Help with contour network for a compression driver

[hasselbaink]

Hello gentlemen,

I have the following filter on my CD:

This filter flattens the response which would otherwise tilt down towards high frequency. Currently the response is this:

The response is a little ragged 1 kHZ and I wish to tweak the filter to attenuate more on the low end - do you guys have any suggestions (no DSP please) .

The 2-3 kHz hump will be taken care of with a notch filter.

Cheers,
Kris

 

[AllenB]

Do you have impedance and response files? Are you trying for flat?

 

[Robh3606]

That a passive crossover or just a contour circuit for shaping? I would add a pad to reduce noise. A notch would work. It that raw on the horn with just the cap and resistor? What does it look like no passive components?

Rob 🙂

 

[hasselbaink]

@Allen yes I have impedance and raw response files.

@Rob It is more of a contour or shelf network, so it doesn’t filter low end properly. The response is with horn.

 

[Robh3606]

You have simulation software? I use a compensation network that has a protection cap, attenuation, a notch filter to take out the hump and a series notch to flatten and contour the HF above 5k or so.

Without software it is going to be time consuming to optimize it or improve what you have. Have you tried varying C and R?

Rob 🙂

 

[phase_accurate]

@Rob It is more of a contour or shelf network, so it doesn’t filter low end properly. The response is with horn.

But is the measurement with or without the contour network in place ?

Just use a different scale on the Y axis and it looks much better ! 😉
Fun aside : When the big bump is taken care of and the tilt EQed with a properly dimensioned shelf you will easily get near +. 1.5 dB response linearity, which is not that bad at all.

Regards

Charles

 

[hasselbaink]

Hi Rob, I use LspCad to simulate.
I was hoping there was a way to combine the shelving network and a highpass to provide relief for the CD.
May I ask you to post a diagram of the network you are using?

The response is with the shelf in place

 

[phase_accurate]

What kind of crossover highpass do you intend to use ?

Regards

Charles

 

[Robh3606]

Here is the schematic to add a high pass just take out the protection cap and substitute. This is pirated from JBL Greg Timber's. I have a thread on Lansing Heritage where I selectively switch out the notches in the original network that the compensation circuit is derived from. Might help you I will link it. You may have an issue getting into the forum still working on it.

The attached are compensation of 2453 on a PTH1010 used in an active system 24dB L/R 1.5K

https://www.audioheritage.org/vbull...nitor-Thread&highlight=passive+monitor+thread

 

[hasselbaink]

That is a beauty of a response. Very linear.

 

[GM]

The response is a little ragged 1 kHZ and I wish to tweak the filter to attenuate more on the low end

Greets!

CD horn EQ is an R/L/C network and easiest to begin with a basic XO with a pot and HF bypass cap.

 

[Robh3606]

Yes as in JBL 4430/35

Rob 🙂

 

[AllenB]

yes I have impedance and raw response files.

It's OK if you don't want to share them. Where did you want to cross?

 

[hasselbaink]

I am crossing at 1kHz.
The speaker looks like so:

I will post impedance plot later.