So I built an enclosure for a ported enclosure for an 8 inch woofer and I tuned it for just below 40 hertz. Thing is, I don't think I did it right because the bass response is weak without any eq and the graph shows the response I get. The box is something like 1.2 cu ft, so I think a little under 40 hertz is reasonable for an 8 inch woofer. Is there any way to confirm that I tuned it to the right frequency? I do see a bump at 35 hertz but there's also a bump around 75 hertz and the response falls off very quickly after 60 hertz. Is there a way to know for sure I tuned this right?
That would be this one...Dayton Audio RS225-4 8" Reference Woofer 4 Ohm
So now tell us about the box.
Mike
So now tell us about the box.
Mike
A simple way would be to measure the woofer nearfield very close to the dust cap. That will show a dip at the tuning frequency. Like in the orange trace here (not my measurement)
Otherwise an impedance measurement where the minimum is between the two low frequency peaks
Otherwise an impedance measurement where the minimum is between the two low frequency peaks
You can verify tuning with an impedance sweep of the woofer. You can get a rough idea by running test tones and noting the frequency at which the woofer is moving the least, or measuring port output nearfield and finding the frequency at which it peaks.
Assuming your modelling and calculations of port lenght/diameter were all right, and that the driver is broken in and TS params are within reasonable tolerance, you should expect something like this:
https://i.imgur.com/dpisPvZ.png
I don't have your port specs so took a guess at length/diameter.
Also keep in mind, that depending on measurement conditions, the room is almost certainly influencing this measurement heavily.
Assuming your modelling and calculations of port lenght/diameter were all right, and that the driver is broken in and TS params are within reasonable tolerance, you should expect something like this:
https://i.imgur.com/dpisPvZ.png
I don't have your port specs so took a guess at length/diameter.
Also keep in mind, that depending on measurement conditions, the room is almost certainly influencing this measurement heavily.
A simple way would be to measure the woofer nearfield very close to the dust cap. That will show a dip at the tuning frequency. Like in the orange trace here (not my measurement)
Otherwise an impedance measurement where the minimum is between the two low frequency peaks
Sorry, I should have been more clear, the measurement I posted was a nearfield measurement, does this mean my tuning frequency is around 45 hertz? That's where the dip is.
If your enclosure models with a flat frequency response, and your near field measurement confirms you got the tuning frequency right, but they still sound bass-light, it's most likely not enough baffle-step-correction. It can also be the room, and that's why I like to keep some reference speakers here to compare.
You can generate a consolidated port+woofer response using nearfield measurements, see this document:
http://audio.claub.net/software/FRD...curate In-Room Frequency Response to 10Hz.pdf
specifically the section titled "Near Field Cone and Port Summation" for detailed instructions.
In terms of your tuning frequency, that's a very small diameter port. To get a 40hz tuning, you would have just a 3cm long port.. that's going to run into turbulence fast.
https://i.imgur.com/1YUrY7B.png
I am again assuming that your box is 1.2cu ft net, internal volume. And that you are using an RS225-4 metal cone, and not paper or shielded version of this driver. How did you model this box, and what were the exact measurements of the port? How far is it from box edges on the outside and inside? And is there any obstruction to flow from stuffing or internal structures like bracing possibly?
http://audio.claub.net/software/FRD...curate In-Room Frequency Response to 10Hz.pdf
specifically the section titled "Near Field Cone and Port Summation" for detailed instructions.
In terms of your tuning frequency, that's a very small diameter port. To get a 40hz tuning, you would have just a 3cm long port.. that's going to run into turbulence fast.
https://i.imgur.com/1YUrY7B.png
I am again assuming that your box is 1.2cu ft net, internal volume. And that you are using an RS225-4 metal cone, and not paper or shielded version of this driver. How did you model this box, and what were the exact measurements of the port? How far is it from box edges on the outside and inside? And is there any obstruction to flow from stuffing or internal structures like bracing possibly?
Design for bass response is more complicated than just ensuring a chosen resonant frequency.
A system is an integration of many variables, some of which are driver dependant, and chosen box size is also dependant on these.
The driver maker will specify a relationship between box size, and the lowest frequency that is obtainable with that.
A system is an integration of many variables, some of which are driver dependant, and chosen box size is also dependant on these.
The driver maker will specify a relationship between box size, and the lowest frequency that is obtainable with that.
Oh and yes, it's the metal cone, I used WinISD to model it and made sure the stuffing was away from the port. I just measured it and the port is 6.3 inches long.
Huh... well, I'm at a loss then. When I model that with the information you've given, I get a very different result, a sort of very droopy EBS alignment tuned to 21hz with extremely high vent velocity.
Quite possibly I've made an obvious mistake or the TS params in the vituixcad database are off from your drivers, so perhaps someone else can attempt to replicate for you.
I will say that I've used the Dayton RS225-8s in a vented box, and I would personally not use less than a 2.5" diameter port with these 8" dayton woofers to keep port noise down. I doubt that's the cause of the behaviour you're seeing, but something to consider.
Quite possibly I've made an obvious mistake or the TS params in the vituixcad database are off from your drivers, so perhaps someone else can attempt to replicate for you.
I will say that I've used the Dayton RS225-8s in a vented box, and I would personally not use less than a 2.5" diameter port with these 8" dayton woofers to keep port noise down. I doubt that's the cause of the behaviour you're seeing, but something to consider.
Huh... well, I'm at a loss then. When I model that with the information you've given, I get a very different result, a sort of very droopy EBS alignment tuned to 21hz with extremely high vent velocity.
Quite possibly I've made an obvious mistake or the TS params in the vituixcad database are off from your drivers, so perhaps someone else can attempt to replicate for you.
I will say that I've used the Dayton RS225-8s in a vented box, and I would personally not use less than a 2.5" diameter port with these 8" dayton woofers to keep port noise down. I doubt that's the cause of the behaviour you're seeing, but something to consider.
No, my bad sorry, I made a mistake when I was quoting your previous comment. Did you see this?- "I'm sorry, I'm a total idiot, the port is actually 2 5/8", thought it sounded too small, just measured and confirmed. It's been a while since I worked on this so the details are fuzzy in my head. I looked back at my drawings and measured and subtracted the thickness of the wood to confirm that the internal volume is 0.95 cu ft, not 1.2. The internal dimensions are 13" x 11" x 11.5" The ports are mounted rear facing and in the corners of the enclosure." Your calculations are probably right 🙂 I messed up because I think I wrote within your quote and posted. Also is it a possibility that it's just the nature of the driver to see a boost around 75 hertz?
Oh right I did miss that! Ok that will help. One more thing, you said "ports". Just one port per enclosure/driver? I wasn't sure if this was a pair or there was more than one port.
Well that all makes more sense I think:
I don't think the hump is inherent to the driver, I think it's the enclosure size and port combination. For example, if I keep all else the same but double box size, We get something like this:
Which looks quite a bit closer to what my tuning looked like for the 8ohm shielded version.
I think you probably want a bigger box if you want these vented. Look around at other designs using the Rs225 (Curt Cambell has a ton, impulse audio has a video review YouTube) they are using larger boxes tuned in the mid-lower 30s.
Your box will work, you're just leaving some performance on the table. If you don't want to change it, You can use EQ to bring the hump down and put a highpass below tuning frequency, which will give you a box that can play louder than the bigger alignments, but not as low. You could also try to stuff the port and test the sealed alignment, your box size gives a nice low Q sealed box which rolls off faster but extends into the 30s and below just as well.
The yellow line is your ported box, for reference, everything else is the same size sealed box. This would probably be what I'd do if a different box isn't possible, I'd take the reduced SPL capability for the better extension and SQ of the sealed version.
I don't think the hump is inherent to the driver, I think it's the enclosure size and port combination. For example, if I keep all else the same but double box size, We get something like this:
Which looks quite a bit closer to what my tuning looked like for the 8ohm shielded version.
I think you probably want a bigger box if you want these vented. Look around at other designs using the Rs225 (Curt Cambell has a ton, impulse audio has a video review YouTube) they are using larger boxes tuned in the mid-lower 30s.
Your box will work, you're just leaving some performance on the table. If you don't want to change it, You can use EQ to bring the hump down and put a highpass below tuning frequency, which will give you a box that can play louder than the bigger alignments, but not as low. You could also try to stuff the port and test the sealed alignment, your box size gives a nice low Q sealed box which rolls off faster but extends into the 30s and below just as well.
The yellow line is your ported box, for reference, everything else is the same size sealed box. This would probably be what I'd do if a different box isn't possible, I'd take the reduced SPL capability for the better extension and SQ of the sealed version.