posted
How would I go about figureing impedince rise,with out haveing the sub's to check ???
I am looking to buy new sub's but want to make sure I get the most out of my amp's. NOW the way my amp's are slaved there only stable at "2 ohm series slaved" I'm sure there are better amp's but these are what I have.
How do I figure what ohm load sub's I need to make sure that when I burp that I'm at a 2 ohm load.....I've been told that I should just buy dual 2ohm sub's and run pallel so that with a "rough" guess I would get my 2 ohm load.
Please help,I need to make sure I get the right ohm load to get the most out of my amp's,
THANK YOU FRO ANY HELP !!!!
-------------------- Super Street No Wall -----TeamTjsAudio-------- Posts: 950 | From: Allegan Michigan | Registered: Jan 2007
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posted
if your subs are stable down to 2 ohm, try to get a config of 1-1.4 with an eq than can cut some of the power down at a specific frequency so resistance can rise above the 2ohm mark.
quote:Originally posted by shizzzon: if your subs are stable down to 2 ohm, try to get a config of 1-1.4 with an eq than can cut some of the power down at a specific frequency so resistance can rise above the 2ohm mark.
What are you talking about????
I'm busy studying right now, I will get back to you on your question with a much better explanation. It will depend on your enclosure and frequency though. Its not necessarily completely dependent on the subwoofers. Although a good rule of thumb is the stronger the motor the more the impedance rise. I will come back and explain why maybe tomorrow night after this test is over!!!
posted
ok, this is what i have witnessed with measuring power with DMM and ammeter.
If I were to measure wattage output at a low volume level, the resistance would be pretty high but the higher i turn the volume up, the lower the resistance would go....lower resistance, more power. However, high levels of constant power would then make the resistance rise due to heat.
Using an eq would allow one to, in simple terms, have a volume control for specific frequencies.
If you burp at 50hz and the eq has a center band for 50hz, that would be perfect since it's centered at 50, but anyways, if your resistance is at 1.7ohms and it needs to be above 2 because amp keeps shutting off, cutting the boost on the eq at 50 would increase the resistance the more you cut. Also, turning the volume down would do the same thing... this summary i guess would be more suited for daily after typing all of this out, hehe AHH!
And to add on something- it is my understanding as to how it is successful to get a better score by rolling the volume instead of just a straight burp at a constant volume level.
The rolling of the volume knob(still in my theory) will quickly add resistance due to heat buildup from so much power. There's so much power that the resistance rise is hardly there so by building up heat from the rolling of the volume will allow the sub(s) to go over the "lowest ohm load threshold" by the time the stereo is at a volume it should be to finish the burp. Again, that's what i believe is happening based on what i have seen when i have measured things in the past.
An example of what i've seen before is low output volume as much as 8-9 ohms in the 200w range and by the time the volume reaches it's max non-clipped level, the resistance would be down to just over 4ohms. Repeated 3-10 sec burps at the same frequency allowed the resistance to go up slowly, maybe 0.2 if i remember but i did notice it. Don't take the previous statement for all equipment as diff setups will react differently but the basic principle is the same.
posted
I am still looking for some more indepth input.
I spoke to amp maker"directed" today and they shed a little more light...."In theroy a 3-8 second burp with a ohm load of less than 2 ohm's will work,probley down near 1ohm....however the life span of the amp will be greatly reduced"
I was advised by directed to run the amp's parrel syned(internal gain matching), 1 amp to each voice coil. This would reduce the chance of damage to the amp's due to improper ohm load.
The amp's running gain syned are rated at 1 ohm.
There is also a dyamic(IHF 202 standered) minimum standered rateing....the power out put is higher at this rateing.....WHAT IS the load being refered to. Is it possable the amp is capable of a lower ohm load than what it's rated for ?????
After some checking I found out that I have (in the past) run 2 of these amp's at a .8 ohm load( running gain matched) with no problem....with the execption of a few song's with REALY deep bass...like 25 HZ. but they played the high note's fine.
I am lookin at Atomic apocalypse series 15's I don't know how strong the motor's are .
Keep the info comeing PLEASE
-------------------- Super Street No Wall -----TeamTjsAudio-------- Posts: 950 | From: Allegan Michigan | Registered: Jan 2007
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posted
To be honest with you, I can't remember if it gives references to rise or not. If I had to guess, I would say it would. Just remember to tell ur friend to see if it does.
I know winisd does but is terribly off vs testing it in real world so I never go by what winisd says about rise.
posted
Bass Box hasn't proven to be accurate in my testing but there are many reasons for this. Anyway I'll do my best to try and explain impedance rise to you.
First of all a wire winding(voice coil) placed in a magnetic field will have properties of an inductor. While the coils aren't exactly inductors they share some of the inductive properties including the frequency dependence for their impedance.
The formula for calculating the impedance of an inductor is 1/jwL where j is the imaginary number(normally "i" in non electrical mathematics), w is the greek letter omega which is frequency in radians per second, and L is the inductance measured in Henries. You will see in most T/S parameters that the inductance of the coil is listed. To convert frequency in cycles/second (50,60 hz etc.) use this relation:
w=2(pi)f where f is your frequency in hertz and "pi" is the constant typically approximated by 3.14.
Also part of the reason we have impedance rise is because of the heat as some of the other guys mentioned.
I believe motor force can also play a part. It resists movement of the coil. If you learn Lorentz Law you will learn that a current through a wire in a magnetic field generates a force. This law will tell you which direction the force is and it is dependent on the direction of the magnetic field. It is because of this law that we have the movement of the woofer. The stronger the magnetic field the harder it is to set the object in motion as the field resists movement.
I'm sure a search on google for electromagnetism, impedance, Lorentz Law, or electrical physics could give you more insight but I think I covered the basics of it here. Feel free to ask questions and I'll do my best to answer them.
While Wikipedia isn't generally accepted as a source at the collegiate level I read through it and the majority of it seems on par with what they are teaching us. That should explain and answer your questions more thoroughly than I can here with limited time.
posted
Ok,I still reading and rereading tyring to under stand. Some of these figures I'm not understanding. Could some one give me a REAL-WORLD exampel of how the figures are used ?
Is there a way to predict the change in ohm's with out haveing the whole thing done ? I'm not talking exact,just a genreal idea of where it would end up at....I don't want to buy these sub's and find out that with the rise I'm ending up at like 4-6 Ohm's seeing how I want to be like 2-3 ohm's.
Thank you for the help so far, you guy's know your stuff.
-------------------- Super Street No Wall -----TeamTjsAudio-------- Posts: 950 | From: Allegan Michigan | Registered: Jan 2007
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posted
Well its going to be dependent on your box, frequency, a motor strength. There is no way of really calculating it without testing. I can tell you this...with Solo X's, CVX's, RE MT's, DD9515's all have had an approximate impedance rise of 3x the nominal impedance. Meaning if I have the amp wired at .5 ohm it generally sees 1.4-1.6 ohms. It could be higher or slightly lower but normally not much lower. You can adjust your impedance rise with the tuning of the box to some extent but I dont have any developed methods of doing so.
You must remember that the impedance of your woofers can go up and down so if you plan to play any music with the amps at a lower impedance you risk the impedance dipping down too low and sending them in protect. For everyday applications always run the amps at the manufacturer's rated impedance. If its just for SPL burps you are just going to have to try and see what happens. Perhaps you should buy some subs that can be reconed to different impedance coils if need be.
posted
I have had success in tuning an enclosure for the rise many times. I know that by changing different variables in an enclosure I have seen everywhere from 2x multiple of Re to 19x multiple of Re.
The only way to know is to build the enclosure and test it. If it isn't what you want change something and test aain.
If you could predict all of these things getting loud would be easy
-------------------- Just some thoughts from a nobody. Posts: 3497 | From: Lakewood,Ohio | Registered: Aug 2003
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