Heybrook HB2 overhaul

[VantheMan]

Now that Audax have come out of hiding in the pro world, they have made replacement voice coils available for the tweeters on my Heybrooks so I am going to tinker both carpentry-wise and, if necessary, with the crossovers.
The crossovers have those Elcap black and red resin ended caps and some Polys by Pro Cond. Falcon would seem to have drop in substitutes for the Elcaps in the form of blue Alcaps but if the polys have drifted, any suggestions on which to use (in the spirit of Peter´s design, if poss.)?
I don´t really expect these HB2s to oust my WD25TExs but I like to live dangerously.

[Shane]

Can't comment on the caps, but I do remember the big problem with the HB2 was the bass units. The rear-facing port was concentric with the bass unit, and had a plastic pipe bracing between the port hole in the back panel and the back of the magnet, with a bitumastic pad between the two. Trouble was, the length of the pipe and the depth of the rebate it sat in were a bit variable, which could result in the rather flimsy pressed steel bass basket of the bass unit distorting as the mounting bolts were tightened, which in turn drove the voice coil off centre. Added to that, the bass unit had a very heavy magnet assembly, so any shock in transit could exacerbate the problem. If you're going to have a go at the cabs, care is needed to get the right balance between bracing the bass unit and distorting it. Other areas to look at would be checking that the bitumastic pads are still attached to the inside of the cabinet walls. They were stuck on after being softened by being gently toasted in front of a calor-gas room heater (very nice for us in winter, as the shed they were built in was a bit draughty), a process which was also subject to a certain amount of variablity!

My sister-in-law has a pair of these in a room around 25' square. It never ceases to amaze me just how good they sound. I'll be interested to follow your progress.

[VantheMan]

Bracing the bass units should be no problem - the cabs originally used a disc of "pressed foam" - the thin white stuff used in packaging electronic goods - between tube and magnet and I´ll draw on the black goo that I used in my WD25Ts for the same function. The bitumastic pads are all in position, no probs there.
I just need to know if the mix of lytics caps with polys is vital to Peter´s design and if so, which polys to buy to emulate the ProConds that were originally used. Mine are still within tolerance (+-20%) but only just and I would like to find a substitute . The Elcap lytics have drifted way out of tolerance and so the Alcaps that Falcon sell are a no-brainer. Someone said on DIY Audio and about a Kef 104 Xover which also used Elcaps and polys that using Alcaps throughout was OK but could be bettered by mixing in some film jobs called Carli Mylar that Madisound sell but I fancy something easier to get.

[Greg.]

My advise based on my own experiences is to not use electrolytic caps at all and use only polypropylene. This should bring a significant upgrade to the sound. Admittedly polyprops are dearer and bigger, but in my view, well worth the effort. If I was doing this, I would get the crossovers out of the cabinet, separate the treble and bass filters and mount in a box that then sits on the floor just behind the speakers. This approach really made a massive difference to the sound of my WAD KLS3's.

Below is a picture of thee separated filters for the treble and midrange units for my speakers which should give you an idea of what I mean.



For completeness, the next pic is the bass filter in a separate box. Note the fat polyprop caps that replaced the lyrics.

[Shane]

Separating the elements of the crossover isn't quite so easy in the HB2, Greg, due to the little network Peter put between the two drivers, (which I think was to smooth out the phase response, but I could be wrong). You'll see what I mean in the circuit diagram in this thread from diyaudio. Note though that the rest of the thread is complete tosh! The values in the diagram are correct, there's nothing wrong with the op's crossovers, and for the record, every pair of speakers that left the factory was subjected to a critical listening test!

http://www.diyaudio.com/forums/multi...ok-hb2-xo.html

[VantheMan]

I´ve always got my Wd25TExs if I want clarity and precision so I reckon I´m going to go for the 50v drop-in Alcap lytics that Falcon offer rather than risk a change of voice using polys. I´ll try and swap like for like as far as poss. Just as a tribute to my mispent youth. All I need now is for me to prefer them to my WDs, after all that sweat and toil. I know someone who will without even turning my amp on - she always said they looked so perfect on their HBS1 stands not like the big "sarcophagi" that dominate the room now. The listening sessions for the Heybrooks will have to be held in secret.

[VantheMan]

Well, the crossovers are done and the new voice coils ready to be fitted. Only a couple of questions : What do you think I should do regarding the yellow foam, sadly disintegrated into a pile of dust, that there was between the soft dome and the tweeter itself. What density might it have been ? should it be formed/cut somehow into a half sphere shape ? What does it do ? and lastly, might the tweeters have been connected out of phase ? I didn´t take any photos.

[Shane]

Originally Posted by VantheMan

Well, the crossovers are done and the new voice coils ready to be fitted. Only a couple of questions : What do you think I should do regarding the yellow foam, sadly disintegrated into a pile of dust, that there was between the soft dome and the tweeter itself. What density might it have been ? should it be formed/cut somehow into a half sphere shape ? What does it do ? and lastly, might the tweeters have been connected out of phase ? I didn´t take any photos.

Can't help you with the foam, but the tweeters were definitely connected in phase.

[VantheMan]

Thanks Shane.
The more I think about the foam insert inside the dome; is this normal practise ? and if so how come domes tend to get pushed in by tiny fingers and stay that way unless the foam has disintegrated ? Or is it to tone down the fizz ?

[VantheMan]

Hi Shane,
I was just wiondering re. the importance of the foam stuffing in the HB2s. Like a prat I took mine out years ago and stuck a gooey Spectral Dynamics mat thingy on the rear baffle on top of the asphalt pads ( following articles by Jimmy Hughes in HI-Fi Answers at the time). I must say I didn´t notice any adverse effects, resonances wise then but after reading your comments on the HB3s filling, do you think I should go back to using acoustic stuffing foam - I vaguely seem to remember the HB2 was positively bursting at the seams with the stuff.
Chris