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Loudspeakers [Types | How it works? How to Listen?]

Audio Basis - educational articles

Read about loudspeaker types and its destination, how speaker works, how to listen and select loudspeakers for an audio systems, frequently asked questions.


Often people say that the last criterion of sound quality assessment is human ear.

If it say exactly, sound quality is very accurately described by specification (numbers and diagrams).
Why then says: last criterion of quality estimation is human ear?

Manufacturer don't measure and provide all diagrams. Often it is technically impossible (too much measurements).
For most of people (non-audio technicians), these diagrams are hard to understanding.

Besides right interpretation, we must integrate all measured data.
It's complex enough for human brains.

Therefore, below we review simple practical advices for non-specialists in the audio.

 

What is loudspeaker?

Speakers have different types: by placement, by destination and we can meet "speakers" and "loudspeakers" terms. Both ones means the same.

Loudsepeaker is converter of electric oscillation (of voltage or current) to acoustic waves. How it works read below...

 

Who invented loudspeaker?

1861 Johann Philipp Reis applied a ​telephone electric loudspeaker to reproduce of tones and low quality speech
1876 Alexander Graham Bell patented loudspeaker (as part of its telephone), that capable to reproduce clearer speech
1878 Ernst Siemens improved the loudspeaker
1898 Horace Short patented a compressed-air-driven loudspeaker
1898 Oliver Lodge established the modern design of dynamic loudspeakers (moving-coil driver)
1915 Peter Laurits Jensen and Edwin Pridham applied dynamic loudspeakers (moving-coil driver)
1924 Chester Williams Rice and Edward Washburn Kellogg patented moving-coil technology that is commonly used now

 

What are different types of speakers?

Destination speaker types

  • home speakers;
    • stereo speakers;
    • front speakers;
    • surround/rear speakers;
    • subwoofers;
    • surround system;
  • studio monitors;
  • concert speakers;
  • cinema speakers;
  • bluetooth/wi-fi/wireless speakers;
  • others.
Type Description
Home speakers Home speakers are intended for home using. This type of speakers is leader in sound quality in general case.
Stereo speakers Stereo speakers is any speakers. Mandatory requirement: it is 2 identical speakers.
Front speakers Front speakers are the same stereo speakers, that included in surround system and placed before listener. As rule, these speakers should the best by sound quality in the system
Surround/rear speakers Surround/rear speakers are included in a surround system may have quality worse that front ones. But for modern systems and recordings, it is recommended, when all speakers of surround system are the same.
Subwoofers It is additional speaker, that used to expand low frequency range of front or stereo speakers. Read more...
Surround system As rule, it is surround system in low budget 5.1 kit of speakers. Also, hi-fi/hi-end vendors provide family of high quality speakers, that including front, surround, subwoofer loudspeakers.
Studio monitors It's intended for music production. Sound quality is desired, but is not mandatory.
Main requirement is reproducing of tiniest sonic details in maximal frequency range. Because, sound engineer should listen all. There should not be hidden sounds.
If frequency or harmonic distortions are there, the engineer can adjust in to target system (hi-fi, radio, car, boombox, etc.).
Concert speakers Main requirement, significant pushing air mass in big rooms and open air. Also, concert monitors for musicians at scene are included in this loudspeaker type. This type of speakers may sound worse, comparing home loudspeakers.
Cinema speakers They rather are intended for big multichannel systems, and reproducing cinema sound effects.
Bluetooth/wi-fi/wireless speakers Are intended for easy wireless connection with a musical systems.

 

Placement types

Home audio speakers have main types of placement:

  • bookshelf;
  • on-floor;
  • built-in.

Bookshelf speakers

Bookshelf speaker

 

On-floor speakers

On-floor speakers

 

Built-in speakers

Builtin speakers

As rule, built-in speakers are used for interior and landscape design. Its placement is matter for sound quality.

Bookshelf loudspeakers allow to place it at walls, when no available place at the floor or by intrerior design issues.

The author, in general case, recommend on-floor speakers due to larger enclosure volume. Especially for big room. But it can't guarantee better sound quality then abovementioned types.

 

Signal feed types

There are 2 signal feed types:

  • active;
  • passive.

Active and passive loudspeakers

Active and passive loudspeakers

As rule, hi-fi speakers have not built-in amplifiers and contains passive filters only.

Theoretically, built-in amplifiers may be better adjusted to speaker drivers, including active and digital, crossovers. But, actually, the author would be prefer check actual sound.

Line input is low voltage input (0.3 ... 2 V) to connect pre-amplifier, mixer, tape, phono preamp, etc.

Also, subwoofers may have both types of inputs: linear and speaker.

 

Driver type by frequency range

There are speaker driver types:

  • Low-frequency driver (woofer, subwoofer);
  • Mid-range driver;
  • High-range driver (twitter);
  • Wide-range driver (full-range drivers).

The frequency ranges are not standard.

As example, subwoofer is designed for frequences in range about 20 ... 120 Hz.

And "full-range" driver cover not full audible range 20 ... 20 000 Hz, but so wide range as it can.

The frequency range is defined by frequency range, where maximal deviation of sound pressure level is lesser than defined value.

These types have different construction. Read details...

 

Why subwoofer is need?

Subwoofer is special speaker to reproduce lowest frequencties.

It is most popular in home theater setups.

There are discussions: is subwoofer need for music or not?

It is need to remember, that music stuff contains low frequencies. And acoustic system, that capable to playback in this frequency range, will reproduce more details of a musical recording.

However, to achieve proper result, subwoofer should be adjusted correctly and have low distortions level.

Why subwoofer is need?

Why subwoofer is need?

How to check phase aligment between subwoofer and loudspeakers

 

Is difference between speakers there?

It is not absolutely correct statement. What do they mean?

Speaker and room are integrated system. You can't "listen speakers". You can listen system:

  • listening room;
  • speakers;
  • amplifiers;
  • (sometime) cables;
  • other equipment.


Quality of speaker depend by quality of loudspeaker's drivers.

Its specification include apart from magnitude-frequency and phase responses also harmonic distortions (that simplistic presented by THD - total harmonic distortions).

In system with other component, the speakers may sound better or worse.

There are ways to adjust listening room mechanically and magnitude-frequency and phase responses electricaly. But these ways are not ideal and harmonic distortions, practically, may not be removed.

The drivers works together with enclosure. So, some issues of constructions may not be compensated.

 

How much does a loudspeaker cost?

DISCLAIMER: There are not hard rules, of course. For different countries the ranges of prices are different. But we'll try find some trend.
Speaker sound equally may be corrected via adjusting magnitude-frequency and phase responses with equalizer.
But we can't correct exactly these characteristics.
Also we must remember: these characteristics are various for different locations of listening room.
We can't affect to harmonic distortions and speaker's push air capacity.

 

What difference between stereo loudspeaker systems for $500 and $3000?

Fidelity of playing for low and very low levels of loudness.
Design and expensive materials are matter too.

 

What difference between stereo loudspeaker systems  for$100 and $500-$2000?

Fidelity of playing for all levels of loudness. More sound "transparency" for more expensive.

For prices more $500-$1500 the increment of quality is less than below $500.

 

 

How does a loudspeaker work [physics]?

Loudspeaker contains:

  • driver;
  • enclosure with system of acoustic wave channels;
  • crossover.

Driver have diaphragm, that works as plunger, pushing air mass.

How speaker driver works

How speaker driver works

The diaphragm is moved via magnetic force.

The force is created by interaction of magnetic field from electromagnetic coil and the magnet.

Coil's magnetic field appear due to alternating electric current, passing through the turns.

The current is managed by alternating voltage from the power amplirier.

 

Back-to-front cancelation

Rear side of the  diaphragm push air behind the driver (rear air). Acoustic wavelength is commensurate with diphragm size. And the wave go around the diaphragm. It called as "diffraction".

Back-to-front cancelation of acoustic wave from speaker driver

Back-to-front cancelation of acoustic wave from speaker driver

So rear and front acoustic waves are interfere. These waves are oscillate in contrary phase (air pressure [of each of the waves] alters in different directions). And pressure on the ear from front wave is attenuated by rear wave.

Speaker spread acoustic waves in all directions (wave rays). These waves bounced and re-bounced from all surfaces at their path.

These rays interfere (summarize) in each location of a listening room individually. It's impossible get identical wave interfere in all points of the room.

Read more...

To avoid or reduce the cancellation:

  • rear wave may be isolated by closure (closed-box loudspeakers); or
  • the diaphragm should be significantly more wavelength; or
  • rear wave phase should be inverted (reflex port).

 

Closed-box loudspeakers

Closed-box loudspeakers

 

Reflex port of speaker

Reflex port of speaker

Reflex port of speaker allow to invert phase of rear acoustic wave of diaphragm to same phase with front wave from the driver. It allow to gain level of air pressure.

Disadvantage of a reflex port is significant dependency on frequency.

 

Large vs small loudspeakers

Larger speaker's driver-diaphragm diameter is capable to pump a higher air mass in environment due to larger square of the diaphragm surface.

Especially it's important in big rooms and open air.

Larger speaker size, move higher air mass

Larger speaker size, move higher air mass


Not any big head will well sound. And don't be tempted on big and, sometimes, cheap acoustics.

As example, big concert acoustics is not always sound quality leader. Concert acoustics for great sound pressure (on open air especially).
Its harmonic distortion requirements are fewer than for home hi-fi acoustics.

If you have place on floor, using of the floor speakers is preferable.
"Have place" it is direct way (without barriers) for sound wave.
If you don't have place on floor, use bookshelf speakers.

 

Diaphragm rigidity

If the diaphragm is not rigid, not all parts of its surface moves together.

When center of the diaphragm begin move, edges of the cone still stays immovable. It cause the surface deformation. Deformation moves from center to edges, together with the center movement.

Example:

Two peoples holds one long wire for both ends. One human begin rock his hand up and down, and wave move from this person to other end of the wire. And the wire is twisted in vertical plain.

Same way mechanical oscillation (surface twisting) from central dome of the driver moves to its external borders.

And each of the parts radiate own acoustic waves with biased phase. Interferention (summarizing) of these waves cause level altering, that depend on frequency.

Speaker driver diaphragm rigidity

Speaker driver diaphragm rigidity

For absolutelly rigid diaphragm all parts of its surface are moved simultaneously.

When we discussed back-to-front cancelation, we seen, that higher diameter of speaker reduce issues of rear-diaphragm-side-radiated acoustic wave. But we should understand, that higher diaphragm diameter reduce the rigidity.

The rigidity issue may be solved via:

  • diaphragm design (cone, dome, etc.);
  • material (paper, kevlar, metal, etc.);
  • size.

Example: design manage rigidity by geometry; material define rigidity directly; size reduce mechanical-twist value.

 

 

 

 

Speaker crossover

Speaker crossover is multi-band frequency filter. It split total signal to several frequency bands for each speaker's driver. Such feeding improve dynamic range of each driver.

Speaker crossover (as rule, it is inner loudspeaker device)

Speaker crossover

 

The splitting is applied via filters. In speaker with line input active filters (as variant, digital ones) may be applied. It allow to improve technical features of the filters, comparing passive crossover.

Sometimes, crossover and amplifiers may be implemented as standalone units, outside the speaker or several speakers (1 per band). Connection may be applied via separate pins for each driver inside the enclosure.

Loudspeaker connectrion to outer single amplifier

Loudspeaker connectrion to outer single amplifier

 

Bi-amp loudspeaker connectrion with crossover

Bi-amp loudspeaker connectrion with crossover

As rule, inner band filters (crossover) of the speaker cannot be turned off outside the enclosure.

Sometimes, bi-amping is applied without the crossover. In this case, improvement is possible, when each of the amplifiers are better adjusted to connected driver.

No obvious advantages between inner or outer amplifier connection. Result is depending on used units and its settings.

 

 

Speaker sound quality

Sound transparency

What is in technical terms? Or it only subjective characteristic for our ears?

Certainly we can to measure the transparency.

Transparency is complex of characteristics, which define the capability of non-distorted throughput for device.

If to say simply: Transparency = minimum harmonic distortions + flat frequency characteristic (lesser +/- 1 dB in declared band).

Usually we apply term "transparency" about hi-frequencies (5-10 kHz). We qualify it as "air" or "airy sound".

What about low frequencies?

The same. But speak nothing about "air" there. Bass notes should not be merged. No bass hum should not be there.


What is harmonic distortion?

If sine signal feed input of device, then at output we have this sine + other sines (harmonics) at other frequencies. Other sines are harmonic distortions.

 

Acoustic issues of a listening room

Bouncing of acoustic waves from walls, ceil, floor, furniture and other surfaces may partially emulate concert hall. It give to us rear sounds (like multichannels systems).
Into sound-insulated and anechoic room we feel discomfort. We listen own bloodstream even. Such room does not suit for listening.

The bouncing with wave interference, sound adsorption cause frequency distortions.
Mechanical resonances of room bring loudness boost at separate frequencies. Compensation may be applied via parametric equalizer or sound traps.

If loudness fall at separate frequencies due to room acoustic properties, compensation with parametric equalizer is impossible.

 

What can give us listening room?

The sound (acoustic waves) from speaker press to the ear-drum. It's direct radiation or direct acoustic waves.
Reflections has time delay relative to speaker's direct wave.

Therefore we have cases:

  1. Speaker's direct and bounced waves push the ear-drum in same phase. Loudness is increased, than without bouncing.
  2. Speaker's direct and bounced waves push the ear-drum in opposite phase. Loudness is decreased, than without the bouncing.

These cases are different:

  • for various points of a listening room and
  • for different frequencies.

But these cases are the same for different loudness levels.

How to eliminate these issues?
We can partitially eliminate the reflections. But it can cause "dead" or "dry" sound.

More number of speakers can cause as increasing as decreasing of loudness (various for different frequencies).

 

Acoustic system tuning

Measurements

To correct frequency distortions, it is necessary to find frequencies of "resonances" and "dampings".

Simplest (most expensive) method is measurement with panoramic SPL-meter. This way real-time spectrum (loudness along frequency range) is shown in a listening point.

Alternatively you can:

  • use simple SPL-meter for manual measurements at separate frequencies.
  • own ears.

Test signals (hardware or software generator of sound frequencies):

  • sweep sine,
  • sequence of frequencies.


Sweep signal isn't very good for detecting by ears of frequency value.

When we check frequency sequence, resonances may be located between these frequencies.

Also, loudness memorization is issue for ears.

The author would recommend the records to test of bass resonances:

  • Cezaria Evora - album "Nha sentimento" - song "Vento de Sueste"
  • Goran Bregovitch - album "New Collection" - songs "100 Lat Modej Parze", "Gas Gas"
  • VA - album "Deep Bass. Low Frequency Sound Adventures" - song "Final Frontier"

What you should listen?
Bass notes must sound as separate notes with proper loudness (non quiet, non excessive), without muttering or buzz.
To control to high frequencies, you can use jazz and acoustic guitar records. Listen sounds of cymbals and string scratches. These sounds should be clear, without "dirt". Recollect the live concert.

 

Equalizers

Parametric equalizer (EQ) can more precisely compensate a superfluous loudness at frequencies, than grapical EQ.

Parametric equalizer

Parametric equalizer
 

 

Graphic equalizer

Graphic equalizer
 

Parametric equalizer provide better localization. Adjusted filter band cause minimal touching of "good" frequency ranges.

However, inter-suppressing direct and reflected waves may not be compensated via EQ. Only changing of listening location, reflection management via acoustic treatment. Use sound-absorbing and sound dispersive materials for wall surface finishing, installing sound traps.

You can calculate room acoustics (without or with assistance). Otherwise - only experimental tuning.

Resume: EQ may be used only for decrease loudness at frequencies with extensive level.

Read more: Where is the Limit of Audio Quality?

 

 

Yuri Korzunov,

audio developer,

Audiophile Inventory

Copyright © Yuri Korzunov
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