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Old 11th June 2001, 10:13 PM   #1
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I want low. Serious low.

In my house, my main room back up to the garage, so I figure I can port / mount subwoofers into the main room while keeping the enclosures in the garage. This opens up all the possiblities since it eliminates the WAF (other than the money, but what the hell). Limitation is the 16" spacing of the stud wall. Would like to keep the opening into the room limited to that 16" square more or less on each side of the wall. Wall length roughly 15'.

So I can go for TL, closed, vented, even IB. I am looking for accuracy, depth and SPL (sorta the Trinity, isn't it?). Which way do I go?
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Old 12th June 2001, 02:23 AM   #2
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...low. Serious low.

Well, okay...let's start by defining by what you mean by serious low. That will determine the accuracy, SPL, and price you're going to be looking at.
1) What kind of music do you listen to? Serious low for chamber music isn't the same thing as serious low for a dedicated organ fan.
2) Most people haven't a clue as to what real low end sounds like. They hear these pathetic boom-boom sound systems in cars at stop lights and think that's low. *Harrumph!* High SPL, yes. Low frequencies, no. Rock/pop/rap/etc. music has no serious lows (excepting keyboards, and that capability is rarely used). Four string bass bottoms out at about 42 Hz; six string basses in the low 30's. Movie soundtracks (should you be thinking home theater--you didn't specify) rarely go below 40-50 Hz, and yes, that includes explosions and such.
Okay, enough of that. The point is for you to define your parameters. Part of that is to educate your hearing as to what true low end is, so that you'll know it when you hear it. (And not be fooled by a loud 50 Hz pretending to be 12 Hz).
->Accuracy: To a first approximation, accuracy isn't going to depend on the cabinet design. It's a function of the quality of the driver.
->Depth: About the best you can hope for with unaided drivers is going to be -3dB in the mid 20's. You can rule out horns before you even start, as the mouth of the horn defines the lowest frequency that the horn can reproduce and a horn that would carry into the 20's (better still, teens) would take up the entire wall of your room. Horn distortions are another matter entirely, but we need not go into that as horns just ain't happening as far as deep bass goes.
->SPL: This translates as how much air gets moved. You have two and only two choices--you can use few drivers and pump them hard (lotsa excursion), or more drivers and lower the excursion. The more excursion, the more distortion. The more drivers, the more costly. Yes, larger drivers more more air than smaller ones. They're also slower, which translates as distortion.
Now, I throw in two wild cards. There are ways to get as deep as you want, but you have to implement them in the electronics.
->Start by knowing your low end frequency response. Design a circuit that will steadily increase the power as the response drops off. This isn't as hard as it sounds. I've played with two or three variations on this over the years, the most recent implementation being four KEF B-139 drivers per channel which I ran with a Threshold S-500 and a nice little circuit that ramped up the power until the mid-teens, then dropped like a stone around 12 Hz or so. Deep, yes. But I never got the SPL I wanted (and I don't listen nearly as loud as a lot of people do) before the whole thing got muddy. Most people wouldn't notice, but I've been playing bass for nearly thirty years, and I don't take 'almost' as an answer for my low end needs. In fact, I've never heard a system using this strategy that I thought was as tight as it could be. A buddy of mine has a set of Kinergetics subs that do the same thing (they choose to call it 'feed-forward,' a term I'm not happy with as it means nothing) and they don't even sound as good as my old KEF subs, although they will play somewhat louder.
->Include the drivers in a feedback loop. There are various ways to achieve this, but most folks use a piezo element in the driver itself as a feedback sensor. This system has the advantage of not only extending the low end response, but lowering the distortion as well. This is the avenue I'm exploring now, but the project's on hold whilst I settle a few other little issues, like the water-cooled Alephs and so forth. I'll be getting back to it soon. For the time being, I've just got standard Thiele-Small enclosures that go down to the upper 20's.
Note that both of these strategies require *lots* of amplification, as they both push harder as the driver tapers off. You have been warned. The upside is that you can go clear into single-digit frequency ranges if you're really serious about your low frequencies. This is not an option with any unaided driver design.
As for cabinetry, it's going to depend on whether you want to go passive or active on these things. I would not, for instance, recommend transmission lines with the 'feed-forward' system. On the other hand, if you go for just a driver in a box, TL's can be fantastic sounding. They are not particularly efficient. Sealed boxes (infinite baffles, totally enclosed boxes...whatever you want to call them) can do well, as can bass reflex enclosures. If you're sticking with straight drivers, the Thiele-Small parameters of the driver you choose will tend to guide you towards one or the other.
If you're getting the feeling that the map is reading Here Be Dragons And Things Unknown, you're right. Make a few basic decisions, then we'll hack at it some more.
Oh, and decide how much you can spend. I bought twelve 12" drivers (6/channel) of a non-trivial variety, and then parts for twelve channels worth of amplification (one for each driver with dedicated feedback loop) and it cost more than a penny or two. Enter into this with the idea that--if you meant what you said about wanting serious lows--you're going to drop serious money.

Grey
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Old 12th June 2001, 10:22 AM   #3
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Default Better reply than expected! Thanks

I had my ears educated many years ago by an organ freak with a 24" Hartly in a 30' TL. Then worked a few years in the sound business, so I have reality measures when it comes to low. 40Kw of Crest amps into Meyers subs (which was the best setup at that time in the business) at 32Hz is approaching pain. It has just been some years since I have been in it, and I would like to get back (now that I have money {g}).

The amplification is done - I have two DH500's that mono out to about 800 into 8ohms. I expect to do some active EQ with the subs. I know that they are old, but unless I hit the lottery, they will have to do for now. Might have to be recapped given their age. Efficency is needed too.

As for the listening requirements, music is what drives the real desire, but movies are an interesting plus. I listen to a wide varity of things, but am drawn to that which has real energy in the bottom. No JBL hump for me. I suspect my real limitation on size and drivers is that opening in the wall.

I pose this question this way since I have no idea what the state of drivers are at the moment. I suspect the kids have driven the industry one way or another, as well as the effect of A/V subs. Without doing a huge spreadsheet of the available drivers with all the box possibilites ran through the software sims, just where does one start? What driver is a reasonable value for the money/sound. I realize that is almost a holy war issue, but I suspect there are a set that most agree are reasonable, even if the group might disagree on the *best*. I suppose the drivers will then make many of the decisions for me.
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Old 12th June 2001, 02:05 PM   #4
Eric is offline Eric  United States
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Lightbulb Low frequency content in movies & music

Try <a href="http://www.svsubwoofers.com/faqs.htm">this link</a> for a list of movies and music CDs that contain very low bass. Bass in movies is increasingly approaching the 20Hz mark and some are coming in significantly lower than that! The web site linked above has waterfall plots of bass in music and movies.

As for new drivers, there are quite a few worth your attention, depending upon your budget. Have a look at the following:

<a href ="http://www.adireaudio.com/cd/shiva.htm">Adire Shiva</a>
<a href="http://www.adireaudio.com/cd/tempest.htm">Adire Tempest</a>
<a href="http://www.audiomobileinc.com/masssubs.htm">AudioMobile Mass Series</a>
<a href="http://www.partsexpress.com/pe/showdetl.cfm?&Product_ID=7773&DID=7">Dayton Titanic</a>

There are others, but this is just a starting place. You will also want to download some enclosure modeling software like <a href="http://www.linearteam.dk/">WinISD</a> and have a look at the forum for the <a href="http://f20.parsimony.net/forum36475/">Cult of the Infinitely Baffled</a>

One final link contains tons of information about tools, techniques, etc for <a href="http://members.tripod.com/~terryctheater/shivaphotoalbum/page12.html">building subs</a>. Most of the ones here use "sonotube" material to build enclosures, but there are lots of other resources as well.

Hope this is a good starting place for you!

[Edited by Eric on 06-12-2001 at 09:12 AM]
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