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Author Topic: Stereo Tri-amp PA - differing amp gains  (Read 940 times)

Chris Grimshaw

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Re: Stereo Tri-amp PA - differing amp gains
« Reply #10 on: July 09, 2021, 08:50:23 AM »

The concern is that while the PLM has a variable amp gain of 22 - 44dB (currently at its default 35dB), the IPD is at a fixed 33.2 dB. I really want to avoid dialing back the PLMs gain to match the IPD due to reduction in system headroom.

Set the PLM gain for 33dB and it'll be fine. Why do you think you'll lose system headroom?

Chris
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Steve-White

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Re: Stereo Tri-amp PA - differing amp gains
« Reply #11 on: July 09, 2021, 02:48:20 PM »

Thank you for this. What to do to help match the amps to achieve a similar sensitivity? The specs listed on the 10,000 show Input Sensitivity of +12 or +26dBu, the IPD2400 +6dBu.

I'm trying to digest this as I'm referring to EAW's comment's on powering their loudspeakers:

"Amplifier Gain Settings - IMPORTANT:
In order for EAW signal processing to function properly for multi-amplified loudspeakers, it is critical that all amplifiers for all passbands be set to the same voltage gain, regardless of the amplifiers' power output ratings.
NOTE: The same gain does NOT mean the same input sensitivity, but the same input to output voltage gain. Consult your amplifier manufacturer if this cannot be readily determined. Do not selectively boost or attenuate loudspeaker levels of the amplifiers in order to balance a system. This should be done at the output of the signal processor."

I don't know what processor you are using so I can look up the specs and capability.  Setting up an active system is much like building a pyramid of similar pieces of brick.  Starting at the processor or crossover the amplifier sensitivity needs to be aligned, amplifier power level should suit the drivers and the driver sensitivity and power handling capability should also be matched up.  Assuming the drivers are all matched up fairly well for maximum acoustic output, and powered correctly, then it's about the settings in the DSP/crossover.

Any mismatch in amplifier power and driver will be the point the system is constrained to for maximum output.  i.e. 2000W subs, 1000W mids and a 10W top end - to get a balanced sound out of the system it can only perform to the level of the 10W top.

If the processor has adjustable on the outputs or drive level, then do it there and leave the amps at maximum gain.

Set it up and play some music through it from a CD or other source - you'll learn a lot more there than on the computer screen.  :)  Hook it up, play with it and then ask more questions.
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Ran Manhart

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Re: Stereo Tri-amp PA - differing amp gains
« Reply #12 on: July 09, 2021, 08:42:42 PM »

We're using an EAW UX8800 processor, there's not much tweaking to those GF Greybox files. I agree about using your ears to tune, tweak adjust. Just trying to get a better understanding of the math before integrating another amp.

Adjusting gain on DSP output leaving amp gain at max is an interesting idea.

Back to geek - previous posts refer to input sensitivity and I'm trying to wrap my head around that. The PLM 10,000Q has an Input Sensitivity of +12 or +26dBu, whereas the IPD2400 has +6 dBu for max output. I think if I get a better understanding of this part of the equation, the rest will fall into place, ie how is that measured, can it (should it) be altered to match, and what to do if it's not possible.

As far as adjusting amp gain, I can certainly try reducing to 33 dBu and see if I there's performance hit. Last time I dropped the PLM's amp gain to 30 dBu as an experiment (making same adjustment at the UX8800), the system sounded seriously choked.
« Last Edit: July 09, 2021, 09:23:30 PM by Ran Manhart »
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Ran Manhart

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Re: Stereo Tri-amp PA - differing amp gains
« Reply #13 on: July 09, 2021, 08:47:45 PM »

i believe the THX spec for gain is 28.
Thanks, I meant what does the acronym THX stand for? Have not be able to find a reference...
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Steve-White

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Re: Stereo Tri-amp PA - differing amp gains
« Reply #14 on: July 09, 2021, 10:34:34 PM »

Thanks, I meant what does the acronym THX stand for? Have not be able to find a reference...

George Lucas in the movie Theatre world made his mark similar to Dolby labs for sound.

Lucas THX

https://www.lucasfilm.com/what-we-do/sound-design/

You don't have THX certified amps or THX certified speakers - it was suggested that you setup your stuff using that standard as your baseline for the amplifier gain.

My simplest system is active bi-amped.  Stage monitors are all also active bi-amped.  FOH & DJ stuff is all 4-way active format.  I was destroying diaphragms in Altec compression drivers back in 1980, threw the passive crossovers in the trash can and bought an Ashly SC-80 electronic crossover and never looked back.

This is a tall order what you're doing.  Trying to get there online is also a tall order.  If there's anyone around that you can talk to, not type to, talk to - I suggest doing that.

What you're doing is fairly simple for an experienced engineer and can net some nice results.  Working this out online, you're going to get numerous opinions and could get pulled in several directions as there's more than one way to skin a cat.

You don't need to replace anything and really should set this thing up and work with it a little to better understand what it can and can't do for you.
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Ran Manhart

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Re: Stereo Tri-amp PA - differing amp gains
« Reply #15 on: July 10, 2021, 12:41:13 AM »

Thanks for the reply, I appreciate your words.

A bit different than the JBL Voice of the Theatre 3 ways (still love those 2405's), MXR EQ, Rane x-over (?), and CS400/800 amps I started with in 1980. Those Peaveys were the 4th Unforgivable Curse >:(

I'm a keyboard player w a decent ear, I'm sure I can tune this system up alright, always have. Just tryin to do justice to what I'm fortunate to be workin with.
« Last Edit: July 10, 2021, 12:47:07 AM by Ran Manhart »
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Steve-White

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Re: Stereo Tri-amp PA - differing amp gains
« Reply #16 on: July 10, 2021, 02:25:46 AM »

You absolutely can and will be pleased with the results.

Yep, the 2405's are probably the best sounding HF drivers ever made.  In the latest iteration of DJ systems, I used JBL 2402's for the top end.  Same voice coil/diaphragm as the JBL 2405, but a different waveguide.  Lower crossover point, and a bit more rugged.  It sports 2x per side splayed outwards 20 degrees in a 4-way active setup.
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Re: Stereo Tri-amp PA - differing amp gains
« Reply #16 on: July 10, 2021, 02:25:46 AM »


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