update() {

		const audio = this.audio;
		const range = this.range;
		const divisionsInnerAngle = this.divisionsInnerAngle;
		const divisionsOuterAngle = this.divisionsOuterAngle;

		const coneInnerAngle = MathUtils.degToRad( audio.panner.coneInnerAngle );
		const coneOuterAngle = MathUtils.degToRad( audio.panner.coneOuterAngle );

		const halfConeInnerAngle = coneInnerAngle / 2;
		const halfConeOuterAngle = coneOuterAngle / 2;

		let start = 0;
		let count = 0;
		let i;
		let stride;

		const geometry = this.geometry;
		const positionAttribute = geometry.attributes.position;

		geometry.clearGroups();

		//

		function generateSegment( from, to, divisions, materialIndex ) {

			const step = ( to - from ) / divisions;

			positionAttribute.setXYZ( start, 0, 0, 0 );
			count ++;

			for ( i = from; i < to; i += step ) {

				stride = start + count;

				positionAttribute.setXYZ( stride, Math.sin( i ) * range, 0, Math.cos( i ) * range );
				positionAttribute.setXYZ( stride + 1, Math.sin( Math.min( i + step, to ) ) * range, 0, Math.cos( Math.min( i + step, to ) ) * range );
				positionAttribute.setXYZ( stride + 2, 0, 0, 0 );

				count += 3;

			}

			geometry.addGroup( start, count, materialIndex );

			start += count;
			count = 0;

		}

		//

		generateSegment( - halfConeOuterAngle, - halfConeInnerAngle, divisionsOuterAngle, 0 );
		generateSegment( - halfConeInnerAngle, halfConeInnerAngle, divisionsInnerAngle, 1 );
		generateSegment( halfConeInnerAngle, halfConeOuterAngle, divisionsOuterAngle, 0 );

		//

		positionAttribute.needsUpdate = true;

		if ( coneInnerAngle === coneOuterAngle ) this.material[ 0 ].visible = false;

	}
Updates the helper. This method must be called whenever the directional cone
of the positional audio is changed.