Pete B
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Posts posted by Pete B
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@fedeleluigi There are several posts in this thread with the AR-9 xo schematic, is that one redrawn,
and the one you are looking for an original from AR? I can look on my 10 year old computer where I
probably downloaded it. On the other hand if the redrawn one is easier to read I might have just
kept that one.
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There's a good chance that they changed the spider also and rarely are they loose enough,
good that you got the correct woofers - enjoy!
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What model tweeter is in the XL, it is different from the non-XL version.
Madisound might have a suggestion, they did for the non version.
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@brianw Did you ever get plates made for a replacement tweeter?
Sorry, got distracted with other projects and never posted the AR9 tweeter measurements. Both
of my tweeters measured fine with an ohm meter. The foam gaskets were hanging off the back
and stuck to the face plate in a few spots. I pulled them off and now on tweeter measures open
circuit, perhaps there was glue on the lead in wire - don't know for sure.
Anyway, here's more on the 3D printer that I've been using:
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The YouTube person who complained about stringing got a lot of comments from other users
who pointed out that one free "slicer" program works best with the Ender printers and that's
what I use. No problems with stringing at all.
I began to have trouble with the first layer sticking to the bed after about 50 prints. The Ender
printers have a unique sandpaper like finish on the print bed, other people print on a smooth
surface, some even use glass for flatness. One of the first things you'll learn when printing on
smooth beds is that you need to help the first layer stick, many use glue stick, some use hair
spray. I did not need anything for the first 50 prints or so and I've come to the conclusion that
some of the rough surface has worn off so now I use glue stick and it works perfectly again.
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Ah okay, thanks Roy good to see you on here, all the best!
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On 2/1/2021 at 3:34 PM, sparklow said:
When I did the center cone repair on two NLA tweeters in the past I think that I could have changed the ferrofluid at that time. I was too busy trying to do the actual repair to add a ferrofluid change to the process, but it could have been done successfully I believe. Typically what are the sonic symptoms of a tweeter that require fresh ferrofluid?
Burnt FF causes diminished output and/or a rise in the moving systems resonant frequency.
Where did you get that replacement center dome?
I have a working NLA tweeter with a smashed dome.
I agree that if you cut the dome off, you can certainly add the FF inside the VC, and if a tiny
hole was cut into the VC former a needle injector could be used to put some FF on the outside
where it is really needed.
The other issue is how to remove the old FF?
I wonder if those glued on center domes have the same response as the originals.
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@Rick U PM message sent to you.
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Bump, has anyone removed a tweeter for transplant?
Also, does anyone know if there were any changes to the shape from the early AR3a to the last version?
Pete
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I tried to open them up here without much success. Is there a materials person who might
know how the paper could be treated to make it less brittle? Or was it designed to be stiff and brittle from the start?
https://audiokarma.org/forums/index.php?threads/disassembling-new-large-advent-nla-tweeters.953989/
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I'm a bit late here but very nice work. That is a very low Fc of 40.5 Hz with just the right Qtc.
I documented the crossovers and listed the NLA woofer inductor with a much lower value
than the OLA which has the powdered iron core inductor:
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@Giorgio AR Those are nice pictures of the woofers.
Does anyone know the correct part number for the AR-6 woofer? There is mention
on here that the Xmax was quite high, higher than the other 8" woofers:
Also was there a ceramic magnet version of the AR-6 woofer?
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I would guess that it can be changed but it would not be an easy job.
I have a blown NLA tweeter that I believe was driven so hard that the insulation
broke down and the voice coil shorted, then the current went way up and the
red donut part of the cone was burnt brown under the tinsel lead in wire.
I want to take a look inside and the red paper lip at the outer edge is already
lifted about 1/3 of the way around. Not sure what to use to release the rest of
the glue. Acetone or MEK perhaps.
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This is in the library as multiple .jpg s, does anyone have it in .pdf?
I seem to remember seeing it years ago.
It mentions measuring the DC resistance of the tweeter and tweeter inductors to test
for burnout.
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Here's 18 TPI Irish Linen:
https://www.123stitch.com/m/18-Count-Linen-style-Cross-Stitch-Fabric
Discussed many years ago in this thread:
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I thought that someone found a source for very similar 16 count grille cloth.
I don't remember where it was mentioned.
There's 12 and 13 TPI here and they look close buy maybe not in real life:
https://dorrmillstore.com/index.php/site/products/category/foundation_cloth/17
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You can try suction with a hose of the right diameter.
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Is boiled linseed oil usually that dark, or does it come in different tints?
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I'm aware t hat the original material cracked, but how do you get the tweeter guts
out to glue into the new piece? Solvent? Heat? Crack it off?
Anyone have the .stl file?
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Enter 40 uf and 1.37 mH into this calculator, and you'll find that they resonate at 680 Hz which is
probably the fundamental resonance of the UMR:
https://www.omnicalculator.com/physics/resonant-frequency-LC
The L and C reactance cancel each other at resonance and you have a short (ideally) with a series
resonance circuit or RDC of the L plus ESR of the cap at that frequency plus the 6 ohms in series.
Call it 7 ohms which is probably the amount required to flatten the impedance, they might over or
under compensate to shape the response curve as required.
Note then that the 24 uF series cap forms a first order network to the UMD, which does not
provide much attenuation at low frequency. I suppose that they get away with it due to the
higher crossover frequency as compared to the AR-3a/AR-11.
Is it correct that all of the drivers are in phase?
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Sorry to be so late here updating
Mine is also from B-A (something like Burnstein Applebee) without the electronics.
I'd like to sell this unit for parts if anyone is interested.
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The "fan thing" is a heatsink, does it move with the cone?
I'd guess that it is thermally connected to the voice coil.
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We can learn a lot by what is common and not, between them all:
1. 41-42 Hz closed box resonance (Fc) which is roughly low E on a bass guitar
2. Closed box Q (Qtc) of about .8 - .85 ish which makes the half space response less than 3 dB down at Fc
3. The OLA and NLA had only about 3mm theoretically linear Xmax (one way) and a huge Xmech of about 13mm.
We can compute an overload headroom as 20 log(13/3) = 12.7 dB of overload headroom.
4. The OLA voice coil former is a very rugged brass/bronze looking type. The later versions had and aluminum type.
5. The tweeters are just OK, the NLA tweeter has an input impedance that is too low. If they were voiced less hot
with more resistance in series then they might work good enough.
6. The Jensen design keeps the Advent bass (42 ish Fc and .8 ish Qtc, not sure if Xmax changed) but the
crossover voicing is not as good IMO.
7. They all need baffle step compensation to sound truly HiFi IMO.
Bi Amping the AR9 - How do you do it?
in Acoustic Research
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Driving a woofer alone is a very inductive load and a zobel across it makes a lot of sense.
It does not have to be a perfect match, I'd put 8 ohms, 50W in series with 4uF across the
woofers.
Was it the woofer or tweeter amp that failed.
The other issue is a very light load allows that amp to go deeper into clipping (slowing down
BJT output devices that can result in cross-conduction). Any load will help avoid this so 22
ohms 50W across the mid-tweeter might help in that regard.
Was the system driven hard when it failed?
Was it a 400 or 700 amp that failed?
There was a post on DIYaudio where a top name in audio was testing a few amps with long
(20ft?) speaker cables into speaker loads and two of them where showing oscillations due to
the tweeter inductance. .1uf in series with 10 ohms cured it and should probably be used in
all speakers to avoid such issues.