On a side note I whipped up a pretty nice looking and simple xo. LR2 @ 2000 Hz. Woofer only needs a series inductor and a parallel LCR notch to control breakup. Tweeter only needs a series padding resistor followed by a 2nd order electrical filter. So 7 parts per side. I have all the parts on hand so I'm going to whip up test xo's and have a listen. Heck, maybe those port resonances won't even be audible at my listening position.
As long as you can get into the box, my 2cents would be try moving the 1in damping foam from the bottom to the wall where the ports are directed internally ???
A pencil or dowel would be a good tool to shove damping in through the ports where needed. This is how seamstresses do thin arms or other stuffed things and make sure the stuffing gets where it should be.
I gave these a good listen this morning with the prototype xos. I like them. I like them a lot actually. I couldn't hear any hint of any port resonances. Forgot how much I like the RS28A's. And 2nd order LR sounds great with these drivers.
It's probably helpful that the upper and lower ports are both on the rear panel, not facing me. And I have a lot of clutter behind them, almost like a diffuser panel.
After I was done taking all my normal measurements I cranked just the woofer up WAY louder than I would ever listen (think Barbie Girl DIY event loud). I was surprised that the air velocity out of each port wasn't really that high. Not that it is related, just surprising.
I did some more listening after lunch. I still can't hear anything that stands out bad. Hmmm? So I set the mic back up and took a 1 meter measurement with the xo in place. Yep, no question, there is almost a 2 dB bump at 600 Hz. Crap!
If it was 10 years ago and these were $10 buyout drivers I would have left them as is and been super happy. But it's 2023 Baby and these aren't cheapo drivers. That said I will most likely replace the upper port with a passive radiator and try to tame the lower port with a bit of extra damping.
Don't forget Scott Sehlin's Volare thread where he drilled the holes in the port to eliminate a resonance. His resonance was quite a bit higher, so I have no idea if it would work or not, but I know you referred to this thread once and are aware of what he did.
I will be ordering two DSA215-PR today. Doing some modeling in UniBox it shows that adding 54 grams to this passive radiator will tune the upper chamber to the same frequency as the 2" port does. Does that seem like too much added mass for an 8" PR? I didn't see a max listed anywhere.
I think this PR has more than enough Vd compared to the SB woofer:
@PWRRYD said:
My PR's showed up today. Not much to them for $30.
Yeah, but they are still among the cheapest PRs out there and they tend to model nicely. I used them in my Bosi 225s at InDIYana - my first (and only so far) passive radiator build. Technically they weren't quite enough Vd per the normal rules of thumb, but I'm cheap and went with them anyways.
At this point I'm thinking about some 1/4" thick CPVC sheet we have at work. With the proper size hole saw (no center drill needed) I could make some block off plates and cement them in place.
I found some masking plugs at work that fit in the ports nice and tight. So that is "temporarily" taken care of. I installed the PR's, port plugs, and drivers. After a few trial and error efforts I have the PR's tuned exactly the same as the ports were (measured impedance curves with DATs). I was expecting that I would have to add more mass to the PR's. It turned out that I had to remove one washer (about 8 grams) and add some polyfill to get the impedance curves to overlay exactly. However, there is now a very small 4th impedance peak at 10 Hz. The peak is only 9 ohms and it is so low in frequency I'm not worried about it. Strange however... no enclosure dimension of this project could ever contribute to a resonance that low. Has anyone else seen something like this with PR's?
I've worked up a crossover design for this project and I am very pleased with how they sound. LR2 at 2kHz. Very smooth on and off axis response. These will be demo'd in Iowa in less than 2 weeks.
@PWRRYD said:
I've worked up a crossover design for this project and I am very pleased with how they sound. LR2 at 2kHz. Very smooth on and off axis response. These will be demo'd in Iowa in less than 2 weeks.
While the crossovers are installed interally, their design is definitely not set in stone. I'm hoping for some feedback this weekend. Anyone who is there and hears these please give me your opinions. Good or bad. I don't get personally hurt by negative feedback. If we all just circle jerked each other none of us would get any better at this hobby.
Comments
On a side note I whipped up a pretty nice looking and simple xo. LR2 @ 2000 Hz. Woofer only needs a series inductor and a parallel LCR notch to control breakup. Tweeter only needs a series padding resistor followed by a 2nd order electrical filter. So 7 parts per side. I have all the parts on hand so I'm going to whip up test xo's and have a listen. Heck, maybe those port resonances won't even be audible at my listening position.
As long as you can get into the box, my 2cents would be try moving the 1in damping foam from the bottom to the wall where the ports are directed internally ???
A pencil or dowel would be a good tool to shove damping in through the ports where needed. This is how seamstresses do thin arms or other stuffed things and make sure the stuffing gets where it should be.
InDIYana Event Website
AND tie some dental floss to the stuffing bundles so you can remove some of it when you over do the damping, later.
I gave these a good listen this morning with the prototype xos. I like them. I like them a lot actually. I couldn't hear any hint of any port resonances. Forgot how much I like the RS28A's. And 2nd order LR sounds great with these drivers.
B & W sells speakers with huge port resonances, and people don't seem to mind.
It's probably helpful that the upper and lower ports are both on the rear panel, not facing me. And I have a lot of clutter behind them, almost like a diffuser panel.
After I was done taking all my normal measurements I cranked just the woofer up WAY louder than I would ever listen (think Barbie Girl DIY event loud). I was surprised that the air velocity out of each port wasn't really that high. Not that it is related, just surprising.
I did some more listening after lunch. I still can't hear anything that stands out bad. Hmmm? So I set the mic back up and took a 1 meter measurement with the xo in place. Yep, no question, there is almost a 2 dB bump at 600 Hz. Crap!
If it was 10 years ago and these were $10 buyout drivers I would have left them as is and been super happy. But it's 2023 Baby and these aren't cheapo drivers. That said I will most likely replace the upper port with a passive radiator and try to tame the lower port with a bit of extra damping.
Don't forget Scott Sehlin's Volare thread where he drilled the holes in the port to eliminate a resonance. His resonance was quite a bit higher, so I have no idea if it would work or not, but I know you referred to this thread once and are aware of what he did.
I thought dual chamber reflex always had double dips in the FR and impedance?
I will be ordering two DSA215-PR today. Doing some modeling in UniBox it shows that adding 54 grams to this passive radiator will tune the upper chamber to the same frequency as the 2" port does. Does that seem like too much added mass for an 8" PR? I didn't see a max listed anywhere.
I think this PR has more than enough Vd compared to the SB woofer:
11 mm x 211.2 cm
vs
5.5 mm x 118 cm
Any thoughts?
IIRC, 200g was close to the limit on the old paper, maybe 250g tops.
InDIYana Event Website
I had no problems with 60g. You will be fine. I used M5 sst washers.
Thanks guys!
My PR's showed up today. Not much to them for $30.
Yeah, but they are still among the cheapest PRs out there and they tend to model nicely. I used them in my Bosi 225s at InDIYana - my first (and only so far) passive radiator build. Technically they weren't quite enough Vd per the normal rules of thumb, but I'm cheap and went with them anyways.
Cut some holes for the passive radiators:
Now I just need to figure out a nice way to plug the upper chamber port:
Plug it on the inside and tell people it's a port tuned passive radiator.
Plug the outside end, and stuff it. It could be a tuned stub to reduce the same issue you are fighting.
InDIYana Event Website
Or try it with both, and net a higher tuning.
InDIYana Event Website
Could cut the hole where the port was? Obviously too late now...
InDIYana Event Website
At this point I'm thinking about some 1/4" thick CPVC sheet we have at work. With the proper size hole saw (no center drill needed) I could make some block off plates and cement them in place.
I found some masking plugs at work that fit in the ports nice and tight. So that is "temporarily" taken care of. I installed the PR's, port plugs, and drivers. After a few trial and error efforts I have the PR's tuned exactly the same as the ports were (measured impedance curves with DATs). I was expecting that I would have to add more mass to the PR's. It turned out that I had to remove one washer (about 8 grams) and add some polyfill to get the impedance curves to overlay exactly. However, there is now a very small 4th impedance peak at 10 Hz. The peak is only 9 ohms and it is so low in frequency I'm not worried about it. Strange however... no enclosure dimension of this project could ever contribute to a resonance that low. Has anyone else seen something like this with PR's?
Does your room have any walls about 30 feet apart? If so, the larger area of the PR could be more sensitive to room nodes.
That is close to half of the Fs of the PR with that amount added mass. Possibly a higher order harmonic in the the box slightly lining up with the PR?
I've worked up a crossover design for this project and I am very pleased with how they sound. LR2 at 2kHz. Very smooth on and off axis response. These will be demo'd in Iowa in less than 2 weeks.
Sounds like a winner!
While the crossovers are installed interally, their design is definitely not set in stone. I'm hoping for some feedback this weekend. Anyone who is there and hears these please give me your opinions. Good or bad. I don't get personally hurt by negative feedback. If we all just circle jerked each other none of us would get any better at this hobby.