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Noob Passive Amp Speaker setup questions
Old 1 week ago
  #1
Here for the gear
 

Noob Passive Amp Speaker setup questions

Hey guys I am new to this forum and to live sound. I just bought some used equipment to use when we throw parties (frequently ) and cant figure out how to get it set up correctly. I just need to hook a phone or computer up to play music, and maybe a microphone. I purchased everything from a DJ who was moving and have lost touch. Here is the equipment:

• Two Yamaha S115IV speakers rated at 250/500/1000 watts (Noise/Program/Max) 8 ohms, Sensitivity 99db
• Two Yamaha SW118IV subs 250/500/1000 watts (Noise/Program/Max) 8 ohms, Sensitivity 96db
• One QSC RMX 850 - 185 watts @ 8 ohms, 300 watts @ 4 ohms, or 530 watts bridged 8 ohms, 830 watts bridged 4 ohms,
• One QSC RMX 1450 – 260 watts @ 8 ohms, 400 watts @ 4 ohms, 800 watts bridged 8 ohms, 1400 watts bridged 4 ohms
• Mackie Mix5

I hooked up the S115's to the QSC 850 in stereo and it sounded very flat. Tried the QSC 1450 and it sounded better but not great. Bridged the 1450 and connected one speaker and it screamed! So I am thinking I could bridge both amps, use the 850 to feed the tops (parallel) and 1450 to feed the subs. But I am concerned the subs cant handle the power.

So if this were your system, how would you set it up? I am not adverse to buying another used amp as long as I can keep it under $200.

Thank you in advance! I have been to 2 guitar centers and they did not know anything about passive speakers.
Old 1 week ago
  #2
Gear Nut
 

I looked at your AMP's owners manual and there are a lot of bip switches that need to be set up right.

As far as running your subs, it looks like your amps don't have a crossover that will work with your set up.

If the subs don't have built in crossovers you will need a DSP/crossover to make them work right with the tops.

If the 50hz filter switch is engaged on the back of the QSC RMX 850 then the tops will sound like there are missing some bass without the subs hooked up.

Sorry but I can't find any data on if the subs have a crossover. Cheap solution would be to buy the behring DSP unit and learn how to set it up.

In the mean time you can learn how to set your amps up right, or find someone to come teach you.

If an AMP at max input level has to much power you can just turn down the input sensitivty(aka gain) and that will how loud the system gets.
Old 1 week ago
  #3
Gear Addict
850 bridged into the subs, 1450 in stereo for the tops.

You need a crossover.

Chris
Old 1 week ago
  #4
Here for the gear
 

Thank you

Thank you both! Sounds like I definitely need a crossover. I am looking at the Nady CX-22SW new or the DBX 223 used. I like the Nady because it has sub out but believe the dbx is better quality. Any recommendations?

The xover has Hi/lo out on each channel but the main speakers only have one input. How would I connect these?
Old 1 week ago
  #5
Gear Nut
 

Quote:
Originally Posted by Tommydog View Post
Thank you both! Sounds like I definitely need a crossover. I am looking at the Nady CX-22SW new or the DBX 223 used. I like the Nady because it has sub out but believe the dbx is better quality. Any recommendations?

The xover has Hi/lo out on each channel but the main speakers only have one input. How would I connect these?

https://3e7777c294b9bcaa5486-bc95634...2_original.pdf

I would go for the DBX, If you go with the 223 with XLR inputs you'll need to get some adapters to go from your mixers 1/4" to the X-overs XLR


Here is the basic system, I am not including a diagram for Bridged mono because the amps are only rated to 4ohm in bridged mono, meaning you COULD blow up an amp if you run the subwoofers in that settings.
Attached Thumbnails
Noob Passive Amp Speaker setup questions-basic-set-up.jpg  
Old 1 week ago
  #6
Gear Nut
 

Here is how I would run the dip switches on the AMPs]

Both amps in stereo mode, both non bridge.

PS, I just finished some antibiotics so use my suggestions at your own risk
Attached Thumbnails
Noob Passive Amp Speaker setup questions-tops-amp.jpg   Noob Passive Amp Speaker setup questions-sub-amp.jpg  
Old 1 week ago
  #7
Gear Nut
 

Here is an alternative set up.

Use the crossovers "LF sum" button to send a single signal cable to the bass amp, this makes the bass mono.



You will have to parralel or duplicate this signal on the amps rear settings. The dips for the subwoofer amps would look like this with this set up.

https://www.qsc.com/resource-files/p...usermanual.pdf
Attached Thumbnails
Noob Passive Amp Speaker setup questions-basic-set-up-lf-sum.jpg   Noob Passive Amp Speaker setup questions-lf-sum-amp-set-up.jpg  
Old 1 week ago
  #8
Here for the gear
 

Downtheline this is VERY helpful. Thank you. A couple more questions

1. If I run both amps in stereo, the watts/channel on the 850 is well under the noise rating of the tops or subs. Isn’t this an issue? I’ve read elsewhere that under powering speakers is as bad as overpowering. If this is a non issue would you pair the 850 to the tops?

2. If speakers are 8 ohms and amp is rated for 4 ohm load, isn’t it safe to bridge one amp and daisy chain subs?

3. Does the “lf sum” scenario provide any advantages over the first scenario you provided?

Hope the antibiotics got rid of what ever was ailing you.
Old 1 week ago
  #9
Gear Nut
 

Quote:
Originally Posted by Tommydog View Post
Downtheline this is VERY helpful. Thank you. A couple more questions

1. If I run both amps in stereo, the watts/channel on the 850 is well under the noise rating of the tops or subs. Isn’t this an issue? I’ve read elsewhere that under powering speakers is as bad as overpowering. If this is a non issue would you pair the 850 to the tops?

2. If speakers are 8 ohms and amp is rated for 4 ohm load, isn’t it safe to bridge one amp and daisy chain subs?

3. Does the “lf sum” scenario provide any advantages over the first scenario you provided?

Hope the antibiotics got rid of what ever was ailing you.
My Bad, Yeah your subs are 8ohm each so you can Run the big amp on your tops and run the sub in mono with the smaller amp brdiged, good for you!

I was looking at some other specs that showed 4ohm subs.

About using LF sum on the crossover.
Since you can run you subwoofer amp bridged and mono, the amp will sum the signal if you plug in 2 signal cables. SO you can sum at the crossover or let the amp sum to mono.

Using one less cable is an advantage.

To set the gain stage, turn you amps all the way down. Plug in your phone, play music with volume set at around 80%, set the input level anywhere from 50-75% to start then turn out the master output knob until you see a solid yellow light on the output meter.

Then turn up the input sensitivity (aka gain) on the amps until its at a volume you like.

Thanks for the well wishes.
Make sure set set dips on sub amp to" bridge mode on"

Pretty nice set up for parties!
Attached Thumbnails
Noob Passive Amp Speaker setup questions-lf-sum-amp-set-up.jpg   Noob Passive Amp Speaker setup questions-basic-set-up-lf-sum.jpg  
Old 1 week ago
  #10
Lives for gear
 

Underpowering speakers is only a problem if you're pushing the amps to where they are clipping. Adjust the volumes/levels so that isn't happening and it's not a problem. If you don't have control over the levels going into the amplifiers and they're likely to be pushed hard, it would be appropriate to add a limiter to protect them. (Obviously, you do have a lower maximum volume when you have less power, though it's not as huge a difference as sometimes people think since the relationship between power and perceived loudness is not really linear.)

If the amplifiers are really small, it doesn't matter much if they clip; they just can't generate enough power to damage the speaker. That doesn't apply here.
Old 1 week ago
  #11
Here for the gear
 

Thank you both for the information. Downtheline, cant thank you enough for your help - the diagrams are a huge help!
Old 6 days ago
  #12
Lives for gear
 
JayTee4303's Avatar
Nobody else did, so I will.

I like my amps to deliver half again, or double, the speakers' rated program power, clean. For a 500 watt speaker, 750 to 1000 watts. Better that you define "clean" for yourself.

I have it on pretty solid authority that newer amps tend to measure less output than published rating specs, though I have not personally measured any myself.

I don't believe I've been inside any QSC power amps, ever, but I've been inside my Crowns and Crests, and inside my boss's powered Meyer and "1000 watt" QSCs regularly (they pay me for that.)

The powered QSCs impress me neither visually nor audibly.

In summation, I think you're underpowering your rig, possibly to the point of risk. Especially with modern "music", if you catch my drift.

This is not an edict. Instead, just a friendly "heads up"... something you might want to look into deeper on your own.
Old 6 days ago
  #13
Gear Addict
Quote:
Originally Posted by JayTee4303 View Post
This is not an edict. Instead, just a friendly "heads up"... something you might want to look into deeper on your own.
QSC RMX will deliver their rated power, although some of them get hot doing it.

Modern switch-mode amplifiers will often only meet their ratings with short-duration signals. That's okay, though - music has peaks (kick/snare drum, for example). These QSC amps do not fall into the "modern switch mode" category - they're big transformers and lots of heatsink, which is probably the sort of amp you like.


FWIW, the idea of a too-small amp burning out speakers only holds if you drive it far into clipping, to a point where the average power exceeds what the speakers can take.
A very large amp would also be able to put out that much average power, but without any blinky red lights.

Chris
Old 5 days ago
  #14
Lives for gear
 

you better have enough rig for the gig - and power to drive it!

Quote:
Originally Posted by chris661 View Post
A very large amp would also be able to put out that much average power, but without any blinky red lights.
...most speakers can take high peaks of clean power much better than distorted signals and the problem with distortion is than one can mostly not hear it much until it's too late: our ears unfortunately are pretty tolerant in this regard.
all amps i'm using are 'oversized' by a ratio of 1.5 to 2 (and even higher for subs); has been working very well for the last 35+ years, not only for me but for most larger live sr rental companies.

Quote:
Originally Posted by chris661 View Post
Modern switch-mode amplifiers will often only meet their ratings with short-duration signals (...) they're big transformers and lots of heatsink
that's true for any amp (rating/specs, that they get hot and the need for heatsink) - problem is that there are many ways how to measure and not all manufacturers give much information on their procedure (nor could the less experienced user interpret and compare data but these are much different topics...)
Old 5 days ago
  #15
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JayTee4303's Avatar
Not arguing with you guys, buy damage aside, undersized amps leave "a lot of speaker on the table" unused.
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