bi-amping question

[gbirdsall]

So thehighschool I graduated from is tossing me a bone and asking me to do an installin their gym.

Now I have done numerous live gigs and am building a decent resume for installsso I’m not walking in completely blind.

Here is the rough specs of the space

110'x60' with the ceiling at roughly 40' (haven't measured yet)

they currently have a horrible 360* speaker orb hanging in the center circa1972, is on its last legs and ready to go out.

My plan is to go with either the JBL (who I get at cost) the AE5212 series, orthe Yamaha IF2112 series (that i get at c+10) in two separate clusterssplitting the difference in the ceiling. At approximately 27' and 82'

in each of these clusters a 60/40 horn on each end and a 90/60 aft of that tocover the bleachers and a 90/90 in the center of each cluster to cover thefloor.

Now both of these cabinets are Bi-amp able or passive with a switch on the backto determine which. They both have a single 4NL connector on the back.

My question is how to Bi-amp these cabinets?

I assume when the switch is put into Bi-amp mode the second pair on the 4nlbecome active and the cross over is bypassed. But the HF is rated at 40w and60w respectively @ 8ohms. and the LF is rated at 300w on both cabinets.

I assume that to Bi-amp these I would run an amp rated at 40w or 60w @ 80hms,and then a separate amp at 300w and y the cable at the amp end to each amps output.

Is this the correct school of thought?

Also can anyone recomend an amp to suit this situation

 

[museav]

So thehighschool I graduated from is tossing me a bone and asking me to do an installin their gym.

Now I have done numerous live gigs and am building a decent resume for installsso I’m not walking in completely blind.

Are you a licensed Low Voltage Contractor (License Classifications - Contractors State License Board)? Do you have appropriate General Commercial Liability coverage? Are you a licensed business? What about Workers Comp coverage? Are you a certified rigger? If you have all of those properly covered that's great, if not then the way to build a decent resume for installs is to involve someone who is properly qualified and work with them.

Have you developed a Program or Needs Analysis for how the school plans to use the system and their expectations? It seems important to find out what is desired and expected so that you end up providing what the Client wants and expects.

How did you develop the solution you propose and have you considered how the room acoustics affect the system or whether acoustics should also be addressed in order to provide the desired results? 250lbs or so per array may not be that much of a load but have you had a Structural Engineer review if the existing structure will support them? Have you looked at the conduit and cabling paths and power available? Things like trying to run 8 to 16 cables where there used to be 1 or 2 or not having sufficient power for the amps proposed can bite you if you don't verify them first.

Assuming you mean the AM5212 (AE is the general series that includes both the AM and AC models) the nominal horn pattern options are 120x60, 100x100, 90x50, 60x60 and 60x40 with those also available in rotatable horn versions. So it looks like 100x100 and 90x50 are the closest to the 90x90 and 90x60 patterns you note. But why are you looking to bi-amp the speakers in this application? According to JBL's specs you potentially gain 1dB for the maximum LF output compared to running them full range while adding the need for a crossover and separate HF amp. It's a two-way box with a 12" woofer in a gym so that added cost might be difficult to justify.

 

[bishopthomas]

Sticking to your questions specifically... Biamping is fairly simple. You're sending one (processed) signal to each of the two components in the speaker. So you'll first need a way to process the signal. At it's basic level a crossover is what you need. I use Crown amps instead of QSC for the sole purpose of having the processor built in to the amp which saves on rack space, but you could use an external speaker processor if you desire. Sending the signal out of the amps depends on how the amp is set up. On most of the newer QSC and Crown amps you can send both signals through one NL4 cable. Channel two's output is internally routed to pins 2 on the Channel One NL4 connector. Otherwise you will need a patch panel (or adapter cable) to combine the two separate signals into one 4 conductor cable. So your signal flow would be:

Mixer to processor input
Processor Lows to Amp Channel One (or two depending on the speaker configuration)
Processor Highs to Amp Channel Two (or one depending on the speaker configuration)
Amp NL4 to speaker switched to biamp setting

Also, if those are RMS ratings I would suggest an amp that is capable of at least 1.5 times the speaker's handling, twice that would be even better. As far as amps I tend to go with QSC or Crown, depending on the purpose, so check out the web sites for applicable models. If you need processing you will need to go Crown, and for this purpose the XTI series would probably do the trick. You are limited with the amount of delay available on these amps, though, so if you're doing fills and such you'll want either an external processor (which you could go QSC at that point) or need to step up to the iTech series.

 

[museav]

I assume when the switch is put into Bi-amp mode the second pair on the 4nlbecome active and the cross over is bypassed. But the HF is rated at 40w and60w respectively @ 8ohms. and the LF is rated at 300w on both cabinets.

I assume that to Bi-amp these I would run an amp rated at 40w or 60w @ 80hms,and then a separate amp at 300w and y the cable at the amp end to each amps output.

The long term (100 hour) power rating of the AM5212 is 300W continuous, 600W program and 1,200W peak in passive full range mode. In Bi-amp mode the long term (100 hour) power rating of the low frequency driver in the AM5212 is 300W continuous, 600W program and 1,200W peak, the 2 hour rating for that same LF driver is 400W continuous, 800W program and 1,600W peak while the 2 hour power rating of the HF driver is 40W continuous, 80W program and 160W peak. The calculated peak output of the AM5212 is 127dBSPL@1m in full range passive mode with 128dBSPL@1m for the LF and 135dBSPL@1m for the HF.

That's a bunch of numbers but put those together and you can see where basing the amp solely on the speaker power rating may not always be the best approach. If you use the program power (2X the continuous rated power or 1/2 the peak power) of both drivers as a guideline then in bi-amp operation the LF would theoretically provide a 125dB output while with the HF driver would be at 130dB, despite the much lower power rating the HF driver's sensitivity is such that it does not have to be driven anywhere near as hard as the LF in order to have a balanced output. Basically, if you had a 600W-800W rated amp on the LF then you apparently might be able to have a 25W or so rated amp on the HF and still have a fairly flat response.

The 128dBSPL max for the LF driver in bi-amp mode and 127dBSPL max output for full range passive mode does not seem to gain you that much in terms of potential output which is also why I question the cost and complexity of bi-amping in this application. It seems like twice the wiring, more amps and more external processing for what might be a very minimal and quite possibly unnoticeable gain or improvement.

Selecting amplifiers for installs is somewhat different than selecting amps for touring or portable use as you typically have some more specific goals in mind, thus you usually back into the amp rating. You start with how loud you want or need to be at any listener, accounting for both average levels and peaks. Then use that to calculate the output that represents at the speaker. Add any extra desired headroom to that number and that defines the SPL level you require from the speaker. You then use the speaker sensitivity to determine how much power is needed to get that desired output, the speaker rating is used purely to verify that the speaker can reasonably handle the power required. One reason you do that is that in an install a speaker system not being loud enough or being more than is required are something you will have to live with so you want to be sure the system can provide the output you require and that you aren't providing more system than is required.

According to http://www.jblpro.com/BackOffice/ProductAttachments/DOC_180.pdf, on the two-way AM series it appears that 1+/1- on the NL4 are full range in passive mode and the LF driver in bi-amp mode. 2+/2- have no function in passive mode and are the HF driver in bi-amp mode.

 

[gbirdsall]

Liability coverage, yes. lisenced business, yes. cirtified rigger, yes. Low voltage contractor, no. But I am doing this through who a co-worker of mine who is and will put his stamp of approval on it and correct any thing i over look but he is 99% hands off. As for the structure of the building, I will be mounting off of 3" I-beams, the doccuments are all available for building specs. Being in southern ca I will only mount to something rated 10x the load for siesmic reasons, the location is about 10 miles as the crow flies from the san andres fault.

The thought of bi-amping them is that another co-worker of mine has installed them before and told me the difference is extremely noticable. But with the specs you guys have given me has turned me away from it simply on a cost level. I understood the concept i just wasnt sure how to deal with the differences in rms ratings of the two channels.

As for the actual needs of the space they are going to be used for sporting events, lectures to a crowd of 600-1200+ of students and parents at various times, 800 student mass'es with a small choir and band (catholic school), and a few school wide rallies at high spl throughout the year. The horn pattern should cover the bleacher seating evenly. So for the majority of events the system will be driven at minimum levels but 6 or 7 times a year it will be driven hard and probably put away wet so i figure these cabinets positioned correctly, and powered correctly will minimise any possible tampering and dammage.

 

[museav]

As for the actual needs of the space they are going to be used for sporting events, lectures to a crowd of 600-1200+ of students and parents at various times, 800 student mass'es with a small choir and band (catholic school), and a few school wide rallies at high spl throughout the year. The horn pattern should cover the bleacher seating evenly. So for the majority of events the system will be driven at minimum levels but 6 or 7 times a year it will be driven hard and probably put away wet so i figure these cabinets positioned correctly, and powered correctly will minimise any possible tampering and dammage.

Think about the room acoustics and gain before feedback. Would it help to be able to switch on/off or even control the level of different 'zones' of coverage? I have designed systems for several very similar situations and arranged it so that the coverage of various areas or 'zones' could be controlled based on the events, for example:

• Perhaps splitting the floor coverage into multiple zones to address where microphones would be located for Mass, pep rallies, lectures, commencements and so on.
• Treating the home and visitor stands as separate zones.
• For Mass, turning off the speaker(s) covering where the microphones are for Mass or providing that zone a 'mix minus' mix without those mics.
• For games, turning off the floor speakers or routing only music sources to them.
• For pep rallies, turning off the visitor stands coverage and maybe routing only music to the floor.
• For lectures, using the pep rally signal routing but with different EQ that emphasizes speech intelligibility in that space.

Maybe something like a matrix DSP with presets for each of the major types of events that are triggered by push buttons and/or providing level controls for each zone.

 

[themuzicman]

Not to be completely rude, but if you have to ask what bi-amping is, and go on to mention that you are spec'ing and installing an entire system, you probably shouldn't. There are probably other acoustical challenges that you aren't savvy to at the moment.

Sit this one out, get an audio company that knows what they are doing to handle this install. Follow them, watch them, learn from them. Tackle a smaller, less expensive venue first, and work on up.

 

[gbirdsall]

Again i would like to restate. I know what bi amping is and have accomplised it on many occasions, but have always delt with 2 4nl's on the back of the cabinet and never withn a single and a switch. The question was (in a nut shell) do the second set of pins become active on both the cab and the amp with settings. I am actually more intune with the accustal aspect as thats what I have worked with the most before. I appriciate your words of caution, but aside from that question I have most of this clocked


@ museav
I thinking about a creston controller, there is one in a space I work in and for idiot proff running its about ass good as you can get in my opinion. program it for 6 settings but thats a large chunck of change

 

[bishopthomas]

The question was (in a nut shell) do the second set of pins become active on both the cab and the amp with settings.e

If you understand the concept then your question is completely gear related. To which all you need to do is RTFM.

 

[Spresley]

I've always delt with 2 4nl's on the back of the cabinet and never withn a single and a switch. The question was (in a nut shell) do the second set of pins become active on both the cab

ohhhhhh

yes.

 

[TimmyP1955]

You need to have someone model the room to see what boxes will cover it properly. And an acoustical contractor to fix the problems that no doubt exist.