Help! HT Sub Box Build & amp!

[Torgus]

this may be the wrong section but i thought you guys might have some ideas for me...

What box design should i design for these 12s?

I have 2 12'' RFR 1812 that are used.

http://www.fortunecity.com/sky....html <-- i assume these specs are correct.

Model RFR-1812Description 12" Punch Power WooferNominal Impedance 8 ohmsRe(DC Resistance) 7.08 ohmsPower Handling(RMS/Peak) 600/1200 WSensitivity 88.0 dBFs 27 HzQMS 3.24QES 0.51QTS 0.44Sd(Cone Area) 83.71 in2Vas 3.5 ft3Xmax 0.4 inVoice Coil Diameter 4 inMounting Depth 5-19/32 in(14.21 cm)

This is going to be a HT box.

I was thinking 7 cubes tuned to around 15hz? does that sound about right? or should it be around 20-25? also how large should the port be? any advantage to 1'' MDF? less box flexing? Should i make supports in the box as i'v seen other do to stop flexing?

Also i would need an amp to push them. does anyone have any suggestions? it looks like i need around 1200rms @ 4...everything i find online is over 1k for that much power. any ideas on a cheaper solution?

I'm hoping these will be extremely loud...thoughts?

oh and to finish the box i figured some textured dark grey spray paint and some rubber feet. i'd like to make the box into the coffee table but if i mount glass above it will it shake like crazy?
Modified by Torgus at 7:13 AM 2/19/2009

[Torgus]

bizump 38 views and none has any input???

i think i found an amp for it tho. $320 shipped and it should do 1400 @4 x1 which is good because until today everything i found was over a grand for that output.

i'm going to make a hinged faceplate for the front where the subs will be. easiest way i can think of doing it and slightly protecting them...thoughts?

again i need to know mainly how big of a box and what to tune the port to...

[Looneybomber]

I'm at work, so I can't write anything too indepth. Plus, once I get home I will plug those TSP's into my modeling software and see what I come up with, however I am seeing a BIG red flag right off the bat.

Xmax 0.4 in

For serious HT use, which I assume you're afting since you're wanting to tune to 15hz, you're really going to want at least twice that. Otherwise, you're going to run out of excursion very easily.

If you already own them and you really want to build something worth while, sell them. If you've not bought them yet, I can point you to quite a few other excellent options for HT use.

1" MDF: Can you use it? Yes. Do you need to, No. 3/4" will work fantastic so long as you have adequate bracing. Ideally I like to use 3-axis bracing and for the most part leave no gap between each larger than 12". You can also use 3/4" plywood and save on weight.

For an amp, the Behringer EP2500 is so far the cheapest watt/dollar amp available that's been 3rd party tested. I own one of those (woofer duty) and also a Crown CE4000 (subwoofer duty).

Here are the test results of the EP2500



Check out that low distortion and excellent S/N ratio. I used it to power the bookshelf speakers on my computer for quite a while.

Side note: HT speakers are usually very different than the not-so-awesome car based subwoofers. They're built differently with usually completely wrong TSP's. (fs too high, vas too small, xmax too small, Qts too high, ect...)

Here's a quick shot of my subs. CSS SDX-15's. http://www.youtube.com/watch?v=gz3s4jKqtTwI got them on sale for 270.00 shipped/each.

Amp, Behringer EP2500. Can be had for 270.00 shipped.http://www.bhphotovideo.com/c/....htmlIt's the cheapest place that you'll find them new. Even cheaper than eBay. Aww crap, it looks like they sold out quick. Umm...My next place to shop is http://www.djdeals.com
Modified by Looneybomber at 2:10 PM 2/21/2009

[Looneybomber]

If that EP2500 helps save a few $$, I would recommend selling those RF subs and buying one of these. http://www.youtube.com/watch?v=XWns-K7HDWI.

It's the Maelstrom-x by Exodus audio. A lot of technologies carried over from the old Adire Tumult. It seems as if everyone and their brother has one of these now. Some, even have four. Exodus is currently working on a 21" version also.

They (Tempest-x and Maelstrom-x) can be had at http://www.diycable.com. Prices just went up too. The Mal-x is now 395.00 plus shipping. Their introductory price was 325.00 shipped. I almost bought a pair and am now kicking myself because I didn't.

Other options (think usual suspects in the HT world) include the SDX-15's like I have. http://www.creativesound.ca/de...SDX15AV-15x or AV-15h from http://www.aespeakers.com These are fairly new.RL-p15 or RL-p18 from http://www.soundsplinter.com

There are other options too, but then you start getting into more nit-picky style builds.

You may notice that I only mentioned/linked to 15 and 18" woofers. That's because in home audio, air displacement (size of cone * distance cone moves) reigns supreme. It requires 2, 12's to equal the same displacement as 1, 18" with equal xmax...which typically larger speakers will also have a greater xmax. That means 12's are even further disadvantaged.

[Torgus]

Thanks for the reply. The only reason i want to use these subs is i have them and got them for free. also if i sell em i bet at most i'd get $100 bucks. i want to do this build as cheaply as possible and see how they turn out. Also if it works out well i'm sure a friend will buy my setup why i'm ready to upgrade.

Thx for the info on the amp. looks like i'll be picking one of those up.

If i ever redo it i'll use some better woofers for sure. probably 2 15s Fi Qs or something of that nature...

the only 'real' concerns now i suppose i have is what to tune to and how large the box should be. everyone has told me they really need to be in a larger ported box then what the manufacture recommends.

thx again for the reply!

edit: oh and some of the loudest SPL woofers in the world have the same Xmax as my sub. Fi BTL for instance. or here is one more SPL sub with 10 mm Xmax which is also a world record holder.. Pioneer 5000 spl.



I don't think that having a larger xmass means it will change or have a better the SQ or tonal quality of a sub with less xmass. or even more SPL necessarily...at least from readying this i dont: http://www.soundsolutionsaudio...=8375

If that EP2500 helps save a few $$, I would recommend selling those RF subs and buying one of these. http://www.youtube.com/watch?v=XWns-K7HDWI.

It's the Maelstrom-x by Exodus audio. A lot of technologies carried over from the old Adire Tumult. It seems as if everyone and their brother has one of these now. Some, even have four. Exodus is currently working on a 21" version also.

They (Tempest-x and Maelstrom-x) can be had at http://www.diycable.com. Prices just went up too. The Mal-x is now 395.00 plus shipping. Their introductory price was 325.00 shipped. I almost bought a pair and am now kicking myself because I didn't.

Other options (think usual suspects in the HT world) include the SDX-15's like I have. http://www.creativesound.ca/de...SDX15AV-15x or AV-15h from http://www.aespeakers.com These are fairly new.RL-p15 or RL-p18 from http://www.soundsplinter.com

There are other options too, but then you start getting into more nit-picky style builds.

You may notice that I only mentioned/linked to 15 and 18" woofers. That's because in home audio, air displacement (size of cone * distance cone moves) reigns supreme. It requires 2, 12's to equal the same displacement as 1, 18" with equal xmax...which typically larger speakers will also have a greater xmax. That means 12's are even further disadvantaged.

Modified by Torgus at 6:48 AM 2/22/2009

[Looneybomber]

Thanks for the reply. The only reason i want to use these subs is i have them and got them for free. also if i sell em i bet at most i'd get $100 bucks. i want to do this build as cheaply as possible and see how they turn out. Also if it works out well i'm sure a friend will buy my setup why i'm ready to upgrade.

Sounds good and in that case I can certainly show you some enclosure options. You can then pick what you want, because who am I to tell you what size/tuning of an enclosure you should use.

Thx for the info on the amp. looks like i'll be picking one of those up.

Do know that it has XLR and 1/4" inputs. No RCA's. You may also want an eq of some sort later. There are various options available.

If i ever redo it i'll use some better woofers for sure. probably 2 15s Fi Qs or something of that nature...

The Fi Q's will work, but due to their high Qts, they require huge boxes...and I'm talking in the 15-20ft area per woofer (30-40ft combined). Which is fine if you can build that big.

edit: oh and some of the loudest SPL woofers in the world have the same Xmax as my sub. Fi BTL for instance. or here is one more SPL sub with 10 mm Xmax which is also a world record holder.. Pioneer 5000 spl.



I don't think that having a larger xmass means it will change or have a better the SQ or tonal quality of a sub with less xmass. or even more SPL necessarily...at least from readying this i dont: http://www.soundsolutionsaudio...=8375

That information is completely useless when it comes to HT. That is all about SPL competition and so are those subs. They're useless in the HT world. Here's why...

For SPL competitions, guys will "burp" at what, 50-60hz? Well for each octave you drop, you must increase excursion by 4 in order to keep the same SPL. So if you're able to hit say 105db (anechoic) at 60hz with 6mm of total excursion, you'd then need 24mm of excursion at 30hz to hit 105db and 96mm at 15hz. In the music world, bass rarely drops below 30hz. In the HT world, there are a LOT of movies with <15hz content. War of the world has a scene with a massive amount of 5-10hz content. So you tell me excursion is NOT important. This is one reason why people will use helmholtz resonators (ports and passive radiators). FYI, 0.4in of xmax = 10mm. 20mm total (peak to peak) excursion. See why I said that was a red flag?

Well for all the modeling, I had to get more TSP's from the RF website.http://www.rockfordfosgate.com...s.pdfAccording to that site, the woofer only has a little over 6mm of xmax, so that's the number I used.

Yellow = Dual RF 1812's in a 16ft enclosure tuned to 18hzPurple = Single of my CSS SDX-15 in an 11.5ft enclosure tuned to 15hz.

Here is the transfer magnatude. This is how the speaker will perform in relation to reference (-0db). For an EBS (Extended Bass Shelf) I like to stick with around a 3db drop, but I don't like a huge shelf so my enclosures typically are a bit smaller than a true EBS3.(db from reference on the right. Frequency in hz on the bottom)

This shows how much power each can handle. The flatline represents the thermal power handling, the dip indicates how much power it can handle at it's mechanical limits. Notice that because of the Fosgate's lack of excursion, even though they can handle quite a bit of power thermally, they can't handle much mechanically before pushing them past their limits. The SDX-15 hits it limit around 1kw, the twin 1812's can handle 85w safely.(Watts on the right, hz on the bottom)

This shows the amount of excursion at the point where xmax is reached for each speaker. 85w (total combined power) for the twin RF's has it reach the 6.1mm xmax, 1kw for the SDX-15 allows it to hit 30mm xmax. This also shows how below tuning, the excursion goes crazy! That's why people will use subsonic filters.

Here is the output (SPL) at 1M with no room or boundry gain with the maximum power each can handle without exceeding xmax. 85w for the RF's, 1000w for the SDX-15. As you can see the single 15 certainly out paces the twin 12's because of it's massive amount of excursion. Still believe excursion is useless? In HT, displacement (cone size x excursion) wins.

And here is what would happen if you fed the RF's with 1kw of power. As you can see they exceed xmax by 350%, which will certainly cause them to fail.

So, moral of the story is you either need a much smaller box tuned quite a bit higher and use them as woofers for music, or build them in a large box, tuned low for movies, and get yourself a 100-150w plate amp.

Or, buy the EP2500 and be super careful. Then when you're ready to upgrade, I can point you to some good directions.

[Torgus]

Thx for all the info man! hmm maybe i should save the 12s for some stereo speakers? just for bumping to music in the house...then tune them to 35hz or so. I'm going to build some anyways and i suppose this stops me from needing other woofers.

again i'm trying to be a cheap a**. next cheapest sub i can think of would be a 15 type R. ever modeled one before?

thanks again for all of your help!

[Looneybomber]

Another option. Use them more as a midbass.

In the HT/home audio world, midbasses are getting more and more attention due to the small woofers used in tower speakers and because of the fact that subwoofers are getting more and more powerful. What's happend is that there's now a gap in performance. The subwoofers, with the awesome HT geared drivers available and the cheap amps we have now, are able to pound out the bass. The full range speakers can belt out some sound, but due to their small woofers, cannot keep up with the subwoofers right near the crossover point.

This brings about a couple problems. They either need to listen quieter, which just doesn't happen, or they have to raise the crossover point to the subwoofer from say 80hz to 120 or even 150hz. What that does is increase Intermodal distortion through the dopler effect and also increases the the directivity of the subwoofer, along with introducing more room effects into the midbass section of sound.

So what folks are now doing is building big massive subwoofers and operate them up to say 50hz. Then they build midbasses to place either nearfield (close to where you sit, with proper time aligning), or near their mains (L,C,R's), and will then operate them from 50-150hz.

Personally, I'm not a fan of midbasses and attribute them to a band-aid style product. The real problem are mains just don't perform to where they need to and really need to be upgraded. However, if a person can't upgrade due to size constraints, or for whatever reason, then a midbass may be your only option.

Right now I am in the process of building some L/R's. I'm still in the planning phase of designing the enclosure. It's a very long and hard process really. The shape, size, angle, and edge treatment of a speaker baffle all effect how the speaker will sound. Furthermore, the placement of each speaker driver on the baffle has a huge effect too. I'm also having to contend with time alignment, phasing, ripple effect, baffle step compensation, and floor bounce, which are all dynamic because if I change something to help one, it will change the others.

Designing subwoofers is EASY. Designing speakers is a little more difficult and wish I was farther along into my electrical engineering degree, but I will soon have to tackle the electronics part of the build; designing the crossover, which has to work with the physical nature of the speaker.

[Looneybomber]

About the bracing.

I'm a firm believer in either fully coupling the driver to the enclosure, or fully isolating the driver from the enclosure. With that said, here's my "test" enclosure I built for testing purposes to determine in-room response of my sub in various locations in my room. The reason I say test is this is a throw-away enclosure, I really have no use for it after I'm done.

here you can see the brace and the magnet fitting into it. Once I add the thick foam strip, it presses hard up against both the inside of the circle and the front (back of the magnet) of that inner support. That support is then coupled to all the rest of the panels in the enclosure, dispersing vibrations out and away from the front baffle where they're typically concentrated.



Once I have my inner skeleton built, I then glue on my outer walls.

BTW, I built that without a circular or table saw, just jigsaw, drill, and router, and used my back steps with a towel as my "work bench"