Go Back   Home > Forums > Loudspeakers > Full Range

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 6th March 2010, 04:28 PM   #1
diyAudio Member
 
Join Date: Mar 2008
Default Mechanical isolation of driver from cabinet

Hi there,

while experimenting i fell over a method useful for mechanical
driver - cabinet isolation. This is not necessarily restricted to FR drivers.

The driver is not directly attached to the baffle anymore, there is
only some soft material as a gasket between the drivers basket
and the baffle.

The driver is magnet mounted using a spring (e.g. damped metal beam),
which is connected at one or both ends rigidly (optional with some damping)
attached to the cabinet. (even a spiral spring with a damper would be
possible or an air spring).

The resonant frequency fd of the driver and the suspension is adjusted
well below the usable range of the driver/cabinet combination.
(e.g. one octave below fs for a closed cabinet).

Above fd the excursion of the driver basket suspended in
its "Pendulum" is "mass inhibited". At fs things looks pretty much like
the driver was mounted conventionally ...

The absence of a rigid connection between driver chassis and cabinet
reduces vibration of the cabinet and thereby structure born sound
radiated unwanted from the cabinet walls, which typically
intoxicates the middle to upper bass region ...

I do not know by now if this is "new" entirely, since magnet mounting is
known practice. But in many cases structures supporting the magnet
are so stiff (and underdamped), that fd is within the usable range of
the speaker, which is counterproductive.

Defined "fd" and "Qd" using a well designed mass spring configuration
and a damping mechanism would IMO improve matters.

Opinions ?


Kind Regards
__________________
Oliver, RFZ believer (?)
www.dipol-audio.de
  Reply With Quote
Old 7th March 2010, 12:19 AM   #2
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I'm completely out of my element here, but I had always understood it was desirable to tightly couple the driver to the cabinet in order to minimize the energy stored in the driver components.

A lot of current full range designs feature heavily braced cabinets and drivers that are tightly coupled to the cabinet via notched braces in tight contact with the magnet assembly. (Like the HCC I recently built)

How do you damp vibration in the basket, flange and other areas of the driver? Based on your comments I assume the driver support/suspension compliance is tuned to some frequency way below the driver/box resonance. Does the compliance of the suspension damp the driver structure in its operating range effectively?

I'm just curious - I don't have sufficient knowledge or experience to know whether this is advisable or not, and hence have no sense of the merit of your idea.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan

Last edited by kevinkr; 7th March 2010 at 12:24 AM.
  Reply With Quote
Old 7th March 2010, 12:37 AM   #3
Account disabled at member's request
 
MJL21193's Avatar
 
Join Date: Mar 2007
I did some experimentation on this idea HERE and I think the results were good.
I'll need to be a bit more thorough in my testing to determine if it is worth the effort.

Sigfried Linkwitz recommends isolating the driver frame from the baffle while rigidly mounting the driver magnet.
  Reply With Quote
Old 7th March 2010, 03:16 AM   #4
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
The FujiTEN Eclipse uses a sysyem where the driver is connected to a mass-loaded base (blue & black) and the shell is floated on that with no rigid contact. Something like the attached sketch.

http://www.eclipse-td.net/

dave
Attached Images
File Type: gif eclipse-mount.gif (12.0 KB, 580 views)
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 7th March 2010, 11:46 AM   #5
pinobot is offline pinobot  Netherlands
diyAudio Member
 
Join Date: Oct 2005
I've also thought about this for quite a long time. Manufacturers are trying to decouple the drivers since forever. One of my first real hifi loudspeakers was a Van Medevoort CD 2.5 (around 1985), it had the drivers glued in place using silicon without any screws. Just recenty i saw a picture of some monitor that had a midtone compartment embedded in foam in a hollow space inside the loudspeaker box.
My own experience is that everything must be as rigid as possible, i find that the speaker sounds less muddy that way. Ofcource it's possible to decouple and retain detailed sound but at a certain point it's just no longer economical or plain silly. You could think of increasing the mass of the driver by adding weight to the magnet but this would put additional stress on the frame, to avoid this you can make a heavy metal ring to attach to the rim of the driver but having that custom made costs a fortune. Another way to dampen vibrations is to use a damper, like the ones on an archery bow, i think a car manufacturer used isomething similar to dampen the vibration of a car engine.
The thing is if you decouple the drive from the cabinet then the cabinet becomes lighter so you have to make the cabinet heavier otherwise the soundpressure will just push away the cabinet. Cost, material and total weight will spiral out of control.
Click the image to open in full size.
  Reply With Quote
Old 7th March 2010, 01:33 PM   #6
diyAudio Member
 
speaker dave's Avatar
 
Join Date: Nov 2009
Location: The Mountain, Framingham
I was an engineer at KEF in the 80s when we were having good success decoupling drivers from the cabinets.

The issue came up with the original KEF 105 (not the 105mKII) that was found to have a fairly nasty cabinet resonance in the middle hundreds. Cabinet stiffening moved the resonance up but never got rid of it so rubber mounting the driver was tried. We found that we could get a strong reduction in the amount of "drive" to the cabinet resonances via decoupling. It was easy to measure and you could hear the difference, especially on test impulses or impulsive sound.

The trick is to get the decoupling resonance low enough. Soft glues, silicon, etc. don't really do it. The 105 II used rubber motor mounts and soft foam tape. We even went to 3 mounting bolts to get the resonance a little lower. You had to be careful that mounting bolts didn't touch the cabinet and "short circuit" the effect. If I remember right the accelerometer measurements showed about a 20dB reduction in resonance levels with decoupling. Even with perfect decoupling their will be an acoustical drive to the cabinet, only the direct vibration coupling is reduced. The later 105 MkII used two woofers in opposition (plus decoupling) for even greater vibration reduction. I think people have even played with dummy motor structures with cone mass substitues that vibrate out of phase and cancel vibration (read about antivibration countershafts in 4 cylinder engines).

Audiophiles will tell you that dirvers must be rigidly mounted because this is a well ingrained part of accepted dogma. Our tests showed that this wasn't the case.

David S
  Reply With Quote
Old 8th March 2010, 10:15 AM   #7
graaf is offline graaf  Poland
diyAudio Member
 
graaf's Avatar
 
Join Date: Jun 2007
Quote:
Originally Posted by planet10 View Post
The FujiTEN Eclipse uses a sysyem where the driver is connected to a mass-loaded base (blue & black) and the shell is floated on that with no rigid contact. Something like the attached sketch.

speaker | ECLIPSE TD series speaker

dave
designed/patented by Yoshii Hiroyuki
decoupling seems to be technically much easier to achieve with upward firing speakers
TIMEDOMAIN :心のオーディオ 〜自然な音のスピーカー
Speaker apparatus equipped with means for producing complicated waveform of low frequency with higher improved fidelity - Patent 6796401
Attached Images
File Type: jpg 008_yoshii9_td.jpg (6.5 KB, 506 views)
__________________
"high phooey and hystereo" - Yascha Heifetz
  Reply With Quote
Old 8th March 2010, 11:06 AM   #8
stevieg is offline stevieg  United Kingdom
diyAudio Member
 
Join Date: Nov 2009
Location: Gwynedd North Wales
Naim and Mordaunt - Short (440?) both gave decoupled cabinets/speakers a lash. IIRC, the MS has a rigid skeleton to which the drive units were affixed, and the cabinet floated around this, sealed/supported with rubber gaskets. Roksan also decoupled tweeters. No doubt Paul Voigt/ Emil Berliner/ Gilbert Briggs/ your own name here suggested a similar system.
__________________
steve
if it ain't broke, I ain't fixed it
  Reply With Quote
Old 8th March 2010, 11:41 AM   #9
graaf is offline graaf  Poland
diyAudio Member
 
graaf's Avatar
 
Join Date: Jun 2007
Quote:
Originally Posted by stevieg View Post
No doubt Paul Voigt/ Emil Berliner/ Gilbert Briggs/ your own name here suggested a similar system.
oh yes, because decoupling is good, it's just good engineering

on the other hand it raises some issues of DFM - additional costs and manufacturing complications

fortunately in DIY where we are free from DFM considerations decoupling is quite easy to achieve, and in case of upward firing speaker it becomes easy as pie
__________________
"high phooey and hystereo" - Yascha Heifetz

Last edited by graaf; 8th March 2010 at 11:44 AM.
  Reply With Quote
Old 9th March 2010, 04:11 PM   #10
diyAudio Member
 
Join Date: Mar 2008
Quote:
Originally Posted by speaker dave View Post
...
If I remember right the accelerometer measurements showed about a 20dB reduction in resonance levels with decoupling. Even with perfect decoupling their will be an acoustical drive to the cabinet, only the direct vibration coupling is reduced.
...

David S
First of all gentlemen i thank you very much for the detailed
input and the examples of constructions which had already
been realized.

@ David: If the reduction of cabinet vibration was that good,
one could ask how much effort would have been necessary in
improving cabinet damping to achieve the same effect without
decoupling ...

I am convinced, that it may be an effective and economically
reasonable method to implement high quality cabinets.

If you have got a set of components that work well in effectivity,
durability, manufacturing effort, ...

you can easily customize them to meet the parameters needed
for different speaker/cabinet situations.

Since in audiophilia there have been invented
(and sold) very much gadgets to compensate minor effects, i
wonder why this has not found a wider application ...

Cabinet vibration - to me - is NOT a minor effect. It is one of
the nastiest hurdles for real musical enjoyment.

A speaker meant to be "high end" which in an appropriate listening
environment can be convicted to exhibit disturbing cabinet
resonances is IMO disqualified.

edit: For shure, direct excitation from the drivers motor is
not the only source of unwanted cabinet vibration.
But in many cases that mechanism is underestimated IMO.


Kind Regards
__________________
Oliver, RFZ believer (?)
www.dipol-audio.de

Last edited by LineArray; 9th March 2010 at 04:19 PM.
  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
driver position in cabinet mikelm Subwoofers 6 28th February 2010 06:53 PM
Cabinet Damping/Driver Isolation Summary? stephenmarklay Multi-Way 2 1st January 2010 03:07 AM
Mechanical issue with mid/bass driver boudy Multi-Way 3 6th November 2009 12:56 AM
Which driver/cabinet should I go for? phresh Full Range 0 25th May 2006 09:12 PM
Driver for TL Cabinet first_1st Multi-Way 3 3rd June 2005 01:07 AM


New To Site? Need Help?

All times are GMT. The time now is 07:58 PM.


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

Content Relevant URLs by vBSEO 3.3.2