stage power amps in the 60s

[sansa]

Hello everyone. my today topic starts from an article I read about the power used nowadays for stadium concerts. reading that the vast majority of touring companies uses from 200000 to 400000 watts of power for their PA system is pretty confusing. I then read that maybe 15000 can be sufficient but a higher wattage can assure a clean sound without clipping. my main question is how could they manage all this in the sixties?
I'm aware of the fact that most of the times many groups in the early part of the sixties were lower than the screams of the public. after some years they managed to reach a proper level of volume to be heard also in big concert of hundreds of thousands people. but still don't understand how do they do with Marshall amps and wem system which still maintained wattages like 100 watts or maximum 200 watts each.
maybe the amplifiers were more efficient?
I still remember "the pig", a rare Marshall 200 watts amp from the 60s which had a crazy volume... that i font think it can be compared to any of the amplifiers that are made nowadays. I tried 1000 watts, 2000 watts.. never at that level...

 

[beaubrummels]

In the 60's, the hall sound was quieter. For example, when The Beatles played Shea Stadium, their entire sound was piped through the baseball announcement horns. Plain and simple - it didn't sound that great. Toward the late 60's, there were master/slave power amp solutions that could power multiple line arrays or towers to project sound further more clearly (Watkins Electric/WEM became the standard at the time in the UK; Can't remember when, but Meyer Sound became the standard in America). It was louder and clearer, but maybe not the same as today. The Bee Gees were known to have the best Meyer Sound P.A. in the business and everyone rented from them in the late 70's - Van Halen, Queen, you name it, rented from the Bee Gees.

 

[idsnowdog]

McIntosh power amps were very popular during the 60s and 70s.

 

[Ascension]

[No message]

 

[Ewizard]

In the '60s and through even a small part of the '70s, having much more than 300 to 500 watts of power for a PA was pretty HUGE. By the late '60s there were only a few companies that could even supply the type of wattage used to do something like Woodstock. Keep in mind that Woodstock was using 350-watt tube amplifiers en mass to power the system. The only way to get more volume was to use more speakers that could utilize the power of the next 350-watt, $1,100 ( in 1960's dollars ) amplifier.

In the earlier years of pro audio, the name of the game was efficiency. Most speakers were horn-loaded so that they could turn every single watt into acoustic output. It wasn't even until the early '90s that speaker companies started to offer MI-grade equipment that was less efficient and ate lots of power that didn't turn into much acoustic output; most of it turned into heat... In the mid-'90s wattage started to become cheap and affordable, allowing for companies to go lax on efficiency in favor of modest sound quality. This opened the door for affordability and that is when we have the big box stores like Musicians friend, Guitar Center, and Sweetwater boom with a new market to sell to.

It wasn't until the earlier part of the 2000s that MI-grade equipment was booming. Prior to this point most bands still couldn't afford to buy an entire PA. Finally, around the turn of the century, class-D amplification, cheap speakers, and lower grade cable and connectors were being sold at the larger box stores with a full market of bands and people that could afford them. I started my sound career in 2000 and at the time there were only three major contenders in the MI market, JBL, EV, and Mackie. At that time Cerwin Vega, EAW, Turbosound, and other names were considered higher grade and were too expensive for most entry-level musicians and sound guys to buy into. QSC was slaying the market with their RMX series which at the time was THE BEST entry-level amplifier you could get.

Today you can buy a 4-channel amplifier with 6,000 watts for about $1,000! The current speaker options today are light years ahead of what was available at the beginning of the 2000s. Modern, affordable speakers handle more power, get louder, sound better, and cost relatively the same as they did 20 years ago! My current PA system has a total of 22,000 watts and my PA is considered small by most sound companies. Contrast that to my first PA where I utilized 2 x QSC RMX-2400's and a Peavey PV-4C ( 500 watts and released in 1994 ) amplifiers for a whole of 6 speakers. I started my career with about 5,000 watts worth of power! Today that would be enough to power one side of my main PA, or about 3 of my monitors. We are getting spoiled with the amount of power we can buy and finally having speakers that can turn that power into acoustic output.

 

[Mincer]

I wonder if you re-created their PA with modern equipment if it would be considerably lighter and actually sound better. What a crazy setup.

 

[sansa]

In the '60s and through even a small part of the '70s, having much more than 300 to 500 watts of power for a PA was pretty HUGE. By the late '60s there were only a few companies that could even supply the type of wattage used to do something like Woodstock. Keep in mind that Woodstock was using 350-watt tube amplifiers en mass to power the system. The only way to get more volume was to use more speakers that could utilize the power of the next 350-watt, $1,100 ( in 1960's dollars ) amplifier.

In the earlier years of pro audio, the name of the game was efficiency. Most speakers were horn-loaded so that they could turn every single watt into acoustic output. It wasn't even until the early '90s that speaker companies started to offer MI-grade equipment that was less efficient and ate lots of power that didn't turn into much acoustic output; most of it turned into heat...

We are getting spoiled with the amount of power we can buy and finally having speakers that can turn that power into acoustic output.

So interesting. thanks for your reply.
what I'm trying to understand is more or less how many class A watts should be used to reach a similar acoustic sound to a nowadays concert.
when I try a nowadays 40 watts amp and I compare it to a Vox or a Fender 40 watts amp I get confused. I'm afraid for the windows of my house...
​​​

​​​​​​What I think is that today's amps are a total waste of power. efficiency reached such poor levels and basically we have amps that seem more heaters than musical instruments.

 

[sansa]

In the 60's, the hall sound was quieter. For example, when The Beatles played Shea Stadium, their entire sound was piped through the baseball announcement horns. Plain and simple - it didn't sound that great. Toward the late 60's, there were master/slave power amp solutions that could power multiple line arrays or towers to project sound further more clearly (Watkins Electric/WEM became the standard at the time in the UK; Can't remember when, but Meyer Sound became the standard in America). It was louder and clearer, but maybe not the same as today. The Bee Gees were known to have the best Meyer Sound P.A. in the business and everyone rented from them in the late 70's - Van Halen, Queen, you name it, rented from the Bee Gees.

thanks for the intervention. I didn't know these details. my main question was about the amount of watts used and the difference from today's PA to the old ones.
​​​​​​obviously the beginning of the 60s was totally different than the end of the 60s but the class of amplifiers was still the same (class=grade of efficiency)

 

[Ewizard]

The class of amp is just a description of the topology more so than the efficiency. A class C amplifier has nearly the same efficiency as a class D amplifier, but it has a very impractical way of making the power, leading it to be only useful for very specific types of amplification ( radio frequencies for instance ). Class G & H are just variations of Class AB. No matter how you classify it though, a watt is a watt is a watt.

Watts are a measurement of heating energy. I.E. watts are the conversion of volts into a load that is converted to heat. This is why a speaker is rated for X watts. Beyond that wattage, it will quite literally burn up. The only real consideration when factoring watts, is how much acoustic output will be created with any given watt.

In the early years of sound production, amplifiers that created any significant wattage was nonexistent. To create as much volume as possible from every watt, you had to have a highly efficient speaker. This is where you see the 1 watt @ 1 meter specification on the speakers you buy. With 1 watt of power, the speaker will produce X db in acoustic output. Physics prescribes that for every doubling of power you will achieve a +3db increase in SPL or acoustic output. This as you can see comes to a point of diminishing returns rather quickly.

Enter the '90s... This is the generation that introduced MI-grade equipment. It was less efficient often having speaker sensitivities of between 89db and 96db @ 1 watt. The only difference was that amplifier power was much more abundant. Acquiring 500-900 watt per channel amps was significantly easier, and as a result, there was no need to spend all the R&D on high sensitivity speakers anymore, you could simply throw wattage at them instead. Speakers went from high sensitivity to simply being able to handle higher wattages. Horn-loaded designs started to fall out of favor for front-loaded designs with lower distortion, but also lower sensitivity.

As for modern Class-D amplfication vs older Class-A designs, the watt is still a watt. In technical terms, a Class A amplifier will still have better overall sound quality. It doesn't have any sort of crossover distortion and there is no switching, or stepping going on. A class-D amplifier works by creating a stepped sine wave. It is just that the steps are so close that we cannot hear them. This is what allows the 90+ % efficiency.

Modern speakers are tending back towards efficiency over brute force. You will notice that the amount of power used for self-powered speakers tends to be around the 2,000-watt mark and has for well over 10 years. This is the point of diminishing returns. To get another +3db, you have to double the power to 4,000 watts!!!! That would mean you have to have a dedicated outlet for every single speaker in order to ensure you don't pop a breaker. So manufacturers are now designing speakers to be more efficient in order to make the most of that same 2,000-watt amplifier. You may have also noticed that most passive speakers have not increased their peak wattage in the past 10 years either? Instead, they are finding ways to make the same wattage speaker just be more efficient.

I would say that we are now closer to the '60s than we have ever been in terms of speaker design and amplifier mantra. We have mega-watt amps, but instead of being for only 2 channels, that power is spread across 4-8 channels. The days of 10,000-watt amps for only 2 channels are over. Now we more commonly have 6,000-watt amps for 4 channels. The Powersoft K20 released around 2010 was probably the most powerful amp of its kind producing 18,000 watts for 2 channels!!!! Their current flagship touring amp the X8 has 8 channels producing only 10,400 watts in bridge mono and up to 5,000 watts per channel @ 2ohms. Now that seems super-duper high considering the amp will produce 5,000 watts over 8 channels, but that is a far cry from the 9,000 watts per channel the K20 would produce. The kicker..... The X8 pulls greater than 5000 watts from the wall! The power plug is rated for 40 amps! You need a specially built power distro just to power the things which they say will pull 32 amps at full output. A 350-watt Class-A amplifier will happily power anything, and you can probably plug several into a single 20 amp circuit. The point is that wattage per channel is starting to shrink, while the speaker efficiency is creeping back up.