Today I noticed amp gain wasn't at 100% and....

[brucek]

I just haven't seen or heard very many scenarios like that

Yeah, I don't have any specifics, but haven't you noticed in some movies that out of the blue your closet doors start rattling. When it happens, I don't hear the tone, but I see the garish BFD LED's indicating signal.

Even so, they aren't about to produce a tone as such that 90% of the systems can't reproduce, so I doubt if the frequency is too low. This bodes well for the low tune LLT design, since the max excursion peak occurs at very low frequencies. Certainly below where most movie information lies.

From what I have seen, actual material is probably 98%+ bursts at varying frequencies, a situation in which the amps are likley to put out more clean power than what their specs say. Then you factor in the sensitivity of most of the bass systems built by DIYers who use multiple drivers, and I'm not really seeing potential for any real world issues.

Yeah, agreed. I think these cheapy pro amps like the 2500 are an ideal bang for buck solution.

brucek

[Blaser]

Hi all!

I have some thoughts I would like to post here...
I think line sag problem are less usual when using a 220 V line, as generally I think there will be min a 15 A line as well. What do you think?

Moreover, unless we are speaking of Aeronautics, buildings or similar...., design is generally not to accommodate the worse case senario. If you take as an example a room to be cooled by an A/C, engineers never chose the required cooling capacity based on the worst senario (very hot day, no curtains, all lights on, heat readiating equipments, 20 persons in, a party going on....) as this does not happen offten, and the results of doing such a concession will not be catastrophic, but will save a lot of money...).

(IMO) same would be practical when considering for ex. port air velocity.
Therefore, I see unpractical to design a subwwofer based on some continous playback (and behaving like a sine wave) that one might find sometime somewhere.

I don't think as well that I can bottom out one of my RL-P 18 LLTs (tuned 13.5 Hz) below tuning (or above) with 2000 W, 55 Lb net (I know it is a true 2000 W RMS from Ilkka) on real program material, and so I don't see a high pass required in my case, and I bet this would be the same for many others.

Concerning the amp tests, I think that while some (sure) will not be able to deliver continuously their rated power, but are not many program materials based on short burst? (what about drum kicks?). From the other side half-power is also only 3 db less, right?

[Blaser]

SteveCallas wrote:

I guess the point I'm trying to make is that while there is definitely value in testing an amp against it's rated specs, in real world usage, few if any pro amps will be taxed to the same level as these tests for HT use, not from any music or movies I have seen at even spirited levels. From what I have seen, actual material is probably 98%+ bursts at varying frequencies, a situation in which the amps are likley to put out more clean power than what their specs say. Then you factor in the sensitivity of most of the bass systems built by DIYers who use multiple drivers, and I'm not really seeing potential for any real world issues.

I second that!

[SteveCallas]

Yes, it's good to know if an amp meets its specs, but if we already know 90% aren't going to, and the ones that are are generally big, extremely heavy, and very expensive, then it seems pretty cut and dry to me. If you are worried about continuous tones and line sag, spend more on your amp. As for amps rlated to powering subs though, seems most are just fine with cheapo pro amps delivering 500-2000 watts in short bursts.

[brucek]

It's rated for 2200W @ 8 ohms bridged from 20hz to 20khz

That looks like a pretty good amp to me. That's an enormous amount of power. I doubt they would publish that specification if it wasn't provable.

Given an amps efficiency, you could hardly draw enough power from the wall to require any more power than that at the load. Most people only have 20 amp circuits. I doubt if many users would need the full power this amp offers. Their house would shake apart.

My reading indicates that there are a lot of happy customers using these QSC's and EP2500's, etc amps. I think it would be pretty good for a subwoofer..... inexpensive too.

brucek

[brucek]

Like I mentioned before, connecting my PLX to a 120VAC/20A circuit with 12 awg wire
plus doing a sine wave test yield in > 20VAC drop in voltage

I suspect you have problems with your electrical service, given that level of voltage drop.

The service should be sized to accommodate this to avoid voltage drops. There are many reasons for excessive voltage drop at the load centre, but most can be rectified. There simply should not be enough of a voltage drop in a properly sized service supplying a device such as this that the line sags 20%. That's outrageously excessive.

If memory serves, the National Electric Code (NEC) specifies that no more than 2% voltage drop is reasonable.

Your service, including transformer and supply wiring is sized to accommodate loads many time what you are using. Motor starting currents on air conditioners etc can easily be six times their running current, and the line is spec'd to handle it.

A simple line monitor would be sufficient for most people to test the drop at any receptacle. If it's a 15 amp circuit, plug a toaster or hair dryer into the line monitor (1500 - 1800 watt device) and observe the voltage. Lucky if it dropped a volt on most lines...... I just tried it - didn't move from 120 volts...

brucek

[brucek]

14 awg wire, 100 foot run
That's about 0.25 ohms. Draw 20 amperes and you have a 5 volt drop

A 20 amp circuit must use 12 gauge wire - 14 gauge is only allowed for 15 amp, with maximum run of 50 ft. Longer runs require 12 guage.

There is 12 volts of loss right there

Sorry, we'll agree to disagree. The drops are not nearly what you quote.

Did you measure the current when doing this test?

Power meter is in line with the toaster. Measures current, voltage, watts (with corrected power factor ).

brucek

[brucek]

There is nothing unreasonable by having a 0.1 ohm contact resistance when you have 'metal to metal' contact, not a soldered connection.

Yeah, fair enough, but my experience tells me that 100 mohm (.1 ohm) contact resistance is about an order of magnitude off. A typical breaker would be about 5 mohms (.005 ohms), and a screw terminal tightened down on a solid copper wire would be between 5 - 10 mohms. When you tighten a screw on a receptacle down onto a solid copper wire it exposes new copper and creates an air tight joint at the point of contact and is considered a cold weld. Very low resistance and quite long lasting. Your biggest enemy at a receptacle is the plug and socket. You can upgrade these fairly cheaply though.

So for a dedicated circuit, the only path resistance is the electrical cable. If I drew a full 15 amps on a 25 foot 12 gauge run, I would lose a little over a volt in the cable. No big deal. Most amplifier will regulate the rail voltage over a fairly wide range.

So again, if you're drawing capacity current on a 20 amp circuit and you're losing 20 volts - believe me, you do have a problem. That's 400 watts of heat, and you'd have a fire somewhere. A 16% voltage sag is way beyond spec. Cabling and service must be sized for a max ~2% loss at the service and ~5% max loss at the furthest point in the home.

I did a web search to see if I can find something with more detail about this topic. I found this.

Yeah, that's a good article. I had read that before and thought it a good entry level read that anyone would understand. A must read for sure, technical type or otherwise.

It can be summed up with their statement:

The peak power demands are satisfied by internal energy storage (big caps). For the rest of the time, the amplifiers only produce a few watts RMS. An astute observer will have realized long ago a simply fact: if your 315wpc x 7ch amplifier can function well off of a 15A branch rated circuit, it must not be doing much WORK.

Exactly, and certainly everyone must realize when Behringer and others claim a 2200 watt output from an amplifier, that it simply isn't going to happen on a standard 15 amp 1800 watt house circuit. The breaker would trip if it were so. But, as a specification where we know they had unlimited current to meet their spec, I'm sure it's at least close to accurate. It's simply a spec, and as long as they are comparing apples to apples over the full spectrum with a certain distortion, etc, etc, then it gives us an ability to compare amps. I certainly don't go along with the notion that we should be testing these monsters with limited current and voltage for some sort of real world value of power. As has been pointed out so correctly already, every home is different. I want a standard spec that I can use for comparison. I think most people also realize that they don't get something for nothing.

I would certainly encourage anyone to buy a simple energy meter to check out the line sag that they might be experiencing where they plug in all their HT equipment. I certainly have Fluke meters and all that good stuff, but I also bought one of these energy meters, because they are so convenient and surprisingly accurate. They even apply power factor correction to the power readout (they just have a simple zero crossing chip inside - neat).

They sell this UPM energy meter device all over the place, in fact they even sell it here at the Shack (how's that for a plug Sonnie ).
Only costs $20, but is quite a nice unit. It displays voltage, current, real watts, energy usage time, max current, max voltage, energy costs, overload alarms, etc, etc. I have used it to check the idle leakage of a lot of stuff when its 'turned off'. You'd be surprised how much power some things draw when off. Also, because it displays max figures, you can plug it into a device and see its idle, and then use the device and see its max current etc. Pretty neat stuff.

You can also plug it into a receptacle and then plug a toaster into it and see how much the line sags when you turn it on. A toaster is good since it isn't reactive and usually draws about 13 amps. On a 15 amp circuit that should tell you if the line drops too much or not. As I said, the spec in your longest run is ~5%. That would be about 6 volts. That's a lot.

brucek

[Blaser]

Hi Brucek,

Always very informative posts!! THX. Can the power consumption of the TA2400 amp be checked with that unit? I think it is limited to 1800W max. Does it support 220V as well?

Thanks.

[brucek]

Does it support 220V as well?

No, that unit is for 120v only.

brucek

[bobgpsr]

I find it easy to trip a 15 amp circuit (nothing else on it) with my Mackie M1400i pro amp driving my DIY sub with sine tones during tests(even though they are shorter than 3 seconds). Does not happen with normal music&movie use although the amp's turn-on in-rush current sometimes trips the circuit. It really needs a 20 amp service.

[Chrisbee]

Some audio fans who take their power supplies seriously use industrial sockets and plugs. These are also used on building sites and caravans (mobile homes) in Europe. Just do a Google image search for <industrial plugs sockets>.

You'll probably only need the three pin type. The wall sockets (US=receptacles?) come in all sorts of designs for fixing to various surfaces and fixtures at different angles. Usually available in only a few primary colours. Blue is usually 3 pin (250V single phase) and red is 5 pin (380V 3 phase).

They are much larger with huge contact surfaces compared with domestic sockets and plugs. They can look quite post-modern in the right setting.

[crackyflipside]

The receiver for my speakers if right by my feet in front me under the computer desk. Bumped it the other day without noticing and was wondering why everything was so loud and there was no bass..... BTW subwoofer volume is controlled independent of speakers.


I know the feeling, Rob. ->

[Exocer]

crackyflipside wrote:

The receiver for my speakers if right by my feet in front me under the computer desk. Bumped it the other day without noticing and was wondering why everything was so loud and there was no bass..... BTW subwoofer volume is controlled independent of speakers.


I know the feeling, Rob. ->

It happens to the best of us