Xrk,
I haven't pulled the trigger on the woofers yet - awaiting your modelling to ensure they will be suitable.
There is an offer on 8 of the SB12NRX25-4 - 4ohm version. Will this make any difference? - as will save me a few pounds!
If not, and the 4 ohm version models well I will order 8. The nice thing with having 4 per horn is because they will be mounted in the corners the shortest port length will be achieved - if I used two larger woofers, the ports would likely be longer if I tried to get them into the corners.
I haven't pulled the trigger on the woofers yet - awaiting your modelling to ensure they will be suitable.
There is an offer on 8 of the SB12NRX25-4 - 4ohm version. Will this make any difference? - as will save me a few pounds!
If not, and the 4 ohm version models well I will order 8. The nice thing with having 4 per horn is because they will be mounted in the corners the shortest port length will be achieved - if I used two larger woofers, the ports would likely be longer if I tried to get them into the corners.
Link to 4 ohm version - more sensitive, slightly lower Fs, slightly higher Qes.
SB Acoustics :: 4? SB12NRX25-4
SB Acoustics :: 4? SB12NRX25-4
That looks promising. Let me see if I can get a model out sometime today. Those are some big magnets - SBA seems like a nice deal. I have to see what these sell for in the US. They are nice compact woofers.
These go for $50 at Madisound - so not cheap but may be well worth it. I like the specs a lot.
These go for $50 at Madisound - so not cheap but may be well worth it. I like the specs a lot.
xBUSH v1.0
Bushmeister,
You are in luck...
I put the WG dimensions into Akabak, put the TS parameters for the SB12NRX25-4 in, adjusted where the bass injection port goes (currently at 10cm back from exit plane at mouth - adjustment closer to front possible with a few dB loss). I used the 2 liter per woofer rear chamber suggested by Byrtt along with Byrtt's estimate of 50cc volume for cone and 34mm dia injection ports that are 30mm long.
For this simulation, we are assuming that the SB65WBAC25-4 couples into the WG perfectly with no throat cancellation effects, and a minimal front chamber effect (volume formed by driver and throat is assumed neglible).
Electrical Filter settings are set as:
SB65WBAC25 is Butterworth -12dB/oct high pass at 350Hz with a 1.12ms delay. Also -3dB padding is applied to get SPL to be closer to woofer.
Qnty 4 SB12NRX25-4's in series/parallel and have -24dB/oct Butterworth low pass filter at 350Hz. A -12dB/oct Butterworth high pass at 80Hz is used to prevent over excursion and for handover to sub woofer.
These electrical filter settings combined with the acoustic filters produce an overall acoustic XO at 500Hz and are Harsch like. This cannot be done until you have actually built it because electrical filters will need to be adjusted to get acoustic target to match the BW4 for the woofer and Bessel 2 for the mid/tweet.
Ok, enough talk, here are the initial results - no EQ applied.
SPL at 2.83v and 1 meter - so first thing we notice is that the system will probably work and the drivers will cover their own territory, the horn is quite efficient and these little 4 inch woofers really can't keep up, 500Hz XO seems to be a sweet spot, note that HF performance of SB65WB above 3kHz is probably not going to be as flat or as high - expect -12dB falloff and several dips due to throat cancellation. Overall a very promising start and I would say the main problem is not enough SPL at 80Hz for the XO to sub. If you are OK with 98dB max at 80Hz then get these drivers. The overall system sensitivity of 91dB that I estimated based on the woofer seems to be good - you can just -ve EQ everything to flat at 91dB and save distortion on SB65WB:
Cone displacement at xmax with 21v (-3dB on on SB65WB) - the SB65WB is hardly moving so the HD should be low:
Max SPL capability at 21v (-3dB on SB65WB) - with proper woofers that have more guts, this system could be quite loud:
Electrical input power at 21v (-3dB on SB65WB) this is excellent and shows all thermal values are not exceeded with some room for EQ'ing the SB65WB:
I will run the 8ohm case just to check but I imagine it won't be much different, perhaps not as good.
Let me know if you have another larger woofer maybe qnty 2 x 6.5in? 4x 5.25in? Will an 8in woofer fit?
Interestingly, if you were to use bass reflex re-injection right along periphery of horn mouth, you can get quite a bit more reach and integrate well with the sub. Here is what it would look like with 4 Liter rear chambers ea and a 1.75in dia x 8.5in long duct x qnty 4 ducts total, the max voltage can go up to 22v and HPF can be backed off to 70Hz:
The predicted impulse response doesn't look too bad actually:
Bushmeister,
You are in luck...
I put the WG dimensions into Akabak, put the TS parameters for the SB12NRX25-4 in, adjusted where the bass injection port goes (currently at 10cm back from exit plane at mouth - adjustment closer to front possible with a few dB loss). I used the 2 liter per woofer rear chamber suggested by Byrtt along with Byrtt's estimate of 50cc volume for cone and 34mm dia injection ports that are 30mm long.
For this simulation, we are assuming that the SB65WBAC25-4 couples into the WG perfectly with no throat cancellation effects, and a minimal front chamber effect (volume formed by driver and throat is assumed neglible).
Electrical Filter settings are set as:
SB65WBAC25 is Butterworth -12dB/oct high pass at 350Hz with a 1.12ms delay. Also -3dB padding is applied to get SPL to be closer to woofer.
Qnty 4 SB12NRX25-4's in series/parallel and have -24dB/oct Butterworth low pass filter at 350Hz. A -12dB/oct Butterworth high pass at 80Hz is used to prevent over excursion and for handover to sub woofer.
These electrical filter settings combined with the acoustic filters produce an overall acoustic XO at 500Hz and are Harsch like. This cannot be done until you have actually built it because electrical filters will need to be adjusted to get acoustic target to match the BW4 for the woofer and Bessel 2 for the mid/tweet.
Ok, enough talk, here are the initial results - no EQ applied.
SPL at 2.83v and 1 meter - so first thing we notice is that the system will probably work and the drivers will cover their own territory, the horn is quite efficient and these little 4 inch woofers really can't keep up, 500Hz XO seems to be a sweet spot, note that HF performance of SB65WB above 3kHz is probably not going to be as flat or as high - expect -12dB falloff and several dips due to throat cancellation. Overall a very promising start and I would say the main problem is not enough SPL at 80Hz for the XO to sub. If you are OK with 98dB max at 80Hz then get these drivers. The overall system sensitivity of 91dB that I estimated based on the woofer seems to be good - you can just -ve EQ everything to flat at 91dB and save distortion on SB65WB:
Cone displacement at xmax with 21v (-3dB on on SB65WB) - the SB65WB is hardly moving so the HD should be low:
Max SPL capability at 21v (-3dB on SB65WB) - with proper woofers that have more guts, this system could be quite loud:
Electrical input power at 21v (-3dB on SB65WB) this is excellent and shows all thermal values are not exceeded with some room for EQ'ing the SB65WB:
I will run the 8ohm case just to check but I imagine it won't be much different, perhaps not as good.
Let me know if you have another larger woofer maybe qnty 2 x 6.5in? 4x 5.25in? Will an 8in woofer fit?
Interestingly, if you were to use bass reflex re-injection right along periphery of horn mouth, you can get quite a bit more reach and integrate well with the sub. Here is what it would look like with 4 Liter rear chambers ea and a 1.75in dia x 8.5in long duct x qnty 4 ducts total, the max voltage can go up to 22v and HPF can be backed off to 70Hz:
The predicted impulse response doesn't look too bad actually:
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Wow! Fantastic work Xrk!
Having done all this - I feel a little guilty looking at other woofers - as it will make more work for you - but, I didn't expect the SB65 to have so much more output than the woofers!
I will just have a re-look at the horn dimensions and woofer options. Give me 10mins!
Having done all this - I feel a little guilty looking at other woofers - as it will make more work for you - but, I didn't expect the SB65 to have so much more output than the woofers!
I will just have a re-look at the horn dimensions and woofer options. Give me 10mins!
OK two of these, per horn (I will have to remove ribs as you suggested) provides almost 3 times the VD cm3:
SB Acoustics :: 8'' SB23NRXS45-8
Fs - 27, Qes 0.41, P-P 13mm.....
Sorry to generate more work for you. I was hoping to avoid removing the ribs - hence the reason for choosing the 4" drivers to fit in between.
SB Acoustics :: 8'' SB23NRXS45-8
Fs - 27, Qes 0.41, P-P 13mm.....
Sorry to generate more work for you. I was hoping to avoid removing the ribs - hence the reason for choosing the 4" drivers to fit in between.
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Hi Byrtt,
Here are the equivalent sims in Akabak. Akabak uses voltage as the independent variable input so I had to tweak that and watch power to get 32 watts. Ended up at 14.37 volts to get 32 watts.
Here is predicted SPL vs Freq for bandpass and sealed:
Here is predicted cone displacement:
Predicted Impedance:
Predicted Electrical Power:
It appears to match your sims. In Akabak there is also the main depth of the front and rear chambers that comes into play (a long one will have resonances). I picked 30mm for the front and 100mm for the back chamber depths.
Here is Akabak script if you ever want to try it out yourself.
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It's not a problem as Akabak is a text script so it's all cut and paste once I have main code in place. It may require fiddling with the chamber volumes and such. But this is exactly why we model first, so we get close and not have an SPL mismatch.
It's amazing how much gain the WG gets you but also remember that the top end is down -12dB so maybe you have to -ve EQ the big gain in the middle? Or boost the HF like I do since there is so much xmax and its just thermal.
I will get back to you with the new double 8's. Still an SBA man thru and thru
Bandpass sim of SB23NRXS45-8
It was good I made the little code package to check the bandpass for Byrtt. I used to to quickly size the rear chamber and bandpass hole for the new 8in SB23NRXS45-8. The driver has a very large Vas but we will undersize the rear chamber to keep the speaker small. It may not have the ideal Q but the powerful motor and EQ will just be used to overpower the box Q and it will comply.
I think a 10 liter rear chamber is not too big and qnty 2 x 65mm dia bandpass holes per driver is needed. I assumed the front volume to be 165cc and the depth of the front chamber to be on average 40mm.
With one driver and a -12dB/oct BW high pass filter at 70Hz, I able to get 110 dB SPL at xmax with 25 volts and f3 of 77Hz. This should cross nicely with the sub. For the horn we can drive in parallel for +6dB at 116dB at 25v.
Predicted displacement:
Predicted Electrical Power:
So a couple of questions for you Bushmeister, is 20 liters rear chamber too big for your bookshelf? We can push it smaller, it will just have a little more of an overshoot bump around 100Hz.
And do you think the WG has enough wall space to drill qnty 4 x 65mm holes? Or make qnty 8 equivalent area holes or about qnty 8 x 50mm holes.
It was good I made the little code package to check the bandpass for Byrtt. I used to to quickly size the rear chamber and bandpass hole for the new 8in SB23NRXS45-8. The driver has a very large Vas but we will undersize the rear chamber to keep the speaker small. It may not have the ideal Q but the powerful motor and EQ will just be used to overpower the box Q and it will comply.
I think a 10 liter rear chamber is not too big and qnty 2 x 65mm dia bandpass holes per driver is needed. I assumed the front volume to be 165cc and the depth of the front chamber to be on average 40mm.
With one driver and a -12dB/oct BW high pass filter at 70Hz, I able to get 110 dB SPL at xmax with 25 volts and f3 of 77Hz. This should cross nicely with the sub. For the horn we can drive in parallel for +6dB at 116dB at 25v.
Predicted displacement:
Predicted Electrical Power:
So a couple of questions for you Bushmeister, is 20 liters rear chamber too big for your bookshelf? We can push it smaller, it will just have a little more of an overshoot bump around 100Hz.
And do you think the WG has enough wall space to drill qnty 4 x 65mm holes? Or make qnty 8 equivalent area holes or about qnty 8 x 50mm holes.
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Nice to see they match and thanks doing it and share script, i have to take the learning curve sometime to get into Akabak so X can have more breath and free time : )
SB12NRX25-4 / SB12NRX25-8:
Maybe its not interesting anymore with the 4" diameter woofers except they probably easyer to position so injection port is at corner and port diameter or say area is as small as possible entrance into waveguide, also think from a bookshelf sized speaker 105dB seen post 28 is not bad at all. Below is SB12NRX25 in 4 ohm verse 8 ohm, most difference seems for a sealed Q 0,7 4 ohm needs 2,636 liter verse 8 ohm 1,999 liter, and BW2 low end roll off in sealed is 97,22Hz for 4 ohm and 108,9Hz for 8 ohm, excursion for 4 ohm is little worse and probably a reason most these differences is Mms for 4 ohm is 0,4 grams more than 8 ohm version. In band pass config it looks BW2 low end roll off for 4 ohm is in 79Hz area and 8 ohm in 88Hz area. It also looks if injection port area is preferred less area the data in the two plots 34mm diameter and 30mm lenght can be brought to 29 mm diameter if length is 19mm.
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xBUSH v1.1 with SB23NRXS45-8
I think this is going to work well with the dual 8 inch woofers. It's almost a perfect match for the little SB65WBAC25. Funny how the WG is such a big equalizer for that tiny driver and two massive 8in woofers.
Here is the predicted max SPL with an 8.0 liter rear chamber for each woofer. I think that works out not too bad. I am using qnty 4 x 65mm injection holes here. We are able to get 112dB at 26v at xmax. Using -12dB/oct BW high pass at 70Hz. The f3 is 82Hz - should be doable for the sub woofer to cross over now.
Here is predicted cone displacement:
Here is predicted electrical power input, at max SPL the thermal rating on the little SB65 is being exceeded so can't operate at max continuously. Should be OK for crest factor though.
Based on this, if two 8 liter chambers are OK, I would get these woofers for this project. A good match and they are nice low distortion drivers.
And for reference, sensitivity at 2.83v is about 93dB:
I think this is going to work well with the dual 8 inch woofers. It's almost a perfect match for the little SB65WBAC25. Funny how the WG is such a big equalizer for that tiny driver and two massive 8in woofers.
Here is the predicted max SPL with an 8.0 liter rear chamber for each woofer. I think that works out not too bad. I am using qnty 4 x 65mm injection holes here. We are able to get 112dB at 26v at xmax. Using -12dB/oct BW high pass at 70Hz. The f3 is 82Hz - should be doable for the sub woofer to cross over now.
Here is predicted cone displacement:
Here is predicted electrical power input, at max SPL the thermal rating on the little SB65 is being exceeded so can't operate at max continuously. Should be OK for crest factor though.
Based on this, if two 8 liter chambers are OK, I would get these woofers for this project. A good match and they are nice low distortion drivers.
And for reference, sensitivity at 2.83v is about 93dB:
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As always guys, I bow to your efforts!!
I will order four 8 inch woofers tonight!
Rear chambers of 8 litres per driver seems very doable.
If I simply created a box to enclose the horn, with the 15x12x11inch dimensions it is going to be over 42 litres volume I reckon - even keeping it tight.
I would imagine calculating for horn volume, driver displacement, a sealed (3 litre ish) chamber for the SB65 there will still be more than 16 litres left over for the two woofers.
I will admit this makes for a fairly large box!
XrK - is it easy for you to work out the volume of the horn using your model? I can subtract it from some box designs and try to come up with something more interesting....If not - I can work it out.
Like you Xrk - I can't believe how that little 2.5 inch full ranger, mounted to the horn equals two high displacement 8 inch woofers! Impressive!
I will order four 8 inch woofers tonight!
Rear chambers of 8 litres per driver seems very doable.
If I simply created a box to enclose the horn, with the 15x12x11inch dimensions it is going to be over 42 litres volume I reckon - even keeping it tight.
I would imagine calculating for horn volume, driver displacement, a sealed (3 litre ish) chamber for the SB65 there will still be more than 16 litres left over for the two woofers.
I will admit this makes for a fairly large box!
XrK - is it easy for you to work out the volume of the horn using your model? I can subtract it from some box designs and try to come up with something more interesting....If not - I can work it out.
Like you Xrk - I can't believe how that little 2.5 inch full ranger, mounted to the horn equals two high displacement 8 inch woofers! Impressive!
One thing Akabak does not do is provide overall volume of the horn. I would just estimate it as a 4 sided pyramid. If you have it already, you can measure it with water. So you like being able to hit 112dB then it sounds like. If you rotate the horn 90 so it it tall, the width is manageable. It's not a small bookshelf speaker by any means. A lot has to do with the WG you pick - that is the foundation that sets everything else. This WG is not huge, but not tiny.
Xrk - regarding port sizing - 2x 65mm diameter ports per woofer gives an injection area of
~ 66cm2 in total. Or 33cm2 per port. I make this approximately 31% the SD of the driver.
Is there any way we can shrink this down a little? Looking at the wave-guide - if I cut these approx 10cm from the throat we will loose a lot of the wave-guide!!
I would be happy to sacrifice some max spl for better CD control.
What are the disadvantages of cutting it closer to the 20% SD of the woofer guidelines?
~ 66cm2 in total. Or 33cm2 per port. I make this approximately 31% the SD of the driver.
Is there any way we can shrink this down a little? Looking at the wave-guide - if I cut these approx 10cm from the throat we will loose a lot of the wave-guide!!
I would be happy to sacrifice some max spl for better CD control.
What are the disadvantages of cutting it closer to the 20% SD of the woofer guidelines?
Your max bass SPL will go down - it may be a sacrifice worth considering. And like Byrtt says, even with the four 4in woofers, if this is really a bookshelf and not a stand mount monitor, the 98dB was not too bad. Holes there are smaller.
Let me run sim with smaller holes. Tell me what size you want - 20% Sd?
Ok, here are qnty 4 x 37mm dia holes - much more reasonable and you give up a few dB. Probably worth it and have max SPL at 110.5db. This is the great thing about having a model - you can try all sorts of things and get closer to the solution or know that the solution is possible.
I think this looks pretty good, 37mm dia holes are not too obtrusive at all. That is 2 holes per driver and 4 total for the horn.
Let me run sim with smaller holes. Tell me what size you want - 20% Sd?
Ok, here are qnty 4 x 37mm dia holes - much more reasonable and you give up a few dB. Probably worth it and have max SPL at 110.5db. This is the great thing about having a model - you can try all sorts of things and get closer to the solution or know that the solution is possible.
I think this looks pretty good, 37mm dia holes are not too obtrusive at all. That is 2 holes per driver and 4 total for the horn.
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