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Characteristics and Properties of Wireless Portable Speakers

the comprehensive guide to everything you need to know about wireless portable speakers

If you’re curious to know about wireless portable speakers, this article goes into great depth on every aspect of these devices from construction, materials, acoustic properties and more.  Boombotix has been building wireless portable speakers for over three years now, so we figured we’d share some of our knowledge for your reference.  If you are looking to build your own wireless portable speakers, you may also want to reference this article on hardware product design.  You may learn a lot from our product design and use it as a starting point for your personal wireless speaker project.  If you have any questions, feel free to comment and we will see if we can be of assistance.  Let’s get right into it.

1. Wireless Portable Speaker Overview
1.1 Primary Parts and Funtions of a Wireless Portable Speaker
1.2 Why most wireless portable speakers use Bluetooth
1.3 Bluetooth Signals and Protocols
1.4 Other wireless audio protocols
2. Parts and Characteristics of Wireless Portable Speakers in Detail
2.1 Speaker Diaphragm
2.2 Speaker Magnets/Audio Transducer
2.3 Impedance Rating
2.4 Weatherproofing/Ingress Protection Rating
3. Portable Wireless Speaker Electronics
3.1 Class-D Amplifier
3.2 Bluetooth Module with Built On MCU
3.2 Lithium Polymer Batteries
4.Mechanics of Wireless Portable Speakers
4.1 Wireless Portable Speaker Acoustics
4.2 Portable Speaker Connectors
5. Firmware Programming on Wireless Portable Speakers
6. Where to buy Wireless Portable Speakers
7. Conclusion

1  Wireless Portable Speaker Overview

This is an exploded view of the Boombot REX2 wireless speaker.  This rendering shows you all of the primary mechanical components typically found in a wireless portable speaker.

This is an exploded view of the Boombot REX wireless speaker. This rendering shows you all of the primary mechanical components typically found in a wireless portable speaker.

Wireless portable speakers are devices that play media from a content source (smartphone, tablet, laptop or any Bluetooth enabled device).  These portable speakers are capable of projecting sound at high volume using low power consumption.  Most portable devices incorporate a rechargeable lithium polymer battery.  The norm for most wireless speaker communication is Bluetooth.

1.1 The primary parts and functions of a wireless portable speaker

  1. Drivers: These are the parts that move the air.  They consist of a diaphragm, voice-coil and magnet.  
  2. Class D amplifier: A line-level signal is put into and amplifier and the signal power is increased with a high level of efficiency and then passed to the drivers.
  3. Passive Radiator: This part is not found on all portable speakers.  These are used to move additional air in the housing and generate greater low-end response.
  4. Speaker Housing: The speaker housing hosts all of the parts.  Typically you want the housing to be a hard material with air tight construction.
  5. Grill: This part protects the speakers from dust and impact
  6. Lithium Polymer Battery: This rechargeable battery is typically a 3.7V power source varying in size depending on design.  They typically can have around 500 charges with capacity maintaining over 70% during aging.

1.2 Why Most Wireless Portable Speakers use Bluetooth

Bluetooth is a great standard for wireless audio streaming.  It offers low power consumption suitable for mobile devices and the costs are relatively low as well.  Lower power consumption means that less strain is put on the battery.  There are a number of different Bluetooth standards ranging from 1.0-4.0 (and certainly more on the way).  The major benefits of Bluetooth 4.0 are not typically seen in speakers since the stream of data coming from the mobile device is constant.  Bluetooth 3.0 offers NFC compatibility which is seen used to connect devices by proximity.  Bluetooth 4.0 focuses more on low power states during idle time.    The bit rate of high quality streaming music is 328 kbps while Bluetooth 2.0 offers capacity of up to 3Mbps.  Bluetooth range can be up to 300 feet but for efficiency’s sake, most portable devices do not transmit greater than 40 feet.  We may expect to see wireless speakers starting to use the Bluetooth 3.0 standard more often to parallel the growth of NFC adoption.

1.3 bluetooth signal protocols and codecs

The audio transmission on Bluetooth protocol is typically A2DP (Bluetooth Advanced Audio Distribution Profile).  This means that the source device compresses the audio into a codec called SBC (subband codec).  When the data reaches the portable speaker, then it is compressed into a digital signal resembling the audio file in as great a resolution as possible.  Integrated circuit advancements have made this process seamless and close to lossless.  Sometimes white noise can be heard on Bluetooth during streaming but this can usually be filtered out with good circuit design.  On Boombotix speakers, we use a number of filters to reduce white noise as well as optimize the equalization curves for the speaker drivers.

1.4 other wireless protocols used in wireless speakers

Some portable speakers connect via Wi-Fi based protocols like Airplay, but these units are typically rendered for stationary at-home use.  There is some speculation that we could see more Wi-Fi enabled speakers.  The benefits are that the overall bit rate can be increased and the audio quality can be enhanced.  Units can also AdHoc network and create multi-speaker systems.  Designers will have to figure out how to offer efficient power consumption while still remaining portable.

2 Parts and Characteristics of Wireless Portable Speakers in Detail

2.1 speaker DIAPHRAGM

There diaphragm of a speaker is the conical/concave surface that pushes air.  Sound is made through moving air in a way that matches the audio signal.  A larger diaphragm can typically move larger volumes of air resulting in greater amplitude.  Larger speakers handle lower frequencies better than small.  Smaller speakers can deliver great high frequency response.  A passive radiator is also considered a diaphragm, but they are not driven by electric current.  Each speaker has two leads on it for ‘+’ and ‘-‘.  These leads send signals of opposite charge and varying amplitude through the voice coil (signal transducer).  This magnetic field in culmination with the built on magnet on a speaker moves the diaphragm around enough to generate noise (or music if that’s what we’re going for).


Photo Credit: How Stuff Works

Photo Credit: How Stuff Works

Choosing a speaker/driver that is power rated appropriately for the application is important.  On many portable speakers, power consumption is kept below ten watts.  Over driving the speaker will result in rapid losses in efficiency and poor sound.  Under -driving a speaker will result in poor output.

When you hear a lot of smaller portable speaker systems distorting, this is usually a result of the speaker being overdriven or poor signal quality.  The speaker is incapable of moving in conjunction with the signal and it introduces a lot of unwanted and displeasing noise. With the use of filters (especially on the low end), wireless portable speakers can sound crisp and hard hitting.  This takes a lot of fine tuning to get right on every speaker which is really what sets great products appart from poor ones.  Attention to detail in wireless portable speaker acoustics makes all the difference.

2.2 speaker magnets/audio transducer

The magnets used in a wireless portable speaker interact with the voice coil to create movement on the diaphragm.  The magnet can be composed of a number of materials including barium, strontium ferrite and Iron Boron.  Because of the heavy weight of some of these magnets, Boombotix portable speakers use neodymium magnets which produce a great field in a small form factor.

2.3 IMPEDANCE rating

The impedance raising of a speaker/driver is equivalent to the internal resistance.  A lower impedance will allow more current to flow through the voice coil of a speaker.  In most portable wireless speakers, an impedance of 4Ohms or 8Ohms is used.  In our Boombot portable speakers, we use 4Ohm drivers in favor of higher power.  The lower resistance also can eat up more power, but the benefit you get in a small form factor makes it a valuable trade off.

2.4 weatherproofing (also known as I.P. Rating (ingress protection

Portable wireless speakers are taken outdoors often, so weatherproofing is really important to withstand the exposure to elements.  There are a series of tests administered to portable speakers to qualify for an IP rating.  I.P. stands for Ingress Protection.

An IP-rating is denoted by two digits (IP-XX).  The first digit refers to the dust resilience.  The second digit denotes the level of water resistance.  All Boombotix speakers are rated minimall to an IP53 rating.  We are using a variety of sealants and connectors to extend the rating of the Boombot REX to an IP67 rating.  This is the minimum rating needed if you wanted to do something like mount a wireless portable speaker to a surf board or kayak.  Below is a table to give you an idea of what level of water/dust resistance a wireless portable speaker has.


Source: 2MccTv

On the Boombot REX  wireless speaker design we integrated aluminum face drivers because of the increased level of water resistance.  We also used connector covers and a number of sealing methods to prevent water from entering the housing.

3 Portable Wireless Speaker Electronics

3.1Class d amplifier

On wireless portable speakers, class D amplifiers are the most commonly used because of the relatively low cost and high efficiency.  In a class D amplifier, the switching controller a triangular wave is combined with an input signal to create a square wave (also known as a binary wave).  This signal can be interpreted by the switching controller to turn on and off and amplify the wave.  On a wireless bluetooth speaker, the input signal comes directly from the pin-outs on the Bluetooth module.

Class D amplifier Circuit

3.2 bluetooth module with built on mcu

Every wireless portable speaker that is Bluetooth enabled has a module.  Typically manufacturers will source a module that has an MCU built on.  The MCU has to handle firmware operations and in some cases has built-in flash to store short audio files.  Our Boombot portable speakers have custom audio files downloaded onto the flash memory so that different modes, states and button presses can play a specific audio file.  The audio files store on-board are compressed .wav files in short lengths.

Our products along with many other wireless portable speakers uses the CSR BC5 Bluetooth chip.  These chips are ideal for audio applications.  CSR has a robust development kit called BlueSuite that allows firmware developers to access a standard firmware stack and customize as needed.  The CSR BC5 Bluetooth module has a number of features that make it optimal for wireless portable speaker applications including:

  • Fully Qualified Bluetooth V2.0+EDR System
  • „ Enhanced Data Rate(EDR) Compliant with v2.0
  • of specification for both 2Mbps and 3Mbps
  • modulation modes
  • „ 16-bit Internal Stereo CODEC -95dB SNR for
  • DAC
  • „ Low-Power 1.5V Operation,1.8V to 3.6V I/O
  • „ Integrated Switched-Mode Regulator
  • „ Integrated Battery Charger
  • „ USB and UART with Dual Port Bypass Mode to
  • 4Mbit/s
  • „ Supports up to 32Mbits of External Flash
  • „ Multi-configurable I2S,PCM,or SPDIF Interface
  • „ Enhanced Audibility and Noise Cancellation
  • „ Support for 802.11 Co-existence
  • „ Rohs compliant

One thing that wasn’t obvious was that the CSR BC5 has a configuration for improving microphone performance as well as a built in DSP (Digital Signal Processor).  We can’t disclose all of the details of our DSP, but I can say that you can play around with different frequency levels to optimize the output signal from the Bluetooth module as a pre-amp procedure.  This has yielded significantly better acoustic performance in our Boombot portable speakers.

3.3 lithium polymer batteries

Rechargeable batteries have become the standard in wireless portable speakers.  They offer great power to weight ratio, and consumers love that there are no additional costs of ownership.  If you are building a product that uses lithium polymer batteries, be sure to find a reliable and well tested source for these.  Chinese battery manufacturers are notorious for using dopants in their cells to reduce their material costs.  This typically leads to batteries with a lower capacity rating and in many cases a battery that completely fails.  In our earlier runs of Boombot portable speakers, we had several batteries that turned into complete MUSH.

4 Mechanics of Wireless Portable Speaker Housing

The most important element of a portable speaker housing has to do with how airtight the housing is.  By creating a greater vacuum between the air inside the speaker and the surrounding air, more air flow can be pushed by the diaphragm and the passive radiator.  Our products use a variety of sealants in conjunction with precision formed plastics to create this airtight seal around the speaker.  If you loosen the screws of the housing, you can immediately hear the loss in performance from air leakage in the housing.  Sealing the housing of a portable speaker is done for both weatherproofing and acoustic performance.

4.1 wireless portable speaker acoustics

Early on in our product design, we made boxes out of acrylic.  We used our electronics and a variety of speakers to test for acoustic properties.  Typically speaker manufacturers offer some guidelines on what kind of volume aire requirement a speaker needs to operate in optimal conditions.  Some other things that can affect acoustics are housing thickness and the security of the speaker on the housing.  Eventually in production, we shifted into making injection molded ABS housing.  ABS plastic is particularly good for portable speaker housings because it is hard and resonates sound quite well.

Wireless portable speakers with passive radiators leverage the internal airflow/pressure of the primary drivers to move even more air with a particular focus on the low end.  The Jawbone Jambox actually has a patented system that weights the radiator down using the battery.  Extra weight on the passive radiator can actually result in even more momentum generated on the radiator equating to even more bass.

Often times manufacturers of wireless portable speakers reference frequency response.  This plotting is typically referring to a graph with the frequency on the x-axis and amplitude (dB) on the y-axis.  You can see where a speaker has stronger amplitude.  Larger speakers often times can drive more bass response characterized by a peak on the left end of the spectrum (20Hz-400Hz).  Smaller portable speakers offer a little less bass but still have distinct performance in the mid-range.

You can see at the left end of the graph that the Boombot REX has close to the same amount of bass response as the Jambox. The Jambox has a tad more at the very low end due to the larger passive radiator. At the middle and higher frequencies, the Boombot REX offers more than 10dB at times rendering it a much louder wireless portable speaker.

The acoustic performance of wireless speakers can be greatly increased through the use of embedded filters on the amp in culmination with digital signal processing done through the source device or embedded into the portable speaker electronics.

4.2 portable speaker connectors

Although wireless speakers do not require cables to operate, connectors are still essential for charging, firmware uploads and connecting to other devices.  Do not underestimate the value of using robust connectors.  The charging connector in particular can undergo a lot of wear and tear in time and if that part fails, the portable speaker is rendered useless.  On the Boombot REX, there are actually two connectors so that users can daisy-chain the speakers infinitely.  There is a unique feature on the line-in connector such that when an audio jack is inserted into this port, the portable speaker automatically switches to play on line-in mode.  We also use a strain relief and extremely robust solder joints to make sure that the connectors can be used for a long time without fail.

5 Firmware Programming on a Wireless Portable Speaker

All wireless portable speakers have embedded firmware on the module.  The firmware stacks (code) are stored on the flash of the MCU.  Firmware dictates different mode settings, states, commands, and functions of button presses.  Firmware programming is a relatively specialized skill set built from Basic C.  On our wireless portable speakers, we use the CSR Development kit which has a PC based desktop app that offers a strong foundation for the firmware you build.  Most contract manufacturers have an in-house engineer to help with firmware design/architecture, but if you need additional functionality beyond the norm, you may need help from a software engineer experienced enough to build or tweak a firmware stack.

Some wireless portable speakers have the ability to upload new firmware.  The Jawbone Jambox uses the MyTalk app in order to have a consumer facing desktop app where users can download new features/functions for their Jambox.  This is an awesome feature for consumers and developers.  If there is a bug in the firmware, manufacturers can release a patch without having to do a full recall.  There are some additional parts on the hardware and software side required to build this type of functionality.  JTAG (Joint Test Action Group) is the standard for firmware upload interfaces.  The tricky part is building a USB interface that serializes into JTAG so that devices do not need an outward facing JTAG to upload new firmware.  If anyone has some embedded hardware experience, we’d LOVE your help on this project.  It’s a beast!

6 Where to BUY Wireless Portable Speakers

Nowadays it seems that Bluetooth speakers are the standard of all wireless portable speakers and they are readily available across a number of retailers including Best Buy, Amazon, and Radio Shack.  If you want to get something a little more unique, be sure to check out our Boombotix online store as we have a number of artist collaboration and limited edition models rotating through on a regular basis.

7 In Conclusion

We hope this article on wireless portable speakers was helpful and thorough.  We covered everything from speaker properties, components, acoustics, design, weatherproofing, electronics, and firmware.  Through implementing meticulous attention to detail over these characteristics, we have built soe of the best wireless portable speaker on the market.  If you would like to compare wireless portable speakers on the market, check out our portable speaker comparisons.  We’ve tested our Boombot REX head-to-head with some of the best wireless portable speakers on the market (Beats Pill, Jawbone Jambox and OT Turtle Shell) and the results speak for themselves.

Thanks for your continued support.  Feel free to grab a Boombot REX for yourself using discount code: WirelessFreq for 10% off our Boombotix Store.  





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