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I need help, It never works...

K

Kelu

Dec 6, 2002
242
2
44
Lille in France
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#1
I always have troubles with my amp..

Here what's I got :
- Ashdown ABM500 evoII (575w)
- Mesa boogie 15' roadready cab (I broke the speaker and remplaced it with a 600w one, I have to buy a 400w one cause I thnk the cab is too little for that power ???)
- Mesa Boogie 2x10 cab (only 200w, too weak for stage, only for room practising..)
- 2 Musicmans

I had several troubles with the Ashdown, I send it back several times, the last time, they put it on oscilloscope and said that it was prefect, but when I plug it, I still hear a little noise on the sustain of the note..

Result : A noisy head, a cab with not the right speaker..
A bad sound...
What would you do if you were me ??
What reparing first ??
What changing in my gear ??
Help me.. I will soon have money to spend in my amp system..
 
#4
Kelu said:
- Mesa boogie 15' roadready cab (I broke the speaker and remplaced it with a 600w one, I have to buy a 400w one cause I thnk the cab is too little for that power ???)
- Mesa Boogie 2x10 cab (only 200w, too weak for stage, only for room practising..)
Click to expand...

The power rating of the speaker refers to the point at which the speaker voice coil takes electrical damage. It is not the primary criteria for selecting a replacement speaker.

The size of the cabinet is not directly related to how much power it can withstand before the voice coil catches fire.

A cabinet designed for 200w could be loud or quiet, depending on the speakers used and cabinet tuning (loud, low, or small, you can pick 2). The figure to look at in that case is sensitivity (how much sound it makes for a given amount of input power).

The noise you hear on sustain- have you swapped cabs, amps, and cables, to confirm that it does indeed come from the head?
 
#7
Kelu said:
What is the primary critera ?
Click to expand...
There are several, but I'll throw out a few. The search feature will reveal others.

'Fs' (free air resonance) detertmines at what point the speaker naturally wants to resonate. At requencies below Fs in a ported cabinet the speaker cone is not well controlled and will end towards distortion.

'Qts' is a measure of how likely the speaker is to resonate. A low Qts speaker doesn't tend to have a strong reaction at Fs, while a high Qts speaker tends to have a definite response hump there. Normally, low Qts speakers are used in ported enclosures (.1 to .4) while sealed enclosures usually use speakers of .5 or more.

'Vas' is a measure of how 'soft' the suspension in the speaker is.

'XMax' is a mesure of how long the voice coil is; once a speaker voice coil starts to move beyond Xmax, the response is no longer linear, and this is perceived as distortion. 3mm is pretty short for a bass speaker, 5mm is pretty common, and 12mm is common for a car subwoofer.

Sensitivity is a measure of how many decibels of sound are produced by a 1w signal. There are several ways to meaure this and it is commonly reported at frequencies that have little to do with bass guitar (1k) or otherwise for a cabinet including the horn (which is very sensitive). A typical bass speaker makes 92 - 100 db for a 1w input.

'Power Handling' is a measure of how much electrical energey the voice coil can withstand before warping, melting, or catching fire. It is usually measured as 'RMS' (root mean square) which is not entirely an accurate use of the term, but describes an 'average' power. Sometimes it will be quoted in 'program power' or 'peak power' or 'peak music power' which don't really have a concrete definition.

'BL Product' is a ratio of magnet power to cone mass; a measure of the strength of the motor. If you have a very small magnet and heavy cone, it will not respond to transients quickly. Expensive speakers have powerful magnet structures.

Some generalizations about commercial bass cabs:

1. A speaker with a high Xmax will also have a low Fs, and a low sensitivity- big heavy cones. These speakers will not go very high.

2. Most cabs operate the speakers beyond Xmax on lower notes, as some distortion is tolerable.

3. Most cabs are designed to ignore the lowest fundamental notes (30-40hz) and be louder on the harmonic (60-80hz).

Others feel free to jump in and correct me where I'm wrong. Most of what I know about speakers I have learned on this forum and I'm always learning more.
 

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