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Raspberry Pi retro gaming console with Amazing Bass:  a truly unbelievable sonic adventure into outworldly realms

 

My custom portable Raspberry pi retro gaming console is different.

It is a show piece for Raspberry Jams and Maker Faires.

It is going to sonicly annoy parents, wives, teachers, and those nasty smelly curmudgeons who wont give your pudding until you eat your meat.

 

People playing my version of the Raspberry Pi retro game console are not just going to play the game, they are going to FEEL the game. 

 

My Retro game console is going to be have AMAZING BASS.

AMAZING BASS packs a thunderous punch in the gut for the gaming groans, explosions, launches, hits, and stomps.

 

My retro game system is going to include a high powered audio amp, a subwoofer, and hand designed & built speaker enclosures

AND

it is going to be INEXPENSIVE ! 

It also needs to match and complement the retro gaming console.

 

Spoiler Alert ! Here are the final comparison videos with a spectrum analyzer showing the power of AMAZING BASS audio on a retro gaming system vs ordinary powered PC speakers. 

You may choose to experience the pleasure and read on about the analysis later. If you cant wait, here are the links. 

https://youtu.be/i-e9XbD4Bdg   Donkey Kong Country

https://youtu.be/2huwAm_euGg  Zombies Ate The Neighbors

 

https://youtu.be/qpAf65nIsLY  Super Mario World

https://youtu.be/VMbXvmfE1Uo Super Mario 3

 

  

THE TESTING METHODS DISCLAIMER:

  • Using a 10+ year old digital camera isnt going to do a good job capturing the audio but the differences can be heard in the undoctored comparison videos. While recording with the spectrum analyzer…my chair creaks, someone stomps around upstairs, cats fart, I bump stuff, etc….adding noise to the results… life ain’t perfect :-)
  • No pink noise or white noise generators with isolated speakers in anechoic chambers……no calibrated and equalized microphones at null and peak points……but enough data to prove what you can hear and feel if you were in the presence my AMAZING BASS audio system for retro Pi gaming

 

Project Milestones: 

 

1.Identify the real expectations of Raspberry Pi analog audio output specs. My retro pi uses an older VGA monitor with an unpowered HDMI adapter, audio from the Pi audio jack.  I don’t expect audiophile dynamic range, hi S/N, and bandwidth or should I ………..?

 

2. Measure DB and bandwidth of a powered PC speaker system fed from the retro gaming RPi2 comparing games: Zombies Ate the Neighbors, Mario Bros 3,  SuperMarioWorld, and Donkey Kong Country.

My old digital camera is used to record a crude baseline for comparison. An uncalibrated phone app will also be used for comparison of the old VS new audio systems. See step #6 for results.

 

3. Select an inexpensive high power amplifier that includes a subwoofer output.

 

4. Select speakers to match amplifier ratings. Cost does matter.

 

5. Explore , design and build enclosures to meet audio objectives  and optimize speakers effectiveness.

Identify Thiele/Small parameters, electromechanical measurements used to define the low-frequency performance of a transducer. Using these parameters and a series of calculations, your installer can predict the performance of that speaker in an enclosure.

Compare calcs to commercially available enclosures, and speakers(drivers) with published data.

 

6. Measure DB and bandwidth of a Amazing BASS project. fed from the retro gaming RPi2 comparing games: Zombies Ate the Neighbors, Mario Bros 3, SuperMarioWorld, and Donkey Kong Country. My old digital camera is used to record a crude baseline for comparison. An uncalibrated phone app will also be used for comparison of the old VS new audio systems.

Make comparison videos. And publish on You Tube.

 

7. 3D print “AMAZING BASS !” nametags for the speaker enclosures

 

Now to the project milestone execution and data:

1. Raspberry Pi Audio jack expectations.

     NOTE : I am using a Raspberry Pi 2 for retro gaming. The audio circuit filtering  is different for RPi3 & 4.

https://raspberrypi.stackexchange.com/questions/9831/what-are-the-specifications-for-the-audio-output

"The audio output is 1v peak-to-peak maximum. It's too low-level for headphones (according to reports - I've not tried). The 3.5mm audio out is approx. 11-bit quality,"

Audio jack circuit details found here: https://hackaday.com/2018/07/13/behind-the-pin-how-the-raspberry-pi-gets-its-audio/

“The values of 270R and 33nF can be calculated to give a cut-off frequency of just below 18kHz,….. The values of 150R and 10uF can be calculated as having a cut-off of about 100Hz, ….. The output from this pair of filters should be an acceptable audio signal, and goes straight to the 3.5mm jack. 

 

2. The PC speakers were turned up full power for the comparison test. Measurements were taken 4 feet from speakers.

Here is an example screen shots of the spectrum analyzer. The comparison videos at the end of this report include the spectrum measurements for both PC speakers and AMAZING BASS! .

 

                Baseline ambient noise measurements were taken, but don’t lend value to this report.

 

3. Select my Amazing BASS  Audio AMP: It needs to pack a punch and be inexpensive. It needs volume adjust on the subwoofer and stereo, and tone adjustment knobs.

I got this TPA3116D2 class D Amplifier on Ebay for $11 .

Specs :  12-24V input 50W X2  and a 100W subwoofer channel.

     I standardize on 12V on my projects whenever possible for commonality of my on hand parts, and to battery power if desired.

     With 12V input , the power output I anticipate is half the specifications 25W X 2  and 50W subwoofer and are more than needed on the retrogame console anyway.  Double checking the      manufacturer’s output spec, the TPA3116D2 IC has a 7.5A max output.

 

 

 

  

the TPA3116D2 data sheet says 10% distortion at 25W with 14.4V input. http://www.ti.com/lit/ds/symlink/tpa3116d2.pdf

@ 12V input this interpolates to ~21 W. i.e. we wont crank this amp to maximum to avoid distortion.

At 100W/12V = 8.3A power supply needed for maximum power RMS output. 6A is likely more than enough for abusive use. This is a variable that can be tweeked. 

 

I have a 12V 10A supply from another project.  SAVE MORE $$$

 

 

 

PROBLEM: When the amplifier is first powered up, it sees the speaker loads and sags the power supply bad , causing it oscillate, sometimes wont come up and makes a lot of undesirable and possibly damaging noise.

To fix this problem, an Arduino nano and N.O. relay outputs are used to keep the speakers disconnected from the audio amplifier until the amplifier is booted up.

 

The Arduino nano waits 3 seconds after power is applied to close the output relays, each one at a time, one second apart, to connect each speaker to the audio amplifier.

The Arduino nano waits 3 seconds after power is applied to close the output relays, each one at a time, one second apart, to connect each speaker to the audio amplifier.

 

The Arduino Nano code:

/*

  turn on relays on a couple second time delay on pickup.

  Relay output HIGH, coil = OFF, the N.O. contacts open

 

*/

// the setup function runs once when you press reset or power the board

void setup() {

  // initialize digital pins as an output.

  pinMode(2, OUTPUT);

   pinMode(6, OUTPUT);

   pinMode(12, OUTPUT);

digitalWrite(2, HIGH);   // turn the LED on (HIGH is the voltage level)

    digitalWrite(6, HIGH);   // turn the LED on (HIGH is the voltage level)

digitalWrite(12, HIGH);   // turn the LED on (HIGH is the voltage level)

  }

 

// the loop function runs over and over again forever

void loop() {

  delay(3000);

    digitalWrite(2, LOW);   // turn the LED on (HIGH is the voltage level)

delay (1000);

    digitalWrite(6, LOW);   // turn the LED on (HIGH is the voltage level)

delay (1000);

digitalWrite(12, LOW);   // turn the LED on (HIGH is the voltage level)

}

 

The audio Amp assembly

 

 

 

4. Selecting speakers ( drivers in audio lingo ):

 

  1. The bandwidth for the amplifier per the datasheet says 14 Hz – 100 kHz…….yea…OK 

 

Cost inexpensive:  reused 2  car speakers , I have on hand.

 

The car speakers are 6 inch diameter , 30W 4 ohm. These Toshiba TS 462 are the perfect wattage for this RetroPi console with AMAZING BASS.

They are designed for use with infinite baffles ( trunk deck) or door panel installation.

 

 

AMAZING BASS subwoofer: Selected this speaker cone for low end characteristics.

Selected the speaker for the AMAZING BASS subwoofer for $20 on Ebay:

4.5” subwoofer.  bandwidth 66-2KHz   40W  6 ohm. I picked 6 ohm to be able to drive more power than an 8 ohm speaker.

The speaker needed to be somewhat compact and portable , at most 50W ( @ 12V driven 41W with 10% distortion).

IC datasheet shows to drive at ~35W for 1% distortion @ 400Hz.

The subwoofer nameplate is fairly useless  :-) 

This chart for the speaker agrees with my calcs, speaker is a good match for this amp's power.

Unfortunately, the amplifier description itself doesn’t say exactly what the amplifiers subwoofer channel output bandwidth is.

 

The speaker and enclosure size needs to be reasonable for portability and aesthetics while still kicking butt.

 

5. Design and build enclosures to meet audio objectives and optimize speakers effectiveness.

References: 

https://www.youtube.com/watch?v=dwm1v2w2tH0

instructions to measure T/S parameters

Elliot Sound Products website: http://sound.whsites.net/tsp.htm Speaker Driver Displacement Calculator Help: https://www.diyaudioandvideo.com/Calc... Speaker Driver Displacement Calculator: https://www.diyaudioandvideo.com/Calc... Sealed or Ported Enclosure Calculator: https://www.diyaudioandvideo.com/Calc... Speaker Box Enclosure Designer / Calculator: https://www.diyaudioandvideo.com/Calc... Closed Enclosure Calculator: http://www.mh-audio.nl/ClosedBoxCalcu... Vented Box Calculator: http://www.mh-audio.nl/ReflexBoxCalcu...

 

https://www.youtube.com/watch?v=EMhmVmtQ4BI

https://www.eminence.com/support/understanding-loudspeaker-data/

 

  1. Evaluate different enclosure types . Reference

https://diamondaudio.com/support/box-building.html

 

Transmission line enclosure , too large and too much work to build.

Bass Reflex enclosure too big.

 

Sealed enclosures could be used for the left and right side speakers, but no no no for the subwoofer.

 

Settle on ported design as best chance for success for the AMAZING BASS! subwoofer

However, real calcs need real Thiele/Small speaker parameters of the speaker(driver)

https://www.diyaudioandvideo.com/Calculator/SpeakerBoxEnclosure/

 

 

 

experimenting with this enclosure calculator,

  • observe the Vas parameter & Q determines enclosure box volume
  • Fs (free air resonance) sets determines vented port dimensions

 

Design details on a $20 speaker arent available.

will have to measure what can be measured and swag numbers from similar already engineered products

 

"Vas (read V-sub-A-S) is one of several well-known Thiele-Small parameters¹ commonly associated with mid- and low-frequency moving-coil audio transducers (aka drivers.)

Vas represents the equivalent volume of air having the same acoustic compliance (i.e., ‘stiffness’ or ‘springiness’) of the driver suspension in free air. In other words, it indicates the equivalent volume of air that would produce an air-spring with springiness (i.e., compliance,) equal to that of the driver’s suspension; it is NOT the recommended box volume for a driver. (For mathematical purposes box or enclosure volume is typically denoted as Vb, read V-sub-B.)

     Vas (in liters or m³) = ρ c² Cas = ρ c² (Sd)² (Cms)

Where

     *ρ is the density of air; approximately 1.18 kg/m³ at sea level, 50% RH and 25 °C

     *c is the speed of sound; typically 345 m/s at sea level and 25 °C

     Sd is the effective surface area of the driver diaphragm (in m²)

     Cas is the acoustical compliance of the driver suspension (in m/N)

     Cms is the mechanical compliance of the driver suspension (in m/N)

     *(Corrected for temperature, pressure and humidity)"

 

researching comparable examples of speakers(drivers) with published parameters. 

https://loudspeakerfreaks.com/Product.asp?mfr=Peerless%20by%20Tymphany&part=NE123W-08&Product_ID=11254

The 40W 4 inch subwoofer speaker(i.e. driver) ( see URL) has a Vas =5.9 L and a Q of .35 , free air resonance = 61Hz.

Surveying several models Q is consistently in the .3 to .4 range.

This 4.5 inch driver Vas=5.5, Q=.4, Fs = 65Hz.

https://loudspeakerfreaks.com/Product.asp?mfr=Monacor&part=SPH-115&Product_ID=5538

 

 

 

The free air resonance can be measured for my speakers.

Refer to instructions:  https://www.youtube.com/watch?v=EMhmVmtQ4BI

This You Tube video provided the audio to do the measurement. https://www.youtube.com/watch?v=3m5d6DlkWj8 I like this one because it stopped every 5 Hz and announced the frequency.

 

My subwoofer measures 80Hz free air resonance.

The Toshiba car speakers measure 150 Hz free air resonance.

 

My video doing the the free air resonance test procedure and taking measurements for this speaker.

https://youtu.be/maRZfj91uuE

 

now, comparing commercially available enclosure for a guideline:

 

Sanity Check dimensions to a commercially available subwoofer enclosure:

 

https://www.ebay.com/itm/2PCS-4-5-6-6-5-inch-Ported-Subwoofer-Enclosure-MDF-Loudspeaker-Speaker-Box-/332029910671

This vendor’s published table:

 

  

 

 

Commercially available subwoofer enclosure for a 5 inch subwoofer

MDF   6.7 inches X 7.3 inches X 5.83 inches

MDF is 5/8th ( .625” ) inches thick, 15 mm,  subtract from dimensions. ~6 X 6.7 X 5.25 = 213 in3

213 / 1728 =   .123 cu ft.   total volume of box + port

 

 

NOW FOR MY AMAZING BASS WOOFER ENCLOSURE CALCS:

6 calcs https://www.diyaudioandvideo.com/Calculator/SpeakerBoxEnclosure/ were made to see effect of driver parameters variance on the enclosure dimensions:

 

 

 

 

 

NOTE: Dv diameter = 1 inch ………1 inch outer diameter PVC pipe has 7/8 inner diameter I used PVC pipe cut to length for port tuning.

 

 

 

Since the certain specific woofer speaker data was not available, it was approximated by comparing to other commercially available examples.

 

6” X 5 “ X ~ 10.5” = 315 cu in     .182 cu ft 

1 inch PVC pipe, 2 inches long used for the port

 

The woofer sides were double reinforced for stiffness. The inside edges and cracks were caulked, and the inside was sprayed with Plasti-Dip spray rubber for a bit of dampening.

 

 

6. Measure DB and bandwidth of the Amazing BASS project. fed from the retro gaming RPi2 comparing games:

Zombies Ate the Neighbors, Mario Bros 3, SuperMarioWorld, and Donkey Kong Country. My old digital camera is used to record a crude baseline for comparison.

An uncalibrated phone app will also be used for comparison of the old VS new audio systems.

The spectrum analyzer comparison videos between the Retro game console with PC speakers and AMAZING BASS audio are posted to You Tube:

https://youtu.be/i-e9XbD4Bdg   Donkey Kong Country

https://youtu.be/2huwAm_euGg  Zombies Ate My Neighbors

https://youtu.be/qpAf65nIsLY  Super Mario World

https://youtu.be/VMbXvmfE1Uo Super Mario 3

 

 

7. 3D printed nameplates