3-way speaker with SB Satori MD60N-6 dome midrange, SBA woofer, Dayton passive radiators and SBA tweeter
Continuing on the very good reputation of dome midrange speakers like the Yamaha NS1000, the ATC speakers, DIY projects with the ATC and Volt dome midranges, we think it’s a good idea to use the new SB Satori MD60N-6 2.5 inch dome midrange in a new speaker concept. First measurements and research of this transducer look very promising.
The VCL EX17 is a concept study of a speaker with this Satori MD60N-6 dome midrange, together with an 8 inch SBA woofer, two 8 inch Dayton passive radiators and a SBA 0.8 inch fabric dome tweeter.
The speaker sensitivity of this VCL EX17 will become around 83dB at 2.83 Vrms, 1m in full space. We are looking to a higher sensitivity version also, using a more sensitive woofer or multiple woofers.
Contents
- Specification Headlines
- Estimation Bill Of Material
- Speaker System
- Cabinet
- SPL and impedance curves of the transducers in the cabinet
- Off axis response, Power and Directivity Index of the transducers in the cabinet
- Crossover Filter
- Maximum excursion and maximum SPL with the LR4 filter
Specification Headlines
- System: 3-way, passive radiator system, analog X-over
- Woofer: 1 x SBA SB23NRXS45-08
- Passive Radiator: 2 x Dayton DS215
- Midrange: SB Satori MD60N-6
- Tweeter: SBA SB21SDC-C000-4
- Low frequency response: F3 = 34 Hz
- Sensitivity: 83 dB at 1m, 2.83 Vrms, full space
- SPL at maximum excursion, 34 – 20000 Hz: 96 dB, 1m, full space
- Crossover: LR4 at 700 Hz and 3500 Hz
- Impedance: mean value between 6 and 20 Ohm
- Cabinet dimensions: width x heigth x depth = 28 cm x 109 cm x 38 cm
Estimation Bill Of Material
- 2 x Woofer SB Acoustics SB23NRXS45-8: 180 euro
- 4 x Passive Radiator Dayton DS215: 120 euro
- 2 x Tweeter SB Acoustics Satori MD60N-6: 260 euro
- 2 x Tweeter SB Acoustics SB21SDC-C000-4: 65 euro
- Components high quality crossover: 800 euro
- Components medium quality crossover: 500 euro
- Cabinet material: 100 euro
- Cabinet Accessoires: 100 euro
- Total with high quality crossover 1625 euro
- Total with medium quality crossover 1325 euro
Speaker System
Transducers
SB23NRXS45-8, Dayton DS215, SBA Satori MD60N-6, SB21SDC-C000-4
The SB Acoustics SB23NRXS45-8 is an 8 inch woofer and with its size capable to operate up to 700 Hz. The harmonic distortion of this transducer is low, better than -50 dB between 100 and 700 Hz. This transducer has been measured by HifiCompass.
The Dayton DS215 is an 8 inch passive radiator. The maximum linear excursion is +/- 10 mm. Two of these transducers together with the 8 inch woofer are placed in a 55 L cabinet. It is a good combination to realize the passive radiator woofer system.
The SB Acoustics Satori MD60N-6 2.5 inch dome midrange is a recent development. The harmonic distortion is low, better than – 45 dB in the frequency operating range 700 – 3700 Hz. This transducer has been measured by HifiCompass.
This fabric dome midrange has a very good constant piston behaviour. Calculating the on-axis SPL using the TS parameters (inclusive the voice coil serial inductance) and comparing that calculated SPL with the on-axis measured SPL, shows that both curves almost have the same shape. It can be seen in the plot below. It means there is no cone break-up in the operating frequency range, the transducer operates as a constant piston. This is an excellent cone behavior.
Midrange MD60N-6, calculated SPL on-axis(grey) vs. measured SPL on-axis (green)
Doing the same calculation for the woofer of this speaker, the SB Acoustics SB23NRXS45-8, we can see in the plot below that the curve shapes are the same up to 1000 Hz. It means that this woofer has a constant piston behavior up to 1000 Hz. For higher frequencies the measured SPL is higher than the calculated SPL. This is a normal behaviour for many woofers and still good if the transducer will be used up to 700 Hz in this speaker system.
Woofer SB23NRXS45-8, calculated SPL on-axis(grey) vs. measured SPL on-axis (green)
The SB Acoustics SB21SDC-C000-4 is a 0.8 inch fabric tweeter. The harmonic distortion of this transducer is low, better than -40 dB between 3500 and 20000 Hz. This transducer has been measured by HifiCompass.
This low size tweeter has a low directivity index up to high frequencies, which results in a flat power curve at high frequencies. This is the reason why this 0.8 inch driver has been chosen for this speaker.
Passive Radiator System – Small Signal Analysis
The 8 inch SB Acoustics SB23NRXS45-8 woofer with two 8 inch Dayton DS215 passive radiators, one on each side wall, is used in this 3 way speaker.
As a reference to calculate the responses of the passive radiator system, the article “Passive-Radiator Loudspeaker Systems” by Richard H.Small is used. In this post only the parameter values and the calculation results are summarized. For a more detailed understanding, the reference article can be used.
For the SBA woofer: fs = 27 Hz; Vas = 94 L; Qts = 0.38
For the Dayton passive radiator: Vap = 43.1 L
For a cabinet volume = 55 L, fp = 23 Hz (total cone mass for both passive radiators together adjusted to 140 g), no cabinet filling and a serial source resistance of 0.5 Ohm
Then: Ts = 5.9 ms; Tp = 6.9 ms; alfa = 1.71; delta = 0.78; QT = 0.42
With the above parameter values, the frequency response on infinite baffle can be calculated, using the formula as mentioned in the reference article.
The green curve shows the passive radiator response, the red curve a Butterwoth B4 response at the same system frequency to compare with. F3 = 34 Hz with these parameter values.
Remark that these responses are a result with low losses, but these calculated responses are already indicative.
Simulating the frequency response on infinite baffle in Leap with the same parameters, is shown in the next graph. The results are comparable. Cabinet filling is applied in the Leap simulation.
As a first conclusion of this passive radiator system study, the cabinet volume can be chosen 55 L and the total mass of each passive radiator cone 70 gram. These values can be fine tuned with measurements.
Cabinet
Cabinet dimensions
At the backside inside the enclosure there is some separate place for the crossover filter.
3-D look in Leap
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 1 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 SB23NRXS45-8 and 2 x Dayton DS215 in the cabinet in free space (blue curve) and on infinite baffle (pink curve)
Impedance woofer SB23NRXS45-8 and 2 x passive radiator Dayton DS215 in the cabinet
SPL SB Satori MD60N-6 in the cabinet in free space (green curve) and on infinite baffle (pink curve)
SPL SB21SDC-C000-4 in the cabinet in free space (red curve) and on infinite baffle (pink curve)
Horizontal polar diagram SB Satori MD60N-6 in cabinet free space at 640 – 1.2 – 2.5 – 3.8 – 5.1 kHz
Horizontal polar diagram SB21SDC-C000-4 in cabinet free space at 2.5 – 3.8 – 5.1 – 6.4 – 12.8 kHz
Off axis response, Power and Directivity Index of the transducers in the cabinet
To choose the optimum crossover frequency for this speaker, the horizontal and vertical SPL off axis responses of woofer, mirange and tweeter have been simulated in steps of 15 degrees, the speaker placed in a free sphere at 3m distance. The power is calculated out of the mean value of the 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.
Horizontal SPL on and off axis of the woofer in the cabinet at 0, 30 and 60 degrees
Horizontal SPL on and off axis of the midrange in the cabinet at 0, 30 and 60 degrees
Horizontal SPL on and off axis of the tweeter in the cabinet at 0, 30 and 60 degrees
SPL on axis and Power of the woofer in the cabinet in a full sphere
SPL on axis and Power of the midrange in the cabinet in a full sphere
SPL on axis and Power of the tweeter in the cabinet in a full sphere
Directivity Index DI in a full sphere of the woofer, midrange and tweeter in the cabinet
The Directivity Index plot shows that, to keep the DI of the sum response flat, the crossover frequencies can be located at 700 and 3500 Hz.
The SPL on-axis dip, the power peak and the corresponding DI dip around 2 kHz are related to the speaker width.
Crossover Filter
Targets Crossover Filter LR4 at 700 and 3500 Hz
Crossover filter schematic configuration
Impedance with crossover flter
SPL on axis of the filtered drivers and the sum at 1m, 2.83 Vrms
SPL off axis of the filtered drivers and the sum at 3m, 2.83 Vrms
Power response of the filtered drivers and the sum in a full sphere at 3m, 2.83 Vrms
The mutual distance between the drivers in vertical direction is not included in this calculation. With this distance included, an extra power dip at the crossover frequencies will appear with a DI peak as a consequence.
Directivity Index in a full sphere of the filtered drivers and the sum
Maximum excursion and maximum SPL with the LR4 filter
Maximum excursion
With the designed LR4 filter, the woofer has its maximum excursion of 6.5 mm peak at 47.7 Hz for a voltage of 12.8 Vrms at the input of the filter.
The excursion of passive radiator, midrange and tweeter have been calculated also at 12.8 Vrms.
Excursion at 12.8 Vrms of woofer(blue), passive radiator (yellow), midrange(green) and tweeter(red)
The woofer has its maximum excursion of 6.5 mm peak at 47.7 Hz. The maximum specified excursion of the SB23NRXS45-8is 6.5 mm peak.
For each passive radiator, the excursion is maximum at 30.2 Hz and is equal to 8.4 mm peak. The maximum specified excursion of the Dayton DS215 is 10 mm peak.
The midrange excursion is maximum at 686 Hz and is equal to 0.056 mm peak. The maximum specified excursion of the SB Satori MD60N-6 is 0.5 mm peak.
The tweeter excursion is maximum at 3337 Hz and is equal to 0.019 mm peak. The maximum specified excursion of the SB21SDC-C000-4 is 0.50 mm peak.
Maximum SPL
The maximum SPL for the total operating frequency range 34 – 20000 Hz at maximum excursion of the woofer is 96 dB at 1m, 12.8 Vrms at the input of the crossover filter.
