Audio Systems: speaker sizing, linear excursion, car installations

Question
Hi there,

Why do high end audio companies still produce 4" component speaker systems for cars when people would usually choose a 6" or 6.5" system over 4"?

The main argument would be that a 6" or 6.5" would produce better lows compared to 4", yet some manufacturers such as BMW install 4" speakers for their front stage? There must be some myths going on here?

Im trying to source a set of Xtant XSC2.6 components which are 6" but its mission impossible however I know I can get the XSC2.4" components but theyre 4". Im building an Xtant only show car hence why I am limiting myself.

Regards, Tommy

Answer
For car installations one is restricted by the opening size made available by the manufacture - unless you are a custom installer and don't mind cutting the door mounting spaces bigger or using custom made rings to fit non-standard speakers.

Speaker size vs performance is sort of a myth.  It is true a larger diameter speaker can move more air for a given displacement but if a small speaker is pushed to greater displacement it can match the performance of the bigger speaker.  So, much is a function of the design of the magnetic circuit and how much linear excursion can be obtained from the smaller cone size.  The smaller speaker sometimes has acoustic properties that are superior due to the suspension characteristics and the free air resonance - not to mention the lower distortion due to a smaller and stiffer cone.  The mass of the smaller cone can be used to increase its efficiency as well.

Further, the automobile manufacturer, and especially the high end car people, may assume that an audio enthusiast would add subwoofers to the system which would thereby obviate the need for the bigger front door speakers, thus allowing more space for other things the door engineers had in mind (strength in accidents and greater range of window operations for example).

So, there are many arguments.  It is an overall systems design question.  There is no reason, in my opinion, if designed correctly, that the 4" system may be equal to or superior to the larger cone system.  In the case of BMW I am sure they are well aware of design trade-offs and have made the system choices based on what they believe are the best solutions.  At least this is true in well designed vehicles.

Hope this helps.