Ed Lester explaining what "Impedance" is, and how Box rise can affect your car audio system. showtimecaraudio.net/ facebook at / showtimecaraudio.net Please subscribe
Voice coils do not "wear out" unless you send them too much power. You can tell by the burning smell they emit but it takes quite a bit to damage typical subs (as you can see in RU-vid videos of people blowing up speakers). Also, when a voice coil heats up, its resistance increases, so your woofer actually doesn't play as loudly as you'd expect it to. This is called power compression. Google that for some interesting info.
Great vid on explaining what box rise is, I have a soundstream tx12600d on an Orion hcca12.2 running at 1 ohm and when I clamped the amp I was only getting 288 watts at a steady 14.4 volts, with a box rise of 6.8, if I was to increase the size of the box would this normally bring the impedance down to get more out of the amp?
yes you got it. Each song can be different and if you change the box or woofer, you will also change that power you will see from the amp. The actual measure power output from an amp is not the same power over all frequencies.
Thank you for an informative piece. Question; if you've gone to great lengths and expense to have a system configured and installed professionally that utilizes a 3 ohm woofer (JL Audio 13TW5-3) that creates box rise, is there a way to combat that without a complete re-design? I've just learned of "box rise" due to a problem I'm having that I described on 'caraudio' forum, from a members feedback.
I can find my test sheets from a bunch of SPL cars I have tested. And the trend is that at the peak SPL frequency, wattage was lowest, Impedance was highest. And that's in ported enclosures just like how they say sealed boxes should work and just like free air
See, and now you know the info I give is the correct info and the info you received before was the misleading info. I make these vids to clear all of that up. I think I am one of the only industry insider, old school veterans giving info out on youtube. So I am here to help. I may not know it all, and I still learn more, but I do spread what I have learned from 17 years of doing this.
I was just thinking about this and decided to look it up. Running 2ohm DVC subs wired to .5ohm. The SCV 6K should easily handle this with the gains set properly and knowing that max volume the headunit can run without distortion.
Usually speakers are rated with their DC Resistance. Which is the resting resistance. If the coil reads around 4ohms with no voltage going through it, it is classified as a 4ohm speaker.
could you talk about box design? aspects such as port location, musical vs spl box, enclosure type, oblong shapes, types of ports. and in that you could talk about cabin frequency and all that.
very informative. so the idea is to achieve the best possible average over all frequencies for music? or rather the bandwidth in which your capable of playing, because depending on the type of box your bandwidth will be shorter or wider. you may have mentioned it, but besides choosing higher quality equipment over cheaper stuff, is there a specific aspect of the system which would provide the most likely positive end result as far as changing something to lower imp rise?
If I have the impedance curve of my woofer in the box can I use a parametric eq to give it less power at the hump. Would that help some of the boomyness I'm hearing. I have an idmax 15 in a 3 ft sealed box. Sounds a bit boomy in my suv. Crossed anywhere from 60 to 80.
This is a common trend in most cars and boxes. An air mass sits in the port and vibrates like a spring. The larger the port, the greater the mass. Air also has an impedance and the larger we make the air mass, usually it will reduce the electrical impedance as a peak, but may raise the average impedance over a wide range. A bandpass works like a ported box in the same manner except that we add an acoustical filter and make this curve difficult to keep flat except in a narrow band of frequencies.
Ed, is there a device that can show me my real time impedance or at least the minimum my amp will see that does not cost $450 like the SMD AMM-1? I have a DATS, is that impedance curve going to be accurate playing music?
also this is in an extended cab truck port up in all cases. Im just wondering if I should maybe try going bandpass to get what I want out of this setup, and maybe anything you could say about ported vs. bandpass walls, sorry about all the ?'s lol
Yes, you are correct, Impedance does depend on frequency but also power. And manufacturers will rate the nominal impedance of a speaker by rounding to the nearest whole number. Usually an even number. When building woofers at the factory I would order a case of 4ohm coils or 2ohm coils or whatever I needed. The coils were rated as such based on their resting DC resistance and that's what we would rate the woofers by. a4ohm rated coil would not always read 4ohms though, usually 3.5ohms.
The woofer I have has more than enough volume but I'm getting intermediate, odd bass shut off during playback. It's strange and the only plausible cause I have to the problem was what someone on a forum suggested as 'box rise." I'm not a tad too naïve on the subject to know which route to take.
How does port size generally effect bandwidth and impedance rise in a musical box? I can tune boxes with the same freq. and volume on paper, but it seems like the bigger I go with the port the lower the over all rise but the peakier the box sounds. A smaller port gives me more rise and less SPL but I feel like it has alot flatter and wider avg. response. Is this true just for my vehicle? Is every vehicle different in this regard or are there any major trends with port size vs rise for all cars?
Box rise is not usually a problem and does not have to be dealt with unless you are an SPL competitor trying to get every ounce of power to the woofer. You can't really a way to combat it without compromises in the enclosure and for daily, good sounding setups, you need a bit of rise to flatten out your response. If you simply want it louder and have more power, I'd suggest a different woofer first.
A ported box can be easier to tune to a flat response over a wider range, and a BP can be tuned to have a wider passband but will suffer on loudness a bit.
Dear Mr. Socket, I've seen you on a Vid. while back of you speaking about Parallel VS Series.. You said that you've done a test on a 12" sub that you had like DB from paralleling VS Series up With the Same Watts.. Could Speak on that Topic again Please an link me with that Sir....
I sent you a link that shows impedance and resonance. And you can do the test yourself, just like I did in the vid and see if your test matched the woofer's rated Fs.
so youre saying a ported box properly built will have a flatter overall music response than a music-oriented bandpass in the same environment? What about the passband? Can you make the overall passband wider albeit less flat over a wide range with a bandpass? Thanks for the response
yes, the goal that people have with imp. rise is to get the most power they can. So they would want to see their impedance not be very much over their nominal resistance rating. It's impossible to stay at nominal resistance so an amp's power rating is just an example and not really guaranteed.
If you only have 1 sub, then nothing has to be changed. And difference in sound may be so small that you won't notice because the only thing you change is airspace due to the cone's shape being in the box, vs being out of the box. This difference is very small. Now, if you have more than 1 woofer and you only want to invert 1 woofer, you need to switch the phase on that woofer, usually by just switching the + and - on the speaker wire.
Hi there ed, can you help me out with understanding my situation better? Well i have 3 re audio se 12s (d4), my wiring options come out to either a 2.67 load or a .5 ohm load. What is the best option on powering these? I was thinking of bridging/strapping 2 audiopipe apsm1500s, what kind of power will these produce? Or can i buy a 2k rms amp and wire it down to .5 ohm . Would box rise bring this .5ohm up to around 1ohm? And i am gna run two batteries with the big three done.thanks in advance bro
Oh, and the other thing I need to mention. Electrical impedance is what your multimeter is measuring (resistance @ resonance) and mechanical impedance (what you are calling box rise) is speed/torque. Though they are both "impedances", they are different aspects of physics and can not be viewed as one.
+Zach Ridgway w0t? Multimeter measures DC resistance, which has nothing to do with resonance, actual impedance at resonance frequency can be more than 50 Ohms for a 4 Ohm speaker, and that's not what multimeter shows you, is it?. Impedance changes with frequency, it will have a peak (it's height and width are described by Q) at resonance frequency. The shape of this impedance curve changes when you put the woofer into the box, either the frequency of where this peak is changes (sealed box) or there will be two or three impedance peaks (vented box/bandpass).
+Zach Ridgway Electrical impedance is what your multimeter is measuring Nope. A standard DMM does not and cannot measure impedance. Even my Fluke 87 can't do it.
Most of the time, more. But this was done at low power (around 1w or less) So that alone will change it, so there is a chance it will be less in your box and car.
I have two 12s dvc 4ohm wire in parrael to 1ohm meter reads 1.8,2.4 at times box ported tune to 34hrtz so wat i am really getting to these subs. So i really whant to c 1ohm on them i should off got the 2ohms wire to .5 n will hobup to .8,1ohm in the area with the same box thanks really good info
Okay lets dumb this down the only way to minimize coil rise it to build a effeicent box "what's an effeicent box?" Well simply put your gonna focus on the ts params of the speaker that everything not just fs and cubic feet then very carifuly using the total x max cone area and displacement of the speaker your gonna want to find out how much air the woofer can displace (usually listed on the woofer spec) usually it listed in litters now that you know this you need to design a box around that but keep in mind that this should also allow the speaker to move peak to peak at fs the ideal situa2 for an effeicent box. Is to build a medium sized with in these parameters and use a good sized port not extremely large not to small then you have successfully minimized the ohm change at peak to peak excursion
Very nice. When I built my ported enclosure for sq I was going for a flat response. But I had help from a guy on a forum who told me that I should tune it a little higher, than where I had it, to get a 4db to 6db gain. So I went back to winisd and ended up tuning it to 36hz and had about 5db gain. I built it and, to me, it sounds freakin' great. But I really wouldn't know. Would you suggest that kind of gain for an sq enclosure?
I have a question I bought two Skar ZVX v2 d2 12, so with two I can only do 1 ohm or half ohm, I messed up, I should of brought two 1 ohm so I can wire them to 1ohm. My question is can I wire the Skar ZVX v2 to half ohm, with ORION HCCA HCCA3000.1DSPLX, Class D Amplifier 3000 WATTS RMS 01 OHM I have the big three upgrade and an xs power 3400 in the trunk. And of course I won't blast it to kill the amp.
A pair of dual 2 ohm subs can be wired to either 0.5 ohm or 2 ohm. Depending on your box and other factors the amp might only see 1 ohm when playing music.
So what if I added a 4ohm speaker to a pair of subs wired at 1 ohm? Would it be at .7 but rise to 1 or above and not damage my 1ohm stable amp? Hmm...I'm not gonna risk it but I'm curious
Yes, a 0.67 or so DC ohm load should definitely rise above 1 ohm on AC. Maybe 1.3 or 1.5 at least. Should be fine for the amp. It will just be working harder and drawing more current at high volume.
It wont necessarily be safe. You cant predict box rise so maybe at some frequencies it will only rise to .5 ohms and your amp will shut off. Also, before the woofers start playing, the amp will see that .25 ohm load and wont even start playing or be damaged.
Most of the time they are measuring their peak power on 1 frequency. It might be their highest power or just whatever power it is on the random frequency they chose. But as soon as they play music, that number will change. So it's more so used just as an example. Kind of like having a street legal drag race car and telling people you have 1000 hp. But you drive around at the speed limit of 25mp or less, and you never actually use that 1000 hp.
Wow....I have an Adire Brahma MKII back in 2004, but saw some RE XXX motors (also XBL^2) that where similar. The first thing I thought when I saw the sub to the right in this vid was Adire Tumult! It is sad that this ANIMAL of a driver never made it to market. :(
This woofer predates the RE. And the RE used design queues from this woofer. Basically it's the RE's daddy. These are extremely rare (only about 12 ever made) And I have 4 I am going to be selling.
Nope, Impedance is highest at resonance. Impedance is caused by the coil creating back voltage and it creates mot of it at tuning. It's because it's most efficient at that frequency and can make more power with less movement. For instance, a woofer can move more at 20hz than at higher frequencies but will make far less SPL than at higher frequencies. This also translates to the back voltage and not just SPL.
suggesting that an amplifier, and amp settings will effect the impedance rise?!? also, "you're gunna do tests at different frequencies, to find your peak impedance, and ah, usually that's gonna be your tuning frequency" impedance is lowest around tuning, unless you consider a dip to be a peak... :/
