Low Sensitivity 2245

[robertbartsch]

I had a couple of dead 2240s that I purchased cheap from a sound reinforcement company reconed into 2245s several months back by my JBL authorized dealer and I finnally got around to getting some suitable cabs and installing them last week for a 5 channel basement HF system.

They are running off a 5 channel Adcom pre-amp sub bass channel being driven by a 500 WPC Crown.

Well, without a ton of time listening, my first impression is that they are a nice addition to my system.

My only complaint is that they seem very inefficent needing tons of power to keep up with the rest of the system (3-ways w/2226s, 2426s, 2504s, etc) . I've tried using only one 2245 driver first and then both drivers in a parallel circuit. The single driver seems to work best.

Anyway, the gain on the non-sub channels needs to be turned down so the 2245s sub-woofs can keep up.

[grumpy]

Not knowing your signal path, amp sensitivity, cabinet tuning, room size,
I'd still say this is not an unexpected result if you're using the 2245 as a
subwoofer... e.g. mostly below 80Hz.

http://audioheritage.org/vbulletin/showthread.php?t=10632

[JBL 4645]

Rob

I’d also keep an eye on the barograph display less is more! If you can produce less power than is needed and yet get a good frequency coverage from the lowest to its cut-off point then fair enough that’s good because you don’t want to run the amp at needless levels where some sub bass frequencies are stuck in (null spot) that is where you’ll over run it and put needless strain on the amplifier and sub bass speaker.

[robertbartsch]

...as far as I can tell, the Adcom pre amp does not allow individual control of the output signal for each of the 5 channels. My only tool for balancing is the gain controls on each power amp.

[short_circutz]

Don't see how that link relates, as the 4645 is loaded with 2242, not 2245.

The 4245 speaker is a "hifi" (or sound reproduction if you prefer that term) grade speaker and will have less sensitivity than the pro-sound (sound re-inforcement) components that are in your 3 way cabs. They will need more power to match spl levels.

2245: 95dB@1w/1m
2426: 110dB@1w/1m on 2470 horn
2405: 105dB@1w/1m
2226: 97dB@1w/1m

Just to keep up with the 2226's you need almost double the power.

What are you using for power amps?

Travis

[hjames]

...as far as I can tell, the Adcom pre amp does not allow individual control of the output signal for each of the 5 channels. My only tool for balancing is the gain controls on each power amp.

Hmm, sounds like you need a preamp with better controls!

If you're doing 5.1, you'd need room-tune capability -
how do you set up the room without level controls?

[boputnam]

They are running off a 5 channel Adcom pre-amp sub bass channel being driven by a 500 WPC Crown.Which model Crown?


I've tried using only one 2245 driver first and then both drivers in a parallel circuit. The single driver seems to work best.So, is that a 4-ohm load vs an 8-ohm load? Does that Crown tolerate a 4-ohm load? :hmm:

I'm also wondering about output impedence / damping factor, too...

[grumpy]

Don't see how that link relates, as the 4645 is loaded with 2242, not 2245.

You caught me... older 4645 was 2245. Main point was regardless of the
driver's spec'd sensitivity, at the low end, in that size box (8ft3), the
response rolls off and you'll have less sensitivity in the utilized bandwidth
than the spec.

You can make it up in room gain, eq, line level adjustment (as the OP did),
but a bigger amp... you will still require. Should not be a surprise.

[robertbartsch]

Crown amps are 802Ds which I believe can run 8 or 4 ohm loads.

Two 2245s 8 ohm drivers in a parallel circuit would be a 4 ohm load to the power amp; right?

Thx....


Adcom pre amp was purchased used and I don't have a manual but I'm pretty sure it does not allow for output adjustments.

[grumpy]

supposed to run 500w/ch at 8 ohms. damping factor >200.

...even spec'd to run 4ohms bridged (which I see no particularly good
reason to do in this case... you'd never see the quoted power from a 15A
service, and the amp would be stressed needlessly).

and yes, in the frequency ranges where a single 2245 would be approximately
8 ohms, two in parallel would be 1/2 of that (4 ohms in those same ranges).

[Don Mascali]

You may be dealing with the sensitivity difference between consumer and Pro amps. The drive voltage is different for each.

I have the exact same Crown amp and drive the top (100HZ and up L100t3) with a Yamaha receiver and a pair of B380 clones one per channel on the Crown. I turn the Crown level controls all the way to 11. and they keep up OK.

Have you tested? Most new subs are over driven until the thrill is gone.

[Don Mascali]

Driving home from work I remembered that there is a level function in setup for LFE.

I guess my comments need to be seen with that in mind.

[hjames]

Driving home from work I remembered that there is a level function in setup for LFE.

I guess my comments need to be seen with that in mind.

Sure - my HK receiver has on-screen setup and I have time delays and level adjustments for all channels at preamp level. I suspect any good AVR system would have them.