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Is the 2.5 way speaker the ideal home speaker?

Time for what I hope is another fun thread. 

One type of speaker which is actually pretty common but which gets little press / attention here on audiogon is the 2.5 way. 

A 2.5 way speaker is almost a 3-way, but it isn't. It is a speaker with 3 drivers, but instead of a tweeter, midrange and woofer (TMW) it lacks a true midrange. The "midrange" is really a mid-woofer, that shares bass duties with the woofer. Often these two drivers are identical, though in the Focal Profile 918 the midwoofer and woofer were actually different drivers with the same nominal diameter (6"). 

The Monitor Audio 200 is a current example of the concept, but I am sure there are many others. It's also quite popular in kit form. One of the most high-end kits I know of is the Ophelia based on a ScanSpeak Be tweeter and 6" Revelator mid-woofers. I haven't heard them, but I am in eternal love with those mid-woofers. I believe the original plans come from the German speaker building magazine Klan Ton. 

However many other kits are also available

But regardless of kit, or store purchased, are you a 2.5 way fan? Why or why not? 

Best,


Erik 
erik_squires
erik_squires OP
16,892 posts
 
Hi @kijanki - I think you are confusing an open baffle and beaming.

Open baffle speakers behave like you describe, with a complete null at the sides. Boxed speakers do not.

The issue with frequency vs. angle is not related to delays, phase shifts or comb filtering, since the sound is coming from a single surface there cannot be any (unless it breaks up and stops acting like a single surface).

The reason you have "beaming" where the frequency response rolls off to the sides is due to the surface area. The larger the driver, the lower it will beam. This has more to do with the waveform. At very low frequencies, the wave is like a semi-sphere. It radiates in all directions, but at high frequencies it is flat, and mostly travels straight ahead.
 
erik_squires OP
16,892 posts
 
Hi @donvito101 -

The term 2.5 way is a term of art. The difference is in the filters on the upper woofer. Here it is:

2.5-way : Has NO high pass filter.
3  -way: Has both a high pass and low pass filter.

What is confusing is that in both a 2.5 and 3 way there are 2 crossover points.
kijanki's avatar
kijanki
4,477 posts
 
Erik - why you ask if you already know the answer?

kijanki's avatar
kijanki
4,477 posts
 
http://audiojudgement.com/speaker-lobing-polar-response/
erik_squires OP
16,892 posts
 
Let me get a little more basic. Typically when you read about a "crossover point" in a speaker, you are actually talking about 2 filters:

A low pass
A high pass

So a 2-way speaker has a crossover point of 3 kHz. That means there’s a high pass filter that goes to the tweeter tuned to 3 kHz, and a low pass filter that goes to the mid-woofer that is also tuned to 3 kHz. I should point out that reality is even messier than this, but let's stay away from that.

A 3-way speaker has 2 crossover points (say 300 Hz and 3kHz) and 4 filter sections.

1 - HP to the tweeter
2 - HP and LP to the midrange
1 - LP to the woofer.

This adds up to 4 sections.

A 2.5 way also has 2 crossover points, but is missing 1 filter section:

1 - HP to the tweeter
1 - LP to the upper woofer
1 - LP to the lower woofer

That missing HP filter allows the upper woofer to play all the bass.
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