Need help on Polk LSi25 cabinet mod - 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 24th January 2013, 05:45 AM   #1
soniky is offline soniky  United States
diyAudio Member
 
Join Date: Jan 2013
Default Need help on Polk LSi25 cabinet mod

Hi, this is my first post on this forum and I think I'll become a long time member since I've been wanting to get into this area as a hobby for a long time. Now I finally have some spare time to do so.

I have a project that I like to do which is to modify the Polk LSi25 cabinet design. The speaker has a 3-way upper chamber hosting a tweeter, a mid and a woofer. It has a lower chamber hosting a 10" sub. I am wanting to enhace the upper chamber at this time only. Would appreciate any guidance and help.

I can't find a cabinet drawing for LSi25 but there is one for LSi9. It can be found at the follow link under Additional Images.
LSi9 - Bookshelf | Polk Audio
They are similar but not the same. In LSi9 there is a board between the mid and the woofer. The board has a large cut-out in the middle for the tweeter and wires. There is also a ported tube to the back. LSi25 does not have the board nor the back port, only the two smaller ports to the front. Lsi9 measure 12" x 5.5" inside and Lsi25 measured only 8" x 5.5" inside. Although Lsi25 has a 15" outside depth,Polk blocked it off inside purposedly to make it a lot smaller.

Lsi25 has clearer highs than Lsi9 and Lsi9 sounds warmer. However, Lsi25 suffers from the interference between the mid and the woofer when played loud. I am thinking if there is a way to give more power and clarity to Lsi25's midrange.

Can I add a board between the two front tubes to separate the mid and
the woofer, and maybe open a port on the back for the mid dirver? I understand speaker cabinet design requires a lot of calculation but I don't understand any of it. Your help would be appreciated. Please let me know if I need to provide any additional information.
  Reply With Quote
Old 24th January 2013, 07:20 AM   #2
Face is offline Face  United States
diyAudio Member
 
Face's Avatar
 
Join Date: May 2007
The lsi9 and 25 do not have dedicated mids. One 5.25 plays up to the tweeter, the other plays only up to the baffle step frequency(800ish). By adding a port to the 25s upper section, you will not increase clarity, but create a bump in response in the upper bass, and the speakers will sound worse.

Somewhere along the line, Polk did lower the value of the resistor in series with the tweeter. I'm not 100 percent sure, but it may have been 1.5ohm down to 1ohm.
__________________
"He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
  Reply With Quote
Old 24th January 2013, 04:12 PM   #3
soniky is offline soniky  United States
diyAudio Member
 
Join Date: Jan 2013
One mid plays from 80hz to 2.4khz and the other plays from 80hz to 800hz. Would it help the clarity if I add a board in between to separate the two mids? Looking at Polk's new LSiM series, all the drivers are closed in each own space.
  Reply With Quote
Old 24th January 2013, 06:02 PM   #4
diyAudio Member
 
Inductor's Avatar
 
Join Date: Feb 2006
Location: Cascais
soniky, I'm not sure about what you find?
Are the crossovers the originals, was the speaker modded?
I would like to make sure of that first. Then my gut felling goes to interference between the two mid drivers, or between them and the tweeter and or baffle. See, the problem when you have two main drivers (or an inverted dome, not in this case) is that you have to deal with phase inversions or nulls. Many times monitor or pro speakers make use of foam* to separate drivers. Another reason could be from power compression or something related when you raise the volume and drivers/crossover (mid/mid or mids/tweeter) having different outputs. Difficult to know the origin of your problem.
*Foam: like any soundproofing foam type or material.
Attached Images
File Type: jpg LSi25.jpg (16.4 KB, 71 views)
File Type: jpg Lipinski Sound L-707 Monitor.jpg (137.2 KB, 67 views)
File Type: jpg Lipinski Sound specially designed Belgian foam.jpg (105.5 KB, 66 views)
__________________
NEXT-proaudio Portugal
  Reply With Quote
Old 24th January 2013, 06:07 PM   #5
diyAudio Member
 
Inductor's Avatar
 
Join Date: Feb 2006
Location: Cascais
Quote:
Originally Posted by soniky View Post
One mid plays from 80hz to 2.4khz and the other plays from 80hz to 800hz. Would it help the clarity if I add a board in between to separate the two mids? Looking at Polk's new LSiM series, all the drivers are closed in each own space.
That's also possible, it very much happens when two drivers have different resonant frequencies. It happened to guru Mr. Bose when he was designing the 901 and had 9 different/same FR drivers and he had to separate all of them in nine individual enclosures.
Note. Before you do that try to fill the cabinet with lambswool (or pillow) or a layer of rock-wool around the inside panels, to stop the back waves reaching the cones of the drivers.
Cabinet damping - Troels Gravesen
__________________
NEXT-proaudio Portugal

Last edited by Inductor; 24th January 2013 at 06:24 PM. Reason: Bose 901
  Reply With Quote
Old 24th January 2013, 06:24 PM   #6
soniky is offline soniky  United States
diyAudio Member
 
Join Date: Jan 2013
Hi, the crossover is modded and I got clean and clearer highs but not on the midrange which is driving me to think about the enclosue. About the foam, there is a 1.5" layer of fiber vertically across the middle of the box and that's it. I don't know what's a baffle but it's basically a 8" x 5.5" box with nothing else besides the 2 drivers and one tweeter and the foam.

I think I can try put a MDF horizontally between the two drivers and see if it makes a positive difference. I just don't want to do anything stupid so I'll not glue it down initially.
  Reply With Quote
Old 24th January 2013, 07:09 PM   #7
diyAudio Member
 
Inductor's Avatar
 
Join Date: Feb 2006
Location: Cascais
Quote:
Originally Posted by soniky View Post
Hi, the crossover is modded
Was it by you? Check the wattage of components, like power resistors before you go further... picture if you can.
__________________
NEXT-proaudio Portugal
  Reply With Quote
Old 24th January 2013, 07:58 PM   #8
soniky is offline soniky  United States
diyAudio Member
 
Join Date: Jan 2013
It's a professional mod. Sorry, haven't figured out how to attach an image. It asks for URL but I have the pic on my local drive.
  Reply With Quote
Old 24th January 2013, 08:03 PM   #9
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
Quote:
Originally Posted by soniky View Post
haven't figured out how to attach an image.

It asks for URL but I have the pic on my local drive.
when you post, go to 'Manage Attachments'
  Reply With Quote
Old 24th January 2013, 08:08 PM   #10
soniky is offline soniky  United States
diyAudio Member
 
Join Date: Jan 2013
Quote:
Originally Posted by Face View Post
Somewhere along the line, Polk did lower the value of the resistor in series with the tweeter. I'm not 100 percent sure, but it may have been 1.5ohm down to 1ohm.
Face, if I understand correctly, Polk changed one resistor from 2.25ohm to 1.75ohm. I checked my XO is using 2ohm. Is it a problem?
  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
Pair Monacor SP-60/4 in a stuffed port aperiodic cabinet? What size cabinet? danielwritesbac Multi-Way 28 3rd April 2013 06:15 AM
Odd subwoofer cabinet question... semi open baffle.. a kitchen cabinet peace brainerd Subwoofers 8 30th November 2012 07:15 PM
Spherical Cabinet vs. ordinary Cuboid Cabinet for full range Speakers tiefbassuebertr Full Range 1 10th January 2012 05:49 PM
Polk RT3 mod ChestofFur Multi-Way 4 21st December 2011 02:21 PM
Polk Sub ??????? ralph-bway Subwoofers 1 20th October 2005 01:39 AM


New To Site? Need Help?

All times are GMT. The time now is 10:24 AM.


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