Hey folks,
I just finished my build of ddvp-20 with sb20frpc30-8; lovely project to keep me busy.
I got a dip between 120-180hz and then a huge drop under 50hz. room placement creates some manouvering space to correct it, but that dip is weird.
Could it be due to the damping i used?
I's polyester wool and cotton felt 6mm thick.
Thanks!
I just finished my build of ddvp-20 with sb20frpc30-8; lovely project to keep me busy.
I got a dip between 120-180hz and then a huge drop under 50hz. room placement creates some manouvering space to correct it, but that dip is weird.
Could it be due to the damping i used?
I's polyester wool and cotton felt 6mm thick.
Thanks!
It could be the design, but I think that’s probably floor bounce cancelation. It’s normal and the only way to do much about it is to mount your driver near the floor, which will actually just move the frequency higher. If you can live with the aesthetics, you could put a thick rug on the floor in front of the speakers which should help all around.
Depending on the microphone distance, it’ll usually occur around 150Hz for a driver mounted around 3’ above the floor.
Lovely speakers btw! How do they sound?
Depending on the microphone distance, it’ll usually occur around 150Hz for a driver mounted around 3’ above the floor.
Lovely speakers btw! How do they sound?
Hi cata02, thanks for the follow-up.
I use lightweight sound absorbing materials that contain a lot of air.
The picture looks like it is 4-5 times heavier than mine, but you can adjust the sound absorbing material to your preference.
Also, the box is raised 10 cm from the floor.
Resonant boxes always produce peaks and dips.
The frequency and sound pressure of the peaks and dips vary with the size, shape, and installation position of the room.
It is noticeable when playing a sweep signal, but it is often not noticeable in music playback.
I hope you can try different things and improve.
I use lightweight sound absorbing materials that contain a lot of air.
The picture looks like it is 4-5 times heavier than mine, but you can adjust the sound absorbing material to your preference.
Also, the box is raised 10 cm from the floor.
Resonant boxes always produce peaks and dips.
The frequency and sound pressure of the peaks and dips vary with the size, shape, and installation position of the room.
It is noticeable when playing a sweep signal, but it is often not noticeable in music playback.
I hope you can try different things and improve.
I agree with satx, the dip at 120Hz is floor bounce.
And the 50Hz drop is perfectly normal for this driver in this box.
Looks good to me!
And the 50Hz drop is perfectly normal for this driver in this box.
Looks good to me!
How do they sound?
Pretty darn nice versus the Dynaudio; they go loud, they fill up th eroom quite nicely; they have that sound of big spekaers (vs Dynaudio).
I am driving them through an old Vincent class AB amp, looking to see if i can upgrade that also, reasonably.
Enough that i like listening to music form them more than from the 20-20000 calibrated Genelec setup i have in the tv room (8330+7350).
Maybe i'll just give up on genelec setup and go to diy route completely.
Hi cata02, thanks for the follow-up.
I use lightweight sound absorbing materials that contain a lot of air.
The picture looks like it is 4-5 times heavier than mine.
Also, the box is raised 10 cm from the floor.
Hi, thanks for the feedback.
I raised them, for absolutely no reason; i just thouht I should. What would be the impact of raising/standing them on the floor?
Also, regarding material, I cna definitely play; i can still access them somewhat through the speaker hole.
What were their specific purpose in this design?
Hi, thanks for the feedback.
I raised them, for absolutely no reason; i just thouht I should. What would be the impact of raising/standing them on the floor?
Also, regarding material, I cna definitely play; i can still access them somewhat through the speaker hole.
What were their specific purpose in this design?
I like the sound of the whole box ringing, so I use hollow pipes to float without blocking the bottom.
If you measure at the opening of the pipe you should get good output at the fundmentl resonce say 50 Hz and hopefully not so much of the third fifth and seventh harmonic at 150, 250 and 350Hz
Mesure the driver at 1-2 cm distance and you should get a sharp dip in output at 50 Hz (maximum radiation resistance)
If you get output from the harmonics try more stuffing between the driver and the closed end.
Mesure the driver at 1-2 cm distance and you should get a sharp dip in output at 50 Hz (maximum radiation resistance)
If you get output from the harmonics try more stuffing between the driver and the closed end.
The sound from the duct outlet varies depending on the position, material, and weight of the sound-absorbing material used, so please adjust the sound-absorbing material while checking.
The characteristics of the duct outlet will not change significantly even if the room or installation position is changed.
The characteristics of the duct outlet will not change significantly even if the room or installation position is changed.
How small is small? You might be able to get down to 50-60L with a PR, but that’s just a guess. I found them really good sealed though in as small as 25L. It all depends on how low you want them to go.
I built sealed 1.5 ways in 40L total giving 25L to the SB20FRPC30 and around 15L to the SB20PFCR30-8. This gives both of them nearly identical roll offs and a Q of just under 1 if I remember correctly. F3 is only around 70Hz, but with the combined SD and mid bass bump they sound pretty impactful and like they play lower than that (and in room, they do). The upside is that I get almost 94db in a reasonable box.
Here’s what they look like disassembled and waiting for me to get around to veneering them. Not stand mounts, but reasonably small imo.
I built sealed 1.5 ways in 40L total giving 25L to the SB20FRPC30 and around 15L to the SB20PFCR30-8. This gives both of them nearly identical roll offs and a Q of just under 1 if I remember correctly. F3 is only around 70Hz, but with the combined SD and mid bass bump they sound pretty impactful and like they play lower than that (and in room, they do). The upside is that I get almost 94db in a reasonable box.
Here’s what they look like disassembled and waiting for me to get around to veneering them. Not stand mounts, but reasonably small imo.
Due to the high-ish Qts sb20 is not a great match for either reflex or passive radiator.
As satx above said they work great in closed volumes and very likely also in tl.
I use mine in 30l aperiodic boxes with Q of 0.707 and the bass is truly magnificent - deep, with great impact and very natural.
One thing to remember, unless you do a 1.5way, you'll need some correction network to deal with the rising response, a parallel LCR, which is in series with the driver does the trick.
As satx above said they work great in closed volumes and very likely also in tl.
I use mine in 30l aperiodic boxes with Q of 0.707 and the bass is truly magnificent - deep, with great impact and very natural.
One thing to remember, unless you do a 1.5way, you'll need some correction network to deal with the rising response, a parallel LCR, which is in series with the driver does the trick.
I still needed some minor correction even with the 1.5 way. Could do without it, but for the most natural sound I wanted a bit more control.
Stanislav Hi Can you share the build details of aperiodic box very keen to try it outDue to the high-ish Qts sb20 is not a great match for either reflex or passive radiator.
As satx above said they work great in closed volumes and very likely also in tl.
I use mine in 30l aperiodic boxes with Q of 0.707 and the bass is truly magnificent - deep, with great impact and very natural.
One thing to remember, unless you do a 1.5way, you'll need some correction network to deal with the rising response, a parallel LCR, which is in series with the driver does the trick.
Hello Tiger,
The aperiodic box is just an extension of the closed box, you introduce a resistive vent, a hole usually at the back which is stuffed with sound absorptive material, foam, felt, etc. Nothing fancy. This greatly reduces the peak of the impedance at resonance.
I used Basta to model the enclosures with QL = 3, with 30L volume that bought Qt to 0.707.
You see the aperiodic vent in the middle photo, there's some felt behind that fan guard.
Some photos below:
The aperiodic box is just an extension of the closed box, you introduce a resistive vent, a hole usually at the back which is stuffed with sound absorptive material, foam, felt, etc. Nothing fancy. This greatly reduces the peak of the impedance at resonance.
I used Basta to model the enclosures with QL = 3, with 30L volume that bought Qt to 0.707.
You see the aperiodic vent in the middle photo, there's some felt behind that fan guard.
Some photos below:
Attachments
I think I was considering those same fan guards when I was planning to go aperiodic, they’re the cleanest looking ones I found and come in a lot of sizes. How much felt did you need to bring the peak down? And did you try it sealed with the higher Q to compare?
@satx: I started with 2 layers of felt, the type that removalists use, but any felt will work.
Then testing with LIMP and checking the impedance peak and also listening to selected material that I know well. Preferred the single layer. The double layer took too much of the life of the sound IMHO.
No, I did not try sealed, always been a fan of the aperiodic boxes which sound open, non-resonant, similar to open baffles.
Re. the fan guards, I also have a pair of the old Variovents, but am keeping them for another project with a much bigger double aperiodic box. Something like some of the old Dynaudio speakers.
@duvixan: here's a link to an online store, which is in AU, might not work for you:
https://www.altronics.com.au/p/f1034-sunon-120mm-plastic-fan-guard-with-filter/
https://www.altronics.com.au/p/f1024-sunon-80mm-plastic-fan-guard-with-filter/
Then testing with LIMP and checking the impedance peak and also listening to selected material that I know well. Preferred the single layer. The double layer took too much of the life of the sound IMHO.
No, I did not try sealed, always been a fan of the aperiodic boxes which sound open, non-resonant, similar to open baffles.
Re. the fan guards, I also have a pair of the old Variovents, but am keeping them for another project with a much bigger double aperiodic box. Something like some of the old Dynaudio speakers.
@duvixan: here's a link to an online store, which is in AU, might not work for you:
https://www.altronics.com.au/p/f1034-sunon-120mm-plastic-fan-guard-with-filter/
https://www.altronics.com.au/p/f1024-sunon-80mm-plastic-fan-guard-with-filter/
Stanislav- 🙏 I assume you don’t find that you’re missing out on lower bass with the aperiodic tuning? I was concerned about one note bass with my boxes and planned on using vents, but then I realized that I love my little two ways that use the AC-130F woofer in small sealed boxes a la JB’s Continuum’s so I went sealed and ended up with a similar Q. I’m happy, but your description makes me want to hear them aperiodic now!
No, actually the inverse is true. These drivers produce remarkably deep bass, bass that you feel, not just hear. I believe they easily reach 40 Hz at a very healthy volume.
Never tested them with a microphone, only running sweeps with Alan Parsons sound check cd and a small android app, Spectroid, and I can see and hear and feel very strong output at 40 Hz, gradually reducing around 30.
My room is 5m long, 4 wide and 3.3 high, so enough volume, reasonably well treated acoustically, so that may also play some role.
Never tested them with a microphone, only running sweeps with Alan Parsons sound check cd and a small android app, Spectroid, and I can see and hear and feel very strong output at 40 Hz, gradually reducing around 30.
My room is 5m long, 4 wide and 3.3 high, so enough volume, reasonably well treated acoustically, so that may also play some role.
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