I'm thinking of building a Aperiodic sub box. other posts have suggested a hatch isn't ideal for this setup but from what I've read this sounds incorrect, unless you are trying for a infinite baffle across the back seats.
anyway my question is how to tune a Aperiodic box? I have read about using a RTA setup and tuning for a flat response. I have also read that you can tune for a flat impedance curve.
I don't have access to an RTA so this leaves tuning for a flat impedance curve. How do I go about this?
thanks
JD
Full Version: Aperiodic tuning?
the reason why you'd want to use a sedan, is so there is no chance of cancellation between the back wave and the front wave
the main aim of a aperiodic enclosure is to minimize subwoofer resonance resulting in a relatively flat impedance curve and relatively flat group delay curve
it is generally best to measure the impedance curve AND then measure the frequency response, so you can smoothen out the frequency response with an EQ - this can be done with a simple radio shack analogue SPL meter (either modded, or with the slight low bass rolloff taken into account) and test tones
(and of course placing the meter in several different locations)
as far as measuring the impedance goes, you can either measure the voltage and current and then calculate the impedance at the frequency you are playing, OR (the better way) you can wire a 1000 ohm resistor in series and then measure the voltage across the speaker (the voltage at various frequencys will mimic the impedance curve)
and check the other aperiodic membrane thread posted in this forum for some good links
------------------
- A proud member of Team Gates - A proud supporter of the CAA SPL project
[Edited 1 time by Bassaholic on 12 October 2002 at 19:41]
the main aim of a aperiodic enclosure is to minimize subwoofer resonance resulting in a relatively flat impedance curve and relatively flat group delay curve
it is generally best to measure the impedance curve AND then measure the frequency response, so you can smoothen out the frequency response with an EQ - this can be done with a simple radio shack analogue SPL meter (either modded, or with the slight low bass rolloff taken into account) and test tones
(and of course placing the meter in several different locations)
as far as measuring the impedance goes, you can either measure the voltage and current and then calculate the impedance at the frequency you are playing, OR (the better way) you can wire a 1000 ohm resistor in series and then measure the voltage across the speaker (the voltage at various frequencys will mimic the impedance curve)
and check the other aperiodic membrane thread posted in this forum for some good links
------------------
- A proud member of Team Gates - A proud supporter of the CAA SPL project
[Edited 1 time by Bassaholic on 12 October 2002 at 19:41]
so if you vent the enclosure outside the car it would be better than trying to seal off the boot from the cabin?
thanks
JD
thanks
JD
possibly, although cutting holes in your car isn't a good idea, so thats why sealing off the boot in a sedan is a better idea
------------------
- A proud member of Team Gates - A proud supporter of the CAA SPL project
------------------
- A proud member of Team Gates - A proud supporter of the CAA SPL project
Also be aware that not all subwoofers are suitable for aperiodic loading. You will ideally be looking for a woofer with a Qts below .45 and a relatively large Vas. Woofers with heavy cones designed to go into small sealed boxes rarely work well in aperiodic enclosures.
Steve Hutchison
------------------
Hutch
Steve Hutchison
------------------
Hutch
the Qts might be a problem it's a type R 15" duel 4ohm Qts 0.48. I might try and swap it for the duel 2ohm version as it has a Qts of 0.38. the Vas is 98L I don't really know if this is large or small for a 15"?
I'm going to try a 2cu.ft sealed box and a 2.2 ported to see what sounds best, on paper the ported designs don't offer any benefits until you get to 6cu.ft.
aperiodic enclosures sound so tempting That I'm going to give it a try since I don't have to do any cutting to vent it outside the car.
where do you get test disks for tunning?
I'm going to try a 2cu.ft sealed box and a 2.2 ported to see what sounds best, on paper the ported designs don't offer any benefits until you get to 6cu.ft.
aperiodic enclosures sound so tempting That I'm going to give it a try since I don't have to do any cutting to vent it outside the car.
where do you get test disks for tunning?
quote:
Originally posted by JD:
I'm going to try a 2cu.ft sealed box and a 2.2 ported to see what sounds best, on paper the ported designs don't offer any benefits until you get to 6cu.ft.
aperiodic enclosures sound so tempting That I'm going to give it a try since I don't have to do any cutting to vent it outside the car.
where do you get test disks for tunning?
generally, you will find woofers that are suited to ported enclosures are well suited to aperiodic membrane enclosures
your subs aren't that well suited to ported boxes and may not sound that great in an AM setup
btw, I'm not sure how you got the idea that ported won't gain anything until 6 cu/ft ported.. on paper the 6 cu/ft graphs look very unsuitable to me
------------------
- A proud member of Team Gates - A proud supporter of the CAA SPL project
I have experimented with aperiodic loading with an Alpine Type R 12" and received less than perfect results. Typically, the best woofers for aperiodic loading are low Qts, high Vas, low Mms, stiff paper cone woofers that when fed into into a box building program give a result for a ported box that would be impossible to fit into a normal car. Having said that, many more 'normal' woofers can work very well, it's a matter of experimentation.
Steve Hutchison
------------------
Hutch
Steve Hutchison
------------------
Hutch
Ok I know these box programs are only as good as the idiot driving them and when it comes to the graphs I qualify for the title.
maybe someone could fill me in on my mistakes.
after punching in the Type R 15" DVC 4ohm Spec's into winisd the magic box it produces is ~6cu.ft and tuned to 20Hz.
the way I read the graph is the speaker has a flat response down to about 24Hz then starts to roll off. I've taken this to mean all frequencies above 24Hz will sound at the same volume (in an ideal situation, neglecting the cars influences).
The phase plot rises steeply which I take to mean the lower frequencies are out of phase with the higher ones. I think it makes sense since the port is acting like a crossover and attenuating the signal below the tuning frequency, which also puts the signal out of phase?
so I read this as reduced output at low frequencies, big deal it's going dam low anyway.
spl is the same as gain only actual theoretical outputs?
group delay rises sharply after 50Hz. so there is a delay in reproducing sounds after 50Hz. it's line ball with a sealed box to around 40Hz. I've forgotten at which point you start to hear a delay 4-6ms? so sound under 40Hz will sound slightly muddy?
To me it seems like the 6cu.ft box should sound quite nice in a ideal room. it goes quite low. it only has trouble with group delay below 40Hz (which I thought there wasn't much down there but low rumbles anyway?). the only draw back seems the ridiculously large box size. dropping the volume and playing with the tuning moves the group delay higher in the frequency range (worse transient response?) and moving the phase out of sync higher in the frequency range (reduced output?). a small sealed box dose the job almost as well as a the large ported box only it roles off sooner, so in an ideal room it doesn't go as low, has better transient response, and while low frequency's are out of phase they never over 160 deg out of phase. I have assumed under these circumstances the sub is suited to sealed boxes.
Hutch if your reasoning is right (& every body else reckons the same as you) the type R should be perfect? it hasn't got the right Spec's but the ported box is the same size as a car.
fill me in on where I'm going wrong?
maybe someone could fill me in on my mistakes.
after punching in the Type R 15" DVC 4ohm Spec's into winisd the magic box it produces is ~6cu.ft and tuned to 20Hz.
the way I read the graph is the speaker has a flat response down to about 24Hz then starts to roll off. I've taken this to mean all frequencies above 24Hz will sound at the same volume (in an ideal situation, neglecting the cars influences).
The phase plot rises steeply which I take to mean the lower frequencies are out of phase with the higher ones. I think it makes sense since the port is acting like a crossover and attenuating the signal below the tuning frequency, which also puts the signal out of phase?
so I read this as reduced output at low frequencies, big deal it's going dam low anyway.
spl is the same as gain only actual theoretical outputs?
group delay rises sharply after 50Hz. so there is a delay in reproducing sounds after 50Hz. it's line ball with a sealed box to around 40Hz. I've forgotten at which point you start to hear a delay 4-6ms? so sound under 40Hz will sound slightly muddy?
To me it seems like the 6cu.ft box should sound quite nice in a ideal room. it goes quite low. it only has trouble with group delay below 40Hz (which I thought there wasn't much down there but low rumbles anyway?). the only draw back seems the ridiculously large box size. dropping the volume and playing with the tuning moves the group delay higher in the frequency range (worse transient response?) and moving the phase out of sync higher in the frequency range (reduced output?). a small sealed box dose the job almost as well as a the large ported box only it roles off sooner, so in an ideal room it doesn't go as low, has better transient response, and while low frequency's are out of phase they never over 160 deg out of phase. I have assumed under these circumstances the sub is suited to sealed boxes.
Hutch if your reasoning is right (& every body else reckons the same as you) the type R should be perfect? it hasn't got the right Spec's but the ported box is the same size as a car.
fill me in on where I'm going wrong?
JD if you have a hatch then just go sealed unless venting AP to outside of vehicle is possible, and remember that unlike the US where this happens a lot, this type of mod to a car would be illeagl unless an engineer is involved. In the US things are not as well regulated.
If you went and cut holes and didnt get it engineered and then had a stack (not your fault) the isnsurance would be voided if insurance co found holes, and you may have to pay for entire accident, even though it wasnt your fault.
Anyway dont bother with AP unless you have a sedan. As for CAD programs, I dont use them anymore as they dont take into account transfer function of the specific vehicle involved and so are no match for an experienced installer.
Forget trying to learn to drive them(CAD programs) as your wasting your time IMO. Try building a few diff sized sealed boxes and playing around and see what your ears tell you, as that will be far more valuable than sticking your head into a CAD program and living in a virtual world that has little relevance to the inside of a car.
just my $0.02 worth
peace
Cyberpunky
------------------
"Electricity is for more than powering windmills" Ali G
"Out beyond ideas of wrong doing and right doing there lies a field. I'll meet you there." Rumi
"forget the specs, and just listen to what is watt" Cyberpunky
"These answers you get, couldnt they be your own signal, bouncing off some object in outer space, some other planet, boomin back atcha???" Freq Nasty
All your base are belong to us! ;)
Like to know more? click here
TEAM Digital-Is-A-Marketing-Gimic Member
TO VISIT MY SITE CLICK HERE
If you went and cut holes and didnt get it engineered and then had a stack (not your fault) the isnsurance would be voided if insurance co found holes, and you may have to pay for entire accident, even though it wasnt your fault.
Anyway dont bother with AP unless you have a sedan. As for CAD programs, I dont use them anymore as they dont take into account transfer function of the specific vehicle involved and so are no match for an experienced installer.
Forget trying to learn to drive them(CAD programs) as your wasting your time IMO. Try building a few diff sized sealed boxes and playing around and see what your ears tell you, as that will be far more valuable than sticking your head into a CAD program and living in a virtual world that has little relevance to the inside of a car.
just my $0.02 worth
peace
Cyberpunky
------------------
Like to know more? click here
quote:
Originally posted by JD:
To me it seems like the 6cu.ft box should sound quite nice in a ideal room.
indeed.
what you haven't realised is that the interior of a car provides natural 'cabin gain'. that is, the accoustics of the small volume of a car cabin provides natural 'boosting' of the subbass.
so in fact, the WinISD curve can afford to roll off much higher than your own choice (which would in fact start to peak down low).
for sealed boxes, where the roll off tends to be more shallow, the F3 can afford to be 35~45Hz. ported boxes will have a much steeper roll off, and prefer a lower F3.
the 'F3' is the frequency on the curve at the -3dB point. you can click/drag the pointer on the graph to estimate the F3.
and i think you'll find that a much smaller box will model well.
hope this helps.
------------------
although I do find CAD programs quite useful at designing boxes, you do have to take a few extra things into account..
as Cyber said, they don't take into account the transfer function (actually, some do but you have to measure it..)
sometimes (read - quite often) the box that winisd comes up with will sound horrid in your car (I do agree, that it may sound good outside)
2 cu/ft sealed should sound decent, 2.2 cu/ft will be louder at certain frequencys, but obviously at the expense of SQ, especially since it is not that well suited to porting (as far as SQ goes)
------------------
- A proud member of Team Gates - A proud supporter of the CAA SPL project
[Edited 1 time by Bassaholic on 15 October 2002 at 23:21]
as Cyber said, they don't take into account the transfer function (actually, some do but you have to measure it..)
sometimes (read - quite often) the box that winisd comes up with will sound horrid in your car (I do agree, that it may sound good outside)
2 cu/ft sealed should sound decent, 2.2 cu/ft will be louder at certain frequencys, but obviously at the expense of SQ, especially since it is not that well suited to porting (as far as SQ goes)
------------------
- A proud member of Team Gates - A proud supporter of the CAA SPL project
[Edited 1 time by Bassaholic on 15 October 2002 at 23:21]
Regarding why Type R does not make a very good candidate for AP loading, I beleive they have a quite high Mms, (Moving mass) and this is typically undesirable for AP applications but very desirable for small sealed box applications.
------------------
Hutch
------------------
Hutch
quote:
Originally posted by Hutch:
Regarding why Type R does not make a very good candidate for AP loading, I beleive they have a quite high Mms, (Moving mass) and this is typically undesirable for AP applications but very desirable for small sealed box applications.
actually the motor strength and suspension stiffness are just as important as the mms
------------------
- A proud member of Team Gates - A proud supporter of the CAA SPL project
This is a "lo-fi" version of our main content. To view the full version with more information, formatting and images, please click here.