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

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/s...ad.php?t=12773
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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

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 ?

Quote:

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Originally Posted by Lee in Montreal

Simple calculations will tell it all.

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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.
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Peter

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.
Attachment 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...
Attachment 76308

As an added bonus, some pics :D
https://www.flickr.com/photos/eauliv...60334894/page1

Quote:

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Originally Posted by Hoerninger

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

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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.

Quote:

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Originally Posted by Horn Fanatic

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.

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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/vbullet...4&d=1310505755

http://www.audioheritage.org/vbullet...6&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/i...db0f71b1/l.jpg

Quote:

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Originally Posted by Horn Fanatic

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.

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

Lee

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.

Attachment 76314

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

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 ;-)

Quote:

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Originally Posted by RMC

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

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BTW Rich

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

Yup 8ft horn.

I accept your apologies

Thank you very muuuuuch. ;-)

Lee

[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?

[QUOTE=Horn Fanatic;403594]

Quote:

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Originally Posted by Lee in Montreal

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?

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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... ;-)

[QUOTE=Lee in Montreal;403600]

Quote:

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Originally Posted by Horn Fanatic

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... ;-)

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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.

Attachment 76321Attachment 76322