Speaker / Amp matchup question

Posted: Mon Mar 24, 2008 10:06 am

Hey guys, maybe you can help. I've bought a crown XTI4000. I want to buy 2 main cabs for it. The amp gives me 1200W/chan at 4 ohms. I'm looking at getting the Yamaha S215V's, which are 1000W at continuous, and 2000w peak. Question I have, as I'm very newe to this, am I gonna be distorting too much because of a lack of headroom? Or do you guys think I'll be okay? I'm also looking at getting a couple of the harbinger HX152's instead of those. However, they're 600W continuous with 1200W peak, and I want to get as much volume as I can out of my system. Any suggestions? Or alternatives? Thanks

Posted: Mon Mar 24, 2008 11:30 am

I prefer to use amps that can push twice the continuous rating of a cabinet. If you use the XTI with the S215 cabs you will not have much in the way of headroom.

I suggest a smaller cabinet, a single 15 should get you there.
I'm not familiar with Harbinger cabinets, therefore I'd stay with the Yamaha brand on the low side of the price range, or look at L-Acoustics or EAW if the budget permits.

Posted: Mon Mar 24, 2008 11:36 am

Can I still achieve a good volume with a single 15 cab? I want to make sure I'm maximizing the volume potential of my amp.

Posted: Mon Mar 24, 2008 12:41 pm

bent wrote:

I prefer to use amps that can push twice the continuous rating of a cabinet. If you use the XTI with the S215 cabs you will not have much in the way of headroom.

The double-power rule is not a bad one for maximizing headroom at each cabinet, but what linkamus wants is maximum acoustic output, and it's not the best rule for that. To use all 1200W per channel (into 4 Ohms), you need to have one or more cabinets per side that will convert the 1200W to acoustic energy with reasonable efficiency.

600W cabinets such as the HX152 are fine for converting 600W into acoustic energy continuously, and for that, a 1200W amp run at half power would be great and give good headroom for the transients that may instantaneously push over the 600W. But 600W cabs will not take 1200W continuous for very long.

To maximize the output power from that amp, he will have to compromise on headroom and set up probably a pair of 8 Ohm 600W cabinets per side that together have a parallel impedance of 4 Ohms and can handle the 1200W continuous.

linkamus - don't forget that a substantial fraction of your output power can be dissipated in the loudspeaker cables, so you will need heavy duty cabling with independent runs back from each cabinet to the power amp output. You should aim for less than about 0.2 Ohm per conductor. Factor that out over the intended distance and you should be able to determine the conductor size required.

Posted: Mon Mar 24, 2008 2:04 pm

Boswell wrote:

bent wrote:

I prefer to use amps that can push twice the continuous rating of a cabinet. If you use the XTI with the S215 cabs you will not have much in the way of headroom.

The double-power rule is not a bad one for maximizing headroom at each cabinet, but what linkamus wants is maximum acoustic output, and it's not the best rule for that. To use all 1200W per channel (into 4 Ohms), you need to have one or more cabinets per side that will convert the 1200W to acoustic energy with reasonable efficiency.

600W cabinets such as the HX152 are fine for converting 600W into acoustic energy continuously, and for that, a 1200W amp run at half power would be great and give good headroom for the transients that may instantaneously push over the 600W. But 600W cabs will not take 1200W continuous for very long.

To maximize the output power from that amp, he will have to compromise on headroom and set up probably a pair of 8 Ohm 600W cabinets per side that together have a parallel impedance of 4 Ohms and can handle the 1200W continuous.

linkamus - don't forget that a substantial fraction of your output power can be dissipated in the loudspeaker cables, so you will need heavy duty cabling with independent runs back from each cabinet to the power amp output. You should aim for less than about 0.2 Ohm per conductor. Factor that out over the intended distance and you should be able to determine the conductor size required.

So would those yamaha s215v's be a good match for my amp would you think? They have a 4 ohm impedence and have a 1000 watt program.

Posted: Mon Mar 24, 2008 3:23 pm

You may not want to neglect to consider all the possibilities of connections.

What the other guys said have merit. In a live situation, do you need two channels, or would bridging an amp for mono be better for YOUR application? If that's a consideration, than you'll have to look carefully at the specs.

That Crown amp will bridge DOWN to 4 ohms OK. Since the Yamaha speakers are 4 ohms each, that will give you too low at 2 ohms paralleled, and reduce your power if you series them to 8 ohms (which is not usually a good idea for your mains pair). So, with that particular setup, you'll have virtually no choice of using that amp bridged, if you get an inkling to do so.

If you had a pair of 8 ohm cabs, than that amp will give you monster power bridged to 4 ohms (paralleled cabs).

Would you want a different amp that has plenty of juice to run one channel for the mains, and run the other for monitors? Or, run a biamped system with an amp that has plenty of oomph for the subs on one channel, and a ton of headroom for the crossed-over mains on the other?

You may want to look down the road just a bit before you decide on a setup, and explore the possibilities. Unless you are doing something special, most gigs don't have to be in stereo, so you may be missing an opportunity to put an amp to better use by either bridging a less powerful one to mono for more power, or for subs/mains/monitor uses. Either way may save some cash, also.

Of course, then again, maybe you already knew all this and actually want to run them like that?

Just a thought.

Kapt.Krunch

Posted: Tue Mar 25, 2008 4:35 am

linkamus wrote:

So would those yamaha s215v's be a good match for my amp would you think? They have a 4 ohm impedence and have a 1000 watt program.

Purely on the figures, yes. You should get the most delivered power this way and for more than a few minutes. However, there is nothing in reserve, as Bent was pointing out. When you run flat out like this, the transients will be limited at best and clipped/distorted at worst. Whether you are prepared to accept this trade-off is up to you to judge, depending on the typical event, program material and sophistication of the unfortunate listeners.

Posted: Tue Mar 25, 2008 8:13 pm

Also, you must take into consideration that when that amp clips it induces DC into the drivers - DC is bad, m'kay - one of the quickest and easiest ways to toast a voice coil.

I had to come back to this thread to add another thought or two I had on my ride home this evening.

It's very rare that one would buy an amp before settling on which cabinet they want to use, and cabinet choice is based on many factors, such as:

1) Coverage
(as with mics, cabinets have polar patterns which show you the dispersion of the soundwaves - typically stated as horizontal and vertical coverage (degree). VDOSC cabinets for instance are aimed with laser pointers based on their pattern as well as #2 below)

2) SPL requirements
(How loud does it need to be in the room (or in the field) for maximum audience pleasure - hopefully not so much that you're gonna kill the folks down front!)

3) Ability to faithfully reproduce the source material.
(No-brainer, standing in front of a lot of cabinets for many years helps here)

4) Budget
(How much cash is available for the purchase? 5 bucks doesn't cut it.)

5) Transportation
(Got a big rig, a moving van, perhaps a station wagon? How's the FOH getting to the FOH?)

Lacking these (and many other) considerations you've put the cart before the horse, making speaker cabinet selection difficult.

Have you thought about the above, and if not - why?
If you did, how did you end up with the amp first?

That's a decent amp, I'll give you that.
I've done a lot of shows with my racks of Crown Macrotechs with IQ cards, I've yet to play with the XTI but they appear solid and, dare I say, fun to play with...?

If you jump on Crown's amp forum you can find a plethora of information concerning amp / speaker matching, as well as the oh so important math involved. I highly recommend you check that out.

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