Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multi-Way Conventional loudspeakers with crossovers

Lpad v single resistor
Lpad v single resistor
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 9th September 2013, 10:48 AM   #1
midrange is offline midrange  United Kingdom
diyAudio Member
 
Join Date: May 2012
Location: London
Lpad v single resistor
Default Lpad v single resistor

I wish to attenuate a tweeter. Assuming a single capacitor for the crossover for the tweeter, there are 2 ways to attenuate that I am looking into.
1) to use an Lpad of 8ohm.
2) to use a series resistor (with obviously a different value capacitor.)

Please could you tell me what is the practical disadvantage of using option 2?
  Reply With Quote
Old 9th September 2013, 11:45 AM   #2
chip647 is offline chip647  United States
diyAudio Member
 
chip647's Avatar
 
Join Date: May 2011
Location: The South
The trouble with the single resistor problem is that if you have an 8 ohm tweeter, you may need a 30 or 40 ohm series resistor to get your attenuation. There is nothing gained by doing this compared to an L-pad.
__________________
_____________
  Reply With Quote
Old 9th September 2013, 01:55 PM   #3
midrange is offline midrange  United Kingdom
diyAudio Member
 
Join Date: May 2012
Location: London
Lpad v single resistor
I am only looking for 3-4 dB attenuation. I am thinking of the series/parallel resistors as an Lpad (not a variable), and I just thought it would be easier to alter just one resistor than two.
  Reply With Quote
Old 9th September 2013, 04:35 PM   #4
pkitt is offline pkitt  United States
diyAudio Member
 
Join Date: Feb 2009
A 2-resistor Lpad between the crossover and driver has the advantage of allowing you to juggle both resistor values to get the desired attenuation while pretty much maintaining a constant impedance as seen by that crossover, thus not shifting the crossover corner, etc.
Paul

Quote:
Originally Posted by midrange View Post
I am only looking for 3-4 dB attenuation. I am thinking of the series/parallel resistors as an Lpad (not a variable), and I just thought it would be easier to alter just one resistor than two.
  Reply With Quote
Old 9th September 2013, 06:17 PM   #5
DrBoar is offline DrBoar  Sweden
diyAudio Member
 
DrBoar's Avatar
 
Join Date: Apr 2003
Location: Stockholm
If you tweak a series resistor you have to adjust the crossover as well anyhow. It is less complex buying pairs of series and parallell resisitors keeping the impedance constant. One additional advantage is that it also flattens the resistance, if you have a high Q tweeter that helps a lot. Especially a first order filter
Philips AD 0160 Tweeter Replacement
  Reply With Quote
Old 9th September 2013, 06:28 PM   #6
Deaf as a Bat is offline Deaf as a Bat
diyAudio Member
 
Deaf as a Bat's Avatar
 
Join Date: Mar 2011
Default L-PAD TUTORIAL

http://www.electronics-tutorials.ws/attenuators/L-pad-attenuator.html

ENJOY.
  Reply With Quote
Old 9th September 2013, 07:31 PM   #7
BlueWizard is offline BlueWizard  United States
diyAudio Member
 
Join Date: Jun 2007
I think the thing to keep in mind is that the impedance of the tweeter is not fixed at its rated 8 ohms. Much like a woofer, a tweeter has a peak followed by a deep valley then a gradually increasing impedance as the frequency rises.

So, with only a series resistor, the ratio of the resistor and the driver is constantly changing. Now, the result of that could be good or bad depending on the circumstances and what you are attempting to achieve. Many people use a series resistor to great effect.

However, if you use a series resistor then the impedance load, even the average load, seen by the crossover is no longer 8 ohms. It is 8 ohms plus the series resistor. You would need to design your crossover accordingly.

The Series/Parallel L-Pad provides a constant impedance to the crossover. More so in that the changing impedance of the tweeter is now in parallel with a fixed resistor meaning the shifting impedance as seen by the tweeter is moderated.

Using a common low cost Dayton Tweeter as an example, and assuming 4dB of attenuation.

The L-Pad Rs and Rp values are Rs = 3 ohms and Rp = 14 ohms.

Using this Dayton Tweeter DC28F-8 -

http://www.parts-express.com/pdf/275-070s.pdf

We see that the impedance is 10.6 ohms at 650hz, 6.2 ohms at 3khz, and 10.8 ohms at 20khz.

If those impedance are put in parallel with a 14 ohm resistor then in series with a 3 ohm resistor, the resulting impedances are -

650hz = 6.03 ohm plus 3 ohm = 9.03 ohms

3khz = 4.30 ohms plus 3 ohms = 7.30 ohms

20khz = 6.03 ohms plus 3 ohms = 9.03 ohms

As you can see the result stays closer to 8 ohms. The shifting impedance of the tweeter has less effect on the crossover.

This is a tweeter with moderate shifts in the impedance. Other tweeters can be substantially more. The 8 ohm rated Morel MDT-29 impedance ranges from about 6 ohms up to 15 ohms. A substantially wider swing than the Dayton.

Again, some people use a Series only resistor to great effect. But you have to understand the effect to use it effectively, and you have to design the crossover accordingly.

Just a few thoughts.

Steve/bluewizard
  Reply With Quote
Old 10th September 2013, 06:02 AM   #8
Deaf as a Bat is offline Deaf as a Bat
diyAudio Member
 
Deaf as a Bat's Avatar
 
Join Date: Mar 2011
Bluewizard, good point. I should add that the calculator I referenced would provide you with a good starting point, but some measurements made at that point would help you see the response with that pad. Adjustments and further refinement (including listening evaluations) could be effected.

I took a several hour tour of the old Glendale JBL works right at the time the L-166 was entering the sales phase. An engineer candidly told us that they were working lots of state of the art science and measurements, but always in conjunction with listening and some empirical wisdom.

I think it would be safe to say that the results were successful.
  Reply With Quote
Old 10th September 2013, 08:14 PM   #9
midrange is offline midrange  United Kingdom
diyAudio Member
 
Join Date: May 2012
Location: London
Lpad v single resistor
Thank you everyone
  Reply With Quote
Old 13th September 2013, 02:27 PM   #10
AllenB is offline AllenB  Australia
diyAudio Member
 
Join Date: Oct 2008
Quote:
Originally Posted by BlueWizard View Post
So, with only a series resistor, the ratio of the resistor and the driver is constantly changing. Now, the result of that could be good or bad depending on the circumstances and what you are attempting to achieve. Many people use a series resistor to great effect.
The result will be response errors. The L-pad has some immunity from this compared to the single resistor.
  Reply With Quote

Reply


Lpad v single resistorHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Attenuation of Ribbon tweeter: Lpad or simple resistor? mondogenerator Multi-Way 2 25th February 2013 05:32 AM
Resistor in series with cap = Lpad?? zerokelvin99 Multi-Way 31 16th April 2012 09:22 PM
Lpad question .. wattage per resistor. kiwilistener Multi-Way 2 8th March 2012 05:30 PM
Resistor/LPAD wattage question DerrickM Multi-Way 13 15th April 2007 09:10 AM
How to put fixed attenuation between preamp and amp. Lpad or just resistor in series? PUCK Parts 1 19th November 2003 03:59 PM


New To Site? Need Help?

All times are GMT. The time now is 06:28 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki