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rloggie
01-14-2006, 09:44 PM
What would be the result if I mixed an 8ohm woofer with a 16ohm compression driver using a 16ohm crossover. ie 130a and 2441. Would I be guessing correctly that the woofer would be somewhat muted?:o:

Mr. Widget
01-14-2006, 09:47 PM
You can and we do mix drivers of various impedances with no problems. The crossover is the critical point. Do you have the network schematic? Is it a JBL network?


Widget

rloggie
01-14-2006, 09:54 PM
Hi Widget,

The crossover is a JBL 3115 and I thought I might try a pr. of 130a 8ohms woofers that are available. My LE15s have a rub and may get a full reconing.

johnaec
01-14-2006, 10:04 PM
The crossover is a JBL 3115...The 3115 is spec'd for 8-18 ohm LF and 16 ohm HF, so you should be good to go: http://www.jblpro.com/pub/obsolete/Frequency_Dividing_Networks1.pdf

Did you pick up those 130A's recently on craigslist?

John

rloggie
01-14-2006, 10:25 PM
Yeah, those are the ones. They may be gone already but I've emailed to find out. I talked to the guy right after they appeared but couldn't get away to pick them up. We'll see if he calls back tonight.

Mr. Widget
01-14-2006, 10:54 PM
The problem isn't the impedance mis-match... the problem will be the sensitivity difference between the LE15A and the 130A. The new woofer will have significantly greater output above 100Hz than the LE15A had.


Widget

rloggie
01-14-2006, 11:05 PM
The problem isn't the impedance mis-match... the problem will be the sensitivity difference between the LE15A and the 130A. The new woofer will have significantly greater output above 100Hz than the LE15A had.


Widget


Since neither of these speakers list sensitivity in the library how does one know the differences on paper?? Or do you know by experience?

Mr. Widget
01-14-2006, 11:10 PM
Since neither of these speakers list sensitivity in the library how does one know the differences on paper?? Or do you know by experience?In this case I do have experience with both... but the info is also in the library.

http://www.lansingheritage.org/images/jbl/catalogs/1974-home/page15.jpg

rloggie
01-14-2006, 11:18 PM
I see. These would go into the Hartsfield cabs. I wonder what the original 150-4 sensitivity was?? It seems to be cut from the same cloth.

http://www.lansingheritage.org/images/jbl/specs/home-comp/130-150/page1.jpg

Mr. Widget
01-14-2006, 11:21 PM
Can't help you there... but if the LE15As were sounding right, the 130As won't.


Widget

Zilch
01-15-2006, 02:20 AM
Do we consider K/E145 an option for Hartsfield?

Their response is closer to 150-4C than LE15A is, no?

[Thinking "Everest" here....]

toddalin
01-15-2006, 11:46 AM
Yeah, those are the ones. They may be gone already but I've emailed to find out. I talked to the guy right after they appeared but couldn't get away to pick them up. We'll see if he calls back tonight.

I have a pair of 130As lying around if you are interested. I would even trade them for a NICE power amp than can be used in mono. This be them:

http://www.largescaleonline.com/eimages/lsolpics/Team_Member_Pics/toddalin/speaker4.jpg

majick47
01-15-2006, 07:14 PM
While your on the topic maybe someone can answer my question from their practical experience with L pads. I have some 3106 crossovers for 2405 tweeters (16 ohm) and noticed the L pads were marked 8 ohm. Would the 8 ohm L pads diminish the output of the crossover or have any other negative impact?

louped garouv
01-15-2006, 08:29 PM
but this time with ALtec N800 Xover and 515Bs (16 ohms)....


I think that the combo w/ 511B (802-8G loaded) sounds fine but what do I know...

Zilch
01-15-2006, 09:00 PM
While your on the topic maybe someone can answer my question from their practical experience with L pads. I have some 3106 crossovers for 2405 tweeters (16 ohm) and noticed the L pads were marked 8 ohm. Would the 8 ohm L pads diminish the output of the crossover or have any other negative impact?8-Ohm adjustable L-Pad is correct. If I were making it out of fixed resistors, I'd build around 10 Ohms:

http://audioheritage.org/vbulletin/showpost.php?p=62922&postcount=51

majick47
01-16-2006, 09:16 AM
Zilch I did a search of the old threads and from what I can gather this also applies to the LE85/2420, ie L200b/q&d 4430, that they would also use 8 ohm L pads. Some of the L pads on my old L200b crossovers are unmarked, mismatched and have dead spots. Time to replace them all with new matched 8 ohm L pads with your blessings.

toddalin
01-16-2006, 10:52 AM
Zilch I did a search of the old threads and from what I can gather this also applies to the LE85/2420, ie L200b/q&d 4430, that they would also use 8 ohm L pads. Some of the L pads on my old L200b crossovers are unmarked, mismatched and have dead spots. Time to replace them all with new matched 8 ohm L pads with your blessings.

No, the N200B uses a 16 ohm L-pad to the LE85. This may be critical as these crossovers do not use autotransformers. I'm building some now that also incorporated the N7000/N8000 circuit (set to about 7,650 Hz) but using superior components (Solen, Theta, ERSE) and by-pass caps throughout and had to order these rather than use the 100-watt, 8 ohm pads I already have.:banghead:

http://manuals.harman.com/JBL/HOM/Technical%20Sheet/L200B%20ts.pdf

Zilch
01-16-2006, 10:57 AM
Hiya, Majick.

It's best to check the schematics for the various crossovers. L200B, for example, says "16 Ohms, 30W." That one seems to have custom resistance values, actually, from what I've measured. It's also a very nice porcelain unit. I'd try opening and cleaning it with contact cleaner first, replacing only as a last resort.

Once you access the L-Pads and remove them from the circuit, you can easily measure the resistance values if they're not marked. The series leg (between terminals 2 and 3) will typically adjust from zero to the nominal L-Pad resistance value.

Earl K
01-16-2006, 11:39 AM
Once you access the L-Pads and remove them from the circuit, you can easily measure the resistance values if they're not marked. The series leg (between terminals 2 and 3) will typically adjust from zero to the nominal L-Pad resistance value.

- Zilch, I believe you're wrong in your description of a methodolgy to test an unknown variable pad for its' circuit impedance.


- Try this method :

(1) Orienting the LPad with the shaft pointing towards you / & with the pad turned fully "down" ( this is fully counterclockwise )

(2) Measure between tabs/pins #3 & #2
( #3 is on the left & #2 is the center tab, in this orientation )

(3) This resistance measurement on one of my older ceramic-type 100W Lpads is @ 15 ohms.

(4) This pad turned fully on ( clock-wise ) gives a resistance reading of only a fraction of an ohm ( about the resistance of my leads at .4 ohms ) between #3 & #2 .

- These readings make sense when one looks at the Lpads conjugate resistance ( paralleled across the 16 ohm load ) .
- For instance , the measurement between tab #2 & Tab #1 ( with the Lpad fully "off" ) is a fraction of an ohm ( say .3 ohms with no load ) . This paralleled with the 16 ohm load equates to a new load resistance of @ .294 ohms .
- Obviously the series resistor portion ( build-out resistor on the source side ) for the Lpad must be in the 15 ohm plus range to restore the circuits' working impedance back to @ 16 ohms .

:)

Zilch
01-16-2006, 12:11 PM
- Zilch, I believe you're wrong in your description of a methodolgy to test an unknown variable pad for its' circuit impedance.Well, you're always a bit more precise about stuff. ;)

Even though it only measures 15 Ohms, I believe we would agree that equates to a "nominal" 16-Ohm L-Pad for replacement purposes.

If it measured 11 Ohms, I'd be lookin' at the other leg for a potential custom specification, yes.... :p

Earl K
01-16-2006, 12:22 PM
Well, you're always a bit more precise about stuff.

Well, thanks for that / OTOH I shouldn't have used "wrong" in my reply /

- so there goes the "precise" hat ( got to "wear" it for 90 sec. ) . :p :D

Ian Mackenzie
01-16-2006, 02:07 PM
Earl is right,

They are sloppy at best but in the case of an 8 ohm version, the series aspect measures .2 - 8 ohms for 0 -40 db attenuation while the shunt arm has resistance of 0 - 35 ohms and then opens to infinite ohms.

The 16 ohm version would have a series aspect of about 16 ohms and shunt arm with a maximum of around 60 ohms.

The tends to be not very accurate at the start for 0 2 db attenuation, that is why in the designs the 0 position is often at - 4 db on the actual Pad.

Back to the issue unless there is actual corrosion it is possible to open and clean them, but the internals are not friendly to prying fingers.

Looking at some of the schematics, they are actually designed for 10-11 ohm impediances for the correct attenuation. The impediance curves also suggest this ..funny about that. The 16 ohm L pads were used for power handling.

Hope this is of assistance.

Ian

majick47
01-16-2006, 06:06 PM
Thanks to the LH experts for the advice and I'll be useing 16 ohm L pads for the crossovers. If I have any more of the old ceramic L pads I'll clean them instead of replacing them being careful I don't damage them in the process. Also I'll keep an eye out for the old style ceramic L pads.