Peter from Tone Chasers explains...
What is a speaker?
Like a lot of electromagnetic devices like guitar pickups, motors, dynamic microphones, speakers rely on coils of fine wire moving in a magnetic field either inducing a signal from that movement or using a signal to create movement.
In the case of a speaker the signal travels from the amplified source to the voice coil this voltage signal causes the voice coil to move in the magnetic field. The speed and power of this movement is directly in proportion to the incoming signal. The voice coil is attached to the spider and the spider is attached to the cone. The cone creates the movement of air that is picked up by our ears.
So, what can go wrong with your speakers?
Fault finding on any system is down to elimination. Below is the input to output process of elimination I would take.
Is the amplifier putting out a signal? Resulting in no speaker movement
Cable from the amplifier to the speaker
Do these look sound? Are there breaks in the cable? Is the signal reaching the speaker? Resulting in no speaker movement
Connections between the cable attachment and the voice coil
These fine wires can be broken if not handled carefully, especially around the back of the speaker cone. Is the signal reaching the speaker voice coil? Resulting in no speaker movement
The voice coil
Are the windings of the voice coil intact? If tested with a multimeter on the ohms setting the voice coil should register around the value of the speaker impedance (not exactly as resistance of the coil and impedance of the coil are different and too lengthy to explain here). If it reads very low or very high the voice coil is either short circuit (low reading) or open circuit (high reading). Resulting in no speaker movement or smoke.
The magnetic flux level of the magnetic field
This can be measured with a Gauss meter (most people will not have one of these). Also you can test whether the magnet is still magnetised by using a small piece of ferric metal. This is quite rare and only included for completeness. Result low and lifeless movement of speaker.
This should be securely connected to the voice coil and in good condition. Result low and lifeless movement of speaker and possible distortion.
The speaker cone
This should be securely connected to the spider/voice coil and in good condition. Result Distorted unpleasant sound.
Every tube amp need to be connected to speakers when switched on otherwise catastrophic and expensive damage can happen to your output transformer. So regular inspection and repair of your speakers is very much overlooked.
Also the speakers that you use can make an incredible difference to the sound of your amplifier. Take a look at this YouTube video if you don’t believe me!
https://www.youtube.com/watch?v=skfVh5qagoo and this is just one manufacturer.
One final thought
Finding it tough to get the right bass drum punch and sound from a live kit? Try using a 12” guitar speaker near to the rear bass drum head as a sub frequency microphone mix some of this in with your existing microphone and get an expanded frequency range. This should result in move low end and power from your kick sound.
Check this out...