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I have a powered subwoofer that in spite of having a MSRP of $1700 still came with an 18AWG lamp cord for power. While it does not have an IEC socket, swaping the cord out for something better is fairly easy. The question I have is what do i need to consider for a subwoofer amp power cord?The sub has a 250 watt amplified that (obviously) only had to reproduce low frequency signals. The sub will produce output down to 18Hz. I am currently setting the crossover betwwen my main speakers and the subs at 50Hz.
When considering the PC of the sub amp, do I need to be concerned about RFI/EMI interference, or is that only a problem for higher frequency reproduction? Can easily replace with 14 AWG or 12 or 10AWG power cord and a good industrial or hosptial grade plug. I've got a lot of Carol brand "SOW" water resistent, rubber covered 3 conductor power cable that i can swap in, but it is not shielded. Does a PC for a sub need to be shielded? If so, I could slip a braided shiled over the the power cable, tie it to the ground at the plug side, and then cover with Shrink wrap, etc. Would that be sufficient? Also the cable does not have teflon insulation. Is that important for a subwoofer amp, or would the benefit be negligible in this application? I assume that the mechanical damping of the heavy rubber casing of the Carol power cord with be a benefit over the existing lamp cord. Would ferrite chokes added to the PC help in a sub? Anything else I should consider doing? Alternatively, I could remove the conductors from the cable put them into a nice RFI rejecting braid, cover them, add a braided sheild and finish the cable, but I'm not sure all that would bring noticable benefits to a subwoofer low-frequency only amp module. Do any of you have any thoughts on this? Any comments or suggestions? Thanks
Follow Ups:
I replaced the stock power cord on my Velodyne HGS 18 with a DIY following ChrisVH's recipe number three. It is a dramatical improvement on the low end. Makes it much more clearer and deeper as well as faster. If anything it appears to make the LFE go in sync with the scenes in movies I watch. Also matches the power cords of the amps.Here is the link if you should need it http://www.geocities.com/venhaus1/diymains.html
Enjoy,
All I ask is for a chance to prove that money can't make me happy.
FWIW, I agree with Alan's comments. I replaced my outlets with Eagles and rewired my 120 watt powered subs with fairly basic 14/3 cable with nice Leviton plugs. Got more punch.While I'm no electrical engineer, I would think that amps with a two octave bandwidth will likely not benefit from exotic shielding.
rw
All shielding does is increase the capacitance. You could parallel a .01uf capacitor on the power cord input to the power supply/transformer and achieve the same thing.Alan
Are you looking for extension and articulation from the sub? If you are build my 4 wire braided power cord (you can find instructions over at avs under Perfect Cable DIY Power Cord). The cable design has a higher capacitance level compared to others and offers a superb upgrade to powered subs and power amps.If you can find the project, I think you'll find several reviews as well. There also was a A/B comparison review written between the 4 wire braid and one of Chris pc designs.
Alan
Definitely DIY!Another easy suggestion: try the 14 gauge Belden/Volex that has been the subject of many discussions here in the past. It costs less than $15 and will give you an idea if a power cord will make an improvement. It is pretty easy to find from vendors like Newark Electronics and even comes with premolded connectors. Just plug it in.
If it doesn't seem to help the sound you aren't out a lot of money. If it does make a difference you can cut off the pre-molded ends and attach fancy connectors. Search the archives and you get the recipe for the famous DIY RCrump cord.
Even if the RCrump formula doesn't work magic on the sub it'll probably do good on at least one component. You can build both Alan's cord and Crump's cord for peanuts.
DIY, DIY, DIY!!!
Well anything will make an improvement. It really depends on what he wants to do. He could take an old design of mine which uses a $2.50 magnet from Lowes to re-tune his present power cord into something special (I'll explain upon request).He could add brass cones under the speaker to thin out the lower bass resonate of the cabinet.
He could upgrade his wall outlet to a brass outlet. The Eagle IG8300RN offers tight bass.
He coud just upgrade the ac plug on the power cord to something like a Marinco 8215-T for better (articulate) bass response.
And the list goes on. My vote is for the outlet, ac plug, or magnet (best with 10/3 power cords). Each one if done right will offer staggering results.
Alan
In lieu of braiding, would a ferrite placed at the subwoofer side of the power cable be beneficial? Both would provide some measure of RFI/EMI rejection, I think, but does the braiding provide some other beneift as well?
Don't waste your time with ferrite clamps. The magnet tweak is 10 times more effective. It's really not about RFI/EMI rejection. What your trying to do is replace or balance the capacitance and inductance level in your main electrical line to perform some type of power factor correction. Just placing a ferrite at the end of a power cord is not going to achieve this. There are really several things involved.But for your situation what your really looking to do is system tuning via the means of a power cord. This is done by altering the present capacitance level in your power supply. This can be done a few different ways. The first is to simply plug a capacitor (AudioPrism or Enacom) into the same wall outlet as your subwoofer. The problem is finding the correct value. That is why these companies tell you to use multiple to find the desired effect (key word is effect).
Another method and the more popular is resonate tuning via increased or decreased harmonic ringing. This is done by changing the ac outlet to a all brass outlet (Eagle IG8300RN) or upgrading the ac plug to a hospital grade (Marinco 8215-T). These two areas increase high frequency ringing which will tilt the balance of the upper midrange and lower treble. In return it also thins out the bass and lower mid region which provides a form of frequency extension in the bass and much better articulation.
The magnet tweak is another form of resonate tuning. This inexpensive tweak allows greater control over each component. By simply placing the magnet about 15" from the end of the ac blade on the plug you can begin (by pulling the magnet toward the component) to dial in the upper mids with greater control. This will allow you to fine tune the performance.
What your doing with anyone one of these ideas is controlling the harmonics on the powerline. Sometimes you can reduce certain harmonics which cause your equipment to run quieter (less mechanical hum) and other times you cause more harm than good. My suggestion is you try each one of these and see what the results are. I can only provide you with ideas. None of us can really tell you what to use because that would be utter non-sense. Unless we measured your electrical line for the harmonics, none of us can really recommend a proper solution.
In my case I live on a US Military base and I deal with huge amounts of distortion. Anything from very low voltage drops, to multiple harmonic distortion, air borne RFI, etc. In my situation I have found a combination of ideas to work. First I use the resonate tweaks to help balance my overall system frequency balance.
Eagle IG8300RN 20A ac outlet
Marinco 8215-T ac plug
Dual Twisted DIY Power Cord (My design)
1st Resonate Filter:
AXON 20uf...1200v x 2
AudioCap PPMT .47uf...2400v x 1
InfiniCap .01uf...630v x 1Next I use balanced power to lower the interaction between components.
Piltron 17Kva balance transformer
Then I use a second resonate filter to reduce the injected noise (harmonic rining) within each ac outlet.
2nd Resonate Filter:
InfiniCap 1.0uf...425v x 1
MultiCap PPMFX .1uf...600v x 4 (one per outlet)
AudioCap PPMT .1uf...2400v x 2 (60+/- to ground)
Eagle IG8300RN 20A ac outletThe balance power conditioner as a whole uses a few different types of resonate ideas to tune the chassis. First is the filter design described up top, another is hardware supplies, such as all brass screws, brass and copper parts (screw, washer, nut) to lock the transformer in place, I use pressure to tune the transformer upper mid frequency response via the brass wing nut. No dampening material is used so I have greater flexibility in tuning the chassis. And last I use a combination of brass (threaded cone and screw), copper (washer), and aluminum (protective disc) to tune the footer (or in this case coupling cone). The chassis is all stainless steel.
Now keep in mind this is a trial and error process (more error than anything), but a very effective tool if performed correctly.
And don't stop there...you can also tune your wall outlet by simply exchanging the screws from steel to brass, and by switching the outlet cover to either brass (better top end detail...use copper washers to help bring ot some warmth in the lower mids)) or wood (better lower midrange warmth) compared to plastic. Change the shelf surface material to reonate tune each component chassis (kind of fill in the blanks where certain parts of the frequency balance is recessed in each component).
Play and Enjoy!!!
Alan
My last message was a worst case scenario.
If you let 250W go out into the room,
You will be seriously hurt and the windows
will all blow out.
A more reasonable level, a few watts.
In fact a comforable listen level mostly
require no more than 1Watt. Ask the `tube-men`!Suppose 25Watts or so in consumtion
gives
220VAC 0.1A - AWG32 resistans: 0.005 ohms/m
110VAC 0.2A - AWG29 resistans: 0.0024 "-Best regards, groman.
I think you misunderstand my posting. First the subwoofer amplifier is supplier with the subwoofer, and is attached to the subwoofer cabinet. It is part of the powered subwoofer and is matched to subwoofer speaker drivers. It is 250 watts because it needs to be 250 watts. A description of the subwoofer is as follows:"wide bandwidth servo-control, inertia-free Bipolar design featuring dual 10" (25.4 cm) woofers, a push-pull surround, 250-watt RMS discrete-class A/B current source amplifier, feed forward servo-control and exclusive EQ circuitry" The amp is 250 watt RMS, and will produce 1000 watt peaks. Frequency response of the subwoofer is: 18Hz-100Hz +0/-3dB. The frequency response of its amplifier is DC to 2000Hz. 1 watt might be good for some speakers (horns etc.), but for a sub to fill a room with 115 db's at 18Hz takes a fair amount of power.
Issues with using only a 18 AWG AC cord would be the amount of voltage drop. Which is significantly reduce with 14 or 12 AWG cables, for example. But most of my concern is not with the size of the cable as I will be putting in a larger cable. My concern is more with the relative need, and importance of insulation/diaelectric choice, and RFI/EMI shielding (+ rejection) for a low-frequency-only amplifier for a subwoofer. Are these concerns more important for full-range anmplifiers and components, do they impact mostly the mid-range and high frequencies, etc.? Would like to hear the collected thoughts and wisdom on this. Thanks for the input.
Even 90dB is loud for normal rooms.
100 dB is high even for discotek-use.
115 dB is impossible to use
without damage to body, ears or windows.
Suppose sub has sesitivity 94dB for 1Watt
At 4 watt= 100dB
at 8 watt= 103
at 16watt= 106 dB
at 32watt= 109
at 64watt= 112
at128watt= 115
but you have no experience of what is
100 dB soundpressure, it seams
I assure you that it is painfull!!!
Ask somebody to compare, with a soundpressurelevel-meter
and wattmeter.
You will see that I am right.In normal musiclistening with HIGH volume
the SPL is probably something like
90-95 dB, which normaly means an
output of 0.5--2Watts.I hope someone else would like to
confirm this.You can search the web for SPL or
soundpressure decibel soundlevel.
There are comparisions with Jet-aeroplanes
taking off, and such things.Kindly, groman
You assumption of 94 db SPL, or even 90-95 SPL is way off. Much more like 85 db or like that. With that, your power requirements go way up. And with tranisients, you need even more. Plus, I have a very big room (16 feet x 40 feet x 9feet), so to keep sound levels high in the room, you need more power still. Also, you should note, that the SPL efficiency ratings at a one meter distance. I don't listen to my speaker one meter away. More like 4 0r 5 meters away, and sometimes further away. So for every 3 db's in lower sensitivitiy you need to double the power. Everytime you double the distance from the speaker you loose 6 db's. So at 4 meters, to produce 85 db'd you need more like 4 watts. To produce 100 db's at 4 meters, you already then need 128 watts. With tranisients, you can easily double that. Strange it is with my full range speakers with an 86 db SPL, that I can bring my 200 watt amp to clipping without making the music unbearable loud - it's a big room. You need to look at you calulations again, and consider distance from the speaker, subwoofer efficiencies (which are low), and room size. You will then come to a very different conclusion. Further your cable gauge calculation is based on the output of the amp. However, the cable doesn't carry the output power. You need to base you AWG cable on how much power the amp takes IN. Since amp's create heat, and nothing is 100% efficient, we can very safely assume that it will take in more power than it sends to the speaker. This increase your AWG requirement again. Fruther more, how LONG your cable is also a factor on what gauge it needs to be. The long you need a cable to be for a given current, the thick the gauge needs to be. I think you need to sharpen your pencil and reconsider your analysis based on reality, not a one meter test condition.
My calculations was based on the information
I had.
And it was also a little overdriven.
But my first calculation, which asumes
worst case 250 RMS Watt output, should
not be invalid.Transiental power output, is not the
same as the power delivered to the Trafo.The losses in Output stage of amplifier
is seldom more than 50%,
but you have a point there!
Nothing can change the fact:
delivered power never exceeds
the power that comes out, in one or another formMy later calculation included an
recommendation, to use dB-meter.
The resulting levels can be quite different
from what you like to believe.
The experts on this, are the competitors
that try to get most decibel in a car.thanks for correcting my miscalculations
but not for taking my other pointings out
as being unserious.
Just my 0.02$ (or Euros as I am from Europe...)
I do not think you can assume that the sub speakers have a 94Db/1W sensitivity.
First we know nothing about its speakers passive characteristics etc..
Second, I have played with simulation tools and subwoofer specs and I can tell you that efficiency will be closer to 88Db/1W or less, especially if it achieves low frequency response at a consequent loudness.
Also, woofers are more power-hungry than mediums or tweeters and a subwoofer usage demands a lot of dynamic power (e.g. home theatre use..)
So, rule of thumb, this amp will consume some power, much more than 1W but not 300W+ full time (assuming electrical efficiency of amp is around 80%).
As for power cable advice, I use thick gauge, shielded and with ferrites. I do not have teflon insulation.
I would think that such details matter less for subs than for other. components.Hope this helps
> Just my 0.02$ (or Euros as I am from Europe...)
That needs an explanation!Dynamic power is a burdon onto mainly (99%?)
capacitors and trafo.
Not to the AC-cord. Transient currents
generated heat is out-contered by cooler
periods and inductans in cable acts
as filter, storing and delivering voltage.I use ordinary 0.75 sq-mm unsheilded
AC-cord.I would like to get sheild, because I
believe AC-cords can act as transmitting
antennas, both for 50Hz and UHF-signals.
If you have 220VAC, about 1 A will maximaly
flow trough AC-cord.
Accepted mini-standard (3A/sq-mm), will
give AWG22 or larger area.
If you have 110VAC, about 2 A max.
Gives AWG19 or larger area.groman, Sweden
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