Limiter/compressor for DIY subwoofer - AVS Forum
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post #1 of 18 Old 04-30-2012, 09:20 AM - Thread Starter
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Hi All

I'm looking into the possibility of adding a limiter/compressor to my sealed DIY subwoofer setup.

A lot, if not all, of the higher end commercial subs available have this built in to prevent overdriving their subs at high SPL levels. Below for example is the sweep from a paradigm sub 2

My question is, what do I need to implement this into my system, and how would I use it? Google has given me very little, as I'm not very familiar with the whole concept.

Many thanks

Tim
LL
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post #2 of 18 Old 04-30-2012, 09:38 AM
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There are several methods you can use:
  1. Amplifier with built-in limiter
  2. External EQ with limiter such as the Behringer DCX2496
  3. Stand alone limiter in signal chain such as Behringer MDX1600
  4. VST Plugin for software playback such as Voxengo Elephant
  5. Playback software with limiter such as JRiver Media Center

You only need a limiter if your amp produces more power than your drivers can handle at the maximum volume you will ever listen to. Commercial subs need limiters since they have to assume some users will abuse the sub by running at levels way too high.

What amp, driver, and enclosure size is your sealed sub?
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post #3 of 18 Old 04-30-2012, 09:48 AM - Thread Starter
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Quote:
Originally Posted by desertdome View Post

There are several methods you can use:
  1. Amplifier with built-in limiter
  2. External EQ with limiter such as the Behringer DCX2496
  3. Stand alone limiter in signal chain such as Behringer MDX1600
  4. VST Plugin for software playback such as Voxengo Elephant
  5. Playback software with limiter such as JRiver Media Center

You only need a limiter if your amp produces more power than your drivers can handle at the maximum volume you will ever listen to. Commercial subs need limiters since they have to assume some users will abuse the sub by running at levels way too high.

What amp, driver, and enclosure size is your sealed sub?

Thanks for your reply

My sub is a clone of the sub 2, I use 6 JL audio 10w3v3 drivers, and am powering it with an FP+14000

I also use a minidsp for LT + EQ

So I definitely have more power on hand than the sub can handle. For the time being I'm playing with various high pass filters to keep the sub from being overdriven, but I feel a limiter will be more practical.

I'll look into the Behringer MDX1600, I feel a standalone unit would give me the most flexibility.

Best

Tim
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post #4 of 18 Old 04-30-2012, 09:58 AM
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I was searching the limiter/compressor as well for subs. My inuke amps only have the limiters, and i figured i would set it since im running it bridged (3kw supposedly) into a 12" lms-r. I figured if anything, it would help if there was a huge burst of bass that would push it past xmax or so.

I did play around with it to see how fast and how much it limits voltage to sub. I ran a DMM onto the leads and measured the AC voltage. Basicly, with no limiters i get 100v. With -1 = 91v , -1.5=85.6 , -3=72, and -4=61. So they do work i guess lol. Obiously this isnt the real way to measure since it was with only the DMM load and no 4ohm or whatever resistors. Might i add, that was with a +6db input signal @30hz.
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post #5 of 18 Old 04-30-2012, 10:09 AM
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Quote:
Originally Posted by TimVG View Post

My sub is a clone of the sub 2, I use 6 JL audio 10w3v3 drivers, and am powering it with an FP+14000

I looked at the pictures of your sub - very nice! I would start by adjusting the voltage limiting on the FP14000 using the DIP switches on the back. Here is the Lab Gruppen input sensitivity chart. The Lab Gruppen manual should show how to adjust the DIP switches even though you have the clone amp. What you want to do is reduce the maximum power output of the amp so it doesn't exceed the driver capabilities. You might want to start at a low output level and then work your way up.
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post #6 of 18 Old 04-30-2012, 10:24 AM - Thread Starter
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Quote:
Originally Posted by desertdome View Post

I looked at the pictures of your sub - very nice! I would start by adjusting the voltage limiting on the FP14000 using the DIP switches on the back. Here is the Lab Gruppen input sensitivity chart. The Lab Gruppen manual should show how to adjust the DIP switches even though you have the clone amp. What you want to do is reduce the maximum power output of the amp so it doesn't exceed the driver capabilities. You might want to start at a low output level and then work your way up.

Thanks for your comments!

I definitely try that, but would it work the same as a limiter? What would happen if I up the volume a notch? Would the response curve become variable, like in the graph I posted from the original sub 2? Or will the amp shut off/go into protection..

Thanks so much for your help!

Tim
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post #7 of 18 Old 04-30-2012, 11:47 AM
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There are two things to adjust on the back of your amp using DIP switches: Input Sensitivity and Voltage Peak Limiter. You may need to adjust both, but it is the Voltage Peak Limiter that I was talking about. You should probably set the mode switch to hard (switches 4 & 8 in the up position). Switches 1-3/5-7 can then be put in 8 different configurations per the chart on the back. When configured properly, the response curve will be variable such as the graph you posted.

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post #8 of 18 Old 04-30-2012, 12:16 PM - Thread Starter
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Quote:
Originally Posted by desertdome View Post

There are two things to adjust on the back of your amp using DIP switches: Input Sensitivity and Voltage Peak Limiter. You may need to adjust both, but it is the Voltage Peak Limiter that I was talking about. You should probably set the mode switch to hard (switches 4 & 8 in the up position). Switches 1-3/5-7 can then be put in 8 different configurations per the chart on the back. When configured properly, the response curve will be variable such as the graph you posted.


Thanks for clearing that out, I'll try it out and post the results!

Once again, thank you very much taking the time to help, I really appreciate it
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post #9 of 18 Old 04-30-2012, 01:17 PM - Thread Starter
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I'm trying it out as I type this, is it normal that when the limiter kicks in, the sound seems like it is distorting?

The goal kinda is limiting output before heavy distortion kicks in.
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post #10 of 18 Old 04-30-2012, 02:44 PM
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Quote:
Originally Posted by desertdome View Post

What you want to do is reduce the maximum power output of the amp so it doesn't exceed the driver capabilities.

Except that power handling is a function of both frequency and how long it's applied.

Noah
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post #11 of 18 Old 04-30-2012, 03:30 PM
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There was a short period of time when I experimented with a compressor in my signal chain. As my situation would have it, I just didn't have enough sub for the room. Insert compressor,.... I still enjoyed strong average levels,...however somewhat flat and lifeless peaks. What it really got me was strong, intelligible dialog, with a nice predictable sub operation w/freedom from unexpected overload.

If one is decently well versed in compression settings and operation, it's a very easy set-up. I had some Behringer Composers, which is a two channel compressor. They are way too veiled, lacking ample MF/HF transparency for any important live work. So, having a few just sitting around, I took one out of it's rack and used it to achieve a nice robust bottom end, without worry of hitting the limits on the big effects.

I don't remember but I likely set the ratio about 6:1, so any signal over a particular point I determine, gets attenuated by a ratio of 6:1. It still increases, so it's not like a limiter. You could set a 6:1 ratio about 3db below your limit, subsequently it'd take a big 18dB transient to hit that limit. These settings are merely approximations, some quick experimentation would be in order.

If there are other work-arounds, I don't recommend it, .... as it neuters the real fun stuff. But it worked for me in my temp scenario. What I was up against was inadequate mains output, insufficient dialog intelligibility because I operated at a level whereby the LFE/RB came thru cleanly,...peaks relatively intact. I found myself constantly gain riding, which quickly became a real pain in the ass. Considering options until things got back to normal, I remembered the old compressors I had, and I preferred compressing the sub, instead of globally compressing the entire mix via the on-board dynamics processing in the AVR at the time.

Good luck

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post #12 of 18 Old 04-30-2012, 03:53 PM - Thread Starter
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Thanks for all the helpful comments so far, keep em coming!

From what I've read in reviews from the top commercial subwoofers, they never seem to make a bad sound, all of those seem to have limiters according to increased SPL sweeps.

Has anyone here heard a DD18+, JL Fathom, Sub 2, Submersive, etc. and would be prepared to make a comment on that? Can you hear the compressor/limiter in action, or does it really just stop getting louder from a certain frequency? Or does it go together with increased distortion?

Has anybody tried/succeeded in replicating this on his DIY sub?
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post #13 of 18 Old 04-30-2012, 10:40 PM
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Yes I have, and do. Here is my DEQ.

It lets you squeeze every last drop of SPL out of your system without bottoming out on the low notes at high power; be it music or movies.

Watch the vid to see how to shape signals with it.
The thing is magical and a life saver.

It is basically a more fancy compressor/limiter version of the DCX.
It has 31 GV-EQ, 10 PEQ/FBD, 3 DEQ, 1 Limiter, 1 Compressor/Expander, 1 Delay/Temp, and 1 RTA/SPL /w Semi & Auto-EQ.
(All concurrently full-on, with Q and Gain adjustment of course.)

The only thing it is missing is 3 channel routing/XO/Phase/Gain.
(The XO can be approximated by eating up a few bands of EQ.)

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post #14 of 18 Old 05-01-2012, 10:48 AM
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I too have the deq2496 and it's way more functional than what 95% of DIY'ers would need. I've never used all of the functions.

YID DIY
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post #15 of 18 Old 05-01-2012, 10:56 AM
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Quote:
Originally Posted by Looneybomber View Post

I too have the deq2496 and it's way more functional than what 95% of DIY'ers would need. I've never used all of the functions.

How do you use it? Which aspects do you utilize?

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post #16 of 18 Old 05-01-2012, 11:53 AM
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Quote:
Originally Posted by Looneybomber View Post

I too have the deq2496 and it's way more functional than what 95% of DIY'ers would need. I've never used all of the functions.

Looney and BassthatHtz,

How do you like the functionality versus the dcx? Is it a little easier for eq? will it still do hi and low pass filters, just not for 2 or 3 way setups?

how many I/O's?

what is the difference between the gv-eq, deq, and peq?

(European models do not accept banana plugs.)

 

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post #17 of 18 Old 05-01-2012, 07:45 PM
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Quote:
Originally Posted by beastaudio View Post

How do you like the functionality versus the dcx? Is it a little easier for eq? will it still do hi and low pass filters, just not for 2 or 3 way setups?
how many I/O's?

what is the difference between the gv-eq, deq, and peq?

You can check out the hi-res pictures of the inputs and outputs, and specs here.
http://www.behringer.com/EN/Products/DEQ2496.aspx

If you can forego all the Auto-EQ stuff and RTA/SPL measuring features, the DCX is the supperior product for all the other more common tasks. Such as Hi-Lo filtering on dual 3-way configs.
The DEQ has no filtering at all, its pure EQ, but unlike the DCX, it doesn't restrict how many eq points you can use when using many aggressive filters.


"what is the difference between the gv-eq, deq, peq, Dynamics Processing:Compressor/Expander/Limiter?

Let's start with Limiters because that is the easiest one. Basically above a given input signal the output will not go higher; it is basically a brickwall. If it is chopping the heads off the peaks like that you can imagine the problem that causes distortion-wise. So...

This leads nicely into the Dynamics processor; a compressor allows you to define how early and aggressively the device will attack the peaks before the limiter point is reached and engages; softening, smoothing and slowing the blow, rather than an abrupt dead-stop at full output clip and/or full excursion.

So obviously... it is better to limit than to bottom out your subwoofer and destroy it. So you set that value to just under max excursion, given a 0db Ref sine-sweep input. Guaranteeing no bottoming, and using the compressor to ease into the mechanical limits of the thing.

Note: I haven't tested it but I would hope that Behringer implemented it as a proper soft-limiter with some input gain servo intelligence behind it rather than a pure brickwall. (I'm curious enough to go forth and test that now )

Behringer's implementation of a "Dynamics Expander", is actually a noisegate. Basically, below a given input level, the signal will not be outputted.

Ok so far all the above was applied on the full signal bandwidth (DC to nyquist).

So that leads nicely into the EQ bits.
Now before we go any further you have to understand the components that define how EQ's operate.
1) Input Signal Level (in db) (aka Threshold) (dynamics only)
2) Output Gain (in db) (the positive or negative amount you desire)
3) Aggressiveness (X db Input for Y db Output) (aka Ratio) (dynamics only)
4) Knee (i.e the Aggressiveness nearest the Threshold value) (dynamics only)

and Last but not least:
5) Center Frequency (in Hz) (aka CF) (i.e the Frequency you care about)
6) Bandwidth (in octaves) (aka BW or QF) (i.e the Frequency range +-3db slope relative to the CF to which EQ will also be affected.)

Ok let's continue...

Let's start with Static EQ, that is the easiest.
It is basically a slider-bar style EQ, it only lets you adjust one thing, the Output Gain. Not very useful, unless your hard up.
Everything else about it is fixed: fixed CF, fixed BW; and no Threshold at all.
(For this reason, those style devices are usually much cheaper.)

Next step up is the GV-EQ, it allows that and BW adjustment, and for this reason is usually digital-domain only from this point onward, and done on a computer screen.

Next step up is PEQ, it allows that and user selectable CF adjustment.

Next step up is DEQ, it allows all 6 adjustables.
DEQ, as you probably guessed, is basically a user selectable frequency-based and level-based compressor/expander(a true gain expander FYI, not a noisegate).

The next step up is fully-auto EQ, which involves a microphone; computer does everything for you, but only when it is on the config mode and playing sweeps.

The next step up is semi-auto EQ, allows you to define a target graph.

The next step up is RTA/FBD, basically auto-EQ, but is always-on, actively listening to the in-room response and making corrections to give the flattest average response and does echo cancellation.

Have I fully cooked your noggin yet?
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post #18 of 18 Old 05-01-2012, 08:06 PM
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I forgot, there are 2 more DEQ capabilities.

7) Attack - How much time passes before it activates. (ms time) (dynamics only)
8 Release - How long it is activated for before disengaging. (ms time) (dynamics only)
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