ironlake Posted September 17, 2012 Report Share Posted September 17, 2012 Why does ar cover the magnet structure on the early woofer for the 4x with masking tape? Link to comment Share on other sites More sharing options...
ironlake Posted September 19, 2012 Author Report Share Posted September 19, 2012 I;ll answer my own question as I found the answer on a much earlier post. It is to cover the open voice coil the goes over the magnet to make the 8 inch woofer a long throw woofer from dust and debris. Link to comment Share on other sites More sharing options...
fran604g Posted September 20, 2012 Report Share Posted September 20, 2012 I think I saw that same post. They did it to get max excursion without having to make the magnet structure/basket deeper, I guess. Interesting stuff. Link to comment Share on other sites More sharing options...
RoyC Posted September 20, 2012 Report Share Posted September 20, 2012 The masking tape prevents uncontolled air leakage past the voice coil and through the cloth mesh dustcap.Roy Link to comment Share on other sites More sharing options...
ironlake Posted September 20, 2012 Author Report Share Posted September 20, 2012 Is that why you can;t get the woofer cone of the 4x to come back slowly when you compress it down. Link to comment Share on other sites More sharing options...
RoyC Posted September 21, 2012 Report Share Posted September 21, 2012 Is that why you can;t get the woofer cone of the 4x to come back slowly when you compress it down.At least some (most?) versions of the 4x were obviously not designed to be airtight. There are many 4x woofers with cloth screen inserts instead of masking tape covering the magnet/voice coil assembly.. Certainly, cabinets equipped with these woofers will never achieve the "slow woofer return" no matter how much glop is applied to the woofer surround.Actually, I have never seen the surround of any original 4x woofer heavily coated with "sealant"...just a light treatment. Allowing some controlled air leakage is known as "aperiodic loading". The goal is to produce more apparent bass response at lower power input levels. The most popular and successful example of this design was the Dynaco A25, which was probably the 4x's primary competitor early in the game. In fact, a forum member posted a photo of an early 4x cabinet with a very original looking fiberglass padded port awhile back...not unlike Dynaco's approach. The AR-4x was not a typical acoustic suspension speaker. The "slow woofer return" rule does not always apply.Roy Link to comment Share on other sites More sharing options...
fran604g Posted September 21, 2012 Report Share Posted September 21, 2012 Ironlake, did you see this post:http://www.classicsp...465 Link to comment Share on other sites More sharing options...
ironlake Posted September 21, 2012 Author Report Share Posted September 21, 2012 yes, thanks, this is where i assumed that the tape was to protect the voice coil as if any of the stuffing got in there it could stop the movement of the voice coil. thats interesting what roy said about the 4x design for dynaco type loading.What would happen to the sound of the 4x if the dust cap was coated with sealant and new foam surrounds were used instead of the cloth? Link to comment Share on other sites More sharing options...
RoyC Posted September 21, 2012 Report Share Posted September 21, 2012 yes, thanks, this is where i assumed that the tape was to protect the voice coil as if any of the stuffing got in there it could stop the movement of the voice coil. thats interesting what roy said about the 4x design for dynaco type loading.What would happen to the sound of the 4x if the dust cap was coated with sealant and new foam surrounds were used instead of the cloth?If everything were sealed it would act like a conventionel acoustic suspension speaker. It could be argued that the masking taped version was intended to be a sealed version of the 4x. Nobody really knows....Another variable is the fact that AR used a number of different versions of the 4x woofer. I came across one recently that had a (deteriorating) foam ring in the center of the cone, just like the AR-3 woofer. Otherwise it was identical to the ribbed cone version with the screen insert over the magnet assembly. That makes 6 versions of the 4x woofer I have seen.Btw, I am sure the masking tape and screen insert both served to protect the voice coil as well.Roy Link to comment Share on other sites More sharing options...
ironlake Posted September 21, 2012 Author Report Share Posted September 21, 2012 I know that when I had applied the simply speakers goup to the 4x cloth surround the speakers got boomy around 60 hz. I now have removed the cloth surround and put on foam for an 8 inch advent speaker which fit perfect.. I have left the dust cap original with its cloth like material and the magnet has the original tape on it. Now I have what I would call a much better bass sound not, boomy at all, more tight or damped sound and it goes much lower on organ pedal notes. I like itAlso I replaced the one tweeter that had the sticky gloss stuff on it with an original tweeter with just normal flat black paper cone. My solo violin sounds and much smoother, not screachy at all. The entire cone had that junk on it and the other speaker had a normal cone. I had turned down the tweeter in the speaker with the glossy cone as it did not match the other in sound. Now both sound the same on public radio in the mono mode with the tweeters full on. The speaker with the glossy stuff on tweeter was number 30148 and the speaker with the normal cone tweeter was number 407409.I think the glossy stuff was put on by someone else as it was still sticky and the simply speakers stuff is like that. Not sure though.I really like these speakers now, and I can listen to them all day with classic music on with no ear fatigue.I could never do that with my large advents which the 4xs replaced. The wood is all refinished now with new grill cloth so the speakers look brand new and sound great.Roy, have you ever seen a 4x woofer with no tape or cloth on the magnet? Just an open magnetic frame. Link to comment Share on other sites More sharing options...
ra.ra Posted September 21, 2012 Report Share Posted September 21, 2012 I have assumed that the pics shown in the 1972 article in the link referenced in post #7 (by fran604g), which show the magnet assembly fully exposed, were done so for the purpose of making the point about the long throw voice coil in the AR-6 woofer. I have to guess that the team reviewing this speaker simply removed the masking tape or removed the screen cap before making the photos with the hand that manually displays the full extension.In the pic below is a summary of the three types of magnet enclosures I've seen with this similar magnet/basket assembly for 8" woofers. The one on the left and the one in the center are AR woofers - - one with the masking tape and one with the black permeable screen cap. Both AR woofers have the permeable dust cap as well. The woofer on the right is from a Rectilinear speaker and has the exact same basket and magnet enclosure. The three obvious physical differences it exhibits from the AR woofers are: solid metal cap on the magnet; solid felt dust cap; and an inverted roll on the cloth surround. Link to comment Share on other sites More sharing options...
ra.ra Posted September 21, 2012 Report Share Posted September 21, 2012 Oops, almost forgot to mention the obvious. For the non-AR speaker I mentioned in the comparison above, that speaker was designed as a very tight acoustical suspension package and it was not the intent to have air pass thru this woofer. In fact, the other two drivers in the cabinet are factory adhered and fully sealed to the baffle board with silicon sealant.Also found this random pic of an early AR-4 woofer with the screen caps on the magnet. Link to comment Share on other sites More sharing options...
RoyC Posted September 21, 2012 Report Share Posted September 21, 2012 Roy, have you ever seen a 4x woofer with no tape or cloth on the magnet? Just an open magnetic frame.Ironlake,I have never seen one without a cover. Many of the AR 10 inch woofers had masking tape covering the magnet as well....no cloth inserts, however.As I mentioned in a previous response to you, most AR-4x tweeters had something applied to the cone. Yours were probably that way from the factory.Roy Link to comment Share on other sites More sharing options...
ironlake Posted September 21, 2012 Author Report Share Posted September 21, 2012 Notice that in the photo of the 3 speakers, the middle speaker with the cloth cover the magnet assemble appears to be smaller that the other two. Is it just the way the photo is or is it actually smaller. Yes, I just checked my woofers from another pair of parts 4xs one speaker has the cloth magnet cover and the other has the masking tape. The masking tape magnet assembly is definately bigger and has a different part number than the cloth magnet cover so now we have another speaker woofer version of the 4 woofer. Link to comment Share on other sites More sharing options...
ra.ra Posted September 21, 2012 Report Share Posted September 21, 2012 Very similar, but best I can tell for magnet dimensions:Tape: 2-3/4" x 2-7/8" x 1-5/8"Cloth: 2-3/4" x 3" x 1-1/2"Metal: 2-3/4" x 2-7/8" x 1-5/8" Link to comment Share on other sites More sharing options...
ironlake Posted September 22, 2012 Author Report Share Posted September 22, 2012 So is the bigger version for more p ower handling etc? Link to comment Share on other sites More sharing options...
JKent Posted September 22, 2012 Report Share Posted September 22, 2012 Another thing about AR woofers: Usually there will be a red dot near one terminal. You'd think that indicated the + side and that the red wire would go there. Not necessarily. I've found it's best to check all AR woofers with a battery to determine the + side.Kent Link to comment Share on other sites More sharing options...
ligs Posted September 22, 2012 Report Share Posted September 22, 2012 So is the bigger version for more p ower handling etc?Typically the power handling depends on the heat dissipation of the voice coil. If all AR 8" woofers have the same VC diameter(1.5") then the power handling is probably the same. More modern speakers have vents behind the magnet structures and some other means of venting(cooling) can handle substantially more power than the older design. Bigger magnet may produce higher sensitivity but put more damping(lower Q) in the bass this could result in less perceived bass in a sealed enclosure. Link to comment Share on other sites More sharing options...
RoyC Posted September 22, 2012 Report Share Posted September 22, 2012 I believe the woofer with the larger magnet was a holdover from the AR-4. Some early 4x's with that driver have been found to have a different crossover, using another 20uf cap (in the woofer circuit).Roy Link to comment Share on other sites More sharing options...
ra.ra Posted September 24, 2012 Report Share Posted September 24, 2012 Apologies for error in my original reporting, but here's an improved update. Subsequent discussion about "larger" magnet confused me a bit since the wider 3" magnet was actually shallower than the others, so I went back to take a second look and re-measure. In post #15, I mistakenly switched the cloth and tape dimensions, and upon closer inspection, the magnet depth of the cloth and metal versions is closer to 1-3/4" than the 1-5/8" originally reported.Corrections are noted here, and all dimensions are: (closed side) x (open side) x (depth) Tape: 2-3/4" x 3" x 1-1/2"Cloth: 2-3/4" x 2-7/8" x 1-3/4"Metal: 2-3/4" x 2-7/8" x 1-3/4"From these corrected dimensions, there is no clear "larger" magnet. If my scale was not currently on loan, we could at least determine the range of woofer weights and maybe infer which magnet might have the most heft.RoyC's last comment is very interesting - I know I have never seen a 4x with more than one capacitor. Link to comment Share on other sites More sharing options...
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