question: Why can't a phone connect to multiple speakers via bluetooth?
comment: It has to do with the frequency range of Bluetooth, and the fact that your devices don't have two transmitters.
passages: 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.
   BULLET::::- Windows XP SP1 : Microsoft released a QFE of its Bluetooth stack (labelled as QFE323183) to install onto Windows XP Service Pack 1. Microsoft only released this directly to third-party companies and did not directly release it to the public. The third-party companies were then allowed to release the QFE as part of their own Bluetooth device's software installation. Microsoft no longer supports this QFE.
   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.
   Current mobile software generally must allow a connection using a temporary state initiated by the user in order to be 'paired' with another device to copy content. There seem to have been, in the past, available reports of phones being Bluesnarfed without pairing being explicitly allowed. After the disclosure of this vulnerability, vendors of mobile phone patched their Bluetooth implementations and, at the time of writing, no current phone models are known to be vulnerable to this attack.
   This poses a potential security threat because it enables attackers to access vulnerable Bluetooth devices from a distance beyond expectation. The attacker must also be able to receive information from the victim to set up a connection. No attack can be made against a Bluetooth device unless the attacker knows its Bluetooth address and which channels to transmit on, although these can be deduced within a few minutes if the device is in use.
  
  Section::::Security.:History of security concerns.:2005.
   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).
   A netgraph-based implementation from FreeBSD has also been available in the tree since 2008, dating to an import of Netgraph from the FreeBSD 7 timeframe into DragonFly, but was possibly disabled until 2014-11-15, and may still require more work.
  
  Section::::General-purpose implementations.:Linux.
  
  The Linux operating system currently has BlueZ included with the official Linux kernel distributions, initially developed by Qualcomm.
  
  Section::::General-purpose implementations.:Linux.:BlueZ.
   BULLET::::- "Just works": As the name implies, this method just works, with no user interaction. However, a device may prompt the user to confirm the pairing process. This method is typically used by headsets with very limited IO capabilities, and is more secure than the fixed PIN mechanism this limited set of devices uses for legacy pairing. This method provides no man-in-the-middle (MITM) protection.
   In October 2009 the Bluetooth Special Interest Group suspended development of UWB as part of the alternative MAC/PHY, Bluetooth v3.0 + HS solution. A small, but significant, number of former WiMedia members had not and would not sign up to the necessary agreements for the IP transfer. The Bluetooth SIG is now in the process of evaluating other options for its longer term roadmap.
  
  Section::::Specifications and features.:Bluetooth 4.0.
   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.
   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.
   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.
   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. 
   The problem of dynamic interference, gradual reduction of available hopping channels and backward compatibility with legacy bluetooth devices was resolved in version 1.2 of the Bluetooth Standard (2003). Other strategies for dynamic adaptation of the frequency hopping pattern have been reported in the literature. Such a situation can often happen in the scenarios that use unlicensed spectrum.
  
  In addition, dynamic radio frequency interference is expected to occur in the scenarios related to cognitive radio, where the networks and the devices should exhibit frequency-agile operation.
   Bluetooth services generally require either encryption or authentication and as such require pairing before they let a remote device connect. Some services, such as the Object Push Profile, elect not to explicitly require authentication or encryption so that pairing does not interfere with the user experience associated with the service use-cases.
  
  Section::::Technical information.:Pairing and bonding.:Pairing mechanisms.
  
  Pairing mechanisms changed significantly with the introduction of Secure Simple Pairing in Bluetooth v2.1. The following summarizes the pairing mechanisms:
   Aiming for a different licensing model, toward the end of 2012, Google switched the Bluetooth stack in Android from the GPL-licensed BlueZ to the Apache-licensed BlueDroid.
   Section::::Wireless.:Bluetooth wireless desktop devices.
  
  Desktop devices using Bluetooth technology are available. With a base station that connects via cables to the fixed-line telephone and also the computer via soundcard, users with any Bluetooth headset can pair their headset to the base station, enabling them to use the same headset for both fixed-line telephone and computer VoIP communication. This type of device, when used together with a multiple-point Bluetooth headset, enables a single Bluetooth headset to communicate with a computer and both mobile and landline telephones.
   Section::::Embedded implementations.:EtherMind stack.
  
  EtherMind from MINDTREE Ltd is a BT-SIG qualified Bluetooth Stack and Profile IP offering.
   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.
   Only L2CAP channels configured in ERTM or SM may be operated over AMP logical links.
  
  Section::::Technical information.:Bluetooth protocol stack.:Service Discovery Protocol.
   However, if the radio frequency interference is itself dynamic, then the strategy of “bad channel removal”, applied in AFH might not work well. For example, if there are several colocated frequency-hopping networks (as Bluetooth Piconet), then they are mutually interfering and the strategy of AFH fails to avoid this interference.
   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.
   This is designed for cordless phones to work using Bluetooth. It is hoped that mobile phones could use a Bluetooth CTP gateway connected to a landline when within the home, and the mobile phone network when out of range. It is central to the Bluetooth SIG's "3-in-1 phone" use case.
  
  Section::::Device ID Profile (DIP).
   Well known implementation is LINUX and WINDOWS available "BlueProximity" solution. The hosting on PC like systems allows for detecting presence of mobile phones in proximity to PC-attached Bluetooth dongle or equivalent interface. PC gets locked on leave. Reported and other simple deficiencies of this solution are:
  
  BULLET::::- just local locking logically independent of other security means
  
  BULLET::::- wide variety of overall receiver sensitivity and RSSI feedback dynamics
  
  BULLET::::- wide variety of transmitter efficiency adjusting to RSSI feedback
  
  BULLET::::- varying lock-up distance with any combination of transmitter and receiver
  
  BULLET::::- manual setting the pairing of mobile phone and PC interface
  