posted
i have 4 eight inch subs in an escort, sealed, shared airspace.. theyre not hitting like i imagined they would.. they kinda seem out of phase, but theyre not.. they just hit, then youll see one of them kinda flex out a bit, making it sound distrorted.. theyre run off a punch800aII bridged wired in series/parallel to get 4 ohms mono someone i talk to on the net told me this "So you have a pair in series, another pair in series, then those two pair wired in parallel? This is *not* good in a shared enclosure. You might be able to get away with it if you had at least 2 chambers, one for each series pair. Any time you wire in series, you get a slight phase shift (or delay) between the two speakers. That's why its recommended to wire subs in parallel -- so they hit at the same time.
Do you have a 2 channel amp? Try this:
Instead of running it bridged, wire one pair in parallel and put it on the left channel. Now wire the next pair in parallel and put it on the right channel. They should all hit at the same time now. Each channel will have 2ohms on it.
What type of amp do you have? Some amps have a switch for stereo/mono/(1+2). If you have this, use the mono setting -- not the bridged setting (1+2). If you don't have these options, check your amp documentation to see if you can get a mono signal to your channels. If you can't do this, you may have to feed a mono signal to the amp and use the amp in stereo. That way you have the same signal going into the left and right channels so playing in stereo will produce the same signal on left and right channels. In effect, your playing in mono. Result -- all subs hit at the same time"
does this sound right to you all, or is it something different.. something i can do to help this
thankx Ryan
------------------ Punkin out with a killer system. sXe all the way!
posted
I have always thought that separating the subs into their own chambers was a prefered way of doing things. Besides, I've been told that the each peice of wood that separates the chambers is a great brace. Just a Thought =)
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Posts: 305 | From: Brooklyn, New York, USA | Registered: Aug 1999
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posted
Ryan, pull those subs out and take a 9v battery and test them at the tinsel leads. Make sure the polarity is labeled correctly on all 4 of them. Next, use a test light on your wiring to make sure that the + marked wires are correct throughout, then reconnect all your subs, just how you had them, and power up your system. Listen to it with only the subs playing. Was one of your subs phased wrong? If it was, your problem is fixed. If not, I would try reversing phase AT THE AMPLIFIER, then listen again. It is possible that your expecting more out of them than is possible too.
------------------ STILL waiting to hear a GOOD pair of HLCD's!!
If it dont fit, force it... if it breaks, it needed to be replaced anyway...
Not only is wiring them in series not a good idea (especially in a shared airspace) because of the phase shift, there is another reason. One is the back EMF that can be produced by a speaker. I didn't want to get into anything too technical when I sent you the email, I'm sorry. I probably should have explained *all* the negative side affects of wiring subs in series, but I didn't have the time to go into details. You could probably find alot of detailed information in most basic electrical engineering textbooks. Get some text on magnetic fields or basic circuit design for reference. I don't remember the exact titles or authors because I don't have mine with me to reference as I am at work (shhhh! don't tell them I'm on here! hehe!). I'm sure you can find the info on the web too.
Basically the phase shift between drivers in series comes from the fact that the electrical current must travel through the first driver (thus actuating the driver), then it reaches the next driver. In essence the first driver gets the signal before the second.
I'd like you to notice one thing too. The speaker has a voice coil. The opperative word being "coil". Yes, and being a coil, it has inductance. What happens when you wire an inductor in series with your sub? Well, besides the fact that you can cut out the high frequencies with the proper value.
Yup, phase shift. 90 degrees with proper inductance. Of course the voice coil of a driver has different characteristics, but it does introduce a phase shift.
Another reason is the difference in characteristics between seemingly identical subwoofers. No two subs are identical. Sure the spec. sheet says they are, but they can be up to 20% off! This is especially true with mass-produced subs. The difference between the subs (however slight it may be) will cause more problems when wired in series. This is mainly where your back EMF comes into play. The difference between the subs can produce very undesirable current flow (or lack thereof) between the two drivers in series.
To get a better grasp of this, remember that a speaker is nothing more than a motor. Yes, it's a motor. The magnet/voice coil is called the motor assembly. When current is introduced to the voice coil, it produces an electromagnetic field which, depending on the polarity relationship between the magnet and electromagnet, causes the electromagnet to either move toward or away from the stationary magnet.
When you rapidly switch the poles of the current (an AC source -- i.e. output from the amplifier), the electromagnet oscillates with the frequency moving toward and away from the stationary magnet. The electromagnet is, of course, attached to the speaker cone which produces the air pressure differences that can be heard. We call this noise, or music.
Now you have a motor. Let me ask you something. Have you ever had a little DC motor that you hooked a battery to to make it spin? Now, have you ever taken the same little motor and connected a small light bulb or LED to it, then spun the motor? If not, try it. You may be suprised at the result. Let me explain...
When you put electricity into the motor, you turn the electrical energy into mechanical energy via the electromagnetic fields. Take the same motor and put mechanical energy into it and you get electrical energy out. Yes, the light bulb will light when you spin the motor. This is usually called a generator. :-) I could go into more details, but I think this is good for now.
Now you know that a motor can produce an electrical current so you can see that a speaker, being a motor, can do the same thing. Push on the speaker and you can get a current at the leads.
This is where the mechanical differences between speakers affects subs wired in series. Anytime the speaker starts to move or stops moving the electrical current to the speaker is affected by the electrical current being produced by the speaker. This is one reason the dampening factor of your amplifier is important, but that's not the topic of this thread. :-)
The mechanical differences between the subs is what causes back EMF. The differences only have to be slight. One cone may weigh slightly more than the other, one surround may be slightly stiffer, or the excursion of one driver is slightly more than another. Even the slightest differences plays into the back EMF caused by the drivers.
Now let's quickly look at what happens when two drivers are wired in series in a shared airspace. Not only do you have the phase shift and back EMF problems, but now you have another problem. Actually it's a back EMF problem, but it's for another reason. When the subs hit slightly out of phase there is a point in time where one sub will be moving out while another is moving in (or stopped). Now each of these subs is creating pressure in the airspace, whether negative pressure or positive pressure. The pressure that one sub is causing is affecting the other sub thus producing mechanical work on the other sub. What does mechanical work do when introduced into a motor? Yup, electrical energy is produced. More back EMF problems.
Let's digress from the EMF problems for a second and picture a point in time where the two subs a wired in series so that they hit slightly out of phase. This particular point in time is when the second sub is at xmax and the first sub is already on its return path inward. Remember the first sub will react before the second so it will travel to xmax before the second hits xmax. (we are ussuming xmax to make a point). Since the first sub hit xmax first, we can also say that it will be on its return stroke first, right?
What happens when your second sub is pushed to xmax and the first sub is already on it return stroke producing a positive pressure in your airspace? Yes! That extra pressure created by the first sub will directly affect the second sub by pushing it out even further! That, my friend, is over excursion. Not a good thing at all.
So, to summarize what I went over: Don't wire your subs in series, especially if they're in a shared airspace. :-)
I'm sorry if this was a little more explanation than you wanted, but I hope I got my point across. If you have a little better understanding on the subject, great! I'm glad I helped. If not, take my word for it. At the very least, even if you have to wire some in series and some in parallel, put them into separate chambers. Separate chambers may not fix all your problems, but they will help eliminate alot of them.
Your best bet is to get and amp that will handle the load of all of them wired in parallel, or trade them for DVC models.
I just looked something up for you. It's not a totally technical explanation, but it helps back up my point. :-)
Look at the JL tutorials, specifically the sub wiring and DVC tutorials. They will tell you basically the same thing... never wire your subs in series.
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