SATOH Hirotaka Architects
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Carpet speaker


2014.04.22

Carpet speaker

[Process of carpet speaker production]

A carpet speaker is a speaker system with an extremely simple structure in which a carpet is simply wound and a speaker unit is mounted.
By making the enclosure with sound-absorbing material, it seems that the characteristic is that it absorbs the opposite phase sound of the speaker back pressure and does not disturb the pure sound of the speaker unit, and it is clear because there is no box or resonance.
Because the configuration is simple, I made my own.

[Materials and equipment]

・ Speaker MarkAudio CHR-70v3 (later changed to ALPAIR7v3)
・ Amplifier SMSL SA-36A
・ Carpet Nitori 80cm x 150cm 571 yen.

[Design / Production]

If you search on the net, you will find various information about carpet speakers. If you just roll the carpet and put the speaker on it, it will be completed in 30 minutes. However, carpets cannot be designed just by rolling them. Therefore···
First of all, I got involved with PU leather. Wrap it around the edge and back.

Carpet speaker leather

Fasteners can be comfortably cracked with magnetic buttons.

Carpet speaker stand

Next is a stand.
Process with a free cone and glue the void tube.

Carpet speaker painting

The painting is our standard ink ink + urethane mat clear.
In order to emit bass, attach rubber feet to the bottom and float about 15mm.

Carpet speaker baffle

A baffle plate was produced in the same way.
Finally, attach the weight to the speaker.

Carpet speaker weight

The weight purchases a lead ingot and melts it in a pot. Set the long screw in the aluminum can and pour the melted lead.

Carpet speaker stand

When it cools, cut the edge of the aluminum can and hit it with a hammer to finish it.

Installing the carpet speaker weight

Fix the nut to the speaker with epoxy adhesive.
Now you can remove or replace the weight at any time.

[Impression about sound]

First of all, put the round speaker on the carpet and play it. I was surprised at the spread of three-dimensional sound with a sense of resolution never experienced with such a simple construction. HQM sounds like a super-resolution and reputed Krypton HQM. Once I experienced the resolution of the carpet speaker, I couldn't go back.
The sound of vocals and violin is very beautiful. On the other hand, the bass is a bit unsatisfactory.

[Analysis on soft enclosure]

Some people say that carpet speakers sound like speakers on the net, but they are not that simple.
In the first place, making the sound of the speakers pure is one of the ideals that is very difficult to achieve.
Normally, extra sound always gets on due to reverberation in the enclosure, resonance of the enclosure, and numerous resonances. However, soft enclosures can be almost eliminated by simple construction.
Often, speakers with strong reverberation are sold as speakers like musical instruments.
But that's an excuse that always makes the sound muddy.

"Comparison with flat baffle and open rear"

The ideal plane baffle is to completely separate the normal sound and the background sound in an infinite plane and reproduce the sound of the speaker itself.
However, in reality, the wide baffle surface resonates and the physical size is limited, so the background sound mixes with the true sound.
The carpet speaker does not completely absorb the background sound, but takes out the bass from the bottom due to its cylindrical shape.
In addition, flat baffles and open back type are severely affected by the reflected sound on the back side, so installation is severe, but carpet speakers absorb back sound in the cylinder, so they can be installed easily anywhere.

"Air column resonance"

The carpet speaker is in the form of an air column resonance tube.
A straightforward example of a resonance tube is a pipe organ. Tubes of different lengths are lined up, and the sound that resonates with the length of the tube is determined.
If the material of the cylinder is hard paper or PVC, it is not hard to imagine that the resonance sounds too loud.
In the case of a carpet speaker, pressure seems to be absorbed and air column resonance does not appear.
This depends on the material, and if you try it on a yoga mat, it will sound like a tube.

"Effect of weight"

In order to clear the sound, it is said that suppressing the vibration of the speaker unit is effective.
I attached a weight to the magnet and raised the weight ratio with the diaphragm to suppress the vibration of the speaker unit.
However, contrary to expectations, no honest effect was felt.
In general, weight seems to have a much greater effect on crimping the speaker to the enclosure and suppressing the vibration of the enclosure itself than the vibration isolation of the unit.

"Electrical correction"

I corrected it with an electric circuit to further enhance the bass.

Carpet speaker circuit

However, the sense of resolution deteriorates in exchange for the deep bass.
I tried adding a high-pass filter circuit and replacing resistors and capacitors, but it did not return to a clear tone.
After all, even though it is simple, the extra electric circuit seems to be accompanied by sound quality deterioration.
Perhaps because it is a carpet speaker with a clear tone.
I think this is why the sound is muddy with speakers equipped with circuits such as multi-way.
Thus, "Carpet Speaker Prototype XNUMX" is completed.
With this simple configuration, it is possible to reproduce open, dynamic, realistic and three-dimensional sound.

Next time I will experiment with bass enhancement.

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