level down before you connect the speakers and gradually increase it. If things don’t get excessively loud at very low volume settings, you will be OK with a direct connect.

Jim

In general, you can use headphone outputs to drive line inputs.

I asked Mac over at Audiominds to help out with the math on a similar question: how much power can a typical line output handle? It came up because some guy said “I plug my amp’s speaker out to line input all the time, no problem!” ( ??? )

The answer was that around 100 W you run a very good chance of frying a typical line input. It’s mostly based on the wattage rating for some resistor in the input stage. And given normal variations, many units would be happy at 100W cranking for some time, and others could crap out at well under that level. Finally, this was a simplistic analysis looking at damage to the input. It didn’t consider the quality loss in the system caused by sinking so much power to the ground rail (through the above mentioned resistor). Mostly likely, signal quality would suffer! And for computer line inputs, who knows what else.

But power for headphones is way below that, so they’re generally safe. IIRC, you might not get as flat a frequency response curve as you might otherwise, but it should still be fine – less than 3dB rolloff in the critical 40-15k frequency range.

All of this being pretty much beside the point, which Nils answered in the first place! :cool:

BTW, Jim, I’d expect line input impedance on active speakers to be at least 10k, and more likely 20k, so that you can daisy-chain a couple without overloading a typical line output. But gear these days doesn’t list the “minimum load impedance”. Any idea why? Are line outputs bullet proof these days, able to handle any load? (I doubt it!) Or is it just laziness at providing important specs? (Also, note that “minimum load impedance” and “maximum load impedance” are synonyms, even though they sound like opposites.)

I wouldn’t be surprized if they don’t mention it because of the confusion about “impedance-matching” which leads many to incorrectly assume that a low-impedance output must have a “matched” input impedance. When connecting passive devices this is important because it provides maximum power transfer but with most gear these days you want a low output impedance driving a high input impedance. The only thing that is transfered is voltage and there is no need to maximize power transfer.

The manufacturers may feel that if they state the input impedance it may cause confusion and possibly missed sales due to misinformed customers. Alternately they may just not be too concerned and feel that consumers in general don’t understand these things and in general don’t need to know. It is frustrating to the technically minded that this fundimental characteristic isn’t always mentioned. It woul also be nice to have a maximum safe input voltage spec which would answer the question more directly.

I would also expect the input impedance to be 10k. I mentioned the lower values to give a more conservative scenario. On some mixers (such as my Yamaha 01V) the balanced inputs are about 3k, which I consider kind of low, especially if you want to use a passive direct box but that is a separate question.

Jim

I agree with what you say about output impedance. But I was referring to minimum load impedance, not output impedance: completely different things. Capisce?

In other words, you don’t short an active output. You probably don’t want to plug a passive speaker into a line output, either. In both cases, the load impedance is too low, causing the output buffers to do one of two things: send too much current (possibly damaging the device) or limiting the voltage (distorting the signal).

20 or 30 years ago, you’d always check a line output’s minimum load impedance, which would be typically 5k, against line input impedance, typically 10k, so you’d know many of those outputs you could passively daisy chain from the one input. In this case, it’s 2. If the input impedance is 20k, you can daisy-chain 4 devices. Well, these days, how many can you get away with? And why aren’t they telling us?

Ah, who knows. I have to thank TASCAM white papers and tech docs for educating me on this stuff! I’m certainly no EE.