AR4x Refurbish

[der]

I've posted this elsewhere but I'd like as many opinions as possible. I began the process of refurbishing a pair of AR4x speakers that I bought used over 40 years ago. I pulled the grills off to find that one speaker has a particle board baffle and the other is wood.

I pulled both woofers and found that the particle board baffle was damaged at one time and badly repaired. It looks like someone used wood putty to fill in damaged spots around two of the t-nuts.

As I removed the woofer, one of the repaired portions crumbled. The other repaired portion around the second t-nut is marginal at best. I'm not sure how the baffles are fitted to the cabinets so I'm unsure if a completely new baffle would be possible or if it would be best to cut away the bad portion of the baffle and somehow epoxy new solid wood in it's place. I welcome opinions and suggestions.

By the way, I've already treated the cloth woofer surrounds, have a couple of new 20 microfarad caps and two refurbished pots to go in.

der

[Carlspeak]

It's not easy to repair a broken t-nut hole like you've shown in your picture. If you search long enough, I recall seeing a thread here at CSP that details the process quite nicely.

Alternatively, you could consider acquiring 4 new t-nuts and drill their pilot holes about 45 degress away from the 4 original holes..

[iso]

der, welcome to this friendly forum...

It might be possible to glue 5 cm x 3 cm reinforcing blocks made from 6 mm MFD board behind broken area, if back side of front panel is smooth enough. After this you can fill broken area with mixture of PVA glue, wood chips and saw dust. It might be good idea to use small amount of filler first and add some new filler when previous layer is dry. Area should be strong enough for new t-nut hole, but you may need longer mounting bolts.

I have reinforced t-nut area in new cabs using reinforcing blocks, when mounting flange thickens has been 12 mm or less. Sometimes nuts have been gone trough from PA cab baffle boards when cabs have bee fallen... this has been happened not only to low cost cabs but also high prized cabs with heavy drive units.

Best Regards

Kimmo

[owlsplace]

I've posted this elsewhere but I'd like as many opinions as possible. I began the process of refurbishing a pair of AR4x speakers that I bought used over 40 years ago. I pulled the grills off to find that one speaker has a particle board baffle and the other is wood.

I pulled both woofers and found that the particle board baffle was damaged at one time and badly repaired. It looks like someone used wood putty to fill in damaged spots around two of the t-nuts.

As I removed the woofer, one of the repaired portions crumbled. The other repaired portion around the second t-nut is marginal at best. I'm not sure how the baffles are fitted to the cabinets so I'm unsure if a completely new baffle would be possible or if it would be best to cut away the bad portion of the baffle and somehow epoxy new solid wood in it's place. I welcome opinions and suggestions.

By the way, I've already treated the cloth woofer surrounds, have a couple of new 20 microfarad caps and two refurbished pots to go in.

der

I would splice in some new wood with epoxy and stabilize the entire inside of the particle board with epoxy using some glass cloth if necessary. Replacing the baffle sounds like too much work.

Roger

[stupidhead]

Hi Lorenzo, I wonder about the overall integerity of the baffle. You say it crumbled which I suspect is a result of water/moisture exposure. Is the breakdown isolated or is the integrity of the entire baffle compromised. I do like the sound of Carl's approach, assuming the rest of the baffle is solid.

[der]

Hi Lorenzo, I wonder about the overall integerity of the baffle. You say it crumbled which I suspect is a result of water/moisture exposure. Is the breakdown isolated or is the integrity of the entire baffle compromised. I do like the sound of Carl's approach, assuming the rest of the baffle is solid.

By crumbling I meant around the repair area of the 2 t-nuts. Does look like a plastic wood type substance. I'm thinking of removing the t-nut from the second repaired area, cleaning that area up then filling the bad sections and then rotating the woofer and drilling new mounting holes for the t-nuts. I just need to find some more t-nuts. The remaining baffle seems to be adequate and structurally sound enough for this approach.

der

[Carlspeak]

The particle board baffle board the OP has was very cheap and comprised of large particles as opposed to the fine dust composition of MDF. Secondly, those large particles were not well bonded to each other.

[iso]

Carl is absolutely right about properties of particle board. It would be next to impossible to get enough strenght by filling bad sections without reinforcing blocks on back side of baffle board.

Best Regards

Kimmo

[der]

The particle board baffle board the OP has was very cheap and comprised of large particles as opposed to the fine dust composition of MDF. Secondly, those large particles were not well bonded to each other.

Absolutely correct. I've really never seen anything that cheap from AR. My 3a's and my other 4x have wooden baffles.

[ra.ra]

Good advice and comments here. As with most any generic product, there are different quality levels with particleboard manufacturing, and this type with the larger particulate and inferior binder should have never been used where the tooling involves routers and a delicate fastener like a T-nut is so close to a cut edge. Apparently, AR used a few different shops to produce their cabinets and subsequently, the raw materials varied. The idea to rotate and install in new holes at 45 degrees is best - - just be sure to fill in all remaining voids in the woofer recess so that you still ensure a good woofer seal.

Be certain to purchase the type of T-nuts with the sharp prongs, and once the pilot holes are drilled, the best way to draw them into the fresh "wood" is to use the original woofer screws (and maybe a washer or two) to slowly pull the sharp teeth into the backside of the baffle.

[der]

I've made my decision on how I'll proceed and am in the process of rounding up materials. I thank each of you for your time and your responses. I'll certainly post progress reports with pictures once I get going. I've also got to re-cap my 3a's soon too.

der

[der]

I received my replacement brass logo badges from John Hollingswork (he has an ebay store, but you all likely already know that) and they are beautiful indeed. I also received my new grill cloth from Michael's. I choose Irish Linen Tea-dyed 28 count because it looked good and was very inexpensive. I have a couple of more items to round up so I can get started. I may go ahead tomorrow and stretch the new cloth to the frames. I need to get some velcro ribbon from the local fabric shop to use to attach the frames.

I've already treated the woofers cloth surrounds with the special rejuvination liquid. The woofers are slightly different and the one's surround seemed very porous before the application. Attached are a couple of photos. The photo of the grill cloth is a bit darker and browner than it really is.

[JKent]

I received my replacement brass logo badges from John Hollingswork (he has an ebay store, but you all likely already know that) and they are beautiful indeed.

Thanks der

Shameless self-promotion: Those badges were from me, and if any CSP member needs some just send a PM and you'll get a discount off the epay price.

Please see this thread in FS section: http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=6002&hl=badges#entry96064

-Kent

[der]

Nothing shamefull about it Kent - you're stuff is great. Highly recommended!

der

[der]

Repaired the baffle board of one of the speakers with KwikWood. Not the greatest but effective. Rebuilt the croosover with a new Dayton 20 microfarad capacitor and replaced the L-pad with another AR control that I refurbished. Got it back together and it sounds very good. Need to rebuild the crossover and install cleaned up l-pad in the other one then stretch new grillcoth on the frames and add my new badges and this project will be finished. I'll post more pics later. Edit: by the way, the old capacitor that is shown was removed before reassemble.

[der]

Not good news. Finished rewiring and recapping the second speaker to find the tweeter dead - not functioning. Checked impedance of the driver and it's 1.5 ohms. Bypassed the l-pad and nothing. Looks like I'll need a replacement.

Pulled the tweeter and found a broken solder joint. It does work after all. Decided to replace most all the wiring in this unit. Need more wire in the appropriate colors.

der

[owlsplace]

Repaired the baffle board of one of the speakers with KwikWood. Not the greatest but effective. Rebuilt the croosover with a new Dayton 20 microfarad capacitor and replaced the L-pad with another AR control that I refurbished. Got it back together and it sounds very good. Need to rebuild the crossover and install cleaned up l-pad in the other one then stretch new grillcoth on the frames and add my new badges and this project will be finished. I'll post more pics later. Edit: by the way, the old capacitor that is shown was removed before reassemble.

der,

Looks like you are having fun. The patch looks decent. You probably will not be driving these very hard anyway. Even the ply baffles flex quite a bit on the 5's. I'm planning on adding some internal bracing on a pair that I'm working on. Like to avoid changing the cabinet volume too much though.

Enjoying your progress.

Roger

[der]

Rewired second speaker and reassembled. Both working great. I'd forgotten just how good these little 2 ways sounded. Refurbished crossovers and l-pads make a big difference. I'm currently listening to them in my listening room and find that in this location (plus the fact they're sitting on the floor) that I have the tweeters full on.

der

[der]

Finished up my AR4x today. Stretched new grill cloth and mounted new badges. I'm pretty happy with how they turned out. Not perfection but certainly worthy of more years of listening pleasure. Many thanks to those that offered help and encouragement.

der

[owlsplace]

They look great in the photo. Always fun to see a classic being appreciated.

Roger

[iso]

Even the ply baffles flex quite a bit on the 5's. I'm planning on adding some internal bracing on a pair that I'm working on. Like to avoid changing the cabinet volume too much though.

Roger

Cab of 5´s is fairly similar than 2ax cab I have been working on recently. European chipboard cab is not too rigid, you can see how back panel and front panel is resonating on some frequencies below 200 hz. Some US cabs seems to use plywood. 18 mm 13 ply Finish birch plywood is stiff, young´s modulus is roughly 3 times higher compared to 19 mm chipboard or MDF. However it seems that 6-7 ply plywood made from softwood has been used in the US cabs. This one is not rigid as 13 ply birch plywood but more rigid than chipboard.

Good thing in chipboard is that decay time of resonance is fairly short due softness and emphasis in panel resonances is in lower end of spectrum. Actually I do not think that AR 2ax cabinet do add too much of its own to sound. Only place I would like to add brace is between woofer and mid/tweet openings, as it is clearly weak place. Back panel resonance can also be seen, but back panel brace will approximately double resonance frequency... so resonance might be more obvious and you might hear it more clearly than without back panel brace.

After 70´s MDF and plywood (especially Finish birch plywood) has been considered superior to chipboard in cabinet construction, but if you do knuckle rap test you will note that chipboard does have fastest decay time of resonance and resonance is least obvious. MDF and especially birch plywood do have other good properties... but additional panel damping is needed when using them.

Best Regards

Kimmo

der cabs look very nice

[stupidhead]

those look very nice. good work resurrecting this set.

[der]

Thanks! Next project - new caps for my 3a's.

der

[owlsplace]

Roger

Cab of 5´s is fairly similar than 2ax cab I have been working on recently. European chipboard cab is not too rigid, you can see how back panel and front panel is resonating on some frequencies below 200 hz. Some US cabs seems to use plywood. 18 mm 13 ply Finish birch plywood is stiff, young´s modulus is roughly 3 times higher compared to 19 mm chipboard or MDF. However it seems that 6-7 ply plywood made from softwood has been used in the US cabs. This one is not rigid as 13 ply birch plywood but more rigid than chipboard.

Good thing in chipboard is that decay time of resonance is fairly short due softness and emphasis in panel resonances is in lower end of spectrum. Actually I do not think that AR 2ax cabinet do add too much of its own to sound. Only place I would like to add brace is between woofer and mid/tweet openings, as it is clearly weak place. Back panel resonance can also be seen, but back panel brace will approximately double resonance frequency... so resonance might be more obvious and you might hear it more clearly than without back panel brace.

After 70´s MDF and plywood (especially Finish birch plywood) has been considered superior to chipboard in cabinet construction, but if you do knuckle rap test you will note that chipboard does have fastest decay time of resonance and resonance is least obvious. MDF and especially birch plywood do have other good properties... but additional panel damping is needed when using them.

...

Kimmo,

The ply on the AR-5 Ponderosa pine cabs I have is 3-ply with a thin pine veneer on both sides. I recapped these and the midrange seems bright but that is easily adjusted with the pot. I may do some more work on these though.

The earlier pair I have with 70's oil-walnut veneer MDF and ply baffle is still in progress. Am planning on doing the HiVi conversion but it might be entertaining to A/B these with the original tweeters.

Was planning on reinforcing the front baffle between the low and mid as you suggested. Am considering adding an oak rib with epoxy fillets since the materials are on hand and the cabs would still appear original on the outside -- will see.

Roger