You are here

independent volume control

Customising, building or repairing your own gear? Need help with acoustic treatment or soundproofing? Ask away…

independent volume control

Postby snowman352 » Mon Apr 23, 2018 5:59 pm

I am part of an organization that wants to add some things to the sound system in the building. Right now they have an Optimus AP Amp and two wireless mics/receivers. There are a couple of problems. One is they get feedback pretty bad and two they need to be able to let guest speakers hook up the audio of their laptop to the system.

The feedback is because the have 12 inch ceiling speakers and the guest usually stands directly under the first set of two speakers.

My suggestion is: run an XLR from the amp to the front of the room and then have an XLR to 3.5mm to connect the laptop. AND to put volume controls on each set of two speakers (6 speakers/3 sets of two) so that we can turn down the volume on the speakers at the front and ramp up the volume as the move toward the back of the room. I am thinking that if I reduce the volume on the speakers they are standing under I will have less problem with feedback.

What piece of equipment would I use to control the speaker and NOT change the amp? I am figuring the signal into the amp, out of the amp into some kind of fader that I can independently control each set of speakers.
snowman352
New here
Posts: 4
Joined: Mon Apr 23, 2018 5:52 pm

Re: independent valume control

Postby blinddrew » Mon Apr 23, 2018 8:46 pm

Hi Snowman, it would probably help if you could provide a bit more detail on the amp and mics but having had a quick google I think you may struggle with your plan.
Most mixers are designed to work at 'line' or microphone level, that's the level that goes into the amplifier. It seems you're after something that would sit between the amplifier and speakers and that's a very different beast because it (if it exists, I'm sure other people will be along to help out soon) would need to handle the power from the amplifier as well as the signal. Which is a very different kettle of fish.
Does that make sense?
How much does the speaker move around? Could you get by with just turning off that pair of speakers? Speaker switching boxes are fairly commonplace.
User avatar
blinddrew
Jedi Poster
Posts: 4460
Joined: Sat Jul 04, 2015 11:00 pm
Location: York
Ignore the post count, I have no idea what I'm doing...

Re: independent valume control

Postby James Perrett » Mon Apr 23, 2018 9:02 pm

If the amp is made by the Spanish company Optimus then you are probably in luck as most of their gear appears to use the 100V line system. You'll find a transformer mounted on the back of the speaker and, with any luck, it will have multiple settings to set the level of the speaker. Just change the setting on the two front speakers to a lower setting.
User avatar
James Perrett
Moderator
Posts: 7299
Joined: Sun Sep 09, 2001 11:00 pm
Location: The wilds of Hampshire
JRP Music - Audio Mastering and Restoration. JRP Music Facebook Page

Re: independent valume control

Postby ef37a » Tue Apr 24, 2018 5:55 am

If it is indeed a 100V line system, one or two of these..http://www.inta-audio.com/background-mu ... ator-p8554

There used to be a 100V line VC that used a very wee "Variac" can't seem to find that at the moment, likely be more expensive but would give finer control*.

For low impedance use, 4-8 Ohms you can buy "L pad" controls. You need to know the speaker's power rating but for a ceiling speaker I doubt that would be more than 25-30W?

*We used to use a 500VA Variac to control a whole bank of 100V speakers to get a 'fade out' in a section of a theatre. The bass end probably suffered a bit but the quality was actually remarkably good!

Dave.
ef37a
Jedi Poster
Posts: 9166
Joined: Sun May 28, 2006 11:00 pm
Location: northampton uk

Re: independent valume control

Postby MarkPAman » Tue Apr 24, 2018 12:49 pm

Yep, if it's a 100V line system, those volume controls are relatively easy to retro fit especially if you're happy to have them in the ceiling next to their speaker. I've done 100s! I'd look for one that goes all the way down to off if the mic's directly under it. *

With regards to the laptop connection, I'd probably consider some sort of interface box on the end of the XLR lead you propose rather than just an adaptor lead.

I have an ART AVDirect Interface box which prevents earth loops, has inputs specifically for headphone signal to connect to and dose a proper stereo > mono conversion. It also has a volume control.


* On thinking further, if "off" turns out to be the best solution, a bog standard light switch could be used here at much reduced cost. Easy to test if this works well in your room by just disconnecting the speaker.
MarkPAman
Frequent Poster
Posts: 657
Joined: Wed Apr 05, 2006 11:00 pm
Location: Somewhere between Portsmouth & Chichester

Re: independent valume control

Postby resistorman » Tue Apr 24, 2018 1:18 pm

ef37a wrote:
*We used to use a 500VA Variac to control a whole bank of 100V speakers to get a 'fade out' in a section of a theatre. The bass end probably suffered a bit but the quality was actually remarkably good!

Dave.
That’s crazy, and somewhat genius :ugeek: Theaters are the testing ground for solutions that cost nothing...
User avatar
resistorman
Frequent Poster
Posts: 542
Joined: Sun Nov 22, 2015 12:00 am
Location: Asheville NC
future26.com

Re: independent valume control

Postby snowman352 » Tue Apr 24, 2018 2:31 pm

MarkPAman wrote:Yep, if it's a 100V line system, those volume controls are relatively easy to retro fit especially if you're happy to have them in the ceiling next to their speaker. I've done 100s! I'd look for one that goes all the way down to off if the mic's directly under it. *

With regards to the laptop connection, I'd probably consider some sort of interface box on the end of the XLR lead you propose rather than just an adaptor lead.

I have an ART AVDirect Interface box which prevents earth loops, has inputs specifically for headphone signal to connect to and dose a proper stereo > mono conversion. It also has a volume control.


* On thinking further, if "off" turns out to be the best solution, a bog standard light switch could be used here at much reduced cost. Easy to test if this works well in your room by just disconnecting the speaker.

for the laptop connection I intend to put a wall plate with an XLR back to the amp but also a vga , hdmi rca and usb back to the projector. I wanted to combine all of those plugs in one wall plate.
snowman352
New here
Posts: 4
Joined: Mon Apr 23, 2018 5:52 pm

Re: independent valume control

Postby ef37a » Tue Apr 24, 2018 3:24 pm

resistorman wrote:
ef37a wrote:
*We used to use a 500VA Variac to control a whole bank of 100V speakers to get a 'fade out' in a section of a theatre. The bass end probably suffered a bit but the quality was actually remarkably good!

Dave.
That’s crazy, and somewhat genius :ugeek: Theaters are the testing ground for solutions that cost nothing...

Mains transformers are actually not bad for audio. The HT-5 guitar amp design was rough hewn with one of about the right ratio.

'S only when people insist on a 20kHz top end and want fancy stuff like low phase shift for nit picking things like NFB that you have to get expensive.

K.I.S.Sir!

Dave.
ef37a
Jedi Poster
Posts: 9166
Joined: Sun May 28, 2006 11:00 pm
Location: northampton uk

Re: independent valume control

Postby snowman352 » Tue Apr 24, 2018 3:33 pm

since the amp has an XLR and a 1/4" plug for mic input, which one should I use to run the computer audio from the front all to the amp in the back of the room? would it be easier and just as effective to use the 1/4" jack?
snowman352
New here
Posts: 4
Joined: Mon Apr 23, 2018 5:52 pm

Re: independent valume control

Postby MarkPAman » Tue Apr 24, 2018 4:00 pm

snowman352 wrote:for the laptop connection I intend to put a wall plate with an XLR back to the amp but also a vga , hdmi rca and usb back to the projector. I wanted to combine all of those plugs in one wall plate.

Good plan, and a second wall plate next to it could house the speaker's volume control. But you'll still need something more than an "XLR to 3.5mm to connect the laptop" to the input of your amp. For a start, the laptop's headphone out is unbalanced & stereo, while your amp's input will (probably) be balanced and mono. Then there's earth loops to get rid of if the laptop's not running on battery only.
MarkPAman
Frequent Poster
Posts: 657
Joined: Wed Apr 05, 2006 11:00 pm
Location: Somewhere between Portsmouth & Chichester

Re: independent valume control

Postby MarkPAman » Tue Apr 24, 2018 4:06 pm

snowman352 wrote:since the amp has an XLR and a 1/4" plug for mic input, which one should I use to run the computer audio from the front all to the amp in the back of the room? would it be easier and just as effective to use the 1/4" jack?

No, use the XLR. The Jack will almost certainly be unbalanced, so is not suitable for a long run. That box I mentioned is this one:
http://artproaudio.com/active_di/product/av_direct/
and you really do need this or something like it to do this job, especially if running different "unknown" laptops. That gives you mic level signal on XLR.
MarkPAman
Frequent Poster
Posts: 657
Joined: Wed Apr 05, 2006 11:00 pm
Location: Somewhere between Portsmouth & Chichester

Re: independent volume control

Postby James Perrett » Tue Apr 24, 2018 8:09 pm

Do you have the exact model number of the amplifier? It would help to make sure that we're giving you appropriate advice (as there are some older Realistic Optimus PA amps which are very different to the Spanish Optimus amps).
User avatar
James Perrett
Moderator
Posts: 7299
Joined: Sun Sep 09, 2001 11:00 pm
Location: The wilds of Hampshire
JRP Music - Audio Mastering and Restoration. JRP Music Facebook Page

Re: independent volume control

Postby snowman352 » Tue Apr 24, 2018 8:28 pm

James Perrett wrote:Do you have the exact model number of the amplifier? It would help to make sure that we're giving you appropriate advice (as there are some older Realistic Optimus PA amps which are very different to the Spanish Optimus amps).

looks like it is the optimus MPA-125
snowman352
New here
Posts: 4
Joined: Mon Apr 23, 2018 5:52 pm

Re: independent volume control

Postby James Perrett » Tue Apr 24, 2018 11:24 pm

snowman352 wrote:looks like it is the optimus MPA-125

As I feared - this is a cheap Radio Shack own brand amplifier rather than the Spanish brand. However, it does have a 70V (rather than 100V) line output and hopefully that's what the system installers have used. The manual contains a very basic explanation on how to use speakers with transformers which is available at

https://www.manualslib.com/download/137 ... a-125.html

(but be very careful to click on the right link - there are several dubious looking adverts on that page that disguise themselves as download buttons)
User avatar
James Perrett
Moderator
Posts: 7299
Joined: Sun Sep 09, 2001 11:00 pm
Location: The wilds of Hampshire
JRP Music - Audio Mastering and Restoration. JRP Music Facebook Page


Who is online

Users browsing this forum: No registered users