Max Sub

Maximizing Subwoofer Applications


This focus is on getting a cabinet to sound better and providing guidelines for the subwoofer speaker selection. The idea is to move the lower frequencies from your top section and redirecting those frequency to a subwoofer. When the elimination of these sub frequencies from the top box these cabinets will run more efficient and can be ram at higher volumes. The idea to send these lower frequencies to a speaker that is specifically designed for that.

There are three aspects of a subwoofer application that needs to be address for maximum performance.

In Cabinet Design:

  • Understand the fundamentals of subwoofer designs.
  • Address misconceptions may have been provided by others.

Speaker selection:

  • Understand parameters for the selection of a subwoofer
  • Selection for requirement to provide reliability


  • Understand the different subwoofer designs
  • Determine how to define the needs of the application.


Subwoofer Cabinet Design

The four types of enclosures designs that include the sealed cabinet, the vented cabinet using ports to extend the frequency range, the front loaded horn cabinet and the folded horn cabinet, There is a combinations design called a hybrid that used a horn loaded design that ports the internal part of the cabinet.

Sealed Cabinet Designs:

  • Not recommended for professional sound applications.
  • Efficiency is very low, requiring too much power for pro applications.
  • Cone excursion requirements are too close to Xmax in sealed cabinet as the frequencies go lower.
  • Low frequency roll off at 12db per octave compared to 24 db for a vented cabinet
  • Do not require as much air (cubic space inside the cabinet) to go as low as vented Cabinet

Vented Cabinet Designs: (bass reflux)

  • Vented cabinet designs are by far the most popular cabinet for subs in professional sound applications.
  • Good selection for small to medium size venues that does not require a long throw.
  • Provide for extended low end response using ports compared to the sealed cabinet.
  • Handle more power because porting produces most of the lowest notes, reducing cone excursion.
  • Increased efficiency compare to the sealed cabinet.
  • Response goal of 40 Hz is good compromise to reach vs cabinet size that increases below 40 Hz.

Horn Loaded and Bass Horn Subwoofers Cabinet Designs:

  • To maximize an application or have a long throw requirement this subwoofer design is required.
  • Ability to extract the maximum capabilities of a low frequency transducer
  • Horn loaded speakers efficiency can be as much as 12 dB louder than a vented cabinet.
  • Note: For every 3dB increase in efficiency the power requirement is decreased by half
  • Voice coils in horn loaded cabinet can run much cooler for the same acoustic output levels.
  • The cooler voice coil property results in less power compression and reduction of output loss.
  • Horns applications in the professional sound can produce the required output for line array systems.
  • Because Low frequencies tend to be Omni-directional,
    • The horn provides a directional characteristic to focus the horn output more toward to the front.
    • This function provided is referred to as long throw characteristic
  • Horn application tend to couple better when placed in groups of four or eight units.


Subwoofer Speaker Selection or Replacement

Speaker selection for a replacement speaker or a speaker for a DIY cabinet, the first focus if the speaker specifications.

A subwoofers design should meet the maximum driver/cone excursion or Xmax at the rated power levels. Without getting into great details, Peak Watts is equivalent to maximum excursion (Xmax). Typically your RMS power rating of the amplifier should be one half the Peak Watts.

  • Power capability is very important to transducer selection.
  • Larger coil and magnet sizes provide more area for heat to dissipate
  • Equally important is the ability of the voice coil to handle thermal energy.
  • Venting allows thermal energy to escape and cooler air to enter the motor structure.
  • Consider the suggested usable frequency range with the power rating to avoid such failures.
  • Sensitivity represents the efficiency and volume expectations from a device relative to the input power.
    • This is one of the parameter that is critical in providing the best application
    • A high-efficiency woofers would be in the range of 98 to 100 dB for the raw speaker
    • The cabinet used for the application will depend on the additional efficiency that can be provided.
    • The additional parameter required is a speaker with a medium to high Xmax parameter.
  • Speaker size for the frequency response requirement.
    • If your focus is in the 30 – 40 Hz range, an 18 or 21 inch speaker should be selected.
    • If your needs are 45 Hz or greater then consider 15 inch speaker.
    • The 15 inch speaker will provide a tighter and cleaner, where an 18 inch will moves more
  • Lower Fs indicates a woofer with lower low-frequency response
    • Less efficient to produce output at frequencies belowFs.
    • Input signals significantly belowFs cause large excursions and can damage the speaker
    • Woofers typically have anFs in the range of 13–60 Hz.
    • A goal would be < 30 Hz with a 24 db per octave 30 Hz High Pass (Rumble) filter
    • This filter is set to keep all frequencies above the Fs and tuning frequency of the enclosure.
  • Xmax parameter for sub application requires a large number
    • Driven high levels at low frequencies, Xmax is defined by measuring excursion at a level where 10% THDis measured in the output. This method better represents actual driver performance.
  • Vd parameter is the Peak Diaphragm Volume (cone volume movement)
    • Vd = Xmax * Sd
    • Where Sd is the actual surface area of the cone
  • Qts of 0.4 or below indicates a transducer well suited to a vented enclosure.
  • EBP is the measurement is calculated by dividing Fs by Qes.
    • An EBP greater than 150 usually indicates a speaker is best suited for a horn enclosure.
  • Bl is the he product of magnet field strength in the voice coil gap and the length of wire in the magnetic field
    • A high BL figure indicates a very strong transducer that moves the cone with authority!

Don’t Get Cheap

One of the biggest problem is some people wants to spend half the money and try to get twice the performance. Once in the real world, they find that they do not have the output and reliability they thought you would have. After a failure, you will end up having to purchase the gear you should have gotten in the first place.

No Mix and Match Games

  • Use the same type cabinets for the sub application as well as the top (mid-high) section.
  • Different cabinet designs provide for inconsistencies in response and end up with holes in the response
  • Different cabinet designs will provide a phasing issue
  • Stay with the same size speaker due to a different with different sizes
  • Horn loaded mid-high cabinet throw different than non-horn loaded types.
  • Like kind will provide a much cleaner overall sound with no headaches.


Defining the Correct Crossover Point

  • For the subwoofer, the lower the cross point the better. Good starting point is 80 Hz
  • Frequencies below 100 Hz, cone excursion and power requirement in full range cabinets rise tremendously.
  • Use high pass filters (80-100 Hz) in top cabinets to provide better performance at high power levels.
  • High pass filter in top cabinet at above value allow for low pass to be used to provide a good transition.
  • Crossover point need to provide a smooth transition
    • The sub crossover should be one octave above the -3dB point of the main speakers
    • If the top cabinet lower bass extension at -3dB point is 40Hz, the crossover point for the sub is 80Hz.
  • If using an amplifier with fully functional embedded DSP, the crossover point can be dictated.
    • This example is from the Behringer iNuke DSP Series amplifiers
    • In the filter/crossover section set the high pass filter for the top speakers for 80 Hz with a 24dB slope
    • In the filter/crossover section set the low pass filter for the subwoofer that same 80 Hz with a 24dB slope.
    • At the same time, set the High Pass (Rumble) filter for 35 Hz for protection.
    • This same function can be provided using a speaker management system.


The Limiting Factor

  • At a minimum, make sure your amplifier comes with a soft clip limiting circuit that can be monitored.
    • Occasional blinking of the limit LED during operation is acceptable.
    • If the limit LED circuit stays on too long, reduce the volume – this is the limitation of the amp.
    • Continuous LED is a warning the distortion is being produced.
    • This type of distortion will cause the voice coil to overheat and eventually fail.
  • An amplifier will perform better running at 4 Ohms than 2 Ohms.
    • Running at 2 Ohm load provides more demands are placed on the amp’s power supply.
    • When running at 4 Ohm load, this will provide for a backup plan.
    • If an amp fails, you can transfer speakers and temporarily run a 2 Ohm load
    • Running a 2 Ohm load is not recommended for a normal configuration.
  • If powered speaker are not used in your application
    • It is recommended to use embedded DSP in the amplifier that is purchased.
    • With existing amp with no embedded DSP it is recommended to use a speaker management module.
    • This will provide High and Low pass filters and a peak limiter to protect you speakers

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