Need to de-bump 4k in studio monitors

Greetings,

I am tasked to "de-bump" a set of studio monitors 2-4db at 4k. Okay, seems easy, but they are balanced audio and needs to be a strictly passive circuit ( no power )

Best solution? Solder and Mouser or off the shelf?

You could use a balanced attenuator,  for example an H pad.  The R in the middle that connects hot and cold gets replaced by an RLC, so you end up with frequency dependent attenuation.

mkiijam said:

needs to be a strictly passive circuit ( no power )

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Why?

Best solution? Solder and Mouser or off the shelf?

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As mentioned before, RLC circuit in the shunt branch of a U-pad, but it's gonna take ages to get the BW right. Getting the frequency is easy using the formula L.C.omega²=1, the attenuation is easy, using a potentiometer, but adjusting BW requires altering the L/C ratio.
Even if you have accurate measurements of the actual bump, it will take trial and error to get it right.
OTOH a modern active filter is tunable in real-time, which would make tuning a cinch.

mkiijam said:

Greetings,

I am tasked to "de-bump" a set of studio monitors 2-4db at 4k. Okay, seems easy, but they are balanced audio and needs to be a strictly passive circuit ( no power )

Best solution? Solder and Mouser or off the shelf?

Click to expand...

Active EQ

JR

I'm guessing these are active monitors?? Is there something inside the amps that can be messed with ???

the easiest solution here would be a graphic eq between the output of the desk or monitor controller and the input to thew powered speakers.
Get yourself a white 4001 and then a second one for the other channel and you are done.

Assuming they are balanced then you may have some switch settings or other DSP  on the speaker itself you can use.

pucho812 said:

the easiest solution here would be a graphic eq between the output of the desk or monitor controller and the input to thew powered speakers.
Get yourself a white 4001 and then a second one for the other channel and you are done.

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A 1/3 octave GEQ may not be precise enough; some specific problems happen on a very narrow spectrum.

In good old days a parallel notch was the obvious solution.
http://www.mh-audio.nl/parallelnotchfilter.asp#IN

moamps said:

In good old days a parallel notch was the obvious solution.
http://www.mh-audio.nl/parallelnotchfilter.asp#IN

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This calculator doesn't say how to adjust the BW...

This part is on top of the site.
http://www.mh-audio.nl/parallelnotchfilter.asp#vance

moamps said:

This part is on top of the site.
http://www.mh-audio.nl/parallelnotchfilter.asp#vance

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  Ah, OK.
Now, how does one evaluates the BW when the bump is less than 3 dB? Even with a 6db bump that would be quite error prone. It's a very common issue in acoustics; how does one make a real-world graph fit a mathematically-defined response? There are programs that do that; they are very complex and pass 33 000ft over my head and give only approximate results.
My experience tells me that real-time adjustment is much more practical. You turn 3 knobs and voila!

abbey road d enfer said:

Now, how does one evaluates the BW when the bump is less than 3 dB? Even with a 6db bump that would be quite error prone

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By using approximations. Anyway, some experimentation is always needed to adjust it right.

My experience tells me that real-time adjustment is much more practical. You turn 3 knobs and voila!

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Agreed. But you can do that with 3 switched boxes of resistors, caps and coils. 3 knobs also. And a real time measuring is needed anyway.  I worked a lot with Sabine and BSS FCS 928 equalizers and think that using it for taming a small bump in FR is over-engineering approach.  It will, btw, cost much more. 

moamps said:

But you can do that with 3 switched boxes of resistors, caps and coils. 3 knobs also.

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What is the costs of such boxes? Eve if you DIY them, you need boxes, switches and a bunch of expensive caps and inductors.

  I worked a lot with Sabine and BSS FCS 928 equalizers and think that using it for taming a small bump in FR is over-engineering approach.

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What's wrong with over-engineering if the cost is contained?

  It will, btw, cost much more.

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A second-hand decent parametric EQ can be had for about $150.
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We're not saying that running through an active eq isn't going to affect the overall sound???
I've never heard the higher end active solutions that are supposed to be great but , from my experience, additional active electronics before the monitor's amps does affect the sound even more.....???? ......

abbey road d enfer said:

.....A second-hand decent parametric EQ can be had for about $150...

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A decent passive notch filter will cost less than 10 Euro/channel.  Multiple it by 3 for extra parts, the cost stays significantly below an active solution.
OP asked for passive solution, no one mentioned  parallel notch so I just posted my opinion and gave a solution.

It hasn't explicitly been stated, but you can use an active EQ to find exactly the dip you want to end up with and then measure that and make a passive network to duplicate the active EQ's curve. The advantage is that you can use your ears (or room measurement tools) to find the correction you need first, and then build a passive network to mimic that curve.  This seems a lot more straightforward than trying a pile of successively tweaked passive networks - use a generic EQ first, and then build a custom filter to mimic it and you'll finish the job in a predictable amount of time.

moamps said:

A decent passive notch filter will cost less than 10 Euro/channel.  Multiple it by 3 for extra parts, the cost stays significantly below an active solution.

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I already said that building your test jig with switchable caps and inductors will cosst much more. The initial spending could b ejustified if you had to do that often.

OP asked for passive solution

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But when I asked him why, he just didn't answer. I have  a feeling he's not interested anymore.

abbey road d enfer said:

I already said that building your test jig with switchable caps and inductors will cosst much more.

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We can once again agree to disagree...

.. I have  a feeling he's not interested anymore.

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and finish this discussion.

Monte McGuire said:

It hasn't explicitly been stated, but you can use an active EQ to find exactly the dip you want to end up with and then measure that and make a passive network to duplicate the active EQ's curve. The advantage is that you can use your ears (or room measurement tools) to find the correction you need first, and then build a passive network to mimic that curve.  This seems a lot more straightforward than trying a pile of successively tweaked passive networks - use a generic EQ first

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+1 this seems like the obvious solution to me.