Disassembling New Large Advent (NLA) Tweeters

[Pete B]

I've been interested to see if it is possible to open up a NLA tweeter and replace the ferro-fluid,
the quick answer is that it does not seem to be practical. I have a pair that are badly burnt
from being over driven and these are the test subjects.

Step 1. Desolder the Lead in Wires

Step 2. Remove the Metal Grille
I did not think that this could be done in a non destructive way so I just started prying,
then I thought to apply a heat gun. This is a very powerful unit for stripping paint and I have
to advise not to use the high setting which burnt the red paper part but finally the grille is off.
Note that these were so badly overdriven that the lead in wires probably started to glow red
hot as you can see (green arrow on the right) a burn mark in the red paper. The rest
of the burn marks on the left and center dome are from the heat gun.

Step 3. Pry and Cut Under the Perimeter to Release the Red Paper, if the paper was not so
brittle one could look for a release chemical for the glue but rather this seems to be hopeless.

Issue 1. The issue that I see in removing the dome is that unlike most paper cones the red
paper is VERY brittle, note the cracked paper indicated by the lower green arrow and the cracks
all around the perimeter. I'd expect paper to tear not crack:


Issue 2. I've found in testing these that the fundamental resonance Fc is not at all consistent.
My initial guess was varying degrees of ferro-fluid decay but now I believe that it is the degree to which
the paper has hardened with age.

Here's a picture of the voice coil windings some on and other off the metal former, all are burnt to
the point of shorting:


Another view:


People, including myself, have reported cracked holes in the domes and I always wondered why it
happened. It seems that the paper has just become too brittle and I don't see any simple way to
restore these tweeters. One could sample and test enough of them to find a solid pair that are in spec
for situations where originality is required but otherwise a modern replacement is the best option IMO.

 

[sparklow]

Those are some toasted tweeters. Have you given thought to a specific replacement tweeter? I have two spare tweeters set aside for my NLAs but the day might come when a modern replacement is required.

 

[Doug G.]

When I first started reading about Advents, I believed it was only the woofer cones that were formed from a slurry and molded into their shape through vacuum. However, I think the tweeter cones were made that way, too. A slurry molded into shape. That's probably why they seem brittle compared to regular paper. They seem to be almost more like a thin, molded, plastic but not as strong as plastic.

Thanks for showing us what the new Advent tweeters look like inside. I imagine the original ones are similar.

Doug

 

[Pete B]

Yes, I seem to remember reading that also for both drivers but I've never read or
heard anymore detail. I'd be very curious to find out what the formula is that went
into the blender. I once heard something about a blender and paper bags but that
might have been speculation. Was there some Elmer's glue in there also, haha?
Also wonder how the molds were made.

Yes, I'd imagine that the OLA tweeters were made in a similar way but without
ferro-fluid. I've only measured one pair and they had a much lower fundamental
resonance around 750 Hz IIRC. The pair were from my family's set that were
never over driven.

 

[wallacefl]

It’s been quite a while ago but I remember seeing the fried orange tweeter frequency response and it seemed to look similar to the Scan Speak 9130!

 

[Guido57]

Those are some toasted tweeters. Have you given thought to a specific replacement tweeter? I have two spare tweeters set aside for my NLAs but the day might come when a modern replacement is required.

I've had thoughts along the same line, but with the idea that a modern tweeter could offer better performance to go with the bass capability of the Large Advents. After considering what it would do to resale value of my bull nose units I decided to pass on the project.

It’s been quite a while ago but I remember seeing the fried orange tweeter frequency response and it seemed to look similar to the Scan Speak 9130!

Might work well, but you'd most likely have to at least tweak the crossover to get the most out of it.

 

[Pete B]

We should basically look for a 1 - 1.25" roughly flat response tweeter with an Fc of
750 ish for the OLA and 1.5K for the NLA.
The NLA tweeter impedance is too low as I've mentioned here so it would be
worth fixing for a better system impedance or just convert them to something
closer to the OLA with a new tweeter. The second order network on the OLA
is better but you need to select the right tweeter.

 

[Guido57]

@Pete B wouldn't Fc of a tweeter be irrelevant as most are closed back or am I thinking of the wrong parameter? Did you mean Fs? Please enlighten.

 

[Pio1980]

Definitely candidates for an Econowaveguide conversion.

 

[Pete B]

@Pete B wouldn't Fc of a tweeter be irrelevant as most are closed back or am I thinking of the wrong parameter? Did you mean Fs? Please enlighten.

Fc is the closed box resonance, tweeters are closed in the back so we want the
low frequency in system rolloff to be the same.

I did a Large Advent Econowave and didn't find a major improvement over the original,
I A/B ed them with a switch. I don't think it is worth the money or effort without a more
significant re-voicing.

When using a replacement tweeter in the OLA it should be mounted with a spacer so
that the face plate is flush with the grille frame. With the NLA it should be flush
mounted so that the grille does not hit the faceplate.

 

[Guido57]

Definitely candidates for an Econowaveguide conversion.

Which is essentially a tweeter replacement.
A pair of bull nosed Advents can fetch maybe $250 to $300 with cabinets in good shape, say 9 out of 10, depending on how long one wants to wait for a buyer.
Econowave them, at a cost of $200 plus per pair, and get maybe $150(?) for them unless one wants to possibly wait much longer. I could be mistaken but I think most people who want Econowaves would rather DIY.

I did a Large Advent Econowave and didn't find a major improvement over the original,
I A/B ed them with a switch. I don't think it is worth the money or effort without a more
significant re-voicing.

Between the variants of the crossovers and compression drivers available I think it's likely there should be some tweaking involved in getting the most from an Ewave.
I'm of the opinion that Ewaving Advents is largely about putting a modern crossover and tweeter together with a woofer that has stood the test of time better than the other components of the speaker. My limited experience is that this can be achieved through other modifications besides the Ewave; not that I haven't been tempted to Ewave my utility cabinets.

 

[Pio1980]

The New England school midwoofers tend to be all excellent, the trick with a two-way is getting an HF driver with enough LF crossover power margin to integrate with it. The E-wave with the recommended components can do that, and get the most/best of the mid-woofer.

 

[Guido57]

The New England school midwoofers tend to be all excellent, the trick with a two-way is getting a HF driver with enough LF crossover power margin to integrate with it. The E-wave with the recommended components can do that, and get the most/best of the mid-woofer.

I agree. My point is that unlike the era these speakers came from there are a lot more tweeters available today are up to the job and available at a not too unreasonable a price.