Bass too loud in stage montior - any devices that can help?

[JCJR]

Jim Y has good ideas.

The "ideal" would be to build a box with a power supply, and input buffers with high-z input and low-z output which drive the filter network, and output buffers with high-z input and low-z output which drives the output jack. Also if throwing that many parts at it, one could also design a fancier filter "in between" the input and output buffers.

The main reason for the active input and output buffers would be to assure "near identical filter performance" over a wide range of source driving impedance or dest sink impedance. When the source impedance is "trivially small" compared to the filter impedance then the source impedance doesn't have much effect on the filter response curve. Similarly if the destination impedance is "much larger" compared to the filter impedance then the destination impedance doesn't have much effect on the filter response curve.

If the source or dest impedance is close to the filter impedance then we can't ignore the contribution any more, and must calculate a more complicated filter circuit including the influence of the source and dest impedance.

A common "rule of thumb" is that a source-vs-dest impedance ratio of 10X or better is enough so we can more-or-less safely ignore the driving circuit and the destination circuit. That is why I tried to figure an RC hipass at the geometric mean of impedance, "in the middle" between typical source and dest impedances. Which was about 8.2X or something.

Just using a capacitor and relying on the amp input impedance for the R part of the RC might work great maybe most of the time. The tuning of such a filter would depend on the speaker/amp input impedance. If it happens to be lower than 10 kOhm then the filter cutoff frequency would get detuned higher, and if the amp input impedance happens to be higher than 10 kOhm then the filter cutoff frequency would get detuned lower.

Using a ground-referenced RC "in between" the typical src and dest impedances, would hopefully "nail down" the filter performance over a wider range of src and dest impedances, but to REALLY nail it down you would want to build a real box with a power supply and active input buffer electronics and output buffer electronics. Trying to nail it down in the mid-impedance point is just a kludge attempting to get as close possible to a buffered circuit performance with only simple passive components.

If you know for sure the amp input impedance will ALWAYS be 10 kOhms (or whatever) then maybe just a series capacitor would work in all cases. Or maybe just a series capacitor would work in most cases. It has been too long and I do not understand the possibilities.

Except for knowing that the manufacturer might say the amp input impedance is 10 kOhms, the rest of the amp input might as well be a black box. Maybe it is a center-tapped 20k transformer? Maybe it is a 10k terminating resistor to ground, and a 100 MegOhm tube or fet or fet input opamp voltage follower? Maybe it is a 10k resistor into the "virtual ground" at the inverting input of an opamp? Maybe it is a 10k resistor into a very low-z bipolar transistor junction?

Perhaps in all of those cases, so long as it is 10k, then just by adding the series capacitor you could guarantee exactly the same filter curve? I don't know one way or the other whether all of the possible amp input "black boxes" terminated by 10 kOhm would respond the same way to a series capacitor. Maybe in every case it would respond the same, dunno.

[egbert]

This thread is a little odd - two posters - lfm and winstontaneous - have raised the rather germane issue of the monitor being on the floor. They get no response.

Bass frequencies are boosted if the monitor is near a boundary (wall, floor, ceiling). This effect is further doubled if the monitor is near two boundaries ( eg wall and floor) and it is doubled again if it is in a corner (ie near three boundaries - eg two walls and a floor).

In these three cases, the bass response which might be flat if the monitor is on a tall stand outdoors (ie in free space) is radiating into half space, quarter space and 1/8 of space in these three cases and the bass boost in these three cases is 3dB, 6 dB and 12 dB respectively.

So getting the mofo off the floor and away from corners could solve this issue.

[Jim Y]

I saw that "on the floor" too, but if it's a wedge monitor then that may be where the user wants it.
You can remove some bass extension simply by blocking the cabinet port, but with a powered monitor, they usually rely on the port airflow to pump some cooling air around the amplifier. If it has external heatsink fins, it probably won't mind a blocked port.

[egbert]

Many of these monitor wedge products - eg Yamaha DXR series etc - have presets for each location - on the floor as a wedge, standing and on a stand. They apply the required EQ to deal with the issue I have already covered.

[miden]

I did not really refer to the "floor" posts, as,well, it's a floor monitor! If I wanted a stand monitor that's what I would have bought. For the record I am totally aware of increased bass resonances when in close proximity to walls, corners, floors!

And if the monitor I have had "presets", then I'd not have created the OP, ne c'est pa?

[egbert]

What were you going for there with the Francais - Je ne sais pas?

If you want it to work with a flat response on the floor you may need to invest in something designed specifically for that job in mind.

[BertKoor]

The "ideal" would be to build a box with a power supply, and input buffers with high-z input and low-z output which drive the filter network, and output buffers with high-z input and low-z output which drives the output jack. Also if throwing that many parts at it, one could also design a fancier filter "in between" the input and output buffers.

Just getting a Behringer GEQ-3102 (esp. second-hand) might be lots easier, tweakable and cheaper. Unless building electronic boxes makes your heart tick faster, then by all means...

[thecontrolcentre]

Wouldn't it make sense to buy a monitor that does what you want rather than trying to fix one that's clearly not up to the job?

[JCJR]

The "ideal" would be to build a box with a power supply, and input buffers with high-z input and low-z output which drive the filter network, and output buffers with high-z input and low-z output which drives the output jack. Also if throwing that many parts at it, one could also design a fancier filter "in between" the input and output buffers.

Just getting a Behringer GEQ-3102 (esp. second-hand) might be lots easier, tweakable and cheaper. Unless building electronic boxes makes your heart tick faster, then by all means...

Hi Bert I agree. Was not advising building something with in/out buffers and power supply. Was explaining that would be the "right way" to do it. The way about any analog device does it. Trying to make the point that any simple passive inline filter is some kind of kludge and explaining rationale for the kludge I picked. Rationale could be made for other kludge solutions.

The advantage of a passive kludge, assuming it turns out to work good enough, is it is cheap and doesn't take up much extra space on stage or in a gig bag.

I would personally probably just tote another equalizer along unless the circumstance was special some way.

I don't understand people saying miden should go buy new speakers or move his speaker around or whatever. Sometimes in live work we have control over such details but often we do not. Mostly get gear that works good enough, and lasts awhile before falling apart, but doesn't cost so much that it makes a profit impossible. If you expect to maybe get paid $20,000 a year gigging but you pay $19,000 a year in equipment then it would be a better career choice to wash cars or flip burgers.

Mainly just put the gear on stage as good as the facilities allow, EQ it as good as the situation allows, and then try to do as good job possible.

I remember one road gig with a band back when, a couple of weeks at this club where the stage wasn't big enough for my keyboard L-stack plus the drummer's rig. The drummer had every drum ever made, double kick drums, from the tiniest roto-tom to giant floor toms, and an entire Plan 9 From Outer Space Flying Saucer Attack Formation of every concievable cymbal.

The drummer was such a prima donna that he was adamant that he couldn't possibly do a proper job on such masterpieces as Disco Inferno or Stayin Alive without every single one of his drums. Simply impossible to do without a floor tom, or even a bell tree or finger cymbal. So for two weeks everybody but me was on stage. I was set up in this dark dank little pit back behind the PA speakers on one side of the stage, because the prima donna drummer couldn't possibly do his job with a pared-down kit. Guess its lucky there was a hole back there or I would have had to set up in another room entirely.

I mean, there's live situations where you just have to do what you have to do.

[miden]

@ JCJR - +1000!!

[miden]

The "ideal" would be to build a box with a power supply, and input buffers with high-z input and low-z output which drive the filter network, and output buffers with high-z input and low-z output which drives the output jack. Also if throwing that many parts at it, one could also design a fancier filter "in between" the input and output buffers.

Just getting a Behringer GEQ-3102 (esp. second-hand) might be lots easier, tweakable and cheaper. Unless building electronic boxes makes your heart tick faster, then by all means...

It's too big! Now if you could've recommended a half rack size EQ (or even a pedal/stomp style that didn't chew threw a battery every 3 hours) I'd have paid attention. JCJR nailed it in the most recent post. If I had thousands to spend on a flash floor monitor, that's what I'd do. If I had the space to fit in a rack size bit of gear, I would! JCJR gave me a solution that could work and be 1.cheap and 2. very unobtrusive!