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Technology Audio DIY DSP Loudspeaker Speakers

Acoustic panels and DSP – Both are beneficial

It is tempting to consider “room correction” with Digital Signal Processing (DSP) as a substitute for acoustic treatment. We implemented both in the same room to see what the effects actually are.

Experimental setup: DSP and acoustic panels

The setup used is a normal living room/home theater. The loudspeakers are Genelec 8351A active monitors with DSP and automatic calibration using a microphone and frequency sweeps.

Home theater with active DSP speakers
The test setup with Genelec active monitors.

Five acoustic panels were placed in the room. They are mineral wool panels measuring 60x60x10 centimeters. Two of them were placed at the side walls in order to address first sidewall reflections and three of them were placed behind the listener by the back wall. The measurement point is also the normal listening point. Measurements were done with REW software:

https://www.roomeqwizard.com/

The effect of acoustic panels and DSP on room response

Effect of acoustics panels and DSP on frequency response.
Effect of acoustic panels (top) and DSP (bottom).

From the magnitude response we see that the acoustic panels bring down some of the peaks in the mid-range. When we then apply DSP and automatic calibration, we get attenuation of the low-frequency peaks caused by room modes. DSP does not really affect the mid-range and the highs. It only raises their level back to where it was earlier. Using DSP and equalizing for mids and highs would be very difficult, because notches and peaks are very narrow.

Waterfall chart showing reduced decay time with acoustic panels
Waterfall charts show faster decay at mid-range frequencies when acoustic panels are applied.

Spectrograms show massive amounts of energy in the bass domain, where we have room modes affecting. Panels this size should not be very effective at long wavelengths according to the manufacturer and our magnitude plot. Yet, adding acoustic panels brings down the energy across the frequency range according to the spectrogram. DSP reduces the bass peaks which, of course, reduces the energy in that region. DSP brings up the mids and highs, so we can see slightly increased energy in that region, which leads to an evenly distributed energy across the spectrum of frequencies.

Effect of acoustic panels and DSP on acoustic energy content
Spectrograms of the reference condition (top), with acoustic panels (middle), with acoustic panels and DSP (bottom).

Conclusions

So do you need both digital signal processing and acoustic treatment? Yes. Looking at the magnitude response, we see that DSP addresses the peaks in the bass region and adjusts for the overall level, while the acoustic panels address the mid-range frequencies. Looking at the energy spectrum, we can see that actually both acoustic panels and DSP even out the energy distrubtion across the frequency range. It is encouraging to see that placing only five panels has a measurable effect. Headphones are immune to room acoustics, but benefit from DSP. Check out our post on headphone DSP: https://rdphysics.com/2021/06/14/dsp-for-headphones

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Categories
Technology Audio DIY DSP Headphones

Digital Signal Processing – Improve your headphones for free

Using a computer as your signal source gives you immense DSP possibilities. It does not cost a thing and reverting back is easy in case you do not like it. There is really no reason not to give it a try. A good place to start is here:

https://github.com/jaakkopasanen/AutoEq
There you will find EQ presets for most headphones and links to applying equalization in your operating system using Equalizer APO. Some users may like the Peace add-on which can be found together with Equalizer APO. If you have issues with system-wide equalization, you may want to try a plug-in for your music player. We can recommend Foobar2000 (oldie but goldie) and Math Audio Headphone EQ.

Math Audio preset files for Porta Pro and HD800S headphones

Here’s the preset file to be used in the Math Audio plug-in when listening to Koss Porta Pro headphones. It’s based on Oratory1990’s EQ profile.

Equalizing curve for Koss Porta Pro headphones
EQ for Koss Porta Pro based on Oratory1990’s measurements

We found the equalizing curve for Sennheiser HD800S to be too harsh, brightening up the sound too much. Therefore, the gains of the peaking EQ were halved and entered into the Math Audio plug-in. You can download it here:

Equalizing curve for Sennheiser HD800S headphones
Modified Sennheiser HD800S EQ

We have got to remember that the EQ files found online are obtained using a measurement head and aiming at a flat frequency response. However, each individual has physically different ears 
and a flat frequency response may not be what we actually want. The recordings that we listen to vary and the type of music varies. The presets are a good starting point, but they should be tweaked to make sure the sound is to your liking. Are there any downsides to processing the signal? There could be some artifacts from filtering such as pre-echo and you could get added distortion from excessive bass boost, but as long as it sounds better to you then that’s all that matters. Give it a try!

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Categories
Technology Audio DIY DSP Headphones Loudspeaker Speakers

Headphones are better than loudspeakers – One factor is behind it all

The argument for headphones instead of loudspeaker as your main sound system is one that you don’t hear too often. Which is why we think it’s important to make it here. It all boils down to one root cause, and that root cause is the room. Let’s divide the consequences of the room into two categories: cost and sound.

Cost

First, speakers are played in a room you need more power. Power means power amplifiers. You need to buy expensive amps to power your loudspeakers. Second, you need to place those loudspeakers somewhere, so you need to buy stands. Or if they are floor-standing speakers you need to buy feet. You need to connect them with cables and buy other accessories. Third, you need to acoustically treat your room, so you need to buy acoustic panels, diffusers, bass traps etc. Fourth, you need to buy presents to your spouse because you’re placing the speakers in the middle of the room.

Sound

You can buy good loudspeakers and ruin them by placing them in a bad listening environment. Optimally, you would have the loudspeakers and the listening position at least two meters away from the nearest wall. However, that is seldom even possible in the available space. You would need a large room. And with this kind of placement, a livingroom quickly becomes a listening room only. Headphones, on the other hand, have multiple benefits compared to loudspeakers:

  • Single point source
  • No crossovers
  • No sweet spot or particular listening position
  • No room effects
  • Tonal balance can be fixed using only DSP

Some of the drawbacks often stated include poor sound stage or imaging. People say that it sounds like the sound is coming from inside one’s head and it doesn’t feel like you’re at a concert. It is a matter of personal preference, but we suggest looking at headphone listening as something separate and different from live events or loudspeaker listening. It is our subjective opinion that crossfeed will not correct for this phenomena and only makes the sound worse. Another common argument is that there’s no physical sensation of bass. While that is true, the pros outweigh the cons.

Recommended hardware

Which ever headphones you use, applying equalizing with the help of DSP is definitely worth considering. Check out our post on the topic:

Sennheiser HD800S open headphones.

 Enthusiast level:

Hobby level:

  • Sennheiser HD650
  • DAC/amp in price range 200-300€
  • DSP at signal source

Budget level:

  • Koss Porta Pro
  • Analog jack or DAC/amp in 100-150€ price class (get one second-hand, for example)
  • DSP at signal source

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Categories
Technology 3D printing Audio DIY Loudspeaker Speakers

Practical 3D printed desktop speakers – FR4

The third version of our 3D printed full-range FR loudspeaker series used metal-filled filament to add density and stiffness to the enclosure. It worked in that regard, but the material was unpractial due to brittleness both during printing and in the final product.

What has changed compared to the FR3 speaker

For the fourth version we switched to wood-filled filament, which is more ductile and easier to process. The surface is quite nice straight out of the printer thanks to the matte surface. A quick touch with an orbital sander gives a smooth finish. The spherical shape of the enclosure remains the same as in the FR3 speaker, because it was proven to be very good in terms of resonances and edge diffraction. The diameter of the driver, enclosure and tripod legs was reduced to obtain a more slender design for desktop use. The binding posts are upgraded to sturdy Dayton Audio binding posts. The driver used is the Tang Band W3-1878, and the leadscrews for the legs are 12 mm. Leadscrew nuts are bonded into recesses in the enclosure and allow for adjustment of the legs. Small TPU feet can be printed and placed at the ends of the leadscrews in order to avoid scratching the desktop. These are satellite speakers and need a subwoofer to compliment the lower frequency spectrum.

You can 3D print your own sub and satellite system by purchasing the STL files from our Etsy Shop.

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3D printing Audio DIY Loudspeaker Speakers Technology

Full-range desktop speakers – FR3

Metal-filled filament and internal support add significant mass and rigidity.

The first version used internal ribbing and bitumen paint to reduce enclosure resonance. The second version used an external carbon fiber shell. Both approaches were a bit cumbersome. For the third version we wanted to fully use the capabilities of 3D-printing. Therefore, a high-density metal-filled filament was used and internal gyroid-shaped support was used even where overhanging surfaces would not have required it. In addition, height and tilt can be adjusted using three threaded rods that form a tripod. The finished enclosure with three 14 mm trapezoid-threaded nuts bonded to it weighs 1.2 kg.

Please support us by using the affiliate link below for ordering the Dayton Audio RS-100 drivers:

SoundImports.eu