Low pass x-over help

[gompka]

Hello everyone,

I am building a home subwoofer, which I will power off of a 200w @ 8 ohm amplifier. However I will need to make a crossover inside of the subwoofer enclosure as the amplifier I am using has no crossover. The speaker will be in a 3.7 cube enclosure (after accounting for speaker and port volume) and will be tuned to 19hz using a slot port. I am using this subwoofer to complement by tritrix speakers so crossing it over at 60hz sound about right?

Here are the thiele parameters:

Woofer Properties--
Driver Description--Name: 88120 DVC
Company: Eclipse (Fujitsu Ten)
Piston: Aluminum cone.
Suspension: Santoprene surround.
Dual mirror-image spider.
Dust Cap: none Frame:
Cast aluminum frame.
Voice Coil: Aluminum former.
Magnet: Double-stacked magnet.
Aero-vented pole piece.

--Driver Configuration--
No. of Drivers = 1
Dual voice coils = separate--

Driver Parameters--
Fs = 27 Hz
Qms = 5 Vas = 90.61 liters
Sd = 511 sq.cm

Running coils series:
Qes = 0.32
Re = 6 ohms
Z = 8 ohms

I would really appreciate the help here, I am good with a soldering iron, and making cabinets, but the actuall x-over design is like an alien language to me.

[Chris Roemer]

Hello everyone,

I am building a home subwoofer, which I will power off of a 200w @ 8 ohm amplifier. However I will need to make a crossover inside of the subwoofer enclosure as the amplifier I am using has no crossover. The speaker will be in a 3.7 cube enclosure (after accounting for speaker and port volume) and will be tuned to 19hz using a slot port. I am using this subwoofer to complement by tritrix speakers so crossing it over at 60hz sound about right?

Here are the thiele parameters:

Woofer Properties--
Driver Description--Name: 88120 DVC
Company: Eclipse (Fujitsu Ten)
Piston: Aluminum cone.
Suspension: Santoprene surround.
Dual mirror-image spider.
Dust Cap: none Frame:
Cast aluminum frame.
Voice Coil: Aluminum former.
Magnet: Double-stacked magnet.
Aero-vented pole piece.

--Driver Configuration--
No. of Drivers = 1
Dual voice coils = separate--

Driver Parameters--
Fs = 27 Hz
Qms = 5 Vas = 90.61 liters
Sd = 511 sq.cm

Running coils series:
Qes = 0.32
Re = 6 ohms
Z = 8 ohms

I would really appreciate the help here, I am good with a soldering iron, and making cabinets, but the actuall x-over design is like an alien language to me.

I'll make a few assumptions 1st, which may or may NOT be true:

You've got a sub with dual 4 ohm coils that you want to series for an 8 ohm load.

Your DVC driver, with the coils in series, has a Qts of 0.30.

It's possible to use TWO 20mH "Super-Q" inductors in series for a total inductance of 40mH with a total DCR of about 1.2 ohms (I've never done this).

If all that is true, then it looks like you could build a low pass filter that's -3dB at 60 Hz using TWO 20mH coils in series for a total of 40mH, wiht a shunt cap (to ground, making a 2nd order electrical filter) of 200uF.

By increasing the shunt cap to about 500uF, the filter should be about -6dB at 60 Hz.

I'm not liking the way your box model looks, given a Qts of 0.30. It's like an extended bass shelf, very low response (output) but at an extended (very low) frequency.

Given a Qts of 0.30, I'd have to prefer more like a 2.1 cf box tuned to 31 Hz, or (at most) possibly 3 cf, tuned to the 31 to maybe 26 Hz range, at the lowest.

Also, the variable impedance (especially in a tuned box) right around the range in which you're trying to passively filter may throw the crossover simulation completely off. I'm not sure.

At $55 for a pair of giant Super-Q coils (I haven't priced them lately, is that price of $27.15 still good? I know the Jantzen coil prices are higher now than they were when the 2010 cat came out.) for an unproven project, and the fact that you won't be able to easily dial in a new Fc if you don't like what you end up with, doesn't the SA240 (which I heard was going on sale for July-Aug) seem like a better idea?

Chris

[jbruner]

I'll make a few assumptions 1st, which may or may NOT be true:

You've got a sub with dual 4 ohm coils that you want to series for an 8 ohm load.

Your DVC driver, with the coils in series, has a Qts of 0.30.

It's possible to use TWO 20mH "Super-Q" inductors in series for a total inductance of 40mH with a total DCR of about 1.2 ohms (I've never done this).

If all that is true, then it looks like you could build a low pass filter that's -3dB at 60 Hz using TWO 20mH coils in series for a total of 40mH, wiht a shunt cap (to ground, making a 2nd order electrical filter) of 200uF.

Chris

Here's why that doesn't work too well.

Also, the variable impedance (especially in a tuned box) right around the range in which you're trying to passively filter may throw the crossover simulation completely off. I'm not sure.
Chris

And so it does...

If you use the other 20 mH coil in a LCR trap instead, you can eliminate the peaking.

I'm not liking the way your box model looks, given a Qts of 0.30. It's like an extended bass shelf, very low response (output) but at an extended (very low) frequency.

Given a Qts of 0.30, I'd have to prefer more like a 2.1 cf box tuned to 31 Hz, or (at most) possibly 3 cf, tuned to the 31 to maybe 26 Hz range, at the lowest.
Chris

I do like the way your box models, if you include the DCR that the passive crossover adds. Are those published parameters or measured? Can be quite a difference. I like to err on the side of a bigger box.

At $55 for a pair of giant Super-Q coils (I haven't priced them lately, is that price of $27.15 still good? I know the Jantzen coil prices are higher now than they were when the 2010 cat came out.) for an unproven project, and the fact that you won't be able to easily dial in a new Fc if you don't like what you end up with, doesn't the SA240 (which I heard was going on sale for July-Aug) seem like a better idea?

Chris

There's the rub. Totally agree.

[jbruner]

There's also the big zobel method-



But I only do this kind of thing because I already have the components lying around. Active is better. I've used an automotive active x-o powered by a wallwart.

[gompka]

The specs are straight from the eclipse manual,so not measured. Also the specs for the enclosure are straight from a Tc sounds engineer, (they made that series of eclipse woofers). The subwoofer is a dual 4 ohm coil model that i will run in series. This subwoofer will be mostly for music with some home theater duty, i was told that going with a tuning frequency at around 20hz will enable it to be good at music while still having enough low end for explosions and the like in movies.

I already have an amp, and I already have the subwoofer, so I was hoping I could save some money doing things this way. Ideally this sub loves power and would do great with a 500+ watt amp, but being stuck at 8 ohms, it would force me to buy a very expensive amp and only use half of the power.

I would consider running a car audio xo off of a wall wart, if prices for an xover are this high.

The enclosure size is being held constant at 3.5-3.7, but the tuning frequency is open to your opinions. This is a solid sub and I don't think it will have any problems down low.

PS. I have this same subwoofer in my car in a 3.2ft^3 enclosure tuned to 29hz running at 1000watts rms, and it sounds amazing.

[johnastockman]

The specs are straight from the eclipse manual,so not measured. Also the specs for the enclosure are straight from a Tc sounds engineer, (they made that series of eclipse woofers). The subwoofer is a dual 4 ohm coil model that i will run in series. This subwoofer will be mostly for music with some home theater duty, i was told that going with a tuning frequency at around 20hz will enable it to be good at music while still having enough low end for explosions and the like in movies.

I already have an amp, and I already have the subwoofer, so I was hoping I could save some money doing things this way. Ideally this sub loves power and would do great with a 500+ watt amp, but being stuck at 8 ohms, it would force me to buy a very expensive amp and only use half of the power.

I would consider running a car audio xo off of a wall wart, if prices for an xover are this high.

The enclosure size is being held constant at 3.5-3.7, but the tuning frequency is open to your opinions. This is a solid sub and I don't think it will have any problems down low.

PS. I have this same subwoofer in my car in a 3.2ft^3 enclosure tuned to 29hz running at 1000watts rms, and it sounds amazing.

Nice car sub. The auto environment relies on cabin-gain for the lows, so it would sound quite different in your house. With the right enclosure, some auto subs can perform well, but not usually. For what it would cost in coils and caps for a passive XO (large values), the plate amp solution would actually be a little less $$. Is your amp just a straight power amp, no pre-amp? If it's a 2-channel, it might not have the proper low-level outputs for the RCA plate amp inputs. Using the speaker-wire ins and outs isn't the best way, either. It does work, but not so good for HT...the built-in cross freq. for the satellites is usually too high, around 150 to 200Hz. You could raise your desired cross frequency to about 80Hz and the sub would still be non-localized. But best to follow the other guys suggestions, they can steer you in the right direction.

John A.

[jmc]

Nice car sub. The auto environment relies on cabin-gain for the lows, so it would sound quite different in your house. With the right enclosure, some auto subs can perform well, but not usually. For what it would cost in coils and caps for a passive XO (large values), the plate amp solution would actually be a little less $$. Is your amp just a straight power amp, no pre-amp? If it's a 2-channel, it might not have the proper low-level outputs for the RCA plate amp inputs. Using the speaker-wire ins and outs isn't the best way, either. It does work, but not so good for HT...the built-in cross freq. for the satellites is usually too high, around 150 to 200Hz. You could raise your desired cross frequency to about 80Hz and the sub would still be non-localized. But best to follow the other guys suggestions, they can steer you in the right direction.

John A.

+1 sorta. I like using the headphone outputs then converting them to rca.
If you have headphone outs that is.


Also, on another note: Jon A - why is it all of your signature quotes have to do with putting something down?

[johnnyrichards]

Crossover costs as much as a couple coils!

Power supply adds some cost but this nice little unit is not necessary. You can use probably any 12vdc PS that provides 200 mA.

[johnnyrichards]

With the above, a guy could highpass his mains and lowpass his sub just by putting this between the source and the amplifiers.

[gompka]

With the above, a guy could highpass his mains and lowpass his sub just by putting this between the source and the amplifiers.

The amplifier is being fed with a line in from a computer, amp is Adcom GFA-2535, i already have a nice little 4amp 12v laptop power supply I can use. Looks like the automotive crossover is the way to go, I see some refurbished ones on ebay for $30. Thanks for the help folks!

PS the sub is basically a tc sounds epic 12" 293-650 so it is in fact well suited for home applications as well as automotive ones.

[davebullet]

Is the PC line level output purely feeding the sub? I presume not. Can you split it and account for the change in impedance?

Maybe this post might have a more cost effective line (low) level solution with much much smaller capacitor values, rather than high level crossover parts:
http://techtalk.parts-express.com/sh...d.php?t=218276

[johnastockman]

+1 sorta. I like using the headphone outputs then converting them to rca.
If you have headphone outs that is.


Also, on another note: Jon A - why is it all of your signature quotes have to do with putting something down?

Well, I'm just a negative, intolerant, crippled fool who goes around putting stuff down that I don't understand because I'm mad at the world...

Seriously, the first one is mine, after a lifetime (and about 300,000 miles on motorcycles) of seeing and riding with poseurs who care more about how they look and how a motorcycle somehow props up their sagging ego or low self-image. A motorcycle "doth not suffer" fools and poseurs...bad combo. They will be maimed or killed. But hey, people can do what they want; doesn't mean I have to accept it or like it. If but*-jewelry is more important to some than skills and riding gear, I can't change that; just offering some friendly suggestions. I've been a champion for getting training and wearing the right gear, but many act like you've just insulted their mom if you suggest rider training or a decent helmet, jacket, boots and gloves. I've ridden with these folks and their skills are severly lacking. They can ride naked if they want, but it reflects on other riders that do care about their skills and their "kit", ie riding apparel. Just my own cause, nothing more.

The other one is not even mine, but from a highly respected individual who knows about these things. It also reflects how I feel about how ball players are revered and other, more athletic disciplines (both mental and physical) are over-looked and marginalized. But, it will most likely always be that way, so don't take too much negativity in how I feel about this subject. Not really a put down, as there is positive in there. But if you've been a stick and ball fan all your life, then that's what you like. Enjoy it, party about it, know all the players names and stats. My opinion is only my own and really doesn't make any difference as to what is good or not-worth-paying-attention-to. I guess having these below my posts is pretentious and aloof, but in no way meant to offend or show that I am superior because I see a bit of injustice. I'll try to find more positive quotes and get back to ya...

John A.

[jmc]

Yes, I'm aware of who John Surtees is. I'm into auto racing of all types basically. That said, baseball is my passion. The game is incredibly fair,
with the rules unchanged for the most part year after year. Even NASCAR,
my favorite 'tv sport', twiddles with its rules so much that right now it's pretty much reached the point of mocking stock car racing's beginnings.

Yeah. I was just wondering at the reasonings for your sig. Don't change it on my account, I was just wondering.

[davebullet]

Well, I'm just a negative, intolerant, crippled fool who goes around putting stuff down that I don't understand because I'm mad at the world...

Seriously, the first one is mine, after a lifetime (and about 300,000 miles on motorcycles) of seeing and riding with poseurs who care more about how they look and how a motorcycle somehow props up their sagging ego or low self-image. A motorcycle "doth not suffer" fools and poseurs...bad combo. They will be maimed or killed. But hey, people can do what they want; doesn't mean I have to accept it or like it. If but*-jewelry is more important to some than skills and riding gear, I can't change that; just offering some friendly suggestions. I've been a champion for getting training and wearing the right gear, but many act like you've just insulted their mom if you suggest rider training or a decent helmet, jacket, boots and gloves. I've ridden with these folks and their skills are severly lacking. They can ride naked if they want, but it reflects on other riders that do care about their skills and their "kit", ie riding apparel. Just my own cause, nothing more.

The other one is not even mine, but from a highly respected individual who knows about these things. It also reflects how I feel about how ball players are revered and other, more athletic disciplines (both mental and physical) are over-looked and marginalized. But, it will most likely always be that way, so don't take too much negativity in how I feel about this subject. Not really a put down, as there is positive in there. But if you've been a stick and ball fan all your life, then that's what you like. Enjoy it, party about it, know all the players names and stats. My opinion is only my own and really doesn't make any difference as to what is good or not-worth-paying-attention-to. I guess having these below my posts is pretentious and aloof, but in no way meant to offend or show that I am superior because I see a bit of injustice. I'll try to find more positive quotes and get back to ya...

John A.

Don't change your quotes. As a keen motorcyclist, I read them and thought they were right on the money. I totally agree with everything above. It sometimes takes a motorcyclist to understand!

PS: Apologies to OP. Back to your regular programming....

[johnastockman]

Don't change your quotes. As a keen motorcyclist, I read them and thought they were right on the money. I totally agree with everything above. It sometimes takes a motorcyclist to understand!

PS: Apologies to OP. Back to your regular programming....

I thought about finding a more appropriate audio-type of quote, but then changed my mind. I appreciate the sentiments from another aware & accomplished motorcyclist. Notice I always say "motorcyclist" instead of "biker". If you want to know the real difference, read a recent column by Fred Rau in Motorcycle Consumer News. It does take another rider to understand. There's much more to it than the nonsense of childish ball-sports players who get most of the attention. If you follow the AMA and the world championships of motorcycle road-racing, you never see riders/support crew shooting each other, beating their wives, abusing alcohol & drugs, going to jail/prison, taking steroids and all the whining, 5th-grade playground behaviour. I guess I didn't need to explain myself, but jmc was the first to ask about it nicely, so I figured he and others might like to know the reasons. I feel a certain connection to you guys here, so knowing a bit more about me is a good thing...even if we don't all agree about ball sports, nascar drivel, and who's on first. Hey dave, send me a PM and a pic of your bike, previous and/or current ones. I'll send a couple of mine back. Thanks again.

John A. (motorcyclist, not biker)

PS: jmc, I do agree with you about nice-car. With all the publicity they've been getting (and the comensurate large salaries), it has devolved into a bunch of kids on the playground at recess fighting and talking bad about each other. Bring back Petty and Pearson, big blocks, and cars that weren't clones of each other. Man, I sound like an old guy!