Proper placement of foam damping material in Large Advent?

[Guest twist72]

Hello,

I'm new to the forum and have a question I hope some of you will be able to help me with.

I am in the process of restoring my pair of Large Advents(made 1/10/79). While replacing the caps and sealing the cabinets I began to question whether or not the damping material was properly placed inside the cabinets. I noticed that there are cut-outs at the top and bottom of the internal brace. The bottom most peice of foam for the top of the cabinet is "curved" throught this cutout and covers the top of the cabinet completly. On the bottom, the previous owner(who did do some work on them) simply stacked the three peices of foam on top of each other and did not cover the bottom of the cabinet in the same fashion as the top. Is the bottom supossed to be covered like the top? There are a total of five peices of dense yellow foam all of which are of apparent equal size (12x12x2)per cabinet.

Thanks

Todd

[Doug G.]

Hi Todd,

Welcome. It sounds like the foam is probably in the correct positions.

While your speakers are probably the New Advents and mine are the originals, the foam is placed in all three of my pairs similarly to what you describe.

When you say there are three pieces stacked, I assume you mean against the back of the cabinet and they butt right up against the magnet on the woofer (your woofers would be higher up in the cabinet than mine). Correct?

Then there is a larger piece that fits into the top of the speaker with a cutout for the tweeter.

Do I have this about right? If so, this is the way they should be.

Doug

[Guest twist72]

Hi doug,

Yep sounds about right. The three bottom pieces are stacked on top of each other parallel to the back of the cabinet. Thanks for the help.

Todd

[Guest One-Shot Scot]

<>

Todd:

I just got signed in to this forum last night, but I have been lurking around for at least 6 months. I don't know how this reply will look when and if it appears on the forum. So far, I have been restoring only New Advent speaker models A3, A4, U3 and U4.

I have never seen the "internal brace" that you mentioned on any A3 or A4 cabinets. However, I did encounter the braces in a pair of U4 Advents that I disassembled last week. There are two particle board braces in each cabinet, measuring 21" x 2" x 3/4". The braces are glued vertically to the center of the right and left inside panels of the cabinets. With the exception of the two U4 utility cabinet braces, the interiors of the A3 and A4 furniture cabinets are identical to the utility models. This makes me wonder why Advent decided to include the braces in the utility model and what differences these braces make to the sound of the speaker system.

I'm sorry, but I can't remember how many pieces of foam were in the U4 cabinets. However, it seems to me that all of my A3 and A4 cabinets had only 4 pieces of foam. Two of the foam squares were stacked under the woofer and the woofer magnet pressed down into the one on top. The other two pieces were curled into the top of the cabinet so that half of the foam was touching the top of the cabinet and the other half was touching the top of the back of the cabinet. This arrangement leaves the crossover exposed.

The design change in the interior of the U4 cabinet mystifies me, even more now that you have mentioned the additional piece of foam. If there is anyone here who knows why Advent added the two vertical braces to the New Advent utility cabinet, I would like to hear about it. If these braces improve sound quality, I will add them to my furniture models.

In answer to your question, I would place two pieces of foam under the woofer and then stack the other three pieces under the tweeter, so that there are no echo chambers in the cabinet.

I will be unable to reply to this post until 5/29/06. At that time I will try to learn the many posting options and also try to set up an email address exclusively for this forum.

Best wishes,

One-Shot Scot

[real1shepherd]

In the large Advents that I have been into, there is a netting type material that is the final cover over the insulation-that's a pretty good indication that everything is there as it should be. Also, above the 'netting' I usually see some bare insulation just behind the woofers just to keep things tight I suspect. That loose piece often varies in size and shape. In addition there are some 'cuts' in the original insulation where wires go through and for x-over parts. My general theory is that anyone who has changed, deleted or replaced the insulation would not have bothered to replicate all that.

What I hate is getting into these speakers that have previously been "refoamed"-wrong. And where they let all the old black foam pieces just fall on the original insulation as they were refoaming in place. That’s a real lazy way to do it, as the woofers should be taken out for the best job and resealed as well. Hell, that’s half the ‘fun’ and accomplishment 'kudos' of refoaming…..! It's a thankless job and I don't think a 'pro' can make any money at it and go to all that trouble for say $50.

Kevin

[Doug G.]

Kevin, it sounds like you have had experience with the earlier Advents when they used fiberglass insulation instead of foam for the stuffing.

I don't know when they started using the foam but all of mine have it. They are all fairly late production. 1975-1976.

There is no netting or the like with the foam. Just the bare foam pieces distributed.

Doug

[real1shepherd]

"Kevin, it sounds like you have had experience with the earlier Advents when they used fiberglass insulation instead of foam for the stuffing.

I don't know when they started using the foam but all of mine have it. They are all fairly late production. 1975-1976.

There is no netting or the like with the foam. Just the bare foam pieces distributed.

Doug"

You're right Doug....I've never seen the foam, so I assumed he was talking about insulation. I'm not even interested in large Advents unless they have the masonite ring, so maybe that usually indicates 'early' models with the insulation?

Kevin

[Doug G.]

Mine are all masonite woofered Advents and ,like you, I am really only interested in them.

My pair of Walnuts came with the all-metal woofers when I bought them second hand (I know they had been changed from the original masonites as Advent didn't have the all-metal woofers in 1975 when these were built) and I replaced them with correct vintage masonites.

But, Advent did start using foam as the stuffing before the release of the New Advent Loudspeaker in 1977. I imagine it was probably sometime in 1974 or 1975 but I don't really know.

As far as any difference in sound quality, I've never had the opportunity to compare.

Doug

[Guest twist72]

Hey Scot,

Yeah Mine are the U3 Utilities. They indeed do have a brace inside not found on the A series. My thinking is that it might be there to secure the foam blocks in place, but its only a guess.

Oh yeah, When I got my U3's the guy that did the refoam job used a generic surround with a super fat roll and removed the original dustcap and replaced it with a larger one. Needless to say I removed these tainted drivers and replaced them with some originals in need of new surrounds. After I fixed them up I noted the polarity on the old ones and simply connected the new ones as such. Well guess what? The polarity on the "new" ones was REVERSED! I had them hooked up backwards for nearly a year! I decided to check the polarity just out of curiousity after completing my recent upgrades to the crossovers. Good thing I did. I always thought the "new' replacement drivers lacked the base of the old "tainted" ones, now I now why. I just orderd a set of Advent 10" surrounds from rssounds.com. I've heard they are almost and exact match for the originals, in regard to the roll and material thickness(I read that they are thinner than most).

Todd

[Doug G.]

Hi Todd,

Scot's and my preference for the masonite Advents (OK I'm really only speaking for myself here) may just be a silly preference because there isn't any reason that the New Advents wouldn't sound just as good (or some have even said they sound better - boo). How much the higher placement of the woofer in the cabinet has on the bass response, I don't know but I wouldn't think it would be that much.

I would think that having the polarity reversed on the woofers (as long as it was both of them) wouldn't have that much effect on the bass response per se because the crossover doesn't really care what direction, at any given moment, the current goes through the VC but it would affect the overall sound as the relative polarity with the tweeters would be upset.

Great idea on getting the RSSound surrounds though. These are what I used on the last pair I did and they are really good. Kind of makes me want to put them in all the rest of my Advent woofers now. Hmmm... it would only be six of them... :^)

Doug

[Guest One-Shot Scot]

<>

<>

Todd:

My feeling all along was that the two vertical "braces" were added to the U3 (and maybe U4 cabinets) to alter the sound in some way. Because the braces are just glued onto the right and left inner cabinet walls -- and they don't touch either the top or the bottom panels of the cabinet -- they add no additional support. It seems more likely that they are baffles intended to deflect the sound inside the cabinet. Why the were installed on the U-series cabinets and not the A-series leaves me mystified.

<<...I noted the polarity on the old ones (woofers) and simply connected the new ones as such. Well guess what? The polarity on the "new" ones was REVERSED!>>

Out of the 15 A/U series Advent woofers that I have checked, I have only found one in which the polarity was the reverse of the normal hookup pattern. In this case, the positive wire went on the left terminal and the negative wire went on the right terminal. If undiscovered, this creates situation in which a stereo pair of Advents can have the tweeters in phase with each other, but one cabinet will have its woofer out of phase with its tweeter as well as having its woofer out of phase with the other speaker's woofer.

As a result of finding this reversed-polarity woofer, I always check the phasing of the tweeters and woofers separately, using a test tweeter and a test woofer whose true polarity is known. After placing two speaker cabinets about two feet apart, side by side, I hook up only the tweeters to the crossover and check the phasing. (Fortunately, I have a test CD which contains in-phase and out of phase test material.) However, the phasing tests can be performed with any true monaural recording. When the speakers are in phase, the sound will appear to be coming directly from the center of the two speakers. When the speakers are out of phase, the sound will be diffused and appear to be coming from a non-centralized location.

Once the correct phasing of the tweeters is determined, I remove the test speaker and repeat the procedure with the other tweeter which is to be mounted in the cabinet. I then repeat this entire procedure with the woofers.

<>

I bought my new speaker surrounds from Woofer Repair at:

http://www.wooferrepair.com/advent.html

The kits from Woofer Repair seem to be as close to the original surrounds in both thickness and elasticity specifications as is possible to obtain. I still have 4 Advent woofers with the original partially-rotted surrounds and these surrounds closely resemble the ones from Woofer Repair in both thickness and shape.

I am familiar with the thicker generic type of material commonly used to repair Advent woofers and it is obvious that these thicker surrounds restrict the movement of the woofer cone, thus preventing the woofer from realizing its full bass potential.

Parts Express maintains a separate section in its printed catalog for Advent Woofer surround repair kits, as opposed to those for Bose and "General Purpose Speaker Surround Repair Kits":

http://www.partsexpress.com/pe/pshowdetl.c...FTOKEN=86467477

http://www.partsexpress.com/pe/pshowdetl.c...FTOKEN=86467477

I have not tried the Advent surround repair kits offered by Parts Express, but I am going to call and ask how closely they resemble the original Advent surrounds.

One-Shot Scot

[Guest westend]

Hi, first poster here. I've just completed a surround repair on a pair of large Advents and thought I'd throw out a few things to help others with classifying/dating their speakers. I used the RSsound foam surrounds and they were a perfect fit. For adhesive I used Allenes tacky glue (why do folks pay $5 + for acryllic foam adhesive, am I missing something?). Both of the cabs are walnut veneer. Both woofers have the masonite rings.

Speaker #1:A186436 This cab has three large blocks of foam on the bottom pressing against the woofer magnet. It has two blocks of foam behind the tweeter. The crossover consists of one ceramic resistor, a small coil,and three larger caps. It looks like someone has been into this cab at some point.

Speaker #2:A48036 This cab has pink fiberglass insulation on the bottom with a piece of cheese cloth towards the woofer. The area behind the tweeter is packed with the same insulation. The crossover in this speaker has a coil mounted on the cabinet back, two caps (possibally three, it's hard to make out one smaller component), a smaller rectangular resistor, and another cylindrical resistor (this is the component that is a mystery, could be a cap). This cab also looks like someone has entered.

Since I'm new to large Advents please don't take my crossover descriptions as gospel. I didn't want to disturb anything to inspect as these speakers were operating good before the surround repair and I'd like to keep them in that state. Remarkably, I couldn't hear any great differences when I initially played them but with the new surrounds they might have a different tone. I'll post later after I have them back together and playing. These are great sounding speakers and the price was certainly right. They were rescued from a dumpster.

[dynaco_dan]

A dumpster!

I'm going to cry.

[Doug G.]

Your speaker #1 is a later production unit (probably 1975) during the foam period. Speaker #2 is an early unit (1971?) during the fiberglass period.

If the crossovers are original, there should be:

Speaker #1:

1.5 mH inductor in series with the woofer

.43mH inductor in parallel with the tweeter

?mH inductor in series with the tweeter (in decrease mode)

16uF capacitor in series with the tweeter (in all modes)

8uF capacitor in series with the tweeter (in extended mode)

3 ohm resistor in series with the tweeter (in normal mode)

So, you have three inductors, two caps, and one resistor and, of course, the switch.

Speaker #2:

The same except the resistor is probably 4 ohms and the second capacitor is 16 uF. The inductor mounted on the back board would be the 1.5 mF.

In later units, they beefed up the series tweeter inductor because of problems with the originals opening (or shorting) due to insufficient current handling capability and this is probably the cylindrical device you see that looks like a resistor.

Doug

[Guest westend]

Doug,

Thanks for the reply. I thought that the speakers might be from different years. What I'm wondering now is if the "dumper" (original owner) possibly had a double set of Advents and either sold a pair or disposed of them. I know who the dumper is so I will follow up on that. My surround repair is giving great results. It's hard to believe these 10" woofers play that low. I do have another problem, though. I am getting no sound out of the tweeter in speaker #1. No voltage is apparent using a DMM. The problem, I think, is the resistor. I noticed when I had the cab open that it had been run hot as the foam that was against it had melted from inordinate heat. It looks like a crossover redo is in my future. I'll look at the posts here regarding crossovers and try to put together some values that will work for me. I am wondering if I match the values of speaker #2 will that better balance the pair. Either follow that approach or rebuild both crossover networks with a better design? Anyone have any thoughts on that?

[Doug G.]

Yes, the low, undistorted bass response has always been one of the remarkable things about the Advents.

To test your tweeter, take an ordinary flashlight battery, attach two wires, and touch the wires to the tweeter terminals. There should be a click when you do this. If there is, then the tweeter is probably OK and the problem is in the crossover.

If the resistor got that hot though, it would be unusual for the tweeter not to have been damaged.

If I were to redo the crossovers on your speakers, I would duplicate the values in speaker #1 (the later one). This has been discussed here and in other forums and it is generally agreed that Advent changed the 16 uF cap (the one that bypasses the resistor in extended mode)to 8uF to reduce the amount of lower mid frequency current through the tweeters. I have never heard one of the earlier speakers so I can't comment as to the difference in sound but it would relieve the tweeter of some stress.

But, they are your speakers and you can do what you want. I don't think you'd go wrong either way. I think I would stay with the values Advent used though.

Doug

I forgot, there is a schematic of the later version of the crossover in the Library section of this site.

[Guest westend]

Thanks Doug. I'll check the library for the scematic. If anything, I thought the set was a little "bright" in the highs. With one tweeter out they are just about perfect. lol , driven by Sonic Impact T amp w/laptop as source. Imaging and stage at low volumes is bad of course. One could experiment with values, departing from the original in small increments, correct?

[dynaco_dan]

>Thanks Doug. I'll check the library for the scematic. If

>anything, I thought the set was a little "bright" in

>the highs. With one tweeter out they are just about perfect.

>lol , driven by Sonic Impact T amp w/laptop as source. Imaging

>and stage at low volumes is bad of course.

One could

>experiment with values, departing from the original in small

>increments, correct?

Hi there;

One should not experiment with capacitor values, as if you were to choose the wrong value too much bass can enter the tweeter, distorting it and or destroying it.

You can always raise the crossover point, but then the woofer has it's natural rolloff point and so there would be a drop-out or suck-out.

Good luck.

[Doug G.]

Excellent advice, Vern! (thumbs up icon here)

Doug

[dynaco_dan]

Thank you, Doug.

There is much I don't know about, please don't tell my kids that, I am still learning.

I wish I was still working and could afford a small selection of assorted brand polypropylene caps, so that I could experiment with them, to determine which cap sounds a little better to my hearing but does not break the bank.

My interest is to just replace existing two way speaker systems tweeter caps to keep things simple and valid.

My interest is not to find the absolute best capacitor, but an affordable brand capacitor that consistantly improves a tweeters output.

I am not referring to distortion, I assume that older caps may be not passing the top highs through the tweeters, or I am all hogwash.

The future will tell.

Solen, does seem to be a brandname that is chosen by many, price, maybe, availablity, definitely.

Mailordering at premium S&H and customs from the USA won't allow me to persue this treck unless I win a lottery. lol

Good luck.

[Guest westend]

I think I've hijacked this thread enough to start a new one. Sorry to the OP. I hope the info I posted and the responses about my two speakers have helped.

[Carlspeak]

>

>bottom of the internal brace. The bottom most piece of foam

>for the top of the cabinet is "curved" though this

>cutout and covers the top of the cabinet completely... Is the

>bottom supposed to be covered like the top? There are a total

>of five pieces of dense yellow foam all of which are of

>apparent equal size (12x12x2) per cabinet.>>

>

>

>Todd:

>

>I just got signed in to this forum last night, but I have been

>lurking around for at least 6 months. I don't know how this

>reply will look when and if it appears on the forum. So far, I

>have been restoring only New Advent speaker models A3, A4, U3

>and U4.

>

>I have never seen the "internal brace" that you

>mentioned on any A3 or A4 cabinets. However, I did encounter

>the braces in a pair of U4 Advents that I disassembled last

>week. There are two particle board braces in each cabinet,

>measuring 21" x 2" x 3/4". The braces are glued

>vertically to the center of the right and left inside panels

>of the cabinets. With the exception of the two U4 utility

>cabinet braces, the interiors of the A3 and A4 furniture

>cabinets are identical to the utility models. This makes me

>wonder why Advent decided to include the braces in the utility

>model and what differences these braces make to the sound of

>the speaker system.

>

>I'm sorry, but I can't remember how many pieces of foam were

>in the U4 cabinets. However, it seems to me that all of my A3

>and A4 cabinets had only 4 pieces of foam. Two of the foam

>squares were stacked under the woofer and the woofer magnet

>pressed down into the one on top. The other two pieces were

>curled into the top of the cabinet so that half of the foam

>was touching the top of the cabinet and the other half was

>touching the top of the back of the cabinet. This arrangement

>leaves the crossover exposed.

>

>The design change in the interior of the U4 cabinet mystifies

>me, even more now that you have mentioned the additional piece

>of foam. If there is anyone here who knows why Advent added

>the two vertical braces to the New Advent utility cabinet, I

>would like to hear about it. If these braces improve sound

>quality, I will add them to my furniture models.

>

>In answer to your question, I would place two pieces of foam

>under the woofer and then stack the other three pieces under

>the tweeter, so that there are no echo chambers in the

>cabinet.

>

>I will be unable to reply to this post until 5/29/06. At that

>time I will try to learn the many posting options and also try

>to set up an email address exclusively for this forum.

>

>Best wishes,

>

>One-Shot Scot

>

>

I just wanted to add the link below to a recent post of mine which is intended to relate my experience with "A3XXXX" series Large Advents. It seems pertinent to the threads posted here regarding bracing and stuffing materials.

http://www.classicspeakerpages.net/dc/dcbo...g_id=1739&page=

It's all about the music

Carl

Carl's Custom Loudspeakers

[Devil666]

I know this is a really old thread, but bear with me. Original Advent speakers had fiberglass insulation, like home wall and ceiling insulation. A few years later, they switched to dense foam, like furniture upholstery or camper mattress. Here is the science....

Loose material in the enclosure that passes sound waves slows the speed of the sound wave, much like water slows a sound wave compared with open air. When the sound wave travels slower, it takes longer (perhaps 10-20% longer) for the wave to reach a wall of the cabinet. As far as the sound wave is concerned, the box is larger than reality. This lowers the roll-off point, the point where the bass sound output becomes less. All sealed enclosure speakers have this low-frequency roll-off. For the Advent woofer in a box of 20 cubic feet, it might be 33Hz. For a box the size of the Advents with the type of woofer they used, that would be about 45Hz. By adding loosely spun fiberglass material, the cut-off drops to about 40Hz. By switching to dense foam, they get an even lower roll-off point, around 37Hz. It doesn't sound like much improvement, and in fact it isn't, but folks tend to judge the world (school grades, car gas mileage, whatever) in steps – 30MPG is more desirable than 29MPG; Thirty-something Hz seems hugely better than 40Hz; a test score of 90 seems much better than 89.

There is a trade off. The sound wave passing through the damping material also decreases the speaker's efficiency – the volume level of sound per watt per meter distance. A speaker with dense foam is less efficient (not as loud) as one with loose spun fiberglass, although only slightly less. For apartment conditions, this may not matter. Your neighbors will match your Klipschorn efficiency by banging on the wall.