Vintage PA vs Modern PAs

JJJr · August 2023

Hope this is alright to post in here, but figure vintage PAs can be similar/used as guitar amps might be someone who can help.

Basically im looking for a PA for my band, very loud band 2x guitars bass etc, and need something that can cut through. Normally used to using/buying Behringer Eurolive 400w passive speakers getting a 1000w power amp and easy peasy you have a PA.

However i stumbled down a vintage PA rabbithole and found so many more affordable options this way, I found a Simms-Watts PA system that has 4 x 12" speakers and 8 x 6" speakers across 4 cabs, however the mixer powering the whole thing is like 100w.

So now I dont know if this is powerful enough to cut above a full band? On one hand modern PA systems are rated at like 1000w (and this is rated at 100w) but this has more speakers than the rest of my band combined and my 120w guitar head can be much louder than a 1000w PA system... so surely a 100w PA system with 12 speakers is gonna do the job...

Can anyone help out? Or possibly answer the larger question of why modern PAs have such a high wattage than vintage ones (which tend to be at the biggest- 200w) yet they're no louder? If wattage is a poor rating of "loudness" is there any other way I can figure out if this Simms-Watts PA is gonna be loud enough?

Thanks for all help in advance as usual.

ICBM · August 2023

If you were in a retro band and want the old look and sound, it might be - as long as your backline isn't that loud. But if you're in a very loud band it won't do the job. The old systems are much more efficient in terms of acoustic volume relative to their rated power, that is true - but at the expense of distortion, clarity, bass and treble response, and punch. It will sound like a radiogram turned up full compared to a modern hi-fi.

Bear in mind that a 120W guitar amp is only having to amplify one instrument, and it can use not only its full power but also go into distortion, which can be equivalent to doubling the power. A good rule of thumb is that you need about twice the power of all the instrument amps put together for the PA, which is why power ratings in the high hundreds of watts or low kilowatt range are normal for PA.

Modern PA speakers sacrifice sensitivity (efficiency) for better frequency response and lower distortion. If you want to see what the difference is, try running the PA signal through your guitar amp at gig volume. Also, just because there are twelve speakers doesn't mean it will be any louder than four - the 6" drivers are for treble, even if they aren't proper tweeters with crossovers, and two 6s are not as loud as one 12 just in basic sensitivity anyway.

JJJr · August 2023

Thanks for this pal, assumed that might be the case that old PAs are basically akin to running vox through guitar head. Might take the dive anyway because it's so so much cheaper and only for practice anyways.

Im running 2x 120w sound city amps at about 1/4 volume + a bass it might just do the job without distorting too much. More speakers just means I can move em so there's not just a single source of sound which may help with clarity but totally understand more speakers dont equate to more volume.

JJJr · August 2023

Just a quick one, is it the speakers that effect the treble/bass response & added distortion at higher volumes? Or can that be remedied by using a much more powerful amp with the same speakers? (simple behringer 750w KM) Im only interested in the speakers to be honest as they're so much cheaper than even Eurolives, the amp/mixer im going to have to get either way.

DartmoorHedgehog · August 2023

FWIW, the band I'm in used to use an old HH 100W mixer head into a couple of 2x12 cabs. We're not stupidly loud like a doom band or something but can be loudish punk/rock/gothy stuff and that old PA was up to the job for just being a vocal PA (rest was all just from the backline). Sounds weedy spec compared with modern PAs (and as has been suggested, probably not the best quality sound at gig volume) but in a live situation it was good enough.

We haven't used it for ages because most of the places we play now seem to have their own house PA.

ICBM · August 2023

The speakers won't have the power rating for a higher-powered modern amp, even though with PA it's best to have the amp more powerful than the speakers in order to avoid distortion, there is a limit and if you put in more power than the speakers can handle, you will burn out the voice coils.

I would guess the 12" speakers will be rated for no more than 50W each, and may be not particularly conservatively-rated even at that. The 6"s will be even lower, although they may be wired in a way that protects them to some extent.

This is what happens when you run a higher-powered modern amp into a vintage cabinet...

Image: https://tfb-user-images.eu-central-1.linodeobjects.com/3af897a869b3081f7f3ace3a3ac3991961af1bde5f6103d907

WEM 4x10" column speaker with about 10W Elac speakers. These have a paper voice coil former, and the voice coil got hot enough to set fire to it, followed by the cone and then the grille cloth.

You should be able to find 80s/90s PA cabinets that wil take a few hundred watts pretty cheaply, they're not popular now.

ecc83 · August 2023

Modern PA systems are very different from the kit 'we' used in the 70/80s which, remember, was usually ONLY reproducing vocals. Guitar and bass rigs were more than loud enough for a big pub or a church/school hall and drummers were and still are 'king loud enough!

Today speakers are almost all active and yes, they are less sensitive than the old stuff and need a kW or so to work. However, quite a lot of that 1000 watts is 'thrown away' in response correction. Also, 'actives' can work the drive units close to their thermal limits safely because there are electronic, often digital controls.

As IC' says, modern PA is more "hi fi" than "guitar" and that demands a lot of power. There are a few, (very expensive!) PA speakers that can deliver 130dB SPL at a mtr but are close to very good studio monitors in their sound quality.

Dave

JJJr · August 2023

Thanks for the help everyone.

Jesus ICBM...
My guess would be the same, 50w for all 4 of the 12"s and probs 15w for the 8 x 6" speakers, the whole rig is apparently powered by a 100w mixer so this doesn't quite jive with the calculations. When you say too much power is bad.. how much are we talking?

If I assume ive got 320w across all 12 speakers and I get a 750w power amp, think that could cause problems? I dont think these speakers have paper voice coils. The 12" speakers are RCF and the 6" are Goodmans

EDIT: also yeah just realised why this convo aint lining up, the only thing the PA is running is a single vox, maybe a second, no instruments are running through the PA, we're talking rehearsal space here not gigging.

ecc83 · August 2023

320 " watts worth" of speaker power handling and a 750W* amp is IMO asking for trouble! In any case, if we guess at a sensitivity for the speakers of a 90dB/W 750 W will produce around 120dB at a mtr and that is bloody loud!

If you MUST use that amp I suggest some inline fusing with a chunky resistor shunting the fuse. 22 Ohms at 50W is cheap and will drop the volume enough for you to know the fuse has popped.

* 750W into what impedance?

Dave.

ICBM · August 2023

JJJr said:

My guess would be the same, 50w for all 4 of the 12"s and probs 15w for the 8 x 6" speakers, the whole rig is apparently powered by a 100w mixer so this doesn't quite jive with the calculations. When you say too much power is bad.. how much are we talking?

If I assume ive got 320w across all 12 speakers and I get a 750w power amp, think that could cause problems?

You can't just add up the speaker power. A 50W 12" and two 15W (if you're lucky - Goodmans aren't known for conservative ratings) 6" speakers with a crossover is a 50W cabinet, not an 80W cabinet. Even if there isn't a crossover and the 6"s are in series and then in parallel with the 12" - the only sensible way without a crossover - then it's still only a 60W cabinet, limited by the pair of 6s.

A 750W amp into four of those will fry them, that's almost 200W per cabinet.

JJJr said:

EDIT: also yeah just realised why this convo aint lining up, the only thing the PA is running is a single vox, maybe a second, no instruments are running through the PA, we're talking rehearsal space here not gigging.

A single vocal will help, but you'll still need it loud. It makes no difference if you're in a rehearsal space if you're playing at gig volume. In fact, you may well be playing louder...

JJJr · August 2023

It's set up as 4 cabinets, 2 x 2x12" and 2 x 4x6" cabs which would make the 2x12s working the same as guitar cabs making them 100w each capacity no? If not then i guess the 100w mixer that comes with it is enough to amply power the rig. Was under the assumption that the amp needs to be around double the total wattage of the speakers to leave enough headroom.

JJJr · August 2023

ecc83 said:

320 " watts worth" of speaker power handling and a 750W* amp is IMO asking for trouble! In any case, if we guess at a sensitivity for the speakers of a 90dB/W 750 W will produce around 120dB at a mtr and that is bloody loud!
If you MUST use that amp I suggest some inline fusing with a chunky resistor shunting the fuse. 22 Ohms at 50W is cheap and will drop the volume enough for you to know the fuse has popped.

* 750W into what impedance?

Dave.

No idea of impedance! information is light as they're 70s and very second hand but fully tested and working. Just much cheaper than any modern PA speakers. I think 320w is a high estimate but it basically has two 2x12" guitar cabs as speakers + 2 4x6" acting as tweeters I guess. Average 2x12 guitar cab is 100w so I guess it's around 300w in total? I mean the marshall 1936 is 150w cabinet made from two 12" speakers.

ICBM · August 2023

JJJr said:

It's set up as 4 cabinets, 2 x 2x12" and 2 x 4x6" cabs which would make the 2x12s working the same as guitar cabs making them 100w each capacity no? If not then i guess the 100w mixer that comes with it is enough to amply power the rig. Was under the assumption that the amp needs to be around double the total wattage of the speakers to leave enough headroom.

Ideally it should be - but in fact, without proper tweeters the cabs are less at risk of damage from distortion, so having the amp the same rating as the cabs or even below it is less likely to cause trouble.

I assumed that the cabs were 1x12" + 2x6" each... if they're 2x12"s and 4x6"s then (assuming 50W per 12" and 15W per 6", then you have two 100W cabs and two 60W cabs, so if they're all the same impedance, the total power handling is limited to only 240W before the 6s are overloaded - you can't just add all the power up, it's four times the lowest-rated cabinet. And bear in mind that Goodmans ratings are often very optimistic.

If you really want these cabs, I'd suggest a 200W amp maximum. There is a reason they were designed to go with a 100W one.

Dave is also right that to be accurate, you need to know the impedance of each cab. If it's not marked on the outside, are the speakers individually labelled? Or do you have a multimeter?

I still find it hard to believe that these cabs are cheaper than a pair of slightly rough used 80s/90s 1x12"+horn or 1x15"+horn speakers - you can barely give those away now.

JJJr · August 2023

ICBM said:

JJJr said:

It's set up as 4 cabinets, 2 x 2x12" and 2 x 4x6" cabs which would make the 2x12s working the same as guitar cabs making them 100w each capacity no? If not then i guess the 100w mixer that comes with it is enough to amply power the rig. Was under the assumption that the amp needs to be around double the total wattage of the speakers to leave enough headroom.

Ideally it should be - but in fact, without proper tweeters the cabs are less at risk of damage from distortion, so having the amp the same rating as the cabs or even below it is less likely to cause trouble.

I assumed that the cabs were 1x12" + 2x6" each... if they're 2x12"s and 4x6"s then (assuming 50W per 12" and 15W per 6", then you have two 100W cabs and two 60W cabs, so if they're all the same impedance, the total power handling is limited to only 240W before the 6s are overloaded - you can't just add all the power up, it's four times the lowest-rated cabinet. And bear in mind that Goodmans ratings are often very optimistic.

If you really want these cabs, I'd suggest a 200W amp maximum. There is a reason they were designed to go with a 100W one.

Dave is also right that to be accurate, you need to know the impedance of each cab. If it's not marked on the outside, are the speakers individually labelled? Or do you have a multimeter?

I still find it hard to believe that these cabs are cheaper than a pair of slightly rough used 80s/90s 1x12"+horn or 1x15"+horn speakers - you can barely give those away now.

Im being pretty stingy and looking within a 50m radius of where im at (ebay, reverb, gumtree, usual suspects) and there's nowt. Behringer passives are golddust second hand, back in the day these things were £80 each for a set of Eurolives, now they're pushing £200 per speaker, nevermind the amp, mixer, stands etc. I was also under the same assumption as you til I started looking that this would be a cheap operation. There's a LOAD of Carlsbro speakers on there but they're all 100w max too

I also thought that from having issues with a pair of 800w modern pa speakers being loud enough, might have more luck with some vintage stuff that I find always tends to sway on the abnormally loud when it comes to guitar stuff. A normal PA set is built up out of two 12" speakers where as this was 4 x 12" speakers + some little 6"ers and Simms-Watts make mean guitar amps but maybe im adding it all up wrong and there's a reason PAs are built different these days.

I thought with PA's the rule of the thumb was to have DOUBLE the wattage of the speakers in the power amp, so if this rig totals 240w, surely i'd be looking for something in the 500w region?

6"s are ... 13ohms the RCF 12"s aren't labelled at all, just plain magnets, they're all part of a set (aside from the mixer which looks like it's not part) so I assume all 4 cabs are supposed to work together but I doubt Simms-Watts used Goodman speakers so I imagine they're modern drop-ins.

ICBM · August 2023

JJJr said:

I thought with PA's the rule of the thumb was to have DOUBLE the wattage of the speakers in the power amp, so if this rig totals 240w, surely i'd be looking for something in the 500w region?

With modern PA cabs with tweeters, yes - the main risk there is amp distortion sending lots of high harmonics to the tweeters and cooking them (and possibly the crossovers), so you want the amp high enough powered that it won't distort first. But with old-school stuff with no tweeters it's the overall power going to the voice coils that's the main problem - which is why that WEM cab caught fire. For that, having the amp about the same power rating as the speakers or slightly below is safer, especially if the amp is valve - overdriven valve amps don't produce the sort of square wave distortion and high-frequency odd harmonics as overdriven solid-state ones do. It's more like a guitar amp in that sense.

JJJr said:

6"s are ... 13ohms the RCF 12"s aren't labelled at all, just plain magnets, they're all part of a set (aside from the mixer which looks like it's not part) so I assume all 4 cabs are supposed to work together but I doubt Simms-Watts used Goodman speakers so I imagine they're modern drop-ins.

The 6s are 16-ohm nominal impedance then - DC resistance is always about 3/4 of it. It's most likely that all four cabs are 16 ohms - four 16-ohm 6s wired parallel-series gives 16 ohms per cab, and two 8-ohm 12s wired in series also 16 ohms per cab. That's a total load of 4 ohms for all four cabs.

The Goodmans drivers are probably original, many makers did use them back in the day, although not many have survived.

It is all very different today, yes - amp power is cheap and light now whereas it was expensive and heavy back then; conversely, modern speakers can handle huge amounts of power so efficiency can be sacrificed in favour of even frequency response and high damping, which gives a clear, punchy sound with minimal distortion - old-school speakers are very underdamped and so produce a much more middy sound with lots of distortion, and the maximum power handling for speakers before the late 70s and fibreglass voice coils was about 50-100W at most... you can get single drivers that handle 1000W now.

JJJr · August 2023

Thanks, this literally answered all my questions. Best

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