Coffee Table Sub with Dayton RSS390HF-4 questions

[fish-24_7]

I'm a relative noob to DIY speaker building. (I say relative because I designed / built a half-baked HT system with my father 18 years ago using Pyle drivers... back when they still made decent stuff, and a couple of smaller 2 way designs while in college - we made several port length calculation errors only discovered by ear afterwards...) Anyway, just about to get back into the hobby after all these years, and now, I have the WAF to consider.;)

The long and short of it: just bought a new house (doing my best to support the housing market and all) and the basement will be split into the man / kid's cave. There is no wall separating our areas, but the walk-out sliding glass door serves as the boundary. My half (the soon-to-be-theater section) measures 20'x13'x8' ceiling. I have a beautiful 58" Panasonic Viera plasma (that I LOVE) that I want to surround with an audio system it deserves. Stage one to get my feet wet again in cabinet construction: the sub.

Coffee Table Sub's preliminary design is based around the Dayton RSS390HF-4, put in a 9.4 cu ft. (internal) box, tuned to 21 hz, yeilding an F3 of 19.76 hz, modeled on BB 6 Pro, powered by the Bash 500 sub amp. I intend to have the driver and port down firing and need to make the box appear like an actual coffee table. It will reside in the virtual middle of my space. I have read a lot on these forums (BTW - you guys ROCK, and I'm glad to be getting back into this because there is SO much more peer support easily available than there used to be...) so I realize that I will sacrifice a lot of room loading due to the location but again, WAF to consider... I forsee the space to be used 65/35 theater / music, hence my selection of the RSS390HF-4 .

My first few (of many I'm sure) questions:
At what air velocity will I notice "port chuff"? (the design currently calls for 2 - 5" vents nearly 20" long modeling 14.4 m/s at 18 hz...)

Is this enough sub for my room given the location? (To clarify - I intend to build the statement / mini statement 5.1 setup to support it next, driving the whole thing with and Onkyo sr-806 receiver - amateurish, I know, but money will be a factor in the powering decision.) :rolleyes:

I am thinking a 1.5" baffle with 3/4" sides and top. (The top will be capped with an oak tabletop on top of the MDF, yeilding 1.5" or more up there.) How much bracing will I need to keep my beer from rattling on the top? (I know, the more the better, but how much will I REALLY need?)

Sorry for the long post! I promise they will be shorter moving forward...;)

Thanks to any/all for any support you can provide in this.

[Rightbrained]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

Hi and welcome back to DIY

1- At 14.4 m/s you have no port noise concerns . From my experience port noise usually isnt a problem until you approach 30 m/s.

2- The single sub may be enough for you , its a matter of personal taste. I prefer corner loading of my subs and the room gain associated with this placement. The Statements and Mini's will be a very nice set up and the Onkyo should drive them nicely (remember to set it to 4 ohm ).

3- In my opinion you should not have a span larger than 12 inches without a cross brace. I am sure others have their own theories on this matter.

Hopefully this will help some . I am up with a headache so I may not be thinking clearly

[fish-24_7]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

Thanks for the quick reply Right! (Sorry 'bout your headache :()

So do you think I can go with smaller (or fewer) ports to raise the m/s speed (such as 4 3" ports [3" PVC is much easier to come by and will fit in the cabinet vertically without elbows] meauring 13 3/4" and yeilding 20.2 m/s) with the same tuning and not suffer chuff?

Any other initail thoughts?

Thanks again for your support! When I can get these questions solidified, this will turn into a well documented build thread, I'm sure...

[Rightbrained]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

fish ,
I didnt model your proposed build but if you only showing 20.2 m/s @ tuning you will have no worries in that department.
One thing to note , make sure the ends of the ports have clearance equal to or greater than the diameter of the port from any wall.
A slot port would be easy to incorporate into your build and would save the expense of buying several port tubes.

[Pete Schumacher]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

Avoid using the RSS390 in a downfiring orientation. Gravity will cause it to sag and you'll lose a bit of excursion.

Also, shoot for a design with a very deep F10. You'll appreciate it when the HT effects kick in. Tune the box to 15 or 14Hz. You'll get better control of cone motion as you go into the infrasonic range where explosions and other effects can really tax a system. The lower tuning will aid that ability. Your room will develop a bit of lift in the bass region, so having an extended F3 may tend to sound a bit overdone in the lowest octaves. A more gradual slope to a deep F10 will more likely have a better compliment to the room curve than one with the deepest F3.

Take a look at a system using 6 cubic feet and tuned to 15Hz with a 4" diameter, 23" long vent. 250W will just be enough to almost reach Xmax at 23Hz, and not again until you hit 12Hz. F3 is 23Hz, and F10 is at 13.5Hz!!! That's where it's palpable. Room lift will bring up those levels below 30Hz by quite a bit too. Not factoring in room lift, the SPL level for 250W would be 110+dB at 30Hz. It's not unreasonable to expect the in room response of the smaller, deeper tuned system, to extend well below 15Hz.


500W will have the driver exceeding Xmax by 4mm, and probably significant distortion, though you're not at the suspension limits I think. So be gentle with the gain setting if you're using more than a 350W amp.

[philiparcario]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

so pete what sub should he use to down fire with a coffee table design. for that matter I know I have seen a few coffee table designs in the last few years maybe a builder could post one for us. I have a rss390hf-4 in an infinite baffle it is really nice. I run it from 15hz to 50hz and cross to a pair of nht1259's they serve as stands for my mains the nht1259's run 50hz to 100hz see pictures below. you could use rss315's or rss265's the same as my nht1259's and wall mount the rss390 behind your couch.

[KeithL]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

[QUOTE=Rightbrained;1568701]Hi and welcome back to DIY

1- At 14.4 m/s you have no port noise concerns . From my experience port noise usually isnt a problem until you approach 30 m/s.


When you are talking 30m/s, is that with one watt or are you talking full power?

[Rightbrained]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

[QUOTE=KeithL;1568714]

Hi and welcome back to DIY

1- At 14.4 m/s you have no port noise concerns . From my experience port noise usually isnt a problem until you approach 30 m/s.


When you are talking 30m/s, is that with one watt or are you talking full power?

I am referring to what I have modeled at full power. The first ported sub I built showed a port velocity of 30 ish m/s at tuning and there was certainly some chuffing. Just posting observations from my experiences.

[fish-24_7]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

Avoid using the RSS390 in a downfiring orientation. Gravity will cause it to sag and you'll lose a bit of excursion.
...
Take a look at a system using 6 cubic feet and tuned to 15Hz with a 4" diameter, 23" long vent. 250W will just be enough to almost reach Xmax at 23Hz, and not again until you hit 12Hz. F3 is 23Hz, and F10 is at 13.5Hz!!! That's where it's palpable. Room lift will bring up those levels below 30Hz by quite a bit too. Not factoring in room lift, the SPL level for 250W would be 110+dB at 30Hz. It's not unreasonable to expect the in room response of the smaller, deeper tuned system, to extend well below 15Hz.

Pete, thanks for the reply. (I really am amazed at the level of peer support on this forum - it is awesome!)

I appreciate your guidance on the design / driver choice. Unfortunately :p the driver must be down firing in said design or the SAF goes down unacceptably!

Can anyone recommend a 15" Dayton driver that can handle down firing, HT and will faithfully reproduce audio (not a muddy noise maker) all at modeled SPL's in the 112-115 range at 1 m? I really thought I found the right driver with the RSS390HF (Heaven knows I've been weighing that very decision for weeks), but perhaps not...

The curve design (shooting for a really deep F10 as opposed to the deepest F3) you advocate is something I had not heard of before. I will definitely take that under consideration along with not overamping the system! Thanks.

What about the bracing question? How much is JUST ENOUGH in everyone's opinion?

Thanks for the support guys!

[Pete Schumacher]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

Pete, thanks for the reply. (I really am amazed at the level of peer support on this forum - it is awesome!)

I appreciate your guidance on the design / driver choice. Unfortunately :p the driver must be down firing in said design or the SAF goes down unacceptably!

Can anyone recommend a 15" Dayton driver that can handle down firing, HT and will faithfully reproduce audio (not a muddy noise maker) all at modeled SPL's in the 112-115 range at 1 m? I really thought I found the right driver with the RSS390HF (Heaven knows I've been weighing that very decision for weeks), but perhaps not...

The curve design (shooting for a really deep F10 as opposed to the deepest F3) you advocate is something I had not heard of before. I will definitely take that under consideration along with not overamping the system! Thanks.

What about the bracing question? How much is JUST ENOUGH in everyone's opinion?

Thanks for the support guys!

Any time you mount a driver in the horizontal position, gravity will cause the cone to sag. Loose suspensions on heavy cones generate a low Fs, and those are the ones that will experience the most sag. Adire had a calculator for sag that I saved a while back.

Percentage of Sag = 24,849 / ( Xmax * Fs²)

Plugging in the RSS390 xmax and Fs generates a sag amount of 6.28%. That's a bit high. The solution for this condition is a woofer with longer Xmax. The Titanic would do the trick as it has significantly more Xmax than the 390. The RSS390HO would also be a better candidate with its higher Fs and lighter cone. Using its Xmax and Fs generates a sag of only 4%.

You lose a little bit of max SPL, but the HO can really perform in a box quite a bit smaller than the HF version.

In 4 cubic feet tuned to 16Hz, the F10 is still around 13.5Hz, but F3 is moved a bit higher. The slope is shallower for the HO version, and more extended. Even with the small sacrifice in excursion, you'll still have in-room levels exceeding 110dB from 30Hz down. Add a second coffee table and you're over 116dB. The HO also doesn't run out of excursion until you exceed 400W. Unloading occurs below 14Hz. The typical high pass on a sub amp should be down enough by then to keep things under control. If not, just tune a bit lower.

You can never have too much bracing. Just be sure to account for it when calculating the box volume. A cross brace every 6" or so should be adequate for most applications, 4" if you can handle the extra box size. Keeping those panels from moving during pressurization is what helps keep the sound clean and smooth.

Consider a 1" dowel rod underneath each mounting hole on the driver, running up to the top panel, creating a cylindrical cage. Then run cross beams from side to side.

[Mayhem13]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

I agree with Pete that the HO version would be a more suitable candidate for your application. Much more managable box size. Consider a slot port as once the math is done, construction is pretty simple. The HO models very nice in 4cuft with a 17hz tune and the built in HP filter Pete mentions will also go a long way towards reducing port noise if it's placed at or right above the tuning frequency. Yes , you'll loose a little bit of output but it'll offer a higher level of safety to the driver and make port construction/performance easier.

On the topic of slot ports, let's say you use the standard thicknes of MDF to your advantage....a slot port 1.5" high(dual layer MDF) by 10" wide gives you enough port area to keep air speed below 25 m/sec and results in a 26" long port...fairly easy to build into the box and add to the structural integrity. I've also used the 'birdcage' bracing method Pete mentioned and it makes for a very sound enclosure with minimal cost/effort. It also gives the driver screws something to really bite into and eliminates the hassles of T-nuts or hurricanes. A box of 18" wide by 20.5" tall by 28" deep gives you the volume you need with the slot port built in to the bottom of the enclosure with the port entry at the lower rear of the enclosure.

[kenmcculloch]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

Yo Fish. Good luck with the man cave project. Check out my recent thread on the end table sub. It is much smaller than you are considering but if you make nice furniture sub the SAF goes way up. See my link to the thread and the old antigue stuff - you may not be interested.

http://techtalk.parts-express.com/showthread.php?t=211193

Here's a photo of a fancier end table that is built like a battleship and has a downfiring 12" sub. about 4cf as I recall. If you're going to put stuff (drinks food etc) on the table you might want to inserts some sound deadening material between the inside top of the sub and the outside top. I've used perforated tool mat liner with carpet adhesive and it does deaden the sound/vibration on top.
Part of the fun is your friends don't know where the bass is coming from. Good luck withyour project.

[fish-24_7]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

Ken - what a great looking build! How did you secure the legs to the sides? I assume it's just MDF under the hardwood?

Pete/Mayhem - based on your guidance I will be changing to the HO version and running around the 4 cu ft range. May just have to build 2!

Thanks to all for your help and guidance!

[brianpowers27]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

Here is one I did recently. I think mine came out close to 75l. I use a rss315hf sealed. I have a pair of these tables. I forget the exact dimensions but it it is something like 20,20,27... Trust me when I say that this is more than enough bass for HT needs... I also house the amplifier in the rack, not on the table. It looks MUCH better this way.

[Pete Schumacher]

Re: Coffee Table Sub with Dayton RSS390HF-4 questions

Ken - what a great looking build! How did you secure the legs to the sides? I assume it's just MDF under the hardwood?

Pete/Mayhem - based on your guidance I will be changing to the HO version and running around the 4 cu ft range. May just have to build 2!

Thanks to all for your help and guidance!

More is definitely better!!! A second unit would be a great way to go. With proper placement, smoother response can result. And of course, there's that extra 6dB total output that wouldn't go unnoticed!!!