STRAIGHT BASS HORN

version francaise

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etat actuel

This page describes the contruction of a pair of bass horns.

Constraints:

-30Hz-300Hz straight horn
-1.3m overhang in the listening room.
-700mm hole in the wall.
-Large mouth to get a large energy, and possibility to place the midrange horn on the same axis.
-Mouth of the horn made of wood to avoid placing the midrange horn in a concrete environnement.
-The 2 horns must be touching each other to be coupled in the low frequencies.
-The horns must not touch the side walls because of the stairs and the windows and other constraints
-It must be possible to extend the mouth size.

Final horn:

38Hz exponential curve has been chosen.

Each horn is 3m long + 0.7m for the 250 liter sealed box and has a 1.8m*1.85m mouth plus the beams.

The throat is a 220mm square, so a 200mm, 250mm, 300mm, 380mm or 460mm driver can be used. Each horn starts in the room on the other side of the wall, crosses the stone wall and then extends over 1.3m in the listening room.

The final driver:

First listening tests made me chose the Altec 515-8G but recently I discovered the le Cyrille-Audio BM38ND76P which is more neutral, more nervous and goes deeper. Its efficiency is also superior. I will publish measurements soon.

BM38ND76P

The screen:

ecran

a film:

projection

Measurement using 2 Altec 515-8G, 300B amplifier, no crossover, no EQ:

2*515G

Measurement using 2 Altec 515-8G, 300B amplifier, 121Hz first ordre low pass filter:

2*515G first order filter

Measurement using 2 Altec 515-8G, 300B amplifier, 121Hz first ordre low pass filter + 280Hz second order filter:

bandwidth: 22Hz - 280Hz

2*515G third order filter

Throat molding:

rear mold

Throat:

gorge

The wood horn is covered with concrete:

concrete

Construction mathematics:

For each plank the cut angle is equal to:
cut_angle:=arcsin(sin(horizontal_progress_angle)*tan(vertical_progress_angle))

For a rectangular horn made of curved plank or parquet planks, if x is the length on the horn axis and if the horizontal and vertical progress functions are known then the corresponding length on the plank before it is curved is:
integrale

So to draw the horizontal progress on the straight plank the relation is:
horizontal_progress_on_the_plank(l) := horizontal_progress(invert_function(plank_length_for_vertical_progression(l)))

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