Tweaking Sextets.

Peter,

I asked ages ago if you wouldn't mind answering questions about some of your old 'speaker work. As requested, I've put it in this forum.

I have 'Mk1' Heybrook Sextets that were later upgraded to 'Mk4' spec. with a new bass driver and crossover and, apparently, extra stuffing in the bass enclosure. The crossover diagram is as attached (values kindly confirmed by Guy Sergeant).

Years ago I externalised the crossover, and upgraded the components. The capacitors are now all Solens and the Inductors are 'Falcon' wound, and have slightly less DCR than the originals. This was a good improvement, but I want more!
Namely, more bass depth and(!) punch, and hopefully a little more midband clarity.

Each bass enclosure is well stuffed with three 10" x 8" x 2" slabs of foam and two big teased out handfuls of fibre. Each midrange enclosure is slightly less well stuffed, having one foam slab and one handful of fibre.
The 'speakers are attached to the 8 Ohm (which I believe may be closer to 6 Ohm) taps of my amplifier.

I am replacing the skinny 'Mk1' hookup wire.
I intend to experiment with the damping and try the 4 Ohm taps.
I have also thought about tweaking the tweeter's resistor up slightly to drop HF energy.
(And I had a mad five minutes wondering about cutting out the back of the midrange enclosure!)

Have you any tips or suggestions?
I am loathe to build another brand new crossover, but would welcome any suggestions for tweaking the existing values.

[petercom]

I don't recognise that xover - it looks as though it was done well after I left, but then memory plays tricks sometimes and it was a long time ago.

The original Sextet used a bass driver made specially for Heybrook in Wales and had twin port tuning with a foam lining in the ports to control turbulence and add a modicum of resistance. When the driver manufacturer went over to car audio only we reverted to a SEAS bass unit (mk2). This didn't suit the tuning quite as nicely as I remember.

The Mk 3 was tuned extensively to overcome these problems, particularly in the crossover department.

You can, by all means, increase the resistance to the Tonegen treble unit. The first Mk1s had a switch which did this - either 1.5 or 1.8 Ohms I think. The 3.9uF to the unit is highly critical of component choice. I suggest the Soniqs SAX 3.3uF plus 0.68uF (the combo is still within 5%).

How is the 125uF to the mid provided? That's a lot of Solens if it is those! I would suggest 100uF Alcap plus Soniqs 15uF and 10uF PXX if not.

Cutting a hole for the midrange chamber is inadvisable - you will change the crossover for the mid to bass too much. You could make it aperiodic, though, as I did in the Mission e82 and Pilastro by adding a short port and filling it with a spiral of our aperiodic foam. The port can be relatively small in diameter.

Once you have done that you will need to adjust the value of that 125uF by bringing it down by 30% or so. As you keep reducing it the midband clarity should increase due to the reduction in LF power getting to it. When it gets too small, however, you will start to loose the cohesion between bass and mid, noticeable on spoken male voice. Radio 4 is a good test, I find.

Experiment with the amount of foam in the bass enclosure. Reducing it might bring in a little more bass thump. Replacing it with heavy duty carpet felt could work better. It's a suck it and see approach, I'm afraid.

[NealG]

Peter, like Matt I have a pair of Sextets (MKIV's I think) they gave way to Spendor S6e's. I keep eying the Sextets wondering if the midrange could be improved, it's too veiled for me. I haven't sold them as I still like the Toingen tweeter and bass. In fact I find the Bass a little too heavy in my room, I may well try lowering the 125uF cap. How could the bass be tamed as well?

Many thanks!

Thanks Peter,
The damping is definitely suck it and see, taking a quarter of it out has given a bit more 'boomp-h', but I know I'll have to keep experimenting. And yes, the midrange of my XXO is rather large (80, 20, 20, 5) - as per Neal I may take out the 5uF and see.

I was half joking about the openback, but that's an interesting idea about the port, I'll sleep on that. For the tweeter a better capacitor is definitely in order, and tweaking the resistor up by a couple of points or so might just swing the balance.


Neal,
Can you remember/re-measure your tweeter resistor's value?

[NealG]

1R I think Matt.

[Brian]

What are the xover points for this speaker?

[A1000]

Originally Posted by petercom

.

The Mk 3 was tuned extensively to overcome these problems, particularly in the crossover department.

You can, by all means, increase the resistance to the Tonegen treble unit. The first Mk1s had a switch which did this - either 1.5 or 1.8 Ohms I think. The 3.9uF to the unit is highly critical of component choice. I suggest the Soniqs SAX 3.3uF plus 0.68uF (the combo is still within 5%).

How is the 125uF to the mid provided? That's a lot of Solens if it is those! I would suggest 100uF Alcap plus Soniqs 15uF and 10uF PXX if not.

I am upgrading Sextet Mk11 and I do not see these values at all!
I see 5.9uf (all MKT) going to the ribbon tweeter and 4.1 ohm resistance (paralleled 8.2)

I have 71.6uf across the bass driver not 125! I could also do with help on the circuit. The mid seems to be in a loop back to the positive side of the bass driver before its bypass. Paralleled with the mid, a 4.39mh inductor and then also paralleled a 2.2uf MKT cap with a 15 ohm resistor in series. Not seen this before.

To be clear, I am not tuning, just upgrading the parts. The iron core inductor, all the caps (The Ansar were probably alright but so well glued they're gone). IT;s just the mid circuit is intriguing. Have schematics and images only loading to WD seems difficult.

[jarmusch]

hi,
I am a newbie here so first greetings to you all from Hungary
now, I am a happy owner of a just recently acquired pair of Sextets - they're simply amazing. I have had several speakers before but they are truly musical performers standing highly proud of the crowd - great job the designers did, I must say.
I, however, have some questions - hence I mainly joined the forum.
that is, I am unaware of my Sextets' model identity. I wonder if anyone could help judge it? S/N are 728207 1122/17 and 18 if this helps, and they just look like any other Sextets, albeit perhaps with a slightly smaller woofer (16.5cm) with a pointed pole piece than the minority of their peers, as it appears on the available photos from the net, and there is no switch on the back for the tweeter.
also, in the X-over, which is surely untouched, the resistor on the bass circuit is 15 Ohms, and there is a blue elko on the mid circuit the value of which, just as of all the yellow polpypropylen (?) caps', which actually look to be ICWs, can't be read for them being (purposefully?) mounted with the values facing down.
moreover, I am okay with these PP caps but feel that that lone elko should be replaced for a new one, or for a PP equivalent, to make sure it won't start to leak.
furthermore, as I see the resistor value on the bass circuit is only 8 Ohms for the MkIV version I wonder what happens if I lower the value of the now existing 15 Ohms one? to note, I have no problem with the bass, just really am curious.
please advise - your input will be much appreciated

Hi,
I would also like to tweak my Heybrook Sextets and think I have the same version as Jarsmuch;as far as i can see the crossover is:
bass: 2.2uf IWC and 15 ohms (brown green, black, gold) with a coil (across them?)
Mid: 60uf electrolytic and two 4.7 and a 2.2uf IWC in parallel making 71.6uf total in parallel across the unit
HF: 2.2uf and 2.2 ohms (red red black silver gold) in series.

I would also like more bass - should i reduce the resistor - maybe by adding another 15 ohms in parallel to halve the resistance? I have no idea how the coil affects that calculation though.... can anyone help please? I have replaced the electrolytic with a solen and have some claritycap ESAs for the rest which i have not yet fitted..

many thanks, Nigel

[Black Stuart]

jarmusch/Nigel,
I have the MK1V version and have used them continuously for over 15 years now, so it's probably time I had a look at the x/over components. I hav'nt bothered because I intend to replace the passive for an active x/over quite soon.

Nigel, I'm not sure you can get much more bass from these speakers, the woofers are quite small after all. In fact I'm impressed with the amount of bass they produce - how about using a centre sub-bass unit to back up what's there.

Passive x/overs are way out of date, the theoretical basis for active x/overs are undeniable and listening to speakers with active x/overs is totally convincing.

Check out Rod Elliot's ESP site and his excellent passive v active x/over article. He also sells a PCB and you have access to software to determine values - you will also find that an active x/over is far cheaper to produce than uprating a passive one.

The Tonigen tweeters are wonderful, so clear and detailed I could not imagine using anything other than a ribbon at the top end in a speaker. Sometime soon I will get round to using the Grand Heils (thank you Andrew) that I have had for some time now.