Live Sound Discussion

NON-DJ chat, the title kinda says it, LOL. I have no problems with whatever is discussed here, as long as it abides by the forum rules. If the discussion is relevant to DJs (some PA topics, like EQ-ing a room for example) that would benefit DJs as well, I can even see how it would fit into the hardware section. But let’s keep it here for now.

On topic: I am a certified live sound/studio engineer and have quite a bit of experience on the “other” side of the street. So, yes, it’s a topic I am interested in.

Great!

so let me try to kick-off this thread with a technical question.

i’ve got 4 passive PA speakers of each 240W programm @8 Ohm impedance.
Lets say i want to connect 2 of them straight into an amp and the other 2 in parallel using out1 to in3 / out2 to in4 to create a square area.
I understand that the impedance reduces to 4 Ohm per speaker.
I am looking for a compatible amp for these speakers.
So here we go:

what should i look for? Slightly over powered, twice the power of the 4 speaker (2kW)?
do i need to take the impedance in acount as well if i only want to connect 2 speakers (in certain circumstances)?

I talked to some suppliers, but get different recommendations…so, would like to know your opinion.

regards,

King of Snake

Wait… did an off-topic thread just get hijacked by an on-topic conversation? 😉

Death right Deathy 🙂

regards,

King of Snake

Never been a real big fan of Peavey as front of house/PA. Their backend stuff obviously is great, no question. PA’s are very personal in a way too and qualitywise they make good stuff.

As far as those speakers go. Program power usually means the same as music power or any other fancy name they stick on it. Marketing terms to let your speakers seem to be twice as “strong” as they really are. Good old Jamo was the worst, they had a term (I forget what it was) that actually came to 3 or 4 times the RMS power.

So, in reality I would assume your speakers to be 120W RMS @ 8Ohm (let us know make/model and we can easily figure that out usually).

You are saying something about using both channels of a (stereo/double mono) amp (because of speaker placement), which has me somewhat confused. Many speakers will have two (SpeakOn or XLR) connectors that are wired in parallel. Meaning you can run your first cable from amp to first speaker, then plug in second cable to first speaker and then out to second speaker. If the speakers don’t have a second connector or have those banana plug connectors or something else horribly “1980s” and not suited for live sound, my advice would be to adapt the speakers yourself. It’s an easy job that you can do/have done. My advice would be to replace whatever connector they have with SpeakOn and put in two in parallel. SpeakOn 2 will do (foregoing the confusion of having 4 leads in one connector). Just replace one connector, make a second hole, drop in the two SpeakOns, solder the speaker and a short piece of heavy-gauge wire to the first connector (doesn’t matter which) and the short piece goes in parallel to the second SpeakOn and is soldered there. If you have no clue what I am talking about, let someone else do it. This will make it possible to use pro-quality cable and connectors and easily do the setup you want to create. Be sure to do all 4 speakers, so you don’t have to worry about “which goes where”. Final tip, be sure to connect the leads in phase (plus to plus pole, minus to minus) otherwise you might get a very unwanted side-effect of sounds cancelling each other out.

Obviously Terry’s calculations and formula’s are right. Just make sure what RMS power you are working with. It’s the only standardized power rating.

If you normally use two parallel speakers per channel, you will get double the power from your amp as Terry said, because the impedance will be half (4Ohm as opposed to 8Ohm). Take away one speaker and you are left with an 8Ohm impedance and you’ll just get half the power. It’s not switching or anything, so yes, effectively it is “done” automatically. In reality nothing is done. Just when you double the resistance you get half the power.

You’ll have to watch two things on an amp:
1) max power rating. It needs to be high enough (per channel) to power two parallel speakers (2x 120W RMS as I am assuming)
2) minimum resistance (impedance) of 4Ohm (some amps still support only 8Ohm, many modern amps can handle 2Ohm loads)

Example 1:
You find an amp that has a power rating of 480W into 2 Ohm/240W into 4Ohm and 120W into 8Ohm. This amp would suit your needs. When you hook up two in parallel per channel you get 240W, hook up only one per side you get 120W

Example 2
You find an amp that delivers 120W into 8Ohm, with a minimum load of 8 Ohm. You can NOT use this amp to power two parallel speakers per channel! The load of 4 Ohm would be half of what the amp can handle and you’d blow the amp.

On the discussion of amp power vs speaker capacity, I am afraid I have to add to the confusing, I don’t agree with Terry.

You see every amp distorts, the distortion gets bigger towards the edge of the power window. Distortion often means the normally sine wave of the signal becomes flattened, topped off (indeed like clipping). If you have an amp that can deliver exactly the amount of power your speakers can handle, then you will be very tempted to run your amps at max power, meaning with a high(er) chance of sending a somewhat distorted signal to your speakers. Especially tweeters (high-freq drivers) are sensitive to this. So, it’s not impossible that you can blow your tweeters with an amp that is the same rated power as your speakers. It’s also the reason you should never use amps UNDERRATED in power to your speakers. The last is a guarantee for blown tweeters.

With high quality, modern, digital amps, the chances of things going wrong are smaller, but still exist.

I like to use a car metaphore.

Let’s say you are going to drive regularly on a highway where you can do 120kmh speed. You need to get a car to drive this bit of road. Would you get a car that can do 120kmh at full speed, meaning you will be driving at full speed ALL the time? Or would you get a car that does 150kmh and drive it at 80% of full speed? Less rpm, less wear, less heat and some overhead. And no straining the engine to work at the edge of it’s power.

As you clearly stated, there is a lot of discussion. And it’s true that the quality of all the components in the signal chain play a role in the decision. If you buy top end gear from one manufacturer (amp and speakers) that is tuned to each other, you should be good, for example.

I don’t know where twice the amp power comes from, that seems overkill. But I usually keep a 20-25% margin and just control my master output (just set the master volume knobs on the amp to -20% and run a clean non-distorted 0dB signal into it from mixer or controller).

This whole discussion shows, once again, that unless you are well versed in matters of FoH/PA issues, the way to go without worries is to use active speakers. Need 10? Just keep daisy-chaining without worrying about amp power or load.

Hope that helps some.

Chuck mentioned EQing a room, would you guys suggest doing so with your ears and an EQ, or would you consider something like a DBX Drive Rack and RTA microphone?

Yep, for one-off gigs, your ears should be good enough. It pays to invest in taking a “listening” course. This will teach you to recognize the center frequencies of each octave (10 in audible range). So when you listen to a room, you’ll be able to tell what frequency is “off”. You then go and use a good multiband full-parametric EQ or 31-band Graphic EQ and correct it. 99% of the time this means you will be CUTTING frequencies. Boosting is something that hardly ever happens. There is a whole theory behind this that has to do with psycho-acoustics but that falls outside the scope of this forum, thread and topic.
It’s funny to see people spending zillions on the most expensive measuring equipment who can’t be bothered to spend some time and a bit of money on teaching themselves what they are listening to.

Which is a nice bridge to RTAs, Feedback destroyers and such. I have an RTA on my smartphone (a paid app!) that I’ll use on occasion if I feel something is iffy but I can’t put my finger on it. Run noise through the speakers and look at the RTA to get an idea. Again, only valuable if you know what you are doing. White or pink noise choice for example.
My phone RTA is good enough for those single gigs (bands, blabla). If you ever do a larger festival or concert, you won’t get near the PA design. This is today a specialisation for sound engineers that use high tech simulation and calculation software to determine what goes where.

Feedback destroyers in my mind are a big no-no. More trouble than solution. You EQ your monitors well, feedback should not happen. Keep an eye on the stage that not some idiot singer goes jump of the stage and stand in front of the main FOH stack and you’ll be good to go. There is actually a neat little app (Sonoma Feedback Detector) that can help you in determining what frequencies to kill on the monitor channels.

With the exception of a few minor things (they have good headphone amps, if you need to run multiple headphones to a practice room/studio for example) I stay away from anything with the Behringer name on it. dbx is about the best budget solution that I’d trust, but even then, no feedback destroyers. Be careful there’s is a db technologies out there too, it’s not the same gear!

Does anyone have experience with digital mixers?

I do. Personal taste, budget and what you actually need are important issues. I can fill a day’s seminar on picking the right digital mixer. If you need lots of channels and you don’t want to spend the cash, then the Behringer is an ok choice. But frankly, Behringer is NOT a brand you will find any serious sound engineer using. It’s great for a no-budget band that wants their own gear for example, but in all my years in live sound I have never seen a single pro engineer with a B-table in front of him. Now we don’t all need, want, can afford Digico tables (which you have to reset 3 times a night too!), but between B and D there is a world to be explored.
IF you don’t need to ride the faders a whole lot, I can seriously recommend the Mackie DL-series iPad mixers. I have the DL1608 for a few years now (since it launched) and with the latest app upgrade it is great for anything up to 16 channels (ALL 16 channels have the venerable Onyx mic preamps!) and offers 6! Aux channels. Delay and Reverb on every channel as well as full parametric EQ and compression. Graphic and Parametric on all 8 output channels. Phantom power and a real small footprint. Hook up an airport express and take your iPad out to walk on stage to do monitor mixes or into the venue to listen and eq the mains. Give each artist the option of controlling his/her own monitor mix from a smartphone.

If you need something bigger (say 24 channel), there are two options I’d look at. One is the Presonus StudioLive. It looks very much like an analogue table and works like one. Easy to learn and easy to teach to someone else.
The problem with digital mixers is that they have a pretty steep learning curve and if you don’t use the table on a regular basis, you’ll never have that muscle memory to work with it comfortably. The old Yamaha series are a prime example. Dragons from a usability point of view.

Another table I have intimate knowledge of is the Roland m200i. It also utilizes an iPad as it’s touch screen interface, but this one has motorised faders and all kinds of goodies. It supports digital snakes and onboard connections, matrix outputs and lord knows what else. Still highly intuitive and the iPad is a great platform for using many of it’s extende features. I think it offers a lot of bang for the buck and still keeps it within a decent footprint (really you don’t want to carry a full 32-channel mixer around if you don’t need to).

Really the need for 32 inputs is hardly ever necessary. More auxes are way more important for example (especially with in-ear monitoring becoming more and more important). And if you are ready to regularly use 32-channel mixers because you actually do large enough events, forget about showing up with a Behringer table. You WILL not be taken seriously. Not saying it’s fair, but it is true.

My long term goal, 2-3 year timeframe, is to expand my PA system to be able to handle up to 500 people in large venues or outdoors.

Frankly, I say get a PA that’ll handle 200-300 people comfortably with high sound levels indoors and slightly less outdoors. For the rest, rent. There are so many factors in deciding the right combination of speakers for a PA/FOH solution.
Between my buddy and I we have 3 18″ subs, 8 12″ tops and 4 passive 12″ monitors with amps. But any party over 200-300 people we rent. That way we always get exactly the right set-up, we can shop (and do) between a number of rental companies that carry differing solutions and get a 15-20% discount on the gear. The customers pays full rental price, the rental company delivers the gear and picks it up and we make 15-20% for just setting it up and breaking it down.

To give you an example, the pricing of larger PA’s/FOH stacks goes up incrementally after a certain size. You can’t just keep adding more 12″ tops. At some point you want a lower number of enclosures. And those have to be exponentially stronger. To get +3dB volume gain you need DOUBLE the power. For +6db you need FOUR times the amp power. You can see how this adds up.

This weekend I am doing my yearly charity event in the Olympic Stadium in Amsterdam again (Deathy, come say hi!) on sunday afternoon. We will have with us a system comprised of only 4! tops (30x30x150 cm each, weighing a ton) and only TWO!!! subs (21″ active control 8kw music power!). Total of well over 8KW RMS and ridiculous amounts of peak power. These six speakers cost about 45-50 thousand euros with amps.

If you play larger venues you’ll need to start thinking about speaker arrays. Now you can no longer stick a speaker on a stand or put them on stage but you have to start flying them.

You get my drift. By the time you get to this point you don’t want to own everything you might need. You need to be the projectmanager and bring in the right people for the right job.

Hope that helps.