How to create a crossover?

[darien87]

Hey dudes,

Now that I've got my beast 15" sub in my system, I'm thinking of changing my 12" sub to be more of a mid-bass. I'm thinking it might be better to have my 12" play 80 - 50hz and then have the 15" do from 50hz on down.

Is there a simple way to make a crossover that would do this? I just need something that I can hook up to my 12" sub that would cross it over. I guess I only need a something that will filter out the frequencies below 50hz since my processor already crosses the subs over at 80hz.

But dammit, now that I think about it, I would need something that would high pass the 15" at 50hz. Now I'm really confused on how to do this.

Anybody have any ideas?

 

[TLS Guy]

Hey dudes,

Now that I've got my beast 15" sub in my system, I'm thinking of changing my 12" sub to be more of a mid-bass. I'm thinking it might be better to have my 12" play 80 - 50hz and then have the 15" do from 50hz on down.

Is there a simple way to make a crossover that would do this? I just need something that I can hook up to my 12" sub that would cross it over. I guess I only need a something that will filter out the frequencies below 50hz since my processor already crosses the subs over at 80hz.

But dammit, now that I think about it, I would need something that would high pass it at 50hz. Now I'm really confused on how to do this.

Anybody have any ideas?

Not easily you would need a an active crossover. Passive crossovers below 350 Hz are bad news.

The next issue is I don't advise the plan. Close spaced crossovers are a bad idea. You get unpredictable band pass gain issues. Ideally crossovers should be spaced 3 octaves or more apart.

A scheme like yours will also introduce unnecessary phase and time issues, all adding up to a lumpy bumpy response.

I see no advantage in these types of schemes, only buying a boat load of problems.

Remember the best crossover is no crossover. I'm strongly in favor of getting the job done with the least number of crossovers and minimizing time and phase aberrations..

To that end in this system on the mains there is only one full electronic crossover. My high pass crossover at 60 Hz is entirely acoustic. There is a fourth order 60 Hz low pass that feeds in the LFE channel, and a first order diffraction compensating high pass crossover that starts first order and transitions to second order, active below 600 Hz. The composite electrical and acoustic slope of this crossover is first order.

The only complete crossover on the mains is at 28 kHz.

The result is a very smooth in room response with no bass dead or loud spots.

So, I would just use one sub, if you want two make them both the same.

 

[MidnightSensi]

TLS speaks the truth.

Also, I think your looking the wrong direction...

Punch comes from the lower midrange. If you want more punch, you need better dynamics at like 500Hz than 50Hz.

I'd go more along the route of larger mains with higher sensitivity and power handling.

*edit* Also you may try to play with the phase of the subwoofer, in case they are mis-aligned at the crossover frequency. Reverse the + and - to your main speakers, then play a sine wave right at your main to subwoofer crossover frequency (i.e. a 80Hz sine wave off any test disc). Adjust the phase on the subwoofer plate amp until you hear the LEAST amount of bass. Now turn off the source and put the + and - back on the mains the correct way. Your subwoofer is now in phase with your mains at the crossover frequency. This will not keep them time-aligned at other frequencies, but the crossover frequency is most important because if they aren't you can get cancellations and maybe that is your lack of midbass. The reason you swap the leads to the mains is it is easier to hear when there is the least amount of bass than it is to hear when there is the most.... not sure why.

 

[darien87]

Not easily you would need a an active crossover. Passive crossovers below 350 Hz are bad news.

The next issue is I don't advise the plan. Close spaced crossovers are a bad idea. You get unpredictable band pass gain issues. Ideally crossovers should be spaced 3 octaves or more apart.

A scheme like yours will also introduce unnecessary phase and time issues, all adding up to a lumpy bumpy response.

But what about the numerous papers that have been written about multiple subs helping to smooth bass response and lessen room modes? This is my main reason for doing this. That and to get a little more tactile feel from the bass in my system. I definitely can tell the difference when I'm running just the 15" sub as opposed to the 15" and the 12" together.

I already have the 12" and 15" subs, so making another one isn't really an option. So should I just get rid of the 12" and use the 15" exclusively?

 

[darien87]

TLS speaks the truth.

Also, I think your looking the wrong direction...

Punch comes from the lower midrange. If you want more punch, you need better dynamics at like 500Hz than 50Hz.

I'd go more along the route of larger mains with higher sensitivity and power handling.

Oh I'm not looking for more punch per se. I'm definitely not looking to change my front speakers. So if doing the mid-bass thing isn't advisable, I'll just leave my system as is. The reason I am asking is that the guy that I bought the 15" sub has 4 subs in his system, 2 playing 80hz to about 40hz and the other 2 playing 40hz on down. I just thought this might be cool to do, since the 15" can play lower than the 12". Kind of like setting your mains to "small".

 

[gmichael]

I would just stick one of these in-line.
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=266-270

 

[TLS Guy]

But what about the numerous papers that have been written about multiple subs helping to smooth bass response and lessen room modes? This is my main reason for doing this. That and to get a little more tactile feel from the bass in my system. I definitely can tell the difference when I'm running just the 15" sub as opposed to the 15" and the 12" together.

I already have the 12" and 15" subs, so making another one isn't really an option. So should I just get rid of the 12" and use the 15" exclusively?

I don't know which sub you should get rid of, but one is a sealed design and the other a resonant system using PRs in place of ports.

You can't make the decision based on driver size. Which sub has the greatest reach and above all sounds best to you, in your room?

I would not think those subs are a good combination at face value as they will have very different Qt. I think this latter issue is where people go wrong mixing subs rather than where F3 is.

 

[lsiberian]

I'd keep the SDX and try selling the rythmik. But sometimes people prefer sealed subs.

 

[darien87]

I'd keep the SDX and try selling the rythmik. But sometimes people prefer sealed subs.

If anything, I'd just move the Rythmik upstairs to the bedroom.

 

[gmichael]

If anything, I'd just move the Rythmik upstairs to the bedroom.

Great idea.
I'm still not sure what I'll do with my 15" once the 18" build is finished. My bedroom has a 12" that is plenty there already though. Maybe the basement?

 

[lsiberian]

Great idea.
I'm still not sure what I'll do with my 15" once the 18" build is finished. My bedroom has a 12" that is plenty there already though. Maybe the basement?

Upgrade the 12"

Then put it out in the workshop to play while your 21" is being built.
http://www.bcspeakers.com/PDF/PRD/21SW152.pdf

 

[darien87]

Great idea.
I'm still not sure what I'll do with my 15" once the 18" build is finished. My bedroom has a 12" that is plenty there already though. Maybe the basement?

Kids' room?

 

[highfigh]

Hey dudes,

Now that I've got my beast 15" sub in my system, I'm thinking of changing my 12" sub to be more of a mid-bass. I'm thinking it might be better to have my 12" play 80 - 50hz and then have the 15" do from 50hz on down.

Is there a simple way to make a crossover that would do this? I just need something that I can hook up to my 12" sub that would cross it over. I guess I only need a something that will filter out the frequencies below 50hz since my processor already crosses the subs over at 80hz.

But dammit, now that I think about it, I would need something that would high pass the 15" at 50hz. Now I'm really confused on how to do this.

Anybody have any ideas?

The rule of thumb I have heard is that a driver should see at least 2 octaves because a crossover will affect the response in some way, regardless of how well it's designed. It's less of a problem with active crossovers but the phase response will still be altered.

 

[darien87]

The rule of thumb I have heard is that a driver should see at least 2 octaves because a crossover will affect the response in some way, regardless of how well it's designed. It's less of a problem with active crossovers but the phase response will still be altered.

So if what you are saying is correct, then with the high pass of my processor set at 80hz, the 12" would need to play down to 20hz to not have any problems. Bummer. But I guess I could try it and see how it goes. The FMOD from Parts Express is only $25. Not a big deal if it ends up being a waste of money.

Eh, maybe I'll just forget the whole thing.

 

[gmichael]

Kids' room?

But she's not even 10 months yet. She already has my Infinity 360's.
Those should keep her happy for at least the first few years.
The sub in the bedroom is jammed behind the bed and wedged in by my stereo rack. It's not going anywhere anytime soon.

 

[gmichael]

So if what you are saying is correct, then with the high pass of my processor set at 80hz, the 12" would need to play down to 20hz to not have any problems. Bummer. But I guess I could try it and see how it goes. The FMOD from Parts Express is only $25. Not a big deal if it ends up being a waste of money.

Eh, maybe I'll just forget the whole thing.

They make other FMOD's as well. Several crossover points are available. Maybe a 30? That's the one I have in my basket now. I may put the 15" behind the couch. It bottoms out below 25 so the 30 might be what I need.

 

[darien87]

They make other FMOD'd as well. Several crossover points are available. Maybe a 30?

I might do it, just to give it a shot. Regardless if it works or not, I won't be out much money.

 

[gmichael]

I might do it, just to give it a shot. Regardless if it works or not, I won't be out much money.

Seems like it might be fun to try. It's not like they are both up front (IE: left & right). With one much closer to your sitting area, it won't need to output nearly as much.
Both of mine will be sealed though. Not sure how one sealed and one ported will work. Might still be worth a try though. If you like it, then who cares if it's supposed to work or not?

 

[TLS Guy]

So if what you are saying is correct, then with the high pass of my processor set at 80hz, the 12" would need to play down to 20hz to not have any problems. Bummer. But I guess I could try it and see how it goes. The FMOD from Parts Express is only $25. Not a big deal if it ends up being a waste of money.

Eh, maybe I'll just forget the whole thing.

Not quite right.

The octave rule comes when a driver is driven from a band pass filter. that is it is connected to a high and and a low pass filter. In a sub situation the woofers of the mains become the band pass drivers effectively.

On you situation the 12" sub would be driven from a band pass filter with very narrow bandwidth. Not a good situation.

I prefer that a band pass driver cover three octaves or more, other wise you have all sorts of problems of which band pass gain is only one.

That is why three way speakers are often so problematic as there is such a dearth of good drivers with wide band width.

 

[darien87]

Not quite right.

The octave rule comes when a driver is driven from a band pass filter. that is it is connected to a high and and a low pass filter. In a sub situation the woofers of the mains become the band pass drivers effectively.

On you situation the 12" sub would be driven from a band pass filter with very narrow bandwidth. Not a good situation.

I prefer that a band pass driver cover three octaves or more, other wise you have all sorts of problems of which band pass gain is only one.

That is why three way speakers are often so problematic as there is such a dearth of good drivers with wide band width.

Thanks again for the help. Like I said, I may just scrap the whole idea.