Hey guys, what's up? I've been reading diyaudio for a while now - over a year, a lot actually, and have a question to ask. In fact, this is something that I have never seen discussed in my travels as far as I know.
I bought an Eclipse 12" DVC subwoofer from a reputable home/car audio store, which also suplied plans for a vented box for use in a home environment based on its T/S parameters. The thing is ridiculous in terms of output, but it has a problem: the bass lags. When I listen to dance music or rap, the bass out of the subwoofer actually hits a few fractions of a second after the mains. Well, to be honest the beat "ebbs" as much as "hits" out of the speaker, but it makes it impossible to enjoy these types of music! What's up with that? Has anyone heard of this? Although I have not calculated SQL or system Q (as if it was a sealed box), I didn't post the T/S parameters because I have a feeling this phenomenon is not related to box size or tuning frequency - the sub has been in three different boxes with different parameters and it exhibits the same phenomenon.
Can anyone help me solve this problem? Thanks for all your help,
Philip
I bought an Eclipse 12" DVC subwoofer from a reputable home/car audio store, which also suplied plans for a vented box for use in a home environment based on its T/S parameters. The thing is ridiculous in terms of output, but it has a problem: the bass lags. When I listen to dance music or rap, the bass out of the subwoofer actually hits a few fractions of a second after the mains. Well, to be honest the beat "ebbs" as much as "hits" out of the speaker, but it makes it impossible to enjoy these types of music! What's up with that? Has anyone heard of this? Although I have not calculated SQL or system Q (as if it was a sealed box), I didn't post the T/S parameters because I have a feeling this phenomenon is not related to box size or tuning frequency - the sub has been in three different boxes with different parameters and it exhibits the same phenomenon.
Can anyone help me solve this problem? Thanks for all your help,
Philip
In order for the sub to have an audible delay with respect to the mains the lag would have to be on the order of at least 25 millisconds, which is exceedingly unlikely. Something else is wrong. Lag is easily heard in the midrange, with delays as small as 5 milliseconds audible at 500Hz. Since your sub should not be reproducing midrange I'd suspect the crossover first.
Yep. Same problem here. I just repositioned everything in my room, and now the sub is about 3 feet behind me on the left side, firing from left to right. The bass sounds delayed too. When I move back 3 feet so I'm right in front of the sub, it sounds fine.Bill Fitzpatrick said:
Just turned the sub so that it's firing forward, and now it sounds good too.
When subs first showed up in the marketplace I used to chuckle at the advertising that claimed you could stick the sub anywhere convenient. Most people bought into it and have suffered compromised sound quality ever since.
Even today most don't realize how to handle the situation.
My approach has been to pretend the room doesn't exist and to get the crossover and woofer to mid spatial relationship technically correct. Then, and only then, do I introduce the room and begin to solve the newly created problems without degrading my previous efforts.
Even today most don't realize how to handle the situation.
My approach has been to pretend the room doesn't exist and to get the crossover and woofer to mid spatial relationship technically correct. Then, and only then, do I introduce the room and begin to solve the newly created problems without degrading my previous efforts.
subwoofer lag or delay
I have read the posts left and there is something to be said about subwoofer positioning and the corresponding response curve. Low frequency response will be reinforced through placement by a wall or corner but this has nothing to do with the phenomenon you described. The problem you are describing is called transient ringing.
Contrary to your feeling of box size or tuning frequency I think this is your problem. The "optimal" design in a vented box is one where the box and port are tuned near the resonant frequency (Fs) of the speaker. This is done for the simple reason that the air mass in the port will damp the speaker and the response will be as flat as possible untill the rolloff frequency. I have never seen speaker manufacturers provide plans that will do this. Most of the time they will make the box too small. The reason for this is a peak at the frequency the vent is tuned at and a decrease in damping the resonant frequency of the driver producing the "rediculous ... output" you talked about.
I have owned a Rockford Fosgate HX2 12 from 2000 model # RFD-1212 and they recommended a 2 cubic foot (56.63 liters) box. I had a "professional" design a vented box at about 3 cubic ft. (85 liters) and still had the same problem. I redesigned to a sealed box at 5 cubic ft. (142 liters) and it solved the problem and improved low end response from 34 Hz to 23 Hz.
This delay is a characteristic almost unavoidable in vented systems. The best way to overcome this if you want to stay with a vented system is to design an "optimal" box, which will most likely be quite large. If you are looking at a sealed box it will also be quite large and you have to make sure that the excursion of the driver is sufficient enough for your needs as it increases greatly as frequency decreases.
For information on simple equations and information on this "optimal" box see chapter 4 of the book Advanced Speaker Systems by Ray Alden. I bought it from Radio Shack but it may be out of print as I did a search for the part # (62-2317) on radioshack.com and there were no results. Try eBay or used books at amazon.com.
A more detailed explanation but a little harder to understand for beginners is The Loudspeaker Design Cookbook by Vance Dickason. As of this post it is in it's fifth edition and is one of the most comprehensive book I know of on the subject.
Hope this helps,
Aaron
I have read the posts left and there is something to be said about subwoofer positioning and the corresponding response curve. Low frequency response will be reinforced through placement by a wall or corner but this has nothing to do with the phenomenon you described. The problem you are describing is called transient ringing.
Contrary to your feeling of box size or tuning frequency I think this is your problem. The "optimal" design in a vented box is one where the box and port are tuned near the resonant frequency (Fs) of the speaker. This is done for the simple reason that the air mass in the port will damp the speaker and the response will be as flat as possible untill the rolloff frequency. I have never seen speaker manufacturers provide plans that will do this. Most of the time they will make the box too small. The reason for this is a peak at the frequency the vent is tuned at and a decrease in damping the resonant frequency of the driver producing the "rediculous ... output" you talked about.
I have owned a Rockford Fosgate HX2 12 from 2000 model # RFD-1212 and they recommended a 2 cubic foot (56.63 liters) box. I had a "professional" design a vented box at about 3 cubic ft. (85 liters) and still had the same problem. I redesigned to a sealed box at 5 cubic ft. (142 liters) and it solved the problem and improved low end response from 34 Hz to 23 Hz.
This delay is a characteristic almost unavoidable in vented systems. The best way to overcome this if you want to stay with a vented system is to design an "optimal" box, which will most likely be quite large. If you are looking at a sealed box it will also be quite large and you have to make sure that the excursion of the driver is sufficient enough for your needs as it increases greatly as frequency decreases.
For information on simple equations and information on this "optimal" box see chapter 4 of the book Advanced Speaker Systems by Ray Alden. I bought it from Radio Shack but it may be out of print as I did a search for the part # (62-2317) on radioshack.com and there were no results. Try eBay or used books at amazon.com.
A more detailed explanation but a little harder to understand for beginners is The Loudspeaker Design Cookbook by Vance Dickason. As of this post it is in it's fifth edition and is one of the most comprehensive book I know of on the subject.
Hope this helps,
Aaron
There is no doubt that a poorly designed vented system rings but I don't believe the problem would exhibit itself as delayed bass. Bass that hangs around too long, yes.
In any event, you couldn't pay me to have a vented system to begin with. The are two places where I draw the line; I won't let anyone kill me and I won't listen to a vented woofer.
Let's all hear it for sealed woofers. Rah, rah, rah!
In any event, you couldn't pay me to have a vented system to begin with. The are two places where I draw the line; I won't let anyone kill me and I won't listen to a vented woofer.
Let's all hear it for sealed woofers. Rah, rah, rah!
Hey guys, thanks for the help and advice.
One of the reasons I am so boggled at this problem is that it has been exhibited in different rooms, from small dorm rooms, to a car (although less evident there), to a 14'X14' living room, in different positions. For that reason, I would be hesitant to say room position could be at fault.
As for the crossover, I use an (inexpensive) Pyramid car crossover wired to work out of AC. There is a phase 0/180 switch, but clicking it back and forth seems to have no effect.
I was told the sub was meant to work in smaller boxes, and most of the boxes have been around 1.5 cubic feet, or 45 litres. I will post the T/S and box parameters, as well as calculated frequncy response tomorrow when I get my hands on the paperwork.
Thanks for everyone's help once again,
Philip
One of the reasons I am so boggled at this problem is that it has been exhibited in different rooms, from small dorm rooms, to a car (although less evident there), to a 14'X14' living room, in different positions. For that reason, I would be hesitant to say room position could be at fault.
As for the crossover, I use an (inexpensive) Pyramid car crossover wired to work out of AC. There is a phase 0/180 switch, but clicking it back and forth seems to have no effect.
I was told the sub was meant to work in smaller boxes, and most of the boxes have been around 1.5 cubic feet, or 45 litres. I will post the T/S and box parameters, as well as calculated frequncy response tomorrow when I get my hands on the paperwork.
Thanks for everyone's help once again,
Philip
Bill Fitzpatrick said:
This effect can also happen if you have a "hole" in your frequency response. eg: mains stop at 80hz and sub starts at 50hz. I ran into this exact same effect while testing some new cabinets I was working on.
I added my existing (Sealed!) sub in for some low end re-inforcement, and forgot that these new cabinets dropped off at 100hz and my sub was still set for 50ish.
Id also haul out the signal generator to see if any of these holes exist in your new system.
Ok guys, got the TS and box parameters, and some very interesting results indeed!
T/S:
Fs - 28Hz
Qts - .68
Vas - 3.45 cuft
Xmax - 1"
Magnet weight - 64 oz
Voice coil diameter - 1.5"
Box:
Vb - 1.6 cuft
Fb - 25 Hz
F3 - 40.81
Fill - normal (but I had it stuffed pretty good until recently)
Wow! So here's what I'm thinking - this subwoofer is seriously overdamped (in other words, it's in a box that's way to small). I didn't calculate it, but I would almost bet that the system Q if I was calculating it as a sealed system would be huge. In fact, in the manufacturers spec sheet, the speaker is only discussed in a sealed and infinite baffle environment, and to get a sealed Q of 1.0, they say you need 2.93 cubic foot box. What does everyone think?
As a side note, I was in this club once that used a prosound line array of sorts, with 4 or 5 6-8" drivers in a row in a box that looked very small. I don't know about the Qts or Vas of pro-sound woofers, but the box did look small for those woofers and the system did exhibit the same phenomenon as mine.
Philip
T/S:
Fs - 28Hz
Qts - .68
Vas - 3.45 cuft
Xmax - 1"
Magnet weight - 64 oz
Voice coil diameter - 1.5"
Box:
Vb - 1.6 cuft
Fb - 25 Hz
F3 - 40.81
Fill - normal (but I had it stuffed pretty good until recently)
Wow! So here's what I'm thinking - this subwoofer is seriously overdamped (in other words, it's in a box that's way to small). I didn't calculate it, but I would almost bet that the system Q if I was calculating it as a sealed system would be huge. In fact, in the manufacturers spec sheet, the speaker is only discussed in a sealed and infinite baffle environment, and to get a sealed Q of 1.0, they say you need 2.93 cubic foot box. What does everyone think?
As a side note, I was in this club once that used a prosound line array of sorts, with 4 or 5 6-8" drivers in a row in a box that looked very small. I don't know about the Qts or Vas of pro-sound woofers, but the box did look small for those woofers and the system did exhibit the same phenomenon as mine.
Philip
I went looking at the plans I got from the store, and they were designed on Bassbox6. It turns out that the program predicts group delay to reach a maximum of 16ms, well below the maximum of 20ms advised by adire audio in their technical papers.
There is no doubt the speaker is up to something strange, so therefore I am wondering as to a possible technical cause of this phenomenon. Also, as these are threads that people will read in the future, I wanted to get input on how it can be predicted in the future - what parameters we need to look at, is it on any graphs, what factors lead to it vs. just saying "don't use that driver in that box," even though that is probably good advice.
Thanks for everyone's input,
Philip
There is no doubt the speaker is up to something strange, so therefore I am wondering as to a possible technical cause of this phenomenon. Also, as these are threads that people will read in the future, I wanted to get input on how it can be predicted in the future - what parameters we need to look at, is it on any graphs, what factors lead to it vs. just saying "don't use that driver in that box," even though that is probably good advice.
Thanks for everyone's input,
Philip
Group delay is not a concern with a sub, but lack of extension certainly is. With your high f3 it's barely operating as a sub, and is probably exhibiting a very peaked response. Go back to WinISD and design a box of large enough size to drop the f3 to 25-30 Hz and your problems will likely disappear. With that high of a Qts it won't work in a small box.
Bill, Dont even tell me you wouldnt listen to a tumult in 6cubic feet tuned to 10hz with a full 1600watts. Of course the box must be well built, the port must be of adequate size to prevent chuffing, and the port must be bent to prevent pipe resonance.
But other than that, you know you'd love the destructive force of infrasound at high levels. And its not that bad on music. You might be suprised!
But other than that, you know you'd love the destructive force of infrasound at high levels. And its not that bad on music. You might be suprised!
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