nasty old resonance - 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 25th February 2003, 07:32 PM   #1
diyAudio Member
 
Join Date: Apr 2002
Location: Baltimore
Default nasty old resonance

Hey all, I haven't been around in a while because of school - I am now a physics student at UMBC, and haven't had much time to come by between class and video games.
Background: I slapped some speakers together before school started so I could have something nice to listen to in the dorm. It's a pair .75 ft3 boxes each housing a hivi f8 and a vifa something or other tweeter. This box is on the small side for these speakers, and they arenn't tuned quite low enough (~45 Hz), so there is a bump in response of about 2dB at ~ 70Hz, according to winisd. I always have found the bass on these to be a little excessive.

What made my problem worse is that I just got some reference headphones (sennheiser hd-280's) and realized just how bad my problem is. These phones sound damn good - almost too good. I found that I can hear low bass better with my left ear because of these damn things. I can hardly listen to the speakers anymore...of course my friends think im nuts.

I have recently been working with a music making program called fruity loops(main reason i bought the headphones), which has a parametric eq on it. I made a test tone, and found exactly where the resonance was (second C, i think), and found that to be ~130 Hz. I put a notch filter there, and it sounds fine.
What could cause a nasty bump at 130 Hz? I don't think it's the tuning...I have an inkling that it is my crappy job of putting padding on the inside of the enclosure, but im not sure. Any suggestions?
  Reply With Quote
Old 25th February 2003, 07:38 PM   #2
diyAudio Member
 
Join Date: Aug 2002
Location: Toronto, Canada
Default Just a guess...

Just a guess, it's the second octave from the total F3 or Fs?
  Reply With Quote
Old 25th February 2003, 07:42 PM   #3
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Maybe it's a panel resonance? Also, if you stuff excessively or your cabinet has leaks (other than the port), your tuning might not be what you think it is. Best thing to do when in doubt is to measure the impedance curve- especially if you can get both magnitude and phase.

BTW, I graduated UMBC in physics in '77. Congrats- it's a terrific department.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 26th February 2003, 02:29 AM   #4
Wizard of Kelts
diyAudio Moderator
 
Join Date: Sep 2001
Location: Connecticut, The Nutmeg State
Default Re: nasty old resonance

Quote:
Originally posted by bostarob
and they arenn't tuned quite low enough (~45 Hz), so there is a bump in response of about 2dB at ~ 70Hz, according to winisd. I always have found the bass on these to be a little excessive...

...I made a test tone, and found exactly where the resonance was (second C, i think), and found that to be ~130 Hz. I put a notch filter there, and it sounds fine...

...What could cause a nasty bump at 130 Hz? I don't think it's the tuning...
Along the lines of what Rino said, the bump at 135 Hz is approx 3 times your tuning frequency. And your tuning frequency was just approximate. I have to admit though, I have never seen a problem occur at 3 times the tuning frequency-I just thought I would point out the relationship.

Just for the heck of it, what are the inside dimensions of your box? Wondering if it is a standing wave.
__________________
"A friend will help you move. A really good friend will help you move a body."
-Anonymous
  Reply With Quote
Old 27th February 2003, 12:37 AM   #5
diyAudio Member
 
Join Date: Apr 2002
Location: Baltimore
9.5" W
7" D
19.5" Tall

The Fs of the woofers should be around 33Hz.

As far as I know, i don't have the means to measure impedance. Maybe the Physics dept. does? But i really don't have the time for that. That could be a summer project. What about standing waves? There really aren't any holes or leaks.

What would measuring the impedance curve give me?

Thanks a lot, guys,
andy
  Reply With Quote
Old 27th February 2003, 04:59 AM   #6
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
If you measure the complex impedance and plot it on the complex plane (real part of impedance on the x axis, imaginary part on the y axis), resonances like leaks and panel rattles will show up as little loops. The main resonances (the ones you want in the bass) will be big loops. Plotting the magnitude of the impedance versus frequency will give you quantitative info on whether the box is tuned the way you think it is.

The equipment to do this is pretty elementary- if you don't have an FFT tester, you can do it with a signal generator and a 'scope.

Standing waves at 130 Hz are highly unlikely for your enclosure.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 27th February 2003, 05:20 AM   #7
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
Are you sure the resonance comes from the speakers and not your listening room ?

Regards

Charles
  Reply With Quote
Old 27th February 2003, 06:56 PM   #8
diyAudio Member
 
Join Date: Sep 2001
What are your enclosures made from. How thick is the cabinet wall. It could be panel resonances. If they are at around 130 Hz you can actaully feel this with your fingers if you hold them in light contact with the box while slowly sweeping a sine wave into the speaker. Alternatively, sweep while putting your ear in close contact with the panel. If this is the cause, then build the box stronger by adding internal bracing.

Andrew
  Reply With Quote
Old 27th February 2003, 07:10 PM   #9
diyAudio Member
 
Join Date: Apr 2002
Location: Baltimore
The two boxes are certainly not in an ideal set up. they are close to the wall, and too close to eachother. They are hugging my computer monitor on either side of my small desk. Additionally, I live in a dorm room with cinder block walls. When I sit right at my computer the ~130Hz peak is most pronounced. Across the room, the lower bass is amplified more.
I really think I should move them around, but I'd have to reorganize and move everything else around too.
Thanks,
andy
  Reply With Quote
Old 2nd March 2003, 08:56 PM   #10
diyAudio Member
 
Join Date: Apr 2002
Location: Baltimore
The front baffle is about 1.5", and the other walls are 3/4 inch.
  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
vol pot on Zhaolu 2.5C: NASTY schro20 Digital Source 3 2nd April 2008 08:13 PM
Nasty ground loop alexmoose Tubes / Valves 2 28th August 2006 05:13 PM
Need input on my TL. FR has a nasty dip in it. GuyPanico Subwoofers 3 22nd May 2005 02:13 AM
Nasty mains sparks. What to do? Netlist Solid State 15 20th November 2003 12:13 PM


New To Site? Need Help?

All times are GMT. The time now is 02:24 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