Need help with 2-way passive crossover

[Rob41]

I've got a pair of Sansui SF2 omni-directional speakers and I'm replacing the drivers with new. I'm not looking for perfection by any means as they are just a secondary thing for the wife to use while she works out. I'd just like to build an adequate crossover for them.

The SF2 uses two 8" woofers with one up firing and the other down firing, sharing the same ported enclosure. They will be in parallel.

Here are the 8" drivers I'm using:
Goldwood GW-8028 8" Butyl Surround Woofer 8 Ohm

• Nominal Diameter8"
• Power Handling (RMS)100 Watts
• Power Handling (max)190 Watts
• Impedance8 ohms
• Frequency Response25 to 6,000 Hz
• Sensitivity84 dB 2.83V/1m
• Voice Coil Diameter1.5"
• Magnet Weight20 oz.

Thiele-Small Parameters

• Resonant Frequency (Fs)36 Hz
• DC Resistance (Re)7.2 ohms
• Voice Coil Inductance (Le)0.5 mH
• Mechanical Q (Qms)3.9
• Electromagnetic Q (Qes)1.21
• Total Q (Qts)0.92
• Compliance Equivalent Volume (Vas)1.54 ft.³

The original tweeter was a small paper cone but I found a dome tweeter that will all but drop right in:

Peerless by Tymphany BC25SC06-04 1" Textile Dome Tweeter

• Tweeter TypeSoft Dome
• Cone / Dome Diameter1"
• Impedance4 ohms
• Power Handling (RMS)50 Watts
• Frequency Response1,350 to 30,000 Hz
• Sensitivity92.4 dB 1W/1m

Thiele-Small Parameters

• Resonant Frequency (Fs)1,350 Hz
• DC Resistance (Re)2.9 ohms
• Mechanical Q (Qms)2.80
• Electromagnetic Q (Qes)2.30
• Total Q (Qts)1.26

Mounting Information

• Overall Outside Diameter2.75"
• Cutout Diameter1.70"
• Depth1.25"

Once the 8" drivers are in parallel I think the drivers will work together crossed between 2.5k and 3k.

I have two questions regarding the crossover.

1. What order would you recommend?
2. What type of slope would be best?
3. When designing a crossover, do I use the posted impedance rating or the DC Resistance (Re)? (google told me it's the actual resistance...Re).

I will be using an L-pad on the tweeter.



Thanks in advance for your help.

 

[AllenB]

1. What order would you recommend?
2. What type of slope would be best?

The needs of the drivers generally dictate the minimum. Their blending can increase those needs. Maybe you could begin with the existing crossover and work from there?

3. When designing a crossover, do I use the posted impedance rating or the DC Resistance (Re)? (google told me it's the actual resistance...Re).

Not helpful. The actual impedance at the crossover frequency will be closer to what you want, but still only a starting point.

 

[Rob41]

Thanks for the reply Allen.

I was thinking a starting point might be about 2.5k and a LR 2nd order but I may be way off based on the actual drivers I'll be using etc.

Anyway, the original 8" drivers are 12 Ohm wired in parallel so end up being 6 ohm.

The tweeter I haven't removed yet so 6 ohms is only speculation till tomorrow.

Here is a picture of the very simple (1st order?) crossover with l-pad.





I didn't think there would be much in common with the original crossover since the new drivers have little in common with the originals, other than fitting in the old locations of course.

 

[Rob41]

Well, it looks like I made a major blunder in my woofer choice. The ported enclosure volume is about 0.88 cu ft. Way to small to accommodate even one of these drivers. I'll have to change my order or send the woofers back and get a more suitable driver. I can't change the volume of the enclosure and I can't think of any way they will work in such a small enclosure.

I think to even have a chance of getting this to work will be to seal the bottom and use a single (different) 8" driver at the top where the bass and mid frequencies can blend omni-directionally with the tweeter.

Goldwood has another 8" driver that looks like it will fit the bill if I single up and mount it at the top with the tweeter. Once the bottom is sealed up, the ported volume will be within .03 cu ft of the recommended volume.

Goldwood GW-8PC-4 8" Heavy Duty Woofer 4 Ohm

• Nominal Diameter8"
• Power Handling (RMS)160 Watts
• Power Handling (max)330 Watts
• Impedance4 ohms
• Frequency Response45 to 7,000 Hz
• Sensitivity90.9 dB 2.83V/1m
• Voice Coil Diameter1.5"
• Magnet Weight30 oz.

Thiele-Small Parameters

• Resonant Frequency (Fs)44.2 Hz
• DC Resistance (Re)3.7 ohms
• Voice Coil Inductance (Le)1.2 mH
• Mechanical Q (Qms)5.98
• Electromagnetic Q (Qes)0.49
• Total Q (Qts)0.45
• Compliance Equivalent Volume (Vas)0.75 ft.³

Mechanical Compliance of Suspension (Cms)0.36 mm/N

• BL Product (BL)8.73 Tm
• Diaphragm Mass Inc. Airload (Mms)36.3g
• Maximum Linear Excursion (Xmax)3.5 mm
• Surface Area of Cone (Sd)205.9 cm²

Any thoughts on my very amateurish quandary are welcomed.

 

[AllenB]

I was thinking a starting point might be about 2.5k and a LR 2nd order but I may be way off based on the actual drivers I'll be using etc.

If a random choice needs to be made, second order LR is one of the better choices to make. The second order filters are somewhat less influenced by the driver impedance and more likely to follow their expected rolloff.. at least compared to first order.

Here is a picture of the very simple (1st order?) crossover with l-pad.

L-pads have an ability to make the driver impedance look more like a resistor. The more tweeter level you need to lose, the more this happens. It would reduce the impedance peak at the tweeter resonance, reducing a response peak caused by the single capacitor.

That said, I think you need to see this as a very simplistic crossover, a value crossover. It may have worked well before but that doesn't mean you need to stick to the original plan because there's little here to follow.

I didn't think there would be much in common with the original crossover since the new drivers have little in common with the originals,

If you cross them within their normal range where nothing bad is happening, the crossover should be less of a problem and more similar to others than not. You need to determine if this is the case based on the original design. If necessary you have the option of changing the crossover frequency, but this involves understanding whether the acoustic design can accommodate it.

 

[lsiberian]

Well, it looks like I made a major blunder in my woofer choice. The ported enclosure volume is about 0.88 cu ft. Way to small to accommodate even one of these drivers. I'll have to change my order or send the woofers back and get a more suitable driver. I can't change the volume of the enclosure and I can't think of any way they will work in such a small enclosure.

I think to even have a chance of getting this to work will be to seal the bottom and use a single (different) 8" driver at the top where the bass and mid frequencies can blend omni-directionally with the tweeter.

Goldwood has another 8" driver that looks like it will fit the bill if I single up and mount it at the top with the tweeter. Once the bottom is sealed up, the ported volume will be within .03 cu ft of the recommended volume.

Goldwood GW-8PC-4 8" Heavy Duty Woofer 4 Ohm

• Nominal Diameter8"
• Power Handling (RMS)160 Watts
• Power Handling (max)330 Watts
• Impedance4 ohms
• Frequency Response45 to 7,000 Hz
• Sensitivity90.9 dB 2.83V/1m
• Voice Coil Diameter1.5"
• Magnet Weight30 oz.

Thiele-Small Parameters

• Resonant Frequency (Fs)44.2 Hz
• DC Resistance (Re)3.7 ohms
• Voice Coil Inductance (Le)1.2 mH
• Mechanical Q (Qms)5.98
• Electromagnetic Q (Qes)0.49
• Total Q (Qts)0.45
• Compliance Equivalent Volume (Vas)0.75 ft.³

Mechanical Compliance of Suspension (Cms)0.36 mm/N

• BL Product (BL)8.73 Tm
• Diaphragm Mass Inc. Airload (Mms)36.3g
• Maximum Linear Excursion (Xmax)3.5 mm
• Surface Area of Cone (Sd)205.9 cm²

Any thoughts on my very amateurish quandary are welcomed.

Perhaps you could just seal up the boxes entirely and then you mass load the walls and brace your way to a good qtc.

 

[Rob41]

Thanks for the suggestions guys. I cancelled my previous order and have the tweeters and the better suited 8" driver on the way. I'll close up the bottom opening that originally housed the second 8" driver and just use a single 8" in the top.

This way the enclosure volume will be correct. Even without the bottom 8" driver, the frequency response should still be better than the original configuration.

I'll hook them up to my active set-up and see what crossover point works best and how much I'll have to attenuate the tweeter etc. Then I'll be able to choose and order the components for the crossovers.

Until the drivers arrive I'll be cleaning the speakers, pulling the original drivers and making a block off plate for the lower opening.

 

[Rob41]

Here is the original tweeter which is 8 ohms.





I'll be reusing the chamber to mount the new Peerless soft dome tweeter. Would any harm be caused by filling the cavity with dampening material?

 

[AllenB]

I'm not familiar with the shape of the cavity. I'd expect it to be shaped as to distribute the sound. Following the right shape is what matters. I wouldn't put damping in there unless trying to correct a shape issue.

 

[Rob41]

I'm not familiar with the shape of the cavity. I'd expect it to be shaped as to distribute the sound. Following the right shape is what matters. I wouldn't put damping in there unless trying to correct a shape issue.

The cavity in question is the cup in the first picture of my last post. It held the original cone tweeter that I'm replacing with a 1" dome tweeter. I think, it won't effect the new dome tweeter. I was just wondering if it would serve any purpose at all by damping it. Perhaps I should try it both ways and see if there is any audible difference.

 

[AllenB]

Would any harm be caused by filling the cavity with dampening material?

If you mean inside it where sound doesn't go, probably not but if you want to stop the iron from ringing there are better things you could do, like attach a bitumen pad.

If you mean outside where sound does go yes, it would cut the highs. Probably not a good thing unless there was a reason for it.

 

[Rob41]

Yeah, I was talking about the inside, but the bitumen pad is a much better idea.

 

[phivates]

Were the original woofers defective? As in having stiffened surrounds?

 

[Rob41]

Not at all. All of the drivers appear to be in excellent condition.

 

[AllenB]

That's interesting. When I design I usually think of the driver choice last. Many would think of it as being the most important thing, so let me turn the question around.. Is there something that you don't like about the current drivers? If you use different drivers, assuming they are each a reasonable choice for the job, and cross them well there should be little difference.

 

[Rob41]

I have to ship out pretty soon so I don't have time for a full on new project but I want to do something to hold me over. I agree, the drivers should be last to achieve the desired goals but I have these speakers which aren't special to me and want to see if I can subjectively, make them sound better. I think I can.

Plus, while I'm comfortable building speakers for use in my main active system, I haven't built anything passive before. This will allow me to get a bit of practice before my next project which will be a 2-way with sub reinforcement. The 2-ways in that system will be passive.

And, just for the fun of it.

 

[Crodrig]

Hi op, I am new to the forum and curious how your project turned out with these speakers. I inherited my grandfather’s along with his Sansui 6060 and I actually really like them. I know this is an old thread but information on these and upgrades is pretty sparse.