DIY Granite Speakers
Radoslav Pancuska  
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DIY Granite Speaker Project
These are do-it-yourself (DIY) speakers that we built using granite for the speaker box.
Photograph 1: DIY Granite Speakers with Seas G17REX/P and 27 TFFC Drivers
Speaker Project Summary
External box dimensions 240 x 350 x 280 mm. Internal box dimensions 200 x 310 x 240 mm. Box material 20 mm thick black granite (Nero Assoluto). Weight 35 kg.
Enclosure volume 14.9 L. Bass reflex enclosure tuned to 45 Hz. Port length 160 mm
Input power 80W. Sensitivity 87.5 dB. Transmission bandwidth 40Hz - 20kHz. Impedance 6 ohm.
Figure 1: Seas Granite Speaker Enclosure Plan
Seas Loudspeaker Drivers
The drivers selected for this loudspeaker system are from Seas who has been producing speaker drivers for over 50 years. The tweeter is the Seas 27 TFFC which has a fabric dome. The Sonolex lightweight fabric dome has high consistency and provides excellent stability against variations in air humidity. The stiff and stable rear chamber allows for a moderately low crossover frequency (~2500kHz). This made the Seas 27 TFFC tweeter the right choice for our granite loudspeaker project.
The woofer we used is the Seas G17REX/P. The woofer consists of a fiber glass cone, a bullet shaped phase plug and a high loss rubber surround. These are carefully matched to each other resulting in smooth frequency response.
Speaker Box and Crossover Design
The speaker box and crossover network were designed by M.Janura and K.Sýkory using the LspCAD speaker design software package. A volume of 15L (dimensions 220 x 350 x 250 mm) and a tuning frequency of 45 Hz was used for the speaker box. The dividing frequency is 2.5kHz and the drivers are connected in phase. The crossover schematic and modeled frequency response are shown below.
Figure 2: Calculated Speaker Box Frequency Response - Seas G17REX/P Woofer
Figure 3: Crossover Schematic - Seas G17REX/P Woofer and 27 TFFC Tweeter
Figure 4: Calculated Frequency Response - Seas G17REX/P Woofer and 27 TFFC Tweeter
The components used in the crossover dividing network are from TESLA. I think that the people in the former Czechoslovakia were able to produce high quality components, but you may use your favorite type. The condensers (capacitors) used in crossover are MKT type - we did not use bipolar condensers because they have disadvantages that I won't further specify. The inductors are air core.
Photograph 2: Crossover Dividing Network for Seas G17REX/P Woofer and 27 TFFC Tweeter
Granite Speaker Box Construction
For the speaker box we wanted to use a very hard material. Thinking long and hard while drinking beer in our favorite pub, we decided to use black granite - Nero Assoluto imported from Italy. The speaker boxes were made at the factory where the co-author works.
Photograph 3: Cutting Granite Slab with Diamond Saw
The granite is not cheap and the manufacturing is also very hard and demanding. All parts the sides are cut at 45 degrees and glued together with natural resin. This way, the speaker box looks like it is one piece of granite.
Photograph 4: Granite Speaker Sides
Photograph 5: Grinding the Granite Speaker Walls
Photograph 6: Gluing Granite Speaker Box with Resin
The inside walls of the speaker box are painted with 3 mm thick asphalt for damping. The speaker box is filled with artificial cotton. The tuning port is on the rear. WBT binding posts were used for the speaker connections.
Photograph 7: Asphalt Speaker Damping
All openings and countersinking were done on CNC machine. The speaker box is filled with artificial cotton. The tuning port is on the rear. WBT binding posts were used for the speaker connections.
Photograph 8: Granite Speaker Box Construction
Loudspeaker Measurements
Measurement of the frequency response and impedance were made using the LAUD speaker measurement software package. The response plots are shown below.
Figure 5: Measured Frequency Response - Seas G17REX/P Woofer and 27 TFFC Tweeter
Figure 6: Measured Impedance - Seas G17REX/P Woofer and 27 TFFC Tweeter
Sound
I was knocked off my feet with the sound after the first track we played: Everlast - Folsom Prison Blues by the legendary Johnny Cash. The song tested bass response of the speakers. We didn't expect such deep and accurate bass from small speakers. The speakers deliver very detailed sound (soft treble and great imaging). They play rock music aggressively and classical music with emotion. As we say: "they play like HONEY" (it means - brilliant) and they look great too.
I would like to thank to Marian Mózer and everyone in the team for their effort and for the job well done. The loudspeaker system is designed by M.Janura and K.Sıkory - named Besie 1.
We understand that most of you will not be able to make speaker boxes of granite. If you are interested in speakers made from granite, please send me an email and we may be able to help you. Thank you and I hope you enjoyed our project.
Photograph 9: Seas Granite Speakers