Poor sounding 4320's....pull the trigger as a project ?

[Steve Schell]

Hi everyone,

Now I don't know much about these newfangled 4320 monitors, as I am stuck firmly in the pre-1950 era, JBL-wise. A friend with a professional recording studio located at his home has been working on an early pair of 4320s, trying to decide if he can use them for playback in his studio's well damped big room. He had refoamed the woofers himself (very nice job), and borrowed a pair of 2405H tweeters to try them as a three way. Echoing Goldjazz' thread starter comments, he mainly objected to them having "no bass." He invited me over for a listen, and had just installed an Allen Organ Co. PP 6L6 stereo tube amp I lent him for evaluation.

The 4320s were on high stands that placed the mid horns at ear level when standing, and they were at least 3' in along the rear wall from the room corners. At my suggestion he moved them close to the corners and we began to hear some bass, though humble. Standing close, it seemed to me that the woofers were simply being outshouted by the horns and possibly the tweeters. He turned down the tweeters but that didn't help much. Though the crossovers had multi-position attenuation for the horn driver set to minimum, they were still shouting. I asked my friend if he had pairs of small value resistors. He was able to put these in series with the driver due to the wire connections on the crossover in back. We tried 4 ohm (slight improvement), then 8, then 12, finally making it to about 20 ohms before I was satisfied with the balance. Now there was plenty of accurate sounding descriptive bass, fine for sorting Fender bass lines from kick drum and etc., but not in Snoop Dog territory. As I have had to learn over and over, too much highs equals too little lows!

Does anyone here have experience with similar problems with these early JBLs? I have understood that some early JBL monitors had been given a goosed-up upper midrange to emulate the Altec 604 and gain traction in the recording studios. Is this what is happening here? We probably knocked the horn response down a good 3 or 4 dB before it sounded reasonable. An iPhone spectrum analyzer app showed a pretty good response to pink noise after the adjustments, though it still looked a couple dB hot to me in the horn's range.

[Mr. Widget]

I assume these 4320s have LE15As and LE85s with an LX5 network plus tweeters. My very first JBLs were S7s and I wasn't happy with the balance until I built my own networks... I wasn't able to tame the mid horn with the LX5's three position switch... and wasn't thrilled with the 500Hz crossover point either.


Widget

[martin2395]

A quick advice - don't power big 15's with tube amps, they very much prefer transistor amps like Crown DC300A for example.

[rusty jefferson]

I see on the specs page of the manual for these the minimum impedance is 12.5 ohms. Does your tube amp have a 4/8/16 ohm taps? Fixed output impedance?

http://www.jblpro.com/pub/obsolete/4320.pdf

A quick advice - don't power big 15's with tube amps, they very much prefer transistor amps like Crown DC300A for example.

I'm not a fan of transistor amps with a lot of feedback, however I'd consider trying one next.