woofer impedance folded horns

[Esoteric]

I have 2 "K" type folded horns with JBL 2205 woofers rated at 16ohms.
I understand that the woofers should be 3.2ohms. Can I place resistors across the woofer terminals ( Pos. to Neg.) to lower the impedance? What values on the resistors do I need?

I am using the LX-5 network ,8ohms, and the 2440 drivers with horn and lens assembly. The LX-5 actually measures
12.5ohms.

[Harvey Gerst]

Uh, that's not a great idea; the resistors would get most of the power and it would just be radiated as heat.

The right answer to the resistor problem would be adding a 4 Ohm resistor in parallel across the 16 Ohm speaker to achieve a 3.2 Ohm load, but it's not the right solution.

The correct solution is to use a different amp that can properly drive the woofer, or recone the speaker to the desired impedance.

[Esoteric]

Why is that?

Hal Cox suggested that impedance and I think Klipsch used 3.2 drivers.

[scott fitlin]

I think the impedance of the original woofers used was a 4ohm woofer, as 3.2 ohms is the DC resistance, not the impedance. Many 4 ohm woofers of the past would read 3.2 ohms on a meter.

[Esoteric]

Uh, that's not a great idea; the resistors would get most of the power and it would just be radiated as heat.

The right answer to the resistor problem would be adding a 4 Ohm resistor in parallel across the 16 Ohm speaker to achieve a 3.2 Ohm load, but it's not the right solution.

The correct solution is to use a different amp that can properly drive the woofer, or recone the speaker to the desired impedance.

Thank you, Harvey for your suggestions.

[Esoteric]

I think the impedance of the original woofers used was a 4ohm woofer, as 3.2 ohms is the DC resistance, not the impedance. Many 4 ohm woofers of the past would read 3.2 ohms on a meter.

You're right. My mistake. The woofers were 4ohms. I don't understand why
because my woofers blend nicely with the 2440s, but I just wondered what I was missing if anything. The curse of us hi-fi nuts!

[scott fitlin]

Yeah, but if the crossover networks were designed to see a 4 ohm impedance, you arent getting the correct performance using 16 ohm coils.

[Esoteric]

Yeah, but if the crossover networks were designed to see a 4 ohm impedance, you arent getting the correct performance using 16 ohm coils.

I understand that, but the crossovers (LX-5s) actually measure 12.5 ohms and not a bad match for the woofers. I want to know why JBL used a 4 ohm woofer in the Hartsfield and Paragons with 8-16 ohms mid and hi freq.drivers which is what Klipsch did. My speakers are very similar to the Hartsfields.

[Esoteric]

I could be mistaken, but wasn't the LX-5 expecting nominal 16 ohm drivers?
(like LE15A, or was there more than one LX-5 version?)
Horn loading the 2205 might raise the driver's impedance some... which
would tend to lower the crossover for the bass driver (only)... perhaps
making a hole where the K-horn is already running out of steam (400-500Hz)

... that's about all I can think of without available measurements with
respect to frequency (impedance and/or amplitude).

Bottom line... if you like what you're hearing, why poke at it?
(OK... I would too :))

Edit: why 4ohm drivers in horn loaded enclosures?
Some interesting reading:
http://www.volvotreter.de/khorn.htm



-grumpy
There were 8 and 16 ohm versions of the LX-5. I have the 8 ohm unit. Thanks for the link, it answers my question. Nick

[Harvey Gerst]

I understand that, but the crossovers (LX-5s) actually measure 12.5 ohms and not a bad match for the woofers. I want to know why JBL used a 4 ohm woofer in the Hartsfield and Paragons with 8-16 ohms mid and hi freq.drivers which is what Klipsch did. My speakers are very similar to the Hartsfields.
Whoa, back the wagon up there, sonny. When exactly did we ever put 4 ohm woofers in Hartsfields? I don't remember that during my time at JBL, and I was the guy putting the speakers in them and testing them.

[Oldmics]

Hartsfields used 16 ohm woofers,16 ohm on the 375 drivers and 16 ohm on the tweeters that were so equipted.

Same with the Paragon drivers.

Oldmics

[RKLee]

Whoa, back the wagon up there, sonny. When exactly did we ever put 4 ohm woofers in Hartsfields? I don't remember that during my time at JBL, and I was the guy putting the speakers in them and testing them.So what kind of speakers did you put in the Hartsfields and Paragons?

[Harvey Gerst]

So what kind of speakers did you put in the Hartsfields and Paragons?When we started putting out Hartsfields and Paragons, they came standard with 150-4C's in both. Even with the first "coffin-back" Hartsfields, they had 150-4C's. After Ed May and Bart Locanthi came up with the LE-15, we switched to those instead.

Most of the Hartsfields were made during the Fletcher Drive years. The coffin-back Hartsfield was designed by Bill Burton and Bart Locanthi while we were still on Fletcher Drive. We started thinking about stereo only during the last year or so at Fletcher Drive, but it became more serious when we moved to Casitas.

The Paragons were all from the Casitas years. Ed May didn't come on board till after we moved to Casitas, so no LE-15's were even designed until well after our move from Fletcher Drive. I remember working on the first Paragon prototype. That's the only time I met Col. Richard Ranger.

[rs237]

[quote=Harvey Gerst;181388]When we started putting out Hartsfields and Paragons, they came standard with 150-4C's in both. Even with the first "coffin-back" Hartsfields, they had 150-4C's. After Ed May and Bart Locanthi came up with the LE-15, we switched to those instead.

quote]


Harvey,

sorry my English is very bad. Do I have correctly understood also in the Hartsfield the LE15 was used?

regards
juergen

[Harvey Gerst]

[quote=Harvey Gerst;181388]When we started putting out Hartsfields and Paragons, they came standard with 150-4C's in both. Even with the first "coffin-back" Hartsfields, they had 150-4C's. After Ed May and Bart Locanthi came up with the LE-15, we switched to those instead.

quote]


Harvey,

sorry my English is very bad. Do I have correctly understood also in the Hartsfield the LE15 was used?

regards
juergenWe were making very few Hartsfields by the time the LE-15 came out, but yes, I think I recall putting the LE-15 in some of the last Hartsfields made. I may be wrong, but catalogs from that period (around 1965) should have it right.

[Esoteric]

[quote=rs237;181389]We were making very few Hartsfields by the time the LE-15 came out, but yes, I think I recall putting the LE-15 in some of the last Hartsfields made. I may be wrong, but catalogs from that period (around 1965) should have it right.

Sorry Harvey. When Hal Cox suggested a 4 ohm woofer for me we were discussing the similarity between my horns and the Hartsfield and I thought that the 150-4-C was 4 ohms. What was the impedance?

Nick

[Maron Horonzakz]

150-4C...16 ohms ,,, 150-4...32 ohms

[Esoteric]

150-4C...16 ohms ,,, 150-4...32 ohms

Thank you, Maron. I guess I'll stick with 16 ohm woofers. Nick

[Harvey Gerst]

Geez, I just realized; that was 42 years ago !!! How the time flies when you're having fun.

[rs237]

[quote=rs237;181389]We were making very few Hartsfields by the time the LE-15 came out, but yes, I think I recall putting the LE-15 in some of the last Hartsfields made. I may be wrong, but catalogs from that period (around 1965) should have it right.

Harvey,

thanks for your answer. I will test the LE15 and the E145 in my Hartsfield project. I hope to find also still a pair 150C(-4).

regards
juergen

[Harvey Gerst]

Harvey,

thanks for your answer. I will test the LE15 and the E145 in my Hartsfield project. I hope to find also still a pair 150C(-4).

regards
juergen
Keep in mind that this only applies to the "coffin-backed" Hartsfields. We never tried an LE15 in the original Hartsfield.

[rs237]

Keep in mind that this only applies to the "coffin-backed" Hartsfields. We never tried an LE15 in the original Hartsfield.

Harvey,

Yes I build the “coffin-backeed” Hartsfields. From the original one there are unfortunately no plans, or has you which ?

regards

juergen

[Harvey Gerst]

Harvey,

Yes I build the “coffin-backeed” Hartsfields. From the original one there are unfortunately no plans, or has you which ?

regards

juergenVern Bender built most of the original Hartsfields, and he kept a set of the plans at home. I don't even know if he's still alive.

[Esoteric]

Harvey,

Yes I build the “coffin-backeed” Hartsfields. From the original one there are unfortunately no plans, or has you which ?

regards

juergen



Harvey, what is the "coffin "back"?

Nick

[Harvey Gerst]

Harvey, what is the "coffin "back"?

NickThe original Hartsfield had an opening below where the 375 driver sat. It was through this small opening that you installed the 1540-4C. It was a knuckle-busting job. They redesigned the cabinet to accept the speaker mounted right on the back, and it had a cover that slightly resembled a coffin, hence the name.

If you can take off the back and see the speaker, it's a newer Hartsfield; if you can't figure out where the hell the woofer is, it's an older Hartsfield.

[RKLee]

When we started putting out Hartsfields and Paragons, they came standard with 150-4C's in both. Even with the first "coffin-back" Hartsfields, they had 150-4C's. After Ed May and Bart Locanthi came up with the LE-15, we switched to those instead.

Most of the Hartsfields were made during the Fletcher Drive years. The coffin-back Hartsfield was designed by Bill Burton and Bart Locanthi while we were still on Fletcher Drive. We started thinking about stereo only during the last year or so at Fletcher Drive, but it became more serious when we moved to Casitas.

The Paragons were all from the Casitas years. Ed May didn't come on board till after we moved to Casitas, so no LE-15's were even designed until well after our move from Fletcher Drive. I remember working on the first Paragon prototype. That's the only time I met Col. Richard Ranger.Being a newbie on JBL speakers, I am only familiar with the Casitas address. Unfortunately I disposed off my only JBL brochure that had the Casitas address. All of my subsequent brochures have the current address of today.

So the Hartsfields had mostly 150-4C's and a few LE15s, and most of the Paragons had LE15s, and a few 150-4C's.

[glen]

The original Hartsfield had an opening below where the 375 driver sat. It was through this small opening that you installed the 1540-4C. It was a knuckle-busting job.

if you can't figure out where the hell the woofer is, it's an older Hartsfield.

Here's a picture of the original Hartsfield setup from the patent application (on this site) showing where the woofer sits, and also a nice drawing of the horn path.

[Hoerninger]

Looking at the patent I get the impression that the primary horn layout gave the possibility to build a backloaded or a frontloaded horn.

The second layout is only useful for a frontloaded horn. And I do suppose that it has advantages in frequency response. This means lesser irregularities and perhaps a higher upper frequency limit (which is most offen a problem with bass horns.)
___________
Peter

[rs237]

Hallo Peter,

yes correctly , in the catalog of 1954 there is the Hartsfield as 208-DH kits with the D208 Fullrange driver as backloadet Horn.

regards

juergen

[glen]

Hallo Peter,

yes correctly , in the catalog of 1954 there is the Hartsfield as 208-DH kits with the D208 Fullrange driver as backloadet Horn.

regards

juergen

from the Hartsfield article on this site:
http://www.audioheritage.org/html/profiles/jbl/hartsfield.htm
"The logic of stuffing a $25 driver into a $300 enclosure was questionable at best and was never a marketing success. This option was dropped within two years. "
© 2000 Don McRitchie

But I wonder if that D208 option might have been influenced by the Lowther loudspeaker single-driver philosophy and designs that were popular with hobbyists in England. The D208 would have been the LE8T of it's time, and there are still plenty who still think the LE8T is the best option available.

Around the same time the Hartsfield was introduced Lowthers were being used in large rear-loaded folded horn cabinets. The TP1 London enclosure, introduced in the 50's and still being made, is a big front and rear-loaded corner horn, but at 39x31x23 inches (102x80x60 cm) not quite as big as a Hartsfield.

Maybe someone at JBL thought the D208/D216 was special enough to spark a wave of interest similar to the Lowther popularity that is still going strong today.

Has anyone ever heard a D208/D216 in a Hartsfield cabinet?

Lowther TP1 picture attached

[Harvey Gerst]

from the Hartsfield article on this site:
http://www.audioheritage.org/html/profiles/jbl/hartsfield.htm
"The logic of stuffing a $25 driver into a $300 enclosure was questionable at best and was never a marketing success. This option was dropped within two years. "
© 2000 Don McRitchie

But I wonder if that D208 option might have been influenced by the Lowther loudspeaker single-driver philosophy and designs that were popular with hobbyists in England. The D208 would have been the LE8T of it's time, and there are still plenty who still think the LE8T is the best option available.

Around the same time the Hartsfield was introduced Lowthers were being used in large rear-loaded folded horn cabinets. The TP1 London enclosure, introduced in the 50's and still being made, is a big front and rear-loaded corner horn, but at 39x31x23 inches (102x80x60 cm) not quite as big as a Hartsfield.

Maybe someone at JBL thought the D208/D216 was special enough to spark a wave of interest similar to the Lowther popularity that is still going strong today.

Has anyone ever heard a D208/D216 in a Hartsfield cabinet?
Believe it or not, I had a pair of Hartsfields for a while with Lowther's in them and they did sound pretty damn impressive. The 208 adapter kit was a curved smaller wood horn arrangement, that sat where the lens goes, and arched down to the woofer opening. I'll try to draw something up today as to what it looked like.

[Thom]

Uh, that's not a great idea; the resistors would get most of the power and it would just be radiated as heat.

The right answer to the resistor problem would be adding a 4 Ohm resistor in parallel across the 16 Ohm speaker to achieve a 3.2 Ohm load, but it's not the right solution.

The correct solution is to use a different amp that can properly drive the woofer, or recone the speaker to the desired impedance.

If your current amp is able to drive the speaker/enclosure to a level you are happy with then there is no reason for a new amp. Now the only question is does the crossover match the woofer. If it doesnt it can be modified or replaced. If it is looking for 4ohms and sees 16 it will cross much higher. This may or may not be audible as you undoubtedly have a lot of mechanical roll off as well.

It's also possible that it is so efficient that you are using so little power that you actually could parallel it with a power resistor but I would make sure that I had a problem before I started fixing it.

[rs237]

Has anyone ever heard a D208/D216 in a Hartsfield cabinet?




unfortunately not. As Fullrange fan I would try it gladly. Unfortunate those the plans of the old Hartsfield are not available.

regards
juergen

[Harvey Gerst]

Very strange to realize I may be the only person on the planet to have heard the Lowthers in the old Hartsfield cabs. I don't remember installing any 8" speaker kits in the Hartsfields while I worked there. We may have built a few, but it would have been a damn few.

The other "weird" system I had was a Metragon with Janzen electrostatic tweeter and their woofers installed. What the "weird" part is that the cabinet shop actually made the Metragon with the Janzen cutouts for me; the only time I think they built something for non-JBL components. I damn near got fired because of it. Bill Thomas actually had to step in and settle the dispute it caused.

[Harvey Gerst]

The 208 "Hartsfield kit" used 1/4" plywood as I recall for the horn part, while the box and 15" opening adapter was 1/2" thick. Excuse the crude drawing but the 208 "Hartsfield kit" kinda looked like this:

[Zilch]

There is no mystery here as to why the Hartsfield was built the way it was. Look at the independent claims of the patent, 1, 4, 7, and 10.

http://www.audioheritage.org/html/profiles/jbl/hartsfield.htm

[Harvey Gerst]

There is no mystery here as to why the Hartsfield was built the way it was. Look at the independent claims of the patent, 1, 4, 7, and 10.

http://www.audioheritage.org/html/profiles/jbl/hartsfield.htm
Damn, you mean I didn't hafta do the drawing?

[Zilch]

It was a test, Harvey.

[And you passed, obviously.... :p ]

[louped garouv]

that's awesome....

:)

[glen]

The other "weird" system I had was a Metragon with Janzen electrostatic tweeter and their woofers installed. What the "weird" part is that the cabinet shop actually made the Metragon with the Janzen cutouts for me; the only time I think they built something for non-JBL components. I damn near got fired because of it. Bill Thomas actually had to step in and settle the dispute it caused.
What the hell!:blink:
Hey Harvey, you gotta give us more details on this story,
sounds good enough to be a whole new thread!
Anybody who came accross that cabinet would have been shaking their head at the weird customization done to a perfectly good Metregon system

[Harvey Gerst]

What the hell!:blink:
Hey Harvey, you gotta give us more details on this story,
sounds good enough to be a whole new thread!
Anybody who came across that cabinet would have been shaking their head at the weird customization done to a perfectly good Metragon system
Yeah, but it's probably not worth a whole thread. George Augspurger and I were always putting together weird stuff, and I was impressed with the clarity of these new electrostatic tweeter panels that I heard at one of the Hi-Fi shows. What I wasn't impressed with was the dispersion. There was none.

Soooo, I reasoned, what if I dump this stuff into a Metragon to give me the dispersion? I bought one, using my employee discount and gave the cabinet shop the layout I wanted for the baffle boards. When the paperwork came across our sales dept. desk, the shit hit the fan.

"The discount is to encourage JBL employees to buy JBL systems; you can't put other peoples components in there." Well, I didn't take that laying down (I was very pushy in my youth).

Ray Pepe and I argued, but we were both unmovable. Finally, Bill Thomas came in and settled the argument - in my favor. It was a kickass sounding system.

[scott fitlin]

Hey, thats a great story.

:D

[glen]

Yeah, but it's probably not worth a whole thread. George Augspurger and I were always putting together weird stuff . . .
Sure sounds like an interesting thread to me, wonder what else you had along with the Jantzen powered Metregon and Lowthers in Hartsfield cabinets.

What happened to those oddball systems?
Do you still have any of them?

[Harvey Gerst]

Sure sounds like an interesting thread to me, wonder what else you had along with the Jantzen powered Metregon and Lowthers in Hartsfield cabinets.

What happened to those oddball systems?
Do you still have any of them?
Nope, they're all long gone. I had a couple of 300Hz horns for 175 drivers that I found in the back room at JBL. They were about 3 feet deep by 3 feet wide by maybe 10 inches tall. Somebody told me they were made for Bolt, Baranck?, & Neuman, or possible Ampex.

Other than the big JBL system (in our Studio A) that Ed May built for himself, all the JBL's I still have are stock stuff.

[scott fitlin]

Nope, they're all long gone. I had a couple of 300Hz horns for 175 drivers that I found in the back room at JBL. They were about 3 feet deep by 3 feet wide by maybe 10 inches tall. Somebody told me they were made for Bolt, Baranck?, & Neuman, or possible Ampex.

Other than the big JBL system (in our Studio A) that Ed May built for himself, all the JBL's I still have are stock stuff.No one off JBL designs?

No things that would have been fantastic but never made it to production because they would cost too much to produce?

JBL had to have a few things no one knows about! Not even 1?

:(

[Harvey Gerst]

No one off JBL designs?

No things that would have been fantastic but never made it to production because they would cost too much to produce?

JBL had to have a few things no one knows about! Not even 1?

:(
Actually, no. Pretty much everything we came up with went into production. Except one.

I remember Ed May built a woofer that put out a ton of pure bottom end without much distortion. He played a 27 Hz sine wave through it, and it was like your head was instantly pressurized; you couldn't talk or hardly breathe. Made everybody sick to their stomach. Don't know what happened to that speaker.

[spkrman57]

Actually, no. Pretty much everything we came up with went into production. Except one.

I remember Ed May built a woofer that put out a ton of pure bottom end without much distortion. He played a 27 Hz sine wave through it, and it was like your head was instantly pressurized; you couldn't talk or hardly breathe. Made everybody sick to their stomach. Don't know what happened to that speaker.

You probably just woke up everyones interest about that woofer.;)

Maybe someone from the past who might happen across this thread might be able to tease us some more.:bouncy:

Thanks for sharing with us Harvey, I always enjoy reading your posts!!!:applaud:

Regards, Ron

[Harvey Gerst]

You probably just woke up everyones interest about that woofer.;)

Maybe someone from the past who might happen across this thread might be able to tease us some more.:bouncy:

Thanks for sharing with us Harvey, I always enjoy reading your posts!!!:applaud:

Regards, Ron
Well, lemme see if I can add a little more information:
The lab and the sound room were at the east end of the building on Casitas, and one wall faced the street. The lab was kinda small and held the chart recorder, polar plotter and the various mics and prototypes. It had wires to both the large sound room, and to the roof (where we'd occasionally run free-field plots).

The sound room was pretty big (I don't remember the exact size) and Ed had set up this kinda big box in one corner of the room. I don't remember if it was a 15" or an 18" woofer.

All I remember is when you opened the door to the sound room and walked in, it was like suddenly being underwater; pressure everywhere. Not really a note; just pressure. You couldn't breathe and you could barely talk.

It was a interesting experience.

[scott fitlin]

Actually, no. Pretty much everything we came up with went into production. Except one.

I remember Ed May built a woofer that put out a ton of pure bottom end without much distortion. He played a 27 Hz sine wave through it, and it was like your head was instantly pressurized; you couldn't talk or hardly breathe. Made everybody sick to their stomach. Don't know what happened to that speaker.Interesting! Ed May.

Harvey, what is it that made certain yesteryear drivers have such viscious bottom end? Especially that super fast transient attack that older JBL, Altec, and Gauss woofers had?

[louped garouv]

sounds like sitting in a SPL competetition bass car...


Wow...

:blink:

[Harvey Gerst]

Interesting! Ed May.

Harvey, what is it that made certain yesteryear drivers have such viscious bottom end? Especially that super fast transient attack that older JBL, Altec, and Gauss woofers had?
A very tight magnetic structure, a small gap, a lot of copper/aluminum wire stuffed in that gap, and a relatively light, stiff cone.

[00Robin]

A very tight magnetic structure, a small gap, a lot of copper/aluminum wire stuffed in that gap, and a relatively light, stiff cone.

Sorry for the effusive gushing,but anything you post,Harvey,IS fascinating. Makes me wish I had been there during those days. At least I'm listening to what you built back then everyday and right now even. Were all you guys from and still in Texas? Does the super dry air of the western states and then the humidity of Michigan cause problems with the older Altec's?
Just wondering since I had to move back to Michigan after 30 glorious years in Wyoming and Montana.

[Harvey Gerst]

Sorry for the effusive gushing,but anything you post,Harvey,IS fascinating. Were all you guys from and still in Texas?
I moved to Texas from L.A. in 1978. Ed May worked at Frazier/May in Dallas before he went to work at JBL. I first met Ed when he went to work at JBL on Casitas. I was at JBL several years before Ed joined us. Ed replaced Bill Burton as Chief Engineer when Bill started Transducers Inc., a subsidiary of JBL, making high intensity sound systems.

[scott fitlin]

A very tight magnetic structure, a small gap, a lot of copper/aluminum wire stuffed in that gap, and a relatively light, stiff cone.I love the woofers, high efficiency LF woofers of the 70,s and 80,s.

Im getting the sound I desire/crave, from brand new GPA Altec 416-8C,s VOTT loaded.

I have tried, in vain, to get into more modern, higher power handling speakers. All to no avail.

I still use six JBL 2395/2441 lenses, and 1 Crown D-150A powers all six horns, and its stunning what just a few watts will do with these.

I still use JBL 2240,s in scoop cabinets, and although not true sub woofers, they sound great, and again, what they do with relatively little power........