Project Harbinger: High Efficiency Loudspeaker System 高効率スピーカーシステム Part 2

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Hello,

こんにちは,

To continue with Harbinger project i would like to investigate the drivers and what could be expected from them. I already mentioned two of the 15 inchers and that i decided to use a version of 8512F.

The motor on this driver is very strong 220mm in diameter, noiseless vent and T-shaped central pole piece for symmetric field in gap as seen below.

 

T-shaped pole piece Loudspeaker

T-shaped pole piece 8512F

 

The original had this set of parameters:

Mms: 144 g
Fs: 41.9 Hz
Cms: 0.1 mm/N
Bl: 26 Tm
Rms: 12.8 mech-ohm
SD: 0.09 m2

This results in the following equivalent electrical components:

Lces: 67.6 mH
Cmes: 213.017751 uF
Res: 52.8125 ohm

Lces -> corresponds to Cms; Cmes -> corresponds to Mms; Res -> corresponds to Rms

First modification was changing the suspension system with a more softer one. The new spider has larger deeper and fewer corrugations. I made this modification so that the woofer can perform better at lower input power.

Spider for 4" Voice Coil 15インチスピーカー、DIYのホーンスピーカー

Original spider of the 15 incher

Spider for 4" Voice Coil 15インチスピーカー、DIYのホーンスピーカー

New spider for the 15 incher

The replacement spider i used before for a 10 inch driver modification to fit in a 4″ voice coil.

At this point i needed to build a new box to put in the woofer and study it’s behavior. I built a 160 Liters vented box with 2 ports each of 72mm diameter and 140mm length.

High efficiency Loudspeaker Enclosure

High efficiency Loudspeaker Enclosure

High efficiency Loudspeaker Enclosure

High efficiency Loudspeaker Enclosure

High efficiency Loudspeaker Enclosure

High efficiency Loudspeaker Enclosure

After placing the driver in the box i ran impedance test and simulation of the model created with the spreadsheet from Electric Equivalent Model of Loudspeakers article. As you can see the model is very close to the measured result.

Spice simulation of loudspeaker equivalent model with LPF

Spice simulation of loudspeaker equivalent model with LPF

Measured impedance of 15 incher with LPF

Measured impedance of 15 incher with LPF

The box wasn’t well braced and needed some strengthening but the output in the bass region was satisfactory. Even at low levels the bass was low with a good amount of punch. My room helps a lot though on the low end. I have wooden floors and ceiling and lots of furniture.

In the next article we will look at what else can be improved on the drivers and the box.

Thank you for visiting,

ご覧いただきありがとうございます。

 

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