Tobler-ONE: Jordan JX92S T-Line Speaker
Page 1: Introduction, Enclosure, Design
Page 2: Construction, Photographs, Costs, Impressions
This webpage is also available in Italian.
This page describe a single driver, Transmission Line (T-Line) loudspeaker enclosure for the Jordan JX92S fullrange driver. For a married individual like myself, the most important factors that affect the design and performance of a Hi-Fi audio system are (in decreasing order of importance):
- WAF !!!!
- the listening room
- the loudspeakers
- the rest of the system (electronics, etc.)
Obviously, in the case of "single" audiophiles, the WAF is generally not an issue.
The idea for this design was born from the need to "retire" from my principal audio system a pair of Cizek Model 3, after more than 26 years of honored service, mainly for aesthetical reasons. If you are familiar with this speaker, you will understand the first among the following requirements:
- a very detailed and equilibrated sound
- a narrow front baffle and external dimensions suited for corner placement (for optimum WAF)
- a budget of 500 Euro (excluding VAT)
- frequency response (far field): 50 Hz (-3 dB) to 18 kHz (-0.5 dB) or better
The principal intended use is to provide music mainly during lunch and dinner, so high SPL is not an issue, nor is the efficiency (about 86 to 88 dB @ 1W/1m is suffiecient).
TRANSMISSION LINE ENCLOSURE
Based on my previous positive experiences with single driver full-range loudspeakers, a Fostex FE206 Bass Reflex and a Hi-Vi B3N MLTL (web pages are in Italian), I opted again for another single-driver loudspeaker, thus avoiding economic and acoustical costs of a crossover. I chose the Jordan JX92s driver for the linearity and wide extension of frequency response, the low distortion characteristics and for the T/S parameters, which make this driver suitable for almost every kind of acoustical load (except perhaps a dipole).
The choice of a Transmission Line (T-Line) enclosure came almost naturally from the need of a tall and narrow loudspeaker enclosure to be placed against a back wall. Being far less critical than a Bass reflex enclosure for frequency tuning, this type of acoustical load has some interesting "tweaking" capabilities. The final part of line can be filled with different filling material densities to obtain different low frequency response (up to almost replicating a closed box response). This can be used to avoid a potentially excessive low frequency augmentation when corner placing the loudspeaker, while maintaining the possibility of low extension if the loudspeakers are placed far from the wall. Adjusting the damping material can also be used to shape the frequency response for amplifiers with low Damping Factors (i.e. high output impedance) like some tube or solid state with no NFB.
In other words, the same loudspeaker design can achieve a high level of flexibility and adaptability to very different situations (different room, amplifier, etc.) and we all know that adaptability gives the best chance for survival in Hi-Fi equipment.
The Transmission Line design is similar to the one suggested at MLTL-48 on the E.J.Jordan website, with a triangular section (to be precise, the section is trapezoidal with a very narrow base). The triangular section is particularly well suited for corner placement and helps also helps in reducing possible internal reflections.
The frequency response for the enclosure has been simulated with the MJ King MathCAD sheets available from Quarter Wavelength Loudspeaker Design. The original proposed line length has been reduced by a couple of cm to fit in a single 15mm thick beech plywood sheet.
Figure 01: Frequency Response
Figure 02: Cone Displacement vs Frequency
Figure 03: Impedance vs Frequency
Figures 05 and 06 show the calculated frequency response corresponding to different polyester fiber density in the port hole.
Figure 05: Frequency Response with d1=0.25 lb/ft^3
Figure 06: Frequency Response with d2=0.75 lb/ft^3
Figure 07 shows the calculated frequency response with added series resistance (to simulate an amplifier with low DF; look at the peak at low frequency).
Figure 07: Frequency Response with Radd = 5 ohm
The calculated frequency response with Radd = 5 ohm and the port stuffed with d2=0.75 lb/ft^3 is shown in Figure 08.
Figure 08: Frequency Response with Radd = 5 ohm and d2=0.75 lb/ft^3
|[ 1 | 2 ]||
Construction, Photographs, Costs, Impressions