Glory B Flat Clarinet
Box Building

Box Building



      BOX BUILDING AND ...WHY?   (WHY NOT JUST GO PREFAB???)


Box building?   Why?  Today there are a TON of "Pre-Fab" enclosures...so why do a "custom box" *(enclosure)
Many reasons.  Best reason is to cosmetically look correct (or better) than a simple rectanglular box stuck in your trunk!

No one is going to make you build an enclosure.  Prefabs can be pretty good...IF you pick the RIGHT enclosure for
YOUR woofer..


Lets start with the "basics".
 

      SUBWOOFER 101


All subwoofers are NOT created equally.   Just because it is a 12 inch subwoofer does NOT mean it works in ANY
12 inch subwoofer 
enclosure! 
 

      SUBWOOFER ENCLOSURES?  WHY?


This is a very complicated and overly discussed topic.  For over 80 years manufacturers and hobbyists have discussed, debated the virtues of having enclosures, vented (ported) versus sealed versus bandpass versus transmission lines.




















It is beyond the scope of this tech tip to discuss all the virtues (pros and cons) of each.  We will keep the discussion to sealed versus vented
as these are the 2 most commonly used enclosures for car audio applications.

Remember there are 2 types of energy in car audio.  Electrical, which ISN'T free, and acoustical – which is FREE.  Typically no one complains to their retailer/installer that they got TOO MUCH BASS!  Everyone complains about not getting enough!!! So let’s FIX that!  Design and build better subwoofer enclosures.

 

 

SEALED

 

      PROS & CONS?

 

 

 

SEALED: Advantages


   1. Simple to build, no real thinking involved.Hard to screw up
   2. Best phase and time response.

SEALED: Disadvantages

   1. Loose typically 3 - 6dB of output versus vented
   2. You’ll need 6dB more power to get to the same point in output
       as a vented enclosure.  Or like going from a 500 watt amplifier to a
       2,000 watt amplifier. And the subsequent additional current draw.
       500 watts is about 58 amperes, versus 2,000 watts which is
       233 amperes (full power current draw)

 
 

VENTED

 

     PROS & CONS?

 
  

VENTED: Advantages

   1. Gain 3-6dB of output over sealed. Or
       roughly the equivalent of having a 500
       watt amp “act” like its 2,000 watts.
       Vented Enclosure is giving you FREE energy

   2. Better transient response.
   3. Less current draw because you can utilize 
       a smaller amplifier.

 VENTED: Disadvantages

   1. Much harder to design and build. Really
       need a modeling program to do that.
       We recommend WinISDPro. Which is
       FREE!    Go to this URL
:                                                                                       http://www.linearteam.org/download/winisdpro/winisdalpha.exe

                                                                                                                                 2. Typically about double the size of a
       sealed enclosure. But still relatively small
       in the scheme of things.
                                                                                                                                 3. If you design the box incorrectly (in other
       words mistune it, for example tune below
       Fs of driver {highly discouraged}) it can
       damage the woofer

 

      TYPICAL RECOMMENED TUNING FREQUENCIES

For 4 door sedans 34-38 Hz.    For longer vehicles (SUV’s ,Vans, etc) typically 30-36Hz

PRE-FAB? OR ..NOT TO PRE-FAB???

These can be “OK”. BUT...the secret is don't get one that is tuned TOO high. Many of these prefab enclosures are tuned to 40 Hz. For most “mature adults
this tends to be too high and give you what is called ”1 note Bass” . Be careful!!   Typically no one complains to their retailer/installer that they got TOO MUCH
BASS! Everyone complains about not getting enough!!! So lets FIX that!

Our MOTTO is  - Design and build better subwoofer enclosures.

* Building notes/ Software to use (ITS FREE!)

There are all kinds of ways to design subwoofer enclosures. Nomograms, charts, on-line design software, etc.  But the BEST, most consistent software(and even
better).....FREE software has been available for over 10 years.

WINISD Pro (0.50a) website: http://www.linearteam.org/download/winisdpro/winisdalpha.exe

(NOTE: ONLY use WinISDPro 0.50a...NOT the newer WINISDPro 0.7!!)

1. Use 3/4 in or thicker MDF, or Baltic (Finnish( Ply (preferred) 

2. When in doubt BRACE!   Woofers can produce MORE than 10 pounds per square inch of pressure!

3. Always deaden the interior (if possible) with deadliner, DynaMat, Hush Mat, etc. Make the enclosure as "dead" as possible.

4. Stuff enclosures about 1/2 to 2/3rds full of polyfill. BOTH for vented and sealed!

5. IF there is a choice between vented OR sealed. For a normal human being...go VENTED!!!!  At least in a car audio system.  Home? Totally a different deal altogether.  Sealed?  You need 4 times the energy (power) to get to the same "output" a vented can get you. And some of the most expensive home speaker systems in the world...use vented enclosures!!

Remember it is ALWAYS easier to be able to turn DOWN a sub then to turn it up.

 

      WINISDPro "SCREEN SHOT"


 






         



















 


Above is a 0.4 SEALED (yellow lline) VS 1.0 CUBIC FT VENTED ENCLOSURE (teal line) Notice how the VENTED IS +9 dB
more output for every watt put into it!! Yes that looks like a peak......I get it…BUT in reality this is what you want from this software. 
Trust me after designing 10’s of THOUSANDS of enclosures for dealers/installers/consumers.  It REALLY works!!

 

WHY DO WOOFERS "BLOW UP"???  

Have you ever wondered...... why?  Other than these woofers are "junk", or "garbage".  What REALLY kills a subwoofer?  Is it too much power?  Too low power a subwoofer?  Meaning the amplifer doesnt "match" the subwoofers power rating.  What REALLY kills subwooffers???

Actually the person turning the volume control is the problem.  NOT the power rating of the woofer or amplifier.  

 

LETS START AT THE BEGINNING (I was a small child in Fullerton California.....about the time the earth was cooling...ok maybe not that far back)

First off ALL audio is AC volts. What comes out of a headunit RCA and what comes out of an amplifier is AC volts.  Like off your wall outlet, just smaller voltage. And the voice coil of a woofer *(the part that moves back and forth inside a magentic field)   A voice coil is basically a toilet tissue tube with small copper wire glued to it.   So think  "heater coil".  AC volts across thin copper wire.

......So lets take a real world situation,  1,000 WRMS amplifer.  Very typical  in the USA.  That is 32 volts out AC. (Power is measured as AC volts squared divided by the impedance)  The current out (yes there is CURRENT too!!) could be in the 10-15 amperage range.  So ....32 volts with 10 amps of current....Hmmm?  That should heat up a voice coil?  Ya think!!!!!


 

HEATER COIL

     
 

 

 

 

 

 

GOOD VOICE COIL ON LEFT SIDE.... BURNED TO A CRISP VOICE COIL ON THE RIGHT SIDE.



So what caused this voice coil to burn?   Was it TOO much power (AC volts)?  Or just a punk A#$ woofer?   (Negative on the second part!!)
And sort of YES the AC voltage...kind of....as Voltage by itself did NOT kill this subwoofer voice coil....the person tuning the knob DID!!!!

Normally all audio is tested with test tones.  Specifically "SineWaves".  Usually 1,000Hz for everything other than woofers and 100Hz (or 50Hz) for woofers.
But the issue is that music doesn't have sinewaves in it.  Music has sharktooth waves, saw blade waves, all kinds of waves...but not "Sine Waves"

So lets look at a typcial 1,000 WRMS amplifier.  This will "swing" 32 volts out as that is 1,000 WRMS into a 1 ohm load as shown below on the O'Scope
The top waveform is playing music.