"hybrid" reconed drivers: Sound & t/s para. Issues: Any available info ?

[RMC]

Hi Ken, Thanks for your quick reply and being helpfull.

First, DUMB ME ! (Famous D. B. Keele once said that in Audio Magazine after having made an elementary mistake while reviewing a loudspeaker !). I checked, my 2214H DO have black Aquaplas on the FRONT of the cone as you mentioned. Since recently, in another thread, you talked a LOT about and showed quality differences between OEM vs Aftermarket recones (e.g. pictures of 2245H voice coil/black Aquaplas on the BACK of the cone vs Mackenzie's cheap recone having none), I must have tought my 2214H were missing that on the back of cone (yea, dumb me again), but it is there on the FRONT of the cone, as well as the white "2214H" stamped on a frame arm and OEM cone number on the back of the cone. So it is the real thing, not a Mitsubishi...

Regarding my 2205H (SFG),

"The AlNiCo frames and ferrite/ceramic frames are dimensionally identical in that lots of recone kits are interchangeable where the speaker becomes the model of the recone kit installed. They don't become actually identical in sound because the magnetic fields are improved inside the gap in the later SFG ..."

"So...a 2205A reconed with a 2235H kit is spec'd by the factory as functionally identical to a a 2235H since the energy in the gap is supposed to be 1.2T for both models and the mechanical dimensions are the same."

Since mine are 2205H (SFG) as stated, is the above still valid ? And regarding "... lots of recone kits are interchangeable..." what could they become realistically if need be (if absence of a proper 2205H recone kit): 2235H, E-140, 2225H, 2226H ? (though you stated "2225/2226 are really not suitable replacements for the 2235H...") Does that imply also 2225/2226 not really suitable replacements for the 2205H ?

"The ferrite models had a foam vent filter which as everyone knows by now disintegrates and causes voice coil movement problems which can lead to failure." The AlNiCo models mostly have a cloth screen which doesn't cause this problem."

Having looked at my 2205H through the boxe's vent with a small mirror and a flashlight I clearly see a fine METAL screen on top of rear vent (under the name plate), but I can't see for sure if there is ALSO (?) a foam inside the driver's back vent(i.e. under the screen), without having to remove the drivers...

BTW here's a little story you'll like that tells a lot regarding most clones. Read in a serious newspaper's car section about 2-3 years ago. A Chinese car company built a "clone" of a BMW X5 SUV (seeing the picture it looked good). It was sent to Europe for certification by the authorities, and didn't pass the tests. It failed dramatically on safety issues, which the original had passed... No I don't drive nor own a BMW.

Considering your time invested here giving all that info/advice you give to the guys, the higher price asked for a better reproduction recone kit is probably well worth it. it's OK that someone still defends quality craftsmanship in a world of counterfeits, and whistles and bells... Keep-on carrying the burning torch for quality at an acceptable price! I'll vote for that anytime.

Richard

[edgewound]

[QUOTE=RMC;404070]

Hi Ken, Thanks for your quick reply and being helpfull.

Hi Richard. You're most welcome.Hope it was actually helpful.

First, DUMB ME ! (Famous D. B. Keele once said that in Audio Magazine after having made an elementary mistake while reviewing a loudspeaker !). I checked, my 2214H DO have black Aquaplas on the FRONT of the cone as you mentioned. Since recently, in another thread, you talked a LOT about and showed quality differences between OEM vs Aftermarket recones (e.g. pictures of 2245H voice coil/black Aquaplas on the BACK of the cone vs Mackenzie's cheap recone having none), I must have tought my 2214H were missing that on the back of cone (yea, dumb me again), but it is there on the FRONT of the cone, as well as the white "2214H" stamped on a frame arm and OEM cone number on the back of the cone. So it is the real thing, not a Mitsubishi...

Good to know you have the real deal. Sometimes it's hard to tell if the Aquaplas is present unless you take a real close look. Some have also had a hard time deciphering the Aquaplas on the rear of the 2240H cone as well. It's there, too.

Regarding my 2205H (SFG),

"The AlNiCo frames and ferrite/ceramic frames are dimensionally identical in that lots of recone kits are interchangeable where the speaker becomes the model of the recone kit installed. They don't become actually identical in sound because the magnetic fields are improved inside the gap in the later SFG ..."

"So...a 2205A reconed with a 2235H kit is spec'd by the factory as functionally identical to a a 2235H since the energy in the gap is supposed to be 1.2T for both models and the mechanical dimensions are the same."

Since mine are 2205H (SFG) as stated, is the above still valid ? And regarding "... lots of recone kits are interchangeable..." what could they become realistically if need be (if absence of a proper 2205H recone kit): 2235H, E-140, 2225H, 2226H ? (though you stated "2225/2226 are really not suitable replacements for the 2235H...") Does that imply also 2225/2226 not really suitable replacements for the 2205H ?

"The ferrite models had a foam vent filter which as everyone knows by now disintegrates and causes voice coil movement problems which can lead to failure." The AlNiCo models mostly have a cloth screen which doesn't cause this problem."

Having looked at my 2205H through the boxe's vent with a small mirror and a flashlight I clearly see a fine METAL screen on top of rear vent (under the name plate), but I can't see for sure if there is ALSO (?) a foam inside the driver's back vent(i.e. under the screen), without having to remove the drivers...

I must confess...I've can't remember ever seeing a 2205H in for recone. They must be pretty rare, since there are TONS of 2225s out there. There is very little different between the two. I believe the only difference is the spider and possibly the voice coil forner material since the Fs is 28Hz for the 2205H and 40Hz for the 2225H/J...same frequency range spec but 2225 is rated for 100 watts more.

Your 2205H is the identical core to the 2225, 2235. But NOT the 2220 variants. The 2220 gap depth is .35" vs. .28" for the others. Reconing a 2220 with another OEM JBL kit is a cardinal sin that should NEVER be passed off as legitimate...though it has been done by Authorized Service Agencies quite often.

BTW here's a little story you'll like that tells a lot regarding most clones. Read in a serious newspaper's car section about 2-3 years ago. A Chinese car company built a "clone" of a BMW X5 SUV (seeing the picture it looked good). It was sent to Europe for certification by the authorities, and didn't pass the tests. It failed dramatically on safety issues, which the original had passed... No I don't drive nor own a BMW.

Considering your time invested here giving all that info/advice you give to the guys, the higher price asked for a better reproduction recone kit is probably well worth it. it's OK that someone still defends quality craftsmanship in a world of counterfeits, and whistles and bells... Keep-on carrying the burning torch for quality at an acceptable price! I'll vote for that anytime.

Richard

On the car clone issue, there is a facility here in Southern California run by Kia/Hyundai. A good friend of mine's buddy works there. What do they do? They buy Mercedes' and BMWs to take to this facility in order to take them apart and re-engineer them to figure out what makes them so good. Surely saves on R&D costs, but compared to the other brands, they're already obsolete in comparison by the time they hit the market. Lower prices and a 10 year warranty sells lots of cars.

Thanks for the sincere encouragement of my endeavors. It would be fun if JBL took the time to dissect the aftermarket/Reproduction recone kits market and picked a candidate to offer "Genuine JBL" quality parts, but I won't hold my breath. I'll just continue to do the best work I can until I get tired of it. I just had a 2245H kit through eBay's Global Shipping program delivered to Switzerland today that was damaged upon delivery. It was real pretty, too! Oh well...that's what insurance is for, right?

Take care and good luck with your speaker stuff.

Ken

[Ed Zeppeli]

I must confess...I've can't remember ever seeing a 2205H in for recone. They must be pretty rare, since there are TONS of 2225s out there. There is very little different between the two. I believe the only difference is the spider and possibly the voice coil forner material since the Fs is 28Hz for the 2205H and 40Hz for the 2225H/J...same frequency range spec but 2225 is rated for 100 watts more.

Your 2205H is the identical core to the 2225, 2235. But NOT the 2220 variants. The 2220 gap depth is .35" vs. .28" for the others. Reconing a 2220 with another OEM JBL kit is a cardinal sin that should NEVER be passed off as legitimate...though it has been done by Authorized Service Agencies quite often.

The 2205H must have been a stop-gap driver between the alnico shortage and their next offering. My re-coner was doubtful as they weren't listed in JBL's 'goes into' list for the C8R2235H. Maybe JBL left it out because it was at that point two generations back.

They just happened to be available and affordable for me to use as cores here on Vancouver Island so I grabbed them. I only knew they would work after scouring the info available here.

Cheers,

Warren

[RMC]

Hi Ken and Warren,

Glad you're still hanging in there pending Flodstroem's reply with an actual computer speaker software simulation regarding a recone into a different frame/basket (e.g, 2225 recone into E-140 frame) and impact on driver specs/performance.

KEN "Hope it was actually helpful."

Yes it is, as usual, now I know for sure what my options are since my now 36 years old 2205H's spider, surround, voice coil former, etc. won't last forever... So at one point in the near future I'll probably need two better made recone kits for these, because I tend to cherish and keep my good stuff a long time. That's why I prefer purchasing quality gear lasting many years (Rane, QSC, Tascam, Mackie, etc., 20+ years !).

"I must confess...I've can't remember ever seeing a 2205H in for recone. They must be pretty rare, since there are TONS of 2225s out there."

When I purchased these brand new in 1981 they had recently been converted from Alnico to Ferrite (late 70's or early 80's) and probably near the end of the production cycle, since, if my memory is correct, the 2225H came out in 1982 or so...

"I just had a 2245H kit through eBay's Global Shipping program delivered to Switzerland today that was damaged upon delivery. It was real pretty, too! Oh well...that's what insurance is for, right?"

That's a real bugger for me sending my drivers far away (from eastern Canada to west coast USA, about 3,000 miles) to get them reconed for example. Most likely they would arrive in California barely good enough for the dumpster, and if not, then for sure on the way back here, knowing Canada Post handling...

My drivers are also real pretty for their age and, unfortunately, no insurance can replace this obsolete model... So, ordering a best fit/better made recone kit from the USA is about the only practical option I can see...

WARREN "They just happened to be available and affordable for me to use as cores..."

Not so for me, I purchased them because I really liked the sound of these drivers, mounted in vented-boxes in a biamp system with satellite speakers (home playback system).

Richard

[edgewound]

Opps....I think I forgot to address a couple of other issues.

The 2225H and/or 2226H are very much suitable replacements for the the 2205H. They will sound different because they are different in a few aspects, so it's best practice to replace them all with the same model. Since aftermarket parts are available for them all they can either be reconed with original spec parts or updated...this being the 2205 and 2225, since the frames/motors are in fact identical.

The 2226 is a whole different animal and can only accept 2226 or VGC style voice coil in the motor. These are not interchangeable with previous generation SFG and/or AlNiCo motors...which are interchangeable since the voice coils are the same ID.

[RMC]

The search continued for some data regarding the use, among other "Hybrids", of a recone kit (e.g. 2235H) into a different frame/basket (e.g. E-140). I have found two older Threads on this site dealing with an aspect of this Hybrid issue, and giving some interesting results in terms of T/S parameters. It confirms a good part of what fellow member Flodstroem was saying in the present thread. Here are the names of the two Threads of interest started in 2004 and 2005, both in the "Lansing Product Technical Help" section. Don't be fooled by their title, they ARE quite relevant with hybrid category of a recone kit into a different basket:

Thread: Does anybody know the M32-8, 15"? Recone to 2235H question... , started May 7, 2004
Of particular interest, see posts # 7 (Mr. Widget), 13 (4313B-Giskard), 16 (Mr. Widget) and 17 (Ralf).

Thread: E140 = 2225??? , started Nov.4, 2005
Also of particular interest, see posts # 2 & 3 (Lancer), 7 (Rob), 10 (Lancer), 11 (Ian), 12 & 25 & 33 (Zilch), 36 (Ian) and 65 (Thom).

In summary, many of the older and popular JBL 22 series drivers have a Flux number of 1.2 Tesla (except 2215, 2220, etc.), contrary to the E-series 120, 130 and 140 with a Flux of 1.35 Tesla. So installing such a 22 series recone kit into an E-series basket named above WILL lead to a change in a number of T/S parameters in such a way that the hybrid driver will not behave exactly as the recone kit number would suggest due to the stronger motor...

Originally Posted by Giskard

The 1.35 T*m assembly (E140 for example) uses the 7/8" thick magnet and the 0.280" top plate.

The 1.20 T*m assembly (2235H for example) uses the 3/4" thick magnet and the 0.280" top plate.

The 1.15 T*m assembly (2220H for example) uses the 3/4" thick magnet and the 0.350" top plate.

The 0.95 T*m assembly (2215H for example) uses the 7/8" thick magnet and the 0.600" top plate.

Originally Posted by Giskard

Two different cores, stock 2225/2235 1.2 T*m core and E130/E140 1.35 T*m core.

Red signifies changes from stock 2234H and 2235H.


See Tables, Lists and Graphs in the Threads/Posts identified above for details. Good reading.

Richard

[RMC]

Speaker driver manufacturers, such as JBL, rarely sell original re-foam kits for their woofers, the norm being a complete recone kit, and in JBL's case installed by a JBL certified reconing shop (for quality of work) or nothing... Yes, its all or nothing.

Naturally, the situation has lead not only to prosper aftermarket recone kits businesses, but also to the creation of another booming sector: the re-foaming business, which includes DIY. Because most aftermarket manufacturers or vendors don't provide (except dimensions/material) customers with much valuable info (e.g. T/S values), we have to try to find relevant specs on our own (like chasing ghosts) or actual measurements done (few do it), including on the impact on performance of using aftermarket stuff. Then, the decision to go ahead would be an informed choice, as it should be, contrary to "the blind leading the blind" type of situation.

Since aftermarket foams/cloth surrounds are not the original JBL stuff, my concern with ANY different surrounds (including mine; same with any non-original recone kits) is will it fly according to flight plan ? In other words, deliver comparable/equivalent performance so that driver AND box parameters are not materially affected (I'm not concerned with such tiny things as Barry's 1 hz difference on Fs measurement, plus its well within production tolerances). Initially, I must say I have some doubts about the equivalent nature (quality, performance, specs, T/S) of the "clones". But I'm quite open to be proven wrong by science or actual measurements. Will I have to take back or nuance SOME of what I said ?

Barry's experiment with Butyl rubber surrounds on JBL 2234 drivers (he's quite delighted with these), appears to give him a headstart on me. With the type of gear and knowledge he has, Its doubtful Barry would have purchased the first surrounds that met the eye, no questions asked. Considering he likes his things proper, as I do, he must have done his homework before jumping into this unconventional rubber surrounds "adventure" for 2234 (Didn't he say if you value your time recone?). So his thing is probably more an "educated guess" than a simple "flip the coin" type of decision.

In my case, to re-foam my 12" JBL drivers I spent time searching for a surround model with similar foam material that not only looked and measured like the original (thickness ?), but was also specifically made for the 2214H, hoping to increase my chances of getting equivalent performance. Did I wasted time and money in doing so, compared to cheaper generic/standard foams ? I don't think so re 2214 foam width.

Re-foam vendors typically claim to bring the speaker back to life at a fraction of the cost of new drivers. Not much more than that, except for mine they claimed these new surrounds last much longer than the original foam (one of Barry's reasons to go with "rubbers" is their longevity VS the re-foaming hassle, agreed). We all know a re-foamed driver will still reproduce sound. Doing it very well is even nicer. How good of a reproducer the modified driver be in that specific box, is the real issue. Is it still optimal or close enough ?

Logically, surround material types (e.g. rubber VS foam) should have an influence, unless both materials used have about the same specs (which we don't really know in this context). Are both materials equally compliant for example? Their thickness the same ? (thicker more rigid, thinner more compliant). I don't recall seeing something on this subject of materials' properties/data with regards to surrounds (other than cloth VS foam).

Finally, the re-foam (or even recone) done and its relation to the selling of the driver. Barry's drivers are probably not for sale, same for me. But what would happen if such vintage drivers were on the market for a new owner? Would a prospective buyer hesitate or downgrade the value (appearance, quality of work, performance) because of the non-original or unconventional surrounds ? Could it be more difficult to convince that buyer that these are equivalent, plus better lasting surrounds ? Tough questions. Depending on what I'm looking at (condition) and asking price, maybe I would hesitate. Or be tempted to discount the price... So if not an original job done, it may have a negative impact on selling price, unless you can prove your claims (e.g. measurements, extensive listening tests, dated invoice, etc.). I think I hear Ken's voice...

TO BE CONTINUED IN THE NEAR FUTURE WITH PART 2. I haven't finished yet "assembling" in a logical way the expert's views I have found on some relevant issues. Plus I have other things to attend or the wife will... me.

Richard

P.S.: Barry mentioned to me "...will try to find some of my own hybrid driver measurments." Real life stuff, icing on the cake, makes it even better! That would be interesting to see after Part 2 to compare expert views with user results... It seems DAVIDPOU here may also have some after re-foaming measurements.

[RMC]

FIRST INSTALLMENT OF TWO, MAYBE THREE, AS THERE IS A LOT OF MATERIAL TO COVER HERE.

While adding Qts here (Barry measured Fs), the question I raised in the "2234 Butyl Surrounds from Japan" Thread in DIY Forum, in my May 15, 2017 post, was if the new surrounds had an impact on the Vas T/S para. used to determine box volume (Vb), possibly on box tuning (Fb), on low frequency response and Xmax.

In post #7 of Barry's Butyl Surrounds Thread, Ian stated "The T/L parameters have nothing to do with the suround," and "The surround minimises reflections back into the cone and provides air tight seal and centres the cone. Nothing else. In modern drivers a foam surround is not considered part of the radiating area."

That view appeared radical and sounded contrary to what I learned over many years. This prompted me to go back to my References. If the situation is such as described above, then the surround's role or impact is quite limited, similar to that of a "zombie following the parade", i.e. passively obeying to cone movement dictated by voice coil/spider. Moreover, it would imply any similar type surround which physically fits could be used successfully (I.e. with results equivalent to the original). That sounds too good and easy to be true I thought, in relation to my question "Did I wasted time and money in doing so..." in my previous post here.

For my part, I've always understood the surround had a more active contribution in a driver's suspension system (e.g. some restoring force along with spider and some part of radiating area).

I'm not sure I know what a "modern driver" is, in terms of year made, to fit the description but referring to a Nov. 1978 AES Preprint, Bullock (Bullock on boxes, 1991, p. 44) does write "The driver piston diameter is equal to the cone diameter plus two-thirds of the surround width." Regarding the measurement of effective cone diameter, David B. Weems says "To get the effective diameter, include the suspension (surround) on one side only with the measurement..." (Designing, Building, and Testing Your Own Speaker System, 4th edition,McGraw-Hill, 1997, p.140), and Ray Alden (also mathematician, like Bullock) adds "The surround also acts as part of this effective piston area, ... Including half the surround on each side of the cone as part of the "effective" diameter helps to approximate the true piston area." (Advanced Speaker Systems, 1995, p. 21) Could they all have it wrong ?

Concerning the other surround's role I mentioned as example, Stan Kelly describes it as: "The purpose of the suspensions (with s) is to provide a known restoring force to the diaphragm/voice coil assembly... " Rest of his phrase being as described by John Eargle below. " The combined stiffness of the front and rear suspensions are formulated to... " "The rear suspension is the major restoring force,..." Not the exclusive force. (Loudspeakers, in Audio & Hi-Fi Handbook, 2nd Ed., Ian R. Sinclair Editor, Newnes, 1995, p. 561-2)

Vance Dickason also says the surround "...provides a portion of the restoring force that keeps the coil in the gap." RE "The stiffness provided by the surround and spider..." "...the spider provides about 80 % and the surround perhaps 20 % of the total compliance." (The Loudspeaker Design Cookbook, 5th ed., 1995, p. 8-9)

SECOND INSTALLMENT TO FOLLOW TODAY (ALREADY WRITTEN).

Richard

[RMC]

SECOND INSTALLMENT OF THREE, MORE INTERESTING THAN THE PREVIOUS ONE.

"Five parameters determine the driver's influence on response." (Bullock, p. 5) And he names the five has being: Re, Fs, Qes, Qms and Vas (here, that last one, is the one i'm interested in). "The remaining influences on response are..." Vb and Fb. Being a mathematician, Bullock probably has a mathematical model to explain why and how much the Vas parameter, linked to suspension compliance, influences the frequency response, but he didn't elaborate at this point. I assume it's related to the close relation of Vas with box volume...

John M. Eargle (JBL), Loudspeaker Handbook, Chapman & Hall, 1997, describes a driver's moving system as having 5 elements: cone, voice coil assembly, outer suspension (surround), inner suspension (spider) and dust dome. Then he writes "The purpose of the two suspensions is to ensure that the motion of the assembly is basically constrained to the axial dimension, with minimal radial and rocking motions. Each of these elements has a profound effect on the response of the driver,..." (p. 25). In his coverage of each item, he doesn't explain how/why/to what extent response is affected by the suspension (spider and surround).

In reality, the "original" suspension compliance parameter is Cms, but it is "translated" into a volume of air (the Vas parameter) "In order to help with this computation" (Alden, p. 16). Bullock adds "... Cms parameter is quite difficult to control in production. " (...) "For a particular driver model Mms is usually consistent from sample to sample but Cms is not. Thus Fs can vary quite a bit." "... formula 1 shows that a 50% compliance variation is possible."(p.9-10 Reader questions) "Cms not only varies quite a bit in production but is also hard to measure accurately."(p.10) Alden associates a driver's Cms with the "compliance of the spider and surround suspension system" (p. 16)

Regarding T/S parameter related to suspension, John Eargle writes: "The stiffness of surrounds and spiders may tend to vary to some degree, causing the Vas and Qts parameters to shift. The main question here may not be the variation itself, but the effect that variation may have on system performance. In most ported systems, the LF alignment is dominated by the enclosure parameters, and slight shifts in these parameters may have little practical effect." (p. 290) In relation to this parameter shift, "There is general accord that a 20% variation in Vas will not have serious effect on the final system response" (Alden, p. 17) This would mean larger shifts in Vas should have more extensive impact on performance.

With regards to determining Vas, Bullock writes "Vas is the most difficult parameter of all to find with acceptable accuracy. It varies not only with atmospheric conditions, but also with time..." Then interestingly adds "Luckily, this parameter's value is not as critical as the others: that is, a system's response will not be as sensitive to errors in Vas as it will to errors in the other parameters." (p. 14)

Bullock simulated (Fig. 5 & 6, p. 23) a ± 10% error in h (box tuning) and a ± 20% error in alpha (box volume), both for driver Qts 0.38 and box loss QL = 10, before concluding: "Notice that an error in alpha (box size) alters the response much less than one in h (box tuning). This state of affairs is desirable because Alpha = Vas/Vb and neither of these volume parameters can be measured with great precision." (p. 24) A 10% box tuning error has more impact on frequency response than a 20% box volume error...

Finally, he also simulated (Fig. 11, p. 24) a ± 20% error in Alpha (box volume) but this time with driver Qts 0.20 and box loss QL = 7. The changes in Alpha (box size) here also show a smaller effect on response compared to a ± 5% and ± 10% change in other parameters (Qts and h respectively). In fact, comparing his Fig. 6 and 11 with Fig. 8, his curves for Alpha changes/errors look more like those milder ones he simulated for the effect of box losses on response with QL 3, 10 and 15 (Fig. 8, p. 24). It does make sense since both QL and Alpha relate to box volume.

THIRD INSTALLMENT, INCLUDING CONCLUSIONS, EVEN MORE INTERESTING, TO COME SOON.

Richard

[Ian Mackenzie]

Hi Richard

Thank you for posting all these references

Interesting read on driver design differences below

http://www.lansingheritage.org/image...-3a/page06.jpg
http://www.lansingheritage.org/html/...s/tech1-3a.htm

Referring to figures 3a the single roll surround is a high compliance type (low stiffness) for long travel

But requires precise choices of centring spider for controlled linearity.

My prior comments on surround while seeming generalist in nature were in context of high compliance surrounds (single roll foam) used on the 2235 and the 2245.

My apologies for not being more specific at the time.

This Jbl document does cover some of the design questions about drivers surrounds

What is obvious is that one should not generalise when discussing components of a driver assembly

I think what is interesting is that forum members were re foaming drivers long before supply of Jbl recone kits started to dry up

As l vaguely recall it was frowned upon then (we are talking 10 years ago)

But given commentary around what may and may not be right with aftermarket recones the foam surround may be the least of all evils.

I am referring to critical components like voice coil, the voice coil wire type, the actual paper pulp mix used, damping formations on the cone, the infamous spider, adhesives.

[RMC]

THIRD INSTALLMENT OF THREE, VAS: THE SOMEWHAT "FORGIVING" T/S PARAMETER, AND CONCLUSIONS

Looking closely at Bullock's simulations of ± 20% variations in Alpha (box size), one can see from his graphs In Fig. 6 & 11 that this corresponds to a low-frequency response change of about ± 0.3 db only compared to target. Though Bullock stated "... that a 50% compliance variation is possible." he did not show such simulation. My guess is: if ± 20% means about ± 0.3 db, then ± 50% will mean around ± 0.75 db on LF response.

This raises the issue of audibility of such minor response changes in listening tests. 0.75 db or less is even smaller than what Mark F. Davis wrote regarding frequency response "... Variations of 1 DB or so (about 10%) are unlikely to be detectable in normal listening." (What's Really Important in Loudspeaker Performance, A Psychoacoustic Investigation, High Fidelity Magazine, June 1978, P. 53, 54). See note (1) below. It seems the ear is not as sophisticated device as we like to think and can be fooled, up to a point.

Some clever speaker Engineers appear to have benefited from the less critical parameter value of Vas. "... Thiele's model shows that system performance is relatively insensitive to variations in certain speaker characteristics, e.g., suspension compliance. Thus, knowledgeable deviation from specified characteristics produces very useful response shapes that depart only slightly from ideal performance." (Electro-Voice, Pro Sound Facts, DL Series Woofers, No. 7, October 1984, P. 1) Similar to what Bullock & Eargle said years later.

Since the driver's spider provides about 80% of total compliance, compared to only about 20% for the surround (Dickason), plus the major restoring force being confirmed as the spider (Kelly), then when re-foaming a driver, in principle, we are working on and "affecting" only the "lighter" part (20%) of the suspension system's total compliance, not the "heavy weight" spider (80%), if things are properly done. Therefore, this should have even less impact (± %) on total compliance data (Vas; used to calculate Vb), and on (± db) for frequency response. {I'm leaving aside Bullock's mention (p. 9-10) that Fs, Mms and Cms are related, so a change in Cms can impact Fs, plus the latter being considered in Qms & Qes they could also be impacted, therefore Qts too. Naturally, a change in Cms also means one in Vas derived from it. At first sight, for our purpose, this chain reaction doesn't appear to be a major issue in practice. HOWEVER, there ARE many ways to "screw up" those parameters, with chain reaction, when re-foaming a driver. Just for Mms I can think of 3 or 4 of these situations as I write this. Shoddy work explains most of them}.

In our fine work context, Bullock's simulations seem more like a "worst case scenario", since these are based on variations of TOTAL compliance (spider + surround), not just on the surround's 20 % or so we work on. Logically, good surround choice (avoiding incompatible ones like much too stiff, of inaccurate dimensions "forced on" or much too compliant lacking restoring force) and good workmanship, should have lesser influence, than what Bullock shows, on the final result: a ± 20 % deviation on 20% only of the total compliance (Vas), will likely have minimal influence on Vb, and therefore on frequency response, when amalgamated with the remaining untouched 80 % spider compliance. In this situation, the new surround related parameter variance that may occur is "diluted" among the whole compliance. That seems the key.

To summarize, in my view three things make this type of work fly, including Barry's job: the suspension compliance (Vas) "forgiveness", working on 20% or so of Vas and appropriate surround/workmanship = minor deviation from ideal, subject to seeing real measurements. That would explain the success, even though on the surface it may not seem proper to put a different rubber surround on a 2234 foam surround driver. It was done for legitimate reasons: benefit from rubber's longer life VS re-foaming hassle, plus experiment on another type of material. On the other hand, re-foaming doesn't appear to be for everyone: not really the type of work for people in a rush or rough working persons, but rather for "Jeweller" style workers, with patient attention to many details. Yes, the evil IS in the details here, because sloppy work will likely lead to more changes in the above mentioned parameters with chain reaction = more deviations. BTW, from the picture Barry posted, his job looked Factory made! I know the videos on You Tube show it's so easy... But again, Barry did say if you value your time recone... I can also confirm that.

Butyl rubber surrounds possibly have similar characteristics/specs (e.g. compliance) that are not far from the original material used by JBL. We might know more when Barry posts his measurements of before and after or reconed VS re-foamed... For my part, at this time, I would still purchase same as I did recently for reasons of foam width and cone travel capability (Xmax) which the 2214H had more of than usual 12" drivers from those days. Also, recall that in part 2A Stan Kelly mentioned the suspensions purpose is to provide a known restoring force, and we don't know what that number is for the original and replacement surrounds. That sounds like an incentive to purchase a replacement surround as identical to the original as possible.

A number of things stated here and in the other parts, may very well explain why Barry is "getting away with it" delighted in terms of unconventional replacement surrounds. I'm glad things turn out this way for him because it means for all of us "ME TOO CAN DO IT". Although, I'm not sure the errors or shifts in parameters considered above could be stretched much more without material consequences... As for enclosure volume tolerance, Electro-Voice says "Variations of ± 5 % of the specified net internal volume will not materially affect performance." (Pro Sound facts, DL Series Woofers, No. 7, October 1984, P. 7)

This text tends to confirm re-foaming, if that is the only problem, does make sense financially and performance wise, as long as the chore is done according to "the rules of the art". To my knowledge, not much has been written anywhere about the technical worthiness/impact of re-foaming, so I had to address the issue indirectly and work my way to get to where I wanted, which made things much more complicated (LOTS of work). First, I had to convince myself re-foaming in general, is a worthy avenue to take (technically sound, not perfect) VS reconing. If it helps others, the better. I sure learned while searching around that surround and Vas are not as critical as I initially thought, but they still have some influence in the process. Box parameters (Vb, Fb) have more impact on the LF alignment, although Vas is used to calculate Vb!

Richard

(1) That article relates some experiments by a bunch of guys from MIT's Engineering Dept. that show the ear may not be quite as sensitive and discriminating, as some suggest, concerning speaker performance values. In addition to Mark Davis, the skepticals may also want to consult some more recent work by Floyd E. Toole (hired for this expertise by Harman 1991-2007 as Corporate Acoustical Engineering VP for all brands, JBL, etc. "Subjective Measurements of Loudspeaker Sound quality and Listener Performance", JAES, V. 33, No. 1/2, p. 2-32, 02/85; "Loudspeaker Measurements and their Relationship to Listener Preferences, Part 1", JAES, V. 34, No. 4, p. 227-235, 04/86; Same, Part 2, JAES, V. 34, No. 5, p. 323-348, 05/86, or purchase his book "Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms, Focal Press, 2008.

[RMC]

Hi Ian,

Your comment about "But given commentary around what may and may not be right with aftermarket recones the foam surround may be the least of all evils." IS quite interesting in relation to new surrounds on original cone VS questionable aftermarket recone install. I had not seen this valid point of view, plus never even mentioned it myself in my long article here ! Good thought. Initially, It seems like an easy decision considering my findings in Part 2C of my article, and less money.

However, in another post (Restored LE 111H) yesterday EDGEWOUND (Ken) brings another issue, that I quickly mentioned in Part 1 of my text, which MAY be a "little wrench in the Wheel" for replacement surrounds:

"The aftermarket surrounds do tend to be thicker, but it also depends on how soft the foam is. The thicker surrounds do last longer.

That said, try breaking them in for a while. Foam surrounds, especially the thicker ones will loosen up with play time. The resin in the lighter surrounds also needs time to loosen up."

Will their compliance still be acceptable ? Not too far from original ? Much too stiff ? Again we don't really know for sure. That thicker lasts longer is nice. But usually thicker material means stiffer. That leaves me wondering...

Richard

[edgewound]

However, in another post (Restored LE 111H) yesterday EDGEWOUND (Ken) brings another issue, that I quickly mentioned in Part 1 of my text, which MAY be a "little wrench in the Wheel" for replacement surrounds:

"The aftermarket surrounds do tend to be thicker, but it also depends on how soft the foam is. The thicker surrounds do last longer.

That said, try breaking them in for a while. Foam surrounds, especially the thicker ones will loosen up with play time. The resin in the lighter spiders also needs time to loosen up."

Will their compliance still be acceptable ? Not too far from original ? Much too stiff ? Again we don't really know for sure. That thicker lasts longer is nice. But usually thicker material means stiffer. That leaves me wondering...

Richard

I fixed my typo. "Surrounds" should be "spiders". New spiders need break-in time more so than foam surrounds.