The Large Advent Crossover Networks

Large Advent Loudspeaker Crossover Networks
Original Large Advent - New and 5002 Versions
1969 - Early 1980s

By Pete B. December 2007 Updated: 12/7/07

1.0 Introduction
The Large Advent (LA) Loudspeaker is one of the most popular high fidelity loudspeakers of all time. The history of the LA from Advent, Henry Kloss' new company, is widely discussed on the Internet: http://en.wikipedia.org/wiki/Henry_Kloss

I've been interested in this speaker since it was introduced and decided to reverse engineer a pair several years ago. There are four basic model updates in the evolution of the Large Advent speaker:
        Original Large Advent (LA) - designed and introduced in 1969, and was simply
                named "The Advent Loudspeaker" when it was their only model.
        New Large Advent (NLA) - This was a major update to the original design.
        Advent 5002 - The tweeter was updated to a black poly dome type, first by Advent
                then by Advent/Jensen. Note that the 5012 is a real wood version of the 5002.
        Advent 25th Anniversary Limited Edition Speaker - essentially a reissue of the 5002/12.

The original Large Advent is most easily recognized by the Masonite wood ring adapting the 10" woofer cone to the 12" frame and an inward facing foam roll edge. The tweeter in the original is a reddish/orange color with a 7/8" dome in the middle and a large outer roll ring.

An all metal frame woofer was utilized in the NLA with the following changes:
        Outward facing roll edge
        Slightly shorter voice coil former, about .25" shorter
        Slightly larger cloth dustcap, 2.25" as compared to 2"
        Much heavier gauge flexible lead in wires, DC resistance usually measures about .2 ohms lower

It was otherwise the same as the original with the same motor geometry. The woofer can be used as a replacement in the earlier LA. The tweeter also utilized an all metal frame and was flush mounted, unlike the original. Ferro fluid was used in the tweeter to enhance cooling and allow for a simpler, redesigned crossover network. The new tweeter has very different parameters as compared to the original and it cannot be used as a replacement. A spongy foam material filled the NLA enclosure as compared to fiberglass insulation in the LA.

Early 5002s kept the same woofer as the NLA but the tweeter was replaced with a new 1" black poly dome unit. A new 3rd order crossover network was employed to protect the dome tweeter from out of band low frequency program content. Interesting that they returned to fiberglass filling material. Some included a tweeter level switch, others did not. Later 5002/12 from Jensen employed a woofer that is very similar to the NLA woofer however the motor is redesigned with a raised back plate. A paper/fiber dust cap is used in place of the NLA's cloth type, it is otherwise identical as far as I can tell at this point. The early 5002s include printing on the back as follows:

        Advent 5002
        Designed and manufactured by
        Advent Corporation
        Cambridge, Massachusetts USA

Cambridge MA is also written on the front. Advent was purchased by the International Jensen Corporation, Inc. and the later 5002/12s read :

        Advent
        a Division of International Jensen, Inc.
        an ESMARK Company
        4138 North United Parkway
        Schiller Park, Illinois 60176

The 25th Anniversary speaker appears to be a reissue of the 5002 but with the 3 way tweeter switch, and minor cosmetic changes. This is based on what I can see from pictures. I've never worked or measured one or read anything about the internal details.

2.0 Large Advent Crossover Designs

The original Large Advent went through several crossover revisions. At first I thought that companies would not change a design without a model change but it seems that they were fine tuning the design and actually went through several engineering changes. Three have been identified so far, based on reverse engineering several crossovers, pictures on the Internet, and one source who actually worked at Advent measuring the original LA. A first order network is employed on the woofer, this did not change within the LA family, and a second order high pass network on the tweeter with a resistive pad. The different revisions are referred to as Rev0 (noted by 16/8/4 uF/ohm components), Rev1 (16/16/3 components), and Rev2 (16/8/3 components) as shown in the schematic diagrams below.

There seems to be only one version of the New Large Advent crossover.

The 5002 Large Advent includes versions with and without a switch but otherwise seem to be the same based on several samples and pictures on ebay.

3.0 Large Advent Crossovers

Rev0 Schematic not available at this time, however I list the component values in
post #10 of this thread: Rev0 Component Values

Figure 1. Rev0 Original Large Advent Crossover

Large Advent Rev1 Crossover, note the off white and red "button" fine wire tweeter inductors.

Figure 2. Rev1 Original Large Advent Crossover

Large Advent Rev2 Crossover, note natural steel color "button" tweeter inductor, and bar shunt inductor.

Figure 3. Rev2 Original Large Advent Crossover

3.1 New Large Advent Crossover

New Large Advent Crossover

Figure 4. New Large Advent Crossover

3.2 Advent 5002 Crossover

The 5002/12 was produced with at least two versions of the crossover, one with a "background/normal" switch and another without. The picture below with the switch shows that there is one additional capacitor and one more inductor. Only the picture is available at this time so it's not possible to determine the component values:

Advent 5002 Crossover With the Tweeter Switch

Advent 5002 Crossover Without the Tweeter Switch

Figure 5, Large Advent 5002/12 Crossover (without tweeter switch)