Ohms Law JBL 240Ti's

[groovey records]

Greetings to the denziens of the Lansing Heritage Salon

To be brief I am a new poster but have owned my JBL 240ti's some 22 years.
They have been restored within the last to years to spec. I am about to get a pair of Atma-Sphere MA 1 Silver Aniversary OTL Mono block amplifiers to replace my also 22 year old Carver Reciever. Both units provide 140 watts but all similarities end there.

With the SS Carver speaker impeadence was not an issue but with OTL design 8 ohms or higher is desired.

I have heard just now of speaker load drift , I don't know how to put it-- Different passages of music create different demands on the amplifier which inturn cause the speaker resistance to drift down or up.

Some speakers are more stable and are immune to this phenommena. I hope this is the case with my 240Ti's.

Does anyone know specificly about this drift in reference to the 240ti's or is there a way to measure it with a multi meter that would be accurate for my purposes.

Thanks in advance

Best Regards

Groovey Records

[johnaec]

Hopefully, someone has a copy of the 240Ti impendance curve they can post.

Not to scare you, but hopefully it isn't similar to the 4315's. I have a set of 4315's, and even though they're spec'd as 8 ohms, they dip down to almost 2 ohms in the lower midrange, causing some 8 ohm amps to go into protect mode at higher volumes. Fortunately, this hasn't happened with amps that can handle 4 ohms.

I suspect that your 240Ti's have a flatter curve, and you'll probably be OK.

John

[Ian Mackenzie]

Because the amp does not respresent a pure voltage source (> output impediance) this will modulate the output amplitude signal +- 0.5 db or more with variations in the impediance of the loudspeaker across the frequency range.


There's nothing you can do about it except use a loudspeaker with a purely resistive load like a Magnaplanar.....a vastly more transparent and more suitable audiophile loudspeaker for this type of amplifier. Save the 240Ti JBL for your TV or Home Theatre HK amp.

[4313B]

Hopefully, someone has a copy of the 240Ti impendance curve they can post.

Not to scare you, but hopefully it isn't similar to the 4315's. I have a set of 4315's, and even though they're spec'd as 8 ohms, they dip down to almost 2 ohms in the lower midrange, causing some 8 ohm amps to go into protect mode at higher volumes. Fortunately, this hasn't happened with amps that can handle 4 ohms.

I suspect that your 240Ti's have a flatter curve, and you'll probably be OK.

John

http://audioheritage.org/vbulletin/showthread.php?t=10615


http://audioheritage.org/vbulletin/showthread.php?t=10621

[johnaec]

You da' man, Giskard! 'Looks like Groovey should be OK.

John

[groovey records]

Well what can I say but thanks! You folks do not fool around. Pure data straight from the horses mouth (no offence Greg ;>) Thanks Giskard.
Now can you introduce me to your sister in the picture. Yes !

I just want to say I have always loved my JBL 240 TI's and after respecing them they sound as good as the day I bought them. Soesterberg, a US Air Force Base in Holland, is where I bought them at less then what they cost back here in the States. The only thing they are missing is the little teak pen that JBL sent me in the mail with my name plates.

I have read with interest the 240ti vs 250 TI debate here and there is only one solution-a pair of each. Unfortunately my dorm room in the barracks would not allow it. Remember back in 84 some people were quad inclined. A pair of 250 front and 240 rear was what was happening then.

Johnaec your intuition was spot on and the 4315s are sweet

Ian isn't the word planar heresy around here. I would of gotten some of BoB Carver's ribbon's long ago if i wanted. No I like my air to move.

Once when I was at a sound check in the afternoon at Carnegie Hall the sound tech was way up high inside a huge Voice of the Theatre setup for that evenings Laura Nyro Concert. As his hair blew in the wind he yelled down "Can you hear any distortion?"

MR Giskard do you have any opinions on Classic Audio Reproductions Hartsfield Speaker. One of their designs is next on my list.

And Thanks 2 Techbot for the documentation Amazing Archive you have here.

Again

Thanks for your Kind attention

Joseph

AKA Groovey Records

Listening to Miles Davis at Carnegie Hall- Columbia PC 8612 180 grm Vinyl

[Thom]

If this dip to 6 ohms (previous posts) is unacceptable, you could put 1 or 2 ohms resistance in series with the speakers. This would keep your impedence where you needed it and couldn't damage anything. There is the possibility of it changing the sound in a way you don't like. It could also change it in a way you do like. You won't know unless you do it. Make sure the resistor is high enough power and non inductive. I'm not saying you need to do this just that it will work if the current impedence won't