"Fast", "Punchy" and other such subjective terms used to describe bass
Posted: Sun Mar 29, 2020 10:41 am
When used according to their direct definitions, there is no such thing as a "fast" subwoofer, it is simply meaning extended frequency response and having midrange that matches well to your subwoofer. The effect I'm talking about here has very little to do with the "speed" or acceleration of the cone within a single cycle as it is correct that the cone acceleration is dependant only on frequency and amplitude and applying more power to a heavy cone woofer will move it the same acceleration as a lighter woofer, therefore it is inaccurate to say that "8s are faster than 15s" or other such expression. Apart from anything else, size and cone mass don't directly correlate. There are some 8" and 10" car audio woofers with heavier cones than a Kappalite 3015lf which has a very light cone for its size.
Often when these terms are used, they are referring to something else in rough terms but the effect is still frequency dependent and heavily variable according to enclosure design:
Group delay: How long it takes the speaker to reach its maximum working amplitude according to the signal entering it.
Waterfall response: How long it takes for the speaker and enclosure to stop making a noise after you have stopped sending a signal to it.
Different woofer designs use tricks to improve their efficiency through combinations of resonance and impedance matching.
A sealed enclosure amplifies bass by resonance of the combined driver and airspace on speaker spring effect. It will resonate at the combined result of the speaker's surface area vs enclosed air and cone mass, and also the suspension compliance according to Hooke's law and the cone mass. A low resonance helps the speaker "get its swing on" and gives more efficient low bass though takes a couple of cycles to build up to maximum amplitude. A high resonance does this with upper bass but doesn't offer aid at lower bass.
If you play bass at a speaker's resonant frequency it will sound inherently "slow" because it will take a few cycles to build up to its stable amplitude (the bass will grow gradually louder when this is happening) and a few cycles to swing to nothing (the bass will grow gradually quieter rather than immediately shutting off).
A ported enclosure will have a similar resonance to the sealed at a higher frequency somewhere in the pass band (where the speaker is moving the most), and a lower resonance of the port air (where the speaker is moving the least). At both frequencies, the speaker will have a tendency to ring. There is also below pass band resonance but usually below your mandatory high pass filters so of little concern with appropriate protection device.
A horn will have a resonance at about its quarter wave and multiples thereof (and possibly some to do with the sealed chamber size hopefully well chosen to flatten out response a bit). Someone saying "My Titan 39 sounds 'faster' than my Tuba 60" is sometimes getting into the misnomer above, but also it takes a larger amount of mouth area to damp the lower resonance of a Tuba 60 as in a fully sized horn. The longer horn might reduce efficiency in the upper bass compared to a Titan giving less subjective "punch". The longer horn might be less well time aligned to midbass chest hits from your mid/high speakers. The lower notes being prominent distract you from the tightness of the upper bass.
Sound waves will reverberate around a loudspeaker enclosure for a while.
The room: A car will have quite a short reverberation time so your bass will sound better here than in a gymnasium with several seconds of reverberation time. This will dwarf any talk of differences between horn, tapped horn, 6th order bandpass and sealed and ported. Outdoors will be good as there is usually no immediate reverberation and the echo there is is usually much quieter than the music in a wide open space. A pair of headphones or earphones is the Holy grail of tight accurate bass response due to this and the fact that the drivers are very light compared to their suspension resistance and any damping of the amplifier.
Speakers and enclosures will have braking forces:
Mechanical suspension resistance: They are not a perfect spring and will dissipate the cone's energy as heat.
Electrical damping factor: A speaker feeds back electromotive force back into the amplifier which is "shorted out" through the output transistor and speaker voice coil loop.
Acoustic brake: The expanding path of a horn will radiate away the cone's kinetic energy converting it into sound - one of the reasons why horns seem to retain the staccato bass hits quite well. A horn that is too small will not do this quite as well as there isn't enough surface area of air at the end of the horn to damp the quarter wave resonance.
Aperiodic enclosures use a foam stuffed tunnel behind the driver to deliberately create air friction to brake resonant behaviour. It creates the same effect to the speaker as does breathing through a cloth. It should offer an accurate reproduction but aren't very efficient as they waste the energy rather than converting it to sound as a horn does. Too much stuffing and the speaker will have trouble moving. A transmission line enclosure is a cross between this and also quarter wave pipe at very low frequencies. You can have a stuffed long port or labyrinth that boosts lower bass and damps upper bass and above which is absorbed in the stuffing.
Also low cone mass and electrical Q allow there to be both less mass swinging back and forth and easier to electrically damp.
I will add this. The larges effect on the subjective quality of the accuracy of the bass is by far THE ROOM. In a car, your bass will sound quite tight and accurate. In a gymnasium it will not.
Often when these terms are used, they are referring to something else in rough terms but the effect is still frequency dependent and heavily variable according to enclosure design:
Group delay: How long it takes the speaker to reach its maximum working amplitude according to the signal entering it.
Waterfall response: How long it takes for the speaker and enclosure to stop making a noise after you have stopped sending a signal to it.
Different woofer designs use tricks to improve their efficiency through combinations of resonance and impedance matching.
A sealed enclosure amplifies bass by resonance of the combined driver and airspace on speaker spring effect. It will resonate at the combined result of the speaker's surface area vs enclosed air and cone mass, and also the suspension compliance according to Hooke's law and the cone mass. A low resonance helps the speaker "get its swing on" and gives more efficient low bass though takes a couple of cycles to build up to maximum amplitude. A high resonance does this with upper bass but doesn't offer aid at lower bass.
If you play bass at a speaker's resonant frequency it will sound inherently "slow" because it will take a few cycles to build up to its stable amplitude (the bass will grow gradually louder when this is happening) and a few cycles to swing to nothing (the bass will grow gradually quieter rather than immediately shutting off).
A ported enclosure will have a similar resonance to the sealed at a higher frequency somewhere in the pass band (where the speaker is moving the most), and a lower resonance of the port air (where the speaker is moving the least). At both frequencies, the speaker will have a tendency to ring. There is also below pass band resonance but usually below your mandatory high pass filters so of little concern with appropriate protection device.
A horn will have a resonance at about its quarter wave and multiples thereof (and possibly some to do with the sealed chamber size hopefully well chosen to flatten out response a bit). Someone saying "My Titan 39 sounds 'faster' than my Tuba 60" is sometimes getting into the misnomer above, but also it takes a larger amount of mouth area to damp the lower resonance of a Tuba 60 as in a fully sized horn. The longer horn might reduce efficiency in the upper bass compared to a Titan giving less subjective "punch". The longer horn might be less well time aligned to midbass chest hits from your mid/high speakers. The lower notes being prominent distract you from the tightness of the upper bass.
Sound waves will reverberate around a loudspeaker enclosure for a while.
The room: A car will have quite a short reverberation time so your bass will sound better here than in a gymnasium with several seconds of reverberation time. This will dwarf any talk of differences between horn, tapped horn, 6th order bandpass and sealed and ported. Outdoors will be good as there is usually no immediate reverberation and the echo there is is usually much quieter than the music in a wide open space. A pair of headphones or earphones is the Holy grail of tight accurate bass response due to this and the fact that the drivers are very light compared to their suspension resistance and any damping of the amplifier.
Speakers and enclosures will have braking forces:
Mechanical suspension resistance: They are not a perfect spring and will dissipate the cone's energy as heat.
Electrical damping factor: A speaker feeds back electromotive force back into the amplifier which is "shorted out" through the output transistor and speaker voice coil loop.
Acoustic brake: The expanding path of a horn will radiate away the cone's kinetic energy converting it into sound - one of the reasons why horns seem to retain the staccato bass hits quite well. A horn that is too small will not do this quite as well as there isn't enough surface area of air at the end of the horn to damp the quarter wave resonance.
Aperiodic enclosures use a foam stuffed tunnel behind the driver to deliberately create air friction to brake resonant behaviour. It creates the same effect to the speaker as does breathing through a cloth. It should offer an accurate reproduction but aren't very efficient as they waste the energy rather than converting it to sound as a horn does. Too much stuffing and the speaker will have trouble moving. A transmission line enclosure is a cross between this and also quarter wave pipe at very low frequencies. You can have a stuffed long port or labyrinth that boosts lower bass and damps upper bass and above which is absorbed in the stuffing.
Also low cone mass and electrical Q allow there to be both less mass swinging back and forth and easier to electrically damp.
I will add this. The larges effect on the subjective quality of the accuracy of the bass is by far THE ROOM. In a car, your bass will sound quite tight and accurate. In a gymnasium it will not.