Speakers: Construction and power
`
`5/15/21, 9:07 AM
`
`Lenard
`
`Search
`
`Subjects ◀ ▶
`
`Speakers
`
`I offer the educational material I have created on this website free of charge to the global community for
`its elucidation and use as it sees fit, with the understanding that it must be attributed to the author, as it
`is copyrighted material.
`
`Having said that however, should you find that it is of value to you, and wish to make a contribution to
`the ongoing viability of this site, I have set up PayPal account for your convenience and hereby express
`my gratitude for whatever you may be able to forward.
`
`Principles
`
`Power
`
`Impedance (Z)
`
`Cabinets
`
`Construction and power
`The construction of speakers is approached in the same way as musical instrument making. Fine
`tolerances and attention to detail make large differences to performance. Large musical instruments and
`speakers suit low frequencies and vice versa. Each speaker and instrument can only function efficiently
`with linearity within 3 octaves (octave is ratio 1:2). Theoretically a single speaker would have to change
`diameter from (1in - 24ft) (20mm - 8m) to maintain similar level and dispersion over the frequency
`spectrum.
`
`Topic 2 of 4
`
`The majority consist of paper or plastic moulded into a cone shape, loosely suspended in a frame so as
`to easily move back and forth to vibrate the air. Glued to the back of the cone is a coil of wire (voice coil)
`within a strong magnet field. Passing electricity through wire causes a magnetic field around the wire,
`which attracts or repels, causing the cone to move back and forth. The larger the magnet and voice coil
`(BL) the greater the power and efficiency if well made. Externally vibrating the cone will cause the voice
`coil to generate electricity. A speaker can work well as a microphone especially for bass drums.
`
`http://education.lenardaudio.com/en/05_speakers_2.html#:~:text=M…20coils%20are%20double,less%20weight%20and%20greater%20accuracy
`
`Page 1 of 8
`
`Apple v. GUI Global Products
`IPR2021-00472 GUI Ex. 2012
`
`

`

`Speakers: Construction and power
`
`5/15/21, 9:07 AM
`
`The energy of the magnet is conducted through the mild steel pole plates and pole piece and concentrated
`(north - south) across the gap. Hopefully the voice coil has been perfectly centred in the gap. The
`clearances are very very small, less than half a bees dick. The smaller the gap - the more intense the
`magnetic field - the greater the efficiency. The slightest variations in alignment during manufacture, cause
`large variations in performance. No two speakers or musical instruments can be identical.
`
`http://education.lenardaudio.com/en/05_speakers_2.html#:~:text=M…20coils%20are%20double,less%20weight%20and%20greater%20accuracy
`
`Page 2 of 8
`
`Apple v. GUI Global Products
`IPR2021-00472 GUI Ex. 2012
`
`

`

`Speakers: Construction and power
`
`5/15/21, 9:07 AM
`
`Voice Coils. Passing electricity through wire causes a magnetic field around the wire. Changing polarity
`of the electric current through the wire also changes the polarity of the magnetic field created around the
`wire. The interaction of the two magnetic fields, causes the voice coil to be pushed out of the gap forward
`or backward, depending on the polarity of the electricity through the voice coil.
`
`Speaker polarity. The standard test for a speaker, is to put a battery across the
`speaker terminals. When the + of a battery is put on to the + marked terminal of
`the speaker the cone should move out. This is also the correct test for checking
`the polarity of speakers in stereo systems. 1.5 Volt battery is safe to use.
`Warning. Never use this test on a compression driver.
`
`Most voice coils are double layered, wound with enamel coated copper wire around a former then bonded
`with an epoxy compound and baked in an oven. Voice coils can also be wound with rectangular
`aluminium wire to achieve less weight and greater accuracy. A cone speaker is approx 2% efficient
`therefore approx 98% of the electrical energy is wasted as heat.
`
`http://education.lenardaudio.com/en/05_speakers_2.html#:~:text=M…20coils%20are%20double,less%20weight%20and%20greater%20accuracy
`
`Page 3 of 8
`
`Apple v. GUI Global Products
`IPR2021-00472 GUI Ex. 2012
`
`

`

`Speakers: Construction and power
`
`5/15/21, 9:07 AM
`
`Voice coil Length. At bass frequencies the voice coil has to move back and forth a long distance,
`especially at high power, compared to the high frequencies. During movement, the % of voice coil in the
`gap must remain constant. The voice coil can be long and the pole plate thin or the voice coil short and
`the pole plate thick to achieve the same outcome. There are argued advantages and disadvantages both
`ways. Mid and high frequency speakers cones only move a small distance, compared to the large
`movement of bass speakers. The voice coil length and pole plate thickness are similar.
`
`Mid and high frequency speakers are approx 6dB to 10dB more efficient than bass speakers. In small
`passive systems the mid and high frequency speakers are attenuated to match the less efficient woofer.
`In active systems the bass speaker is driven with higher power. An example is two 15in woofers driven
`with 400 Watts to match a 12in mid speaker driven with 200 Watts.
`
`Voice Coil Diameter. On the same diameter speaker a small voice coil has less control over the cone
`compared to a large voice coil. With a small voice coil the cone is able to be more resonant compared to
`the same size cone with a large voice coil. Some small voice coil speakers may appear to be more
`efficient but this extra efficiency may be only at the one resonant bass note. At frequencies above this
`resonant bass note the speaker may be less efficient compared to the same cone with a larger voice coil.
`Cost and performance of speakers increase with voice coil size.
`
`The larger the voice coil the better the control over the cone, and therefore improved damping and linearity.
` Large voice coils are expensive to make (limit approx 4in 100mm). Assembling the speaker is also more
`
`http://education.lenardaudio.com/en/05_speakers_2.html#:~:text=M…20coils%20are%20double,less%20weight%20and%20greater%20accuracy
`
`Page 4 of 8
`
`Apple v. GUI Global Products
`IPR2021-00472 GUI Ex. 2012
`
`

`

`Speakers: Construction and power
`
`5/15/21, 9:07 AM
`
`difficult, tolerances taken to greater accuracy. The larger the voice coil diameter - the larger the area of
`the magnetic gap. To keep the flux density of the magnetic energy (per unit area) in the gap the same (for
`the speaker to retain the same efficiency) magnet size and therefore mass of the speaker must be
`increased. The major advantage of larger voice coils is greater power-handling.
`
`Square Wave. It is not possible for a speaker or musical instrument to produce an acoustic square wave.
` A square wave can only exist in electronics where 'physical' mass and force do not exist. A speaker will
`average the electrical energy of a square wave as the fundamental period of a sine wave, with discordant
`third harmonic resonances.
`
`A speaker responds only to the resultant energy of an electrical signal, but not to the separate
`characteristics of phase between voltage and current within that signal. Also to understand this
`demonstrates how much of the audiophile and professional audio myths about 'electronic time alignment'
` are simply marketing fabrications. However acoustical wave-length time alignment between the physical
`distances of speaker components (woofer and tweeter) is important and should be taken into
`consideration.
`
`What governs the 3 octave rule?
`
`Sound is a wave motion of air having length and co-responding height, described as frequency. At
`frequencies where wave-lengths are equal to and become longer than the speaker diameter, decreasing in
`frequency, the frequency response is smooth, and dispersion widens (directivity).
`
`Theoretically to maintain the same power, the cone must move 4 times the distance, for each octave
`decrease. Cone mass, and reducing air resistance as the frequency decreases, cause this. The same
`as a musical stringed instrument (constant velocity).
`
`The upper limit for high frequencies is where wavelengths become smaller than the speaker diameter.
`This causes node and lobe distortion within the cone (chaotic resonances). Dispersion narrows to a beam
`and the frequency response becomes chaotic, sounding harsh and screechy.
`
`http://education.lenardaudio.com/en/05_speakers_2.html#:~:text=M…20coils%20are%20double,less%20weight%20and%20greater%20accuracy
`
`Page 5 of 8
`
`Apple v. GUI Global Products
`IPR2021-00472 GUI Ex. 2012
`
`

`

`Speakers: Construction and power
`
`5/15/21, 9:07 AM
`
`The lower limit is where wavelengths become 10 times the speaker diameter. Cone movement is so
`great it becomes inefficient, non-linear and generates inter-modulation (affecting other notes). The
`fashion for bass speakers to be small compromises performance regardless of marketing claims.
`
`An ideal system will have 4 speakers, each covering 2-3octaves. Eg.
`(1in for the harmonics). (4-5in for upper voice). (8-10in for lower voice). (12-15in for bass).
`professional systems use horns and compression drivers for extra power and efficiency.
`
`Speaker power
`
`Cone Speakers are approx 2% efficient. power and efficiency is dependant on BL, which is magnet and
`voice coil size. B is the total magnetic energy in the gap. L is length of voice coil wire. Also mass and
`area of cone, suspension compliance and frequency.
`
`Bass power. The maximum distance the cone can move limits bass power. To maintain the same
`acoustic output the cone must move 4 times the distance for each octave decrease and vice versa. 1/4
`distance, for each octave increase. Two times due to cone mass changing direction. Two times because
`air is slippery. As frequency decreases air slips sideways decreasing resistance. As frequency increases
`air doesn't have time to slip sideways, increasing resistance against the cone (radiation resistance).
`
`At wavelengths greater than 10 times the speaker diameter, cone movement is so great it becomes non-
`linear and inefficient. Some manufacturers make the suspension tight to limit cone movement,
`compromising bass performance for a higher power rating.
`
`http://education.lenardaudio.com/en/05_speakers_2.html#:~:text=M…20coils%20are%20double,less%20weight%20and%20greater%20accuracy
`
`Page 6 of 8
`
`Apple v. GUI Global Products
`IPR2021-00472 GUI Ex. 2012
`
`

`

`Speakers: Construction and power
`
`5/15/21, 9:07 AM
`
`High frequency power is limited by excessive heat that can destroy the voice coil.
`
`Speaker manufacturers have difficulty specifying power handling. In marketing there has been a modern
`trend to sell speakers as being capable of 1,000 Watts plus, similar to selling a motor vehicle as being
`capable of going at the speed of light. At bass frequencies the cone excursion is limited by the tightness
`of the suspension and may be at maximum between 20-100 Watts. Above maximum excursion the bass
`notes become compressed.
`
`Cone movement can be so great that at the point where the voice coil and cone are joined it can hit the
`pole plate, making a loud cracking sound and therefore warning. The voice coil may be capable of 50-200
`Watts before it burns out (depending on time). At mid and high frequencies, cone excursion does not limit
`power handling. The voice coil will keep getting hotter until it burns up, and stop abruptly without warning.
` Sometimes excessive heat will cause the voice coil to become loose from its former. This will be heard
`as an annoying mechanical rattling sound.
`
`Other types of speakers
`
`Dome the majority of tweeters are dome, similar to the cone speaker.
`
`Ribbon tweeters are expensive, less efficient, not common, have excellent performance.
`
`Electro-static speakers are expensive very fragile and have a niche following, excellent transients.
`
`http://education.lenardaudio.com/en/05_speakers_2.html#:~:text=M…20coils%20are%20double,less%20weight%20and%20greater%20accuracy
`
`Page 7 of 8
`
`Apple v. GUI Global Products
`IPR2021-00472 GUI Ex. 2012
`
`

`

`Speakers: Construction and power
`
`5/15/21, 9:07 AM
`
`-- To be continued ----
`
`End of Topic 2
`Created: 17-Dec-2008
`
`Speakers
`Principles
`
`Power
`
`Written by John Burnett
`
`Impedance (Z)
`
`Cabinets
`
`Contact
`
`© 2008-2016 Lenard Audio. All Rights Reserved Worldwide.
`
`◀ ▶
`
`http://education.lenardaudio.com/en/05_speakers_2.html#:~:text=M…20coils%20are%20double,less%20weight%20and%20greater%20accuracy
`
`Page 8 of 8
`
`Apple v. GUI Global Products
`IPR2021-00472 GUI Ex. 2012
`
`