Request some crossover design help - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

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
Reply
 
Thread Tools Search this Thread
Old 26th January 2010, 01:43 AM   #1
mark_1 is offline mark_1  Canada
diyAudio Member
 
Join Date: Dec 2009
Default Request some crossover design help

Hello everyone. This is a great site, I enjoy prowling around.

I'm rebuilding my Mission 737R's; a LF/MF driver has failed. So I'm replacing those with SEAS P21RF/P, and replacing the HF units with Morel MDT30.

For the crossover, I plan to use a 2nd order Linkwitz-Riley.

My question is this: should I calculate the component values using the "nominal impedence of 8 ohms for each driver"; or "the supplied R(e) of 6.4 for the SEAS and 5.2 for the Morel"; or "the value from the impedence curve of each at the crossover point I would like to use"???

Also, is there a free/shareware program that I could use to simulate these different ideas.

Cheers!
Mark
  Reply With Quote
Old 26th January 2010, 02:48 AM   #2
DcibeL is offline DcibeL  Canada
diyAudio Member
 
DcibeL's Avatar
 
Join Date: May 2003
Location: Saskatchewan
Welcome to DIYAudio, Mark.

I think you are getting over your head. Crossover design is not simple, it is what makes the speaker, considered more important than the drivers themselves by many.

I had recently tried to help someone understand the complexities in designing a good crossover, but he did not want to listen. Just put a couple numbers in an online calculator and viola, a great speaker. Not so much. You may end up with something that makes sound, so it "works" but is far from optimal, and in many cases can even make excellent speakers sound bad. It is much too often that people think that speakers are just that - speakers in a box.

I suggest some research first in the following areas:
-Baffle Step Compensation
-T/S parameters
-Frequency response, impedance
-electrical and acoustic phase
-polar response

Maybe electrical filters as well, some study there after looking at an impedance plot should show you why "nominal impedance" when applied to a filter will not create the expected result. Speakers are not resistors.

What a crossover creates is a transfer function, a frequency response that is subtracted from the driver's frequency response to create your target response. Location of the drivers on the baffle, their "acoustic centers" will affect this response as "phase" is important to determine the frequency response at any axis.

You can design a loudspeaker with software only, with very good results if done right, but don't expect it to be easy. There are lots of resources online, with the help of Excel and some spreadsheets, much can be simulated:

The resources:
FRD Tools

Guides:
RJB Audio guide
Jay_WJ guide

The spreadsheets are not very user friendly, but they include documentation - read it thoroughly. Some of the numbers you enter are not what you will think they should be off the bat, so it is important that everything is done correctly.

Good luck.
__________________
The power of Science compels you!
  Reply With Quote
Old 26th January 2010, 11:21 AM   #3
diyAudio Member
 
Inductor's Avatar
 
Join Date: Feb 2006
Location: Cascais
Quote:
Originally Posted by mark_1 View Post
My question is this: should I calculate the component values using the "nominal impedence of 8 ohms for each driver"; or "the supplied R(e) of 6.4 for the SEAS and 5.2 for the Morel"; or "the value from the impedence curve of each at the crossover point I would like to use"???
Anyway, after what was said, impedance should be at about the one at xover band.
__________________
NEXT-proaudio Portugal
  Reply With Quote
Old 26th January 2010, 12:45 PM   #4
ksporry is offline ksporry  China
diyAudio Member
 
Join Date: Jan 2010
Location: Shanghai
I noticed the online calculator thing as well, and after what I heard/read on this forum, I couldn't really believe the online calculator is so simple. As many explained to me, the x-over function is influenced by the enclosure, the drivers, the music you listen to, the room you are in, etc, none of which is included in those calculations.

Troels uses a program called LspCAD quite effectively. Although it doesn't take into consideration the environment or music type, it does use driver specific data, and enclosure data to model the effect of a x-over you plan to use.
This seems an itterative process, but it allows you to simulate the effects of changes to your x-overs to match what output you desire.

I'm reading up on x-overs now, and it will take a while to get my head around it.

Note: LspCAD6 allows use of real measured data instead of manufacturers data, which means you can plot measured data to see the actual response of your speakers.
  Reply With Quote
Old 26th January 2010, 09:34 PM   #5
diyAudio Member
 
Join Date: Feb 2002
Location: Western Sydney
re:"the value from the impedence curve of each at the crossover point I would like to use"

Crossover Design Calculators
L pad calculator - attenuation dB damping impedance decibel loudspeaker - sengpielaudio Sengpiel Berlin
__________________
Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
  Reply With Quote
Old 26th January 2010, 10:51 PM   #6
mark_1 is offline mark_1  Canada
diyAudio Member
 
Join Date: Dec 2009
Default Thanks

Thanks for your advice/inputs, I really appreciate it!

I have done a fair bit of reading on loudspeaker design but that was several years ago , so I will definitely be checking out those suggested links from Dcibel and PeteMck.

Knowing full well that a voice coil is an inductor and that its impedence changes with freq, I thought "what if" about using the Z at the x-over point for the calculations. So thanks for your collaboration Inductor.

LspCAD is now on my hit list ksporry.

I'll eventually report back on my success, or potential lack of!

Cheers,
Mark
  Reply With Quote
Old 26th January 2010, 10:52 PM   #7
DcibeL is offline DcibeL  Canada
diyAudio Member
 
DcibeL's Avatar
 
Join Date: May 2003
Location: Saskatchewan
PeteMcK, please, never post that again.
__________________
The power of Science compels you!

Last edited by DcibeL; 26th January 2010 at 10:55 PM.
  Reply With Quote
Old 26th January 2010, 11:03 PM   #8
diyAudio Member
 
Join Date: Feb 2002
Location: Western Sydney
re: 'please, never post that again. ' why? it's something that many newbs don't get, thus needs to be repeated often; - if you disagree, please give reasons...
__________________
Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
  Reply With Quote
Old 26th January 2010, 11:13 PM   #9
DcibeL is offline DcibeL  Canada
diyAudio Member
 
DcibeL's Avatar
 
Join Date: May 2003
Location: Saskatchewan
The best thing someone can teach a "newb" is how to do something right the first time, so that mistakes like using some silly online calculator are not repeated.

For reasons why one should not tell someone to use a simple online calculator, whether they are entering impedance at the crossover freq or not, see post #2.

When I first joined this forum I did not know what I was doing, and made some silly speakers and mistakes...learned from mistakes and made better speakers, eventually came to something that I feel can be described as a great speaker...If only I had done it right or somewhere close to it the first time.

Most will just tell a "newb" to build something designed by someone more knowledgable, like Zaph or Mark K, which is fine if all you are after is a great speaker, but IMO that's more DIY assembly than DIY audio. You don't learn anything from it, and if you are interested in loudspeaker design it will likely get you nowhere.
__________________
The power of Science compels you!
  Reply With Quote
Old 26th January 2010, 11:59 PM   #10
diyAudio Member
 
Join Date: Feb 2002
Location: Western Sydney
re: 'silly online calculator ' - most online calculators work fine, and give perfectly acceptible results if you know how to use them. Sure, the more knowledge you have the better results you will get because you will understand more of the factors that need to be taken into account. But everyone has to start somewhere, as you yourself have found, you will learn from your mistakes...
Speaker design dosn't need to be rocket science (the 'only an expert can do it right' syndrome), and gross mistakes aside, there's plenty of margin for error, not to mention personal preference...
__________________
Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
MLTL design review request bzdang Multi-Way 9 25th March 2008 04:49 PM
I need to design a crossover. j.burtt Multi-Way 3 11th May 2006 10:10 AM
Design Critique Request Miles Prower Solid State 15 9th May 2005 09:03 PM
Something different - request for quote, PCB design? RHosch Swap Meet 1 20th October 2004 03:13 PM
Filter design request Nicwix Solid State 15 2nd May 2002 12:19 AM


New To Site? Need Help?

All times are GMT. The time now is 03:30 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2