l see most midrange drivers with no enclosure. how low before a sealed box starts playing a role.

 

Every mid will be different. My 4" cone mids are in .015ft3, and are playing from 200hz and up. I know some cone mids are recomended to use no enclosure at all (like the Hybrid Audio 3).

What mid are you using? Is it a cone or dome?

 

I've never really searched for the answer to your questioned, but I'll give you my opinion.

Frequency really is not the issue that determines whether or not an enclosure will affect the driver.

The VAS of the driver is the primary predictor of whether or not the driver will be affected by an enclosure.

For example, I have Focal 3W2Be's and they only play down to about 180 Hz if in an enclosure about equal to the drivers VAS. If the driver is mounted IB or in an enclosure 2X to 3X VAS, well you don't want to play it 180 Hz.

Some tweeters actually port the air behind the cone. Some would say the BL and flux field is the major change but it also changes the air spring for the tweeter cone.

Although the air behind the cone of a tweeter may act as an air spring/enclosure, most tweeters will not specify a VAS.

Meaning that you can mount it in a box or not in a box and the box enclosed air volume will not have an effect on the cone.

A typical tweeter, which normally does not need an enclosure, will play 2k Hz to 25k Hz.

Mean while, my 8" driver can play to 8k Hz and it's enclosure dependent.

My 3" mid plays to 12k Hz and it's enclosure dependent.

Some 3" dome drivers are enclosed similar to a tweeter and are not enclosure dependent (because they are built with an enclosure) and play 300 Hz to 6k Hz.

Planer drivers really have an enclosure designed into the driver, so as a driver, it does not need an enclosure. Depending on the size of the planer driver, it may play down to 25 Hz and up to 40k Hz.

So, IMO it depends on the driver and its VAS not what frequency that is being produced.

 

if drivers share an enclosure (usually an issue in home audio.. not so much in car audio) I would not want my mid to be affected by the excursion of my mid-bass driver.

An enclosure goes a long way to 'voicing' a driver so the proper enclosure size for a system is important (a slow mid-bass would sound great with a non aggressive HF driver but it would sound less good with a highly detailed upper-mid and HF setup)

 

my tweeter is completely sealed
my midrange vas is 5.8. it responds well from 100 to 5000 and is a cone and res is 65.

l will put it in the dash and run it from 3.2khz to well my enclosure can only accomadate barely 2 litres. hoping to cross over at 160.

assuming the higher the highpass the less vas l need.
they recomend 7 litres but i wont run it that low.

 

Based on the info you provided, your driver is looking for IB or a very large box relative to the driver size.

You may find the driver to have a colored sound if used in the enclosure size you are providing for the frequency range you want to reproduce.

 

l believe the 7 litres is to achieve a 60hz roll off. l have no choice of volume if l go dash. if l go IB l guess the crossover point will be the limiting factor of exceding the limits of excursion.