Would like a better understanding of a 2.5-way design

[tf1216]

Hey guys,

I am not quite clear on how one implements a 2.5-way design. Is it absolutely imperative that the two midbass drivers are identical? What if the two drivers in question were from the same manufacturer but they had different motor designs, ie. underhung and overhung motors?

Can this be accounted for in the crossover design or would this then mean the speaker would have to be a 3-way or you are SOL?

[sreten]

Hi,

It is a lot easier if the two drivers are identical. If they are not it
is more complicated but still possible. It will be easier for the
different drivers to have separate airspaces but if they do share
the same airspace it is more complicated, and may not work well.

Really depends what you have in mind ...... or the drivers ......

/sreten.

[tf1216]

Thanks sreten.

Here is what I have in mind. Currently, I have a 2-way with a 7" driver. The 7" driver does not play very low in a sealed cabinet. I was thinking that if I added another 7" driver (overhung motor) to the mix if it would allow me to keep the save crossover configuration.

Probably be easier to just design a 3-way?

[sreten]

Hi,

Is the 2 way fully BSC'd ? In that case a subwoofer may be easier.

If the 2way is not BSC'd at all then its a candidate for a 2.5 way.

One option is adding a vented extra driver, (separate air
space obviously), in this case it may not necessarily need a
longer excursion driver, only modelling can really tell you this.

An example : http://www.humblehomemadehifi.com/Auriga.html

Note for the above case the driver is not really suited to sealed box
loading (except as a satellite for subwoofers), and in fact the whole
arrangement gives no more bass depth than a vented 2 way.

What is does do is have 6dB more voltage sensitivity (albeit 4 ohm)
and higher maximum bass levels as you have two bass drivers.

Shown is a typical current 6.5" unit actually designed for vented
loading in a sealed cabinet versus a larger vented cabinet :

Note a 3-way with 7" mid is likely best designed with no BSC
on the 7", this being filled in by the bass drivers overlapping the
mid unit somewhat, see :
http://www.deadwaxcafe.com/vzone/david/david.htm

For the vented box most of the extra work is done by the port in
the low bass region and output is equivalent to 4 sealed drivers.

/sreten.