question: Why do Bluetooth speakers take so long to connect to phones that are regularly connected to the speaker?
comment: It helps to think about the Bluetooth connection like a hose with lots of spurting instead of a nice stream. To make the audio you hear seem smooth, the receiver will usually have some buffer it uses to store the information before playing it. This is kinda like having a bucket with a smaller hole which you run the hose into so that as long as more is going in than out, the stream stays smooth. Once the buffer is full the first time, the audio starts playing and any connection issues get smoothed over. The delay is probably one part the actual connection time and the rest is the buffer filling up so it can start playing.
passages: As with all wireless transmission, the range and accessibility to most Bluetooth advertising depends on the transmitter power class and the individual portage of the receiver equipment. However, with advances in mobile devices technology, this distance for proper receiving is increasing to reach 250 meters or more in nowadays smart phones, tablet computers and other mobile devices.
  
  The selectivity goes down with extension of range. Hence the transmission power raise as well as receiver sensitivity raise will reduce the contextual connection between actual location of receiver and contents of broadcast message.
   The signal frequency range used by wireless speakers is generally the same as that used by cordless telephones — 900 MHz. The RF signal can traverse walls and floors/ceilings. Most manufacturers claim the signal transmits over a range of 150 to 300 feet (50 to 100 m). Many wireless speakers feature variable transmission channels that can be set using a tuning knob to overcome potential RF interference with other nearby wireless devices, such as cordless phones or baby monitors. Bluetooth devices use a radio communication frequency such that the devices do not have to be in a visual line of sight with each other.
   Many wireless mobile headsets use Bluetooth technology, supported by many phones and computers, sometimes by connecting a Bluetooth adapter to a USB port. Since version 1.1 Bluetooth devices can transmit voice calls and play several music and video formats, but audio will not be played in stereo unless the cell phone or media device, and the headset, both have the A2DP profile.
  
  Section::::Wireless.
   Bluetooth handsfree options are now also easily found in any high end automotive as part of the vehicle's stereo system, or in after market stereo system units. This option utilizes the vehicle's speakers to transmit the caller's voice in the phone call and have an embedded microphone in the stereo unit itself, the steering wheel, or use a separate wired microphone that can be placed anywhere in the vehicle.
  
  Section::::Mobile phones.
   Section::::Bluetooth.
  
  Bluetooth technology is a wireless short range digital communication that allows devices to communicate without the now superced RS-232 cables.
  
  Section::::Proximity systems.
   Your mic can be regular or USB. One advantage of USB, if well designed, is that the long cable won’t pickup stray signals like the call-connection on GSM phones.
   Most Bluetooth applications are battery-powered Class 2 devices, with little difference in range whether the other end of the link is a Class 1 or Class 2 device as the lower-powered device tends to set the range limit. In some cases the effective range of the data link can be extended when a Class 2 device is connecting to a Class 1 transceiver with both higher sensitivity and transmission power than a typical Class 2 device. Mostly, however, the Class 1 devices have a similar sensitivity to Class 2 devices. Connecting two Class 1 devices with both high sensitivity and high power can allow ranges far in excess of the typical 100m, depending on the throughput required by the application. Some such devices allow open field ranges of up to 1 km and beyond between two similar devices without exceeding legal emission limits.
   BULLET::::- For "numeric comparison", MITM protection can be achieved with a simple equality comparison by the user.
  
  BULLET::::- Using OOB with NFC enables pairing when devices simply get close, rather than requiring a lengthy discovery process.
  
  Section::::Technical information.:Pairing and bonding.:Security concerns.
  
  Prior to Bluetooth v2.1, encryption is not required and can be turned off at any time. Moreover, the encryption key is only good for approximately 23.5 hours; using a single encryption key longer than this time allows simple XOR attacks to retrieve the encryption key.
   Devices that are typically used for handsfree communication use Bluetooth as its wireless technology. They still require a smartphone or other device to initiate a call. These devices include Bluetooth headsets, hands-free car kits (HFCK), and personal navigation devices (PND). Originally introduced as optional features connected by a wire to smartphones or other communication devices, they now generally are available with wireless technology. 
   BLE devices are detected through a procedure based on broadcasting advertising packets. This is done using 3 separate channels (frequencies), in order to reduce interference. The advertising device sends a packet on at least one of these three channels, with a repetition period called the advertising interval. For reducing the chance of multiple consecutive collisions, a random delay of up to 10 milliseconds is added to each advertising interval. The scanner listens to the channel for a duration called the scan window, which is periodically repeated every scan interval.
   It used to be the case that due to security fears, or a desire to save battery life, many users keep their Bluetooth devices in OFF mode, or ON but not set to be 'discoverable'. Because of this, often regions where Bluetooth proximity marketing is in operation it is accompanied by advising via traditional media - such as posters, television screens or field marketing teams - suggesting people make their Bluetooth handsets 'discoverable' in order to receive free content - this is often referred to as a "Call-to-Action." A 'discoverable' Bluetooth device within range of the server is automatically sent a message asking if the user would like to receive the free content.
   The first "Bluetooth Headset" model was released on 1 November 2010, using a similar design to the IE2 earphones. Ambient noise sensing automatically adjusts the volume level based on background noise so that, in theory, the user should not have to adjust the volume when walking between quiet and noisy environments. Signal processing attempts to amplify the caller's voice and reject background noise, allowing the caller to be heard more clearly; however, in practice call quality is poor for models without A2DP. The Bluetooth Headset was criticized for having poor call quality, a lack of features and a high price tag.
   Bluetooth exists in numerous products such as telephones, speakers, tablets, media players, robotics systems, laptops, and console gaming equipment as well as some high definition headsets, modems, hearing aids and even watches. Given the variety of devices which use the Bluetooth, coupled with the contemporary deprecation of headphone jacks by Apple, Google, and other companies, and the lack of regulation by the FCC, the technology is prone to interference. Nonetheless Bluetooth is useful when transferring information between two or more devices that are near each other in low-bandwidth situations. Bluetooth is commonly used to transfer sound data with telephones (i.e., with a Bluetooth headset) or byte data with hand-held computers (transferring files).
   The Sound BlasterAxx SBX 8 is the only speaker that does not have Bluetooth capability.
  
  The Sound BlasterAxx SBX 10 and Sound BlasterAxx SBX 20 are Bluetooth capable and can be used for answering phones calls from iOS and Android smart phones. The Bluetooth version for the speakers is Bluetooth 2.1(Enhanced Data Rate). The Bluetooth codecs supported are SBC and AAC, aptX is not supported. The speakers also do not support ASIO and do not have the Scout Mode feature.
   Section::::Wireless.:Bluetooth.
  
  Bluetooth technology is widely used for short-range voice transmission. While it can be and is used for data transmission, the short range (due to using low power to reduce battery drain) is a limiting factor. A very common application is a hands-free Bluetooth earpiece for a phone which may be in a user's pocket.
   Most Bluetooth headsets implement both Hands-Free Profile and Headset Profile, because of the extra features in HFP for use with a mobile phone, such as last number redial, call waiting and voice dialing.
  
  The mobile phone side of an HFP link is Audio Gateway or HFP Server. The automobile side of HFP link is Car Kit or HFP Client.
  
  Section::::Human Interface Device Profile (HID).
   In 2001, researchers at Nokia determined various scenarios that contemporary wireless technologies did not address. The company began developing a wireless technology adapted from the Bluetooth standard which would provide lower power usage and cost while minimizing its differences from Bluetooth technology. The results were published in 2004 using the name Bluetooth Low End Extension.
   Multiple users reported that the microphone can randomly stop working. A possible solution is to blow into the microphone.
  
  Some units suffer from Bluetooth connectivity issues.
  
  There is an issue where Google Assistant does not work with some Bluetooth headphones.
  
  Section::::Issues.:Other issues.
  
  The Pixel 2 XL comes with a charger capable of fast charging at 18W, but the phone is not able to charge at more than 10.5W, taking two and a half hours for a full charge. Below 20 °C (68 °F) the charging speed is just a mere 3-4W, but the phone will still display "Charging rapidly", which is misleading.
   Any device may perform an inquiry to find other devices to connect to, and any device can be configured to respond to such inquiries. However, if the device trying to connect knows the address of the device, it always responds to direct connection requests and transmits the information shown in the list above if requested. Use of a device's services may require pairing or acceptance by its owner, but the connection itself can be initiated by any device and held until it goes out of range. Some devices can be connected to only one device at a time, and connecting to them prevents them from connecting to other devices and appearing in inquiries until they disconnect from the other device.
   There are strong concerns that the ever-listening microphone of smart speakers presents a perfect candidate for a wiretap. In 2017, British security researcher Mark Barnes showed that pre-2017 Echos have exposed pins that allow for a compromised OS to be booted.
  
  Section::::Privacy concerns.:Voice assistance vs privacy.
   TADs with digital storage for the recorded messages do not show this delay, of course.
  
  Section::::Pure voice operation.:Remote control.
  
  A TAD may offer a remote control facility, whereby the answerphone owner can ring the home number and, by entering a code on the remote telephone's keypad, can listen to recorded messages, or delete them, even when away from home.
   Bluetooth is a packet-based protocol with a master/slave architecture. One master may communicate with up to seven slaves in a piconet. All devices share the master's clock. Packet exchange is based on the basic clock, defined by the master, which ticks at 312.5µs intervals. Two clock ticks make up a slot of 625µs, and two slots make up a slot pair of 1250µs. In the simple case of single-slot packets, the master transmits in even slots and receives in odd slots. The slave, conversely, receives in even slots and transmits in odd slots. Packets may be 1, 3 or 5 slots long, but in all cases the master's transmission begins in even slots and the slave's in odd slots.
   BULLET::::- Some users also reported problems with the unit's microphone. They claimed that voice clarity on the recipient's end of the connection was poor, akin to talking "inside a cardboard box." (koreth, Slashdot). Users have found that bluetooth-enabled wireless headsets or fixed headsets seemed to be an effective work-around.
  
  BULLET::::- Another problem people reported is that the handset's earpiece made it difficult to hear in loud environments. Using a bluetooth-enabled wireless headset would also take care of this problem.
   Seeking to extend the compatibility of Bluetooth devices, the devices that adhere to the standard use as an interface between the host device (laptop, phone, etc.) and the Bluetooth device as such (Bluetooth chip) an interface called HCI (Host Controller Interface)
   BULLET::::- Turning off encryption is required for several normal operations, so it is problematic to detect if encryption is disabled for a valid reason or for a security attack.
  
  Bluetooth v2.1 addresses this in the following ways:
  
  BULLET::::- Encryption is required for all non-SDP (Service Discovery Protocol) connections
  
  BULLET::::- A new Encryption Pause and Resume feature is used for all normal operations that require that encryption be disabled. This enables easy identification of normal operation from security attacks.
  
  BULLET::::- The encryption key must be refreshed before it expires.
  