Studio Monitors (audio, music) - Input protection ? - Page 1
Forum section: electronics / projects

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: July 16, 2013, 12:46:52 pm
content: Howdy.Let's say, I tinker with audio circuits. Am not extremely experienced. And may screw up more often and more severely than a professional engineer.I'm planning to buy a studio monitor speaker, active. I'd like to really hear what's going on, so it would be bad to buy a cheap one "just in case I break it".And I certainly don't want to kill a more pricey one, nor my ears!What would be good measures to protect the monitor? As in, stuff I can build and put between my dangerous circuits *g* and the monitor input.I was thinking of making sure some peak level will not be exceeded.And perhaps enforcing a maximum RMS boundary, especially for higher frequencies??, so I will not kill the speakers OR my ears.I wouldn't know how to do either of them appropriately, like tried & proven stuff, so I can have peace of mind ;-)Any suggestions? Additions?

author: Lightages
author_rank: Unknown
timestamp: July 16, 2013, 03:16:50 pm
content: Trying to protect tweeters is not an easy thing to do. Tweeters usually deal with very transient signals and as such their average dissipation is very very low. Feed them a pure sine wave in their range, even a very low one, and they get damaged very easily. A very fast blow very low value fuse is used sometimes but this causes problems with proper reproduction. Selecting a correct fuse is also very difficult.Overall speaker protection could be accomplished in many ways and none are perfect. Have a read here:http://www.epanorama.net/links/audiospeakers.html#protection

author: David_AVD
author_rank: Super Contributor
timestamp: July 16, 2013, 10:16:51 pm
content: Are they passive or active monitors?

author: IanJ
author_rank: Unknown
timestamp: July 16, 2013, 10:36:50 pm
content: Hi,Thinking out loud you could probably buy an in-line XLR or 1/4" line level attenuator/input protector. There's bound to be something.Ian.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: July 16, 2013, 10:55:38 pm
content: Quote from: David_AVD on July 16, 2013, 10:16:51 pmI think I'm going for active

author: David_AVD
author_rank: Super Contributor
timestamp: July 16, 2013, 11:55:46 pm
content: The tricky bit will be finding something that doesn't colour the sound below the protection threshold you set.

author: Mike Warren
author_rank: Unknown
timestamp: July 17, 2013, 05:23:21 am
content: What are you driving them with? Is this the output from an audio interface on a computer, a mixer or something else?In my studio I have a limiter in the line to the amplifier which normally runs below the gain reduction threshold. If I do something stupid (Iamexperienced - 30+ years with small studios - and I still stuff up every once in a while) the limiter reduces the gain significantly.This is mostly to protect my ears, rather than the speakers, but I learned many years ago when I left bands in the control room listening to their demo that I can't trust them to not touch the master level.If you are running directly out of a computer audio interface and you use reasonable software, you should be able to insert a compressor/limiter plug-in in the control room feed at no cost.BTW, I suggest you get yourself a sound pressure meter and make sure to always monitor at no more than about 80dB. Going louder will not only increase your risk of hearing damage, but it also colours the mix so you won't get an accurate representation. It's very easy for the volume to creep up during a long mixing session if you're not careful.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: July 17, 2013, 11:36:43 am
content: Quote from: Mike Warren on July 17, 2013, 05:23:21 amAs they're going to be active, it may just be self built synthesizer hardware directly connected, for instance.Quoteyeah some limiter will certainly a lot better than nothing.Will stuff of the Behringer class do the job?QuoteWell, if I can get stuff to protect my ears, but protecting the speakers is too difficult,then I'll take that.New speakers I can buy, ears not ;-)QuoteInteresting suggestion. When I'll actually use the monitors to do mixing, I'll hopefully remember that!

author: Mike Warren
author_rank: Unknown
timestamp: July 17, 2013, 11:46:34 am
content: Quote from: TinkeringSteve on July 17, 2013, 11:36:43 amUnless you're spending upwards of $10K on your monitors, yes. The main problem with Behringer is reliability. If you're not depending on it for your living, it'll be fine.

author: madires
author_rank: Super Contributor
timestamp: July 17, 2013, 12:52:22 pm
content: Quote from: TinkeringSteve on July 16, 2013, 12:46:52 pmAn active monitor makes it very easy :-) Just add a limiter, if possible at the line input of the monitor internally. Then adjust the limiter to the maximum level you like to have. If you put the limiter inside the monitor nobody will be able to overdrive it or change the limiter level unintentionally or by mistake. Long time ago I built a small active monitor prototype for a vendor of musical instruments. They liked it and my boss was happy too

author: SeanB
author_rank: Super Contributor
timestamp: July 17, 2013, 04:28:19 pm
content: Bass units will be happy with a fast blow fuse in the feed ( cue audiphiles whine here, but just use a regular fuse and a decent set of PCB mount clip sockets on a small PCB, so you have to remove a panel to change the fuse as a reminder next time to be careful, and place 2 boxes of fuses in a small mailing bubble wrap cover there as spares, if you blow 20 fuses you are doing something wrong) while the tweeters will need a lower value fuse and a set of clipping zener diodes back to back across them after the crossover as protection ( same fuse principle here with clips and a shedload of spare fuses) which should be selected to only be needed at a large overload beyond normal levels.Active systems be sure to have a mute circuit for power on and power off that works really well, and if DC coupled to the amplifier you need a DC offset detector to trip the amplifier off reliably even if a power device fails and applies a power rail to a speaker. These can be combined to use the same relay to switch them, and use the spare relay contact ( NC one) to switch in a resistor to provide a DC path for transients to not have a click on switch on.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: July 20, 2013, 12:03:14 pm
content: Quote from: madires on July 17, 2013, 12:52:22 pmInternally you say. Which probably means I'll have to build it myself.Is it hard to build a decent limiter?

author: madires
author_rank: Super Contributor
timestamp: July 20, 2013, 12:51:56 pm
content: Quote from: TinkeringSteve on July 20, 2013, 12:03:14 pmIf you dare to void the warranty :-) There are some audio limiter ICs or tons of simple circuits with a few OPamps. I'd guess you could also get kits.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: July 21, 2013, 12:10:22 pm
content: Quote from: madires on July 20, 2013, 12:51:56 pmWell. I guess I'll test the box rigorously before I'll do any "surgery" ;-) If something says "send it back" I'll do that, if not, I might dare. I bought one (only need one) that's just somewhat over 100 EUR, which is also a decent amount of money, but I have seen that this is pretty cheap for a monitor, but the thing is said not to be as bad as some other cheapies (an ESI uniK 05), and I guess for the task at hand, it will do the job, I'm not going to mix music with it. If I'll ever have enough space for a studio, I guess I'll get a pair of better monitors.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: July 21, 2013, 08:03:59 pm
content: Quote from: madires on July 20, 2013, 12:51:56 pmI found this:http://www.silonex.com/audiohm/pdf/limiter.pdfThe interesting thing is that is uses the LDR based opto coupler that I have incidently lying around, because I used it as a variable resistor some time.Will that circuit do the trick here?

author: madires
author_rank: Super Contributor
timestamp: July 22, 2013, 12:23:21 pm
content: Quote from: TinkeringSteve on July 21, 2013, 08:03:59 pmDo you got a breadboard? Put the circuit on the breadboard and test it. The OPamps are standard types, so there won't be any waste :-) Regarding the LDR controled amp I'm a little bit unsure because LDRs can be quite slow in reaction.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: July 22, 2013, 06:30:42 pm
content: Ah yeah, right, I remember someone using such LDR based stuff exactly because it's slow, so I guess this is not what I want, better keep looking :-DThose Behringer limiters I looked for, all that stuff is only available as 19" unit, smaller units just for guitar etc.I'd buy something used to not have to build it myself, but such a 19" thing is way too large...

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: August 04, 2013, 12:08:00 pm
content: I ended up doing the real cheap & low parts count thing:I built a voltage divider with, at the signal input, a resistor of a couple 100 ohm at the top and two serial pairs of 1N4148 diodes antiparallel at the bottom, connected to GND, the output is between diodes and resistor.Not adjustable, but this clips the signal to about +/- 1V and is fine for the monitor box I got myself, which is at speech level loudness with -30dB input setting and +/- 0.5V input.Now I just need to take care not to be confused when the signal sounds strangely harmonics rich because I forgot to watch the input level not coming too close to 0.8V or so, when the diodes start to kick in doing their job :-DI thought about using red LEDs, although starting at 1.8V is a bit high already, I also have been told they tend not to be too fond of high reverse voltages. Would have been nice to see them light up when clipping is going on.

author: madires
author_rank: Super Contributor
timestamp: August 04, 2013, 02:00:37 pm
content: Quote from: TinkeringSteve on August 04, 2013, 12:08:00 pmThat's called a hard limiter :-)QuoteSell the monitor for twice the original price as "special effects monitor"QuoteThe maximum voltage of a line-in (RCA type) is about 0.5 - 2V for most audio stuff, so LEDs would be more like an input protection with a built-in optical indicator :-)

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: August 04, 2013, 10:32:11 pm
content: Quote from: madires on August 04, 2013, 02:00:37 pmHow about "monitor with extrawarmtube simulation sound" ?

author: jmole
author_rank: Regular Contributor
timestamp: August 05, 2013, 01:23:04 am
content: The best way to do this is to buy an active monitor with XLR inputs, then use an isolated XLR Balun to connect your source to the monitors.since your monitors are active, just turn the volume down, and you won't blow anything.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: August 05, 2013, 09:15:04 am
content: Quote from: jmole on August 05, 2013, 01:23:04 amApart from that not being fail safe, for some reason the volume goes only to -30dB, not -infinity dB, so I could still blow the thing.The balun thing sounds interesting, looks like those things are not quite for free, though.

author: mrflibble
author_rank: Super Contributor
timestamp: August 05, 2013, 09:34:32 am
content: A cheapo way to convert your unbalanced to balanced is use theDRV134 from TI. I use those for my Behringers. Grab some XLR goodies from ebay/dx and you're all set. (Doesn't solve your input protection problem though. XD )

author: madires
author_rank: Super Contributor
timestamp: August 05, 2013, 09:40:50 am
content: Quote from: TinkeringSteve on August 05, 2013, 09:15:04 amXLR: balanced signalRCA: unbalanced signalA balun is simply a balanced-to-unbalanced (and vice versa) transformer.

author: David_AVD
author_rank: Super Contributor
timestamp: August 05, 2013, 10:04:37 pm
content: Quote from: madires on August 05, 2013, 09:40:50 amSmall correction - they are both connector types. What signals are on them and if it is a balanced is another matter.