E-170 Loudspeaker Enclosure


Banff National Park AL, Canada (Photo by Yuichi)
About Alpine DLX-Z17W woofer (DD Linear)

The driver unit is designed originally for car audio purpose. However, the design concept and implementation is unique. Therefore, I tried to design and build a enclosure for pure audio by using this driver. Driver spec and TS parameters are as follows. (Data from Alpine catalogue)

Impedance 6 Ohms ReDC 5.2 Ohms
Peak Input power 200 W Fs 67 Hz
Nominal Input (RMS) 50 W Qts 0.73
SPL 89 dB/W (1m) Qms 5.0
Frequency Range 28Hz - 12KHz Qes 0.85
Recommended Cutoff 3KHz - 10KHz Vas 8.9 Liters
Weight 1.7Kg Sd 129 sqcm
Le 0.18 mH
Cms 0.38 mm/N
Mms 15 g
Bl 6.2 Tm

This Alpine woofer driver has two major ideas. One is DD (Dual-gap Dynamic Linear) magnetic circuit construction to obtain linear driving power output from voice coil. The other is double gathered surround construction which yields linear compliance. These two ideas generate incredible small distortion in large amount of piston motion of the diaphragm. Some of the data is shown later.

About Alpine DLX-Z30T tweeter (3cm Ring tweeter)

Impedance 4 Ohms
Peak Input Power 120W
Nominal Input (RMS) 20 W
SPL 89 dB/W (1m)
Frequency Range 3.5KHz - 60KHz
Recommended Cutoff 8 KHz - 10 KHz
Weight 300 g

Ideas of Alpine Z17W and Z30T drivers


DLX-Z17W Woofer (Data from Alpine technical paper)
Traditional woofer driver has voice coil with over hung and under hung types. Both have pros. and cons. Over hung type can yield strong voice coil motor power, but does not show good higher frequency response due to heavy coil and associated parts. Instead, under hung voice coil type has better high frequency response. But has smaller power. This idea reaches heavy magnet. Both struggle with length of lineality of voice coil motion. Alpine DD Linear has two magnets in its construction to have longer motion area. DD Linear surround construction is double gathered as shown in the photo above.

Above two new ideas give us very linear motion of voice coil. As bottom line, Alpine DD system yields very small distortion even in case of large displacement of diaphragm.
Above graph shows that longer linear zone of driving force of voice coil. Above graph shows longer linear zone of elasticity of voice coil (diaphragm) movement.
DLX-Z30T (Data from Alpine technical paper)
DLX-Z30T has another idea. In traditional tweeter construction, a voice coil is located outer side of diaphragm whichever it is a soft dome or a hard dome materials. Soft dome has larger mass but has smaller resonance. Instead, hard dome has light mass, which has nicer higher frequency property. But it has many diaphragm resonances on the surface.

Z30T has soft dome system with two voice coils. One is located out side and the other is inner side.

Design and build of trial enclosure


TS parameters of DLX-Z17W are indicated as Fs=67Hz, Qts=0.73 and Vas=8.9 liters in its data sheet. However, when I measured my driver, those are Fs=72.1715, Qts=0.7804 and Vas=5.2278. Differences are within tolerance due to different measurement environment. Anyway, I put my values into WinSpeakerZ simulator of True Audio like left hand picture.

In this case, I obtained very flat low frequency response under V(B)=20 Liters and F(B)=45 Hz conditions. Where V(B) is cabinet volume and F(B) is vent resonance. In the picture, there are three curves indicated. The parameters are F(B)=40, 45 and 50 Hz with F(B)=20 fixed. You can compare the differences.

Then, I decided to make trial enclosure as below.

Enclosure volume V(B)=20 Liters
Vent resonance F(B)=45Hz
To have 45Hz resonance frequency, I adopted following vent size.
-Vent Area S(v)=25 Sq cm
-Vent Length L(v)=14.5 cm

Trial enclosure looks like left side photo. Tweeter is temporarily put on the enclosure. Internal sound absorption material is shown in the left.
Woofer and tweeter frequency response curves are shown below. Then, crossover frequency may be in between 3KHz to 8KHz, I feel. Since woofer and tweeter output is identical, there is no tweeter attenuator needed. This is good because most of future system failures come from those movements. I used 6dB/oct crossover network and obtained total frequency property as below. I felt 1uF and 2.2uF better to be much higher, but this one works fine, too.
One more point is that the vent area is better to be much larger in this case. But we have to think about the vent length. Because if vent area gets larger, vent length also gets longer.
CLIO system by Audiomatica is used for measurements

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