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

How to calculate floor bounce reflection(cancellation)
How to calculate floor bounce reflection(cancellation)
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 23rd September 2011, 04:28 PM   #1
jtsaudio is offline jtsaudio  United States
Account disabled at member's request
 
Join Date: Dec 2007
Default How to calculate floor bounce reflection(cancellation)

I have a 6" two way tower speaker that I may add a larger woofer to for more extended bass.

I read somewhere that there is a floor-bounce cancellation related to woofer height (Allison effect?).

The 6" driver is approximately 30 inches from the floor.

How do I determine the frequency at which this occurs, and how will/should this affect my choice of lower-end crossover frequencies?

Thank you.

Joe
  Reply With Quote
Old 23rd September 2011, 04:48 PM   #2
dantheman is offline dantheman  United States
diyAudio Member
 
dantheman's Avatar
 
Join Date: May 2008
Location: Mountain View, CA
This will help:

Floor/Ceiling Reflection Calculator
audio blog: A little more into boundary conditions

Dan
__________________
My Blog
My Music Recordings
  Reply With Quote
Old 23rd September 2011, 05:10 PM   #3
CharlieLaub is offline CharlieLaub  United States
diyAudio Member
 
Join Date: Mar 2007
Location: Michigan
This Excel spreadsheet based modeler written by Jeff Bagby does the same, and more:
Loudspeaker Design Software

-Charlie
  Reply With Quote
Old 23rd September 2011, 05:17 PM   #4
DBMandrake is offline DBMandrake  Scotland
diyAudio Member
 
DBMandrake's Avatar
 
Join Date: Nov 2010
Location: Glasgow, UK
For a really quick, back of the napkin calculation, there is also this useful page:

Floor/Ceiling Reflection Calculator
__________________
- Simon
  Reply With Quote
Old 23rd September 2011, 05:36 PM   #5
Michael Chua is offline Michael Chua  United States
diyAudio Member
 
Join Date: Jul 2006
Location: Calais, ME
Quote:
Originally Posted by jtsaudio View Post
I have a 6" two way tower speaker that I may add a larger woofer to for more extended bass.

I read somewhere that there is a floor-bounce cancellation related to woofer height (Allison effect?).

The 6" driver is approximately 30 inches from the floor.
The floor bounce is real. I picked this up while I was designing a 2-way with Zaph's ZA14W08. Speaker was on a 30" stand.

The cancellation doesn't show up in near field measurements. However, when the mic was placed 1 meter away, an in-room 20-20K ungated sweep registered a deep notch at approx 150Hz.

That's one reason why mid-bass is missing sometimes.

More measurements can be found at SWIFT
Attached Images
File Type: jpg ZA14_SYS_FR.jpg (110.3 KB, 1091 views)
__________________
ampslab
  Reply With Quote
Old 23rd September 2011, 06:09 PM   #6
CharlieLaub is offline CharlieLaub  United States
diyAudio Member
 
Join Date: Mar 2007
Location: Michigan
Quote:
Originally Posted by Michael Chua View Post
The floor bounce is real. I picked this up while I was designing a 2-way with Zaph's ZA14W08. Speaker was on a 30" stand.

The cancellation doesn't show up in near field measurements. However, when the mic was placed 1 meter away, an in-room 20-20K ungated sweep registered a deep notch at approx 150Hz.

That's one reason why mid-bass is missing sometimes.

More measurements can be found at SWIFT
A 3-way with the woofer located at or very near the floor, and the woofer-midrange crossover point at or above 200Hz, can completely eliminate this problem.

-Charlie
  Reply With Quote
Old 23rd September 2011, 06:10 PM   #7
Wayne Parham is offline Wayne Parham  United States
diyAudio Member
 
Wayne Parham's Avatar
 
Join Date: Feb 2004
Quote:
Originally Posted by Michael Chua View Post
The floor bounce is real. I picked this up while I was designing a 2-way with Zaph's ZA14W08. Speaker was on a 30" stand.

The cancellation doesn't show up in near field measurements. However, when the mic was placed 1 meter away, an in-room 20-20K ungated sweep registered a deep notch at approx 150Hz.

That's one reason why mid-bass is missing sometimes.

More measurements can be found at SWIFT
Floor bounce definitely is real. So is the notch from the wall behind the speakers. Vertical axis room modes also tend to fall in this frequency range. Really messes up the lower midrange.

I tend to suggest flanking subs to mitigate this problem. Run a "helper woofer" just a smidge on the high side, like just north of 100Hz. It will smooth the lower midrange, sort of filling in the holes from the self-interference notches.
__________________
Visit the π Speakers website
High-quality audiophile loudspeakers and kits
  Reply With Quote
Old 23rd September 2011, 06:14 PM   #8
Wayne Parham is offline Wayne Parham  United States
diyAudio Member
 
Wayne Parham's Avatar
 
Join Date: Feb 2004
Quote:
Originally Posted by CharlieLaub View Post
A 3-way with the woofer located at or very near the floor, and the woofer-midrange crossover point at or above 200Hz, can completely eliminate this problem.

-Charlie
Definitely. I either run a three-way with mid and woofer blended between 100Hz and 250Hz or, if I run a stand-mounted two-way, I run flanking subs, which effectively do the same thing. I don't usually run flanking subs quite that high, but I do let them blend in the octave above 100Hz.
__________________
Visit the π Speakers website
High-quality audiophile loudspeakers and kits
  Reply With Quote
Old 23rd September 2011, 06:28 PM   #9
bbggg is offline bbggg  United States
diyAudio Member
 
Join Date: May 2007
Quote:
Originally Posted by jtsaudio View Post
How do I determine the frequency at which this occurs, and how will/should this affect my choice of lower-end crossover frequencies?
It's dead simple both to visualize and to calculate. You have to imagine a mirror image of the driver deep inside the floor. When sound emission from the driver itself and from this subterranean image are in antiphase, there is cancellation. This happens when path length difference is half a wavelength. You calculate the path length difference by calculating two hypotenuses and subtracting one from the other, and then divide the speed of sound by the result: this number is twice the frequency in question.
  Reply With Quote
Old 14th April 2013, 03:41 PM   #10
fatmarley is offline fatmarley  England
diyAudio Member
 
Join Date: Aug 2003
Location: Cheltenham
Could I use a 10" wide baffle and still cross over around 200Hz with a floor mounted woofer? Or do you have to use a wider baffle for this to work?
  Reply With Quote

Reply


How to calculate floor bounce reflection(cancellation)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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
need to bounce some tonearm ideas around... Jim Leach Analogue Source 10 10th March 2010 12:27 PM
Contact bounce rho Solid State 6 10th March 2005 08:31 PM
pga2310 and switch bounce biff584 Digital Source 4 3rd April 2004 01:42 AM
Ground Bounce/ Oscillations in SPDIF fmak Digital Source 24 6th March 2004 07:52 PM
HOw close does driver need to be to floor to avoid floor bounce? Kanga Multi-Way 8 24th April 2003 06:09 AM


New To Site? Need Help?

All times are GMT. The time now is 09:02 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki