First time subwoofer design questions

[unclejunebug]

Ive been looking into building a subwoofer for a friend of mine to round out his home theater after he finishes some home renovations. I'm trying to stay within a reasonable budget but still end up with something that will sound great and produce some quality low end. Right now I'm looking at using the Dayton DCS2054 8" Classic Sub paired with a Dayton SA70 plate amp. I built Paul C's Swopes for my own home theater so I have some speaker building experience but I've never designed an enclosure before so it's been a learning experience. As I've been going through this process I've been running into a lot of things I haven't thought of before or didn't realize were things to consider (chuffing for instance).

So far I have downloaded WinISD and have gone through several online tutorials. I added a database entry for the Dayton sub with all the relevant specs from the datasheet and have been tweaking several different box volumes, tuning frequencies, etc... I'm at the point where as a first time designer, I feel like I could use some feedback so I'm turning here to hopefully get some guidance.

Some of the assumptions I've made so far for this build are... (feel free to disagree or correct me)

• The size of the sub and the rated wattage of the amp calls for a ported enclosure as I don't think a sealed box with 70amps would get nearly loud enough.
• My friend built some Overnight Sensations for his systems and my assumption is that this sub setup would be a good compliment.
• I plan to use 3/4" MDF for the enclosure as I'm wary of using 1/2" MDF for a subwoofer.

What I've come up with so far in WinISD is a 0.75ft^3 vented enclosure that's tuned to 34Hz. This gives me a F3 of about 35Hz with a 10"x0.5" vent that's 13.63" long. The Rear Port air velocity graph shows a max of about 23m/s at 31Hz. This is the point where I feel like I need some feedback to really know if what I've come up with so far will work well or if there's something that needs to change...

• As mentioned, I'm trying to stay within a reasonable budget but I also realize that a smaller sub moves less air than a larger one. Am I wasting my time with this combo?
• What effect does the tuning frequency have on the sound produced by the subwoofer?
• After reading about chuffing I've been fairly worried about it being an issue. What's unclear to me is if there's a specific air velocity speed that a design should stay under in order to avoid it. I've also read that port/vent flaring reduces chuffing if air velocity is an issue. Would the 23m/s max I'm getting with my current design be an issue? If so would flaring the vent make it acceptable?

• XMax of this sub is 8.8mm and WinISD's cone excursion graph shows a line that exceeds this (max of about 11.75mm) between about 13-25Hz. The sub datasheet states a usable frequency range of 30-200Hz. Is it OK that the graph goes out of spec for this sub if it's in a non-usable range?

Thanks in advance for any help!

- Steve

[trevordj]

Everything looks good that you have come up with. It looks like you have done your homework. I don't think you are wasting your time with this combination and I think this small sub would be a good compliment to the OS.

Think of the port as another speaker that plays a single note very well. It's not that simple but it helps for visualization. That note that it plays well is the tuning frequency. How loud that simple speaker can play is dictated by the cross sectional area, the larger that is, the louder the port can play without becoming turbulent and sounding bad (chuffing or distortion). The downside is the larger the cross sectional area the longer the port has to be to reach a given tuning frequency. Given this visualization it becomes apparent how the port contributes to the sound. Typically the port tuning is at or near the woofer's fs. At Fs, the woofer has an impedance peak. By tuning a box near fs the port (remember simple speaker) will have a minimum acoustic impedance. In other words, as the woofer becomes less efficient near Fs, the port becomes more efficient. The result is the subwoofer and enclosure will play louder at the tuning frequency than a sealed box at the same frequency. The downside? As the system plays below port tuning the port no longer is able to resist the movement of the woofer cone and efficiency is reduced. In other words, a ported system has a steeper rolloff than an equivalent sealed system.

To avoid chuffing the generally accepted goal is to keep port velocity below about 20m/s. What you posted should work well. I modeled your woofer in Jeff Bagby's excellent excel program and got a somewhat different result. If you want to do a slot port that would work but a round port a 2" diameter round port 10" long does quite well.

There are some very smart designers here, I am sure I butchered some of the technical explanations above so hopefully others chime in where I messed up.

[Kornbread]

Just a quickie .... somewhere on here there is a GRS ($24?) subwoofer build. It was ridiculously inexpensive with good results. If the 10" ($32) sd270a is anything like its smaller 8" ($24) sd215 sibling, they might also be a better choice than the dcs for a good low budget sub. The sd215 also plays nice with smaller drivers, like the b4n in the OS, where the sub may need to play higher in frequency, cleanly, than a typical sub. For the $, I am impressed with the sd215 despite its flimsy stamped frame.
I'm generally less concerned with subwoofer chuffing than that in a monitor because at higher volume volume levels, the sub tends to cover up the port noise. Flaring helps. Even a ¾" roundover router bit can help. ½" mdf is fine if you brace sufficiently. There is another thread 'Light cabinet construction techniques' that might be of interest.

[rpb]

If you can go with a bigger box. I'd move up to a ten, or twelve inch driver. I know money doesn't grow on trees, but a 2 cu-ft box will perform better than 1 cu-ft.

[unclejunebug]

Wow, I appreciate all the responses! I'll try and return the favor...

Think of the port as another speaker that plays a single note very well. It's not that simple but it helps for visualization. That note that it plays well is the tuning frequency. How loud that simple speaker can play is dictated by the cross sectional area, the larger that is, the louder the port can play without becoming turbulent and sounding bad (chuffing or distortion). The downside is the larger the cross sectional area the longer the port has to be to reach a given tuning frequency. Given this visualization it becomes apparent how the port contributes to the sound. Typically the port tuning is at or near the woofer's fs. At Fs, the woofer has an impedance peak. By tuning a box near fs the port (remember simple speaker) will have a minimum acoustic impedance. In other words, as the woofer becomes less efficient near Fs, the port becomes more efficient. The result is the subwoofer and enclosure will play louder at the tuning frequency than a sealed box at the same frequency. The downside? As the system plays below port tuning the port no longer is able to resist the movement of the woofer cone and efficiency is reduced. In other words, a ported system has a steeper rolloff than an equivalent sealed system.

I think this makes a lot of sense, thanks! I think I chose the tuning frequency I based on the port length I was getting from WinISD. The Fs of this 8" Dayton is 32.3Hz and I ended up choosing a tuning frequency of 34Hz so it sounds like I ended up with something close to what it should be.

To avoid chuffing the generally accepted goal is to keep port velocity below about 20m/s. What you posted should work well. I modeled your woofer in Jeff Bagby's excellent excel program and got a somewhat different result. If you want to do a slot port that would work but a round port a 2" diameter round port 10" long does quite well.

I came across that excel program myself and tried using it but it seemed to have a much steeper learning curve and I didn't find any online tutorials (As I found who Jeff Bagby was I was sorry to hear of his passing). If I select a 2" round port in WinISD it gives me a port length of 8.26" which is great as far as fitting it in a smaller enclosure but the port velocity jumps up to over 36m/s. Perhaps I'm doing something wrong in WinISD? I would much rather go with the 2" flared round port if I could.

Just a quickie .... somewhere on here there is a GRS ($24?) subwoofer build. It was ridiculously inexpensive with good results. If the 10" ($32) sd270a is anything like its smaller 8" ($24) sd215 sibling, they might also be a better choice than the dcs for a good low budget sub. The sd215 also plays nice with smaller drivers, like the b4n in the OS, where the sub may need to play higher in frequency, cleanly, than a typical sub. For the $, I am impressed with the sd215 despite its flimsy stamped frame.
I'm generally less concerned with subwoofer chuffing than that in a monitor because at higher volume volume levels, the sub tends to cover up the port noise. Flaring helps. Even a ¾" roundover router bit can help. ½" mdf is fine if you brace sufficiently. There is another thread 'Light cabinet construction techniques' that might be of interest.

I took a look at the sd215 when I was hunting for a driver but the product page stated an optimal vented volume of 3.71ft^3 (As determined by Bass Box 6). I've never used that software and can't speak for it's accuracy, but that volume scared me off as the cabinet itself would have been way too large. I will check out that construction technique thread, thanks!

If you can go with a bigger box. I'd move up to a ten, or twelve inch driver. I know money doesn't grow on trees, but a 2 cu-ft box will perform better than 1 cu-ft.

Originally I was thinking the box itself needed to be on the smaller end in order to fit in the space it will go in. Though I am trying to do this on the sly and don't know the exact dimensions of available spaces it could go in just eyeballing it says it needs to be on the smaller end. My friend has mentioned he'd want a sub that's more unassuming so I was trying to stay on the smaller side. I could pull out a tape measure next time I'm there and start measuring sections of his living room but he might think I'm a little crazy haha. Personally I would prefer to go up to a 10" or 12" if possible, I'm just not sure there would be space for it.

[a4eaudio]

I took a look at the sd215 when I was hunting for a driver but the product page stated an optimal vented volume of 3.71ft^3 (As determined by Bass Box 6). I've never used that software and can't speak for it's accuracy, but that volume scared me off as the cabinet itself would have been way too large. I will check out that construction technique thread, thanks!

Per the product page, the SD215A-88 has an optimal vented box of 0.95cf. It is less sensitive and has less xmax than the DCS205 but also half the price.
I have three SD215A's and 70w plate amps but have not built anything with them yet. They did seem to be a good match when modeling, whereas I think the DCS205 deserves a more powerful amp. My thoughts were multiple SD215As w/ 70w amps were good bass for the money.

[Kornbread]

Already had the sd215 loaded in unibox.
1.5ft³ sealed and ported @70 watts w/3" x 8.27" port. Take note of port velocity and xmax. This is just one of many options.

[Kornbread]

1ft³ sealed and ported @70 watts w/3" x 12" port. Take note of port velocity and xmax. This is just one of many options.

[unclejunebug]

Per the product page, the SD215A-88 has an optimal vented box of 0.95cf. It is less sensitive and has less xmax than the DCS205 but also half the price.
I have three SD215A's and 70w plate amps but have not built anything with them yet. They did seem to be a good match when modeling, whereas I think the DCS205 deserves a more powerful amp. My thoughts were multiple SD215As w/ 70w amps were good bass for the money.

You're correct, my mistake. I meant to say the optimal vented volume of the SD270A was 3.71ft^3.

[Chris Roemer]

A few things ...
I think a 1/2"w slot is just too narrow (for a mid-size sub, anyhow). I think you should have more port area. I'd only go 2" (which I consider small-ish - for an 8") if you use a "Precision Port" (OR, can make your own w/a pretty large radiused exit - like 3/4"). If it were me, I'd go w/3" PVC w/a "roundover" exit. THAT needs to be 20" long - which is pretty long to fit into 0.75cf.

SOMEtimes, you can shorten the (acceptable) port length by making the box not much larger. Going up to 1.0cf shortens a 3" port down to about 15". Looks pretty good. I think I'd go 100w MIN for that 8" Classic sub.

The SD 8" (cheap, DVC) driver LIKES the SA70 amp in about 1.5cf, ported. That might be more in the budget.
Also TangBand's W6-1139siF (the cheaper vers., NOT the "neo") works well in 0.75cf tuned near 30Hz - I'd go w/a 10" long 2" "PPort" here as well (unless you can make a "generous" roundover on the exit). I'm sure it could keep up w/a pair of O.S. As always, EYE prefer to "aim" the port away from the listening position.

[donradick]

While port chuffing can be a real concern (adds distortion) - consider the application - the models are showing 105dB passband, and that's "dinosaur stomp" loud!
You will not be able to play the Overnight Sensations that loud! So if you drop the power level for max of 95 or maybe 100 dB, the chuffing on a 2 inch port should not
be a problem. This is a good, cheap, small sub for the OSs. I would advise checking out the GRS sub that was mentioned. Some very good values can be had.

[LOUT]

I think that SD215a-88 can reach a similar ~35hz in a slightly larger 1ft-cu box. The SD215 is cheaper and a hair more sensitive/efficient watt-per-watt than the DCS205, so it should perform very similarly with a 70watt amp and a slightly larger 1cu box compared to the DCS205 in an 0.75cu box, BUT the DCS205 can push louder if you're willing to move up to a ~150watt amp because of its higher wattage-handling and its extra XMAX.


If you're aiming for the smallest box possible on a budget and you're fine with 35hz and 70watts and if the DCS205 is likely a little louder than you'd need anyway, you might consider the slightly cheaper/smaller DCS165 which should reach ~35hz in an 0.4ft-cu box.

[wogg]

Huge fan of the SD215-88. I used it in this project, hitting it with 70W. Box is about 0.9cu ft, using a 10" long 2" precision port that I flush mounted and painted to look OEM. The recessed grill also worked out really well, it doesn't look home built at all and got really good feedback at MWAF a couple years back. My amp and crossover is custom to do a full 2.1 self powered setup, but the SA70 is perfect as well.

It won't rattle your teeth like a bigger sub, but it fills the room nicely down into the 30's.

[unclejunebug]

I appreciate the responses everyone and sorry to disappear for awhile (new job, more travel, yada yada). After all the recommendations for the SD215A-88 and looking at what I was planning to do with the DCS205 I think it makes more sense to go with the SD215A-88 and a slightly larger box. The DCS205 would be nice but I'm not too keen on driving it with less than half it's rated power handling and moving up in amp wattage about doubles the amp cost. Not to mention I'd still only be up to 100w rather than 150w (why aren't there any 150w plate amp options?)

Huge fan of the SD215A-88. I used it in this project, hitting it with 70W...

wogg, thanks for that project link! I like this overall design and it fits in my budget well. After talking to my friend a little more about his plans and the space he intends to use I think I'm looking at making a down firing low profile enclosure rather than a more standard box design. The mounting depth of the SD215A-88 (3.74") seems like it should work well for this application. Are there any considerations to make about how much free air space there is between the back of the woofer and the inside of the enclosure? I was planning to use the same internal box volume and port length as your project but change the enclosure dimensions to make a low profile design.

Another thing I'm re-considering is the plate amp. Initially I was planning to use the SA70 but due to the change in enclosure design the amp would have to go on the top or the bottom of the enclosure. Ideally I could place the amp on one of the narrow sides of the enclosure and came across the Lepai LP210PA amp. Anyone have experience with this amp?

[wogg]

Only concern on back of driver clearance: The pole piece is vented, leave about an inch behind the magnet. Otherwise your plan is solid.

No experience on the Lepai amp, though I would be concerned that it produce the power it says it does.