I listened to the SB15CRC30-8 driver several times over the last couple of weeks. As I wrote above, I applied some modest EQ to notch out the 6.5k resonance peak, and added some gentle baffle step EQ.
Overall it sounded quite good. Ignoring the limitations in the bass and upper treble, it sounded like a very nice full range driver. I heard nothing that would make me reconsider using this driver.
The Dayton RS225-8 woofers arrived last week. I have not had a chance to unpack them and do an impedance sweep, which is something I do with all drivers when I get them. Most defects can be revealed with an impedance sweep.
Also arriving were the Dayton DS270PR passive radiators. At this point in the design, I am decided upon using a passive radiator instead of a vent. This combination of woofer and PR has very nice simulation performance, and a PR allows me to sidestep issues of midrange leakage and vent resonances. As I stated in the first post, I wanted this project to be an opportunity to use a PR for the first time.
j.
Here is a conceptual sketch of the speaker cabinet. I have not decided if the passive radiator will be front mounted or rear mounted. I expect there will be very little performance difference between the two PR locations, so it will come down to aesthetics and internal cabinet layout considerations.
My working name for the speaker is MT-8.3PR... MT stands for Mini Tower. It is only 36" tall, so to me that is pretty "mini". I plan to make a 5" tall plinth that will raise the tweeter to ear height, and this plinth will house the crossover.
j.
My working name for the speaker is MT-8.3PR... MT stands for Mini Tower. It is only 36" tall, so to me that is pretty "mini". I plan to make a 5" tall plinth that will raise the tweeter to ear height, and this plinth will house the crossover.
j.
I may have to Unwatch this thread if you can't come up with a better name than that! 🤣
I am much too late to contribute.
Principally I like stiff cones for all drivers.
So metal cones are my personal favourite.
The next thing I usually look at is if possibly all drivers could have faraday rings minimizing distortion.
Then the time domain of multi ways are far from ideal.
So only DSP'ed systems are more attractive to me.
In germany Klang und Ton magazine and Hobby Hifi magazine which I get monthly mostly offer classic multi way constructions.
There is no lack for choosing between a lot of well made and proved concepts.
However I appreciate the effort of building them and testing for DIYers here on DIY Audio Forum.
Many never buy a diy hifi magazine and rely only on the web.
I must say that the driver measurement tests and hifi multi ways I have seen documented for 30 years until now in these magazines gave me a lot of insight into this work I could not gather only relying on the web.
Principally I like stiff cones for all drivers.
So metal cones are my personal favourite.
The next thing I usually look at is if possibly all drivers could have faraday rings minimizing distortion.
Then the time domain of multi ways are far from ideal.
So only DSP'ed systems are more attractive to me.
In germany Klang und Ton magazine and Hobby Hifi magazine which I get monthly mostly offer classic multi way constructions.
There is no lack for choosing between a lot of well made and proved concepts.
However I appreciate the effort of building them and testing for DIYers here on DIY Audio Forum.
Many never buy a diy hifi magazine and rely only on the web.
I must say that the driver measurement tests and hifi multi ways I have seen documented for 30 years until now in these magazines gave me a lot of insight into this work I could not gather only relying on the web.
@b_force - A PR was part of the original concept in post #1 because I have never designed a PR speaker and I wanted to try one. I gave serious consideration to using a vent, but I decided a PR would simplify my design/development process by eliminating the possibility of vent resonances and midrange leakage. A vent can complicate internal cabinet construction, because the vent can sometimes interfere with efficient bracing.
If the vented resulted in better performance than the PR, I would have chosen vented. But the performance was roughly equal, so the choice was made to go PR...
@A4eaudio - yes the name is lame. I came from a world where the coolest things were given completely uninspiring names like AGM-154 JSOW and GAU-8. So I am not well practiced in coming up with good names... I am open to ideas...
If the vented resulted in better performance than the PR, I would have chosen vented. But the performance was roughly equal, so the choice was made to go PR...
@A4eaudio - yes the name is lame. I came from a world where the coolest things were given completely uninspiring names like AGM-154 JSOW and GAU-8. So I am not well practiced in coming up with good names... I am open to ideas...
That can be correct yes, although that doesn't take price into consideration as well as non-linearities. 🙂
But that's all that matters! 🙂
Gives a certain classic look and feel!
edit: nevermind, most 8 inch PR's have a OD that is smaller than the RS225.
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Just out of interest, I quickly simulated a PR design with the RS225-8 and DS270-PR.
You could potentially run into the max cone excursion of the PR at very low frequencies (around 20-25Hz).
Theoretically you could run out before you run out of excursion of the RS225.
For most music this won't be a big deal, but it is something to consider.
Also the PR rolls off a little quicker of course 🙂
You could potentially run into the max cone excursion of the PR at very low frequencies (around 20-25Hz).
Theoretically you could run out before you run out of excursion of the RS225.
For most music this won't be a big deal, but it is something to consider.
Also the PR rolls off a little quicker of course 🙂
I think the PR on the front looks better as there is a nice size progression of cones instead of a big blank space.
What about Terra Incognito or New Ground , just somecideas aftercscanning ypu introduction atcthecstart of this thread.
I agree, after thinking about it for a while. If mounted on the front, the PR can not be recessed, it will have to be surface mounted, as there is not enough edge distance to the start of the bevel. This is the main reason I was considering a rear mounting. But the flange is fairly thin, so a surface mounting will not be cosmetically obnoxious, and it certainly will have no sonic impact. In addition, front mounting makes cabinet design/construction easier. Thanks for your thoughts.
Terra Incognita - Latin for "unexplored land" ... Nice ! Thank you @JanRSmit ... That is the name of this project ! It has been 27 years since I designed a 3-way passive speaker, and back then I used rudimentary measurements and primitive circuit simulation, so I consider this a new experience. All three drivers are new to me, and using a passive radiator is new to me as well. It is a great name.
@hifijim: I haven’t simulated, but why not go for 2xRS225 on the front? I think that looks better and for sure performance is improved. Even cost is higher, time spent is about the same.
You could experiment with magic cap in bass, to get more bass. Not sure if it works in vented/PR cabinet or it is closed only. In closed cabinet it works for sure.
https://sbacoustics.com/wp-content/uploads/2018/05/Capacitor-Tuning.pdf
You could experiment with magic cap in bass, to get more bass. Not sure if it works in vented/PR cabinet or it is closed only. In closed cabinet it works for sure.
https://sbacoustics.com/wp-content/uploads/2018/05/Capacitor-Tuning.pdf
A rough calculation shows the value to be about 700 uF.
@Rokytheman - thanks for your thoughts. I could have used 2x RS225-4 in series in this 40 liter box and I would have maintained the 8 Ohm load I need. At 40 Hz the rolloff would be about -8 dB, and I wanted a bass extension that is more full range. Your large cap idea is interesting, and I will have to simulate it to see how it might work.
For this project, the drivers are selected and purchased, so that part of the design is fixed.
@Rokytheman - thanks for your thoughts. I could have used 2x RS225-4 in series in this 40 liter box and I would have maintained the 8 Ohm load I need. At 40 Hz the rolloff would be about -8 dB, and I wanted a bass extension that is more full range. Your large cap idea is interesting, and I will have to simulate it to see how it might work.
For this project, the drivers are selected and purchased, so that part of the design is fixed.
^ Cap in series reduces electrical damping so the response peaks some. You can play with this in VituixCAD enclosure tool, there is series cap on the filter tab. It's not too useful on all size boxes if I remember, I think it helps too small a box a bit. But, now you increase group delay if it matters so it's just another variation one can use to get some system response.
In German this is called GHP, Geschlossen Hoch Pass (closed high pass).
It gives a similar response as a BR, with a bit of boost an Q manipulation.
Except with the benefits of a true BR, so nu excursion dip.
I never found the idea all that useful, while still costing quite a bit of money.
In this case we have plenty of space for either a port or PR.
The biggest limitation with the Dayton PR, is the excursion of the PR at very low frequencies.
I recommend either a pair of mass balanced PRs or a port system optimized to reduce midrange bleed and tube resonances. I had a Sunfire sub that had a heavily mass loaded PR that would literally walk across the floor when producing 20 Hz content, due to the mass imbalance. This sub produced as much tactile output as acoustic output at those frequencies, which was acceptable for Home Theater, but not so much for music reproduction.
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On the subject of low frequency SPL limits: Every speaker will have a maximum SPL limit at a given low frequency. The various bass loading designs (sealed box, vented box, passive radiator, etc) will all hit their limit in a different physical effect.
A sealed box design will exceed Xmax, and will eventually hit X-limit. If DSP is being used to extend the bass response, the speaker is at risk of hitting X-limit at very low frequencies.
A vented box will usually hit the point of turbulence and compression in the vent, but sometimes the limit will be the driver hitting Xmax first. At frequencies below Fb tuning, hitting X-limit is quite possible.
With passive radiators, either the driver X-limit or the PR X-limit will be the constraint, depending on the design.
I do not design my active speakers with self-protection in mind. They can be destroyed by idiotic use of the volume control knob, or mindless switching between sources, or incompetent cable swapping. I understand that in a live sound performance application, or a recording environment, self-protection strategies are needed.
This passive speaker project is intended for use in a home listening environment, by normal sane people. So of course it will have some limit to low frequency SPL, and the user will need to stay within that limit. In this case, the PR and the woofer both hit their limit at about 20.4 Vrms when driven by pink noise.
For full range music speakers (i.e. not home theatre subwoofers), I use 40 Hz as a design point. I assume that music content drops off at at least 6 dB/octave below 40 Hz… of course there are songs and tracts with significant content below this, but again, I am assuming the user controls the volume knob.
Dayton RS225-8 + DS270PR, 40 liter, 20.4 Vrms
A sealed box design will exceed Xmax, and will eventually hit X-limit. If DSP is being used to extend the bass response, the speaker is at risk of hitting X-limit at very low frequencies.
A vented box will usually hit the point of turbulence and compression in the vent, but sometimes the limit will be the driver hitting Xmax first. At frequencies below Fb tuning, hitting X-limit is quite possible.
With passive radiators, either the driver X-limit or the PR X-limit will be the constraint, depending on the design.
I do not design my active speakers with self-protection in mind. They can be destroyed by idiotic use of the volume control knob, or mindless switching between sources, or incompetent cable swapping. I understand that in a live sound performance application, or a recording environment, self-protection strategies are needed.
This passive speaker project is intended for use in a home listening environment, by normal sane people. So of course it will have some limit to low frequency SPL, and the user will need to stay within that limit. In this case, the PR and the woofer both hit their limit at about 20.4 Vrms when driven by pink noise.
For full range music speakers (i.e. not home theatre subwoofers), I use 40 Hz as a design point. I assume that music content drops off at at least 6 dB/octave below 40 Hz… of course there are songs and tracts with significant content below this, but again, I am assuming the user controls the volume knob.
Dayton RS225-8 + DS270PR, 40 liter, 20.4 Vrms
Quite a few companies have used this solution. It used to be common in Infinity speakers, today, for example, in speakers from Gauder Akustik, in stand models that are closed designs.