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Another "How to wire my sub" questions

Discussion in 'Audio' started by 73k5blazer, Jan 15, 2006.

  1. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    I've got a Polk C500.1 monoblock class d amp, rated 350w@4ohm, and 500w@2ohms. 2ohm stable amp.
    I have an Infinity 10.1d DVC subwoofer (just 1) rated 350w RMS, (or 175w per coil). each coil is 4ohms. 1400w peak (or 700 peak per coil)

    Now, this sub is also rated acceptable for "free air" use. My K5 is all fiberglass body tub (US Body), and where the OEM K5 sidepanels (the cardboard ones) would normally go in a steel body , I have a fiberglass panel, that is part of the body, effectivly creating a quarter panel cavity. 4" thick at top, 7" at bottom (where body side swoops out). Same cavity where taillights mount in the rear, and I will have the rear speakers (6") mounted in a more forward position on this panel as well. I will be mounting the sub to this panel (and in the cavity) (why, because I value my space, and I really don't like sub boxes) This cavity, I esitimate to be about 3-4 times the recommended ported enclosure volume,so it will effectivly run as "free air",which according to the manufacturer, will cut it's rated power in half. (which is part of the question, I don't really get that statment, will it be cut in half, or are they saying, don't put more than half of 350 into it?)
    So, with that said, how should I wire this sub to the polk amp? Present the 8ohm load(wire the coils in series), or the 2ohm load (parallel wired coils)? My concern is if I go the 2 ohm route, I will me massively overpowered (or will i?)and blow the sub. But I don't have a good enough understanding how speakers and amps work together.

    The amp has 2 sets of speaker outputs (only 1 channel though),they are just parallel wired if you hook a sub (or a coil) to each set. Here's the amp wireing chart:
    [​IMG]

    Any insight, is, as always, greatly appreciated.
     
    Last edited: Jan 15, 2006
  2. Cmoe

    Cmoe 1/2 ton status

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    If your going to run your sub in the same panel as your mids (freeair sub) You'll need to build a box around your rear mids to keep the one in the same panel as your sub from been over extended... Your gain will adjust the amount of power that is sent to a speaker. Your not wantong to clip the amp anyway which would be full amp output..
     
  3. chevyin

    chevyin 1/2 ton status

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    Wire the sub in series for an 8ohm load. This should provide approximate half the rated 350watts@4ohms from the amp, which according to the manufacturer is about right. What the manufacturer is saying about cutting the power rating is half is, as you place a speaker in an infinite baffle situation, it basically has no air cushion from an enclosure behind it now, its relying solely on its own suspension to control cone motion (keep it staying linear and from over-extending). This is why a person must make sure they have a sub rated for IB (also called free-air) when chosing this mounting method, as you have already done. This means the cone is easier to move back and forth than when its mounted in an enclosure, which means the amount of power (in watts) it takes to reach full cone excursion is less (in this case they say cut in half). But the up-side is this means it only takes half the amount of power to reach the subwoofer's maximum output potential. Running your amp at 8ohms will keep it nice and cool, stable, and clean anyway.

    Amplifier gains should only used to limit amplifier output when the person knows exactly what they are doing. Many times to properly set the gain, it must already be in the minimum position, leaving no room to turn it down for power limiting purposes. At this point, power limiting relies solely on your discretion with the volume knob, which many times ends up badly. ;) I many times recommend using amp gains to 'tweak' a system, adjusting outputs of various speakers in the system to blend together. But, I rarely recommend people use a gain to limit output from a grossly overpowered amplifier.

    I agree, mounting the mid and subwoofer in the same airspace will lead to problems. The sub pressurizing the enclosure space will affect cone motion of the mid, which is trying to do its own thing.
     
  4. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    Ok, that's what I kinda thought, if I use the 8ohm series method, I would only be asking for 175w from the amp.
    So, about the other speaker in the same space, I did think about this, but I dismissed it as a problem, because the cavity is so large, I estimate approximatly 4-5cuft. What kinda of problems will it lead to, damage problems or poor sound? I guess it doesn't matter, either case is bad. I can build boxes I guess (that prospect doesn't excite me, but I'll do what's nessesary to ensure a as clean, and good sounding system as I can get). How sealed off from it does it need to be? Would a divider do the job, or does the 6" speaker need to be it's own sealed box. If I do that to one side too, I need to do it to the other to keep it balanced I would naturally assume.

    Thanks for all the help.
     
  5. Z3PR

    Z3PR Banned

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    Personally I'd wire it for 2 ohm. You can always turn down the gain on the amp if the bass overpowers the mids and tweets. I'd also get a box for the sub, but that's just me.
     
  6. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    Could I build a box inside my quarter panel for the sub? (If physically possible?). Would that solve both my issues, meaning, would I still, if the sub was in a sealed enclosure in that cavity, need to worry about the 6" speaker, and then I'd be free to wire it for full power?

    The amp does have that remote gain knob, which I already mounted in the dash. From the manual though, I thought this to be more of how much bass, like an extra slider on an EQ, and I think I would be hesitent to use it to limit thepower to the speaker, just like I wouldn't turn down the EQ slider because the speaker can't handle it. I don't think what it's for, but I'm no expert here.
     
  7. Z3PR

    Z3PR Banned

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    Probley be easier too get speaker baffles (box) for the 6" midrange speakers. The remote gain turns up/down the volume for that amp. Works well for "blending" if your headunit doesn't have settings for sub gain.
     
  8. chevyin

    chevyin 1/2 ton status

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    Most bass knobs are either a gain adjuster (bad) or a bass boost (artificially boosts freqs not originally intended by the artist... bad again). I would tweak the system to sound the way you want with the bass knob at zero. Then if/when you want a little extra bass in a song, turn it up a bit. Otherwise, id personally leave the bass knob alone.

    The most ideal way to handle the same space issue would be to build an enclosure for the sub probably. Infinite baffle can be tricky to get right, as absolutely sealed the front and back waves from each other is critical, and difficult. IB is a great install method, if you have the room and the means, but honestly trying to get it right in those panels will likely be hard (do the panels seal air-tight against the floor AND quarterpanel, for example? Even under pressure? Also, most car audio midbass/midrange drivers are designed to work infinite baffle (in a car door). Placing the mid ina small sealed enclosure will likely kill its low-end response.

    If builidng a small sealed box for the sub is not an option, just put a divider between the two speakers (leaving enough so the mid still has room to breath), just make sure its sealed.

    Running the amp at 2ohms is a bad idea imo. You will be overpowering the sub already, according to its specs, AND running it infinite baffle where there will be zero enclosure backpressure to maintain cone control. Running that sub, at 500watts, infinite baffle... you'll be about 90% likely to destroy your sub, quickly. And that's only referring to the mechanical problems that would surely arise, you might have some thermal issues runngin that much pwer through the sub as well. And lastly, as I said above, most times its a poor idea to decide to grossly overpower a speaker, and think you'll just tweak the gains down to compensate. Rarely do things work out that neat and tidy, nor does that situation usually end up positive for a beginner. That amp puts out exactly the power the manufacturer recommended for your sub in an infinite baffle situation. I see zero good reasons to run it at 500watts instead, thereby risking damage to your sub, and running your amp harder so it gets hotter (shortening its lifespan too if nothing else), creating more distortion, etc etc. And all this for maybe a 3db increase going from 175watts to 500... maybe. If you do run it IB, run the amp at 8ohms.
     
  9. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    Those panels are air tight against the floor. These glass bodies are built very very tough, and thick. Those panels are definaltly sealed at every intersection. Before I had the thing Line-x'd (the truck is line-x inside and out, top and bottom) I took a power washer and balsted the piss out of lots of areas to ensure these areas were sealed off from other areas (I didn't want water to get in there because I knew I would be putting amps and speakers in there), not a single leak, then it was Line-x'd very thick, further sealing them off. However, the holes I drilled for the access to the removable top nuts would be the biggest problem. I could make sealed covers for those holes. So if I can ensure the front and rear sections of the speakers are completly non-accessible to each other (I think I have that, save for the access holes mentioned above), is that an ideal setup. You say it's a great install method, is it also acoustically better? What about when the top is removed, then I'll have those bolt holes open into that cavity. I could seal those off too somehow, I guess.
    I'll see how hard it is to get dividers in there, I might be able to do 2 dividers, place the sub in an area not below one of the access holes, and place the "dividers" on each side of the sub, trying to get as close to 1cuft as I can and that can be my sealed "enclosure". I'll have to play with it to see. Matching the outer body panels' contour is probably going to be the toughest.
    I knew that amp was a little big for the sub, but I wasn't sure how much sub I would need, so I got that amp just in case I wanted to add another sub, I knew it could handle it. I'll start with 1 divider, to see how hard it is.
    I know I'm a begineer here, but I like to learn, I read alot, take things very slow, and try to do it right.
    Again, thanks for all the replies and help!
     
  10. chevyin

    chevyin 1/2 ton status

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    Acoustically, infinite baffle is arguably the best install method for pure SQ. Output tends to be limited versus an enclosed woofer, but the transient response and low-end extension are unrivaled by other install types.

    For the bolt holes, can you simply thread the bolts back in place once the top is removed? No this would no create an absolutel air-tight fit, but it would probably be fine.

    I guess the ideal situation would be 1) the mid is mounted IB... definitely, and 2) the sub is either IB seperated from the mids, or run in an enclosure mounted behind the panel. I'll leave it up to your judgement as to which you;d prefer to do, and listen to.

    No offense to you with my beginner comments. First off, I really dont know your background so I should not presume to, secondly there is nothing wrong with being a newb. :) We all started somewhere.

    Feel free to post any further questions you may have.
     
  11. divorced

    divorced 3/4 ton status

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    I would try it at 8 ohms first, and only switch to 2 ohms if more power is needed. An 8 ohm load will make for a much "cleaner" sound than a 2 ohm load.
     
  12. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    No offense taken! Last system I did was in this very same K5 when I bought it in 1993. I've since done a frame off and used this fiberglass body. Anyhow,
    ALOT has changed since 1993 in the way of car stereos, I didn't have much money then either, so I didn't go all out.

    So, I think I will try 1 divider and see how sealed I can get it. I think I can get it pretty well if I work at it long enough, I have the giant 9 1/8" sub hole to weasel it in there. What's the best material to use for it? Plywood, MDF or something else? Once it's in there I can glass over the edges to seal it.


    A different question, would it be bad if I ran the RCA cables outside? It's going to get done regardless, I guess the question is more do I need to put my industrial plastic/vinyl flex solid conduit for them, or would they be ok running down the frame rail by themselves? My guess is not, and I'll need to protect them with the conduit. I can't find detailed specifications on RCA cables like you can for standard wire and what insulation type and what they can withstand. I have python 25footers for the job. I find alot of this car stereo stuff on the market is more looks than performance, the "free amp kit" that came with my eBay bought new polk amp, I looked up the spec on the huge 4 gauge cable that was in that amp kit, looked pretty cable, but the spec on it was crap, only rated to 60c do not use near any gasoline, diesel , or oil source, the spec for it specifcally stated "Do not use in automotve engine compartment"), :haha:And the rca cable looked pretty too, but I could take my fingernail and poke through the insulation. I got that auction because it was the cheapest price for the amp in a new sealed box, not for the amp kit. I have quality crosslinked SXL insulated wire from 2 gauge to 18 gauge, so I'm covered there.
    Anyhow, thanks for all the replies and help,from everyone, it is greatly appreciated.
     
  13. chevyin

    chevyin 1/2 ton status

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    The best material to use for the divider would probably be mdf, as its denser than things like plywood. You are not talking about a major woofer with alot of power here, probably 5/8" or maybe even 1/2" would do the job, provided its held securely in place. Judge the thickness you need by the size of the panel you have to make. Yep, using fiberglass resin to seal it once in place is a great idea, exactly what I would have suggested. :)

    For the RCA cable question, well I don't know for sure. Ive honestly never ran the RCA's outside the vehicle before (power/ground yes, signal wires never have). My gut tells me the same things yours does, probably not the best idea. But I really dont know, it may be fine. I guess Id say if you do alot of trail riding/mudding/etc, probably a good idea to protect it. If so, just run down to the local hardware store and buy some flexible conduit (such as the Liquitight stuff).

    Most car audio wires are not rated for contact with gasoline etc because the emphasis is on flexibility of the insulation (and the wire as a whole), rather than protection like industrial wire is.
     
  14. Z3PR

    Z3PR Banned

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    Personally, I think 8 ohm will not be enough power, wired at 2 ohm may blow the sub if the gain is set at max. Nobody ever said the gain needs too be turned all the way up.
     
  15. chevyin

    chevyin 1/2 ton status

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    Do you know the output voltage rating of his headunit, or the inpuit sensitivity range of his amp? If the situation is right (or wrong, dpeneding on your perspective) the gain may already need to be set at the minimum. This would leave no adjustment for turning it down to limit power. Again, that would mean a fairly complex situation involving adjusting the gains up on other components to compensate, and deduce what volume setting on the headunit would output the proper amount of power. Or, leaving the gain above minimum (for blending to the other components) and limiting your headunit volume control that much more. Possible? Sure. Likely for someone besides a veteran? Not likely. Running the amp at 8ohms will give basically exactly the amount of power the manufacturer recommends for his situation (IB). Im not seeing the problem with that. :) Especially not when the alternative has so many possible (and likely) consequences.

    Why do you think 175watts would not be enough power?
     
  16. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    Here's the listed "audio" specs for the HU, if it changes anybodies opinions on how best to do this:
    HU is a Pioneer DEH-P77DH
    Built-in Speaker Power MOSFET 45W x 4
    Equalizer EEQ (3-Band Parametric)
    Equalizer Presets 5
    User Equalizer Settings 1
    Loudness 3 Mode
    FIE (Front Image Enhancement)
    Crossover Network Two-Way Crossover
    High-Pass Crossover (HPF) 50/80/125Hz, -12dB/Oct.
    Subwoofer Crossover (LPF) 50/80/125Hz, -18dB/Oct., +/-12dB
    RCA Preouts 3 pair (Front, Rear, Sub/Non-Fading)
    Preout Voltage & Impedance Hi-Volt (4V), 100 Ohm
     
  17. chevyin

    chevyin 1/2 ton status

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    Even barring the possible signal voltage problem I mentioned earlier, I would still recommend the 8ohm setup, if you run it infinite baffle. But, if you seal it up in a small enclosure, sure, 500watts will probably be fine and give you a bit of headroom. I can almost guarantee if you run that much too much power to that sub while running it infinite baffle, you will have problems with it bottoming out. There's a reason manufacturers cut the power handling in half for such a setup, it needs it. Going the opposite way (overpowering by a large amount) just doesn't make sense.
     
  18. Z3PR

    Z3PR Banned

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    But that amp would only be 175watts at 8 ohm with the gain set at max. (Not recomended because of clipping) At 2 ohm you wouldn't need the gain turned up much and that'd ellimate any possiblity of clipping. My MMATS D200hc is wired at 1 Ohm (DVC sub with 2ohm voice coils) but I have the gain set at just under 1/2. Powers my 12" Kicker L7 very nicely. I'm no expert by any means, I just know what works for me. I can easily be wrong, so take my advice for what it's worth.
     
  19. chevyin

    chevyin 1/2 ton status

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    Okay, I see the problem. :) What you aren't understanding here is an amplifier does not only put out max output at the max gain setting. An amp's gains do not need to be set at their maximum in order to clip. Given the right situation, an amp can easily be clipped even with its gain set at the minimum.

    What the gains are for is to match input sensitivity to signal voltage. In other words, the amp manufacturer doesn't know what headunit will be used to feed signal to the amp. It may be a model with a max signal output voltage of 8 to 10 volts, or as low as a 1/2volt. So, they add potentiometers (gains) that allow you to adjust the sensitivity of the input stage to match the signal voltage of your particular headunit. What this means is, given a high voltage headunit, you can easily meet and exceed the point of clipping even with the gains set well below max.

    For example, you have an older amplifier with a max input signal voltage of 4volts and a headunit capable of a max of 4volts of signal output, where do you set the gains? The answer is you set them at the minimum setting, so that the input stage is the least sensitive to voltage as possible. But, if your headunit only puts out up to 1volt, you will be setting the gain higher to increase the input stage's sensitivity. The lower the signal voltage is, the higher the sensitivity needs to be to make up for it. The higher the signal voltage, the lower the gain setting to make up for it. You are looking for an equilibrium if you will. Both of those scenarios will have the amplifier clipping at the same output level, the only difference will be the amount of signal voltage between the amp and headunit at that point.

    For another example, say your amp accepts 4volts, but your headunit is capable of 8volts of output... what then? What you do in this situation is first, set your amp's gains at the minimum, but there is still a discrepancy between what the amp will allow even at minimum gain (4volts), and what the h/u will produce (8volts). The key is in realizing the h/u's signal voltage varies according to the volume setting. In other words, your h/u will not produce that 8volts unless the volume is set to maximum. Using an o-scope to watch for the clipped waveform, you can adjust your volume up until you see it, then back off one volume setting. This is the maximum volume setting you could run, given the 8v h/u and 4v amplifier.

    Hopefully that makes things more clear. :)
     
  20. Z3PR

    Z3PR Banned

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    All I can say is that I do notice a increase in volume by tirning the gain up, but sounds the best to me is setting the gain on my amp at just under 1/2 and the sub volume on the headunit at -2. Now the gains on the 4 channel amp are both set at roughly 3/4. Everything is "blended" quite nicely, with nothing over powering anything else. Granted everybody's system will be different, and require different settings. I don't know all the tech stuff, just what sounds good to my ears.
     

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