Help: Plugging Laptop Directly Into Powered Speaker

[colinlove]

Hi. I'm new to performing live, and am still accumulating equipment. I just bought a single Mackie TH-15A Thump Speaker. I'll buy another when I have the $. The speaker's only input takes an XLR male cable. At present, I have my MacBook hooked up to the speaker directly via a 1/8" to 1/4" (TRS) cable, attached to a TRS/XLR male adapter.

I know, I need a mixer and an audio interface. For the record, I am planning on buying an M-Audio Fast Track Pro asap.

Anyway, at first, I could only get some tracks (in Ableton, of course) to come out of the speaker, and others, like the drums, not at all. I figured out that if I pan each track all the way to the left or right, it comes out just fine, but if the balance is dead center, some of the tracks don't play at all. If I try to play from iTunes, it just sounds like- well, it sounds bad.

Is this a mono/stereo issue? A channel issue? Will it all be solved when I get the audio interface? When I get a second speaker? When I get a mixer?

How should I prioritize my expenditures? And in the mean time, is there a simple workaround I can do by changing some settings and buying a cable or two?

I am extremely appreciative of all knowledge shared. Thank you!

[ark]

Hi. I'm new to performing live, and am still accumulating equipment. I just bought a single Mackie TH-15A Thump Speaker. I'll buy another when I have the $. The speaker's only input takes an XLR male cable. At present, I have my MacBook hooked up to the speaker directly via a 1/8" to 1/4" (TRS) cable, attached to a TRS/XLR male adapter.

This won't work! (as you've discovered)

Here's what I expect is happening happening: Your MacBook puts out one stereo channel on T and the other on R, with S being the common ground. This goes through your cables and winds up putting one stereo channel on one signal pin of the XLR plug and the other channel on the other signal pin, with the common ground going to the ground pin.

The problem is that devices that accept XLR inputs expect that input to be balanced. In other words, they treat the incoming signal as the *difference* between the two signal pins. That means what what you will hear through your speaker is only the out-of-phase content in your stereo output. Anything that is perfectly centered will disappear.

A quick fix is to put a "Utility" audio effect as the last item in the signal chain of your master channel and click either but not both of the Phz-L and Phz-R buttons. That will invert the phase of one channel and you will now get the sum of the two channels in your speaker rather than the difference.

A better way to do it is to get a direct box that mixes two channels to one and does impedance conversion and isolation. I use one of these and like it. You can use a TRS mini->TRS mini cable to connect your laptop to the box and an XLRM->XLRF cable to connect the box to the speaker.

[colinlove]

Ark, thanks for letting me know what's going on. As soon as I get home I will give this a try. The Utility audio effect is a nice solution for me since I can easily get rid of it once I have the proper equipment. I also appreciate your suggestion re the DI Box. I'll check it out.

Does anyone know if the M-Audio Fast Track Pro, or any other audio interfaces, do impedance conversion and isolation? I'll get the DI Box if necessary, but you know, less is more.

[mikemc]

Ark, thanks for letting me know what's going on. As soon as I get home I will give this a try. The Utility audio effect is a nice solution for me since I can easily get rid of it once I have the proper equipment. I also appreciate your suggestion re the DI Box. I'll check it out.

Does anyone know if the M-Audio Fast Track Pro, or any other audio interfaces, do impedance conversion and isolation? I'll get the DI Box if necessary, but you know, less is more.

Check the specs on the Fast Track, but main outs on most interfaces are 1/4". If you are getting two of these speakers, you should either look into a stereo DI box (the Radial AV2 would do that, or they have another stereo 1/4" to XLR) or a small mixer with XLR main outs. You could probably get an inexpensive mixer with additional inputs for the same price as the stereo radial DI box, but it wouldn't be as quality a mixer as the DI box for that price.

[colinlove]

I did as Ark suggested and put the utility effect on the master channel of my live set. This worked fabulously-thank you so much.

A couple more questions re the long term solution-the audio interface v. di box. If the audio interface has balanced TRS outputs, will that take care of the "out of phase content" problem on the XLR inputs on the speaker (using a TRS --> XLR male cord)? Or do I need a device, like the DI Box referenced in this thread, that has XLR outs?

[ark]

I did as Ark suggested and put the utility effect on the master channel of my live set. This worked fabulously-thank you so much.

You're quite welcome.

A couple more questions re the long term solution-the audio interface v. di box. If the audio interface has balanced TRS outputs, will that take care of the "out of phase content" problem on the XLR inputs on the speaker (using a TRS --> XLR male cord)? Or do I need a device, like the DI Box referenced in this thread, that has XLR outs?

If the audio interface has balanced TRS outputs--i.e. one output per channel, then one TRS->XLRM cable per channel is just the thing. I would not expect you to need any additional hardware.

[The Carpet Cleaner]

I have a fastrack pro with snow leopard and I have driver problems with it. And I m not the only one who got the same exact problem, last time I checked on thier forums.
Also we had to use beta drivers for a long time before they "correctly" supported leopard ( that was 1 year ago I think ).
Anyway I would suggest another soundcard from another brand.

[colinlove]

Thanks to everyone who has contributed their knowledge to this thread.

For anyone else who has the same problem I had, and needs a little basic knowledge on the subject, check out this simplified explanation of the problem from apple: http://support.apple.com/kb/HT2743?viewlocale=en_US

My initial thought after checking out some of the devices made specifically to convert laptop unbalanced output to balanced, is that for the amount of money, you are better off just getting a normal di box and/or an audio interface. More bang for your buck.