Speaker Hum/Hiss

Speaker design is Paavo's special interest so post away.
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doogle
Posts: 34
Joined: Thu Jun 30, 2005 1:56 am

Speaker Hum/Hiss

Post by doogle »

High guys.
I just bought a set of Event Precision 8 active monitors.
They sound great.
However i have a question for the guys out there that are experienced with speakers with regards to hum or hiss.
These speakers have a switch on the back called input sensitivity.
The input sensitivity is a trim potentiometer.
Is a slight hum or hiss common in speakers, i don't have any dedicated power filters or anything of that nature. Would this help.
The speaker are plugged straight in to the wall.
2nd Question is. I'm using the digi 002 with the events.
When i turn the unit on this also causes a different type of hiss, different from the speakers themselves. Its like a 12k sine wave.


But anyway, when turning the input sensitivity all the way down to -20db it is very minimal. But apparently the optimal sound is supposed to come from these speakers with input sensitivity set to max, not minimum which is what i have set it for.

Tech support said i am degrading the signal, but in an extremely minimal way, with the input sensitivity set to minimum.

So basically that's my dilemma. I thought id ask you guys and see what you think.

Thanks guys.
HarBal
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Post by HarBal »

Do you know where the trimmer actually sits in the signal chain? Is it a passive attenuator at the input or is it somewhere further down the chain? If the former then there should be no problem using it to set up the sensitivity. If it is the latter then I'd suggest wiring up a special cable with inbuilt paasive attenuation to the level required. The noise degradation provided by either approach is minimal. It is just the thermal noise of the resistors used to attenuate the signal. In all likelihood it will probably make no audible difference to the noise performance provided you keep the resistor values small enough. You basically want the impedance looking in to your attenuator cable to be no more than 10kOhm. That certainly shouldn't present a drive problem for you digi002 or any other device for that matter, and the added noise will be low.

Line filters won't do anything to improve the noise performance of your active monitors but they will improve the situation if you have a lot of power line noise in your area. If you do you'd be experiencing a lot of clicks on the output. If not then it's not going to help.

Hum issues are usually a result of poor design or poor earthing / wiring. Usually hum comes about with multiple ground return paths, for instance, if you amp and the device plugged into it are both earthed. Fortunately most sound equipment these days are double insulated and not earthed, which resolves a lot of the problems with hum. On the other hand desktop computers are earthed so you need to be careful with connection inputs or outputs to gear that is also earthed to minimise the effects of hum in ground loops. If you do have to connect to something that is earthed make sure that it connects to the same power board as your DAW.

The final issue about the high frequency noise from your Digi002 sounds like line noise from your monitor. Do you have a CRT (tube) monitor? If so that is most likely the source of the noise/interference. Alternatively, it could also be noise derived from the computer power supply (switch mode power supply). Either way, you may have difficulty getting rid of it. Certainly, if it is due to the monitor you could replace it with a flat screen. If it is due to the computer power supply then you are a bit stuck.

Paavo.
doogle
Posts: 34
Joined: Thu Jun 30, 2005 1:56 am

Post by doogle »

Hi Paavo, thanks for your reply. The high frequency tone i mentioned was due to me switching on the 002 before powering on the speakers. So this problem is fixed.

http://www.event1.com/Images/SP_Brochur ... lockLG.gif heres a link for the Block diagram


The noise that is still present which does regulate when i alter the input sensitivity is quite low and bearable but obviously if i could eliminate it i would. It also regulates in time as in a little bit louder at times then not so loud.
Do all speakers emit some type of noise Paavo.
BTW these are great speakers and they go down to 35 hz. Just thought id throw that in.
Ive never heard music so clearly.


Cheers Paavo




Thought this might be of use also

Low Frequency Driver: Magnetically shielded 8" mineral-filled polypropylene cone with neodymium magnet, 1-1/2" diameter high-temperature voice coil, and damped rubber surround

High Frequency Driver: Magnetically shielded 1" diameter ferrofluid-cooled soft dome neodymium radiator

Frequency Response: 35Hz – 20kHz, ą3dB, ref. 500Hz

Amplifier Power: Biamplified, 280 Watts; 200W LF driver/80W HF driver; toroidal transformer

Crossover: 2.6kHz, active asymmetrical fourth-order

Low Frequency Trim Control: Continuously variable; maximum cut/boost setting produces ą3dB @ 100Hz; ą2dB @ 400Hz

High Frequency Trim Control: Continuously variable maximum cut/boost setting produces ą3dB above 2.6kHz

High Pass Filter: Pushbutton in/out; 80Hz, second-order filter slope

Input Sensitivity: Continuously variable; 1.1V input produces full output with Input Sensitivity Control at Max

Inputs: Balanced XLR and 1/4"

Indicators: Power-on/Clip LED

Protection: RF interference, output current limiting, over temperature, turn on/off transient, subsonic filter, internal fuse, magnetic shielding

Dimensions: 16" H x 12.5" W x 11.875" D; 32.5 lbs. ea.
HarBal
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Post by HarBal »

From the block diagram it looks as though the signal goes straight into the balanced preamp so If you need signal attenuation you would want to do it with a passive attenuator, though from the specs I can't see why you'd need it. Id assume the maximum output of most sound cards and your digi002 would be less than 2 volts and the input sesitivity on max is 1.1V so they should be pretty compatible. Why is it too loud? Is it because you are not bringing down the level with the master fader?

The other question I have is are you using a balanced or unbalanced connection and if unbalanced, is the unused line earthed properly. If it isn't then it may pick up quite a bit of noise, particularly if the input impedance of the preamp is high. It should really be shorted to ground if it isn't in use.

Regards,


Paavo.
doogle
Posts: 34
Joined: Thu Jun 30, 2005 1:56 am

Post by doogle »

HarBal wrote:From the block diagram it looks as though the signal goes straight into the balanced preamp so If you need signal attenuation you would want to do it with a passive attenuator, though from the specs I can't see why you'd need it. Id assume the maximum output of most sound cards and your digi002 would be less than 2 volts and the input sesitivity on max is 1.1V so they should be pretty compatible. Why is it too loud? Is it because you are not bringing down the level with the master fader?

The other question I have is are you using a balanced or unbalanced connection and if unbalanced, is the unused line earthed properly. If it isn't then it may pick up quite a bit of noise, particularly if the input impedance of the preamp is high. It should really be shorted to ground if it isn't in use.

Regards,


Paavo.


High Paavo. When you say master fader do you mean within my daw or on the 002.
But the speakers are quite loud and if i have the input sensitivity on max for a comfortable listening level i can only turn the 002 main volume control a tiny amount.
At the moment the input sensitivity switch is on minimum and this allows me to turn the 002 volume control to half way.

Im using planet waves 1/4 cable, i dont know if they are balanced or unbalanced.

I dont think the 002 has anything to do with the hiss. The noise is present with the 002 off. The noise also varies with the input attenuation and the noise does fluctuate whilst in operation.

With the input attenuation set to minimum the noise is very low.Im thinking of buying a power regulator/filter. Are speakers supposed to be dead quiet Paavo.

Thanks again for your help.
HarBal
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Post by HarBal »

Hi Doogle,

Yep I did mean the master fader on your DAW but if it is as you say I can understand your need for an attenuator. From what you describe it does sound as though you may have stray noise being picked up by a poorly earthed line on the balanced input. I'd suggest wiring up a passive attenuator in the plug shell of the plug you are connecting to your monitors.

By the way, is the plug a 1/4" or a canon XLR? If it is a 1/4" is it stereo or mono type? If it is the mono type then you should replace it with a stereo type with one channel earthed (ie. stereo 1/4" are used for balance cables). It is important that you put the passive attenuator in the plug that plugs into the monitor and not the other end. That will ensure the best noise immunity. If you don't know how to solder or don't have the gear you could always ask an electronics repair technician in your area. Just be sure you know how much attenuation you want so they know what resistor combination you need and tell them it should have a total resistance of around 10kOhm. Getting a technician to wire this up for you won't be much different in cost than your power line filter but the result will be much better and you'll be able to set your monitor input attenuator to minimum.

Regards,


Paavo.
doogle
Posts: 34
Joined: Thu Jun 30, 2005 1:56 am

Post by doogle »

Hi Paavo. Thanks again and again.

I am using 1/4 jack. I dont know how to determine weather its mono or stereo, i had no idea about this.
Are xlr cannon stereo by default. Are there any sonic differences between xlr,jack,mono,stereo.
HarBal
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Post by HarBal »

Have a look at the pin on the 1/4 inch plug. Does it look like the plug on a guitar cable or does it look like the plug on headphones. The former is mono, the latter is stereo. Like I said, I'd recommend you get someone to wire up an attenuator in your cable. It should solve your problem better than any line filter can.

Paavo.
doogle
Posts: 34
Joined: Thu Jun 30, 2005 1:56 am

Post by doogle »

Thanks Paavo your a champ.

Im on to it.

BTW i highly recommend these speakers they are awesome.
I previously had Alesis M1 Mk II i thought i could get good results with those but its real hard.
These things are a joy. They pack an awesome punch and have awesome detail and stereo imaging.
Its so good listening and working with good speakers.

Anyway thought id ad how wonderful they are.

Thanks again Paavo
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