JBL 4435, Mcintosh 7270 experiment

[Scott 99]

Am I imagining this or does my theory below sound plausible?
After looking at the impedance curve for the JBL 4435. I noticed the low end frequency dipped into the 4 ohm range. JBL specs state the 4435 has an 8 ohm nominal impedance (4 ohm minimum). Most of the frequency range is closer to 8 ohms but I was curious to try the 4 ohm connection on my amp. I am using a Mcintosh 7270 amp that produces 315 watts before clipping.
After listening, I think the lower frequencies are enhanced when using the 4 ohm connection and have not noticed any problems with the other frequencies. What I have noticed is that my amp is working a little harder, producing around .27 watts peak. not sure but I think it was producing around .027 watt peak when using the 8 ohm connections at a comparable volume. One of the other possible improvements is that my amp sounds better when it needs to produce a little power. Either way this amp is barely working with these speakers.
So am I imagining this enhanced bass? Should I not be using the 4 ohm connections because of the possibilities of damaging something? I am a low sometimes moderate volume listener. Looking at the chart most of the frequency range is closer to the 8 ohm impedance which makes me want to stick with the 8 ohm connections. What do you think?

 

[twiiii]

Normally speaker systems impedance by convention is selected to be the lowest reading above the resonant peak of the woofer. In this case around the 85 Hz vicinity, would be just over 8 ohms. By changing to the 4 ohm tap you are dedicating the availability of more current where required with out over heating the amp. But as you say .27 watts or about 90 db at 1 meter is of no real concern. But if you were running 27 watts or 110 db peaks, then we could have a discussion. By the way 27 watts would be about concert level at your listening position leaving you 10+ db head room for instantaneous peaks. Seems like an Ideal match to me.

What you are hearing is how the source impedance of the amp reacts to the impedance of the speaker system. Choosing the 4 ohm tap gives you different a different source impedance which interacts differently with the properties of the speaker. 4 ohms sound a little faster and the bass a little tighter, I know it worked that way with 2200's and 2250's with my speakers. The 7200 gave the best performance compromise. Crown amps were very dry and Mac tube amps were just euphonic and mushy.

4435's are probably one of the best two way monitor systems I have ever heard. Only Urei 813 with the 604 Altec and a supplemental 15 inch woofer approaches the 4435 performance. Maybe the 4435 rolls of on the very high end, but thats not a bad thing and the bass is very solid, with low distortion and great dynamic capability. How do you suppose speakers with their multiple 6 and 8 inch woofers keep up with two JBL 15" woofers? They don't/ it would take eight 8" woofers arranged in a square patter to equal the two 15's. To fill the hole in the center lets make it nine. Jbls can be a little on the bright side, so I would tone down the over all out put of the horn a couple of db and the top octave range a few db more. But those are my preferences.

Wish you great listening.

 

[Zonker92]

Interesting; maybe I'll try those taps on my MA6600.

 

[Scott 99]

Thank you for such a great explanation!!!
Is there any possibility of this set up creating more distortion in the 500Hz -1000Hz frequency range that I have not noticed yet? The impedance looks to be much higher in this range. Or should I just figure that if it sounds good and the amp is not over heating, its a good thing for all frequencies?

Zonker, I would be interested to hear what you think if you try the 4 ohm taps.

Thanks again,
Scott

 

[Zonker92]

4435's are probably one of the best two way monitor systems I have ever heard. Only Urei 813 with the 604 Altec and a supplemental 15 inch woofer approaches the 4435 performance. Maybe the 4435 rolls of on the very high end, but thats not a bad thing and the bass is very solid, with low distortion and great dynamic capability. How do you suppose speakers with their multiple 6 and 8 inch woofers keep up with two JBL 15" woofers? They don't/ it would take eight 8" woofers arranged in a square patter to equal the two 15's. To fill the hole in the center lets make it nine.

Hear, hear. The bass on these things is just jaw-dropping. Mine literally shake pictures off tables.

Zonker, I would be interested to hear what you think if you try the 4 ohm taps.

I'll try it ASAP, Scott!

 

[toddalin]

They don't/ it would take eight 8" woofers arranged in a square patter to equal the two 15's. To fill the hole in the center lets make it nine. Jbls can be a little on the bright side, so I would tone down the over all out put of the horn a couple of db and the top octave range a few db more. But those are my preferences.

Wish you great listening.

Your math is off. Seven 8" speakers would be comparable in cone area to two 15" speakers, both a bit over 350 sq inches.

Of course the 15" speakers probably have more cone travel so even though the area is comparable, the volume of air movement can be greater for the 15s".

 

[damacman]

Thou shalt not compare area.
Rather, thou shall compare volumetric displacement.

 

[twiiii]

I agree, compare volume. As for the higher impedance in midrange it just means the drivers are requiring less current but are producing the desired linear output, so I wouldn't worry. For that period of time the 4435 was a very low distortion 2 way system. Most systems have to be 3 or 4 way to approach the performance. The more crossover points the more issues to block perfection.

If you will look at the DD series its basically an updated 4435 with a super tweeter added above the limits of your current system, 16. 5 to 17,5 khz. KHZ. JBL did decide to control the vertical dispersion as the speaker was to be used on the floor, where most 4435 were to be suspended from a ceiling pointed at the mixing console. If I were going to have a JBL Museum I would want the Harkness, Paragon, 4435, and DD 67000 for starters each being driven by my favorite electronics of the period. MC 60's for the Harkness, Mc 7200 for the Paragon, and MC 1.2 k for the DD 6700. The 4435 would be the hardest choice, but Maybe a MC501. If I were choosing all tubes, Mc3500, for them all. except the MC 60.for the Harkness. I would use modern pre-amps, Disck players, Turntables and cartridges.

OH! Could I cheat and update the ring radiators in the Harkness and Paragon?