Ringing Out The Room – Channel or Overall PEQ?

[MarkPAmanParticipant]

OK – Just reading numbers from specs is not exactly like real life, but it does tend to give some clues!

The desk has “Nominal Output” “+4dBu = 0dB meter reading” (page 82)

So even the first yellow on the meter is hitting the max for your speakers if you set them at +4. Turn the attenuator on the speakers up (clockwise), and you’ll just hit that same maximum with the desk on a lower level.

At that gig when you turned it all the way up – does that say -36dB on your speaker? – you were hitting maximum even before the second green LED on your meter came on. But it’s still the same maximum whichever way you get to it.

Once you hit that maximum, the limiter in your speaker starts doing things to the sound, which makes it more probable that it will feed back.

[[XAP]BobParticipant]

I use msr400s quite often, and tend to have the volume dial at about 9 o’clock (else I hit clipping before the meter moves appreciably)

But… they aren’t 400W RMS, look at the electrical plate – max electrical input is 130W, they just can’t push 400W for any length of time.

Personally I prefer the Mackie 450s when I have them available, but the MSR are in stock, so they get the brunt of the work. I’ve run the MsRs with a studio spares (stop sniggering at the back) sub (600W) borrowed from a local theatre when I needed to run e-drums and the full power from the Bass through them, and that worked well. Normally the Bass amp provides 80% of the volume, I just top it up from the FOH 🙂

[jet1968Participant]

OK, I’ll put it another way…

If you spent more on the mixer than the PA, then you didn’t spend enough on the PA

[coffee_kingParticipant]

If you spent more on the mixer than the PA, then you didn’t spend enough on the PA

I didnt spend more on the mixer than the PA.

[[XAP]BobParticipant]

That might be a bit harsh nowadays – when the mixer does so much more than mixers of old.

With my RacPac Id have agreed, but with the digital mixers… I can’t think *what* I’d spent £1600 (£2k if you include a tablet as well) on in terms of PA for smallish venues.

I don’t often do gigs at football stadiums, and when I do I know a man who can provide me with 6-12kW of PA – but that takes a transit van to deliver, the MSRs fit in the boot, along with the desk and various other sundries…

[Lee7Participant]

I find the Mackie SRM 450’s fantastic value for what they can achieve, when I do a medium sized PA job I will install up 6 SRM’s and 6 SWA 1501 bass bins, even with just 2 boxes a side I have never hit the limiter’s in them. All my Mackie gear is the original Mk1 Italian/US RCF gear. Harder to get replacement drivers for them these days so I just search the globe picking up bits where I can.

For monitors I run up to 8 Wharfedale EVP 12 & 15PM wedges, again, take a barrage of abuse but deliver when needed.

[[XAP]BobParticipant]

I think your idea of medium and mine differ 😉

[Dick ReesParticipant]

I find the Mackie SRM 450’s fantastic value for what they can achieve, when I do a medium sized PA job I will install up 6 SRM’s and 6 SWA 1501 bass bins, even with just 2 boxes a side I have never hit the limiter’s in them

These are 90 degree pattern speakers. If you deploy them PROPERLY, you will splay them so that the patterns do not overlap and cause significant degradation of and uneven response in the sound. The ONLY reason to use two/side would be if you need 180 degree coverage. Doubling them up will “look cool”, but the minimal output increase of 3dB will not really be audible and the interference/comb filtering will render channel EQ adjustments much less effective, sounding different at individual listener positions across the sound field.

Using 90 speakers doubled up for less than 180 degree coverage is just plain bad policy if you care about sound quality. If you just need “the look”, put up 2, turn on 1. If you need louder, you MUST buy/rent/use higher output boxes or horn loaded boxes with enough pattern control to be arrayable.

Sorry, that’s just the way it is…

[Dick ReesParticipant]

Here’s a graphic representation of what happens when you use two sound sources lacking effective pattern control to cover the same area. Some frequencies cancel at various distances, some reinforce. Result?

Inconsistent sound/response across the listening area…for NO useful increase in output.

It’s physics.

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[[XAP]BobParticipant]

Although can be minimised by design. Tannoy VX8 have a 90 degree dispersion, but are designed to be paired – no idea what voodoo they did, but it works (at one angle, cunningly encoded into the cabinet)

[Dick ReesParticipant]

Although can be minimised by design. Tannoy VX8 have a 90 degree dispersion, but are designed to be paired – no idea what voodoo they did, but it works (at one angle, cunningly encoded into the cabinet)

The crux of the matter is: how far down does the pattern control extend? The sad fact is that only premium speaker manufacturers provide the information about where the dispersion pattern is measured. A cheap cabinet (like the Mackies in question) only mention in their literature that the pattern control goes “all the way up to 20kHz”. This is salesman hype. Sure it’s easy to have pattern control of the HF. Wave-lengths are very, very short and require only a small horn to exert some control. But the average consumer speaker is lucky to have the published “pattern control” from the cross-over frequency on up…and almost completely un-tamed audio dispersion below that.

So at what frequency are these Tannoys exhibiting 90 degree dispersion? What is the total output frequency range of the cabinet? Without accurate information in these areas any sensible discussion is severely compromised, if not impossible.

If the “90 degree” cabinets are meant to be arrayed, the angled mating sides of the boxes would have a 45 degree angle/box. Total splay: 180 degrees.

[[XAP]BobParticipant]

Can’t remember – it’s been two years since I was poring over data sheets and software packages to work out what we were likely to need. From memory (and given that I bolted them to wall on Saturday, after they had been hanging in place for a long while) the total angle isn’t 180, it’s more like 130..

The two angled sides are at 30 degrees (just found the manual) so that’s 120.
Ten degrees off by eye from memory isn’t too bad 🙂

This is the recommended configuration for pairing the speakers, and from experience with them, it works. No combing that I can detect…

[Dick ReesParticipant]

The two angled sides are at 30 degrees (just found the manual) so that’s 120.
Ten degrees off by eye from memory isn’t too bad 🙂

This is the recommended configuration for pairing the speakers, and from experience with them, it works. No combing that I can detect…

OK…

1. 30 degrees doubled is 60 degrees, not 120. From the pictures, the angled portions are on the rear corners, but they ARE there.

2. This is not really a fair comparison for the OP and those using the 450’s as the Tannoy is designed for a bit of a different purpose. It is an install speaker, so designed for indoor, permanent deployment. It’s maximum rated (peak) output is 119dB which, in the world of PA speakers for bands and such, is just not nearly enough. The Mackies mentioned are rated at 127dB in comparison…twice as loud, but still kind of low-end for real PA work.

3. If you want to hear the comb filtering, play pink noise through the system and walk across the sound field. Hear that “swishing” sound?

Comb filtering will not be perceived readily from a fixed listening point by the less experienced. Yet it will still render any accurate EQ’ing less effective…or not at all effective depending on the severity of the cancellations/reinforcements.

I remember one folk festival where they’d hired someone to provide sound…who just stacked up a pile of mis-matched speakers in a pyramid on each side of the stage. It looked impressive, but the comb filtering was severe enough to manifest itself thusly:

When the mandolin soloist (PHC alum Peter Ostroushko) played an ascending run, scale or arpeggio, the notes at the points of maximum interference disappeared while those at the points of maximum reinforcement jumped out louder. This was audible to anyone in the listening area, although the affected notes would be different for those at different listening positions.

What one strives for is uniform response across the spectrum. The fewer speakers, the more even the response. Once you have more than a single speaker, you MUST deal with the fact that there will be interference. The task is to minimize it. There are various ways and considerations to be taken into account.

DR

PS

The VX8 is a 90×90 conical pattern, so as a PA speaker for the typical performers, a significant portion of the (limited) sonic energy available is wasted in the vertical plane…where it will tend to reflect off of the ceiling and cause yet more problems with clarity. Basically, they are install pieces which should be deployed to their best advantage. For real-world PA work they simply do not qualify…no matter how good they sound in the near field.

[[XAP]BobParticipant]

This is a permanent install, 2*30 gives a total spread of 120, once you include the 90 degree cone…

And yes we did play pink noise and walk across the field – no combing that I could detect, amongst the battery of other (limited) analysis we did. Some really weird effects at (off the top of my head) 6.2kHz->7kHz (circa 2 inches, and therefore probably tweeter size related) but nothing else of ‘interest’ to report…

[coffee_kingParticipant]

Thanks everyone, interesting reads (Even if I dont understand a lot of it) but I feel this is getting a bit off topic now.

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