GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Horn-Loaded Speakers
In the Thread: Macondo’s Midbass Project – the grown up time.

Post Subject: Why elephants don't jump ropePosted by jessie.dazzle on: 10/11/2010

Romy wrote:

"...In regular audio we accustom that any loud midbass tone get converted to sort of speed bump. You run a high speed, hit the bump and have your “point of no return”, what you fly in air and you have a generic expectations that the landing is coming. Interesting that sending you to air is very much depending from the leading profile of the speed bump. Your return however hardly read the back side of the speed bump (unless you drive VERY slowly) and it would be mostly the subject of your car mass, electricity of your suspicion, force of gravity for your given planet and so on… Sounds familiar? Here is where my midbass horn behaves differently it reads the back side of the midbass speed bump with a fanatical precision...."

With horns, not only does one roll over that "speed bump" at a slower speed, but the bump is not as high.

To produce a given SPL, the diaphragm of a direct-radiating driver must travel a greater distance than if it were correctly horn-loaded. Because of this, if the direct-radiating diaphragm is to keep time with the music (or with the horn-loaded driver), it must move at a greatly increased speed; a speed where its own inertia really starts to come into play.

The larger the diaphragm, the more the mass; the lower the frequency, the more the excursion (somewhat mitigated by fewer the cycles of LF). When compared to horns, the effect may well be most obvious in the case of large-diameter bass drivers, as they have physically larger and therefore heavier diaphragms which, in order to produce LF, must travel further.

But that's not all; assume the diaphragm of a direct-radiating driver and a horn-loaded driver have identical masses; assume also that the direct radiator has to move its mass twice as far (not unreasonable). Moving that mass over twice the distance in the same time requires that the mass travel at twice the speed. Twice the speed requires not twice, but four times the force, in both accelerating and breaking. Translation: The amp becomes a sort of micro-manager of the diaphragm.

In a horn, the diaphragm not only moves a lesser distance, and therefore moves slower, but it is also typically lighter weight.

All this means the driver is able to get its job done using more of its own "talent".

Yes "horn-loading" means exactly what it says; the diaphragm is presented with a greater load (the air in the horn), but..
1) It does not "see" that load immediately; not in the beginning of its stroke or transition; the load is progressively applied (the air is compressable)
2) Its own weight and therefore inertia is typically lower (quicker starts/stops/transitions)
3) It does not have to move as far (less speed and again less inertia)
4) Because the excursion is less, the coil is reacting against the most saturated part of the permanent magnetic field (the most powerful part of the motor)

In the case of a direct-radiator, the motor "sees" an immediate load, in the form of the inertia of the diaphragm, which must be looked at not only as a result of its own greater physical weight, but especially from the point of view of the motor, which has just received a message that it must move that greater mass a greater distance in the same time, making the diaphragm "appear" much heavier; in this case, it is the diaphragm, not the air that presents most of the load.

jd*

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