Speaker Asylum

Posted by Timbo in Oz (A) on September 23, 2014 at 15:28:14

In Reply to: RE: We are going to try the 1st order acoustic slopes only, first. posted by Presto on September 23, 2014 at 08:53:04

Also see my response to Inmate51.

My budget is likely tiny compared to yours, it will only dribble in. I am very happy that I will have access to an RTA, laptop, measurement mike combination, and an experienced spkr builder!!!

Phase 1 is one pair of the WR driver spheres and 1 pair of the bass-only spheres close to the floor. Ph. 2 is adding a second pair of bass spheres in a vertical array. Phase 3 is to put Mangers in reduced VB spheres into the array.

Clearly, I'll be doing a lot of learning!

If I find that a transient accurate (TA) crossover is not possible with these items at 170 Hz, I think I'll be able to live with that. I do hope to be able to stick with a 1st order HP for the Mangers, in the hope that they will be TA from the midrange on up, at least, or seem to be!

Can the Manger driver do it? I've corresponded with JC Morrison - he used to post here a lot - about using the Mangers in an 8L enclosure, HP'd 1st order at 150 Hz, AND with a small valve amp of no more than 20 watts. He believes it will work quite well.

There may be a BDS issue but we can compensate for that too, at line level, with two pots a mike and an RTA and ears. It is entirely possible that the final HP acoustic slope will NOT be a pure 1st or 3rd. A good blend and clean behaviour when loud is the target.

The existing WR driver is a Coral Flat5/III. In its small (15L Vb) sphere it is flat to an octave below 170Hz from its BDS up near 300hz. The port tuning is 60 Hz IIRC. So there would be a 1st order HP slope at 170 Hz, kneeing down at 4th order from 60 Hz. If we sealed the encl. we should get a summed slope approximating to 3rd order, when summed with the 1st order passive-line-level PLL input filter on its amp's inputs.

If we find that there is a problem with the smaller sphere's kneed slope blending with the two bigger sphere's slopes, we can try sealing the small spheres.

Using a spare 2nd order active crossover - which is being blue-printed to get a matching 3rd order LP for the bass.

It is possible to use asymmetric 1st/3rd order slopes in such arrays. So we may try them as we move along.

The active crossover can also be used to HP filter the Mangers more steeply. But I hope I don't have to.

The mid-bass driver in the larger spheres (were 2-ways) is a Foster FW 202. These larger spheres are flat from around 40 Hz to 3.3Khz and then roll-off cleanly.

The enclosure's sensitivities do match at the crossover point. At 170 Hz I wouldn't expect there to be a LOT of mismatch for dispersion and room-sound. I also have two, same model, matching voltage gain power amps. rebuilt/modernised LEAK St20s. So, I decided to try matching line-level HP and LP, 1st order input filters.

Reviews of both the 2-way Audiospheres and the Leaks are here at AA.

LBNL - with the 2-way spheres, since the early 1980s I've been consistently detecting polarity, and switching for it. Yes, most of what I listen to is acoustic music.

For me the central take-home concept about music, how we hear it and are affected by it it is the primacy - for us - of starting transients aka attacks. Way more so than the continuous tone - for those instruments that actually have a continuous tone. This fits rather neatly - IMO - with polarity mattering.

I do mostly listen to acoustic music, and prefer simple stereo miking.

Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger

Edits: 09/23/14   09/23/14