Tech Talk

By An Nguyen, Distinguished Engineer
HARMAN Luxury Audio

Introduction
The JBL 4309 is a smaller version of the JBL 4349, and it belongs to the JBL Studio Monitor series. It carries the traditional JBL classic Studio Monitor look and is packed with latest JBL technologies such as high dynamic range transducers, HDI horn and computer optimized flared port and enclosure. Loaded with these technologies, the JBL 4309 reproduces effortless and accurate sound throughout its operating bandwidth and renders a 3D soundstage that contradicts its size. The JBL 4309 is available with blue baffles in black ash veneer and black grille, or classic walnut veneer and blue grille.

Why the JBL 4309?
Music or sound is recorded/mixed in studio environments by recording engineers using studio monitor type loudspeakers. The 4309 was created to bring that same experience into home environments. In order to do so, a loudspeaker has to be neutral, accurate and dynamic. The 4309 meets these challenges with transducers and horn technologies from our JBL Professional Audio Division and tuned for various home-friendly applications.

Top Technologies
• 2410H-2 compression driver: It has the same diaphragm technology used in the top-of-the-line D2 compression driver but with a single annular Teonex diaphragm. The patented compression chamber, formed by the front plate and top plate, together with the Teonex diaphragm and high energy Neodymium magnet, create a very high efficiency HF device with low distortion. This high efficiency audio device has high dynamic range and low power compression which warrants the 2410H-2 frequency response consistency throughout the operating bandwidth and at various output levels.

• J165P-4 low frequency transducer: In order to keep up with the highly efficient 2410H-2, the 6.5-inch woofer is designed to have high dynamic range and low distortion. It employs a 1.5-inch diameter voice coil with 1-inch peak-to-peak excursion for high dynamic output, low power compression and extended bass. It's loaded with the latest transducer technologies from JBL Professional such as a vented pole piece to reduce air noise, symmetrical field gap to improve position-dependent magnetic force, which reduces harmonic distortions at low frequency, Copper ring/cap (Eddy-Current ring) to reduce the distortions caused by the reluctance force at high frequency and decrease the self-inductance, and an aluminum ring (shorting ring) to reduce flux modulations cause by AC flux induced by voice coil, which reduces harmonic distortion at low frequency. All this means the 4309 can play loud with low power compression and distortion.

• HDI horn: Computer simulation software is used to optimize the shape of the horn, especially area near the throat, for consistent frequency response from 2k Hz to 17k Hz. It is important to have off-axis frequency response curves look similar to the on-axis frequency response curve, but only different in level since these curves set the timbre and excellent width, depth and consistency of the soundstage in the JBL 4309. These curves below show consistent frequency response of the HDI horn and 2410H-2 in various angles.

• Crossover network: It is configured for single input or bi-amp/bi-wire applications. Air core inductance and Mylar film capacitors are used in the HF section for better handling sharp voltage and current spikes at high frequency. The steel laminate core inductor is employed and better suited in the LF section due to better quality factor and efficiency.

• UHF control: This control would change amplitude response (boost or cut) according to specific level from 7k Hz to 20k Hz. These settings help to maintain the timbre of the 4309 in various applications depending on size and absorption of the room, location of loudspeaker and near or far-field application.

• Computer optimized flared port and enclosure: Computer simulations help to optimize the port tube shape to maintain the laminar flow condition throughout the port as much as possible given the high air velocity inside the port. Once this condition is achieved, the port ensures proper tuning frequency at various output levels to maximize low frequency output and minimize port noise.

FEA software (Finite Element Analysis) is used to analyze and optimize the enclosure for cost effective material thickness, overall enclosure rigidity, & minimize the vibrations induced by the woofer to the enclosure. Proper bracing is added to stiffen the enclosure without interfering with acoustic requirements inside the enclosure. This process would ensure only sound comes from HF & LF device arrived to the listener, not the unwanted vibrations sound from the enclosure.

Summary
The JBL 4309 Studio Monitor employs many of the best technologies from HARMAN international. It is engineered at the HARMAN Center of Excellence at Northridge, California. It will be enjoyed by people who appreciate classic high end JBL quality and great sound, and can be used in a wide range of applications in home systems.