What is "mass loading?" - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 11th January 2011, 11:24 PM   #1
diyAudio Member
chrusion's Avatar
Join Date: Jan 2011
Location: Chattanooga, TN, USA
Default What is "mass loading?"

I see/read this term bandied about without any specific definition, as if everyone knows exactly what is implied in the context of its usage. However, I do not.

I've googled the net and searched these forums for an emphatic definition only to discover that mass loading is the classic definition of a horn in reverse (aka a tapered quarter wave), the addition of physical mass (sand, stone, concrete, et. al.) to an enclosure to reduce cabinet resonance, and/or "coupling" the rear of a driver (its magnet) physically to the cabinet with a brace (wood dowel or similar).

So, which one is being referred to when some one says, "You should mass load your design for better... blah, blah, blah" or "Your design is more like a mass loaded... blah, blah, blah"? That is, it seems to be used more frequently as a generic term in many cases of enclosure design and less often as a specific procedure.
Dean A. Scott, mfa
owner / animator, chrusion | FX
  Reply With Quote
Old 11th January 2011, 11:57 PM   #2
expert in tautology
diyAudio Member
bear's Avatar
Join Date: Apr 2002
Location: New York State USA
I think you have covered the possible uses for the term WRT speakers... there may be some others, but I suspect that most of the places where you hear this bandied about it is more like marketing hype than anything else... just speculating.

Although bracing a driver to the rear wall is not mass loading, afaik. Placing MASS (a weight) behind the driver might be called "mass loading" but that's not really "loading" exactly, imo.

It's more like the addition of weight (mass) to a Passive Radiator, or the cone of a woofer to lower the Fs, that is mass loading.

http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- every once in a while I say something that makes sense... ]
  Reply With Quote
Old 12th January 2011, 12:25 AM   #3
diyAudio Member
Join Date: Jun 2004
Location: Indiana
Might find this interesting...

Generic Signature
  Reply With Quote
Old 12th January 2011, 01:20 AM   #4
diyAudio Member
Join Date: Feb 2004
Location: Los Angeles
Some of those definitions sound like misunderstandings. And some do not apply to speakers-they apply to trying to reduce resonance in speaker stands or speaker enclosures. That's the most common use of the term "mass loading"-for instance, filling a hollow metal speaker stand with sand &/or lead shot to increase the mass and reduce vibration.

Applied to a speaker, it's different. The moving mass of a speaker consists of the physical moving parts PLUS the air load on the diaphragm. Mass loading thus means techniques which increase the air mass load.

For instance, sticking the speaker on a horn lets the speaker "grab" the nearby air more efficiently. Instead of trying to push all the air in the whole world, the diaphragm is just pushing air right in front of it and can push it more effectively. I suppose those analogies probably aren't technically correct, but useful for thinking.

Now the purpose of a horn is not really mass loading. But some makers put their subwoofer cones facing the floor, or firing into some kind of slot, or facing each other in a manifold. Again since the cone is not trying to grab all the air, but a concentrated piece of air right in front of it, the air mass will be somewhat higher.

From the hazy past, I don't recall if these techniques really change the total mass very much. My vague feeling is the sound is more likely affected by:
- Resonances in the cavity formed by the slots, which can introduce response peaks.
- Blockage of high frequencies from radiating directly to listener's ears, which may reduce the audible distortion.
  Reply With Quote
Old 12th January 2011, 01:45 AM   #5
MJK is offline MJK  United States
Account disabled at member's request
Join Date: Feb 2002
Location: Clifton Park, NY
From my site, this is the best description of what I have called mass loading of a TL or TQWT. I am guessing that this is what you are referencing.

Enclosure Design and Construction for the Lowther DX Series of Drivers

"The ML TL enclosure can be thought of as a form of transmission line where quarter wavelength standing waves are used to provide the spring for the mass of air in the port. To physically model a straight uniform TL, clamp a yardstick to the edge of a counter or desk and pluck the free end so that it starts to vibrate. The vibration pattern is analogous to the air velocity in a TL. The TL's air velocity is zero at the closed end as is the yardstick's motion at the clamped end. The TL's air velocity is a maximum at the open end as is the yardstick's velocity at the free end.

There are two ways of changing the frequency of vibration for the yardstick. If you shorten the length cantilevered off the counter, the frequency of vibration will increase. Make the length longer and the frequency decreases. This is how straight TL's have traditionally been tuned by adjusting the length. The second way of tuning the frequency of the yardstick is to add a lump of mass to the free end. Put a piece of modeling clay on the free end and watch the frequency decrease. What I have done to the classic TL is put a lump of mass at the terminus end using a restrictive port. For a given frequency, I can shorten the TL (make it stiffer) increasing the tuning frequency and then add mass (air in a port) to pull the frequency back down and get a similar tuned result. One other benefit of having a lump of mass at the terminus is a rolled off port output above the first quarter wavelength resonance. This result is similar to a bass reflex port's response. I did this first with the ML TQWT and then with a straight TL. If you try the yardstick analogy, I think by changing the length and adding mass to the end you can demonstrate to yourself exactly what I am doing in my MathCad computer models."
  Reply With Quote
Old 12th January 2011, 07:07 PM   #6
diyAudio Member
chrusion's Avatar
Join Date: Jan 2011
Location: Chattanooga, TN, USA

Thank you! That was very helpful. I had a suspicion that the mass referred to had something to do with air volume/pressure/damping/etc. when coupled with QWL designs rather than the three definitions above. Your analogy of the vibrating ruler was superb.
Dean A. Scott, mfa
owner / animator, chrusion | FX
  Reply With Quote
Old 13th January 2011, 08:53 PM   #7
Thawach is offline Thawach  Thailand
diyAudio Member
Thawach's Avatar
Join Date: Dec 2007
i ever had the simple thought when no has mass loading. it's like i flying on the moon with my apollo 11. this make the sense to understand the mass loading
  Reply With Quote
Old 14th January 2011, 08:47 AM   #8
diyAudio Member
Join Date: Jan 2008
Location: Toronto and Delray Beach, FL
Originally Posted by head_unit View Post
snip Mass loading thus means techniques which increase the air mass load.

For instance, sticking the speaker on a horn lets the speaker "grab" the nearby air more efficiently.

Thoroughly stupid, when think about it, trying to vibrate the thin air with any kind of precision by shaking a massively heavy block of cardboard, even with a very strong motor (magnet).

Mass loading is crucial to good sound production just as shock absorbers are to a car and for analogous reasons.

(In reply to head unit, woofer horns do try to create air mass loading. And in such cases, they do increase efficiency through impedance matching - although efficiency per se tends not to be an important goal now-a-days.)
HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio

Last edited by bentoronto; 14th January 2011 at 08:49 AM.
  Reply With Quote
Old 15th January 2011, 05:47 AM   #9
diyAudio Member
Join Date: Jun 2007
Originally Posted by chrusion View Post
That is, it seems to be used more frequently as a generic term in many cases of enclosure design and less often as a specific procedure.
Hi Dean,

Mass loading usually means that the enclosure design includes a port or tube open at both ends that is short enough so that the air in the tube moves as a whole, without appreciable compression. In other words the component behaves primarily as an acoustic mass.

If a tube rigidly closed at one end is used instead, then the air will be compressed and the component acts primarily as an acoustic compliance.

Kind regards,

  Reply With Quote


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
Horn-loading the "new breed" of pro sound 6.5-8'' drivers Swedish Chef Multi-Way 62 9th February 2014 05:15 PM
"Optimal" output grid loading? solder slinger Tubes / Valves 0 19th October 2009 05:04 PM
Mass Loading Woofer Moondog55 Subwoofers 2 18th March 2008 01:55 AM
mass loading aznboi3644 Subwoofers 1 13th March 2008 11:47 PM
"mass added to cone" I'm confused about it's meaning Jimmy154 Multi-Way 12 8th July 2002 02:53 AM

New To Site? Need Help?

All times are GMT. The time now is 02:47 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2