clip led on amps

[v1rtu0s1ty]

hi folks,

I've got a question on my amp. I built a manifold for an IB but I haven't really installed it yet on a false wall. I've been using as open and it does work but of course, I'm missing the performance. But anyways, my question is about the amp and the driver. I do see my amp's clip led blink quickly like less than a 1/2 second. This happens when I play insane LFE like from "The Haunting". I contacted QSC and they told me that 1 second light on clip LED is fine.

So, how will I know that I am fully utilizing the limits of my 2 Fi Car Audio 18" IB driver? It's because, I have seen some youtube video of ficar drivers and I can see the cone really go really high and fast.

Does your amp clip led turn on for a long time and driver still performs well? Do you set CLIP Filter to OFF position?

Thanks.

http://restricted.dyndns.org/qscamp/

[kouack]

Will depend how many watts and freq you apply to your sub and specific installation, you did not specified wich qsc amp you own but they range from 200 watts to 8000 watts.

1: if you get the sound level desired you are ok without major clipping of amp.
2: if you hear a klonk or metal sound this is not good you reach max xmech of speaker

[v1rtu0s1ty]

It's a QSC PLX 2402. I'm currently driving my 2 FiCar 18" drivers in bridge mode. According to Sonnie, I have configured it at 2400watts.

Are you saying that even if I am seeing continuous dim/shimmering/flickering/blinking of red CLIP LED during heavy LFEs and I am not hearing the klonk or metal sound, my amp is still good?

[Ricci]

In my experience clipping is very noticeable and sounds really bad, as does woofer bottoming. Especially with high excursion subs and large pro-amps. It usually goes from sounding "fine " to "don't do that to me anymore" and "turn me down a bit", with not much in between.

What kind of box do you have the drivers in?

[v1rtu0s1ty]

I built a manifold for my future IB which will be started some time this year. You will see the manifold here.

http://www.hometheatershack.com/forums/83812-post1.html

I noticed the other day when my friends were there, they requested a demo. I turned the volume from my regular listening/watching -14.5db on Yamaha master volume to -12db. It was still very clean. I did see the CLIP Led flicker but dim continuously on Flight of the Phoenix where the airplane was crashing. They really love that moment.

So I don't know if I should try -10db. Oh, I remember the QSC amp was warm only but not hot.

[Ricci]

When you are demoing this stuff do you have the open back end of the box facing into the floor? You are basically operating these free-air right now and they will not have anywhere near the spl or sound that they will when they are properly isolated from the back wave.

[v1rtu0s1ty]

Yep, I noticed it too that when it was facing down with a little air gap, it was more tight. But I'm aware that I can ruin my drivers if I do that since it doesn't have much air to breath. So if I am the only one, I play it at -14.5 db. When I demoed it, it was facing us and it was at -12db. We still did feel it but I guess, I'm missing a lot of SPLs like what you said. Someone told me that if it's open, the back wave and front wave will collide which reduces the SPL.

So am I correct that I'm fine with the flickering dim red CLIP as long as it doesn't bottom out or clip?

[tonyvdb]

Clipping of an amp no matter how short a time is never good as this causes distortion in the signal. In extreme cases this will damage not only the driver but the amp as well. Clipping of an amp in some cases can momentarily turn off the signal this causes a "pop" or "crack" sound, on other amps this is a soft clip meaning that the amp gives up and wont output any more volume and usually some distortion is heard.
On Most QSC amps the clip light is a warning that you have reached its limit and you should turn the input signal down slightly to avoid this. If the LED stays on for more than a second you've got a bigger problem and now you will cause dammage.

[v1rtu0s1ty]

When you said "LED stays on for more than a second", you are referring to a SOLID on correct? I have never seen it do like that. It's always flickering and dim and only during heavy LFEs. I will take a video of it tonight.

[tonyvdb]

As distortion is not as easily heard in the lower frequencies this may not be a big deal but if the LED is coming on you are introducing some no matter how short it is.

[Ricci]

Also if you insist on driving your subs hard they way they are now, you should place the manifold opening on the floor. This will help isolate the frontwave of the drivers from canceling out the back wave and should make them act like they are in a small, leaky, sealed box. This would protect the drivers from overexcursion a little better.

If the amp is clipping, knock it back a notch.

[v1rtu0s1ty]

Ok. I need some help or clarrification. I was taking a video of the LEDs.

The manifold opening is facing me and not the floor. I played the LFE demo scene from "The Flight of the Phoenix plane crashing" at -14db on my Yamaha master volume.

I heard a loud "TAK" during the middle of the scene. I can't tell if it was from my mains or my subs. My mains are set to SMALL and BASS is only set to SWFR.

However, I forgot to restore what I did last night. I was playing with the cross over setting on my Yamaha. When I saw it, it was set at 160hz. My normal setting is always at 80hz. I always watch this scene and I never heard that loud "TAK" sound even at -12db setting on my Yamaha.

So is it possible that the 160hz crossover setting which I forgot was the culprit that allowed it to produce that loud "TAK" sound?

[v1rtu0s1ty]

Ricci wrote:

Also if you insist on driving your subs hard they way they are now, you should place the manifold opening on the floor. This will help isolate the frontwave of the drivers from canceling out the back wave and should make them act like they are in a small, leaky, sealed box. This would protect the drivers from overexcursion a little better.

If the amp is clipping, knock it back a notch.

So maybe, the reason why I wasn't hearing the loud TAK sound previously is because the manifold opening was facing the floor.? However, I was told that having the manifold opening facing the floor could promote to the early failure of my drivers since the driver is a modded for IB use.

I think, I should start building the theater soon.

[v1rtu0s1ty]

As promised here is the video of my QSC amplifier in action while playing the LFE scene from The Haunting.

http://restricted.dyndns.org/QSCPLX2...eHaunting.html

The jet engine noise in the background is from my Sony 1272 CRT projector.

[thxgoon]

It's possible that the higher crossover allowed something into the sub which ended up sounding like 'TAK', but if you are simultaneously clipping the amp then there might be other issues involved. If I were you I'd be careful with your current setup and stay away from clipping all together if you want your woofers to last until your theater is done. When you clip an amp you end up sending strong DC to the woofers (and through the amp) that don't get used for any useful work and have to be dissapated as heat. In the short term it may not hurt anything but I would not push it. Just turn it down a bit and give yourself all the more reason to finish your theater

[v1rtu0s1ty]

Thanks. I will follow your advice.

[Ricci]

Right that TAK sound is what I was talking about, how things will let you know for sure when something isn't right. Believe me running your subs with the manifold facing into the floor to create a quasi sealed box will be safer than just straight free-air. I would not be pushing things as hard as you are right now in either case. You are playing with fire.

[v1rtu0s1ty]

Ricci wrote:

Right that TAK sound is what I was talking about, how things will let you know for sure when something isn't right. Believe me running your subs with the manifold facing into the floor to create a quasi sealed box will be safer than just straight free-air. I would not be pushing things as hard as you are right now in either case. You are playing with fire.

Ok. I reduced the LFE gain on my yamaha before I left the house this morning. Then open side is now facing the floor again just how I had it previously. I'll check it again. I got to get my theater up and running.

Oh, since I am doing a room within a room(floating) home theater in the basement, am I correct that my subwoofer won't move the room(due to vibration/shaking) since after the room is done, it's going to be really heavy? If so, there is really no need for me to screw down the floating floor to the concrete floor.

Thanks guys!

[deromax]

thxgoon wrote:

When you clip an amp you end up sending strong DC to the woofers (and through the amp)

Actually, harmonics of the fundamental tone are produced by the clipping. No DC is produced.

[v1rtu0s1ty]

let's assume my theater is built, and ib is installed as well. What is the proper way of calibrating the sub? This is how I calibrate it and tell me guys if I am missing or the steps or are incorrect.

1. Zero everything out in receiver, sp level of all channels. Also set to zero the treble and bass.

2. Put RadioShack SPL meter at listening position. Point it towards the point where wall meets the ceiling. That's somewhere 30 to 40 degrees. Set Radioshack at 80db, C weighting, slow.

2. Pop in AVIA disc. Then play tone on LEFT front channel.

3. While tone is playing, adjust receiver master volume so that needle on meter stays at 85db.

4. Play next channel(center, right, SR,SL) and adjust the SP LEVEL of each channel so that needle is also at 85db.

5. Now calibrate SWFR, play the tone and adjust LFE LEVEL so that needle stays at 85db.

What do you think guys?

[Jerm357]

Does your receiver have negative numbers that get smaller the higher you turn it up? If so what I do is get Avia to play 85db at 0 on the receiver (or 82 I believe if your receiver goes from 1-100) for all channels.

[v1rtu0s1ty]

Jerm357 wrote:

Does your receiver have negative numbers that get smaller the higher you turn it up? If so what I do is get Avia to play 85db at 0 on the receiver (or 82 I believe if your receiver goes from 1-100) for all channels.

Yes, master volume I guess is from -74db to +16db. So when I make it louder, it goes like this

-20
-19.5
-19
.
.
.
.
-1.5
-1
-0.5
0
+1
+1.5
and so

[thxgoon]

deromax wrote:

Actually, harmonics of the fundamental tone are produced by the clipping. No DC is produced.

It depends on the design of the amplifier but with most solid state amps both are produced. Here's one quick and dirty link.



In this image of an amp clipping, those flat areas at the top and bottom of the wave represent the DC component of the output. Notice that this DC is at the level of max output.

[Jerm357]

v1rtu0s1ty wrote:

Yes, master volume I guess is from -74db to +16db. So when I make it louder, it goes like this

-20
-19.5
-19
.
.
.
.
-1.5
-1
-0.5
0
+1
+1.5
and so

Good, so instead of doing #3 on your list just set the main volume to 0 and adjust every thing to 85db from there. Or do what I do and set the Main volume to -15 and make sure every thing reads 70 db. This will get you to the same place as 0 main volume and 85db but you wont have to make your ears bleed to do it. The reason to this way is so main volume will have meaning. Say your listing at -20 on the main volume, you will know your at 20 db under reference level. This is why receivers have negative numbers and how its ment to be done.