Ported subs or sound treatment - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 4 Old 12-13-12, 11:58 AM Thread Starter
Join Date: Jun 2008
Location: Boise, ID
Posts: 87
Ported subs or sound treatment

I'm on the fence on my next project for my HT. I've always been itching to port my two 12" Titanics but at the same time I've always wanted to venture into the world of sound treatments as well with some DIY panels.

I recently acquired a 2 x 400 watt amplifier which has spurred the desire to do some upgrading.

Below are my WinISD models for the titanics. If I do the sub build I will be building two sonotubes. I figured WinISD was good enough to calculate enclosure size and port length. I can handle converting all that into the volume of the cylinder. I plan on going with 14" cylinders, and using pvc pipe to build my ports.

First big question is, am I missing something with the sonotube calculations? I don't want to over simplify it but cubic feet is cubic feet regardless of shape

The WinISD files show a 22 Hz tune and a 25 Hz tune. Both models have a 20 Hz highpass filter on them. I planned on using the Harrison Labs in line filters (20 Hz) that I have lying around. The Titanic is flatter at the 25 Hz tune so I was wondering how much I would really miss between a 22 and 25 Hz tune. Given the models there is maybe a 2 dB difference. I'm inclined to go with the 25 Hz tune unless convinced otherwise.

Seems like a better model overall, flatter response and higher 1st resonance frequency with the port.

Everything I see on forums says tune to 20 Hz but when the 20 Hz tune is sacrificing response at higher frequencies is it really worth it?

Last question back to the sound panels. I would be building (5) 4'x2'x4" panels using Rockwool 60. Three on the backwall behind the couch and two as bass traps in the front corners of the room. Is that enough panels to make a noticeable difference in sound or is that just a good start? If that isn't enough I'll just build the subs.
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post #2 of 4 Old 12-13-12, 02:10 PM
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Join Date: Apr 2007
Location: Chitek Lake, Sask.
Posts: 19,397
Re: Ported subs or sound treatment

Enter your WinISD project info into Sonosub. It accounts for everything you need and it's a free download.

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post #3 of 4 Old 12-13-12, 02:23 PM
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Join Date: Aug 2008
Location: Pittsford, NY
Posts: 302
Re: Ported subs or sound treatment

Guiria wrote: View Post
...If that isn't enough I'll just build the subs.
Oohhh, where to start... this looks like a good place. Let's start with your objective - is it "do an HT project" or is it "improve the HT room's bass response?"

If the former, build the subs. If the latter, build acoustic treatments based on analysis of your room's acoustic needs. The latter may include subwoofer changes, but in service of a known objective.

Everyone likes the gear, but subwoofers interact very strongly with rooms, to both our benefit and our dismay. You have a pair of 12's; can I assume they're in 3.5 cu ft sealed boxes? That should be enough for them to work fairly well; this has to be the only Dayton sub I haven't modeled.
- what amp did you get?
- what kind of filters are you using (both low-pass and high-pass)?
- how large is the room? How's it build? Major features (doorways, windows)?
- how loud would you like it to play?

Three factors determine how much subwoofage you need to be happy:
- room gain, a function of room dimensions
- subwoofer frequency response
- amplifier frequency response

Assuming the goal is flat response, the trick is to pick the right amp to go with the sub/room combo.
- sealed with boost and little/no SSF
Let the air cushion protect the driver from over excursion and give it enough power to make up for the sealed FR characteristic. Takes more power, doesn't get as loud, but goes very, very deep.
- ported with no boost and strong SSF
Air behind driver no longer protects is, so strong electronic filter needed at low frequencies (unless LLT) and no boost. LF extension is limited, but it plays louder with less amp power.
- horn loaded with no boost and strong SSF
Same as above but larger, louder and cleaner.

If your new amps have some boost, or you have a signal processor involved, you may be all set. Nothing goes lower than big sealed....

Three factors determine how much subwoofage you need to be happy
- room modal pattern, also a function of dimensions
- subwoofer placement relative to the listening position
- room acoustic properties, primarily wall reflection efficiency for low bass

While you can't generally move walls around, you can understand your room's characteristics, and alter sub location and room treatments to achieve good sound in a limited listening area. Again, the assumption is that the goal is now "flat response over the entire listening area."

Modal analysis will point to potential problem frequencies. Room construction will determine the severity of the modes - cinder block is bad, wood framing is good due to their differing reflectance of infrasonic acoustic energy. If you're in a basement, major trappage may be needed, while room leakage above ground, and aborbance within the walls may take care of you above ground.

The idea then is to add frequency-specific absorbance to the room. Bass would include broadband absorbers arranged for bass effectiveness (your corner traps) as well as tuned absorber(s) if there are bad modes. At higher frequencies, room furnishings become important at some frequencies, requiring a little customization to maintain a flat reverbration time vs. frequency.

So... what's the scoop on the amps? What's the room like?

HAve fun,
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post #4 of 4 Old 12-13-12, 05:53 PM Thread Starter
Join Date: Jun 2008
Location: Boise, ID
Posts: 87
Re: Ported subs or sound treatment

fbov wrote: View Post
Let's start with your objective - is it "do an HT project" or is it "improve the HT room's bass response?"
Do a project while improving bass response

My titanics are each in a 1.5 cubic foot enclosure. Kinda small but not too far off of the standard .7 Qtc. Originally they were powered with a CS400x, only 200 watts per channel. Now that I've doubled the power I sit and think how not having these ported is leaving so much on the table.
- what amp did you get?
- what kind of filters are you using (both low-pass and high-pass)?
- how large is the room? How's it build? Major features (doorways, windows)?
- how loud would you like it to play?
-Amp is a Peavey CS800X, capable of 400 watts x 2 at 4 ohms
-Room is a bonus room over the garage roughly 15x20x8. One large window down a sidewall, an entry door, and a small closet. All AV equipment including speakers sit on shelves built into the wall. The subs will be moved out into the room if I were to build cylinder subs. I run a receiver with Audyssey MultEQ and have a BFD on top of that to fine tune the response if needed. Currently I only have two filters on the BFD after running Audyssey.
-As loud as it can without buying new equipment I actually rarely watch movies at anything higher than -10 db reference but when I do I want the goods to be working. 90% of movies are between -15 and -20 since I'm normally watching while kids are sleeping.

If the previously mentioned sound panel idea would be helpful then I'd consider it, If not then I probably won't. I'm not even sure about how to measure where a sound panel is needed and whether it should be broadband absorbing or targeted for high frequencies.

This is more of a goodbye to home theater for a while and last fun project to do before I move in the summertime. (Hopefully I'll be going to med school!).
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dayton titanic 12 , ported , sonotube , sound , sound panels , subs , treatment

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