Hi all, please forgive what to a lot of you are very newbie questions. I have searched quite a bit for answers, but it's kind of hard to digest and apply everything in practice...
I'm building a subwoofer for music / HT use in my living room. It's going to replace an XTZ 10.17 (non-edge). For several reasons, I'm limited to a relatively "thin" and small box. I've bought a used RSS315HO-44 in very good condition that I'm going to use for the project. I understand this is a driver that should work well in small enclosures. Haven't bought an amplifier for it yet.
I don't listen crazy loud, but I like proper low extension, and I feel the XTZ lacks just a little bit in that area. It works OK enough for my needs, and I could probably have lived with it for the sound alone, but it doesn't really fit in the living room so I want to get rid of it. My living room has one open side, meaning the total room is quite large.
I was originally thinking to build a sealed box. According to WinISD, in a sealed box of ca 25 liters (I could go up to 41 liters), the driver at Xmax will give me around 97.5 dB @20hz and 104 dB @30Hz (700W) (using the SPL tab in WinISD). I believe this is around 1 dB better than the XTZ at 20Hz but around 5 dB worse at 30Hz. The -3dB point is in the mid 40s. If I make the box vented, 32 liters net volume (when vents, bracing, driver etc are subtracted), tuned for 24 Hz, vent pipe dia 9.74 cm, vent length 114 cm, I get 102 dB @ 20Hz and 110 dB @ 30 Hz, with a very flat response from 100 to 27 Hz. Port velocity is a bit high at 28 m/s max, but I believe I'll never reach that level with music, and for HT it might be OK. Driver excursion seems to be OK provided I high pass it @17 Hz. I'm thinking to stuff the box with polyfill.
Ok, so here are my questions:
1. Based on the WinISD simulation, the vented version seems like the obvious choice. It gives a lot flatter response in general, and a lot more dB below 45 hz. But still, I see a lot of people recommend sealed boxes and one of the arguments is that room gain gives the sealed box quite a bit more output in-room than the simulation indicates. What do you guys think? The sealed version is of course a bit easier to build, especially for a first timer.
2. I understand I could do EQ or even Linkwitz transform for the sealed box (provided I could get a proper DSP in the chain), but I would still be limited by the xmax of the driver, right? So I can't really get more output @ 20 and 30Hz than what WinISD gives me above?
3. Since I'm very inexperienced, dB numbers are a bit hard to relate to. I don't really know if 97.5 dB @ 20Hz and 105 @ 30 Hz might actually be quite sufficient for me. But as I said, I feel the XTZ lacks just a little bit (not much) of power for my needs in that large room. What are your experiences, what dB numbers would you think I should aim at (using the SPL tab in WinISD)
4. If I do vented, do you see a problem with the long vent pipe? I'm thinking to use flared ports (inlet and outlet). I know it's generally recommended to not go above 20 m/s but I believe my music listening will not exceed that, and for HT it's maybe not that important?
5. If I do vented, I'm thinking to use thin PVC pipe (HVAC air pipe) with 1.3 mm thick walls for the vent, and buy "aeroports" for the flared ends. Do you see any problems with this, or do you have better solutions to recommend?
6. The driver can be connected in 2 or 8 ohm configuration. It's easiest and cheapest to get an amp that can do 700 watts @ 8 ohm (bridged) as far as I can see. Does this give any disadvantages over using 700 watts @ 2 ohm (paying a bit more for an amp that is 2 ohm stable)?
7. Any general input or recommendations for the build?
I'm building a subwoofer for music / HT use in my living room. It's going to replace an XTZ 10.17 (non-edge). For several reasons, I'm limited to a relatively "thin" and small box. I've bought a used RSS315HO-44 in very good condition that I'm going to use for the project. I understand this is a driver that should work well in small enclosures. Haven't bought an amplifier for it yet.
I don't listen crazy loud, but I like proper low extension, and I feel the XTZ lacks just a little bit in that area. It works OK enough for my needs, and I could probably have lived with it for the sound alone, but it doesn't really fit in the living room so I want to get rid of it. My living room has one open side, meaning the total room is quite large.
I was originally thinking to build a sealed box. According to WinISD, in a sealed box of ca 25 liters (I could go up to 41 liters), the driver at Xmax will give me around 97.5 dB @20hz and 104 dB @30Hz (700W) (using the SPL tab in WinISD). I believe this is around 1 dB better than the XTZ at 20Hz but around 5 dB worse at 30Hz. The -3dB point is in the mid 40s. If I make the box vented, 32 liters net volume (when vents, bracing, driver etc are subtracted), tuned for 24 Hz, vent pipe dia 9.74 cm, vent length 114 cm, I get 102 dB @ 20Hz and 110 dB @ 30 Hz, with a very flat response from 100 to 27 Hz. Port velocity is a bit high at 28 m/s max, but I believe I'll never reach that level with music, and for HT it might be OK. Driver excursion seems to be OK provided I high pass it @17 Hz. I'm thinking to stuff the box with polyfill.
Ok, so here are my questions:
1. Based on the WinISD simulation, the vented version seems like the obvious choice. It gives a lot flatter response in general, and a lot more dB below 45 hz. But still, I see a lot of people recommend sealed boxes and one of the arguments is that room gain gives the sealed box quite a bit more output in-room than the simulation indicates. What do you guys think? The sealed version is of course a bit easier to build, especially for a first timer.
2. I understand I could do EQ or even Linkwitz transform for the sealed box (provided I could get a proper DSP in the chain), but I would still be limited by the xmax of the driver, right? So I can't really get more output @ 20 and 30Hz than what WinISD gives me above?
3. Since I'm very inexperienced, dB numbers are a bit hard to relate to. I don't really know if 97.5 dB @ 20Hz and 105 @ 30 Hz might actually be quite sufficient for me. But as I said, I feel the XTZ lacks just a little bit (not much) of power for my needs in that large room. What are your experiences, what dB numbers would you think I should aim at (using the SPL tab in WinISD)
4. If I do vented, do you see a problem with the long vent pipe? I'm thinking to use flared ports (inlet and outlet). I know it's generally recommended to not go above 20 m/s but I believe my music listening will not exceed that, and for HT it's maybe not that important?
5. If I do vented, I'm thinking to use thin PVC pipe (HVAC air pipe) with 1.3 mm thick walls for the vent, and buy "aeroports" for the flared ends. Do you see any problems with this, or do you have better solutions to recommend?
6. The driver can be connected in 2 or 8 ohm configuration. It's easiest and cheapest to get an amp that can do 700 watts @ 8 ohm (bridged) as far as I can see. Does this give any disadvantages over using 700 watts @ 2 ohm (paying a bit more for an amp that is 2 ohm stable)?
7. Any general input or recommendations for the build?
"Room gain" applies equally to any enclosure, but a bass-reflex box drops off at 24dB per octave below Fb (box tuning), so there may be less to gain.
That's correct.
Loudness is subjective, and it takes progressively more SPL (sound pressure level) to sound "equally loud" at low frequencies as can be seen in an equal loudness contour chart, 97.5dB at 20Hz sounding only as loud as ~45dB at 1kHz. Conversational level at one meter is above that level.
At 1kHz, a +10 dB change in SPL sounds twice as loud, at 20Hz just +5dB sounds twice as loud.
Distant thunder may be around 97.5dB at 20Hz, and can still be perceived as loud.
Most VLF is also accompanied by upper frequencies that mask port noise.
Sympathetic vibrations from rattling windows, wall hangings, HVAC pipes etc. may be louder than port noise.
1.3 mm is rather thin for high powered use, standard PVC plumbing pipe with the same internal diameter would be better.
Flaring both ends of the port(s) is a good idea to reduce port noise.
A lower impedance requires larger speaker cable to provide the same damping factor as a higher impedance, so would be a disadvantage in cost, with no advantage.
Stuffing a sealed box with polyfill increases it's apparent volume, stuffing a ported box with reduces it's output.
Ported boxes benefit from a HP a few Hz below Fb to reduce useless excursion.
Art
Wow, thank you very much for taking the time to write such a thorough and detailed response. This is really helpful!
One more question, how much can I trust WinISD simulations to give me the correct numbers? For instance when it comes to air velocity and cone excursion, can I trust the numbers, or do I need to allow a large margin for error?
So, basically, any closed sub, independent of volume and shape, and no matter which parts are used, will always be SPL-limited by the driver's xmax? And this is a physical limitation that no EQ or other trickery can overcome? It seems logical. Which means that provided you already have enough amplifier power at hand, the only way to increase SPL from a closed sub is to get a driver with larger cone area or larger xmax?
Ok, interesting. I read somewhere on this forum (I believe) that the vent pipes didn't need to be strong as long as they are fairly rigid, I thought a lot of people are actuallly using cardboard cylinders?
One more question, how much can I trust WinISD simulations to give me the correct numbers? For instance when it comes to air velocity and cone excursion, can I trust the numbers, or do I need to allow a large margin for error?
Xmax is "linear excursion", the driver reaches ~10% distortion at Xmax. It's possible to drive beyond Xmax, but as the voice coil leaves the magnetic gap, BL (magnetic strength) drops, and distortion increases while progressively more power is needed to make less excursion and more heat.
Yes, there is no replacement for displacement in a sealed enclosure.
The smaller the enclosure, the more power required to reach Xmax.
Since ~98% of the power is turned to heat rather than sound, voice coil temperature rises (faster in a smaller sealed enclosure) raising the impedance, and amplifiers produce less power into the higher impedance, "thermal compression".
The cardboard cylinders are generally 3mm or more thick, more rigid than a 1.3mm plastic pipe.
From what I've seen, they generally are "close enough for rock and roll".
That said, simulation programs assume linear parameters, past Xmax they are not accurate.
A 32 litre enclosure (net volume) is quite small as far as subwoofers go. Do you really need such a small enclosure?
Your computed vent length is 1.14 metres, and the volume of the vent is 8.5 litres. That's an extremely long vent.
If the volume of the vented enclosure is increased to 50 litres, keeping tuning the same with Fb=24Hz, this results in a vent whose length is 67.7cm, which is almost half the previous vent length. Below is the predicted response when a 2nd-order 17-Hz high-pass Butterworth filter is also being used.
Thank you so much for taking the time to respond in such detail! Yes, unfortunately, I have to stay within a 42 liters box, baecause this has to fit into a piece of furniture... (long story...) and I've counted 10 liters for bracing, vents and driver volume. I agree that the vent is long, but it'll be possible to fold it with three 90 degree bends. Do you see a problem with using such a long vent with three bends, except for the fact that it occupies a lot of box voulme? I could add another driver and do sealed instead, and get even better SPL at both 20 and 30 hz, but this is of course more expensive and the FR is far from flat like I get with a vented box.
Such long ports will most probably be about 25-30% shorter to get the desired tuning.
Anyways long story short, in the upper range, meaning above tuning and above 35Hz, where you might begin to hear any important structure of the sound, and transients, IF you eq the ported box to the frequency response of the sealed box, ESPECIALLY in less than ideally treated room, you are not going to recognize ported and closed box using your ears.
In other words, go for it.
Anyways long story short, in the upper range, meaning above tuning and above 35Hz, where you might begin to hear any important structure of the sound, and transients, IF you eq the ported box to the frequency response of the sealed box, ESPECIALLY in less than ideally treated room, you are not going to recognize ported and closed box using your ears.
In other words, go for it.
Interesting... Is this because of the resistance from the pipe walls slowing down the air? Or what's the science behind it?
At home nobody listens to 112 dB subwoofer volume with 700 watts at 10% distortion.
Normal 4 layer voice coils are in series. " Dual Voice Coil " is a gimmick.
They just tap the 2 coil layers = pointless. 2 ohm loads are ridiculous loads regardless even if the amp pretends it can do it.
4 ohms is fine Anything from 400 to 600 watts is fine
Anyways, usually seeing ridiculous models most the time.
witwald seemed to place a decent model.
The port velocity doesn't have to be designed for " Max SPL "
More like 87 dB and 98 dB on a risky party night
So you can actual fit the port inside the box, yes basic round tube flare.
End tables for a couch are usually bigger footprint than most subs.
Default leakage for WinIsd is set to high ( 10 ) is impossible.
Set it to 7, as seen in witwalds model.
Without going through countless theory math to find out a ideal enclosure.
Vented. that was easy.
WinIsd is a spreed sheet based on proper theory.
When you select " vented" it will recommend a proper alignment.
that one, build it. Or do the math to find out it was that one all along.
You dont want too long ports. Find realistic SPL
Normal 4 layer voice coils are in series. " Dual Voice Coil " is a gimmick.
They just tap the 2 coil layers = pointless. 2 ohm loads are ridiculous loads regardless even if the amp pretends it can do it.
4 ohms is fine Anything from 400 to 600 watts is fine
Anyways, usually seeing ridiculous models most the time.
witwald seemed to place a decent model.
The port velocity doesn't have to be designed for " Max SPL "
More like 87 dB and 98 dB on a risky party night
So you can actual fit the port inside the box, yes basic round tube flare.
End tables for a couch are usually bigger footprint than most subs.
Default leakage for WinIsd is set to high ( 10 ) is impossible.
Set it to 7, as seen in witwalds model.
Without going through countless theory math to find out a ideal enclosure.
Vented. that was easy.
WinIsd is a spreed sheet based on proper theory.
When you select " vented" it will recommend a proper alignment.
that one, build it. Or do the math to find out it was that one all along.
You dont want too long ports. Find realistic SPL
Fair enough—the design requirement is what it is.
Since you are using this as a subwoofer system, port resonances caused by the long tube length may not be a problem. The fundamental frequency of a pipe open at both ends, whose length is L=1.14 meters is f=343/(2*L)=150Hz. That's almost one octave higher than the typical low-pass filter set to 80Hz that is usually activated on a subwoofer. That low-pass filter will heavily attenuate the input signal that would otherwise excite those resonances. However, it needs to be kept in mind that the pipe resonances are likely to be quite lightly damped (high-Q), so they can still have some significant acoustic output.
Three 90° bends will of course introduce some air flow losses. These will be exacerbated at higher operating power levels, and so turbulence noise may start to intrude.
Thanks @witwald, very helpful!
Yeh, I'm building this into a kind of stool that goes at the end of the chaiselounge part of the couch, so the dimensions are set. I've made the box now, tested it yesterday in sealed config with the full volume (42 liters), which is too much for this driver I think. Still sounded very nice to my ears, and already more and better output than my old sub. I think I'll still go for vented though, even just for the learning and fun of the process.
I'll keep this in mind. I usually lowpass my main speakers at 80 Hz but could probably even cross them lower if needed, they go quite deep. I do feel they're a bit more "effortless" when crossed at 80, but this could also be just a mind trick I guess.
When vents get long, convert to an inverse tapered TQWT to 'have your cake and eat it too' 😉.
I've done a simulation of the Dayton Audio RSS315HO-44 in a sealed 42-liter enclosure. I added a 4th-order Linkwitz–Riley low-pass filter (LPF) with its cut-off frequency set to 70Hz. The computed frequency response is plotted below for an input power level of 330W re 8 ohms (the solid black line). From these results, I can understand why your listening test indicated that the sealed subwoofer was producing very good results.
For comparison, I've included the frequency response of the 32-liter vented enclosure, with a 4th-order Linkwitz–Riley LPF with its cut-off frequency set to 80Hz added into the system. The dash-dot light blue line is that of the SPL response of the vented system for an input power level of 150W re 8 ohms.
In the frequency range between 22Hz and 100Hz, the two sets of SPL response functions are very similar. Initially, I was a bit surprised by that, but it seems clear that the slow natural roll-off rate of the sealed driver has affected the overall response. Of course, the LPF acting on the sealed driver's response needed a bit of tweaking to get to that quite reasonable level of agreement between the sealed and vented systems.
To get an idea of the driver displacement achieved by the vented system at a 150W input power re 8 ohms, take a look at the following plots. The driver displacement in the vented enclosure is way less for the same level of SPL output. Here the vented SPL is plotted using the magenta solid line, while the dashed light-blue line is the sealed subwoofer system.
If you are not too bothered by the sealed enclosure achieving a maximum SPL of around 105dB, then the sealed enclosure produces more output SPL below 22Hz. The sealed subwoofer will also benefit a bit more from room gain below that frequency, due to its slower roll-off rate. If its maximum SPL is deemed to be adequate, then the sealed subwoofer does seem to offer some benefits. By 16Hz, the sealed subwoofer system has about 5dB more output, but at that frequency, the driver has exceeded its Xmax by a few millimeters, while the vented system is more or less on the Xmax limit.
It seems that you may have a few options to consider...
Thank you for taking the time to model and explain in such detail, it's very much appreciated! You're quite right that I've a few options to consider.
One question: Dayton specifies "Optimum Cabinet Size" for this driver to be 14 liters for sealed and 38.5 liters for vented. So 42 liters is almost 3x the optimum size. I've read in other threads on this forum that too much volume in a sealed box can cause bad driver behavior due to lack of "air spring effect" if I understand it correctly. If I choose to keep the sealed config, should I reduce the volume of the box?
Correct, depends on your performance goals, i.e. the sealed ideal is a 0.5 Qt for transient perfect and 0.707 Qt for max flat. Per HR, 14 L = ~ 1.0 Qt, so for high power apps; 42 L = ~ 0.73 Qt.
Can it be thin and tall?
11ft Single Fold TH = 67.5" High x 14" Wide x 12.25" Deep external.
For this driver, that definition of "Optimum Cabinet Size" seems to pertain to a closed-box alignment of around Qtc=0.8. This is not maximally flat, as it introduces a small peak in the low-frequency response. The peak results in some additional ringing in the step response.
A Qtc=0.577 alignment requires a larger box volume of around Vb=39 litres, which is close in size to your Vb=42 litre closed-box enclosure. Hence, your enclosure results in a more damped transient response, close to that of a Bessel low-frequency alignment, which some users consider "optimal".
The following plots show the response change for the sealed subwoofer with different box volumes. In each case, the response is low-pass filtered using a 4th-order Linkwitz–Riley filter set to 70Hz. The magenta solid line corresponds to Vb=42 litres (CL42.0 in the plot). For a subwoofer application, I would regard Vb=42 litres to be more optimum than Vb=14 litres (CL14.0 in the plot).