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[Ivan Beaver]

I took this to mean that in practice when mixing a live rock show that a pair of TH118s would limit around the same time as a single 4883 in terms of even output.  So 2 4883s a side handling the low mid pushed to limiting (probably more output than I would need normally) would require 4 TH118s per side to provide adequate LF energy to match.

There is a big difference in drive voltage (coming from the amplifier) and the output SPL.

Generally most shows that have a "decent" bass output (not light jazz), have the subs SPL that is 15-25dB higher than the rest of the full range system.

For EDM shows, I have measured this sub to top ratio to be 30 to 35dB.  It all depends on how much capability each system has.

So that needs to be part of the system design capabilities.

Of course different people have different desires out of systems.  What is to much bass for somebody has others wondering when the bass is going to be turned on.

So your mileage will vary and needs to be considered.

An easy way to do this is setup a system and balance it (subs to fullrange) as you desire by ear using music of the type that will be used.

Now use an RTA and look at the difference in levels so you will have an idea what you need when looking at different parts of the systems output capability.

[Ivan Beaver]

Using the old I-Tech 8000 which has an output of 4000W per channel at 4 ohms would each channel provide unnecessarily too much power for a single TH118?  I happen to have 4 of those amps so I could have 8 channels to devote to 8 TH118s.

They would be fine and they would be "real happy" just running 4 ohms per side.  Just be sure to set the limiters to protect the drivers.

[David Sturzenbecher]

When we are using 12 - 4886s per side, 3 JBL 4880As seem to be a good match for most modern rock, alternative, country. We just go straight from the 86s to the 80As, no need for the 83s.  I end up cutting a bunch of 120-250 due to line length anyway.


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[Aaron Carian]

They would be fine and they would be "real happy" just running 4 ohms per side.  Just be sure to set the limiters to protect the drivers.

What is the recommended peak voltage for the TH118?

[John Rutirasiri]

Thank you Tom that really helps.  I sort of felt like 6 would work well for my needs but not leave a whole lot of headroom for the largest gigs and 8 would be better matched.  Which looks like lines up exactly with that your experience has been.  Are you running one TH118 per channel of the 12000HD?

I run 16x TH118's on (4) IT12000HD's  No problem.
My only "issue" is the TH118 tends to"walk" when standing up.  I need to strap them together.

You will not be disappointed in the TH118's. 

Also check out JTR's Orbit Shifter.  In the same league as TH118 output-wise.  But different sound.
http://jtrspeakers.com/portable/orbit-shifter-pro/

John R.

[Ivan Beaver]

What is the recommended peak voltage for the TH118?

"Peak voltage" means different things-depending on how you look at it.

So follow along-and for more information regarding setting limiters.
 
The TH118 is rated for 1700 watts @ 4 ohms with a 6dB crest factor.

That is 82V. 

6dB higher (peak power) would be double that voltage (double power =3dB, double voltage=6dB), so that would be 164V.

That would be the RMS value of the 6dB crest factor applied.

HOWEVER-a good number of amplifiers use the "peak" of the voltage waveform-NOT the RMS value of that same waveform, when setting peak numbers.

The peak is 1.414x RMS.  So that is 232V (164x1.414).  Which is the number that should be entered into the DSP.

BUT HOWEVER-remember that the AES test is a "near death experience" for a limited period of time.  I do not recommend setting limiters totally based on this.

YES, my opinion was different years ago, but I have done a lot of testing (blowing up drivers) and my opinion has changed.

I am currently working on programming the DSPs for a system/job that has over 1,000,000 "available" watts in it.  But the "watts into loudspeaker loads" is only around 650,000 watts.

So I have been spending a lot of time "watching and measuring the limiter action".  I don't want to blow anything up on this job .

What I recommend for "normal" usage is to set the voltage that is "peak", at twice the continuous rating.  That is "assuming" that the peak value presented is 1.414 the RMS value.

So that would equal the "program rating" (twice the continuous rating) of the driver.

Now this is where it gets interesting. 

Not all thermal or heating limiters act the same.  Some are VERY different than others-so it is very important to understand how they work and this helps to guide setting the RMS and thermal limiters.

Let's say you set it for 3 seconds for a large driver such as a sub.

Some of them start to reduce the level as soon as this level is exceeded and it takes 3 seconds to reach the set voltage-or at least 80% of it.  I consider this to be "normal operation of a limiter".

Others (like in the Crown) wait for 3 seconds and THEN start to reduce the level.  Nothing happens (in the thermal limiter section) until this level has been exceeded for that time period.

The overall action of heating on the voice coil is different for these 2 types of limiters.

So for the Crowns, my current recommendation of limiter settings are as follows.

ALWAYS turn the amp clip eliminator ON.  This is NOT in the limiter section, but rather in the output block (last block?)

After you have set the xover settings, hit the "automatic" button for the release times.

This will set your release times based on the xover freq.

Then turn it to advanced.

Figure out the continuous voltage rating of the loudspeaker (in the case of the TH118 this is 1700 watts or 82V).

Halve this value (41V) and put that into the thermal limiter with an attack time of 3 seconds.

Double this value (164V) and put that in the peak limiter.

Now multiply this (42V) by .707 and enter that into the RMS value =58V.

Of course it never hurts to drop any of these values a tad for a little more protection without really affecting the actual SPL enough to be realized.

In this case I would use 80V as the starting point.

Hopefully that helps a little.

[TJ (Tom) Cornish]

The limiters in the 12000 is a voltage limiter.  So it does not matter if there is 1 or more speakers hooked up.  They will all get the same voltage/same limiting.

Aaron's interpretation is correct.  When the system is acoustically balanced, the ratio that works out at least for the styles of music I work with (moderate rock, a little bit of hip hop), is 2 TH118 per 1 4883 with the 4883 covering from 60Hz - 120hz.  Fully utilizing the output capability of 6 4886 boxes would require 2 4883 boxes and at least 4 TH118 per side.

[TJ (Tom) Cornish]

Thank you Tom that really helps.  I sort of felt like 6 would work well for my needs but not leave a whole lot of headroom for the largest gigs and 8 would be better matched.  Which looks like lines up exactly with that your experience has been.  Are you running one TH118 per channel of the 12000HD?

I have run 2 TH118 per side of the ITHD12K.  This works fine, but definitely requires a 208v 20A circuit, and is harder on the ITech as well as makes an amp failure more catastrophic since you will lose the output of 4 subs instead of just a pair.  I have recently acquired more amp channels and going forward will run one Danley per ITHD12K channel. 

The IT12K has enough power to damage a single 4Ω TH118 if left with no limiting.  It probably doesn't have enough voltage output to damage a single 8Ω TH118.

Ivan's idea of 8Ω TH118s run 2 per side on an ITHD12K would indeed work and the resulting output would be more than a single TH118, but each TH118 would be under-driven a couple dB, so you're leaving some output on the table.  Ivan is also correct that the ITHD12K has peak output power at 2.7Ω, so you could run 3 8Ω TH118 per side and still get more out of the amp, but again you're leaving some sub output on the table.

One alternative is to look at the ITech 4x3500 which can do 4 channels of 4000 watts burst/2500 watts program at 4Ω.  http://www.crownaudio.com/en-US/products/i-tech-4x3500hd 

Note that running the 4x3500 at full output power will again require high voltage and/or high current supply, so you might be better off with 2 IT12K than a 4x3500 if you frequently need to run from regular 120V 20A circuits.

[TJ (Tom) Cornish]

When we are using 12 - 4886s per side, 3 JBL 4880As seem to be a good match for most modern rock, alternative, country. We just go straight from the 86s to the 80As, no need for the 83s.  I end up cutting a bunch of 120-250 due to line length anyway.


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The 4883s run in cardioid mode help with low-frequency pattern control and make the main hangs more full-range, but there's no doubt the subs can run high enough to meet the 86s if desired.

[TJ (Tom) Cornish]

I run 16x TH118's on (4) IT12000HD's  No problem.
My only "issue" is the TH118 tends to"walk" when standing up.  I need to strap them together.

Yep - I do this as well.  The 4883s I stack on top  will go flying off if not held down, too.  Bonus points if your ratchet straps are some color other than orange. 

[ProSoundWeb Community]