Beginners PA Guide: Questions Thread

[DJ Vintage]

Terry_42, post: 40012, member: 1843 wrote: Some comments on part II (especially for Chuck):
I agree that for a guy that already payed some dues a grafic EQ would be more sufficient, especially if your controller can act as a mixer too. However the guide is aimed at total newbies and in my experience a grafic EQ is overwhelming for most people who first encounter them. A 3 Band EQ on a small PA mixer is less intimidating and you can start getting the idea how the whole soundcheck thing works…

Ok, time to put this issue to bed :).

I agree with you on the fact that sounding out (EQ-ing) a room is an art, a skill that requires lots of dedicated training and practice. Even with tools like noise generators and Real Time Analysers it is not a job to be taking on by someone that doesn’t have a clue. I personally don’t even use a graphic EQ anymore (for live sound), but have a Roland true 2x 4-band full parametric EQ. I need the needle point bandwidth (very narrow, narrower than even the 1/3 octave of a graphic EQ) and at the same time the broad bandwidth (wider to do more of a filtering/shelving EQ) to get it right. And sometimes all the problems are close together in frequency and being able to set every EQ band exactly where I need it is very helpful. I figure if there are more than 4 serious problem areas (frequencies), then the place is an acoustic nightmare and I just tackle the 4 worst bits and be done with it.

Where I disagree is that a PA mixer, or more specifically it’s EQ is a good alternative tool. EQ-ing is done for three very specific reasons (and I know you know this already, but I am trying to make the general point for the other readers):
1) As an effect. This is the way us DJ’s use it when we turn down the bass on the incoming song in a mix, or mix out the mids to get rid of some conflicting vocals.
2) As a sound shaping tool. This is the realm of recording/mastering engineers and, to an extend, of live sound engineers. It is a creative/corrective tool to make live performances or recorded material sound as intended.
3) As a means to correct a room’s acoustics.

Now for 1), the EQ on controllers/DJ mixers is just fine. No finesse, just basic fixed bandwith, fixed frequency control.
For 2) at least 3 or 4 band (partially or full) parametric EQ is needed. In DAWs you see even higher band numbers now.
And then for 3), which is the issue at hand. The EQ on a PA mixer is, by definition, meant to shape sound, correct for little flaws in the recorded sound and mostly to provide for space in the mix. Especially on the smaller mixers that have been brought forward as a good solution, the EQ is pretty much the same as on your DJ mixer. But, where on a DJ mixer/controller it is exactly the right tool for the job, it is unsuitable to compensate for room acoustics.

Short example. The mid EQ on a PA mixer is very broad bandwidth, meaning that if the center frequency is say 2 KHz and you turn it up or down, it will affect frequencies from as low as 512Hz or 1 KHz up to as high as 8KHz. So if the room has a nasty bug at 4KHz and you would want to bring that down, You would dial it down til the bug is gone. At that point, a whole lot of frequencies that were just fine have been lowered too, most noticeable 2KHz which has gone down more than the 4KHz. So, using the EQ on a PA (bar some exceptions) to compensate for the room is virtually impossible. I dare state that using it in that way inevitably leads to a total sound that is worse than the original bug you tried to fix with it.

I am not very good at drawing, but since a picture says more than a thousand words, I gave it a shot. This is a highly simplified rendition, but it should serve to show the point I am trying to make.

What you see is a frequency chart. In (non-existing) ideal circumstances, if a room is totally flat, you would measure 0dB in all frequencies if you send pink noise through your speakers.

In the top graph, you see our example room, with a nasty bug @ 4000Hz or 4KHz. At that particular frequency, for whatever reason, this room sounds +6dB louder. The rest is flat (for clarification purposes).

The second graph displays what happens to the frequencies if you turn down the mid EQ with a 2KHz centre frequency to the point where there is a -6dB dip @ 4KHz.

In the third graph I have overlayed the frequency curve from the EQ setting over the room graph. The result is that the 4KHz spike is gone. The very bad news is that you have done significant damage to the sound between 1KHz and 4Khz, with a -12dB dip!!! at 2KHz.

The 4th graph shows you what a graphic 1/3 octave equalizer could do (again, simplified for clarification). It has about the same graph but inverted AND you can turn it down at the 4KHz, leaving all other frequencies untouched. With this kind of EQ it is (theoretically) possible to get a room totally neutral/flat.

If you now compare the first and third graphs, you can clearly see that a relative precise problem, a +6B spike @ 4KHz, by using an unsuited EQ has turned into a broad problem. Ask yourself, would you rather have the spike @ 4KHz and have all other frequencies sound fine? Or do you want no spike and accept that a big part of your sound has suffered for it?

Please don’t attack me about EQ curves being a bit more narrow on fixed EQs and all kinds of technical details. I know! But I wanted to make a visible point so that those not in the know get a basic understanding how fixing one thing can lead to (bigger) trouble elsewhere and why you need the right tools trying to tackle a problem

Which draws me to the following conclusion for DJs that use a PA (rented or their own) in an unknown venue:

• Unless you have the skills, the knowledge, the practice and the tools to do it, stay away from messing with the room acoustics. Assuming you have a decent to good sounding PA (neutral that is), trust me that it will sound best untouched.

An important thing to remember here is the expectation of the crowd. I think I mentioned the medieval cellars in my home town Utrecht before. It is (even with the right gear) not possible to get the sound right there. However, the people that come there expect it to sound like you are playing in a medieval cellar, so they are not disappointed if the sound is not like in a theater or rockpodium.

Same with 19” stuff, now my mobile setup I have a “quarter rack” with amps, EQ and 19” top loaded PA mixer… This stuff is nearly perfect, but would blow any newbie out of their socks budget wise and technically.

Agreement again. 19″ outboard racks can be very impressive and overwhelming in all their glorious buttons and lights extremes. So going for a more “familiar” look of a PA mixer seems a good plan.
As I have explained before, the extra EQ I think should not be used, so can be left out of the equation.
PA mixer are primarily made to handle mono instrument channels and most channels are geared for microphone usage. Microphones need preamps. Sound automatically goes through the preamps when you use the XLR connectors. I have seen DJs with mixers with XLR outputs stick them straight into the mic inputs of a PA mixer and then wonder why the heck they have to keep their master output almost closed and the gain on the PA mixer all the way down to prevent from redlining. And microphone preamps do color the sound (a bit, but still. Some more than others) and can introduce artifacts into your sound, including extra noise. Thus you need to use the 1/4 jack connectors, this is the line in for the channel and passes the mic preamp. On many PA mixer there might be an insert 1/4 jack as well. This does something completely different, but if you stick your jack in it, be sure that you don’t get sound or that it comes into the sound chain in the wrong place. This means a lot of things can go wrong just hooking up your DJ gear to a PA mixer if you don’t know what you are doing!

Finally, to control, for example, 3 stereo source (2 DJ setups, a backup/intermission iPod) and 1 extra microphone (wireless for the MC of the evening for example), you already need a 7 channel mixer which doesn’t exist, so 8-channel bare minimum. And you have to worry about two faders per stereo hookup.
That is why I suggested a DJ mixer. You can find a simple 4-channel DJ mixer that can take line inputs on all 4 channels and still has an input for one or two microphones for very little money. Don’t touch the EQ on it (like with the PA mixer), but one fader per stereo input, RCA connectors that can only take the line level output from your DJ setup and VERY familiar for a DJ. If you can use a controller, you can use a DJ mixer and there is nothing on there to confuse you.

In closing, an alternative is using a line mixer. Line mixers have 4,6 or 8 inputs (typically) for -as the word suggests- line inputs. The good news is that it utilises BALANCED 1/4 jack inputs. So from your controller/mixer XLR or balanced jack into the line mixer without having to worry about hums, noises and loss of signal.

On the front simple rotary buttons for volume. Either a volume and pan (left/right balance) button or a L and a R volume.
Some have on/off push buttons or switches on the front too. Usually they will have one or two mic inputs also.
And they don’t have EQs and mic preamps (on the stereo channels) to worry about.

300-400 euro should get you a good one that will serve your purpose for a long long time.

It’s become quite an explanation, but I hope I have made my opinion clear. It is up to everyone to decide for themselves what they want of course. Wish everybody good luck with the choices they make and I hope this information can help a little in making those choices.

Greetinx,
C.

[Terry_42]

Holy mother that was a wall of text to read. 😉 Nice writeup.

I think we are pretty much on the same page. I agree that a PA mixers 3 bander is usually “not enough” if you want to do real acoustic shaping for a specific venue.
However where I still think it is enough is the simple 2 things that usually happen in for example a wedding situation:

1. You have a pretty “bald” room that gives you too much deflection in highs.
Now of course it would be better to isolate specific frequencies that are the cause and eliminate only those, for a newbie simply tuning down the highs a little and re-tuning the mids so it still sounds OKish is most of the time “not perfect” but the 80% enough that all the people at the wedding will still have a good time.

2. Help my bass is getting eaten by the room.
While again this is actually usually to an error in the mid frequencies and can be effectively eliminated by EQing out that frequencies a bit, it can be solved by simply turning up the bass EQ on the PA mixer just a little and compensating the mids and highs. Again only a 60-80% solution, but it will do in most cases and by far better than doing nothing.

I think we agree on most things, the only difference is that for some cases I think 80% is enough if you do not have the cash or are not yet ready. As a grafic EQ in the hands of the wrong person can make things A LOT worse than the above shortcuts.

However excellent discussion, I love such brainstorming things on the open forum. It keeps me and I guess the readers open minded to the ends that “there is no final answer, and after reading such a guide you have to get experience under your fingernails yourself” and you bring up very valid points for striving towards 100% as fast as you can. So keep going Chuck 😉

[DJ Vintage]

Thanks.

I understand your point about the 80%. I have to say that with the current quality of PA speakers I find that un-EQ-ed fits my definition of “80%” these days. I’ll admit that I don’t even take any EQ with me to mobile DJ gigs anymore. Either the room is more or less ok and the venue will suit the expectations of the guests or it stinks acoustically and then simple solutions won’t help (enough). I guess I chalk it up to the “venue character” now :-p.

When you soundcheck in a “bald” room when it is empty, I find that usually the influx of the audience dampens that sufficiently. So I tend not to worry if an empty room is a little harsh. Add to that the fact that most people over 30 will have a drop of in high frequency hearing increasing with age … :).

Some rooms can be real bass-traps indeed. I usually end up turning up the bass on my DJ mixer channels and just remember that “zero” that day is +3dB or so.

I received NO complaints all of last year and have played from the medieval cellar to outdoor noisy markets and from a church to a wooden pancake hut :). And I know it has been less than desirable on a few occasions (and also that short of putting an extra hour in and bringing in extra gear I could not have fixed those problems). Point being that most people don’t really care unless it is really really horrible.

That money is an issue I understand too. I

My point is that rather than spend a little money on something that might not be the right tool or do damage in the wrong hands, it is better accept the room as is and just go with what you got :).

As I said on the blog in one of my comments: “If only there were simple answers” !

Greetinx,
C.

[donnyboybelfast@yahoo.co.uk]

About the recommendation of 5 W per person wedding, 10 w per person raving, is this overall RMS – so if I have 2 300w speakers for top/mid and 2 300w Subs/bass bins then I could count as 1200w – this is RMS – so could do for 120 raving or 240 wedding? Thanks again, cheers, Don

[Terry_42]

For a rough calculation you can count them together (RMS) and your assumption on the end is OKish.
But take into consideration that on some weddings the venue can be quite large and you would need to compensate with more power. So be sure to not only know how many people attend, but also for how many people max the venue is suited.
If there are less people in the venue (say size is 200 max, but the wedding has 100 attendees) then a good rough estimate is to cut the needed power for the “empty seats” in half.
I hope you know where I am getting at…

[DJ Vintage]

Effectively it is easiest to take total power. What the subs do is give the top ends more power for mid/high freqs, so yeah. Unless you are really low-heavy (say 4x 18″ @ 800W/ea with only 2 12″ top ends @ 600W/ea). You’d have 4*800=3200 plus 2*600=1200 for a total of 5000W. According to the above rule of thumb good for a 1000 person wedding. Not gonna happen! In this case you’ll have a way too bass-heavy sound (although you may just be into that), but your top ends will fall short of delivering sufficient sound levels at their frequencies (low mids to high) for that many people.

Something else to take into account is the speaker effiency. For example, let’s say you have a 2.000W RMS system powering speakers with a rated SPL of say 98dB. This means that at 1 metre from the speaker, putting in 1W RMS you will measure a sound level of 96dB.

The way the dB scale works, to get a 3dB increase in sound pressure you have to DOUBLE the amount of power. In order to get from 96 to 99dB, you’d go from 1 to 2W, to 102dB to 4W and so on, see table below.

You can understand that if you get speakers that have a rated SPL of 99dB, this equals DOUBLING the amp power with the less efficient speakers! So, RMS power in Watts is only part of the equation, speaker efficiency is just as important.

You’ll look at the table and say: “wow! I can get almost 130dB of sound level with a 2KW system … way kewl!”. Unfortunately, you are about to be cheated out of your happiness. You’ll also notice the massive amounts of power it will take as sound levels increase to keep upping it. Something else is that although a 3dB increase in sound pressure requires double the amp power, to our ears, it takes 10dB increase to feel like it is twice as loud. So, if you want something to sound twice as loud, you have to increase the power with at least a factor 8.x!). In the example, to go to twice as loud would take a massive 16.000+W increase.

The maximum sound level (here in Holland) is 103dB at 10 meters from the speakers.
This is at 10 meters though, not at the 1 meter we measured before. Sound loses power as it travels through the air. And it does so at a rate of -6dB for every doubling of the distance. In order to achieve maximum level at 10m you would have to start with 128-129dB at 1m. That is just about the max the 96dB speakers can achieve with a 2KW amp!

There are some very intelligent people and some very sophisticated (software) tools to help PA engineers calculate the necessary sound levels and the matching amounts of speakers, amp power and their positioning. Now, as DJ’s we don’t have to worry about that. But I do think that it is a good idea to know just a little about the background.

Greetinx,
C.

Attached files

SPL.pdf (272.8 KB)

[Terry_42]

Thanks Chuck, yes understanding that dB is not a linear scale is a very good advise and it should go into a revised version of the guide.
Manufacturers love to disguise the SPL charts, why I left them out. If you buy from a major brand (Yamaha, HK, JBL, db, Mackie,…) their SPLs from their main line and budget lines are almost at par.
So guys please take a look at one of the major brands and if you choose to go with a less known or known as “cheap” brand, then simply compare the main line of the major brand to the brand in question.
Again: If it sounds to good to be true, it probably is…. there are no miracles in sound. And the worst thing that can happen to you (and happended to me 20 years ago) is buy your first PA and it sounds OK in the shop, then crank it up at the party and the mid frequencies have gone out the window…. and you are left to play bass heavy techno with female voices only…

[fassool]

Hey all, i need speakers for my room 6meters wide – 7 meters long- 3 meters Height but i dont know what to go with Qsc K10 or Ev Zxa1 or Big studio monitor Adam A77 with or without Sub & how many Speakers ?
Appericate ur help .

[DJ Vintage]

Howdy,

Just for practicing reasons, or to potentially use as small PA or monitors playing outside?

I personally am no big fan of true studio monitor speakers when practicing, but if you are producing (too) they might just be the ticket.

So, tell us a little bit more about your plans.

Greetinx,
C.

[Terry_42]

That was the final part of the PA beginners guide, however I am already working on the next guide to enlighten you on another topic 😉
Keep discussing and of course I will answer any questions as good as I can.

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