A Question of Power and JBL

[geode]

I'm toying with the idea of mating up my 4425 Studio Monitors with a lot more power than they are currently being used with. Right now I am using a Marantz 250 amp rated at 125 wpc. I want to use my Citation amp rated at 450 wpc. The speakers are rated for 200 watts continuous power. I do listen to my music at pretty loud levels sometimes. I certainly don't want to fry my speakers, but the Citation is a much nicer amp than the Marantz. So, I guess what I'm asking all of the JBL Gurus out there, is, can the speakers hold up.

[subwoof]

3db of power headroom is suggested for all monitors. that's double the nominal.

[grumpy]

Yep. If you weren't clipping before, and don't plan on listening at higher SPLs
than with the Marantz, no problemo.

It's not the amp rating that's the issue...

[geode]

3db of power headroom is suggested for all monitors. that's double the nominal.

So, it seems that the Citation is a better match for the JBLs than the Marantz. I believe you're saying that it takes twice the power to get a 3db increase in volume. And the 3db increase is a noticeable difference to the human ears (read it someplace). Thanks for the response.

[geode]

Yep. If you weren't clipping before, and don't plan on listening at higher SPLs
than with the Marantz, no problemo.

It's not the amp rating that's the issue...

Hello Grumpy. I haven't had the speakers very long and had the woofers refoamed. I have been listening to them at moderate levels using the Marantz. I wanted to take it easy on the new foam and let it stretch a bit. I probably have about 30 hours on the new foam. I do have a rather large area to fill with 20' ceilings and 26' width X 26' length. That is why I anticipate cranking them up The JBLs have replaced a pair of Yamaha NS-690s also powered with the Marantz. I know the two speakers aren't really a true comparison, though. I could get the Yammies fairly loud with the Marantz but the power meters on the amp were pretty maxed out. So, enter the JBLs and the Citation.

[robertbartsch]

I believe drivers often get "killed" (e.g., voice coil burn out) by feading them a distorted signal at moderate to high SPLs and not necessarily by using an amplifier with more headroom than the recommeded power they are designed to handle.

As a general rule of thumb, if you begin to hear distortion, then you are at risk. Obviously, the nice thing about JBL/Altec drivers is they are very effecient, providing moderately high SPLs with very mininmal power levels.

In other words, these babies really crank in a normal size room with 15 - 20 watts of power.

[grumpy]

Yep. That all said, you still can burn stuff up if you try, including crossover parts, as one
of our Norwegian buddies found out (K2's in a -large- room w/ -big- amp):

http://www.audioheritage.org/vbullet...ad.php?t=21389

... careful with your ears, keep those L-pads clean (less likely to fail), and try to
not crank up bass controls (or use loudness switch) and volume at the same time.

Citation 7.1 (bridged) is your 450w/ch amp? Should sound pretty nice.

[geode]

Yep. That all said, you still can burn stuff up if you try, including crossover parts, as one
of our Norwegian buddies found out (K2's in a -large- room w/ -big- amp):

http://www.audioheritage.org/vbullet...ad.php?t=21389

... careful with your ears, keep those L-pads clean (less likely to fail), and try to
not crank up bass controls (or use loudness switch) and volume at the same time.

Citation 7.1 (bridged) is your 450w/ch amp? Should sound pretty nice.

Well, the ears are pretty shot. A lot of abuse through the years, yes. I usually always run everything flat and never use the loudness button. I sometimes use the low-filter on the preamp. And you hit it right, it is a Citation 7.1 bridged.

[subwoof]

Must read for the "low power - high volume" readers:

http://www.jblpro.com/pub/technote/lowpower.pdf

sub

[geode]

Must read for the "low power - high volume" readers:

http://www.jblpro.com/pub/technote/lowpower.pdf

sub

Thanks for the link SubWoof. I think I have the "Low-Power" part of the equation solved, which incidently solves the "High-Volume" part too.

[geode]

Citation 7.1 (bridged) is your 450w/ch amp? Should sound pretty nice.

Well after hooking it all up...and listening a while...you are right, it does sound pretty nice. Plenty of room-filling volume without a hint of distortion. Now, hopefully the meltdown doesn't happen to my ears

[toddalin]

Must read for the "low power - high volume" readers:

http://www.jblpro.com/pub/technote/lowpower.pdf

sub

Maybe a "must-read," but does include a serious technical error.

The average power is NOT "one-half the peak power" but actually 0.637 times the peak power. I don't know how JBL could let a mistake like this go by.

"When a sine wave test signal (a signal consisting of a fundamental
frequency without overtones or harmonics) is displayed
on the screen of an oscilloscope, its top and bottom
extremes will exhibit normally rounded contours. Average
output power is one-half the peak output power."

[Doctor_Electron]

I seem to recall that it actually takes 10x the electrical input power to a speaker to get 2x the acoustic output level. Is that correct?
For (small, medium?) format monitors such as 4310's and 4410's, I have used these amps... Hafler 220 power amp (110 WRMS/CH @ 8 ohms), Borbeley mosfet kit power amp from Audio Amateur Magazine (50 WRMS/CH @ 8 ohms), SAE MKIII CM power amp (200 WRMS/CH @ 8 ohms), Dynaco 70 (35 WRMS/CH @ 8 ohms), Dynaco 400 power amp (200 WRMS/CH @ 8 ohms), an Alesis Matica 500 pro power amp with bipolar topology and 80 V/uS slew rate (very conservatively rated at 225 WRMS/CH @ 8 ohms), an Advent 300 Receiver (20 WRMS/CH @ 8 ohms), a mid-1970's Sansui Au-7700 Integrated Amp ( 64 WRMS/CH @ 8 ohms), and my current rig, a 35+ year old Sansui 3300 Receiver (28 WRMS/CH @ 8 ohms).
With the big 200W/ch amps I never had a problem, other than unplugging a preamp-out cable going to the Dyna 400 while powered up. That broke the spider glue joint on a Jubal woofer and drove the cone nearly out if the frame. A VERY loud event.
The Dyna 70 had not the guts to make the 4310's sound very good, and the low end was oatmeal.
The Sansui Au-7700 had outstanding sonics and more than enough balls to make the 4410's really shine in a smallish room. It developed a loss of one channel condition, or it would still be my # 1 amp. Anyone know where I can get a top notch repair on it?
The Advent 300 in a small nearfield control room kicked total butt when cranked to what would seem ridiculous levels for such a small amp, but sounded great as long as audible clipping was avoided.
The Sansui 3300 is very musical and fairly punchy on the 4310's and 4410's. Many CD's of older music, such as the first (not remastered other than for CD) generation Beatles CD's sound more like the vinyl versions. I find this to be both curious and wonderful.
IMO a top quality amp with superb sonics and stability could probably put out as much as 1000 W/ch without problems if properly used. If I had such a system I would invest in or build a basic SPL meter to keep an ear on the average SPL being output.

[ratitifb]

I seem to recall that it actually takes 10x the electrical input power to a speaker to get 2x the acoustic output level. Is that correct?

n n ... in linear range of operation, 10dB more in electrical power = 10dB more in acoustic output level.
Only subjective loudness is approximatly 2X

IMO a top quality amp with superb sonics and stability could probably put out as much as 1000 W/ch without problems if properly used.

+1

[bone215]

A JBL paper on speaker power requirements.


http://www.jblpro.com/pub/technote/spkpwfaq.pdf