Now that the woofers are out for refoaming, what next?

[Guest gaparker]

Now that the woofers are out for refoaming, what next?

First, I thought other Advent-heads might be interested in production variations. I bought my Large Advents as floor samples in mid-1976 along with my Sherwood S-8900A receiver (yup, still have it). SN U176948 has a tweeter marker NOV (something) 1975. The speaker mounting baffle and the back panel of the cabinet are both dark, unpainted particle board. OTOH, SN U177306 has a tweeter stamped DEC 2 1975, the speaker mounting surface is painted black and the back cover is painted in a medium brown.

The masonite ring woofers will be sent to Carl on this list for refoaming. I’ll replace the 16 uF caps which are always in series with the tweeters, regardless of the switch setting in these “16/8” crossovers. I already have some 16 uF/250 V film caps for the job, and even if I didn’t such parts cost only about $6 each.

I’ve read other threads here about crossover mods. Can anyone point to a posting, or retell from personal experience, a careful test showing a noticeable improvement in sound by replacing the 1.5 mH, 0.3 Ohm DCR inductor with an equivalent air core part? These are $26 each (Parts Express #266-360) and I question if they’re worth it.

I understand from my EE background that it’s cheaper to make an inductor with a ferrous core and less copper wire, than to achieve the same inductance and resistance using more and bigger copper windings with no core (air core). Indeed, the use of air core inductors and film capacitors in place of iron cores and electrolytics are one differentiator between high end products and mass market loudspeakers. Under high volume/high loudspeaker current the ferrous core could start to saturate, leading to lower inductance and thus a reduction of high frequency rolloff. Yet if the inductor is “properly specified”, it should not experience saturation. Any thoughts on this, folks?

Now, about the woofer mounting holes: The driver mounting baffle is ¾” particle board. The factory screws are conventional tapered wood screws. The particle board is a little chewed up around some of the screw holes. I was thinking of replacing the woodscrews with machine screws and pressing in (actually, pulling in behind the baffle with a C-clamp) sets of one of the following from Parts Express:

Barbed Insert Nuts #081-1094

Hurricane Nuts #081-1082

6-Prong T-Nuts #081-1088

Has anyone here had experience or recommendation with any of these options?

Thanks,

Gary

[Guest russwollman]

I don't know what hurricane nuts are. With T-nuts I've not had good results. I know particle board/MDF has some useful qualities, but I hate the stuff. Look at it wrong, and it crumbles.

Why not just rotate the woofers a little bit, drill new holes, and use appropriate screws? They shouldn't come loose. Maybe you could use a lockwasher under the screw head?

[JKent]

I hve not used hurricane nuts or barbed nuts. I agree that T-nuts are not that great in particleboard. The barbed nuts do not look, to me, as though they would work that well for application. I would give the hurricane nuts a try (thanks for pointing them out) but as I said, this is just speculation

[dynaco_dan]

Hi Gary;

I've used T-nuts and they are great.

Access through the woofer opening allows a little more elbow room than through the tweeter opening. lol

I drilled the appropriate hole size, just a hair under slip size, and used a bolt and washer to draw the T-nut into the wood, for proper bite.

I then ran a small bead of glue around the T-nut's perimeter, inside the cabinet.

Time consuming, but strong.

Assuming that when I had installed a woofer and had only one more holdown screw to go, the last T-nut would fall inside the cabinet, Murphy's Law.

There is a selection of different number of teeth, and I feel that the stock 4 is more than adequate.

You must be certain that when you drill through the recess rim that you are certain it is dead center of the drivers mounting hole pattern.

Trying to move a T-nut to fit a different angle can cause cross-threading.

Take your time and your efforts will be worth it, in my opinion.

When I worked at the local AR warantee depot I can remember only once ever finding a factory tee nut that was not connected to the machine screw.

It was pushed in to cabinet during assembly and wasn't corrected there.

This was not the problem that speaker was in for.

Properly installed, you cannot have a more solid mounting method, short of epoxy cementing the drivers in.

This will allow for future access, this will be needed, if not 10 or more years away.

The woodscrews used by several manufacturers was a cheap shortcut.

Now that I have said that, price the number of T-nuts, and machine screws, even in bulk, they are not cheap, but will last a lifetime.

Drilling the holes, mounting the T-nuts, screwing in the machine screws, as well as AR buying them cost a little extra, once only.

Dynaco and Advent are just two very successful classic speaker manufacturers that used just the woodscrews.

I am not familiar with the other two you mention.

For everyones interest, could you please post a photo and spec's of each, please.

We can then evaluate their use, or not, for our application here.

Just because AR used T-nuts, does not mean other available fittings cannot be used as well, after all we are a worldwide database of information here, T-nuts may be limited to North America only as well.

The very first time I ever saw T-nuts outside of an AR speaker was at a furniture upholstery shop, they appeared to buy them by the 5 or 10,000 quantity carton.

That may or may not be a source for less expensive T-nuts.