carpet speaker

[Background of making carpet speakers]

A carpet speaker is a speaker system with an extremely simple structure, in which a speaker unit is placed on a carpet wrapped around it.
By making the enclosure out of sound absorbing material, it absorbs the sound of the opposite phase of the speaker back pressure and does not interfere with the original pure sound of the speaker unit.
Since the configuration is simple, I made my own.

[Materials/equipment]

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

[Design and production]

If you search the internet, you will find a lot of information about carpet speakers. If you just roll up the carpet and put the speakers on, it will be completed in 30 minutes. However, simply rolling up the carpet is not enough in terms of design. Therefore···
First of all, I rolled it with PU leather. Wrap both the ends and the back side.

The clasp can be fixed comfortably with a magnetic button.

Next, make a table.
It is processed with a universal cone and the void tube is glued.

The painting is our standard ink + urethane matte clear.
In order to emit low frequencies, the bottom has rubber feet and is floated about 15mm.

The baffle plate is also produced in the same way.
Finally, attach weights to the speakers.

For the weight, buy a lead ingot and melt it in a pot. A long screw is set in advance in an aluminum can and molten lead is poured into it.

When it cools down, cut off the edges of the aluminum can and hit it with a hammer to complete it.

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

[Thoughts about sound]

First of all, the carpet is rolled up and played with a speaker. I was surprised by the three-dimensional sound with a sense of resolution that I had never experienced with such a simple construction. Compared to Krypton's HQM, which has a reputation for super resolution, HQM sounds muffled. Once I experienced the resolution of carpet speakers, I couldn't go back.
Vocals and violins sound great. On the other hand, the bass is a little unsatisfactory.

[Analysis on soft enclosure]

Some people on the Internet say that carpet speakers sound just like speakers, but it's not that simple.
In the first place, it is an ideal that is very difficult to realize to hear the sound of the speaker purely.
Normally, there will always be extra sounds due to the reverberation in the enclosure, the resonance of the enclosure, and many other resonances. However, the soft enclosure can eliminate most of these by making it simple.
Speakers with strong reverberation are often marketed as instruments-like speakers.
However, that is an excuse, and the sound is always muddy.

"Comparison with flat baffle/rear open type"

The ideal planar baffle is an infinitely continuous plane that completely separates the sound from the original sound and reproduces the sound of the speaker itself.
However, in reality, the wide baffle surface resonates and the physical size is limited, so the back sound is mixed with the normal sound.
Carpet speakers don't completely absorb the background sound, but their cylindrical shape allows the bass to come out from the bottom.
In addition, flat baffles and open-back types are difficult to install because the sound reflected from the back side is strong, but carpet speakers absorb back sound inside the cylinder, so they can be easily installed anywhere.

"Air Column Resonance"

A carpet speaker is in the shape of an air column resonator tube.
An easy-to-understand example of a resonator tube is a pipe organ. Tubes of different lengths are lined up, and the length of the tubes determines the resonating sound.
If the material of the cylinder is hard paper or PVC, it is not hard to imagine that the resonance sound will be too loud.
In the case of carpet speakers, it seems that pressure is absorbed and air column resonance does not occur.
This depends on the material, and if you try it on a yoga mat, it will leave a pipe-like sound.

"Weight effect"

To make the sound clear, it is said that suppressing the vibration of the speaker unit is effective.
I tried to suppress the vibration of the speaker unit by attaching a weight to the magnet and increasing the weight ratio with the diaphragm.
However, contrary to my expectations, I honestly did not feel the effect.
In general, I think that weights are much more effective in crimping the speaker to the enclosure and suppressing the vibration of the enclosure itself than the vibration isolation of the unit.

"Electrical Compensation"

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

However, resolution deteriorates in exchange for deep bass.
I've tried adding a high-pass filter circuit and replacing resistors and capacitors, but it doesn't return to a clear tone.
Even if it is a simple one, an extra electric circuit seems to be accompanied by a deterioration in sound quality.
It may be that it is noticeable because it is a carpet speaker with a clear tone.
I think this is the reason why multi-way speakers and other circuit-equipped speakers sound muddy.
Thus, "Carpet Speaker Prototype No. 1" is completed.
With this simple configuration, it is possible to reproduce open, dynamic, realistic and three-dimensional sound.