subwoofer choice: why not DAYTON AUDIO RSS315HFA-8?

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lecriquet

Member
Joined 2020
#1
Hello everyone 🙂,
I have a pair of DIY column whose design is attributed to Mr. Troels Gravesen and the realization to myself.
The project: CA18RNX floorstander
The measurement :
spl_drivers_B.jpg

I will take the measurements at home when I have a UMIK, but we can think that they go down to 150Hz or even 100Hz in the range +/- 5db
I want to add a sub to have an extension in the bass (20Hz would be cool).
I mainly use my system in HiFi, no nightclub. I enjoy listening to music, but not at unreasonable levels. I am nevertheless in a house without adjoining neighbor, so I can push the level if I want to.
The installation is in a living room of +/-130m3, and my couch is approximately at 2.5m from speakers.
I have space for a 150L box (minus wood, speaker, etc... the box can be 60*50*50cm outside).
It will be powered by a Behringer a800, measured by Amir
Nevertheless, if the amp is limiting, it could be swapped.
I played around a bit with Dominique Pétoin website and loudspeakerdatabase. One particuar subwoofer hold my attention: the DAYTON RSS315HFA-8
Surprisingly, Dominique's website gives me a simulation, but only with events that are much too long...
Wininsd does better.


Image2.png

Image1.png


These simulations give me, if I do not misinterpret, an f3 at 19Hz and SPL at 3m/100W of 95db up to 30Hz.
That would be just perfect for my needs.
But ...
I think it's too good to be true, so I'm coming to see what you think?

Thanks for the help
Alex
 
#2
Greets!

Well, T/S max flat = ~129 L/20.5 Hz and HR 'says' a 6" dia vent is required for 18 m/s vent mach @ Xmax limited 200 W/m/30 Hz, so at 100 W peaking at 110 dB/W/m/2pi, then 95 dB/100 W/3m/2pi is fine, though still need at least a 5" dia. vent.
 
#3
GM said:
Greets!

Well, T/S max flat = ~129 L/20.5 Hz and HR 'says' a 6" dia vent is required for 18 m/s vent mach @ Xmax limited 200 W/m/30 Hz, so at 100 W peaking at 110 dB/W/m/2pi, then 95 dB/100 W/3m/2pi is fine, though still need at least a 5" dia. vent.
Click to expand...
Well, thanks for the quick answer.
I don't know where you got/calculated all these datas, though! 🙂
Could you please explain the calculation ? I could therefore do it by myself
Best
Alex
 
#4
This can also all be simulated in WinISD. I do it like this:

Basically, I try to keep the air velocity below 20 m/s at Xmax. So I first display "Cone excursion" and increase the input power under "Signal" until Xmax (the horizontal red line, if Xmax was specified in the driver parameters) is reached above the tuning frequency fb.

Then I display "Rear port - Air velocity" and increase the cross-sectional area of the port under "Vents" until I am at just under 20 m/s at peak. That's about where it often hit for me with a cross sectional area of 1/3 * SD.

In your case - 120 liters @ 20 Hz - a practicable bass reflex design with ports is hardly possible: one third of the diaphragm area of a 15 inch driver would be about 270 cm², according to WinISD the port would then have a length of 1.5 m. In this case, it would be better to use passive membranes if bass reflex is still wanted.

I hope that was understandable. English is not my native language.....

Many greetings,
Azrael
 
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#5
Azrael said:
This can also all be simulated in WinISD. I do it like this:

Basically, I try to keep the air velocity below 20 m/s at Xmax. So I first display "Cone excursion" and increase the input power under "Signal" until Xmax (the horizontal red line, if Xmax was specified in the driver parameters) is reached above the tuning frequency fb.

Then I display "Rear port - Air velocity" and increase the cross-sectional area of the port under "Vents" until I am at just under 20 m/s at peak. That's about where it often hit for me with a cross sectional area of 1/3 * SD.

In your case - 120 liters @ 20 Hz - a practicable bass reflex design with ports is hardly possible: one third of the diaphragm area of a 15 inch driver would be about 270 cm², according to WinISD the port would then have a length of 1.5 m. In this case, it would be better to use passive membranes if bass reflex is still wanted.

I hope that was understandable. English is not my native language.....

Many greetings,
Azrael
Click to expand...

Thanks a lot for the procedure.
Indeed, vent lenght is limiting!!
Is it possible to bend the tube to get those 1.5m? Because in a 60*50*50cm box, I could technically do it, but it would be weird 😀

I tried with a laminar vent. Again, a 5*40*110cm long vent is "doable", not sure if it is a good idea.

I have never designed a box with a passive radiator but I tested with this one: DS270-PR
If I did it right, for a 110L box, f3=25Hz, xmax is never limiting (350W @ 3m gives +/- 100db). I added Mms (100g) to "added mass to cone" because it was not asked before, but not sure if it's correct.

If it's too hard to design, I'll switch to another subwoofer.

Best,
Alex
 
#6
lecriquet said:
Well, thanks for the quick answer.
I don't know where you got/calculated all these datas, though! 🙂
Could you please explain the calculation ? I could therefore do it by myself
Best
Alex
Click to expand...
You're welcome!

Margolis-Small's HP 67/97 & 41C calculator program: http://www.aes.org/e-lib/browse.cfm?elib=3902

net volume [Vb] [L] = 20*Vas*Qts'^3.3

box tuning [Fb] [Hz] = 0.42*Fs*Qts'^-0.96

[Qts'] = [Qts] + any added series resistance [Rs]: http://www.mh-audio.nl/Calculators/newqts.html

There's lots more math that I quit using once accurate 'enough' freeware (HR nowadays) became available to do it for me, so just load these specs (or some other box alignment) and a mouse click away gets the rest and more!. 😉
 
#7
Azrael said:
Then I display "Rear port - Air velocity" and increase the cross-sectional area of the port under "Vents" until I am at just under 20 m/s at peak. That's about where it often hit for me with a cross sectional area of 1/3 * SD.

In your case - 120 liters @ 20 Hz - a practicable bass reflex design with ports is hardly possible: one third of the diaphragm area of a 15 inch driver would be about 270 cm², according to WinISD the port would then have a length of 1.5 m. In this case, it would be better to use passive membranes if bass reflex is still wanted.

I hope that was understandable. English is not my native language.....
Click to expand...

Right, the pioneers started at Av = Sd for max acoustic efficiency, though low power/Xmax drivers can often get by with just 20%, but low Fs, Vas, high Qt specs often dictates morphing a BR into an inverse tapered TQWT.

Agree with the PR, but have already shown it's doable in BR since the vent(s) while long are still < the Onken 61 cm tested limit, though personally would use the TQWT.

Perfectly, which is far better than many of my neighbors, even some of the ones whose American Heritage goes as far back as my early 1700s. 🙁
 
#11
Hi,

I usually find closed box woofers better sounding and also better matching the room acoustics and easier to build and equalize.
The Dayton would fit a 70L cabinet resulting in a Qtb of ~0.7 and a Fb of ~35Hz.
Driving the sub actively via a active xover featuring a variable 2nd order HP filter would provide for the required or wished-for amount of equeing.
Even smaller cabinets (Qtb of 0.8-1.0) would be possible utilizing Linkwitz´ double-T equalizer.
Certainly there´s not much need for large resonator cabinets that only exceed in maximum SPL, but stay behind a CB on almost all other aspects.
Thinking more complex electronically You might even consider motional feedback (mfb).
See https://piratelogic.nl/ for DIY-modules.

jauu
Calvin
 
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