The Speaker

THE SPEAKER

Two speakers.....

In the series about rock music hardware, we take a look at the loudspeaker.
Technical and musical greetings from
Kurt Starlit
- aka CykelKurt

This series includes:
1. The electric Guitar 2. The Stomp Box 3. The Microphone 4. The Amplifier 5. The Speaker 6. Organ & Synth 7. Record & Music Production 8. Drums & Rhythm Boxes

Latest update: 2016.April.16

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A speaker - the key to succes

In the real world you'll find many different types of speakers. In this chapter, though, we'll only take a look at those being used within a rock context.

The term "speaker" is often used rather nonchalant. So, in this context, it will be used in two meanings.

- Either: a (loud)speaker unit, meaning a stand-alone unit
- or: a speaker cabinet with built in speaker unit(s).

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Sealed Box Enclosure

A sealed box enclosure is characterized by being completely closed. For this reason, there can be no interaction between front and rear side of a speaker, mounted in the enclosure. For the same reason, the cabinet can be made very small. BUT, at the same time, it has to be taken into consideration, that the size of the cabinet is determining how low in frequency the speaker system (speaker & cabinet) will perform. This is also called "the frequency response" of the system.

A closed cabinet also has the advantage of being permanently in control of the speaker unit. The unit never starts to fluctate, because it is controlled by the closed casing, pressing like a spring at the rear of the membrane.

Because of this, the system will perform linearly (= with the same sound pressure) all the way down to the resonance frequency of the system (loudsp. + enclosure).

After this, the sound pressure will decrease smoothly, while the speaker unit is still controlled by the closed casing, and NOT start to helplessly fluctate back and forth like, for example, an open system like bass reflex or horn.

A disadvantage of the closed enclosure is, that roughly half of the sound is missing being trapped in the closed cabinet.

In other words, the efficiency is low. As mentioned elsewhere, there is a correlation between efficiency and sound quality.

All in all, pressure chamber loudspeakers are not suitable for stage applications, which usually requires high efficiency and high power output.

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Vented Box Enclosure

Vented box enclosure, that's what we call the type of cabinet with a (usually round) hole in the baffle or rear of the cabinet. The idea of the hole is that sound from the back of the loudspeaker unit shall meet sound from the frontside of the speaker unit in such a way that the two sound waves reinforce each other.

The design of the hole determines in which frequency range the two sound waves reinforce each other. A well tuned vent will make the system (speaker unit plus cabinet) to perform one octave deeper than a closed cabinet. After this, the sound pressure decreases dramatically.

With this type of cabinet, you'll get a significantly better performance compared to a sealed enclosure.

Soundwise, a vented box should be ranged somewhere between the horn (which is ideal when it comes to sound quality and efficiency, but is big and clumsy) and the sealed box (which can be made very small, but lacks the efficiency and sound pressure level).

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Horn Loaded Enclosure

The horn speaker cabinet got its renaissance during the 1970s because with this type cabinet, you had very low distortion, at the same time achieving a full bodied bass. The speaker unit only had to vibrate very little to produce an enormous sound pressure. What this means, is great sound and very little distortion.

The only disadvantage of a horn loaded enclosure is its size. For this reason, the horn only got limited succes.

Personally, I fell in love with these monstrous boxes. So, in late 1970s, for my home stereo I had two 350 litres horn loaded enclosures, each with a 15" Cerwin Vega bass speaker front mounted. I got the horns from a rock group, who had given up dragging these monstrous bins in and out from concert venues.

Horn Page

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Three types of cabinets: sealed box, vented box and horn loaded enclosure.

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Efficiency and sensitivity

The efficiency of a speaker, is defined as the ratio between the electrical signal sent INTO a speaker compared to the acoustic sound pressure level coming OUT from the speaker. The higher effiency, the higher sound pressure level.

The efficiency of a speaker is calculated by sending an electrical power of 1 watt (at 400 Hz or 1.000 Hz frequency) INTO the speaker, and then with a microphone and a measuring instrument determine how big a sound pressure the speaker is delivering. The ratio between input and output power is converted into percent. The efficiency of most speakers is around 5% or less, the better speakers (e.g. those used in combo amps) are 10%, and the best speakers is as much as 30%.

For your information, a speaker with high efficiency also sounds better! This is due to the quality and size of the magnet and voice coil. A magnet with high flux density makes the speaker quick reacting. This means that transients (momentary high SPL, which most languages and instruments are full of) are clearly audible. A speaker with low effiency will frequently fail to react before the transient has disappeared and it is all over.

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How do speakers make sound?

large pic.

Speakers (also called loudspeakers) push and pull surrounding air molecules in waves that the human ear interprets as sound. You could even say that hearing is movement detection. So what makes a speaker travel back and forth at just the right rate and distance, and how does that make sound?

You'l get an idea of this by visiting the home page of Jacob O'Neal:

How speakers make sound.

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The perfect speaker

Let's make it perfectly clear: The perfect speaker does not exist.

But if it has got

- high effiency (= playing loud with only a few watts input)

- high power rating (= can take a lot of watts without breaking down),

- wide frequency range (= being able of reproducing a broad variety of tones), and

- wide dispersion (= can be heard from all sides),

then we are well off.

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Super speakers
The American Fender company produced guitars and amps. They had a reputation because of the fantastic Fender sound. Only years later I found out what really makes a Fender amp better than the rest: the loudspeaker!

If you take a look at a Fender-diagram, you'll probably find nothing indicating this amp should be any better than any other. No, the secret is in the speaker unit: JBL, James B. Lansing. Using a JBL speaker unit in any combo amp makes it play like a dream, e.g. 12 inch speaker K120.

If you take a look at a speaker unit's data sheet, one thing should be noticed in particular: the Sound Pressure Level - abbreviated SPL. The SPL is telling how high acoustic level this particular speaker will provide, when supplied with 1 watt of electrical power.

The K120 is providing a SPL of 101 dB, when supplied with 1 watt of electrical power (in the frequency range 500 - 2500 Hz). Many "ordinary" speakers has got a SPL of 90-93 dB - a leap of 10 dB. This is a lot!

Talking 'bout watts, 3 dB equals a doubling or halving. This is something that can be heard!

Other quality speakers:

Celestion Gold

Weber, model 12F150

Weber, model Silver Bell

Eminence, model Private Jack

Eminence, model The Govenor

Eminence, model The Wizard

Eminence, model Cannabis Rex

All these speakers are very sensitive with a SPL around 100 dB. This will make any combo amp sund like a much bigger unit.

And it's the same if you play the bass, only we are now dealing with a bigger speaker unit, usually 15" or 18".

Most speaker manufacturers are cutting on speaker quality, to make the amplifier competitive - keep the price down. But the fact is, that the speaker is the source of good sound - not the amplifier. Most amplifiers are more or less the same - it is the speaker that makes the difference - not the amp.

JBL Professional

JBL, K-series

Links

Loudspeaker (Wikipedia)

Audio Frequency (Wikipedia)

Hertz (Wikipedia)

Building a speaker

What does sound look like?

Altec Lansing (Wikipedia)

Celestion

Cerwin Vega

DAS Speakers

Fane International

Goodmans (Wikipedia)

Goodmans Power Range

Martin Audio

Philips

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Articles dealing with the rockscene of the sixties:
The Rock Scene of The Sixties Musikhuse Spillesteder Rock Elektronics Pigtrådsøkonomi Fender Jazzmaster

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This page is under constant consideration and expansion.
Have you got any opinion on this site in general
or technical detail in particular, don't hesitate to contact me.
Please write:

Thak you very much!

Kurt Starlit
aka CykelKurt

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