Sujet Les gri-gris en Hi-Fi

Nan nan l'écran fait bien 2m, mais les enceintes font 6m de diagonale.

Pour le rodage des HPs, l'essentiel est de faire bouger la suspension pour l'assouplir. Du coup le Pink noise est pas ce qu'il y a de plus efficace.

Un bon 20Hz à faible niveau et hop

The old running in of speakers myth - this is what I wrote about this some time ago and I see no reason to change my opinion -

Many years ago, all car engines had to be run in for about 1,000 miles. At the end of this period, the customer brought the car to the dealer and there the various bolts were tightened up and the oil was changed.

This arrangement was far from ideal, some people were more careful than others and some dealers did a better job than others, so one engine manufacturer used a computer programme to run the engines against dummy hydraulic loads to simulate 1,000 miles of perfect running in driving. Then the engines were put into the cars and no running in was required.

Customers complained and were mystified. How can a car already be run in? That does not make any sense!

So this particular manufacturer did a test. They told a group of customers that they had to run in the engines with religious care and they were even given totally over-the-top instructions on what to do. There was of course absolutely no point to it, they were perfectly run-in already.

Another group was told to just drive. They were told the truth, there was no need to run them in, a computer programme had already done a far better job than any customer could have achieved.

These two test groups were revisited over the next few years and there future choice of cars and overall behaviour as customers was observed. The results were really surprising - not only did the run-in cars have slightly fewer faults than the non-run-in cars, but the customers expressed greater satisfaction with them and were significantly more likely to buy the same brand the next time.

The testers came to the conclusion that by actively involving the customer in the care of the car right at the beginning, an emotional bond had been created. This in turn, meant that they took greater care of the vehicle, drove more carefully and enjoyed the experience more.

Monitors are high quality (we hope!) hi-fi speakers. In the main, all monitor manufacturers are also manufacturers of hi-fi speakers and put exactly the same drivers in both types. The only differences are marketing and sometimes that the studio monitors also contain amps and crossovers to make them active.

With one or two minor exceptions, all driver cones are made of materials that, to all intents and purposes, do not fatigue. For example KEF and B&W use glass-fibre and most paper cones are impregnated with various substances, such as epoxy resins and UV resins that prevent warping and bending and also counteract the effects of fatigue that paper alone would otherwise be subject to.

I have fatigue tested and repaired many, many speakers in my lifetime and the only places where a speaker driver gets damaged is on the suspension and on the coil. Over time, the suspension can wear down (paper) or rot and crack (rubber). A change in the sound only takes place when the suspension is badly damaged. Even a cracked rubber surround is not audible until that crack goes all the way through the material, from front to rear, in which case the speaker will start to buzz at certain frequencies.

Some manufacturers actually tell their customers that by running in their speakers, they are making them more pliant. In the case of glass fibre and epoxy resin impregnated cones (and remember that is nearly all of them) there is no bending and they are carefully constructed to avoid bending anywhere other than at the suspension. A driver is suspended at the throat and at the outer edge of the cone. In a hi-fi or monitor driver, both are extremely soft and pliant, so that the only effective resistance to movement is air. This is done to improve the response rate (the ability to mirror the incoming signal accurately).

All hi-fi and monitor drivers for mid and bass have soft suspensions such as a rubber surround or a cloth surround that allows the driver to move forward and back fully and completely, like a piston. The main factors that decide the sound of a speaker is the mass and size of the cone and the compliance of the air mass to the front and to the rear. All these are a given. You could drive that speaker for 100 years and the air, the diameter and the weight of the cone will be the same. The same rules apply to the tweeter, which works as a fully enclosed system.

There is one type and one type only of speaker that I have seen that changes its characteristics over time and that is the stiff-suspension guitar cab driver. In these, the suspension used to be made of the same materials as the cone, i.e. paper and with time, the whole cone and suspension would become softer texture when the fibres separated as the whole thing vibrated.

The changes are slight. We tested the changes that occurred over time with a stroboscope, so that we could see the bending take place. A stiff-suspension causes the driver to bend the cone into patterns at higher frequencies and in some cases, a worn cone would create slightly different patterns at given frequencies, when compared with a newer sibling, but these changes are enough to give the final sound more harmonic distortion, not unlike that of a valve (tube).

It is this creation of patterns that causes some of the sound that a certain guitar cabinet to produce a type of distortion that the musician is looking for, so picking the right driver for the cab is important.

On the other hand, the main resistive load for a monitor driver in a closed box with soft suspension (rubber or silicon) is the air it has to move and the air in the box in particular. Modern polymers as are used by all (as far as I am aware) driver manufacturers are very elastic (ability to return to original form) and very 'un-plastic.'

This is not true for paper cones that alter their mechanical characteristics significantly over time.

For that reason, guitar amp drivers that have been on the road for a few years have more overtones than a brand new driver. Both the suspensions and the cone itself are made of thick paper that loosens its structure with age and use and the resonant frequency of such a driver can drop significantly. Paper cones loosen their structure and therefore reproduce certain frequencies and harmonic combinations differently as they get older.

Paper cone guitar speakers rely on the stiffness of the suspension for a large part of their resistive load. This can vary between 20% and 60%, depending on a whole host of factors, including volume, stiffness and construction of the surrounding cabinet.

The stiffness of the suspension of a studio monitor is kept fairly low and at the same time, the cones are made as stiff as possible, all by use of modern materials such as polymers and complex glass fibre and polymer combinations.

Also, studio monitors are not supposed to be used to the full extent of the travel of the cone. Put simply, they are (or at least should be) used at lower volumes, so as to avoid mechanical distortion.

These are built into either fully enclosed or deeply ported cabinets and the resistive load of the air is therefore far greater than for an open guitar cab.

Those two factors combined, mean that the mechanical resistance of the suspension accounts for less than 20% of the total resistance. At low volumes, less than 10%.

Given that modern materials only marginally alter their elasticity and plasticity and that tiny change effects a factor that makes up just 10% or less of the overall compliance of the driver, we are talking about something that might alter a fraction of a percentage of the mechanical compliance of the driver.

Headphone membranes are usually made of biaxially-oriented polyethylene terephthalate, which is a pre-stressed (drawn) version of the same stuff that is used to make pop bottles (aka PET bottles). This stuff behaves in a very similar fashion to modern studio monitor cones.

In short, run in the speakers on the your guitar stacks. The older and 'fluffier' the paper, the more harmonics they will create - a bit like old valves really.

But the drivers in your high quality studio monitors use air as their resistive load and last I heard, you can't run in air.

Pour les spécialistes: un haut-parleur de 17 cm neuf qui possèderait un fréquence de résonnance (fs) de 60 Hz environ, peut atteindre, après plusieurs heures de rodage sur un générateur de fréquences, une nouvelle valeur de Fs de moins de 40 Hz!

Il est ainsi tout à fait normal d’avoir un son un peu « vert » lors du déballage de l’enceinte.

Le son va s’améliorer au fil du temps, ce sont surtout les woofers qui vont évoluer. le grave va se libérer et descendre bien plus bas, le medium va s’ouvrir et deviendra plus naturel, même le tweeter sera plus doux!

Pour obtenir le même son que celui que vous avez écouté lors d’une démonstration en magasin, il suffit de brancher vos enceintes et de les faire fonctionner ! Rien de plus.

Vous n’êtes pas obligés de mettre le son à un niveau faible lors des premières heures d’écoute. Au contraire, si vous souhaitez roder vos enceintes rapidement, mettez des disques qui ont de bonnes basses, à un niveau d’écoute confortable (pas éxagéré non plus!).