DIY subwoofer questions/thread

jinjuku

jcandy wrote: »

You'd want to equalize them together. Remember 2 subs will already work wonders for taming room modes. The challenge of separate sub eq has also been discussed on various forums.

Are you saying that you would apply the same filter and EQ to both subs regardless of location?

I agree work on placement and room treatments first. EQ as little as possible.

Outside of the distortion bug the other issue with the SMS-1 is it can't do stereo. With the DCX 2496 you could run your L/C/R through it and with the receiver set to Large fronts or Main+LFE use the xovers to take 80 or 90 and below and go to your subs.

thejck

OK so what is the best 15 inch driver for a sealed sub money can buy...hehehe.. ok I dont know what to put down as a $ limit but I would like to look at a few and see what would work best for my dual sealed sub setup.
So far the ones I have looked at are the TC sounds LMS-R 15, Dayton but the HO driver not the titanic, the tempest x2 and the AV15H from AE if I want to wait for a while and this one AV123 MFW-15 that i dont know anything about.
Any other thoughts. Isnt the TC sounds driver supposed to be excelent in a sealed setup due to its high xmax?

jcandy

jinjuku wrote: »

Are you saying that you would apply the same filter and EQ to both subs regardless of location?

Yes. Its not immediately obvious that you won't get a better result by separate optimization, but I've heard this issue discussed and the conclusion was that it was more complicated and not recommended.

jinjuku wrote: »

I agree work on placement and room treatments first. EQ as little as possible.

Right. Surely this is a good "general" approach.

jinjuku wrote: »

Outside of the distortion bug the other issue with the SMS-1 is it can't do stereo. With the DCX 2496 you could run your L/C/R through it and with the receiver set to Large fronts or Main+LFE use the xovers to take 80 or 90 and below and go to your subs.

Right again. You know, I thought about doing this with my FBQ2496, but discovered that its only appropriate for LF equalization -- again because of distortion issues. Perhaps the FBQ is cleaner. This is a separate topic, with all sorts of alternatives!

jcandy

thejck wrote: »

OK so what is the best 15 inch driver for a sealed sub money can buy.

I honestly don't know. I think the best 15 inch woofer (not subwoofer) may be among the Acoustic Elegance TD15s. What I do know about the Daytons is that for the money they are very hard to beat.

jcandy

As a baseline room-gain function, this can probably be assumed as a first approximation:

Face

Some more reading material: http://www.diyaudio.com/forums/subwoofers/8114-subwoofer-qtc-tightness.html

Great software: http://audio.claub.net/software/jbabgy/WBCD.html

jcandy

So, based on the plot above, you can see why a sub which is flat to 20Hz is going to sound unnatural (boomy) in a typical room.

jcandy

+1 for Jeff Bagby's software. In fact, I'm slowly porting all of it to linux.

ben62670

I like well implement PR's. You can get away with a smaller box than ported. Keep in mind that you do not need to calculate the volume lost do to the port being inside the cabinet. The problem is using software to design the box. Most would agree to build the box to the volume that you would to design a ported sub. You will need to tune it. An SPL meter is fine with some test signals via test CD or a PC. SVS has the correction chart for the Radio Shack meter. The lower frequencies are not measured very accurately with an SPL meter. Basically you write down the SPL level at say 10,15,20,25,30hz... You add more mass to the passive to lower the tuning frequency. This is how I did it with the PR's on my custom SDA's. The nice thing about that is you can tune your sub for different locations by adding or subtracting mass from the passive. Still for music I like the sealed box.

FTGV

I like the multiple sub approach and after some experimentation found that this arrangement suggested by John K works very well in my small-ish rectangular room.http://musicanddesign.com/DP_woofer_room.html

The two subs are nothing special,consisting of 12" Infinity drivers in small electronically assisted sealed boxes(essentially Bag End clones) .

greyford1979

I forgot to mention, if you ever do decide to go to ported if you are not happy with sealed...to give you an idea of size for the 15" I built for myself, the dimensions are 27"x20"x23". Which after subtracted for driver, bracing, port, etc. it's right at 5 cubic feet of volume and tuned to 15 hz.

JimAckley

How about the WAF factor for this? With the grill on, it shouldn't look like much more than any other entertainment center style table. One LMS Ultra 5400 and two 18" PRs. Using small neodymium magnets just below the paint to hold the grill on. Also, in addition to the front, the sides and back will be piano gloss black as well. I didn't have that done yet in this mockup, but just wanted to share with the class. :biggrin:

thejck

Are you building this? What is the length of that box?

wife says to me the other day that maybe 2 subwoofers are too much. So I am looking at single subs now. I really like the idea of using passives. If I am going with a single sub that would offset the cost of the passive drivers as well.
This one will be placed in the front corner of the room.

thejck

I see your thread now.. following closely..

JimAckley

thejck wrote: »

Are you building this? What is the length of that box?

wife says to me the other day that maybe 2 subwoofers are too much. So I am looking at single subs now. I really like the idea of using passives. If I am going with a single sub that would offset the cost of the passive drivers as well.
This one will be placed in the front corner of the room.

Well the beauty of a passive design is you can get the output of a ported enclosure without the additional volume required for ports. Obviously in my build, volume isn't a concern. But a PR system is great for those who have space constraints. Also, it takes port noise and coloration out of the equation.

If the Mrs is saying two is too much, consider an end-table project or full table project like mine. They never seem to mind when it looks good.

Now, keep in mind that a PR system generally requires 2x the excursion of a single driver, so you have to use two PRs. The way it's typically designed is the driver on the front with a PR on each side to cancel out vibrations. Never use a PR in a downfiring or upfiring configuration. The PR will sag with time if you do. Down/up with your driver is okay though. I did mine all front-firing for the sheer menacing look of three 18s. The consequence though is that I'll have to overkill-brace my enclosure, so it's gonna be one heavy SOB to move upstairs and get in place. Using 10s or 12s, you should be able to make a reasonably sized subwoofer.

JimAckley

I would register on the hometheatershack.com forums and ask those guys some questions. They've got some large forum sections dedicated purely to DIY projects.

Face

http://www.diyaudio.com/forums/subwoofers/

thejck

JimAckley wrote: »

I would register on the hometheatershack.com forums and ask those guys some questions. They've got some large forum sections dedicated purely to DIY projects.

I have been reading threads on that forum. Just havent taken time to register yet. Lots of good stuff on there. thanks for the tip

JimAckley

No problem. The site Face mentioned is a good one too.

What's your room like? Where are you wanting to place your sub? What's the associated gear that will be used?

thejck

Room dimensions
16 by 20 (10 foot ceilings)..open to kitchen along 16 foot length kitchen area is 30 feet long. there are then door size openings (no door) to the dining room and foyer.. foyer is height of 2 stories.

I have SDA 1.2 that are powered by a parasound amp and a 2 channel preamp. not sure if I want them hooked up to the sub and not sure how I would be able too since the preamp doesnt have any sub management.

I want to add the sub to the receiver I have in the same room. This runs to a set of rti10's csi5's and rt55i's. The front towers are powered by another 2 channel parasound amp.

Initially I wanted to have 2 seperate subs on the back wall of the room on each side of the couch. However now after moving things around I might be able to do a single sub in the front corner of the room.

thejck

Face wrote: »

Here's an option for amplification: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-811

I like how it's rack mountable like a pro audio amp, but has many more features to help tune in the sub(s).

If I use an amp like this which is rated at 950 watts RMS at 4 ohms and I have 2 drivers hooked up to it in such a way that the combined resistance is 4 ohms.

If each driver is rated for a max RMS of 1000 watts RMS and say I, hypothetically, was really pushing the sub like crazy. What does the fact that there are 2 drivers each rated for 1000 watts connected to it do to the amp?

My physics classes from a long time ago says that since the amp is seeing a 4 ohm load that all it cares about and should be fine. But then again I was never very good at physics..:-)

JimAckley

thejck wrote: »

If I use an amp like this which is rated at 950 watts RMS at 4 ohms and I have 2 drivers hooked up to it in such a way that the combined resistance is 4 ohms.

If each driver is rated for a max RMS of 1000 watts RMS and say I, hypothetically, was really pushing the sub like crazy. What does the fact that there are 2 drivers each rated for 1000 watts connected to it do to the amp?

My physics classes from a long time ago says that since the amp is seeing a 4 ohm load that all it cares about and should be fine. But then again I was never very good at physics..:-)

The subwoofer's wattage rating means they're capable of having 1kW RMS driven through them. It doesn't mean that each subwoofer is going to attempt to draw 1kW from your amplifier. So to your answer your question, it does nothing to your amp. The only thing that really changes your amplifier's output is the overall impedance it sees. Your physics class was correct

To dive in a little further: your amp is putting out 950w RMS @ 4Ω, and you've got two subwoofers conneted to it, your two subwoofers will split that 950 in half. They'll each receive approx. 475w RMS at your amplifier's maximum output. If you wanted to power them up to their maximum potential, you'll want an amplifier capable of around 2kW @ 4Ω.

thejck

OK..well some dreams never die. I am back to dreaming about this sub build with a few changes in my ideas. One I am going to bring my Velodyne 15 inch upstairs to the living room from the theater room. I decided that my 1.2 do not need subs and so it will be hooked to my receiver and only be used for movie/tv duty up there.
Now I want to build the subs for the basement room.
Due to cost restrictions I am thinking about the cheaper dayton reference drivers. Due to me being a man I am thinking about the 15 inch ones the RSS390HF drivers.

here is my plan to keep the wife happy.
I had a wooden stand built for my TV and used that wooden plank to hide the space underneath which is essentially wasted. I can fit 2 fairly large passive sub boxes in there. and then I can replace the plank with a similar size grill and the subs will never be seen.
I will use a regular rack mount amp to power them so that takes care of the problem of ventilation.
The boxes will be built slightly smaller than the opening so that its decoupled from the sides and so should not cause vibration to the tv stand (I HOPE).
The 15 inch driver will have a clearance of about 1/2 an inch on the top and bottom the box external dimensions will be 17.5 inch tall and 27 by 27 wide and deep.
the internal size would be about 5cuf. it will be well braced and I will be using 3/4 MDF and might do 3/4 inch plywood in the front so that I can stain it to match the cabinet.

Anyone have any thoughts on this?
Is there anyone that can tell me what kind of problems/advantages I would have placing them in the front of the room like that?
The room is about 16 wide and about 18 to the back with a double wide pocket door open to the rest of the basement.

thejck

any thoughts?..i know we have some sub builders here

JimAckley

Let me dig a bit and I'll hit you back with my .02

thejck

JimAckley wrote: »

Let me dig a bit and I'll hit you back with my .02

apreciate it.

JimAckley

That sub models well. It's a shame you don't have that whole bottom area to use for one instead of it being split into two areas. One enclosure for one sub tuned to 17 Hz that fills that whole area would've given you a super-flat response down of approx 114dB down to 23 Hz, with a -3dB point of 16 Hz. What a beast!

That being said, for your given dimensions, it would need some equalization in the 20s to flatten out, should that be what you desire. A pair of these is going to be beastly. Tomorrow I'll model the 15" and 12" from the various Dayton lines, and throw some comparison graphs up in this thread so you can see what you can expect to get out of your usable enclosure dimensions with the various drivers.

-Jim

thejck

My receiver has Audyssey and has a boost point down to 25 hz. Can that just work for boosting the signal there?
I wanted to do sealed cause I wanted to keep it simple seeing that this will be my first build. I had wanted to do with a TC sounds driver but for the cost I think 2 dayton 15's could be able to keep up with that easy.
Do you see any problems with the placement in the room?
From research the HF driver does not need a lot of amp and needs a filter to protect it.

JimAckley

Well the "problems" of placement are honestly better discovered via trial and error.

I'll model sealed vs ported and get back at ya. Going ported isn't that complex. I'll help you where I can.

JimAckley

After graphing everything, get the 15, build a box of the dimensions you gave me. If you make it a vented enclosure, you'll gain a few dB in the 30-40Hz region. Slot porting is easier, but round ports (e.g. PVC pipe) will consume less interior volume and has a little less surface area to potentially cause turbulance. You'll either want two 4"-diameter ports @ 28" long, or one 6"-diameter port @ 30.5" long. If you'd rather do a slot port, a 2"x15" port along the wall of the enclosure @ 35" long will get the job done. These all achieve an approx. 20Hz tune. Be sure to round-over your port's edges to decrease turbulence.

An enclosure this size will most definitely need bracing. Some people like to do a double-faced front and recess the driver for an even sleeker look, plus the benefits of a less-resonant baffle.