Noob Questions!

[oligoon]

Ok guys - I'm fairly new to sound engineering - so go easy on me ;)

 

I've just done my first gig using my new PA set up at the local schools battle of the bands. The music was quite diverse from Blink 182 and Foo Fighters stylee to acoustic guitar/singer.

 

My rig consists of:-

 

2 off PA Speakers - home built using each with 15" Precision devices low range speakers (8 ohm) and 2 CTS 1188 Piezo's

1 off Chevin A1000 Amp

1 off BSS FCS 966 31 channel graphic

3 off SM58 for vocal

3 off SM57 for instruments

 

This was hooked together using the schools desk (Allen & Heath 25 channel desk) & I used the schools powered mixer & speakers for foldback.

 

The speakers were designed using WinISD are are good from about 48hz up. I went for the piezo's for simplicity (no crossover), low weight, low(ish) cost, accepting that sound quality would not be hifi :unsure: .

 

Generally I was pleased with the way that the system performed, with people saying that it sounded better than normal :P . And I had no real feedback issues with careful monitor/mic placement and taking out offending frequencies on the graphic.

 

However there were a few issues:-

 

1. the overall sound was a bit muddy most of the time.

2. on the quiet acoustic guitar/female vox the sound was thin, coarse and strained.

3. for the loud foo fighters stylee bands where the vocalist was shouting into the mic pushing the system into clip (shown on the graphic - amp was ok).

 

My questions are these:-

1. Using the filters on the desk restrict each input channel to a frequency "slot" to clean up the overall sound (issue 1). Is this correct? Or is there a better way to do it?

2. Use a separate box mounting compression drivers (and appropriate crossover - have a BSS FDS360 and will bi amp) instead of the piezo tweeters to improve sound quality to help with issue 2? Should I use a high quality condeser mic for "quiet" music rather than the SM58?

3. I assume a compressor will help with issue 3? However where do you compress - on the way into the desk or on the desk output? Any suggestions on compressors? Is a gate just a compressor with a hard cut off at the thresh hold?

4. Reverb - is this done on the way into the desk or on the output? Again any suggestions on reverb units - there seems to be a massive difference in the price of them!

 

Any other suggestions would be most helpful.

 

Thanks for your time.

[Chris Adam]

Sound like your system is just a bit too small for what you are expecting and wanting to do with it. Young bands tend to turn things up to 11 straight away meaning you have to push your desk into the red - instantly a problem. There's no way you can get your HF over a screaming guitar / bass / drums combo.

Without knowing the products you've mentioned I couldn't comment on the quality you'd expect from the system, but so long as you've got decent headroom, you should be able to get decent clarity on the vocals.

As for the acoustic stuff, I'd always DI an acoustic if it has the outputs or use a condenser if not, but I'd also put tis down to inexperienced mic technique on the part of the acts. Nobody has shown them how to sing into a mic properly or how close a mic needs to be to the guitar. A little bit of kind education goes a long way with younger players. (just to clarify - the SM58 is totally fine for vocals, if not perfect. it's your safest bet)

 

For reverb, I can only assume that you dont want to put this across the whole mix so this is how you would do it from a desk:

1 x aux send / fx send goes to Input on reverb unit

output of FX unit come back into input channel on desk (or FX return if short of channels).

This way you can affect the EQ of the reverb on the way back into the desk helping with feedback if used for vocals. For school stuff you would easily get away with the Behringer / samson / insert cheaper brand name here stuff as it all does a purpose and does it fairly well. My preferneces are TC Electronics M1XL, Yamaha SPX990 or any Lexicon, but you'll pay for these. Ex rental gear from pro companies is maybe the best way to go if you want something great for cheap.

 

Also, I'm not meaning any offense here, but it sounds like you could be doing with a book on live sound too. This will explain the ins and outs of compressors, gates, reverbs, graphics and system set up. I got a cracker when I started called basic live sound. It was a wee pocket sized thing from borders books and was great just to have in my bag at gigs. (many a bluff done with that!!) A good bet is The LSI online book shop. They have hundreds to chose from. Might be a good Topic to start - which books.

[MarkPAman]

2 off PA Speakers - home built using each with 15" Precision devices low range speakers (8 ohm) and 2 CTS 1188 Piezo's

 

This is only a guess, but there may well be a fair sized dip in the speaker's response above what the 15" drivers can reproduce & below the Piezos. This would account for problems 1 & 2.

[weatherhead]

Hi, just putting in my twopence...

As you mention, the filters built into many desks (mainly HPF on the mic channels) are often very useful, but there is normally no reason to indiscriminately activate them on all channels... otherwise they wouldn't put switches on them would they?

 

Use your HPF to get rid of annoying rumbles from kick drums into your vocal mics, or rumblings from improperly secured mic hardware. Always use your ears! Your real "tone -shaping" should be done at source to a certain extent (although less so in a live situation than in studio), and you should not be afraid to use your desk channel EQ to sort problems out! You are NOT trying to recreate the exact sound on the bands' recordings, you're trying to make it enjoyable to the audience. Since as has been mentioned you're probably lacking mid range clarity in your speakers, I would be probably applying a boost to mids on vocals and probably gently cutting other things out, and adding more top end in general. This generally can help with clarity in some situations. Always try to cut EQ rather than boost it though, the more boosts you do the more feedback will become a problem. In order to tailor the system to the room (if you're not familiar with the room) I would recommend playing through some commercial material and adjusting your master GEQ to a suitable starting point.

 

Your choice of mics sounds fine for a live situation - I've never been convinced by any of these "live condensor" type models - there just seems a lot to go wrong to me, for very little gain in quality in most live systems short of really high end level.

 

As for compression, I generally like to have at least one genera; master dynamics unit in a live situation, which I can throw accross the mix insert to use as a master limiter. Also useful to set up as a gate to get rid of any inter song low level hiss. I also recomend compressing vocals and possibly bass/guitar at the desk end with channel compressors (if available). This can often help get more out of a quiet vocalist, and, as you say, can be used to help with the clipping problems etc. Just make sure you've thoroughly played with your dynamics unit on all types of material and you know how to use the compressor. Done badly, at best it will be sitting there with some flashing lights, at worst you'll make everything sound very 80's!

 

Reverb - If you've only got one to play with, set up as a send is undoubtedly the way to go. Just helps to gel things together and can be again very helpful with vocals, especially quiet ones. I really like some of the budget digital models around at the moment, and I generally go for a plate setting. Of course, you should experiment during the sound check, though having done quite a bit of these type of concerts myself, I realise also that soundchecks are often either non-existant or at best very pressured.

[oligoon]

Thanks for the replies. I will try to answer in order - but it'll probably end up as a brain dump - sorry :)

 

The 15" drivers (PDN.15SB40) start to dip at around 2kHz and then run out at over 4kHz whilst the piezos are good to below 1kHz - so there is plenty of cross over frequency - maybe too much. Will the over reinforcement of the 800Hz to 4k cause issues?

 

Why are subs only driven up to 250Hz as they will deliver useful sound above this? Is it to ensure that the sub amp is able to concentrate all its power on the low frequencies?

 

I will certainly invest in a book - the basic live sound book is on amazon and should be winging its way to me!

 

I've got a pair of 18's (PD186) in their boxes ready to go into cabs & I will invest in some decent compression drivers as well (probably Eminence PSD2002). I'll look for a decent 2nd hand reverb unit & compressor and amp to drive things on fleabay.

 

Just dont tell the missus about all the extra loot I need to spend :)

 

Anyone have a good suggestion for monitor speakers? I was thinking of a 8" driver + tweeter as you don't real bass for monitors. How much power do you need for monitors? With a reasonable efficiency driver even 25W will give nearly 110dB @ 1m.

 

Agree that the sound checks were pretty chaotic - fortunately I could setup during the day and then spend the time from 3.30 when the school finished to the 7.30 start doing them. Not so good was that most bands went home and then appeared at 6.30 expecting a full sound check. For those who I had a bit of time I did try to teach them how to use a mic.

 

Thanks again for your help.

[Rob_Beech]

I find that with most of the instruments on stage, there is very little useable content within the area that the channels HPF cuts out. I must admit I do have a tendency to have HPFs on unless I need them switched off for channels with useable LF Content (some drums, bass, some guitars (dependant upon style of playing), keyboards, )basically whatever requires it to be switched off.

 

And you don't have to chose at the start of the gig either. The band might play a song that requires a slight change in the HPF status on a couple of channels. Change them. Then change them back if necessary. The same goes for eq, compression, gates, anything else. These are there to be used, but they are not there to be set during the sound check and left. Often you'll be able to do that, but don't be afraid to alter things during the show to suit the current song or part of song.

 

I would also question whether boosting the mid range is going to help much. It appears you are dealing with a pair of drivers that don't like to reproduce these frequencies. (too high for the 15 too low for the HF driver). Boosting these frequencies is going to make their feeble attempt to reproduce them more prominent.

 

Yes, a different HF driver may well be a good idea, but if you are building these, look into something inbetween aswell (maybe an 8, or a 6.5). This of course would require more work on the crossover / amp channel side of things.

 

 

Rob

[jamesperrett]

The 15" drivers (PDN.15SB40) start to dip at around 2kHz and then run out at over 4kHz whilst the piezos are good to below 1kHz - so there is plenty of cross over frequency - maybe too much. Will the over reinforcement of the 800Hz to 4k cause issues?

 

Are you sure about the spec for the piezos? 1kHz seems very low unless it is actually a midrange driver. Chances are you are asking the drivers to work outside the range that they are happy with so, while you'll get some output at that frequency, it may not be as useful as you expect. You may have cancellation issues between the two drivers due to phase shifts at the extremes of their frequency range.

 

Anyone have a good suggestion for monitor speakers? I was thinking of a 8" driver + tweeter as you don't real bass for monitors. How much power do you need for monitors? With a reasonable efficiency driver even 25W will give nearly 110dB @ 1m.

 

I don't want to be rude - but I think you really need to gain a little more real world experience. I know someone who thought in a similar way to you when he first started building his own PA gear. He soon realised that the first set of gear that he built just wasn't up to the job and that there is a reason why manufacturers do what they do. Unless you can site the monitors close to the player's ears, 10" speakers are an absolute minimum and 12" are possibly better in my opinion.

 

Once you've used decent sized monitors with plenty of power in reserve you won't want to go back to an inadequate system like the one you propose. You will certainly need bass in some of the monitors on a big stage - the drummer will usually want some kick drum in the monitor and a band will play more tightly if they can hear rhythmic instruments through the monitors rather than rely on the longer path through the air.

 

Cheers

 

James.

[weatherhead]

As a bassist, keyboard player and drummer, I argue with the fact that you don't need bass in a monitor system.

In most small venues you don't GET any, but it's important not to confuse these two points!

 

EDIT:spag

[gnomatron]

You should probably look into getting your own desk seeing as you've spent all that time making your own PA speakers and such.

 

Maybe your piezo drivers can produce 1Khz, but have you had a look at the response curve? They might be capable of reproducing those frequences, but not necessarily very well.

[oligoon]

guys - thanks again for the comments -

 

the basic live sound book has arrived and I'll try to give a good read this weekend!

 

I'm as sure as I can be (without testing them) that the CTS1188 are good to below 1kHz. Every reference on the web states this - although I have yet to find a proper frequency response chart for one :)

 

on the speaker size for monitors issue - taking your comments about needing to hear bass for timing etc and having looked again at WinISD the 8" speakers dont have enough Xmax to be able to drive much in the way of bass. damn gonna have to give myself more back pain with 10" monitors! what sort of SPL do you think you need for monitors? 110 should be enough at the 2m listening range. interestingly hearing damage due to short term exposure starts to occur at 120dB.

 

I was thinking of getting my own desk as the skool one is too big for my needs. Are the Heath & Allen ones good? I would like to stay with them as the it would be easier to transfer between the 2 desks.

[paulears]

Stage monitors don't exist just for volume - to be honest, I have no idea what the spl of my monitors is at any distance? I've got a few different types, some 12" with horn (NOT piezos - they are really well know for being, well, horrid - piercing HF, wierd sound and not something that sounds smooth), I've some 2 x 12" with central horn, and some 15" versions too. The thing to remember is what monitors are being used for. Let's use the bass player as an example. If he's standing in front of his kit, then he wants, assuming his amp is loud enough, other members of the band that he needs for timing - so maybe keys, certainly drums. And the essential timing comes from kick and snare. So if he's blasting away, the kick needs to be easily heard over the sound of his own playing. The drummer will want the bass through his, as drums and bass kind of lock together in the rhythm dept. So I'd give both of these a 15" drivered monitor. The vocalist may not want or need the bass end, so smaller drivers will work. 12" monitors are very convenient - that's why they are popular. 8" monitors I'd not go near - certainly not go near if I wanted bass in any quality or quantity!

[oligoon]

link to the CTS application datasheet for the piezo drivers.

 

http://www.ctscorp.com/components/Datashee...cation_Note.pdf

 

sadly it does not have the frequency reponse chart for the 1188 - but does for a smaller piezo (the super horn) which rolls off around 4kHz.

 

interestingly it states that at the turn on frequencies the speaker may sound harsh. This combined with the off axis effects of >2kHz sounds from the 15"'s probably accouted for much of my crappy sound. Hmmm will have to think about this a bit more!

 

Some thing else that has been bugging me is :- is there any point keeping left and right speakers on separate channels. What I mean by this is that you mix in mono - the only time in a gig you'd want stereo is if you are playing music before gig etc. Any comments?

[Rich]

Good on you for experimenting with loudspeaker construction! If you can design, model and build your own speakers I think you develop can a much better understanding of brand name products and how to set them up.

 

I'd look at your top end and try to replace the peizos with some compression drivers. In your shoes I'd be looking at a 1.4" or 2" to allow you to use a relatively low crossover point of let's say 1.2KHz. Your 15s will start do display poor dispersion much above this frequency. If you're on a budget look at the P-Audio drivers, and if you can afford it look into B&C's and Beyma's. Beyma produce a particularly good 1.4" neo which is quite expensive, however it's ferrite brother looks very good value for money. All of these products are available from www.proaudioparts.co.uk. 18sound make a nice 1.4" exit horn which I've heard raved about. It's just a bit smaller than a 15" driver though so quite big, I think Noise Control Audio are distributors for them.

 

Use an LMS to crossover your boxes. For the money it is impossible to beat the Behringer Ultradrive.

 

With these changes your boxes will sound much better, and a pair of 186's underneath them will give you a decent rig.

 

Rich

[jamesperrett]

what sort of SPL do you think you need for monitors? 110 should be enough at the 2m listening range. interestingly hearing damage due to short term exposure starts to occur at 120dB.

 

Performers expect the monitors to be louder than the onstage backline. Given that a loud drummer can induce hearing damage with no amplification, your monitors are going to have to cope with that kind of level - especially if the other performers are wearing hearing protection to cope with that loud drummer!

 

The speakers that I use for monitors have a maximum SPL of 117dB which is fine for acoustic bands that play at a sensible level but they struggle with a blues rock band with a loud guitarist.

 

Cheers

 

James.

[weatherhead]

You mix in mono??? why, exactly?

There's no reason not to set up at least a basic stereo field even when live mixing, in fact this can help with separation when all the band members have bazillions of watts of gear and are all shouting "POWAAA" (think jeremy clarkson).

 

You should also be very very careful when wiring speakers into the same amplifier channel about impedance issues etc. Of course if you are just wanting to wire your mixer output into both sides of your power amp, there's no problem.

 

Also, if you do decide to go mono and dont have a dedicated mono output (as on for example soundcraft live desks), then make sure all your channels are panned/balanced hard to the side you are using. Otherwise, depending on the panning law you could be losing as much as 3db of clean level per channel.