Audio Systems: Speaker sizing, amplifier gain, crossover design

Question
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: Hi Tommy,

A decent 4" is very capable of reproducing most of the human hearing range.
Due to speaker positioning in car audio we usually use a speaker that can do 180-200Hz and up for a midrange (crossed over at 6-12 Db/octave in most Bi-amped or Tri-amped, low to medium powered systems/situations). This gets in to a great number of things having to do with expectations and proper crossover design/usage.
Of course (even with tweeters in the dash or upper door) if you only have an available stock location for a 6-6.5" in a door (like in a Nissan truck for instance) you definitely need that larger cone for bass.
To be quite honest, if a system has proper, dedicated subwoofers, midbass speakers AND proper crossover and amplifier gain settings..a THREE inch could suffice as great midrange.
So IMHO the simple answer to what size may be best is:
It depends on the available speaker locations first and the scope of the system design second.

I hope this helps :)
GL on the system. I had 27 brand names in my IASCA rig :)

JM

---------- FOLLOW-UP ----------

QUESTION: Hi Jerry,

Thanks you for responding, very informative answer. I am considering to turn a 4" componant system into a 3 way semi-active system.

I was thinking to run 6-6.5" woofers off one amp and run the 4" system as a midrange and highs instead, in passive form. However the complication with this which I am most worried about is, whether I need to build custom passive crossovers for the 4" midrange and tweeter. I dont think I can use the factory crossovers supplied with the component set as it covers the whole frequency range, thus allowing the 4" speaker to produce low frequencies.
Perhaps I can cut the frequencies of the 4" speaker so it remains in the midrange and make use of the factory passive crossovers. I wouldnt want to venture into the world of custom passive crossovers, it would cost me too much and the headache would not be worth it. Im not very keen on running full active too, as this would mean a lot of tuning and a very heavy trunk.
Regarding speaker locations, I will be installing them in fibreglassed pods, so space is not really an issue.

regards, Tommy

Answer
Hay Tommy.
Glad to be of assistance.

To be honest... for accuracy's sake you will have a lot of tuning (either way).

Since most vehicles are pure poop (for listening rooms), I prefer Butterworth active crossovers for most situations in mobile audio due to the fact that you can tweak it easily. Passives will due just fine but you can spend months testing them out.
My Nakamichi actives weigh about 7 ounces each and if an amp has a built-in crossover it barely adds a few ounces to the amplifier weight.
A decent plan for a passive system usually starts with an active one that is adjusted to where it needs to be then is rebuilt passively. If you have a Real Time Analiser it can really speed things up either way.

My advice would be to start with actives for at least part of it and then (using the performance/results of that data) create a bandpass filter for the 4" mids.
How high they should go will depend on the mid/tweeter locations/directions AND how well the tweeters do low Freqs. If you get a pair or tweeters that go down to 500 Hz it changes everything about the bandpass filter for the mids (over a tweeter that only goes down to 2500 Hz, for instance).


cheers and have fun!

JM