If you have been around the mobile electronics industry for any amount of time, you will know that certain terms are often used incorrectly. One term that has been over-abused lately is Bluetooth. Product manufacturers, retailers and consumers have developed an expectation of what Bluetooth is, and what it does. Sadly, those expectations can lead to confusion and undesirable results. This article explains what Bluetooth is, and how it is used.

What is Bluetooth?

Back in the dark ages, we had to connect electronic devices with wires. We also created wheels from boulders using animal bones as tools. RS-232 was a popular type of communication protocol for devices like modems, printers, scanners and cameras. Two wires would carry data between these devices and your computer. In 1994, Ericsson – a telecommunications and network equipment manufacturer in Stockholm, Sweden – introduced a wireless alternative to RS-232 called Bluetooth.

Bluetooth is a low-power, high-speed wireless communication protocol. Bluetooth operates using short-wave UHF radio waves in the frequency band of 2.4 to 2.485 GHz. Within this range of frequencies are 79 dedicated Bluetooth channels. Bluetooth uses Frequency Hopping Spread Spectrum to reduce errors and allow multiple devices to operate within the same frequency spectrum.

Bluetooth is used for short-range data communication between devices like computer and keyboards, video game controllers and consoles, and cellular phones and wireless devices. There are applications for medical applications such as monitoring heart rate, blood pressure and glucose levels. That said, many industrial applications exist between sensors in production systems and control computers.

Bluetooth Profiles

The misconception many people in the mobile electronics industry have is that Bluetooth exists to let cellular phones make calls and stream music to our radios. Bluetooth is far more involved and flexible than that.

Any talk of Bluetooth functionality is a perfect segue to introduce us to profiles. A Bluetooth profile is a set of instructions and commands that operate over a Bluetooth connection. Profiles simplify the communication between devices. In our industry, we are used to four common profiles:

PBAP – Phonebook Access Profile

HFP – Hands-free Profile

A2DP – Advanced Audio Distribution Profile

AVRCP – Audio Video Remote Control Profile

These profiles are used in varying combinations to allow you to connect your phone to your car radio so you can make phone calls and stream music. A few companies that have wanted to provide an Internet connection to their radio have used DUN to accomplish this task.

PBAP Profile

The Phone Book Access Profile allows your source unit to receive phonebook entry information, as well as manage it. Phonebook entries are transmitted and managed by the radio in vCard 2.1 or vCard .0 formats. Missed, received and dialed numbers are listed as well.

HFP Profile

The Hands-free Profile carries monaural audio between the phone and a secondary device. The profile also supports commands to answer or reject incoming calls; place a call; use memory data to place a call, terminate a call or manage phone volume level; and send phone status information, including battery, roaming status and signal strength . These functions are included in version 1.5 of the Hands-free Profile. Future versions, such as 1.7, will include support for wideband speech and the use of external audio compression and decompression codecs.

A2DP Profile

The Advanced Audio Distribution Profile operates within another profile called the Generic Audio/Video Distribution Profile (GAVDP). A2DP is responsible for allowing us to stream audio from a device such as a smartphone to a radio or powered speaker. The basic profile allows for stereo audio to be transmitted at a sampling frequency of 44.1 kHz at up to 328 kb/s. The use of a third-part codec such as aptX from Qualcomm or LDAC from Sony may further improve on bandwidth.

AVRCP Profile

Functioning alongside the GAVDP profile is the Audio Video Remote Control Profile. AVRCP is responsible for the display of song title, artist and album information, and control over playback device functions. If you can imagine a button on a DVD remote control, the AVRCP is likely to support it. Most car audio source units include functions like play, pause, fast-forward and rewind. The most recent versions of AVRCP include support for folder navigation and searching.

What Bluetooth Doesn’t Do

Although the Bluetooth Special Interest Group (SIG) works to manage the different Bluetooth communication and profile standards, there are variations in functionality between profile versions and, more importantly, between smartphone vendors. This latter fact can be a significant issue for buyers of car audio source units. The expectation that it “should work,” while not unreasonable, is not always possible. To expect a seven- or eight-year-old radio to work flawlessly with a brand-new iPhone 7 or Samsung Galaxy S8 isn’t reasonable. The hardware in the older units cannot be upgraded.

How to Buy Bluetooth

If you are shopping for a new source unit, take any smartphone you want to use with it to the retailer. Ask to pair your phone with the demo unit on display. Check that your entire list of phone contacts transfers as expected. Make sure you can use voice control functions if they apply to your phone. See that you can make calls easily. Finally, check that your phone reconnects reliably to the source unit by cycling power on the source a few times.

If you purchase a new radio and have it installed, only to find out it is not compatible with your smartphone, there is often nothing that can be done quickly. Some manufacturers do release updates for Bluetooth functionality, but these updates are not going to turn a Bluetooth 3.0 system into a 4.0, or add AVRCP 1.4 to a system that shipped with AVRCP 1.2. Do your research before you buy!

If you are looking for a hands-free solution to make phone calls or stream music to your audio system, drop in at your local mobile electronics specialist retailer. Bring your phone, pair the Bluetooth connection and experiment with the options.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

If you are a mobile electronics enthusiast like we are, then it’s quite possible that you enjoy reading product specifications. You can learn a lot about the design and application of a product from the specs. Amplifier power ratings are probably the most popular specs, but there are a lot more. One product specification that tends to confuse people more than help them is speaker efficiency. This article explains what the numbers mean and how you should analyze the appropriateness of subwoofer specifications, one subwoofer to another.

Speaker Efficiency

In a nutshell, the efficiency specification attempts to quantify how much sound a speaker will produce when provided with a given amount of power. Manufacturers provide the specification in two common methods. The most common are decibels of output when fed with 1 watt of power and measured at 1 meter from the speaker, written as 1 W/1 m. The other specification method involves replacing the 1 watt power measurement with 2.83 volts. For a 4 ohm car audio speaker, 2.83 volts works out to 2 watts of power or 4 watts into a 2 ohm speaker. Make sure to take the impedance of the speaker into consideration with the latter format.

For a subwoofer, we derive this efficiency number with a formula that includes the driver’s resonant frequency, equivalent suspension compliance and driver’s electrical Q. In reality, the resulting number is purely theoretical and applies most directly to output in the frequency range above where most subwoofers play. There is the heart of the matter: The efficiency specification doesn’t describe how loud the subwoofer is at low frequencies. The only way to predict and compare performance is to model the behavior of the driver in simulation software.

Frequency Response Simulation

Let’s compare two 10-inch speakers. For sample A, we will use a very high-quality car audio subwoofer. Since we want to make this example somewhat extreme, we will use a 10-inch pro audio woofer as Sample B in our comparison. We will use BassBox Pro 6 to make the comparisons.

Sample A has a calculated efficiency of 93.21 dB when driven with 2.83 V. Sample B has an efficiency of 95.07 dB. Without modeling the low-frequency behavior of the driver, you’d happily think that Sample B was the louder of the two by 1.86 dB.

We modeled each driver in a sealed enclosure with a volume that provides a total system Q (Qtc) of 0.707. The car audio subwoofer is in 0.694 cubic feet, and Sample B is in 0.378 cubic feet net.

As you can see from the graph, the output of the two woofers varies dramatically. Sample A is louder at 40 Hz by an impressive 4.95 dB. That is contradictory to the efficiency specification, isn’t it? It is, however, not wrong.

Subwoofer Specifications

When an engineer designs a speaker, the first thing to decide is the application. Will this be a high-SPL car audio speaker, or a pro-sound speaker? The differences make a great deal of difference.

Our sample subwoofers also have dramatically different excursion capabilities. Sample A has an Xmax of 17.6 mm and Sample B has an Xmax of only 4 mm. It is worth noting and reminding everyone that cone excursion quadruples for every halving of frequency. If these speakers were given enough power to play 100 dB at 80 Hz with an excursion of 1 mm, then they would need to move 4 mm at 40 Hz. At 20 Hz, they would need to move 16 mm. An excursion requirement of 16 mm is no problem for Sample A, but will likely rip Sample B to shreds.

Comparing the output of two drivers requires that we ensure the driver can handle the excursion requirements necessary to meet our needs.

In the case of our subwoofer simulations, due to excursion limits, Sample B can produce a maximum output of only 94.9 dB at 40 Hz. Sample A can produce 108.3 dB at the same frequency. That is a difference of 13.4 dB. This difference is significant. Sample B simply cannot produce 100 dB of output at 40 Hz in this enclosure. Thus, Sample B not a suitable choice for a subwoofer, which makes sense, since it was designed to be a bass guitar speaker.

Choosing the Right Subwoofer

Unless you own speaker-modeling software and know how to use it, it can be tricky to determine the performance of one subwoofer versus another. Even more difficult is attempting to predict how one sounds when compared to another. Frequency response is just one of the many criteria that differentiate one subwoofer from another. Excursion capabilities, enclosure requirements, distortion characteristics and – of course – cost are all factors to be considered.

Many people think that just because it is harder to hear distortion at low frequencies, the design of a subwoofer matters less than that of a midrange speaker. You would be stunned at how a good subwoofer can bring out details in your music that you may have never heard before.

When it is time to go subwoofer shopping, visit your local mobile electronics specialist retailer. Discuss your needs with them and work with them to find a subwoofer solution that fits your application. You will be happy that you did.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.