Crossover help

[Lynx4 5]

Hello all.

  Need some help figuring out my crossover for a set of bookshelfs I'm doing. So I am using a dayton nd105-4ohm for the woofer and dayton nd25fa-4ohm per bookshelf. I have built my crossover and it sounds great but the issue arises when the woofer is under a decent amount of load and the resistor in its filter begins to heat up to the point of burning my finger. Just wondering if there is a solution or a reasoning why this would be happening, everything else on the crossover is cool to the touch. I have a photo of it built and will upload a photo of the design when i can. 

Thanks 

[mwhouston 4,449]

16 minutes ago, Lynx4 said:

Hello all.

  Need some help figuring out my crossover for a set of bookshelfs I'm doing. So I am using a dayton nd105-4ohm for the woofer and dayton nd25fa-4ohm per bookshelf. I have built my crossover and it sounds great but the issue arises when the woofer is under a decent amount of load and the resistor in its filter begins to heat up to the point of burning my finger. Just wondering if there is a solution or a reasoning why this would be happening, everything else on the crossover is cool to the touch. I have a photo of it built and will upload a photo of the design when i can. 

Thanks 

Post a schematic and highlight the hot to touch resistor. 10W resistors will burn your finger when only carrying 3W. It maybe OK. But does sound a little odd. 

[davewantsmoore 6,276]

You could replace that resistor with multiple resistors in parallel, and/or with resistance rated for a higher wattage.

[davewantsmoore 6,276]

1 minute ago, mwhouston said:

Post a schematic

He did?!   It's the woofer resistor.

[Lynx4 5]

1 hour ago, mwhouston said:

Post a schematic and highlight the hot to touch resistor. 10W resistors will burn your finger when only carrying 3W. It maybe OK. But does sound a little odd. 

Hey so its this resitor 3ohm 10watt. I was thinking about putting two 6ohms in parallel to spread the load. But I wasn't sure if it was my wiring or not. 

[Lynx4 5]

1 hour ago, davewantsmoore said:

You could replace that resistor with multiple resistors in parallel, and/or with resistance rated for a higher wattage.

Yes that was what I was thinking. Just didn't know if it was my wiring, if I did something wrong or not. 

[andyr 5,043]

14 minutes ago, Lynx4 said:

Yes that was what I was thinking. Just didn't know if it was my wiring, if I did something wrong or not. 

 

And have the multiple resistors:

1. lifted off your board, and
2. spaced apart

... so you get airflow round them.

 

Andy

 

[Wozza_Lee 85]

Not uncommon. Resistors turn current to heat..


Doing two in parallel will help with power handling

[Guest Muon N']

In the diagram there are 4x resistors total, 2 resistors used in the tweeter section and 2 used in the woofer section. 1 in series and 1 parallel in each section.

 

In the actual crossover you have built you have 2 resistors only total, one in on the tweeter side in series, and one on the woofer side parallel?

[Lynx4 5]

9 minutes ago, Muon N' said:

In the diagram there are 4x resistors total, 2 resistors used in the tweeter section and 2 used in the woofer section. 1 in series and 1 parallel in each section.

 

In the actual crossover you have built you have 2 resistors only total, one in on the tweeter side in series, and one on the woofer side parallel?

No the small resistors is the distance from the inductors. 

[Guest Muon N']

Deleted

 

Never mind, there is a reason I don't build speakers

Edited November 9, 2019 by Muon N'

[BioBrian 606]

Who designed this crossover?

 

3 Ohms parallel to the woofer is just wrong. It should not be there. Maybe it should be in series with the cap?

[Ittaku 3,906]

29 minutes ago, BioBrian said:

Who designed this crossover?

 

3 Ohms parallel to the woofer is just wrong. It should not be there. Maybe it should be in series with the cap?

Agreed, that's really odd as it will guarantee a resistance of less than 3 ohms, and even with the tiny 0.29 ohms in series, it still wouldn't be more than 3 ohms. That's a very low forced impedance for a woofer, the woofer itself will likely bring it down to 2 ohms in real world.

[BioBrian 606]

The series inductor for the woofer is of very low value, which would be pretty ineffective. . Who decided upon that?

 

In your built crossover, the smaller gauge inductor looks to be on the woofer side. Are you sure you got them the right way around?

[Lynx4 5]

1 hour ago, BioBrian said:

Who designed this crossover?

 

3 Ohms parallel to the woofer is just wrong. It should not be there. Maybe it should be in series with the cap?

Design was done through vituix. The 3ohm resistor in parallel eliminated a spike at the higher end of the woofer crossover point. I tried taking out the resistor completely but it resulted in this spike being way to harsh. I can try putting it in series with the capacitor and see what it sounds like. This is why I decided to ask on the forum as this is my first attempt. 

Thanks

[Lynx4 5]

8 minutes ago, BioBrian said:

The series inductor for the woofer is of very low value, which would be pretty ineffective. . Who decided upon that?

 

In your built crossover, the smaller gauge inductor looks to be on the woofer side. Are you sure you got them the right way around?

Fairly certain I can upload the spl graph to show yous. I could have just completely fudged it all up maybe I need to start from scratch. 😥

[Lynx4 5]

This is the graph with the crossover as is. 

Maybe I should revisit and try something else?

Edited November 9, 2019 by Lynx4

[afa 60]

Hi, Redesign the crossover so that you dont have to use a parallel resistor across the woofer, even though it might achieve a reasonable acoustic outcome, its not a good electrical one as it wastes amplifier power,  stresses the amplifier and can cause component/structure damage due to excessive heat dissipation.

 

 

 

[Lynx4 5]

9 minutes ago, afa said:

Hi, Redesign the crossover so that you dont have to use a parallel resistor across the woofer, even though it might achieve a reasonable acoustic outcome, its not a good electrical one as it wastes amplifier power,  stresses the amplifier and can cause component/structure damage due to excessive heat dissipation.

 

 

 

Ok can do. I'll have to order more parts lol 

Thanks a bunch to everyone who chipped in to help my newby ness.  

[andyr 5,043]

46 minutes ago, Lynx4 said:

Fairly certain I can upload the spl graph to show yous. I could have just completely fudged it all up maybe I need to start from scratch. 😥

 

The graph you posted IMO doesn't show much.

 

49 minutes ago, Lynx4 said:

Design was done through vituix. The 3ohm resistor in parallel eliminated a spike at the higher end of the woofer crossover point.

 

Sorry, don't know 'vituix'.  Please tell us the nominal impedance of the woofer.  If it is, say, 8 ohms ... then putting a 3 ohm resistor across it (ie. in parallel with it) reduces the resistance value which the bass LP XO components - ie. the series coil and the parallel cap - see, to 2.2 ohms.

 

If the XO values of 0.2mH in series and 30uF in parallel were calculated for an 8 ohm bass driver at roll-off frequency 'X', then the XO roll-off point will be driven much higher by the XO 'seeing' only a 2.2 ohm load (instead of an 8 ohm load).

 

Your XO schematic shows, for the bass driver:

• a series coil (0.2mH), and
• a parallel cap (30uF).

This delivers a 2nd order (nominally 12dB slope) bass LP filter.  IMO, the 0.29 ohm res which is shown in series, in your schematic, is neither here nor there:

• it will reduce the asymptote level at the low end of the bass output.
• but exactly the same effect could be had by using a series inductor made of much thinner wire.

Perhaps the value of 0.29 ohms is exactly that - the DC resistance of the 0.2mH inductor - so not an actual resistor?

 

For the tweeter, you have:

• a 12uF cap in series
• plus a 2.4 ohm res to attenuate the (asymptote level of the) tweeter ... as it must be more efficient than the woofer
• and a 0.05mH coil / 0.1 ohm res in parallel with the tweeter.

This delivers a 2nd order (nominally 12dB slope) tweeter HP filter.  But these values lead me to suggest that the "0.1 ohms" is in fact the DC resistance of the 0.05mH inductor - not, in fact, an actual resistor?

 

49 minutes ago, Lynx4 said:

I tried taking out the resistor completely but it resulted in this spike being way too harsh.

 

Which resistor?  And this is according to your measurements ... or what?

 

Andy

 

[afa 60]

6 hours ago, Lynx4 said:

dayton nd105-4ohm

4 ohm

[Ittaku 3,906]

5 minutes ago, afa said:

4 ohm

That means the DC resistance to the woofer is a tiny 1.7 ohms with the 3 ohm resistor in parallel. That's a serious load for a woofer. For the crossover to work properly with that parallel resistor it means the values for the cap/inductor are assuming a much lower impedance so they're probably the wrong values to work directly with the woofer's impedance.

Edited November 9, 2019 by Ittaku

[Lynx4 5]

3 minutes ago, Ittaku said:

That means the DC resistance to the woofer is a tiny 1.7 ohms with the 3 ohm resistor in parallel. That's a serious load for a woofer.

Yeah I think I was to focused on the spl and completely forgot about basic of electronics. I'm going back to the drawing board on this one. 

[afa 60]

Try using this sim

https://www.diyaudio.com/forums/software-tools/259865-xsim-free-crossover-designer.html

[VanArn 587]

I looked up the basic specifications for the speakers used in this project and it would seem that the crossover circuit  by Lynx4  is on the weird side. Perhaps starting with a conventional  Butterworth or Linkwitz/Riley  second order filter would be a better approach.  For a 3kHz crossover frequency with a four ohm impedance, the inductance value is 0.3mH for both coils and the capacitors are 9.4 mFd in the case of the Butterworth  filter. An impedance correction network is required for the  low frequency section and using the impedance and phase  derived from the D.A.T.s  graph from the  Parts Express site ( and trusting that these are accurate ) a series network consisting of a  resistor of 4.5 ohm  /10 watt and a 36 mFd  capacitor placed in parallel across the bass speaker', would suit.  A "L" pad  is required to be fitted to the tweeter to allow the sensitivity to match that of the bass speaker and I would suggest a series resistor of  1.3 ohm and a parallel resistor of 10 ohm would be suitable values to use. The inductors should be wound with a heavy gauge wire, say 1.4mm, to avoid a high d,c. resistance loss.

Edited November 9, 2019 by VanArn
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