Please help - DIY 7 band 1/3 oct parametic EQ

[tipicreeper]

Hi everyone,
I'm hoping for some help with a sanity check.
I have been looking at ESP's Parametric eq and thought I might be able to tailor one specifically for my sub.
Project details can be found here:
http://sound.westhost.com/project28.htm

Attached is a proposed diagram of what I am thinking. I hope someone may have the time & inclination to see if I am on the right track.
This is my first venture into this area and looking for some sage advice.

[sreten]

Hi,

Generally speaking subwoofer EQ for correction should be confined to
cut. Any form of boost (such as a Linkwitz Transform) should be built
into the default transfer function of the subwoofer. Trying to boost
output to correct a null in response is somewhat futile and will lead
to compromised dynamic range, i.e. overload problems.

Transient phase and delay response of a 7 pole equaliser will not be
pretty and it will not be a flexible "cure all" for bass problems. The
correct centring and overlap of multi-pole EQ filters is an art in itself,
many designs essentially prevent sharp EQ changes in one band.

There are types of EQ's where at all sliders set to full response is
flat and only ~ flat when all set to the middle. Conversely there
are types where all sliders set to minimum = no signal and again
~ flat all set to middle positions.

TBH I'd say 2 (or 3) fully parametric cut filters, with adjustable Q and F,
covers the main room modes and peaks of a typically placed subwoofer.

Precision centring of each filter is needed, not possible with a multiple
band fixed EQ, and neither is a good setting of Q, i.e. bandwidth cut.

Generally by cutting the peaks bass levels can be set higher and this
to a degree improves any nulls, i.e. makes them less severe comparatively.

30 band 1/3 octave EQ's are OK for manipulating overall balance subtlely
but they are not good for correcting troublesome frequency points.

Nothing wrong with the Gyrator type of EQ though ......

/sreten.

Not sure what supposed to be "Digital" about this thread .....

[tipicreeper]

Sreten,
Thank you so much for taking the time.
I understand bass management alot better.

If I change my fixed frequency points back to pots maybe I would have a little better control over Q.
I could drop a few bands to maybe 3 or 4 with so overlapping frequency points. I could also change the valves of the cut/boost pots to provide more cut then boost.

I realize that this is not a digital project. My bad, it is my first post and I dropped it in the wrong catagory.

So, it laymens terms... you're not seeing anything catastophic?
-David

[tipicreeper]

sreten,
That's what I am missing. Something to change the bandwidth.
Do you have any ideas how to go about doing that?
-David

[kevinkr]

This thread is in the wrong place, it ought to in analog(ue), solid state or ?

[tipicreeper]

Originally posted by kevinkr
This thread is in the wrong place, it ought to in analog(ue), solid state or ?

As a new member all my posts are still under review & I am unable to contact anyone's e-mail due to my noob status.
I do realize I have started this thread in the wrong area but, unfortuniatly there is nothing I can do about it due to my new status.

I am hoping a moderator will come along soon and move the thread accordingly.

Thanks for your input Kevin.
-David

[kevinkr]

You might also want to read up on state variable filter design, this would allow you fully independent control over Q, frequency and amplitude, but you would probably need several to do the job..

The gyrator topology you are using is difficult to tune, the best place to do that is in a circuit simulator like LTspice (switchercad III) which is free and very powerful. Don't expect to be able to change the Q of these using a pot over a very big range without shifts in symmetry and center frequency of the gyrator.

Note that you really ought to measure the subwoofer response in the room before you get carried away trying to design an equalizer for it.

Sreten's point about dynamic range is an important point, follow his suggestions and you will need less eq and less amplifier power for a given spl level in your room. There should also be less likelihood of exceeding xmax (distortion, and woofer damage possible) on very demanding material if you do not need much boost.

[tipicreeper]

Thank You Kevin,
For moving the thread and also giving me some reading on the subject.
It would look as though I have got some reaserch to do.
Point taken on the cut/boost situation. Better to cut the spikes and turn up the gain overall.
-David

[kevinkr]

Originally posted by tipicreeper
Thank You Kevin,
For moving the thread and also giving me some reading on the subject.
It would look as though I have got some reaserch to do.
Point taken on the cut/boost situation. Better to cut the spikes and turn up the gain overall.
-David

Can't take responsibility for the thread move, only a mod can do that..
Cut the offending peaks and leave most dips alone if possible.

If possible use two subwoofers in your room. Room modes should be somewhat less of an issue. Placement in the room can be pretty critical as well. Response measurements are best done around the actual listening area, if possible average the response from several measurements at different locations and equalize against that.

Don't let this stop you from getting started though, consider it part of the long term optimization process, just make sure you understand what you need to build first.. I'm still working on my Onkens 18 months after the build was finished.

[sreten]

Originally posted by kevinkr


Note that you really ought to measure the subwoofer response in the
room before you get carried away trying to design an equalizer for it.

Hi,

Or at least do some room modelling to see where the peaks are.



Blue is uncorrected, red is some correction, note only 2 filters needed < 100Hz.



Room response uncorrected, note linear frequency scale, only 1 filter needed < 100Hz.
(Another 2 filters are needed > 100Hz if you want to EQ further up.)

In other words do not build something to fix a problem you do not have.
Find out what problems you may have and build something to address those.

/sreten.