[ttan98]

Danny,

I have bought some M130 and M165X drivers from you before and I am quite happy with them. I am thinking of building a transmission line spkrs based on 2.5 way configuration. I will buy more drivers if the config. is proved to be feasible i.e. able to get below 30Hz.

I would still like to maintain the use of M130 as the mid range and I wonder I can use M130X as the lower woofer so that I don't have to apply that much Baffle step or none at all. With this config I should be able to get about 87-88dB spl min.  Would M165X be even better or do I maintain the use of M130 or M130X?

Any advice is welcome.

[Danny Richie]

The problem with a true 2.5 way design is the delay caused by the large inductor that you have to use on the lower woofer. You almost always have to compensate by flipping the polarity of it.

I once built the best 2.5 way that I could using those drivers. Then I built a standard MTM with the same drivers. To make a long story short, the MTM crushed it, and had higher sensitivity to boot.

You know, you can order any of our kits minus the drivers that you already have.

[ttan98]

The problem with a true 2.5 way design is the delay caused by the large inductor that you have to use on the lower woofer. You almost always have to compensate by flipping the polarity of it.

I once built the best 2.5 way that I could using those drivers. Then I built a standard MTM with the same drivers. To make a long story short, the MTM crushed it, and had higher sensitivity to boot.

You know, you can order any of our kits minus the drivers that you already have.

I have used your 3 drivers, t2,  m130 and m165x in OB I use a 3.3mH on m165x I don't have to reverse polarity.

Also from Troel website his 2.5way does not encounter reversed polarity, see website below:
http://www.troelsgravesen.dk/CA18RNX.htm

another of his 2.5way no reversed polarity encountered.

[Danny Richie]

Any inductor value will cause a phase rotation. Smaller ones much less so than larger ones.

A 3.3mH still allows the woofer to play well up into the range that the tweeter will cover. That is a minor phase rotation. I use bigger values than that on some two ways.

A true 2.5 way design where the woofer is only rolling in at the bottom end will usually use a value in the 10mH to 12.5mH range. And in that case you may have to reverse the polarity. And the woofers will need separate air spaces.

[Vapor Audio]

Just to add, since I have quite a bit of experience with the 130x and 165x.  Their natural response curve doesn't lend itself well to a 2.5way approach.  Because the bottom end of both drivers is already up a db or 2, once you add a full 6db of baffle step that you get from a 2.5way, you'll end up with a very bass heavy presentation. 

I did do one build where I used an MTM of 130x's on top (with no BSC and wired in series), and a single 165x on bottom in it's own air chamber as a .5 woofer essentially.  I didn't save my network, very unconventional but it worked well.  It wasn't a 3-way because there was no highpass on the 130x's, and the 165x's only job was to handle BSC.  Because of it's slightly lower output sensitivity compared to the two 130x's, it ended up being between 3-4db of BSC which is what you want.  I think the 165x network was a 6mh with a 3ohm resistor after to shape the knee. 

[Danny Richie]

When I design with those drivers I typically use only 3 to 4db of BSC as well.