Looking for Audax HD20B25H mid/bass Driver

Yeah i think that's the problem all round. I'm going to remove baffle and upgrade the areas with new closed density foam strips. I also think I haven't sealed the driver to the baffle very well sob I'm going to look for some kind of sealant gel type stuff. I have a product I use on my camper called Sikaflex which is a flexible black sealant I may put a bead of this round the join between driver/baffle too. In general I think you remotely diagnosed correctly and it is leakage. Old men and old speakers suffer same condition :)
Wish I could hear this speaker! I'm not sure the problem here is the woofer gasket. SEAS drivers do take some breaking in, by all accounts. Honestly, a piece of cardboard cut from a box of cornflakes would do as much good. :D

We have severely winged it on the crossover, which we think is this:


I don't like it much. Maybe it works with the original woofer, but we are in entirely new territory with the SEAS replacement. But do note the tweeter is wired in negative polarity.

Problem I see now is excessive brightness at crossover. This loudness may be making the bass appear to be lacking. FWIW, closed box probably works best close to the wall, which always adds bassyness. Closed box also benefits from stuffing material, like a pillow.

I was hoping we could avoid crossover mods, but these appear to be necessary. It was always on the cards that tweeter level might need adjustment, and that is just a question of changing the 4.7R. The capacitors could benefit from swapping round too, IMO. Better impedance. The tweeter circuit is actually then quite conventional Celestion style.

I would prefer a more conventional bass circuit like the one below too.

Really, I'm just gathering thoughts here. Let's mull this over. But this isn't hard to fix, IMO.


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    Lentek Mods FR.JPG
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  • Lentek Mods Circuit.JPG
    Lentek Mods Circuit.JPG
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Just a bit more detail, (bear with me):
I'm convinced (albeit it may not affect the woofer issue that much) that there is not a 100% seal round the driver to baffle. Although I did apply tape, I haven't totally covered the fixing areas round screws.

When I place my hand over tweeter there is very little bottom end coming out the woofer and little to no "movement" of the coil even when cranking with heavy dub bass or punchy bass.

I didnt touch the wiring of the tweeter from the crossover. I did replace the Red/Black wires coming in from the terminals as they were very tatty and breaking but i matched the red/black possie/neg to what they were originally.
What i have assumed in respect of the red/black wires coming from the crossover to the woofer is that the red wire went to the plug, on the driver, that was marked (painted) in red. if this was the wrong way round would that affect the woofer polarity? although I would have assumed that a connection painted red would mean red wire needed attached to that post.
I really don't think the gasket is making much difference. :)

If bass is lacking, you might suspect that somehow you have wired one of the woofers up in negative polarity.

Then the bass sort of cancels out, or it just sounds phasey.

Simple test. Switch off and disconnect the amplifier. Find a 1.5V penlight AA or AAA battery. When you connect positive to positive on the speaker leads, the bass should move forward.

On both speakers. You follow?
Running the balance control full left or right would have ruled out a phase problem. The bass would be there on left or right but not in the middle.

Stubbs04 you said one of the Audax woofers blew out. What did that mean? what happened? Crossover, amp damage or just a driver failure?

Those woofers should have bass if properly installed in those cabinets. The crossover shouldn't have any affect on the bass range, mid-range yes, bass no.

I thought if anything might go wrong with putting in these woofers, I would have expected a mid-range issue not wimpy bass.
They are totally goosed. The front plate on the magnet is warped and split from the test of The magnet. There's no way that one could recentre a voice coil.

So I went back and looked. So did it get dropped? If it shorted out the voice coil that could cause problems with an amp but I'm grasping to see how that would just affect the bass. There is an otherwise good speaker company here in the States who used some crappy epoxy on the magnet assembly of a certain driver which is now famous for it's shifting magnets. Once they got older even a small bang would break them loose.

The red wire from the crossover should go to the red dot on the woofer.

Did you mount the woofer on the front of the board or into the rebate on the inside surface?
When I bought the speakers second hand I then noticed the woofer issue. I've no idea what caused it but there did seem to be water damage of some kind but nothing really obvious.
I mounted the drivers to the front of the baffle. They are too wide to fit the same as the Audex drivers were.
Tomorrow I'm going to double check polarity and apply some gasket to cabinet see what happens.
Yay! Bass! If you just can't get a decent seal with the foam tape you could resort to latex caulking as used around sinks and bathtubs. It comes in black and if necessary you can remove the driver by running a single edge razor blade around it. Since you can remove the whole front panel on the S4's, being able to easily remove the woofer isn't a deal breaker.
Once they're sorted and broken in be sure to report on what you think.
stubbs04, if your wooden baffles are so severely damaged by water ingress, which you didn't think to mention initially, it is probably time to replace them, rather than messing about with gooey sealant! :confused:

AFAIK, these excellent replacement SEAS P21RE/P drivers come with a gasket:
Seas P21RE/P H0942-08 Woofer. H0313 2015 remake

Diyaudio is a hobby. Which, by definition, is an INTERESTING waste of time. :D

I've been doing this stuff for years. I think you now need to learn about woodwork. You need new front baffles, cut to size for the enclosure and drive units. IIRC, B&Q will do this for you. You might have to buy a jigsaw and a drill to cut the holes.

As it goes, those Audax tweeters are ancient and unreliable. I would fit these new babies:
H1499-06 27TBCD/GB-DXT

I would then redesign the crossover. We are in it for the long term.
Latex caulk is a last resort. Just get them sealed and then listen to them and see what you think. You've already spent your budget and everything was OK until the woofer broke so just evaluate them for a while.
For what it's worth, I have, I think, 4 pairs of those tweeters. They work just fine.
Chris, you may not appreciate that you can go to a hardware supplier called B&Q in the UK and pick up a piece of chipboard or some offcuts, and if you are nice to the people in the woodwork section, they will use a fantastically expensive and precision saw to cut things to size. :)

I think you get 6 cuts for free, but I have always found these people helpful. I rarely spend more than £10 on this.

This should be an end to all this awkward sealing. Cutting driver cutouts with a hand jigsaw or fretsaw is easy. You drill a start point and follow the marked circle.

Where it gets even better, is with some forward planning and measurement, you could then upgrade this 8" plus 1" speaker to a three way:

Built around a £58 each SEAS MCA12RC in about 2 litres of wooden box stuck on the back of the baffle. You'd mount the woofer low in the box. No reflex necessary here. H1304-08 MCA12RC

Of course it would be nice to use the recommended SEAS 27TFFC: H0881-06 27TFFC

But I am sure you could use the Audax tweeter. IMO, rebating and edge mounting is optional. I don't think it makes much difference.

Trust me on this. A three way is in a different league from a two way. Goes loud without effort or distortion. So leave the option open! :cool:
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Posting on another forum, I bumped into CM6, who told me about this thread.

I’m wondering how you got on with those replacement drivers as I too have an issue regarding some old HD20B25s. Do they sound good?

The issue I have is that the surrounds on mine have shrunk. They are modified for the speakers they are in, so I’m keen to ideally have the surrounds replaced so that I can keep them. There is however quite alot of uncertainty at the moment as to what material exactly the surrounds on mine are made of, and what a suitable replacement material would be so as not to change the sonic properties of the driver, or at least not too radically from original spec.

Mine appear to be early iterations with a light coloured surround, that was apparently a kind of pvc that was quickly identified as one that shrunk with heat exposure, so all the later and more commonly found examples have the black pvc surrounds.

Do any of you know of any experts in the field of vintage speaker surround replacement based in the uk? I’m also in Edinburgh by the way.

Thanks in advance, Dave
Thank you to the mods for opening this thread And to the members for sharing valuable information.

I am trying to replicate the crossover of the Tangent RS2 (KEF T27 + Audax 8" HD20 B25J). So far have been successful in sourcing the Audax 8" driver + the T27 from Falcon.

Would really appreciate any guidance on the crossover and if any improvements needed over the original.

Thanks in advance!