back to
www.audiodesignguide.com

To get more information contact me at: webmaster@audiodesignguide.com


 

Hi-Eff loudspeakers system
March 14 st , 2009 

INTRODUCTION

This project born to create a loudspeaker with very high efficiency and low cost to be driven by low power single ended amplifier with one or two 2a3 (SE or PSE).
To reduce the cost has been decided to use only 2 drivers with the lower crossover frequency possible.
I will use a compression driver loaded by a good horn and a 15" woofer to get high
sensitivity and good low frequency band.
I have opened a forum about this project to get some contributions:
Hi-End and Hi-Efficency loudspeakers (horn + onken)

HIGH FREQUENCY

To limit the cost I have decided to use 1" driver with an 800Hz-1KHz crossover.

As horn has been used a good
Tractrix model of the www.stereo-lab.de series.
My choice is the cf600 with a cut-off limit at 600Hz with these
dimensions:
- Diameter ca. 200 mm (~ 7.88 inches)
- Length ca. 175 mm (~ 6.89 inches)
- Thickness ca. 10 mm (0.39 inches)
This horn have an artificial stone without resonance, milled flange, black structural studio coat.
The cost is only 79 euro each, buy on Stereo-Lab Ebay shop.

The Beyma CP380M compression driver has been the first choice because it have a low distortion and a very linear frequency band.
Many DIY prefer this driver to other components because the sound of CP380M is very natural if compared to other compression driver (see www.speakerplans.com forum 13807  or tt12.html or www.speakerplans.com forum 10871).
Someone have suggest me a cheaper compression driver near the 50$ like the
Selenium D220T used in the Econowave collaborative project but I have discarded this because the distortion level of this driver is very high (see differences).
The cost of CP380M is only 139 euro each.

Follows the first measurements of CP380M loaded by the cf600 horn at 1m.

I have used in all the measurements the Clio system by Audiomatica with the Transit by M-Audio to use the USB port of my portable pc (instead of the PCI audio board).

A very flat response in the band 800Hz - 20KHz.

LOW FREQUENCY

Now about the woofer we need a 15" with:
- linear frequency band until 3-4KHz to prevvent problem after the crossover frequency
- moving mass no more than 90 gr to be fast
- sensitivity  near to 100dB to be drivven with low power amp. like 2a3 single ended
- low resonant Frequency, near 35Hz, to have a good bass frequency band
-Thiele-small parameters to be fit in a max 150lt reflex or sealed box to be fit in my room
- An high min impedance value to get the mosst high system impedance to be easy to drive

 

Beyma 15MW Nd
 


not very good linearity

Fs=42Hz (a little high)

Sensitivity=96-99dB (good)

Mms=90gr (good)

Min. Imp = 5.8ohm

Beyma SM115N

not very good linearity

Fs=29Hz (a little high)

Sensitivity=95-99dB (low)

Mms=77gr (good)

Min. Imp = 7.4ohm

 

Beyma 15LW30

good linearity

Fs=32Hz (good)

Sensitivity=95dB (low)

Mms=83gr (good)

Min Imp=7ohm

 

 

Beyma 15P80Nd

 

good linearity

Fs=35Hz (good)

Sensitivity=100dB (good)

Mms=99gr (a little high)

Min Imp=6.2ohm

B&C Speakers 15NDL76

good linearity

Fs=37Hz (good)

Sensitivity=98dB (good)

Mms=96gr (a little high)

Min Imp=6.7ohm

B&C Speakers 15PH40

good linearity

Fs=38Hz (good)

Sensitivity=97dB (good)

Mms=72gr (good)

Min Imp=7ohm

 

RCF L15-554K

bad linearity

Fs=35Hz (good)

Sensitivity=97dB (bad)

Mms=91gr (good)

Min Imp=7.9ohm

Faital PRO W15N8-350
 

good linearity

Fs=32Hz (good)

Sensitivity=98dB (good)

Mms=85gr (good)

Min Imp=5.9

 

Eminence OmegaPro 15A

bad linearity

Fs=33Hz (good)

Sensitivity=97dB (little low)

Mms=94gr (a little high)

Min Imp=6.5ohm

 

Celestion FTR15-3070C

 

good linearity

Fs=40Hz (good)

Sensitivity=97dB (good)

Mms=70gr (good)

Min Imp=8ohm

 

Monacor IMG Stage Line SP-38/300NEO

good linearity

Fs=36Hz (good)

Sensitivity=101dB (good)

Mms=71gr (good)

Min Imp=7ohm

 

Monacor IMG Stage Line SP15A/402PA

medium  linearity

Fs=36Hz (good)

Sensitivity=101dB (good)

Mms=87gr (good)

Min Imp=8.5ohm

 

these should be the best:

- Monacor IMG Stage Line SP-38/300NEO
- Monacor IMG Stage Line SP-15A/402PA
- Beyma 15MW Nd
- Beyma 15P80Nd
- Beyma 15PH40

- Celestion FTR15-3070C
- Faital PRO W15N8-3500
- B&C15NDL76 - B&C 15PH40

Now I am will try to simulate these in a standard bass-reflex box for the best alignment using WinISD (free beta pogram)

good result for:

- SP-15A/402PA to get the best sensitivity
- W15N8-350 compact box and good bass freq.
- 15MW Nd  enough bass frequency and goood
sensitivity
- Celestion FTR15-3070C good bass and good sensitivity
-
15PH40 good bass and good sensitivity

less good result for these:

- SP-38/300NEO too large box necessary
-15NDL76 too bad low frequency band
-15P80Nd bad low frequenccy band
- 15LX30 low sensitivity

Follows the bass frequency simulation with Onken spreadsheet by Cyr-Marc Debien 2000 © cdebien@cmaisonneuve.qc.ca.
After original research from M. Eijiro KoÔzumi and Jacques Mahul and Jean Hiraga calculations.

model volume dB 1W/1m F(-3db)  
Beyma 15LW30 166 97.3 44.6  
Beyma 15MW Nd 164 96.7 43.0  
Beyma 15P80 68 98.0 63.7 bad bass frequency
Beyma SM212 139 95.5 41.9 low sensitivity
Monacor SP15A/402PA 158 97.1 44.6  
Monacor SP38/300NEO 361 96.3 32.7 too large box
Faital PRO W15N8 177 96.8 42.3  
B&C 15PH40 183 97.6 44.3  
B&C 15NDL76 67.3 97.8 63.3 bad bass frequency
Celestion FTR15-3070C 163.4 97.0 43.4  

So now are 6 the best woofer selected for this project.

The price is a factor to consider because this project born to be cheap so probably I will buy a pair of Celestion FTR15-3070C available for few money at Lean shop only £99.95 (normal price in US is about 220-245$ and in UE about 220-250 euro).

From Celestion website:
 
Designed for high-end sound reinforcement applications, Celestion FTR aluminium chassis, 
for efficient cooling, reducing thermal compensation and minimising distortion. 
Exceptional BL and stiffness (K) symmetry further contribute to low distortion, while FEA-optimised 
magnet topology reduces inductance, also minimising distortion. 
The FTRs use water-resistant, glass fibre impregnated cones with sealed surrounds and added 
damping for reduced cone resonances. FTR-HDX drivers are among the lightest in their class

 

 

 

 

 

 

Follows the simulation of the bass reflex for the best alignment using WinISD and Onken configuration (larger box) 

Follows the final Onken box design

I have selected 30 millimeter birch plywood for the cabinet in order to raise cabinet resonance to a point well above the radiated frequencies.

Follows the measued impedance on air and the measured Thiele-Small parameters

9gr

FS 44.4072 Hz
VAS 255.3118 L
RE 6.1000
W
QMS 3.1876
QES 0.5349
QTS 0.4580
B
l 12.0248 Tm
dBSPL 98.2345
SD 0.0804
m2

CMS 0.2827 mm/N
MMS 45.4404 g
RMS 3.9775
WM
CAS 1.83E-0006 m5/N
MAS 7.03 kg/m4
RAS 615 WA
CMES 314.2594 mF
LCES 40.8739 mH
RES 36.3534
W
RAT 4280 WA
RMT 27.6816 WM
MMD 32.5311
g
ZMIN 7.3081
W
ZMAX 42.4534 W
ZAVG 16.6360
W
h
0 4.0128 %
L1kHz 0.7112 mH
L10kHz 0.3356 mH

78gr

FS 44.4072 Hz
VAS 14.0645 L
RE 6.1000
W
QMS 3.1876
QES 0.5349
QTS 0.4580
B
l 51.2330 Tm
dBSPL 85.6450
SD 0.0804
m2

CMS 0.0156 mm/N
MMS 824.8739 g
RMS 72.2028
WM
CAS 1.01E-0007 m5/N
MAS 127.53 kg/m4
RAS 11163 WA
CMES 314.2594 mF
LCES 40.8739 mH
RES 36.3534
W
RAT 77689 WA
RMT 502.5008 WM
MMD 811.9647 g
ZMIN 7.3081
W
ZMAX 42.4534
W
ZAVG 16.6360
W
h
0 0.2211 %
L1kHz 0.7112 mH
L10kHz 0.3356 mH

15g

F
S 44.4072 Hz
VAS 196.0080 L
RE 6.1000
W
QMS 3.1876
QES 0.5349
QTS 0.4580
B
l 13.7238 Tm
dBSPL 97.0865
SD 0.0804
m2

CMS 0.2170 mm/N
MMS 59.1887 g
RMS 5.1809
WM
CAS 1.40E-0006 m5/N
MAS 9.15 kg/m4
RAS 801 WA

CMES 314.2594 m
F
LCES 40.8739 mH
RES 36.3534
W
RAT 5575 WA
RMT 36.0569 WM
MMD 46.2795
g
ZMIN 7.3081
W
ZMAX 42.4534
W
ZAVG 16.6360
W
h
0 3.0807 %
L1kHz 0.7112 mH
L10kHz 0.3356
mH

 

For this purpose I have used www.officinelettroniche.it of Ivan De Cesaris. 

Are necessary 250 euro for the chassie and 240 euro for the wood + tax.

 

For this large loudspeakers it is impossible use the normal damping articles for loudspeakers because in this case the cost would exceed the cost of wood.
Following the suggestion of my friend Andrea of PuntoMusica I have used two different damping materials used in the cars: 

1) panels composed of fabric processing residues bottom tar for the base and the back
2)
moquette with longhaired and bottom in lute