Restoring the Acoustic Research AR4xa loudspeaker

Beautiful restoration.

 

Well done Rob.

 

A little update.

If you look at the 1m response plot above you'll see its decently even, but the bass driver shows a rising trend in the 500hz-2khz region.
The original AR4ax of course used a large air cored inductor on its bass driver, so I decided to try this on the 18 driver and see what happened. Now I know this driver was built to run 'open' but it does have some peaking at the top, and of course the 18 is renowned as a rather forward sounding 'rock monitor'. In use I find it sounds well projected and direct but also a little cuppy and hollow on vocals.

Inserting the inductor addresses the excess energy at the top of the bass driver and in the process introduces a little baffle step compensation.
Used this way, the cuppy quality is banished and traded for a slightly softer, warmer overall balance.
However, if you unwind 30 turns from that large inductor you get a nicely flat mid response with just a hint of presence dip - it sounds very nicely balanced indeed.

Here's the response before and after adding the full inductor - with 30 turns removed the dip is just a little shallower.
Tweeter here is set to the mid point:



AR bass inductor


You can also get a smoother top end, particularly around the bottom of the tweeter range by reducing diffraction effects. Use some 8mm thick acoustic foam and cut so that it fits snugly within the grille cut-out, then punch a hole slightly larger than the tweeter cone area.
8mm thickness brings the foam flush with the grille cloth:



IMG_0907

These will be at Scalford in March so if anyone wants a listen, do pop in.

 

According to Richard Dunn (NVA), who worked for AR in the UK in the early 70's, the ones you appear to have (US made?), were much better put together and with superior cabinets too..

 

good afternoon rob,

recently i bought a pair of ar4xa speakers too and i am about to start restaurating them.
searching the internet for information i came to your report of your restauration. i think you did a very good job.
my set is from 1976 and has the latest tweeter type and looks very good also. i'm only missing 1 of the two logo's and the information on the backside of the cabinet.
i have to refoam the woofer but i can do this myself and do some work on the filters.
i have the original cloth but it is kind a dirty.. i hope i can clean them.
can you please help me with the picture of the information on the bach of the cabinet?

regards,
stefan

 

Click to expand...
good afternoon rob,

recently i bought a pair of ar4xa speakers too and i am about to start restaurating them.
searching the internet for information i came to your report of your restauration. i think you did a very good job.
my set is from 1976 and has the latest tweeter type and looks very good also. i'm only missing 1 of the two logo's and the information on the backside of the cabinet.
i have to refoam the woofer but i can do this myself and do some work on the filters.
i have the original cloth but it is kind a dirty.. i hope i can clean them.
can you please help me with the picture of the information on the bach of the cabinet?

regards,
stefan