Red measurement please.
Also you said your port measurement is:
Port 20cm in diameter and port length is 14cm.
Can you please recheck the diameter?
Also you said your port measurement is:
Port 20cm in diameter and port length is 14cm.
Can you please recheck the diameter?
Last edited:
Well, you said your port is wider than the length. I have assumed about 6cm.
I'll deal with your design in a few posts. I'm posting this publicly for scrutiny / challenge incase I have anything wrong.
Enclosure
Your box is too big really for this woofer. A 23L enclosure with a 6cm diameter and 14cm long port provides a box tuning of Fb 42.6Hz. This yields the following response:
It's not the end of the world, but that "slump" between the box / port tuning frequency and say 200Hz is due to an oversized box and trying to tune it too low for the woofer you have in mind. In anycase, it will work.
The biggest problem you have is your port is too small if you intend to get maximum bass. Here's your port velocity at 47w input:
The bottom yellow line at 17m/s is where you want the red curve to be under, ideally. You may hear chuffing sounds at higher volumes and this will lead to compression.
For the same power input, here is excursion showing that the port will be the limiting factor
The solution (if you don't want a smaller box) is to install a wider diameter port. This would need to be 7.5cm diameter and 23.5cm long to maintain the same tuning. This gets you down to under 17m/s port velocity.
In reality, like all ported boxes it is the area below the tuning frequency where excursion goes crazy. if you are really going to play these loud, you probably want to invest in a <30Hz (not quite but almost) subsonic filter.
I'll deal with your design in a few posts. I'm posting this publicly for scrutiny / challenge incase I have anything wrong.
Enclosure
Your box is too big really for this woofer. A 23L enclosure with a 6cm diameter and 14cm long port provides a box tuning of Fb 42.6Hz. This yields the following response:
It's not the end of the world, but that "slump" between the box / port tuning frequency and say 200Hz is due to an oversized box and trying to tune it too low for the woofer you have in mind. In anycase, it will work.
The biggest problem you have is your port is too small if you intend to get maximum bass. Here's your port velocity at 47w input:
The bottom yellow line at 17m/s is where you want the red curve to be under, ideally. You may hear chuffing sounds at higher volumes and this will lead to compression.
For the same power input, here is excursion showing that the port will be the limiting factor
The solution (if you don't want a smaller box) is to install a wider diameter port. This would need to be 7.5cm diameter and 23.5cm long to maintain the same tuning. This gets you down to under 17m/s port velocity.
In reality, like all ported boxes it is the area below the tuning frequency where excursion goes crazy. if you are really going to play these loud, you probably want to invest in a <30Hz (not quite but almost) subsonic filter.
Crossover:
Frequency response:
The slope up from 100Hz is ok. I haven't given you full baffle step compensation - this is about 4 dB of compensation with a nominal system sensitivity ~ 84dB
Here is your impedance:
Lastly as I was going for LR targets, here is your "reverse null" and phase:
Phase:
Frequency response:
The slope up from 100Hz is ok. I haven't given you full baffle step compensation - this is about 4 dB of compensation with a nominal system sensitivity ~ 84dB
Here is your impedance:
Lastly as I was going for LR targets, here is your "reverse null" and phase:
Phase:
No, you'll lose too much bass. I think it's ok. You might experience a bit of a one note bass though around the tuning frequency.
Blue dashed = port open, black - port closed:
Blue dashed = port open, black - port closed:
Light blue = your 23L ported box. Dark blue your 23L ported box sealed. Black = 12L box tuned to 45Hz.
You may actually like a bit of extra oomph at 50Hz and it may even blend in with a room node.
In short - don't worry about it
You may actually like a bit of extra oomph at 50Hz and it may even blend in with a room node.
In short - don't worry about it
It's a mild nuisance that you can buy 10 and 12 microfarad caps, but not 11!
The way to get the 11 value is to 'parallel' two caps together, i.e. 10 +1; 4.7 + 6.2.
Geoff
The way to get the 11 value is to 'parallel' two caps together, i.e. 10 +1; 4.7 + 6.2.
Geoff
Hi Dave, I found a couple of empty speaker boxes from speaker hospital here are the measurements Dimensions each approx. 21x41x29 cm (WxHxD)
would it be worth considering or just sticking with what i already have.
would it be worth considering or just sticking with what i already have.
Apart from dimensional issues (which might affect the crossover) , what are the cabinets made from, are they thicker material or higher/lower quality than the Focals, etc?
How do the cabinets cope with the 'knuckle rap' test, i.e when you hit them is there a dull thunk or a resonant sound?
Are the driver layout and cut-outs the same as the Focal?
I'd stick with the Focals as Dave B has worked out the box performance and crossover based on their dimensions.
Geoff
How do the cabinets cope with the 'knuckle rap' test, i.e when you hit them is there a dull thunk or a resonant sound?
Are the driver layout and cut-outs the same as the Focal?
I'd stick with the Focals as Dave B has worked out the box performance and crossover based on their dimensions.
Geoff
thanks Geoff i think you are right the Focal box is one of the most solid ive come accross hence the reason i held on to it.
Hi Dave based on the cost to upgrade the XO I may have to re-think my budget for all this, but just wanted to say a big thank you for your time and effort it really is much appreciated. 🙂
Yes that's fine. I try to get +/- 5% components where possible as you want speakers to match and eliminate the variables.
Notch filters tend to be more sensitive to being "off" in value - especially if they are high Q (that is they operate on a very specific and narrow frequency band). In the crossover I did for you, the 0.22mF (or 220nF) capacitor does that. It strikes the primary breakup of the RS180P at 5KHz which should reduce 3rd order HD at 1,666Hz (not shown on these graphs as these are frequency response only)
Are those outside dimensions? If so, assuming the boxes have 18mm thick walls thats about 20L internal volume - give or take.
I'd just stick to your existing boxes for now - especially if you have drivers mounted and port in place.
The break-up of the RS180 - be it the aluminium or paper/kevlar versions - is another reason why a stock crossover won't work.
The nasties in their frequency response and distortion, and the frequencies at which they occur, mean those issues really need to be properly dealt with in the crossover.
That could be with a notch filter, as per Dave B's crossover above, or by clever design and component selection in the woofer circuit, as done so well by the late Jeff Bagby in his RS180 (aluminium version) designs.
Geoff
The nasties in their frequency response and distortion, and the frequencies at which they occur, mean those issues really need to be properly dealt with in the crossover.
That could be with a notch filter, as per Dave B's crossover above, or by clever design and component selection in the woofer circuit, as done so well by the late Jeff Bagby in his RS180 (aluminium version) designs.
Geoff