Opinion: Amplifier Headroom and the Active Versus Passive Speaker Debate
“Because BIG power amplifiers SOUND GREAT!”
The debate over active versus passive loudspeakers has been raging for some time now, and I’ve written about it in the past.:
I won’t go through all the pros and cons again fully in this post, but here’s a summary.
With my own systems, I’ve always used passive loudspeaker systems in conjunction with amplifier racks. In systems that use multiple speakers including front of house arrays, sub arrays and, of course multiple stage monitors, I like the idea of centralising the power requirement. This is a particularly powerful argument when it comes to distributed and permanently installed sound systems. For outdoor gigs, I like it that the part of the system requiring power (i.e. the amp rack can be housed under the stage (or somewhere else under cover) and that the system components more likely to be open to the elements (i.e. the loudspeakers) don’t require an electrical power feed.
I worry about control. I have concerns about the transparency of active speakers, and I worry that the DSP processing inside active loudspeakers may be doing something I’m unaware of such as bass enhancement to achieve a more pleasing ‘showroom sound’, rather than delivering a more useful flat/transparent response. Related to that, is that the space within the box taken up by the amplifier/processing modules reduces bass response, and I’ve always really just liked the idea that specialist amplifier manufacturers make great amps and specialist speaker manufacturers make great speakers.
I get some of the pros of active boxes. No losses caused by running high level signals down speaker cables. But I think most of the pro arguments made for active PA speakers really centre around convenience rather than sound quality. Weight issues, portability and having fewer item to move around are major factors, and valid arguments.
I think it’s true that for most portable PA systems, customers are choosing active speaker systems.
But I think one factor that is often missed when it comes to the active versus passive argument is that of amplifier headroom. Headroom is essentially how much spare power an audio system has. The idea is that a system running at half it’s capability will always sound better than a system of equal quality running flat out, and part of this is amplifier headroom. Again, a high powered amplifier running at 50% of it’s capability will always sound better than an amplifier running close to it’s specified limits. Assuming, of course, the amps are of the same design/quality, etc. In my experience, I’ve always found this to be true.
It’s one of the reason why hi-fi enthusiasts often have large power amplifiers in their systems, even for small living room spaces. 300 watt per channel amps in applications where a 20 watt amp would do the job. These amps may often be running at 10-20% of their capability but will sound all the clearer, cleaner and more detailed for it. Some people may be familiar with such hifi type amplifiers made by manufacturers such as Krell and Mark Levinson.
Active speakers, on the other hand, tend to have amplifiers that are quite closely matched to the speakers capability. Again, size, weight, and convenience lead the design brief here rather than sound quality, clarity or detail. Larger amplifiers can also generate more heat and therefore ensuring that an amp is cooled properly in a speaker enclosure may be more difficult than in it’s own dedicated box. So you’re more likely to reach the amplifier’s limits.
I think the emergence of great sounding, high powered yet lightweight power amplifiers represents a great opportunity for clients to really take advantage and utilise amplifier and system headroom in a way that active loudspeakers don’t. These amplifiers usually use Class D type circuitry alongside switching power supplies that don’t require a transformer. The technology has taken some time to develop with earlier models not really delivering in terms of sound quality, and were often quite a bit more expensive than their traditional counterparts, but now there are some really great sounding models available. They are higher powered, lighter, and more affordable than ever.
It’s a ‘have your cake and it it situation’. Now you can have lots of amplifier power and headroom, delivering great sound quality, but still within modest size and weight limits, and reasonable budgets.
I would suggest taking a look at models by Crown (XLS2 Series), QSC (GXD) and Peavey IPR2 Series. Those blessed with slightly bigger budgets may also take a look at the fabulous RAM Audio products and Lab Gruppen amps. Some examples are pictured below (click the images for more information).
Then pair them up with great passive loudspeaker boxes by the likes of Martin Audio (the Blackline X products offer sound quality, transparency and versatility in spades), QSC and EV have some great products, and The Noizeworks own GSS Series boxes are well worth a look.
But rather than pair them up with amps of similar power rating, buy yourself some headroom. Get an amp rated at twice or three times the power of the speakers. You’ll notice the difference. So much more clarity and purity, and if you play one of your favourite CDs through it you’ll hear things you never knew were even there before. Get yourself a system that most active boxes can’t really match.
Come into The Noizeworks and see us. Bring your favourite CD with you and we’ll demonstrate the power of amplifier headroom through one of our systems. You’ll be amazed.
I’ll take a closer look at the high power/lightweight power amplifier in another blog post in the coming weeks and take a closer look at some specific models.
Until next time.
As with all The Noizeworks posts, the information here is offered on a informal basis in the hope that it mighht prove useful to readers with an interest in the subject. We accept no responsibility for any circumstances arising from the application or mis-application of the information here. So there!