Distortion in Subwoofers (1 Viewer)

[Rory Buszka]

What is the largest source of distortion in subwoofers? The purpose of this thread is the explore ways to produce subwoofers with low distortion.

 

[Mark Larson]

The largest source... i think it would be when you feed too much low frequency to a sub when the amp can't handle it. (This is why small subs need more watts and still distort more)

 

[Michael R Price]

Well, there are several reasons for subwoofer distortion:

Amp clipping: if you try to reproduce such a loud signal, or if the amp uses EQ boosting and needs more power than it can handle, it will clip, causing a flopping or cracking sound.

Driver (BL) distortion: The more the driver has to move back and forth, the more distortion it will produce. A very loud bass signal, especially below the tuning point of a vented sub, will cause a lot of driver movement and hence distort the sound.

Port noise: If a sub has inadequate porting area or is overloaded with information near or below the tuning frequency, the ports may have so much airflow that they create a whistling noise, distorting and compressing the sound.

So low distortion subwoofers have large amplifiers (or are very efficient and don't require a large amplifier), drivers capable of moving large amounts of air linearly, and a lot of port flow capability. A good example is SVS's CS+ line, with 500 watts of amplifier, a driver capable of 1.8 or so liters of linear displacement, and three 3" flared ports. There are many other examples of very low distortion subs, especially DIY.

 

[Rory Buszka]

What about this? Using an 18" kevlar cone, with a star-shaped reinforcing thingy in the middle (with 7 spokes which extend 3/4 of the way from the center to the edge of the cone, and the spokes are not symmetrical but channel the motion energy to the center of the structural-star), where the cone is only designed to move 6mm in and out on a stiff suspension and a very linear motor, rather than, say, a typical 12" woofer? Also, the woofer could have very high power handling, something on the order of 600 watts, so a 350-watt plate amp can't blow it. The driver could be designed to work in an enclosure 20" high, 32" long and 12" wide with a 4" flared port

Also, can you reduce amplifier clipping or improve transients by sticking a larger capacitor across the power leads that carry power to the amplifier form the power supply?

 

[ThomasW]

What about this? Using an 18" kevlar cone, with a star-shaped reinforcing thingy in the middle (with 7 spokes which extend 3/4 of the way from the center to the edge of the cone, and the spokes are not symmetrical but channel the motion energy to the center of the structural-star), where the cone is only designed to move 6mm in and out on a stiff suspension and a very linear motor, rather than

Nope.....

 

[Mark Seaton]

Rory,
The first thing I would say is to start working your way through ALL of this thread: XBL^2 driver thread
In there you will also find a link to Klipple's website, a gentleman who has done a great deal of work in studying non-linearities in drive units. For subwoofer use you will find that diaphram/cone strength has almost no effect at low frequencies. Driver breakup is an issue at higher frequencies in a driver's operation, but this is generally not a problem in subwoofers. For a subwoofer it is more important that it doesn't really have any peaks in the upper response as these will magnify distortion products. You can also look at our website at www.soundphysics.com to see our designer's solution to the problem. The ContraBass Corner also has some good info and graphics.
The short answer is that producing clean deep bass is all about coupling to and moving large volumes of air in a linear fashion.