VCL EX-17, 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.

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February 01, 2021
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

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February 01, 2021
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

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February 04, 2021
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 freqencies, 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.

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February 05, 2021
Cabinet



Cabinet dimensions

At the backside inside the enclosure there is some separate place for the crossover filter.


3-D look in Leap

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February 05, 2021
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

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February 05, 2021
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 single hemisphere at 3m distance. The power is calculated out of the mean value of the curves. In this case, the power is represented as the SPL of an omnidirectional source at 3m distance in a single hemisphere 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 single hemisphere

The SPL on axis in grey and the power in blue.


SPL on axis and Power of the midrange in the cabinet in a single hemisphere

The SPL on axis in grey and the power in green.


SPL on axis and Power of the tweeter in the cabinet in a single hemisphere

The SPL on axis in grey and the power in red.


Directivity Index DI in a single hemisphere of the woofer, midrange and tweeter in the cabinet

DI of woofer in blue, DI of midrange in green and DI of tweeter in red


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.

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February 06, 2021
Crossover Filter


Targets Crossover Filter LR4 at 700 and 3500 Hz


Crossover filter schematic configuration

The component values are not stated in the schematic. Please contact us for more details if wanted.


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

SPL on axis in black, SPL at 30 degrees in green and SPL at 60 degrees in blue.


Power response of the filtered drivers and the sum in a single hemisphere 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.
The power dip of about 2 dB, that can be observed between 400 Hz and 1500 Hz, is caused by the baffle step behavior of this 28 cm wide rectangular speaker.


Directivity Index in a single hemisphere of the filtered drivers and the sum

DI of the woofer in blue, for the midrange in green, the tweeter in red and the sum in black
The DI peak of about 2 dB between 400 Hz and 1500 Hz is also caused by the baffle step behavior of the cabinet.





February 06, 2021
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.



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