PDA

View Full Version : THE JBL 4520 BASS CABINET PAPER TRAIL: AN 8 FT or 13 FT folded horn ?



RMC
03-07-2017, 04:19 PM
I've gone back into JBL Pro catalogues and other sources to find out the real story, and put this issue to rest.

As far back as 1962 ! In that year's catalogue the C 55 (ancestor of the 4520) is described as "This large rear-loading horn ... the 8-foot exponentially flared horn..." . The 4520 image fellow member Lee posted on March 3, 2017 is in fact one of the C 55 taken from an article written by George Augspurger, Importance of Speaker Efficiency, Electronics World, January 1962, page 3. Even if this image is missing dimensions making it uncertain to calculate exactly the horn length, it would seem, based on above-mentioned 8 ft, that fellow member Lee deserves an apology on this horn's length (though I don't recall seeing him say where he took his 8 ft figure), which I would be glad to do, since I'm a believer in truthful science. In the JBL catalogue, the exterior dimensions of the C 55 cabinet are given as 50 1/2" H, 35 3/4" W and 29 3/4" D. The C 43 (ancestor of the 4530) is also there with no mention of horn length. No weight is given for C 55/43. In the 1967 catalogue there are no mentions about the C 55's horn length.

HOWEVER, starting with the 1971 JBL Pro catalogue things turn around on horn length, even though the 4520 outside cabinet dimensions are virtually the same as those of the C 55 : 50 1/4" H, 35 3/4" W and 29 3/4" D, weight 215 lb without drivers (JBL, Professional Series, Low Frequency Enclosures, May, 1980, page 2 - See frequency response curve here (minus 15 db at 32HZ !) in conjunction with "usable to 30 HZ" below. The uniform response to 50HZ (-3 to -4 DB) appears to be a more meaningful number in practice, unless mutual coupling and/or corner placement are used to boost very low level, but the issue of cone excursion remains at high power/very low frequencies, see next para.). The 1971 Pro catalogue describes the 4520 as "Thirteen-foot folded horn with maximum loading to 42 HZ...Uniform response to 50 HZ, usable to 30 HZ." As for the 4530, "Seven-foot horn with maximum loading to 50 HZ ... Uniform response to 60 HZ, useable to 50 HZ ." The 1974 JBL Pro catalogue adds "A short throw, 13-foot folded horn, the 4520 ... high level sound projection up to 75 feet". "The 4530 is a short throw (to 75 feet) 7-foot folded horn...". The above facts/numbers re 4520 have remained the same in the following JBL literature (1976 Pro, 1978 Pro) up to and including the above-mentioned May 1980 Data Sheet. In the 1980 Pro catalogue horn lengths are the same (13 ft and 7 ft), but it adds an additional driver the E-140 to the recommended 2205 for 4520/4530, and two other drivers for the 4550A/4560A : the E-140 and E-145 in addition to the 2220 and 2205. The 4520/4530 have disappeared since the 1982 Pro catalogue, leaving space for the more recent 46 series, though the 4550A/4560A, both described as long throw directional horns, remained in the book for a few more years.

By the way, an interesting note appears in the 74, 76 and 78 Pro catalogues re 4550/4560 if used with the 2205 driver instead of the usual 2220: "When the 2205 is used in a 4550 or 4560 low frequency horn, some unloading of the driver cone will be experienced at very low frequencies. Power usage, therefore, should be somewhat more conservative than normally specified for the 2205." A similar note related to cone excursion striking the horn throat exists in the above May 1980 Data Sheet when using 2205, E-140 or E-145 in a 4550 or 4560 cabinet instead of the usual 2220. Moreover, a somewhat similar note also exists for both 4520/4530 using 2205 or E-140 drivers (since essential T/S parameters for both are quite similar), when "... the excursion limiting load presented by the horn is reduced," this could lead to "excessive cone excursion and possible damage," therefore "power input at very low frequencies should be restricted." Better be safe than sorry. Because of 4520/4530 abuse, the 2205/E-140/2225 are probably the most reconed drivers...

Back to our question. Outside dimensions of the C 55 and 4520 are almost the same, therefore pointing in fellow member Lee's argument of an 8 ft horn. What about inside these specific JBL cabinets one might ask ? Any weight difference cannot be singled-out since we don't have a number for the C 55 (a heavier 4520 could possibly have been explained by additionnal horn folds inside the cabinet to create a longer horn). It may also be caused by different material used over the years such as regular plywood, Baltic Birch or MDF...

JBL bass horn cabinets are certainly the most copied low frequency enclosures I've ever seen. There's so many of them out there, you have the full quality spectrum: the good, the bad and the ugly, plus everything in between... Many imitations are modified (e.g. for a larger 18" driver; for a smaller 12" driver without success), some get discouraged over build complexity and cut corners, etc. I'm interested in the real thing here, ORIGINALS. I don't think JBL ever published an official plan with ALL dimensions for these since it would have been an invitation to copy (a patented product ?). Likewise, the 4530 plan posted from Helmut Lengefeld is another home-made thing (could be perfect, could be bad) we don't really know, it's not an official JBL document. I tend to rely on proven facts from known sources, instead of hearsay for example:

"It is common knowledge among 4520 afficonados that JBL published a typo that time. ;-)"

Maybe, that time (re 1980 Data Sheet). However, how could such an important typo error on horn length be repeated systematically for close to 10 years (as shown above) in official JBL documentation without ever being noticed and corrected ? Either someone at JBL has been sleeping pretty deeply on the red flag for about 10 years!, or the horn's length is 13 ft as stated by JBL, who knows... Another fellow member may be of some help here. SUBWOOF already addressed this 4520/4530 horn length question here in 2007:

View Full Version : 4530/4520 horn lengths
Jonathan W
01-04-2007, 08:21 AM
Is anyone able to tell me how come the 4520 twin 15" scoops are described as having a 13' horn length, whilst the 4530 single 15" scoops are only 7' long. They don't appear to be that different in cross-section. Is width a factor? Am I just missing something?

Also, while I'm here: Wouldn't a horn length of approx. 11'6" be more suitable, so as to bring the reverse sound-wave from the scoop back in phase with the direct sound-wave at the 150Hz crossover point between the two (150Hz wavelength at room temp. = approx. 7'8")?

Many thanks for any help that may be offered,
Jonathan Weatherill
Hoerninger
01-05-2007, 04:04 AM
Some thoughts can be find here:
http://audioheritage.org/vbulletin/showthread.php?t=12773
___________
Peter
subwoof
01-05-2007, 06:27 AM
I have built hundreds of each....the difference is the depth and height.

Lugging a loaded particleboard 4520 up a flight of stairs is a real joy so we were happy to see higher power amps + cones come along in the 80's so the SR buisness could switch to vented boxes.

But they sure pound out the lows for a dance club and are still preferred by installers if they have the room.

The 4530 is 24" deep and about 39" tall.

The 4520 is 30" deep and about 50" tall.

Both have added bases to allow casters, crossovers, etc to be mounted since they were popular as roll-around systems for theaters.

That added length really makes a difference below 50hz but neither goes below 30 or so without risking cone damge from unloading.

sub

Surprisingly, Subwoof who claims having built hundreds of each (4520/4530) didn't contradict the 13 ft horn length mentioned in the question ( I suppose he would/should have done so if exagerated), but rather goes on to justify the differences in length, and concludes "That added length really makes a difference... ". He appears to believe in the 13 ft and 7 ft lengths (his height measurement on the 4530 should be 47-8"). At first sight, the only numbers he gives don't seem to add-up to 6 more ft, unless there would be more horn folds inside the 4520 cabinet than meets the eye to increase horn length...

It looks like the "13 ft controversy" just won't go away now... In the mean time, even if it doesn't seem to be conclusive one way or another about the 8 or 13 ft horn, it appears the probabilities are slightly in favour of an 8 ft horn for the 4520, based solely on the above data/comparison between JBL's C 55 and 4520 cabinets, not because Tom, Dick or Harry thinks so, because this wouldn't be scientifically sound.

I hope some of the "horn specialists" here will jump in with regards to the method possibly used by JBL to state this 13 ft length. I guess the "horn guys" could do some quick "reverse engineering" to clarify the feasibility issue. Also, some of the "Tech Bible" guys here such as Giskard, Techbot, 4313B and others may have some old records or inside documents ( as they often do) from JBL on this issue. This would bury this issue for good ...

Richard

Lee in Montreal
03-09-2017, 08:31 PM
Simple calculations will tell it all ;-)

Speed of sound 1,125ft/s

1/4 wave 13ft horn
1,125 / 13 / 4 = 21.6Hz horn (even the huge Bertha w/ Levan extension doesn't load that low. It loads down to 25Hz)

1/4 wave 8ft horn
1,125 / 8 / 4 = 35.1 Hz horn (Exactly what JBL 4520 literature says)

1/4 wave 7ft horn
1,125 / 7 / 4 = 40.2 Hz horn (JBL 4530)

So. Is the 4520 cab w/ 8ft or 13ft horn ?

Hoerninger
03-10-2017, 12:35 AM
Simple calculations will tell it all.

Good point.
dispite of the appropriate flare rate a bass horn should have a length of one qarter of the lowest frequency. Otherwise you will get problems with a straight frequecy response.

The mouth opening should be big enough, depending on placement (from free on the ground to corner plcement).

With HORNRESP by David McBean you can simulate even backloaded horns. It is a versatile program but not easy in the beginning.
___________
Peter

Eaulive
03-10-2017, 08:46 AM
Happy to chime in... hi guys :)

I know for a fact the horn on the 4520 is not 13', but it's longer than the 4530s horn for sure.

The box appear almost identical, but for starter the 4520 uses the full height of the cabinet while the 4530 has a integrated "pedestal" originally of around 6 inches.
76309
The 4520 is also deeper, but does it amount to a change of 6' in the horn length ? no, never.

Did JBL came up with a savant calculation or was it a mistake? Don't know :blink:
Could the 13' be a way of expressing the "double" characteristics of the 4530? Maybe the 4530 was 6.7' and they doubled it for the 4520... if you round the numbers up, it fits... :dont-know:

I have 4520s at home (not original but really well built) which seem to be fairly close to the many available drawings out there, I also made a lot of research, and the measures I trust the most are those.
This is a drawing I did after much search and cross references of pictures and datasheets...
76308

As an added bonus, some pics :D
https://www.flickr.com/photos/eaulive/albums/72157626260334894/page1

Horn Fanatic
03-10-2017, 09:44 AM
Good point.
dispite of the appropriate flare rate a bass horn should have a length of one qarter of the lowest frequency. Otherwise you will get problems with a straight frequecy response.

The mouth opening should be big enough, depending on placement (from free on the ground to corner plcement).

With HORNRESP by David McBean you can simulate even backloaded horns. It is a versatile program but not easy in the beginning.
___________
Peter


Greetings -

Without having gone to the trouble of drawing the cross section of the wave guide full scale to determine it's physical length down the center line, the answer to your question of the length of the 4520 and 4530 horns may lie in what is called the Effective Length.

Consider this. A tuning duct for a bass reflex enclosure has a physical length, and an effective length. The effective length being on either end of the duct whether it be a hole in the baffle or a tube of length. The effective length may or may not be symmetrical. For example; a four inch long duct may have an effective length of two inches or so on the outer end, and one inch or so on the inner end, bringing it to approximately 8 inches.

The parameters of the aperture then become an acoustical issue. The properties of an aperture include the acoustical resistance of the outer flanged and, and the inner un-flanged end, along with the acoustical mass on either end. Once a frequency is introduced through the aperture it then becomes a separate element with it's own impedance. As you must know, impedance is frequency dependent. Hence, the impedance of the aperture constantly changes.

The effective length of the 4520 may extend two to three feet past the horn mouth subject to frequency. As for determining the length of said horn, calculating the length base off a quarter wavelength of some frequency guess is incorrect for a rear loaded horn. The length of a rear loaded horn is determined by calculating multiples of 1/2 wavelengths of the roll-off frequency of the acoustical low-pass filter which is created by the combination of the speaker parameters, horn throat area, and chamber volume. The roll-off frequency occurs when the acoustical resistance of the chamber is at unity with the acoustical reactance of the throat area. At that point the phase angle between the two elements is at 45 degrees. This is done in order to ensure a phase match between the speaker cone and horn mouth. When at or about that frequency is produced, the whole front of the box behaves as a single diaphragm. The slope of an acoustical low-pass filter is 6dB / octave. Very sloppy when it comes to passive dividing networks, but smooth sounding for rear loaded horns. If you sweep a sine wave generator from about 500 Hz down to 30 Hz on a rear loaded horn such as the 4520, you can actually perceive aural movement of sound from the woofer to the horn mouth.

If you'll remember, in the JBL literature is claimed the speaker acts as a direct radiator above 150 Hz. I disagree with that claim. As I have designed scores and scores of rear loaded horns I discovered the typical roll off frequency ranges from an average of 300 to 400 Hz. What is the 1/2 wavelength of 350 Hz, which is my estimate of the roll off frequency for the 4520, based on the velocity of sound at 1130 feet/second? 19.375 inches. Multiply that by 5, you get 96.86 inches.

Suspended in free air, the mouth area for a 4520 is barely large enough to support 135 Hz before standing wave distortion kicks in. Horns operate more efficiently when deployed in a reduced solid angle.

I hope I have been of some help,

H.F.

P.S. Some kind soul on the forum a few years ago posted frequency nomographs of the RLA horn. Considering that thing begins to tank at 50 Hz, I find it odd that many folks call it a sub-woofer.

P.S.S. IMHO, the 2220 is the proper speaker to load into the 4520, 4530, and C34 enclosures. It is the commercialized version of the 130A. Both drivers share the exact Thiele-Small parameters. The 2226 is ill suited for horn loading, and the 2225 is a poor choice, as the volume of the chamber required is much greater than the chamber volumes of the JBL rear loaded horns. The 2225 has a low Efficiency Bandwidth Product. Loading a driver with a low EBP into a rear loaded bass horn such as the JBL series will produce mushy, ill-defined bass, flawlessly.

Lee in Montreal
03-10-2017, 12:01 PM
P.S. Some kind soul on the forum a few years ago posted frequency nomographs of the RLA horn. Considering that thing begins to tank at 50 Hz, I find it odd that many folks call it a sub-woofer.

If you are making references to Richard Long's Waldorf, which is an improved version of the Jensen Imperial, it is indeed a 7ft horn that gives great kick but doesn't go low. Just like the 4530. But it sounds better than a 4530 because the horn path has a very different configuration. It has very little nuls as it has no 180 bend. Only one 90 bend at the back, then goes down into the scoop portion.

One can see the throat on the top portion of the cabinet.

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=52024&d=1310505755

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=53376&d=1319306371

The Waldorf is a kick bass, which is why it was used on top of RLA's own Bertha w/ Levan horn for the two bottom octaves.

http://a1.ec-images.myspacecdn.com/images01/89/888e63b962851ac0e489fd74db0f71b1/l.jpg

Lee in Montreal
03-10-2017, 06:02 PM
Greetings -

Without having gone to the trouble of drawing the cross section of the wave guide full scale to determine it's physical length down the center line, the answer to your question of the length of the 4520 and 4530 horns may lie in what is called the Effective Length.

That's a great idea. I will draw a centerline this weekend to definitely answer the question...

Lee

Lee in Montreal
03-10-2017, 06:53 PM
Actually, here it is. I used the drawing posted by Eaulive yesterday and reproduced at 100% scale, then measured the center line. Perhaps a couple more inches can be squeezed in by increasing the numbers of radiuses for calculation. But this shows we are a long way from JBL's claimed 12 or 13ft.

96" / 8ft is what that horn seems to be. ;-)

Now, perhaps somebody has an explanation as why JBL claimed it was 12ft. Mine is it was a simple typo, and it got reproduced everywhere.

76314

RMC
03-10-2017, 08:18 PM
Hi guys,
Thanks to all of you for your replies. Haven't been here much in last few days, too many things to do, but did see quickly you've brought some very good food for thought on this issue. Haven't had time to digest all that yet... I WILL be back later to look at this further. In the meantime, here is some additionnal info I found on the subject pointing towards a possible 8 ft length horn in 4520. See you later.

Read on to better understand why dimension/weight changes MAY have some significance re horn length.

Going through some notes and revising data re 4520 cabinet, I noticed an error in my post dated March 7, 2017 In the paragraph starting with "HOWEVER," The 4520 outside cabinet dimensions and weight given are those from the May 1980 product Data Sheet, not those from the 1971 Pro catalogue as it should have been (not a big deal it seems). The correct dimensions and weight in 1971: 50 1/4" H, 35 3/4" W, 29" D, weight 240 lbs without drivers. The dimensions/weight given in my previous article are correct for 1974-1980 versions.

Compared to its 1962 C 55 ancestor, the 1971 4520 cabinet is 3/4" less deep (and 1/4" shorter). Again, comparing the 1971 cab. to the 1974-1980 editions, the latter took back that 3/4" D. Also, the 1971 cabinet had a stated weight of 240 lbs compared to 215 lbs for the 1974-1980 versions. So it has lost weight, 25 lbs to be exact, while being 3/4" deeper (other dimensions untouched). It looks like something happened between the 1971 and 1974 versions of the same box...

The 4530 stated dimensions (47 3/4" H, 23 3/4" W, 23 3/4" D) have remained the same from 1971 to 1980 (including the 7 foot folded horn), while its C 43 ancestor also remained stable at 48" H, 24" W, 24" D from 1962 to 1967, which is quite close to the 4530 dimensions. Curiously, the 4530 has gained weight from 100 lbs (less driver) in 1971 to 120 lbs in the 1974-1980 editions, at the same time the 4520 was losing some ! This 4530 addition of weight MAY be explained by the use of different construction material, like a possible switch from plywood to heavier MDF/HDF and/or thicker panels/improved bracing.

However, for the 4520 the weight loss cannot be explained only by similar possible changes in construction material/panel thickness/bracing, because then the 4520 box should also have gained weight, which is not the case... Why two enclosures from the same family, with same operating principle (rear loaded folded horn) and same general appearance/shape be treated differently ? Both enclosures use the same recommended driver since 1971, the JBL 2205, then described as a Heavy Duty 15" woofer, except for two of them in the larger 4520 box for added power, output SPL and lower bass frequencies... Quite puzzling !

Could JBL have simply reduced build quality, therefore weight, of the 4520 box between 1971-1974 ("cheapin out" as some say) ? Very unlikely in my opinion for many reasons: at that time JBL was a first-rate manufacturer, it was seriously establishing itself in the pro market as a leader and quality pro gear supplier, plus remember their famous phrase in every data sheet: "JBL continually engages in research related to product improvement. (...), any current JBL product may differ in some respect from its published description, but will always equal or exceed the original design specifications unless otherwise stated." etc.

In that context, logically, I doubt they would have reduced cabinet build quality (e.g. thinner wood panels, less bracing, etc.) in their larger double Heavy Duty woofers and pretty high output low freq. box, while at the same time improve build quality of their smaller single woofer lower output box. It wouldn't appear to make much sense, considering the 4520 really "rattled the silver", much more than the 4530...

It seems there is another and logical explanation for the 4520 weight loss... I suspect it MAY have something to do with a horn re-design(*) and possible reduction of horn length (from stated 13 ft to about 8 ft ?), by removing some horn folds inside the cabinet to achieve a shorter path. If so, this would mean Engineering forgot to tell Marketing who repeated year after year in the catalogues the 13 ft horn length, or maybe it was decided not to bother about such change in the brochures since it didn't materially or substantially affect practical performance and box size ? The horn's previous design may not have been optimal ?

(*) D. B. Keele and Ray Newman described (1976-04, IEEE preprint, Application of Recent Australian Loudspeaker Research...) some of the frenzy going-on in many speaker manufacturers' engineering dept. when R. H. Small's and A. N. Thiele's works were published at about the same 1971-1974 period in the JAES. They had to digest a mountain of new information and rush to transform new theory into products.

Richard

Lee in Montreal
03-10-2017, 09:07 PM
The 2-1/2" difference in height is most likely the pedestal. Some cabs have it, some don't. Just like the 4530. Also, the constraint being that the sidepanels must be cut from a 4'x8' sheet most likely dictate the cab's height. Not everyone has access to furniture industry-standard 5'x10' sheets.

Hopefully the Twelve Feet Horn-gate is now settled ;-)

Lee in Montreal
03-11-2017, 09:45 AM
As for Lee's comment about the length of the 4520 folded horn, he should read what the designer/manufacturer of that horn says: JBL, Professionnal Series, Low frequency Enclosures, dated May 1980, page 2 where it specifically states " Model 4520 dual driver horn, thirteen-foot folded horn ..." Yep ! At the same time having a look at the frequency responses provide by JBL for 4520 showing it is already down -5db at about 42-3HZ, -10db at 37-8HZ and -15db at 32HZ ... JBL also warns about excessive cone excursion and possible damage, suggesting power input be restricted at very low frequencies. Is Lee pretending to be more knowledgeable or smarter than JBL Engineering ?

Richard

BTW Rich

Perhaps it is time to recognize your threw unfounded accusations ? ;-)

Yup 8ft horn.

I accept your apologies

Thank you very muuuuuch. ;-)

Lee

Horn Fanatic
03-11-2017, 05:46 PM
[QUOTE=Lee in Montreal;403570]The 2-1/2" difference in height is most likely the pedestal. Some cabs have it, some don't. Just like the 4530. Also, the constraint being that the sidepanels must be cut from a 4'x8' sheet most likely dictate the cab's height. Not everyone has access to furniture industry-standard 5'x10' sheets.

"Hopefully the Twelve Feet Horn-gate is now settled ;-)"

How can the argument be settled when you haven't calculated the Effective Length? You DO know how to calculate the Effective Length, don't you? Physically measuring just the center line of the 4520 cross section cannot reveal the horn cut-off frequency. You DO know how to calculate that, don't you? I mean, you being a horn design expert, and all.

Perhaps asking Richard for an apology was a bit premature.

You wrote; "Not everyone has access to furniture industry-standard 5'x10' sheets"

Sure they do. That size material is available to anyone who finds out where it can be purchased. It's not rocket science, or a trade secret.

BTW - I noticed you drew a center line starting at the underside of the enclosure top panel. It that where you think the horn throat is?

Lee in Montreal
03-11-2017, 07:14 PM
[QUOTE=Lee in Montreal;403570]The 2-1/2" difference in height is most likely the pedestal. Some cabs have it, some don't. Just like the 4530. Also, the constraint being that the sidepanels must be cut from a 4'x8' sheet most likely dictate the cab's height. Not everyone has access to furniture industry-standard 5'x10' sheets.

"Hopefully the Twelve Feet Horn-gate is now settled ;-)"

How can the argument be settled when you haven't calculated the Effective Length? You DO know how to calculate the Effective Length, don't you? Physically measuring just the center line of the 4520 cross section cannot reveal the horn cut-off frequency. You DO know how to calculate that, don't you? I mean, you being a horn design expert, and all.

Perhaps asking Richard for an apology was a bit premature.

BTW - I noticed you drew a center line starting at the underside of the enclosure top panel. It that where you think the horn throat is?

Well, please let us know how the 4530 can be 7ft horn and the 4520 is 13ft. As for starting from the bottom of the top panel, I entirely know it is not the throat, but you'd end up with a 6.5ft horn... ;-)

BTW That Richard dude din't make any explanation or demonstration. He has no actual experience with the 4520 except for having friends who used them... So, if he's the expert, I am waiting for some clarifications about the 13ft horn... ;-)

Horn Fanatic
03-12-2017, 01:37 PM
[QUOTE=Horn Fanatic;403594]

Well, please let us know how the 4530 can be 7ft horn and the 4520 is 13ft. As for starting from the bottom of the top panel, I entirely know it is not the throat, but you'd end up with a 6.5ft horn... ;-)

BTW That Richard dude din't make any explanation or demonstration. He has no actual experience with the 4520 except for having friends who used them... So, if he's the expert, I am waiting for some clarifications about the 13ft horn... ;-)

I did provide you a plausible explanation, but it appears to have gone over your head like an SR 71. No surprise.

You wrote; "He has no actual experience with the 4520 except for having friends who used them... So, if he's the expert, I am waiting for some clarifications about the 13ft horn... ;-)"

I don't believe Richard has tried to pass himself off as an expert. That is why he is here asking questions. But it appears your only experience with the JBL and RLA folded horns is to post photographs, clever drawings, regurgitating text you have read on audio forums, condescending emoticons, and quoting David McBean endlessly. Which by my interpretation means your experience in horn design ends with a purchased canned program and uneducated guesses.

gibber
03-12-2017, 02:48 PM
7632176322

Horn Fanatic
03-12-2017, 02:57 PM
7632176322

Thank you for posting. Were those frequency graphs taken in half space, or free space?

RMC
03-12-2017, 07:05 PM
Hi Horn Fanatic,
These two frequency response curves were taken from the document I mentioned at the end of my next post coming in a few minutes. It doesn't say in which environment (half space or free space). Check next post coming in minutes...

Richard

RMC
03-12-2017, 07:21 PM
Hi guys, thanks for your patience.

I consider we are like "working" in the Lab on this site, searching, digging, exchanging views, sharing info, learning, etc. To me this is a gold mine ! "This is why he is here asking questions." Absolutely true. I never pretended being a horn design expert. I HAVE questioned in other threads: curious ways of stacking randomly in the same tall pile long throw horns (low/high) with short throw horns (low/high freq.) which didn't seem to make sense acoustically (example picture in this thread I avoided commenting); interior skating rink and use of many horns VS challenging acoustics. The comments were fair game. I have often referred to/quoted my sources, and did request HELP here from "horn specialists", "horn guys", "Tech Bible" guys on this site I named (my post March 7, 2017). Now on with our business, trying to stay on track.

To be clear on my position, in absence of justifications from JBL, I'm willing to accept any 4520 horn length number as long as it's scientifically defendable or logical. I have already indicated: I'm a believer in truthful science, and a few times recently said things seem to be pointing (physically) in the direction of an 8 ft or so horn. But interesting new stuff from HF now changes the approach to this issue...

EAULIVE: Hands-on practical re-building 4520 experience that's pretty good (huge job, I'm impressed!). Since you've been there/seen that , I understand why you are categorical about (physical) horn length. That's exactly what I'm trying to find out if JBL has a "high-flying" (U-2 type)(written before HF SR-71) way of calculation for this horn's length (see Horn Fanatic's very feasible explanation; horns do appear to be "rocket science" compared to vented boxes, for the "common man"). I never even thought about your point of possible "rough doubling" of the 4530 horn length number they MAY have taken. Though it would seem careless on their part, it could(?) have been a form of Marketing hype Greg Timbers talked about in his recent interview elsewhere on this site, as Engineers say Marketing is Marketing. However, this would not be really worthy of a Company I happen to respect.

Out of curiosity for myself, why 2225H (recones) on E-140 frames for the 4520 ? Why not E-140 recones ? Or 2225H recones on 2225 frames ? Only thing available/on hand ? Cheapest solution (money, ya that bugger)? For the longer cone travel of 2225 (5mm) VS E-140 (3.56mm)? For the smaller .17 Qts of the E-140 (closer to 2205 Qts of .21) compared to 2225's .28 Qts ? Since there's a lot of other "hybrids" out there (e.g. 2205 reconed with 2225), I have always wondered what happens in these cases to driver T/S parameters, a mix of both ? And how does the driver reacts in the box: acoustically like a 2225H but electrically like a E-140 ? A mix of both ? (I MAY SEND THIS ISSUE TO A NEW THREAD IN THE NEAR FUTURE, SINCE I'M REALLY CURIOUS TO KNOW ANSWERS ABOUT THESE QUESTIONS.)

HORN FANATIC: Great short primer on this issue. Glad you share with us. The effective (horn) length concept is in fact used in the 1952 or so brochure description of the "JBL Signature No. 34 rear-loaded folded horn corner console enclosure", mentioning an "... effective length of six feet." In the plan, the sound path is shown. In the catalogs outside cabinet dimensions have varied a little (1952: 39 3/4"H, 23 3/4"W, 22 1/2" D, a bit different from the brochure; 1962 C34: 39 3/4" H, 23 3/4" W, 23 3/8" D). Some dimensions are not mentioned in the plan, but from the many available, it appears cabinet size is not too far from the 4530 measurements (less pedestal). Two 15" woofer numbers are given in the brochure for this box: 130A, D130. Every time I try to upload something on this site, it just won't work... So if a few people (not 200 persons hopefully) are interested in having the 1952 or so 2 page brochure for this No. 34 box I'll be glad to forward it to them free, if they provide an e-mail address.

The analogy of a horn with a ducted port is very clever for understanding purposes (good for me I'm more of a vented-box guy, with a genuine interest in horns, up to the point where the math get too complicated ). "The effective length being on either end of the duct..." Since "The effective length of the 4520 may extend two to three feet past the horn mouth subject to frequency." then, in theory and subject to your disagreement with JBL's mention of direct radiator above 150HZ, when considering also the other end of the horn (symmetrical or not), I understand it MAY happen that effective length reaches up to 13 feet (subject to calculations). If that is the case, then what would be missing in JBL's more recent documentation is the mention of "effective horn length" or something like "practically acting as a X ft horn..", even though the physical length may be around 8 ft. For my own knowledge, can the rear chamber or any part of it, somehow have to be included/considered in the effective length calculation, or is it unsound thinking ?

As for driver choice to load the 4520/4530, I agree with you the 2225 and 2226 are not the best choices considering their T/S parameters with regards to the enclosure, but I understand it was roughly the closest things JBL had left in the catalog after they discontinued so many drivers. Based on many JBL documents I've seen, the 2225 appears to have been made in 1982 with the 46 series in mind (e.g. Cabaret series). With regards to the 2220 being the proper driver to load into 4520/4530, I must disagree with you for a few reasons. First, to my knowledge, JBL never recommended the 2220 for these cabinets, but rather the 2205 and K/E-140. Second, my understanding is that the 2205 was designed for use in these boxes and released at the same time in 1971, being presented as a "Heavy Duty" woofer (no wonder why, JBL sure anticipated they'd be beaten like they were). Third, a number of essential T/S parameters of the 2220 are similar to 2205/K/E-140 making the 2220 quite compatible for use in 4520/4530 I agree on that, however, for real life commercial use (clubs, discos, etc.) where it WILL be given the ride of its life, it's another story: it has less power handling, less cone stiffness, less cone excursion, and 5-7 HZ higher Fs(*). Though it was not a JBL specifically recommended driver for these cabinets, a number of people did use the K/E-145 with good sounding results since some of its parameters were not far off (e.g. a little higher Qts than 2205), but more important to all of these guys it had much greater cone travel to use and abuse...

Best regards,

Richard

(*) "The lower resonances and longer excursion capabilities of the 2205, E 140 and E 145 enable these loudspeakers (4550/4560) to provide somewhat better deep bass response compared to the 2220 at the expense of some midrange sensitivity." In the field, this phrase was also applied to the 4520/4530... JBL, Professional Series, Low Frequency Enclosures, May 1980, page 3.

Horn Fanatic
03-12-2017, 08:20 PM
[QUOTE=RMC;403636]Hi guys, thanks for your patience.

"For my own knowledge, can the rear chamber or any part of it, somehow have to be included/considered in the effective length calculation, or is it unsound thinking ?"

That will be a no. The acoustical low-pass filter is a separate element in the horn circuit. The constriction of the filter is the horn throat.

The analogies are thus;

The chamber volume represents an acoustical compliance, or in electrical terms, a capacitance. Both measured in Farrad.

The chamber volume also is comprised of an acoustical resistance.

The horn throat presents an acoustical mass, or in electrical terms, an inductor. Both measured in Henry.

The math for either is worked in the same manner. When you resonate a mass with a compliance, or capacitance with an inductance, you have a low-pass filter.

I have physically test an acoustical low-pass structure many years ago, and it does what it is designed to do. Roll off.

Good luck, HF

Hoerninger
03-13-2017, 03:11 AM
Hi guys,
I have tried to follow, but I'm slow as English is my second language.
As far as I have understood there is the question about the physical length of a JBL-horn.
Neither do I have the correct data nor a JBL horn itself. Without these the answer can't be given.

There came up the proposal to make a kind of reverse engineering by using the „lower frequency limit“. There may be differences between the definition of the term and what is claimed in a brochure. The graphes uploaded by Gibber seem to clarify but there is another obstacle. What is the „effective length“? Seen from a physical point of view of it makes sense. But there is no defined mathematical approach:

Classical horn theorie, Weber 1919, uses plane wave fronts, so there is no clearance about „effective length“.

In 1927 P.G.A.H. Voigt patented the so called Tractrix horn, He argues that the wave front will be orthogonal to the boundaries and with this not plane. He describes a graphical solution, he does not realize that he uses the tractrix function and he gives up the exponential law. Further more he says in his patent:
„In a horn constructed according to this invention, the taper at any point is as nearly as possible such that the sound is expanding as if the source was at a fixed distance which is at least a quarter wavelength, of the lowest frequency at which full efficiency is required, away.“
With this he falles back to classical horn theorie, as the demand for a quater wave length is derived by using plane wave fronts.
The tractrix uses no „flare rate“, so it is comprehensible when Dr. Bruce Edgar says that the Tractrix is not suitable for bass horns. BTW. a Tractrix horn has a directivity similar to exponential horns (AES, Lambert and Jensen, 1954).
The theorie of tractrix horns does not help to define the effective length of a horn.

The KLANGFILM labs (Germany) invented the spherical Wave Horn (Kugelwellentrichter), patent starting 1940 as I discovered about a year ago. There is obviously a difference between the geometrical length and the physical /effective length. But it should be cleared whether the approach with a constant radius all over the horn for all frequencies is proven by experiments.
The Kugelwellentrichter may be ended by a plane as the tractrix horn does and it has an improved divergence.

It is unlikely that JBL knew this patent and that it is applied for their scoops.
Klangfilm used this patent since about 1952 for their mid/high horns and for bass horns (EURONOR II and EURONOR junior).
____________
Peter

Horn Fanatic
03-13-2017, 06:53 AM
[QUOTE=Hoerninger;403647]Hi guys,

Greetings, Hoerninger -

"What is the „effective length“? Seen from a physical point of view of it makes sense. But there is no defined mathematical approach:"

Yes, there is a defined mathematical approach, and it is quite simple. It is spelled out in detail by Leo Beranek in his 1954 book titled, 'Acoustics' in chapter 5 under Radiation Impedance, and pp. 132-133 on Acoustic Elements. The subject was also sighted in Phillip M. Morse's 1936 book titled, 'Vibration and Sound', pp. 235 & 247. The effective length is the volume of air exiting an orifice which has yet to dissipate. In essence, a continuation of the air column outside the tube or horn which is subject to area and frequency.

And I do believe you're referencing Arthur Gordon Webster's 1919 paper titled, 'Experiments on the Vibration of Air in Conical Horns'. And Lambert's two part paper, 'Acoustical Studies of the Tractrix Horn'.

The Tractrix curve dates back to a study conducted by Christiaan Huygens in 1692. I am not convinced of Bruce Edgar's opinion that the Tractrix curve is unsuitable for low frequency horns. Technically, Tractrix horns should be round, but I have heard round high frequency Tractrix horns, including his, and IMHO, they sound awful. Edgar is a very smart guy, but I have little faith in his ear. John Tucker and Jeff Markwart designed their full Tractrix system they called the Exemplar Horn many years ago, and it sounded wonderful. The transition between the bass horn and high frequency horn was acoustically seamless. Planer like is my description.

BTW - It's nice to see someone here who knows their horn design history.

HF

Hoerninger
03-13-2017, 10:24 AM
...
And I do believe you're referencing Arthur Gordon Webster's 1919 paper titled, 'Experiments on the Vibration of Air in Conical Horns'. And Lambert's two part paper, 'Acoustical Studies of the Tractrix Horn'.
HF, thank you for your response.
The second paper you are mentioning is o.k. the first one is
A.G. WEBSTER. 1919, Acoustical impedance, and the theory of horns and of the phonograph, Proc. Natl. Acad. Sci. (U.S.) 5, 275–282.

reprinted in: Journal of Audio Engineering Society, 1977, 25(1-2), 24–28

which I got as a copy in my students time.
Unfortunately I missed to write down a remark similar to the following which I read somewhere:
websters work was highly appreciated as with his theorie it was finally possible to build good sounding gramophone horns.but he was blamed for the late publication, as he had kept it in a drawer for quite a while.
As said, I do not know where I have read it.


the Chapter of Beranek I will read in the afternoon, thank you for the hint.


I have only little experience with Tractrix horns (mids), only this one:
(http://http://www.audioheritage.org/vbulletin/showthread.php?11909-Paragon-XXL&p=121157&viewfull=1#post121157)http://www.audioheritage.org/vbulletin/showthread.php?11909-Paragon-XXL&p=121157&viewfull=1#post121157

My next idea is a front loaded horn with Kugelwellen shape, which is comparable short (similar to EURONOR II but with compression chamber).
____________
Peter

Horn Fanatic
03-13-2017, 11:36 AM
[QUOTE=Hoerninger;403663]HF, thank you for your response.

A.G. WEBSTER. 1919, Acoustical impedance, and the theory of horns and of the phonograph, Proc. Natl. Acad. Sci. (U.S.) 5, 275282.

reprinted in: Journal of Audio Engineering Society, 1977, 25(1-2), 2428


Ha! I do have that paper also. It was paper clipped behind the conical horn paper. I thought the title of the paper you sighted sounded familiar.

HF

Eaulive
03-16-2017, 07:27 AM
Out of curiosity for myself, why 2225H (recones) on E-140 frames for the 4520 ? Why not E-140 recones ? Or 2225H recones on 2225 frames ? Only thing available/on hand ? Cheapest solution (money, ya that bugger)? For the longer cone travel of 2225 (5mm) VS E-140 (3.56mm)? For the smaller .17 Qts of the E-140 (closer to 2205 Qts of .21) compared to 2225's .28 Qts ? Since there's a lot of other "hybrids" out there (e.g. 2205 reconed with 2225), I have always wondered what happens in these cases to driver T/S parameters, a mix of both ? And how does the driver reacts in the box: acoustically like a 2225H but electrically like a E-140 ? A mix of both ? (I MAY SEND THIS ISSUE TO A NEW THREAD IN THE NEAR FUTURE, SINCE I'M REALLY CURIOUS TO KNOW ANSWERS ABOUT THESE QUESTIONS.)
Originally I was planning on loading the cabs with 2225s but since I had a bunch of E140 frames on hand I checked the possibility and tried to predict the behaviour of the E-140/2225 mix.
Both frames have the same gap width and length, the only difference lies in the magnet strength. The 2225 has a 1.2T motor while the E-140 has a 1.35T motor so I figure after much reading here and elsewhere that the only difference would be in higher frequency response outside the band I was planning to use them (my 4520s are crossed at 150Hz with my midbass horn) so I went with that.
Besides, I don't like the aluminum dust cap on a speaker system that is intended to be a sound "reproducer", not a sound "producer" :p

A friend had original 2225s so we swapped them for fun and did not see a difference for that specific application (4520s crossed at 150Hz)

As for the other "mixes" a 2225 on a 2205 frame is basically a 2225 because the frame and magnet structures are identical, the big NO-NO is using these cones on a 2220 frame as I saw in the past... Lee will remember the source of my 4520s and the drivers the guy wanted to push on us ;-)

RMC
03-16-2017, 02:29 PM
Thanks EAULIVE for your input. Very informative. As you know this issue is now continued in a separate new thread re "Hybrid" reconed drivers... I have transfered your reply in this new thread. Thanks again .

Richard