Couple box tips

[KU40 173]

This first part is how having the correct crossover makes a world of difference in how a subwoofer setup sounds. When I first set up my amp for my new sub I put the crossover on 80 hz because I had heard that was the general concensus for a decent starting position. I left it there for a few years and I figured everything was good. Then I think one day last year I got bored and just played around with my front stage, seeing if I would want a 3 way setup or something. Sometime during that I turned my crossover up to 100 hz on my sub and forgot about it. A year passed and I hadn't really noticed it until lately I played some Crystal Method and I was like man, my sub sure is boomy. I think just that week I had read on this forum some people talking about having subs crossed over at 60 hz or so, so I decided to go out and turn mine down to there to see how it sounded. That's when I found out the crossover had been turned so high before. Doh. So I turned it down to 60-65 (my crossover just goes from 50-250 with no markings between, so kinda hard to precisely do by sight). I turned on some rock and man it made a huge difference. Not only did it blend with my front stage better (I think their crossover is around 70-80), but the sub sounded tighter. In fact, it's very tight, even moreso that I would have thought it would get. and it's in a ported box! (another one of those myths that could be arguably debunked here)

The second tidbit is about how having too small of a ported box can rob SPL. Years ago I had 4 12" subs in a sealed box in my trunk and I would hit about 153 db on the Audiocontrol mic. The box was 4 cubic feet, i.e.- 1 cube per sub, per manufacturer recommendation. One day I decided to try porting it to see if I could gain SPL. I was burping 53 hz with the sealed setup so I figured 45 hz would be ok for my tune. I put in the port, and at the next comp I hit exactly the same SPL, 153. So there's my evidence that having a ported box (it was probably only 3.5 cubes after port displacement) that's too small will rob SPL. True there could have been other factors involved, like box impedence differences, etc., but I did found that the same 53 hz note was the loudest with the ported box as well. So at least that was constant.

[audio-neon 34]

This first part is how having the correct crossover makes a world of difference in how a subwoofer setup sounds. When I first set up my amp for my new sub I put the crossover on 80 hz because I had heard that was the general concensus for a decent starting position. I left it there for a few years and I figured everything was good. Then I think one day last year I got bored and just played around with my front stage, seeing if I would want a 3 way setup or something. Sometime during that I turned my crossover up to 100 hz on my sub and forgot about it. A year passed and I hadn't really noticed it until lately I played some Crystal Method and I was like man, my sub sure is boomy. I think just that week I had read on this forum some people talking about having subs crossed over at 60 hz or so, so I decided to go out and turn mine down to there to see how it sounded. That's when I found out the crossover had been turned so high before. Doh. So I turned it down to 60-65 (my crossover just goes from 50-250 with no markings between, so kinda hard to precisely do by sight). I turned on some rock and man it made a huge difference. Not only did it blend with my front stage better (I think their crossover is around 70-80), but the sub sounded tighter. In fact, it's very tight, even moreso that I would have thought it would get. and it's in a ported box! (another one of those myths that could be arguably debunked here)

The second tidbit is about how having too small of a ported box can rob SPL. Years ago I had 4 12" subs in a sealed box in my trunk and I would hit about 153 db on the Audiocontrol mic. The box was 4 cubic feet, i.e.- 1 cube per sub, per manufacturer recommendation. One day I decided to try porting it to see if I could gain SPL. I was burping 53 hz with the sealed setup so I figured 45 hz would be ok for my tune. I put in the port, and at the next comp I hit exactly the same SPL, 153. So there's my evidence that having a ported box (it was probably only 3.5 cubes after port displacement) that's too small will rob SPL. True there could have been other factors involved, like box impedence differences, etc., but I did found that the same 53 hz note was the loudest with the ported box as well. So at least that was constant.

I think your venture for ported vs. sealed had too low of a tuning for competition. 47hz would have probably been louder.

The idea is that you take a box, and make it smaller and smaller in spl. It will get louder and louder until you hit that magic box volume.

[mrray13 30]

small box and HUGE power make spl numbers go big. IIRC, it's called compression porting, or something silly like that.

but i'm dead tired, so i might not have a clue, lol.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[audio-neon 34]

small box and HUGE power make spl numbers go big. IIRC, it's called compression porting, or something silly like that.

but i'm dead tired, so i might not have a clue, lol.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

It's a balance. Adding power=smaller box. I could go into the details in finding the optimum enclosure size for spl but it is a huge explanation.

[KU40 173]

I think your venture for ported vs. sealed had too low of a tuning for competition. 47hz would have probably been louder.

The idea is that you take a box, and make it smaller and smaller in spl. It will get louder and louder until you hit that magic box volume.

Well I did make it 45 hz, so that's not far from 47. At any rate, it didn't work for me. Didn't make the box more efficient, I should say. Now could it have handled more power and thus get louder? Maybe/probably.

[95Honda 486]

There is no myth or mystery here. It's Hoffmans iron law of size, extension and efficiency. You change any one of the parameters and the others most change. The larger a box, the more efficient and the lower the extension. The smaller the box the lower the efficiency and the less low end extension. Any time you have to add more power because you have done something like make a box smaller, you have made the whole alignenment less efficient and due to thermal compression ( all else being equal) it cannot be as loud. There may be all kinds of examples people can give to say otherwise, but you can't cheat physics.. Many times if some goes with a smaller box and can get a higher SPL, it is do to another factor they aren't taking into consideration that they don't know about, and not becasue of the difference in box volume.

Eventually you will get to diminishing returns with box size and a response that has too much ripple to listen to music with (in the case of ported). And with sealed alignments you can get a Q that is too low that most of us will find sounds lifeless with most music, even though we have gained a ton of low end efficiency. Finding the optimum size is a balancing act between this, extension and efficiency goals. Many times we disregaurd the efficiency goal because we have #1 a ton of power on tap and #2 drivers that can handle a ton of power....

99.999999% of the time a (vented) subwoofer will gain peak output capability with an increase of enclosure size, all else being equal. Additionally a sealed subwoofer will gain low end efficiency and play as loud with less power with an increase in enlosure size as long as the Q isn't signifigantly lowered (like less than .5)

[mrray13 30]

There is no myth or mystery here. It's Hoffmans iron law of size, extension and efficiency. You change any one of the parameters and the others most change. The larger a box, the more efficient and the lower the extension. The smaller the box the lower the efficiency and the less low end extension. Any time you have to add more power because you have done something like make a box smaller, you have made the whole alignenment less efficient and due to thermal compression ( all else being equal) it cannot be as loud. There may be all kinds of examples people can give to say otherwise, but you can't cheat physics.. Many times if some goes with a smaller box and can get a higher SPL, it is do to another factor they aren't taking into consideration that they don't know about, and not becasue of the difference in box volume.

Eventually you will get to diminishing returns with box size and a response that has too much ripple to listen to music with (in the case of ported). And with sealed alignments you can get a Q that is too low that most of us will find sounds lifeless with most music, even though we have gained a ton of low end efficiency. Finding the optimum size is a balancing act between this, extension and efficiency goals. Many times we disregaurd the efficiency goal because we have #1 a ton of power on tap and #2 drivers that can handle a ton of power....

99.999999% of the time a (vented) subwoofer will gain peak output capability with an increase of enclosure size, all else being equal. Additionally a sealed subwoofer will gain low end efficiency and play as loud with less power with an increase in enlosure size as long as the Q isn't signifigantly lowered (like less than .5)

i can indeed relate details of nothing more then going smaller box and gaining spl. with nothing else changing, including voltage, power, box location, port area/tuning and subwoofers. i can't explain it, but i have indeed see it happen. maybe it has something to do with the longer ports, i dunno, but i do indeed know it has happened.

the rest i completely agree with.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[95Honda 486]

Sometimes you may not realize it, but by going smaller you may have moved the box resonance closer to the vehicle resonance... Were as if you would have done the same by higher tuning in an even bigger box you would have also gained (possibly more) SPL...

But honeslty, like I said earlier in this thread, there will be many examples people will have showing something different than what I stated... But as far as box alignments go, can't get around Hoffman....

Edited June 14, 2008 by 95Honda

[mrray13 30]

Sometimes you may not realize it, but by going smaller you may have moved the box resonance closer to the vehicle resonance... Were as if you would have done the same by higher tuning in an even bigger box you would have also gained (possibly more) SPL...

But honeslty, like I said earlier in this thread, there will be many examples people will have showing something different than what I stated... But as far as box alignments go, can't get around Hoffman....

could be. and i can't really argue with hoffman, but as i said, i've seen what would appear to be a direct contradiction. can't explain it, but the meter showed it.

if i had ///M5's equipment, we could definitely find out what caused it.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[95Honda 486]

Sometimes you may not realize it, but by going smaller you may have moved the box resonance closer to the vehicle resonance... Were as if you would have done the same by higher tuning in an even bigger box you would have also gained (possibly more) SPL...

But honeslty, like I said earlier in this thread, there will be many examples people will have showing something different than what I stated... But as far as box alignments go, can't get around Hoffman....

could be. and i can't really argue with hoffman, but as i said, i've seen what would appear to be a direct contradiction. can't explain it, but the meter showed it.

if i had ///M5's equipment, we could definitely find out what caused it.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

-Word

[mrray13 30]

i wonder if would get sean to test that theory. i'd be willing to be you are correct, the smaller box resonated at/near vehicle frequency. all boxes tested were single layer 3/4" mdf, various sizes, all tuned 45hz and only difference were size and port length.

this jsut hit me as well, smaller box= less impedence rise= more actual power. of course that means more heat, which could result in a wash..lol...

damnit man, you got me thinking too damn much.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[shizzzon 461]

i thought smaller boxes had higher impedance rise?

[audio-neon 34]

i wonder if would get sean to test that theory. i'd be willing to be you are correct, the smaller box resonated at/near vehicle frequency. all boxes tested were single layer 3/4" mdf, various sizes, all tuned 45hz and only difference were size and port length.

this jsut hit me as well, smaller box= less impedence rise= more actual power. of course that means more heat, which could result in a wash..lol...

damnit man, you got me thinking too damn much.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

But mrray, what's more heat in a 3 second burp. It's really a null factor.

[95Honda 486]

i thought smaller boxes had higher impedance rise?

I honestly think there are too many variables for a firm answer on this... There are so(!) many factors that can determain impedance (saying "rise" really isn't accurate, because it dips alot also) it would be tough to coorelate box size with impedance curves in some kind of repeatable manner. Impedance usually varies alot depending on how much an alignment can readily (or easily) achieve resonance, or how under-damped it is.... And this can be real serious with big boxes also....

Also, when we talk about impedance, DCR (what you read with a DMM) doesn't mean a whole lot... When a sub reads .7 on a DMM, there isn't an amplifier in the world that will ever, and I mean ever, see a .7 ohm load. This is impossible. As long as the coil has any sort of inductance at all (they all do, if they at least have over 1 turn of wire, so that's every single one) The impedance will ALWAYS be more than the DCR, I cannot stress this enough, and the higher the frequency, the higher the impedance will be (not factoring in system resonance wich makes it even higher) due to inductance. I think it is funny when I see people talkling about what a coil "really measures", because if you don't have an impedance bridge (or something similar), you are not really measuring anything that has to do with audio... I guess what I'm trying to say is don't get hung up with what your DMM says, it is good for checking shorts or consistency. But, for impedance, trust what the manufacturer specs out, they give you a much more accurate "average" of what the driver impedance will be.

Thermal compression a big deal with 3 second burps? Maybe, maybe not.... But when you get into 1/10th of a db FTW, it's the small things that can make a difference...

[audio-neon 34]

i thought smaller boxes had higher impedance rise?

I honestly think there are too many variables for a firm answer on this... There are so(!) many factors that can determain impedance (saying "rise" really isn't accurate, because it dips alot also) it would be tough to coorelate box size with impedance curves in some kind of repeatable manner. Impedance usually varies alot depending on how much an alignment can readily (or easily) achieve resonance, or how under-damped it is.... And this can be real serious with big boxes also....

Also, when we talk about impedance, DCR (what you read with a DMM) doesn't mean a whole lot... When a sub reads .7 on a DMM, there isn't an amplifier in the world that will ever, and I mean ever, see a .7 ohm load. This is impossible. As long as the coil has any sort of inductance at all (they all do, if they at least have over 1 turn of wire, so that's every single one) The impedance will ALWAYS be more than the DCR, I cannot stress this enough, and the higher the frequency, the higher the impedance will be (not factoring in system resonance wich makes it even higher) due to inductance. I think it is funny when I see people talkling about what a coil "really measures", because if you don't have an impedance bridge (or something similar), you are not really measuring anything that has to do with audio... I guess what I'm trying to say is don't get hung up with what your DMM says, it is good for checking shorts or consistency. But, for impedance, trust what the manufacturer specs out, they give you a much more accurate "average" of what the driver impedance will be.

Thermal compression a big deal with 3 second burps? Maybe, maybe not.... But when you get into 1/10th of a db FTW, it's the small things that can make a difference...

I guess where I'm going with this is: Smaller boxes are "peakier" and there is a volume that will in itself be optimal in the Hoffman law relationship. It may have something to do with box resonance, I have never measured box resonance. All I know is that when working with new sub woofers, I always start with a decent sized box and start removing box volume and keeping the tuning the same until the box stops producing louder #'s. It's that magical volume that I have recorded for woofers that I have used in competition. And when I try something new out, I have a chart of optimal box volume/tuning that makes my new designs that much easier. Of course there is more to it than just that. I'm not letting all of the secrets out of the bag.

[shizzzon 461]

yea, i try to tell people that but i dont know if they actually believe or understand what i'm saying.

People may know about impedance rise but they think just because they bought a dual 2 ohm sub that wiring it in parallel is exactly 1ohm and when hooked up to an amp that is stable to 1ohm that the amp at some point will output it's rated power at 1ohm realistically... wrong, hehe.

You're right about the dmm, besides making sure you get the right reading to ensure everything is wired right, that's all u need to know for now...

Now, once i get my other amp back, what i like to do is when i do an install, i like to keep records of as much info about that install as i can so i have something to compare if i ever changed installs.

So when i get my other amp back, i take impedance rise measurements at low volume and max unclipped volume throughout the entire playable frequency range and see what i am actually doing. I also do that for power draw as well so i can if it's pulling a ridiculous amount of current for a frequency that i can barely hear anyway.

[95Honda 486]

Yes, you can find a volume that resonates easily, and this is sometimes near driver Vas.

If you get a chance, do some reading on RF tuned cavities, helped me understand resonance very well...

It may happen that this resonance falls in line with all other factors increasing overall system efficiency, and sometimes it may not (like if it is at 20Hz, LOL!!)

Really, there are so many factors, what works for one may not work for others, I guess if it was textbook easy all the time, it wouldn't be much of a competition then, would it?

[95Honda 486]

yea, i try to tell people that but i dont know if they actually believe or understand what i'm saying.

People may know about impedance rise but they think just because they bought a dual 2 ohm sub that wiring it in parallel is exactly 1ohm and when hooked up to an amp that is stable to 1ohm that the amp at some point will output it's rated power at 1ohm realistically... wrong, hehe.

You're right about the dmm, besides making sure you get the right reading to ensure everything is wired right, that's all u need to know for now...

Now, once i get my other amp back, what i like to do is when i do an install, i like to keep records of as much info about that install as i can so i have something to compare if i ever changed installs.

So when i get my other amp back, i take impedance rise measurements at low volume and max unclipped volume throughout the entire playable frequency range and see what i am actually doing. I also do that for power draw as well so i can if it's pulling a ridiculous amount of current for a frequency that i can barely hear anyway.

Sounds like a solid plan.

[95Honda 486]

If you have a computer, I would really suggest buying something like the Parts Express Woofer Tester. This can give you a real impedance curve, an impdeance curve of the whole she'bang.....

The accuracy of a clamp meter can be sketchy with reactive load AC (back EMF pretty much f*cks the readings up on the cheap ones) and my not be the most accurate way, that and you have to make about 100 measurements, all the while double checking to make sure the drive voltage is EXACTLY the same EVERY time (when is the last time someone really did this right?)....

Edited June 14, 2008 by 95Honda

[audio-neon 34]

Here is the link for the woofer tester:

http://www.partsexpress.com/pe/pshowdetl.c...FTOKEN=58009509

[shizzzon 461]

have u actually used it before?

Several reviews are stating it's inaccuracy when doing measurements.

Yes, it does take a LONG time to do it with a dmm and ammeter, i have to dedicate an entire day to pen and paper, hehe.