Underpowering JBL 250TIs....??

[Ian Mackenzie]

Ti Dome,

Those are nice amps!

Ian

[subwoof]

Power in reserve is everything...think of this example.

You are driving on a small highway at normal speeds and you need to pass 3 slow cars at once due to circumstances and the lack of balls of the drivers in front of you.

With a 100hp generic sedan you need to wait until (A) road is level or downhill, (B) there is a lot of room on the other side, and (C) Some wonderful alignment of road conditions makes it possible. The you hit the gas and do it...maybe..

Now with a 400hp muscle car, you simply stomp on it and make the pass and return to normal speed without even THINKING about all the previous conditions / circumstances needed.

Now in both scenarios you are driving the same speed, the same road, the same idiots in front of you and such. With the power in reserve ( headroom / horsepower ) it is made much easier and actually SAFER.

Now with your system you are playing a quiet passage and suddenly there is a fast snare drum attack or saxophone "bleat" that taxes your electronics. With a 100 watt amplifier it probably will go into distortion for that super-quick moment and probably not hurt anything BUT your ears have registered it as an annoyance and unless you know exactly where the limits are, you might chalk it up to karma...or blame your CD player..the wires..the cat...whatever.

Now do the EXACT same passage with a 400 watt amp ( that's ONLY a 6db increase ) and the passage goes thru with NO clipping or distortion and you suddenly don't notice that "limitation" anymore.

The "transient" was so quick it didn't heat up the coil, didn't over excursion the cone / diaphragm and since you DIDN'T clip the amp, you also did NOT create unbelievable weird waveforms from sending a square wave thru a PILE of passive components ( ever look at all the stuff on your crossover?? )...No coils saturated...no caps turned into clamping circuits...no smoke..

Get the picture??

Power is cheap. Repairing components is NOT.

And suffering thru limited headroom on 3 thousand dollar speakers since you only have a little amp makes no sense.

The nak is ok for bookshelve speakers, I would spend some $$ and get a 400 watt/ch+ amplifier.

This is basic physics - not marketing hype.

sub

[Storm]

Subwoof --

You have got me scared, now.

So, what amp should I get that is 200 to 400 watts per channel that is reasonably priced?

Would an ADCOM be suitable?

Thanks.



-Storm.

[majick47]

I had an opportunity to hear a pair of 250tis and they were impressive. They were powered by a 420 watt amp and the owner held nothing back and the volume was right up there even for me. Not a bit of distortion/clipping was I able to detect. If you decide to go for a larger power amp try to audition it first if possible. I just switched amps, it was an even swap as the rateings go (250 watts X 2) but one listen told me I had made the right move. I now have my L300 powered by a Threshold S500 Series II. Clipping, distortion, not a chance, everything was cleaner and with a lot more impact at my normal listening level which is quite moderate for a large room.

[JSF13]

Subwoof --

You have got me scared, now.

So, what amp should I get that is 200 to 400 watts per channel that is reasonably priced?

Would an ADCOM be suitable?

Thanks.



-Storm.

Typically,for me at least,once you get up into the 400 wpc plus range the only affordable option, unless you get extremely lucky, is to go the pro amp route,ie QSC,Crown,or get a couple of smaller bridgeable amps.

I used to have a pair of 4430 clones that I ran off of a QSC mx1500 @ 375 WPC that would just never run out of gas. I now have a pair of genuine 4430's that I run off a 250 wpc Yamaha M80 that I can push to its limits quite easily. Overall however I'd have to say the Yammy sounds better within it's limits,(based on my 10 year old memories, lol). JMO.

[BMWCCA]

Power in reserve is everything...think of this example.

You are driving on a small highway at normal speeds and you need to pass 3 slow cars at once due to circumstances and the lack of balls of the drivers in front of you.

With a 100hp generic sedan you need to wait until (A) road is level or downhill, (B) there is a lot of room on the other side, and (C) Some wonderful alignment of road conditions makes it possible. The you hit the gas and do it...maybe..

Now with a 400hp muscle car, you simply stomp on it and make the pass and return to normal speed without even THINKING about all the previous conditions / circumstances needed.

Now in both scenarios you are driving the same speed, the same road, the same idiots in front of you and such. With the power in reserve ( headroom / horsepower ) it is made much easier and actually SAFER.

Is there an audio equivalent to torque? Because that's what you're talking about in your example. Horsepower will get you to the ultimate top speed but torque is what gets you moving. More torque, faster acceleration. Of course they usually go hand-in-hand until you put a modern European turbo-diesel in the mix and then all conventional wisdom goes out the window. And how 'bout weight? 100-hp is much more effective on a 400-pound motorcycle than it is in a 3700-pound "muscle car". There's got to be a similar resistance to movement in speaker mass or motor response in audio, or is that simply called "efficiency"?

(I figured this thread had gotten so off the mark already, another detour wouldn't hurt it.)

[edgewound]

Is there an audio equivalent to torque?

Maybe....Something called damping factor.

The higher the damping factor, the quicker the amp can stop and start the voice coil...Very effective for tight, deep bass response.

It's really noticeable when damping factor is greater than 500. That's what made the Crown K2 so attractive....a damping factor of greater than 3000.

1 horsepower = 745 watts.
400 horsepower = 298,000 watts

[subwoof]

Well I guess the equivalent of torque would be a combination of the slew rate ( change of voltage on the output with respect to input ) and the internal resistance.

Here is another analogy ( sorry )...

You are in the desert southwest in a small town hauling ore samples to the assayer along a dirt road. You have ONE horse and a small cart.

Your speed is fairly slow but it gets the job done. Now you want to haul 5 times as much ore at the same time. You get a bigger cart, fill it up and your horse tells you to eat dung and die.

Now you get 4 more horses and they now can pull the larger cart together.

BUT it will NOT be any faster even though you have 5X the horsepower...minor variations in speed and elevation are also smoothened due to the larger mass / inertia. You just hope that they are friends and your emission controls can keep up ( whew ).

Now in an amplifier, a small amp will have a small power transformer and as few as 2 output transistors ( horses ) per channel. When you look at the big amps you will see LARGE transformers and a LOT of output transistors.

The crown single channel 10K amp has EIGHTY of them...A D150 channel has only 2.....

And if you remember your math, putting resistors in parallel reduces the overall resistance so the more outputs, the lower the internal resistance ( and this relates to the damping factor in a big way..

Amplifier suggestions??? I only do crowns and urei's and do not know much about the semi-pro / home tweako market but they do have pretty feet and heatsinks but like cars they are subject to marketing whims and outright "creative" science.

Physics is still the same no matter what picard or cochrane say.

Probably the cheapest option is a JBL/UREI 6290 at 300 w/ch. I have seen them on epay for 200-300 but shipping is up there for any large amp.

Crown's macro reference models are also a good choice but start at 1500.

Of course a 400 watt rarium model transmorgifier with unobtanium beveled heatsinks that you can audition at the big city "emporium" will also do an outstanding job and you don't even need the hot water bottle acessories or compass ( you do orient your wires to the van allen belt right ? ) to use it but it will cost you as much as your hybrid in the driveway

oooooo i like doing that...



sub

[edgewound]

Nuthin' like good 'ol horse sense subwoof.

High Fives to ya.

Van Allen Belt......lmao

[Rolf]

So many advices in this thread.

The bottom line Storm is what Ian says. You need a bigger, and not to forget a better amp.

Many years ago I tried both the PA-5 and the PA-7 on my JBL's. In my opinion none of them can be recommended on a large JBL. They are to weak, not enough headroom or Amper. In specs, yes, in practice, NO.

Why not get yourself a newer amp? There has been a lot going on in "the amps world" since those Naka amps.

Much more than in "the speaker world".

[DavidF]

Yes, it does.

When it clips, two red LEDS flicker.

With the valencias, I cranked it up so high I clipped it a couple times. Learned my lesson quickly.

-Storm.

A 100w rated amp pushed to clipping through the high-sensitivity Altecs seems very, very loud. Or the amp may be overrated at 100w. You ran it this loud in an apartment? Was there equalization in the circuit, a la a bass boost? If you have the need and ability to drive Altecs that high- with no EQ- and try to match that volume with the JBls, you will need lots of power. And be concerned about your hearing as much as your tweeters!

David F

[BMWCCA]

Now you get 4 more horses and they now can pull the larger cart together.

BUT it will NOT be any faster even though you have 5X the horsepower...minor variations in speed and elevation are also smoothened due to the larger mass / inertia. You just hope that they are friends and your emission controls can keep up ( whew ).

Horsepower in the classic sense!
Not the same as a unit of power in a car we call "horsepower". Torque is what's pulling that ore, even if the unit is "horse". And all horses are not created equal! The Crown Macros are Clydesdales! And, sadly, discontinued.

[Zilch]

Issue: Input sensitivities of consumer vs. pro amps; constant gain vs. constant sensitivity....

[subwoof]

I have 4 of the 10K and 12 ( I think ) of the 2K monoblocks in the shop storage area...need power???

The big amp is 3 phase BUT if you are very very good with electrical distribution, you can run these off single phase by rectifying the 120V AC line...a few more main caps are needed ( about 30,000 uF at 200v will do )

The 2K monoblock is standard 120 and since it has 32 output devices for a modest 1400 into 4, and dual power supplies, it packs one helluva punch for the low end and they are DC coupled so no meddlesome coupling caps to get in your way of in-phase reproduction all the way to DC.

You can start your car, weld an eye bold and shock a few thousand worms with these guys...

Sadly the world is sliding towards the self-regulating, self-correcting DSP based switching power supply type amplifiers which work well but it's like a new gee-whiz hybrid car.

Me, I like the big-block V8 approach. it may not be the most current technology but when the low end is going good, breathing is difficult and the cat is throwing up in the next room.

sub ( and I don't mean boat )

[louped garouv]

I have 4 of the 10K and 12 ( I think ) of the 2K monoblocks in the shop storage area...need power???

...



sub ( and I don't mean boat )

building home theater subs, for the neighborhood?





i agree with the notion of having lots and lots of headroom....

when i had the Altec M19s, they sounded absolutely grand on a 350 WPC amp..... they did well with 14 WPC EL84 push pull job, but hook up some real power and they really, really blew me away....

but don't kill your ears by turning it up too high....