Not a lot of Amps drawn, not what I expected!

[iUSERTLO72p]

Hello all, My sub doesn't draw much current, why?

To be honest, I'm indoors with it, and I'm not sure where I should post it? I could have asked in the Power Supply forum or Subwoofers.

I have a 12" 4ohm woofer on 1 pair of a 4 channel amp, bridged and being fed Linkwitz Transform. The car amp is 4 x 100w so i guess 4 x 35 rms, not sure of power or believe what they say, but anyhow, I'm using this amp because I havn't bought a mains jobby yet. I've set the Transform @20hz and this comes via 40hz 24db lowpass filter. My power source, a PC 300w psu. I've been happy with it, but have been curious about the power my amp's drawing. So I installed my DMM in 10A range and although its late, its displaying 0.70 Amp +- 1Amp. Even when theres no music playing, it reads the same. I began turning it up to my normal daytime level, and it read 0.80Amp. The test signal was Dance music on a satelite tv channel and then some Hip Hop, with which it managed 1.02Amps. I deduce that 99% listening time, the system isn't doing much. The gain on the Amplifier is maxed, without you being able to listen, its hard to ask, but, do you think with modern music and the use of a Linkwitz Transform, I should be drawing more current? The 12" cone is moving no more than my 6" mains.

At 12 volts 12 x 0.7 = 8.4 W

Confused.

iUSERTLO72p

 

[Eva]

Consider these facts:

A woofer in a proper sealed enclosure exhibits a wide high impedance peak around 50..60Hz, it may be well above 10 or 20 ohms across one entire octave. This is particularly true if Qts is low and/or the enclosure is big. You can try modelling your system with some software.

A DMM does not measure peak current, it only does a slow average.

Music demands high peak power but low average power. A 100W amplifier may be delivering only 20W or 30W of music when it starts to clip.

Most music has actually little content below 50Hz, most of the stuff we perceive as bass is in the 50Hz to 400Hz range.

Anyway, such a low reading suggests a lack of DMM precision.

 

[jol50]

You will also find at high volume the load starts to pick up faster. It can go quite loud with little power, then it ramps up.

 

[ppia600]

Where do you have the meter connected to measure current? Is it between one of the 12v power leads going into the amp?

 

[iUSERTLO72p]

Hello

Yes meter inbetween 12v and batt in on amp.

Cheers iUSERTLO72p

 

[iUSERTLO72p]

Also

See here
http://www.diyaudio.com/forums/showthread.php?s=&threadid=115179

Cheers

 

[jol50]

I just ran a 150wrms x2 amp on a battery with a 2A charger on it. It has about 12.6-12.8v with the amp and HU idle. I put my meter on the amp and it draws 1.26A at idle and 1.46A playing at quiet volume inside the house but loud enough to hear fine. This was running a sub full range bridged, actually a DVC so 8 ohms. I turned it up louder and it went to 2A, a good listening level but far from blasting so maybe close to 1 watt (often what a standard TV is WOT), and the sub does not sound the best full range but is making bass well...that way I could tell what song it was. So then I take the meter off and start cranking on it harder, a little 10", getting the cone moving good. The amp quits. I look and had forgot to remove the 10A fuse I had in it to start it up. I put the two 30A back in and run it louder yet, but with no subsonic filter it starts getting to xmax of this 400w 10 in the ported box. I put the LP on and it sure has some port huffing, lol, but doubt one would ever hear it in use.

 

[tsmith1315]

tl072 wrote:

At 12 volts 12 x 0.7 = 8.4 W

That sounds reasonable for average power consumption.

Eva wrote

A DMM does not measure peak current, it only does a slow average.

Music demands high peak power but low average power. A 100W amplifier may be delivering only 20W or 30W of music when it starts to clip.

Absolutely.

Transient power is what your speakers are using the most of and average power or current doesn't reflect that.

Run a 30 Hz sine wave through it and you should see larger numbers on the meter. I'd be curious how your PSU holds up, too.

tl072:

I've set the Transform @20hz and this comes via 40hz 24db lowpass filter
(snip)
The test signal was Dance music on a satelite tv channel

Eva:

Most music has actually little content below 50Hz

And dance music qualifies for that statement. PA systems have a hard time filling a large room with lower frequencies at significant volume. 50Hz wouldn't be an unreasonable F3 for a club PA, as dance music doesn't go much below that.

To add to that, your LP is at 40Hz with 80Hz at -24dB. Which should work very well if your mains can meet the subs way down there. I always prefer the lowest possible crossover frequency for subs.

Tim

 

[jol50]

Old dance music used to get down there, like janet jackson/madonna/etc. Yeah old, certain songs I could count on to blow my amp fuses. Lots of sine waves in there more or less except it was actually music.

 

[ppia600]

ATB and Ian Van Dahl = Bass

 

[iUSERTLO72p]

Hello

And dance music qualifies for that statement. PA systems have a hard time filling a large room with lower frequencies at significant volume. 50Hz wouldn't be an unreasonable F3 for a club PA, as dance music doesn't go much below that.

Granted, the Dance music these days is crap. My kind of dance music is Harddance, HardHouse, quite a lot of low content availiable. You wouldn't hear it on the radio though

What must be happening, then, is my sub mustn't be doing much work yet? IS THAT RIGHT, please?

I built the thing to experience some low bass, what can I do to bring the output up without boosting the 50hz region???

Ah, I guess I'm talking EQ? I'd be wrong, but EQ is the cheapest option, I/We got another baby on the way and need to buy a new car.

So, could I EQ? This would be easy when the music don't provide the lows, or can you suggest something better?

Cheers, the one with the quiet sub

 

[iUSERTLO72p]

Excuse me

Sorry about my language

iUSERTLO72p

 

[Eva]

"Low bass" alone is perceived as "slow" and resonant rumble, it's completely useless without powerful "high bass" (both together sound nice)

 

[jol50]

You could figure out how to get more gain, more input to amp...or cut back the highs to get more sub. Or yes you could simply get an auto EQ to run on the amp...or a home unit. The cheap car EQs tend to have noise but might not be an issue in your house depending on your power supply.

Also your highs may be falling off (rolling off) sooner than you think, giving you a hole between them and the sub.

 

[iUSERTLO72p]

Are you talking about my mains?

These reach about 75hz. They're floorstanders, reflex, but I've blocked the ports.
Low bass" alone is perceived as "slow" and resonant rumble, it's completely useless without powerful "high bass" (both together sound nice)

Yes, but the quantity of low is practicaly no existant. 90% of usage is via the Satellite Tv reciever. We watch more tv than listen to music. Ironicaly, if I put a DVD on, I get the sound I like along with lows, especialy with 24/96. Obviously broadcast material is already compressed, then its got to be converted to mpeg2 or whatever lossy format they use. So maybe, I have two systems in one, one works but not the other!

iUSERTLO72p

 

[tsmith1315]

These (mains) reach about 75hz. .

And your subs are [email protected] 40Hz, right? Can you bump that up a tad for a closer match?

I think you've discovered your own answers by now, if DVD's sound better. Sounds like the satellite signal is lacking low end, and there is a gap, as jol50 predicted, between the sub and mains.

Tim

 

[iUSERTLO72p]

It used to be........

...variable.

Hi, 12 db of the 24db were fixed resistor the other 12db, I used a pot. I found I had to lower the frequency, because the sub boomed so much. Yeah, DVD sounds good, but obviously I need to EQ for the TV. I would like to crossover with better quality. The worst is, probably, that the sub is in a corner, inbetween the two mains which are across the corner. Naughty, but Wife likes her floorstanders. I understand that Home Theatre is okay across a corner and Hi-Fi should be on a wall end.

Hope I don't get told off, this could be a Subwoofer thread. Sorry Moderator.

Anyway, maybe I should try some room EQ,(YIKES ), Wife won't let me move sub anywhere else, so I must have some nasty things going on.

So, I have a £40(sterling)microphone I bought from Tandy,(RadioShack!), about 10 year ago, if I plugged this into my Creative Live 24bit oundcard and used a Spectrum Analyser bit of software, would this be acceptable for a basic Room Analysis session to see if I have nasty Peeks or Troughs.

iUSERTLO72p

 

[jol50]

You could try a 12v coustic crossover, they are fairly good and cheap around here. If it is booming probably need to change the slope so you let some of the boom through. Those are why active crossovers are so nice. If you can get a hold a used Behringer, they make some nice rack mount items with crossovers, T/A, EQ, etc., and are not that expensive.

 

[iUSERTLO72p]

Hello jol50

Behringer, they make some nice rack mount items with crossovers, T/A, EQ, etc., and are not that expensive.

I live in the UK, everythings expensive. Gordon Brown is being very greedy. So are the Oil Barons, gas and electricity going up @ 20%.

It would be simple for me to put together some circuits from http://sound.westhost.com/ , and hopefuly use some filters, my mic and my PC with some tools to see if I can tame some nasties.

iUSERTLO72p

PS, I'd better buy some TLO72's