511B Damping

After a bit of tapping with a screwdriver handle and damping with finger and thumb pinched around points on the bells and flanges, I get the impression that damping of the horn body top and sides might be going too far.

I will use sound damping sheet which comprises a thickness of a bitumen-like material which is backed by a semi-rigid aluminium sheet on one side and is self adhesive on the other side. This product, with some heating, will conform to surface shapes, e.g. Altec horns. This product is traditionally used on auto firewalls and other areas.

Do the horn top and sides need to be damped for home use?

Regards, Marshall.

Depends on who you ask, the horn's environment/listening distance, the XO point/slope and what you mean by 'damped'.

Right now, my 511/500 Hz XO'd horns are perched on top and only the bells are damped with a thinner version of what you propose (still damped enough though), but in no way do they audibly measure up to my originals that were encased in a multiple layered, inches thick sprayed on insulation designed for insulating the inside of a commercial building's metal roof.

If I were to increase the XO to 1200 Hz/2nd order, it may not be necessary and at 2400 Hz/1st order, my SWAG is none would be needed. Doubling/quadrupling the listening distance should yield similar results.

The best compromise then is to damp the entire horn and raise the XO point to both quell any potential ringing and reduce horn 'honk', i.e. the M-19 is one realization to the extent that not increasing the XO point as much is offset by encasing the horn in a somewhat damped box to isolate any potential body ringing, 'killing three birds with one stone' (these two plus cosmetics).

GM

Addendum: To get an idea how much body damping is ideally required, listen to it setting on top with the woofer disconnected, then get two big bags (50# or more) of sand, kitty litter, grain, dog food or similar and nestle the horn on one and listen again, then lay the other on top of it.

Let us know what you think is a point of diminishing returns. ;)

I used Jim Dickinsons method of paint with layers of sand between each coat. Cost is almost zero, all it will take is some of your time & because of that you can do the complete horn area, including flanges, bells, etc.

Just mask of the areas that will be visible....I even did part of the external bell areas.

Six or seven coats will do the job & I guarantee they'll be as dead as....well they'll be dead!

There have been a number of threads, so worth a forum search...

Last ones I played wit I used sheets of automotive damping...

Mah, I don't think you can go too far with horn damping. In theory a horn functions purely as a boundary for the air column, and ideally should contribute nothing to the sound otherwise. Generally speaking, the closer one approaches this goal the better the results.

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Originally Posted by J Henry

I even did part of the external bell areas.

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That is the most important part John.When I installed those new foams on my 19's they touch the bell areas and kill most if not all the ring my ear's could detect.They touch the bells both top and bottom in two places.Good enough IMO.