ProAc 2.5 clone tuning thread #3242

[n_martin]

Maybe some of you can help me.

I built the Proac 2.5 clone, with the troels modified crossover (+notch filter). I am new to diy loudspeakers, and audiophilia in general. In fact, the only real hi-end speakers I have heard recently are my step uncle's Acoustat 4+4 (full range electrostatics), and some good dynaudio speakers at some point.

I am having trouble tuning these speakers.

- at first, the upper midrange (vocals, mostly) seemed distant and far away, while sibilants were unnaturally harsh. Adjusting stuffing did not affect this, but I switched the polarity of the tweeters and everything sounds much better in that sonic region. I am not sure if I corrected a mistake or caused one in doing this, but it sounds much nicer now.

- the big problem I am having is mid-bass. I bought a flared port tube that requires a 5" cutout, and the calculated length that the port manufacturer recommended was longer than the box allowed. Since I had already cut the hole, I installed the tube without the inside flare piece, cutting it to a length that seemed to sound good.

- what I have since been adjusting is stuffing. It seems that if I add too much stuffing, the bass is muffled, but relatively continuous (ie not just one infra-sonic thonk from bass drums but a musical note). However, this amount of stuffing makes everything else sound congested, with reduced dynamics and notes that seem to decay unnaturally fast. Actually, everything sucks when I do this.

- If I have too little stuffing, the midrange and treble sound great, but mid-bass is totally absent, or rather, there is no integration of middle and low frequencies. There are pretty violent bass sounds on some recordings but it just doesn't sound right top to bottom.


Is my problem the port? Should I install the suggested 3"diameter x 5.5" length and go from there?

Or is this a problem with my amp/related equipment? My system consists of:
digital: squeezebox / giga lab moon dac (NOS) (huge improvement over SB)
analog: Technics 1200 / shure m97 / bellari vp 130
integrated NAD c325BEE

Other info: the boxes I built were slightly larger than specified, but I think that bracing and other materials bring it into the correct volume range. I have not built bases for them yet, but plan on casting some concrete plinths for them. I have installed the 3/4" sound barrier material from parts express on the top, sides and back, down to the level of the port tube (about 14") but not further down. The boxes are pretty well braced. Stuffing is quite light around the drivers right now, but a bit firmer down low.


I get the feeling that the NAD isn't really suited to this relatively inefficient speaker and can't really manhandle it the way it wants. Sometime in the future I will try to audition some of those nuforce amps.


So what response do the wise men have? Install port, adjust stuffing, look at xover, get a better amp?