4-way speaker with an Acoustic Elegance 15” woofer and 8” lo-midrange, the new Bliesma 3” beryllium dome as hi-midrange and a Bliesma dome tweeter
- This is a 4-way speaker concept using the recently developed Bliesma 3 inch dome midrange. The specification of this driver looks very promising to realize a very good sounding loudspeaker.
- The transducers are the 15 inch Acoustic Elegance TD15H-8 as woofer, the 8 inch Acoustic Elegance TD8M-8 as lo-midrange, the 3 inch dome Bliesma M74B-6 as hi-midrange and the Bliesma T25B-6 1 inch dome tweeter.
- The speaker cabinet is a tower of 109 cm high, 45 cm wide and 40 cm deep. The netto internal volume is 125 L and the woofer and lo-midrange speaker system are closed box, the woofer in 105 L and the lo-midrange in 18 L.
- The midranges and the tweeter are placed horizontal asymmetric on the front baffle to improve the SPL on axis and the DI index responses of the transducers mounted in the cabinet.
- The speaker sensitivity is 89 dB at 1m, 2.83 Vrms, full space.
The low frequency response F3 = 50 Hz, F6 = 38 Hz and F12 = 26 Hz.
For a woofer maximum excursion condition at 50 Hz the speaker maximum SPL is 115 dB @ 50 – 20000 kHz at 1m, free space. - A digital crossover filter will be designed, it can be used for the first listening tests.
Using the voltage transfers of the final digital filter a 4-way analog active filter with opamps or tubes can be designed.
Also a 4-way passive filter can be an option. It will become rather extensive but possible.
Contents
- Specification Headlines
- Estimation Bill Of Material
- Speaker System
- Cabinet
- SPL and impedance curves of the transducers in the cabinet
- Polar diagrams of the transducers in the cabinet
- Off axis response, power and Directivity Index of the transducers in the cabinet
- Digital Crossover filter
- Maximum excursion and maximum SPL with crossover filter
Specificaton Headlines
- System: 4-way, woofer and lo-midrange closed box system, digital and analog X-over
- Woofer: Audio Elegance TD15H-8
- Lo-midrange: Audio Elegance TD8M-8
- Hi-midrange: Bliesma M74B-6
- Tweeter: Bliesma T25B-6
- Low frequency response: F3 = 50 Hz, F6 = 38 Hz and F12 = 26 Hz
- Sensitivity: 89 dB at 1m, 2.83 Vrms, full space
- SPL at maximum excursion, 50 – 20000 Hz: 115 dB, 1m, full space
- Crossover: LR4 200, 800 and 3200 Hz
- Cabinet dimensions: width x heigth x depth = 45 cm x 109 cm x 40 cm
Estimation Bill Of Material
- 2 x Woofer : Acoustic Elegance TD15-8 incl. Apollo upgrade, excl. taxes: 1050 euro
- 2 x Lo-midrange: Acoustic Elegance TD8M-8: 612 euro
- 2 x Hi-midrange : Bliesma M74B-6: 1290 euro
- 2 x Tweeter: Bliesma T25B-6: 500 euro
- Components high quality crossover: 1500 euro
- Components medium quality crossover: 1000 euro
- Cabinet material: 200 euro
- Cabinet Accessoires: 100 euro
- Total without crossover filter or amplifiers for the digital version: 3752 euro
- Total with high quality passive crossover 5252 euro
- Total with digital filter and amplifiers tbd
System
Transducers
For the woofer we have chosen for a 15 inch transducer, the AE Dipole TD15H-8. With its high sensitivity of 94.8 dB @ 2.83 Vrms, 1m and its high maximal lineair excursion of 14 mm peak, it is very suitable to realize an overall sensitivity around 90 dB for this 4 way loudspeaker.
As lo – midrange the 8 inch AE TD8M-8 is chosen. The sensitivity is 95.5 dB at 2.83 Vrms, 1m which makes this transducer very suitable to take over at 200 Hz. This transducer is well known for its good sound.
As hi – midrange the new Bliesma 3 inch dome M74B-6 will be used. The sensitivity is 97 dB at 2.83 Vrms, 1m. The harmonic distortion of this transducer is very low, better than -60 dB between 900 and 3000 Hz at 2.83 Vrms. With a resonance frequency of 440 Hz and with its high sensitivity, this driver is capable to take over at 800 Hz, within its maximum lineair excursion of 1.2 mm peak.
The Bliesma T25B-6 is a 1 inch beryllium dome tweeter. The harmonic distortion of this transducer is low, better than -55 dB between 2200 and 8000 Hz at 2.83 Vrms.
Woofer – Small Signal Analysis
The 15 inch AE woofer is placed in a closed box of 105 L filled with sheep wool.
For this woofer: fs = 21 Hz; Vas = 467 L; Qts = 0.26 on infinite baffle (datasheet values).
Placed in the 105 L cabinet filled with wool: fc = 42.8 Hz and Qtc = 0.55.
The amount of filling can be determined by measuring the maximum impedance of the transducer at the frequency fc. It has to be about 43 Ohm for Qtc to be 0.55.
Lo-Midrange – Small Signal Analysis
The 8 inch AE TD8M-8 midrange is placed in a closed box of 18 L filled with sheep wool.
For this woofer: fs = 98.0 Hz; Vas = 6.7 L; Qts = 0.70 on infinite baffle (measured values by a DIY forum member).
Placed in the 18 L cabinet filled with wool: fc = 105 Hz and Qtc = 0.74.
The amount of filling can be determined by measuring the maximum impedance of the transducer at the frequency fc. It has to be about 27 Ohm for Qtc to be 0.74.
Cabinet
Cabinet dimensions
SPL and impedance curves of the transducers in the cabinet
These are the SPL and impedance curves of the transducers placed in the cabinet in free space at 3 meter, 2.83 Vrms . Also the SPL responses on infinite baffle are shown to see the impact of the cabinet shape on the response.
These simulated curves are used for a first crossover filter design.
SPL woofer in the cabinet on-axis in free space (blue curve) and on infinite baffle (pink curve)
Impedance woofer in the cabinet
SPL lo – midrange in the cabinet on-axis in free space (brown curve) and on infinite baffle (pink curve)
Impedance lo – midrange in the cabinet
SPL hi – midrange in the cabinet on-axis in free space (green curve) and on infinite baffle (pink curve)
Impedance hi – midrange in the cabinet
SPL tweeter in the cabinet on-axis in free space (red curve) and on infinite baffle (pink curve)
Impedance tweeter in the cabinet
Polar diagrams
Horizontal polar diagram woofer in cabinet free space at 80 – 160 – 320 – 640 – 1200 Hz
Vertical polar diagram woofer in cabinet free space at 80 – 160 – 320 – 640 – 1200 Hz
Horizontal polar diagram lo – midrange in cabinet free space at 80 – 160 – 320 – 640 – 1200 Hz
Vertical polar diagram lo – midrange in cabinet free space at 80 – 160 – 320 – 640 – 1200 Hz
Horizontal polar diagram hi – midrange in cabinet free space at 0.64 – 1.2 – 2.5 – 3.8 – 5.1 kHz
Vertical polar diagram hi – midrange in cabinet free space at 0.64 – 1.2 – 2.5 – 3.8 – 5.1 kHz
Horizontal polar diagram tweeter in cabinet free space at 2.5 – 3.8 – 5.1 – 6.4 – 12 kHz
Vertical polar diagram tweeter in cabinet free space at 2.5 – 3.8 – 5.1 – 6.4 – 12 kHz
Off axis response, Power and Directivity Index of the transducers in the cabinet
To calculate the power response and directivity index, the horizontal and vertical SPL off axis responses of the woofer, the midrange and the tweeter are simulated in steps of 15 degrees, the speaker placed in a full sphere at 3m distance. The power is calculated out of the mean value of these curves. The power is represented as the SPL of an omnidirectional source at 3m distance in a full sphere with a SPL value equal to the power.
Woofer
Horizontal SPL on and off axis of the woofer in the cabinet at 0, 30, 45, 60, 75 and 90 degrees
Vertical SPL on and off axis of the woofer in the cabinet at 0, 30, 45, 60, 75 and 90 degrees
SPL on axis and Power of the woofer in the cabinet in a full sphere
Directivity Index DI in a full sphere of the woofer in the cabinet
Lo-midrange
Horizontal SPL on and off axis of the lo-midrange in the cabinet at 0, 30, 45, 60, 75 and 90 degrees
Vertical SPL on and off axis of the lo-midrange in the cabinet at 0, 30, 45, 60, 75 and 90 degrees
SPL on axis and Power of the lo-midrange in the cabinet in a full sphere
Directivity Index DI in a full sphere of the lo-midrange in the cabinet
Hi-midrange
Horizontal SPL on and off axis of the hi-midrange in the cabinet at 0, 30, 45, 60, 75 and 90 degrees
Vertical SPL on and off axis of the hi-midrange in the cabinet at 0, 30, 45, 60, 75 and 90 degrees
SPL on axis and Power of the hi-midrange in the cabinet in a full sphere
Directivity Index DI in a full sphere of the hi-midrange in the cabinet
Tweeter
Horizontal SPL on and off axis of the tweeter in the cabinet at 0, 30, 45, 60, 75 and 90 degrees
Vertical SPL on and off axis of the tweeter in the cabinet at 0, 30, 45, 60, 75 and 90 degrees
SPL on axis and Power of the tweeter in the cabinet in a full sphere
Directivity Index DI in a full sphere of the tweeter in the cabinet
All transducers
Directivity Index DI in a full sphere of the woofer, lo – midrange, hi – midrange and tweeter in the cabinet
- All the 4 transducers show a smooth DI curve as a function of frequency. In the medium frequency region it is realized by the asymmetric horizontal position of the midranges and the tweeter on the front baffle.
- The DI dip of the tweeter at 2 kHz is caused by a diffraction by the top edge of the front baffle. The tweeter operating range will be chosen at a higher frequency.
Active Digital Crossover filter
A Linkwitz-Riley 4th order crossover filter is designed. To realize flat curves for SPL, power and directivity index versus frequency, the crossover frequencies are chosen at 200, 800 and 3200 Hz.
The crossover filter is designed using analog functional blocks. For this digital design the blocks are transformed to digital biquads that can be programmed on a digital platform, like miniDSP for example.
Crossover filter targets LR4 at 200, 800 and 3200 Hz
Crossover filter schematic with functional blocks
woofer filter: 6 blocks; lo – mid filter: 6 blocks; hi – mid filter: 6 blocks and tweeter filter: 4 blocks.
SPL on axis of the filtered drivers and the sum at 1m, 2.83 Vrms
SPL horizontal off axis of the sum at 0 , 15, 30, 45 and 60 degrees at 3m, 2.83 Vrms
Power response of the filtered drivers and the sum in free space at 3m, 2.83 Vrms
Directivity Index in free space of the filtered drivers and the sum
Maximum excursion and maximum SPL with the LR4 filter
With the designed Linkwitz – Riley 4th order filter, the woofer has a maximum excursion of 14.0 mm peak at 50 Hz for a voltage of 56.3 Vrms at the input of the filter.
The excursion of the lo – midrange, the hi – midrange and the tweeter have been calculated also at 56.3 Vrms.
Excursion at 56.3 Vrms of woofer (blue), lo – midrange (brown), hi – midrange (green) and tweeter (red)
The lo – midrange excursion is maximum at 162 Hz and equal to 1.6 mm peak.
The maximum specified linear excursion of the AE TD8M-8 is 3.0 mm peak.
The hi – midrange excursion is maximum at 800 Hz and equal to 0.29 mm peak.
The maximum specified linear excursion of the Bliesma M74B-6 is 1.2 mm peak.
The tweeter excursion is maximum at 3152 Hz and equal to 0.16 mm peak.
The maximum linear excursion of the Bliesma T25B-6 is 1.0 mm peak.
Maximum SPL
The maximum SPL for the operating frequency range 50 – 20000 Hz at maximum excursion of the woofer is 115 dB at 1m, 56.3 Vrms at the input of the crossover filter.
