need help with passive notch filter design
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Multi-Way Conventional loudspeakers with crossovers

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 9th October 2012, 10:31 PM #21 Pano   diyAudio Moderator     Join Date: Oct 2004 Location: SW Florida Martin J King and John K do as well. Important reading for the OB fan.
jimbones
diyAudio Member

Join Date: Nov 2004
Location: ny
Edge response

I ran Edge but I don't know how to post results (graph)
Attached Files
 mid bass dipole response edge.txt (5.6 KB, 15 views)

wintermute
just another
diyAudio Moderator

Join Date: Aug 2003
Location: Sydney
Hi I'm a bit late to the party but here is a post that I wrote before on calculating notch filters.

Quote:
 Originally Posted by wintermute Hi I don't know the speaker you are mentioning, but if you want to learn about notch filters I found this wikipedia page invaluable. It takes the guess work out of it! RLC circuit - Wikipedia, the free encyclopedia go to the parallel RLC section (but it helps to read the preceding stuff as well. If you are like me and shy away from maths, it looks intimidating but you really only need the Q formula and the Wo formula to be able to work out a filter suitable for your desired frequency. Note that Wo is in radians, so you need to divide by 2pi to get Hz. (edit: the original formula I linked to was incorrect I've now fixed it, sorry for any confusion!) Swapping the values for C and L will change the q (without changing the centre frequency) and the resistor determines the amount of cut. Choose a value for C or L and the frequency and then work out what the value for the unknown component (L if you chose C) is. adjust until you get usable values and the desired Q. The higher the Q value the narrower the notch will be. I found this to be a much better starting point for simulation (very close to the desired frequency) than the methods I'd found in my speaker books. Tony.
The centre frequency is easy and accurate using the formula in my experience, getting the Q right is another matter!! Also don't be surprised if the notch has an affect on the lower frequencies outside the range of the notch!

I only recently became aware of the series RLC in parallel with the driver as a form of notch filter. It wasn't until I thought about it that it dawned on me how it could be useful. It is basically a bandpass filter shunting to earth via a resistor (which allows you to control the amount of cut). What it allows you to do (and I'm only thinking about this from an academic standpoint as I've not implemented one) is set the lower and upper frequencies (with cap and coil respectively) and everything in between those frequencies will be attenuated roughly evenly (ignoring any non lineararity of resistance with frequency), thus allowing a sort of shelving circuit only over a given frequency band.

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos

wintermute
just another
diyAudio Moderator

Join Date: Aug 2003
Location: Sydney
Quote:
 Originally Posted by Pano Edge is very simple and easy to use, PCD has a different usage. If you have good frequency and impedance measurements you can use PCD to figure your notch filter. Knowing the cause of the peaks is important, there may be a better way to fix it than the notch filter. As Jay points out, 1150Hz is going to be tough. You'll hear every little thing you do there, so you might want to make the notch broader and shallower than the FR indicates. Listen, try, listen.
Hi Pano, I found that PCD gave me less than accurate results (maybe because initially I was using relatively high DCR coils (around 0.28 ohms) Speaker workshop allows you to specify the DCR of the coils and gives VERY accurate simulations.

I'm curious about the comment on impedance, I didn't think it mattered at all for paralell RLC notches....

I just saw your latest post, my comments above are from my experiences with BOX speakers so it may be completely different with OB which I've never tried

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos

 10th October 2012, 01:04 PM #25 jimbones   diyAudio Member   Join Date: Nov 2004 Location: ny Dipole peak Wintermute, i like math. no problem. I figured how to post the graphs that I did in Edge. I'll post them tonight. And yes, I will add the Wiki article to my library! Thanks much!~
 10th October 2012, 04:50 PM #26 Pano   diyAudio Moderator     Join Date: Oct 2004 Location: SW Florida Tony, If you are doing a shunt notch filter, you're right, the speaker impedance shouldn't matter for the RC part. How deep it is will matter with the R part.
xjr100
diyAudio Member

Join Date: Sep 2012
Quote:
 Originally Posted by jimbones I ran Edge but I don't know how to post results (graph)

What you want to notch there?
__________________
Auricap XO, Mundorf, Jantzen capacitors, coils, MSolder, terminals, DH-Labs interconnect & speaker cables, internal wiring for DIY & upgrades are here: www.audiohobby.eu

 10th October 2012, 10:15 PM #28 tvrgeek   diyAudio Member   Join Date: Dec 2009 Location: Md A notch is a notch is a notch. It does not know what kind of box you have. All of these filters, be they they series or shunt are effected by both input and output impedance. As you are trying to deal with a hump, you will be doing a "parallel filter" which is in series with the driver. Parallel refers to the components of the network in parallel, not the position of the network in the circuit. To understand how it works, you might want to simulate it in LTSpice. ( D'Apolitto will even give you a model for a speaker) No matter the simulation, you still need to test. Simulation gets you close. It tells you that you are on the right track.
 10th October 2012, 10:20 PM #29 tvrgeek   diyAudio Member   Join Date: Dec 2009 Location: Md The graphs above show all the symptoms of baffle step hump at about 650. A notch is not the best way to deal with it. Lower the first pole. It also shows pretty bad breakup at about 2200. You may need to put a notch on that puppy if you are not using a very steep crossover.
wintermute
just another
diyAudio Moderator

Join Date: Aug 2003
Location: Sydney
Quote:
 Originally Posted by Pano Tony, If you are doing a shunt notch filter, you're right, the speaker impedance shouldn't matter for the RC part. How deep it is will matter with the R part.
I was thinking it didn't matter for the parallel series connected but I was wrong! perhaps it doesn't matter so much for the centre frequency but it certainly matters for the Q or the amount of cut....

I just did a check in speaker workshop by doubling the impedance of my MTM measurement and then comparing with the same notch filters.
results shown below.

green is the non filtered response (on the baffle)
blue is with the actual impedance of the speakers
black is with the impedance doubled.
red I just added in, it is a second order bessel target at 2.8Khz (my crossover frequency, the final crossover is actually 4th order bessel at 2.8khz with some added components.

Tony.
Attached Images
 notch_compare.png (35.3 KB, 154 views) notch_filter.png (6.7 KB, 157 views)
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Aussie Amplifiers         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post dtm1962 Multi-Way 10 8th February 2010 03:17 PM Horizons Multi-Way 3 27th February 2009 05:22 AM fotios Solid State 8 7th July 2008 08:29 AM ChocoHolic Subwoofers 36 13th October 2007 05:25 PM Puggie Multi-Way 4 3rd February 2006 02:19 AM

 New To Site? Need Help?

All times are GMT. The time now is 03:31 PM.