TL subs in the Attic? and Triangular Cabinets

[ralph-bway]

Hi all,

Besides my intro this is my first post, so please be ......... gentle.
Some of the questions may be foolish, but I'm relying on you to unsilly me. Thanks

I would like to install TL subs in my attic where I would have virtually no size constraint considerations. My questions are:

Everything I've read about TLs is to have a path 1/4 of the wavelength of the Fs you're looking for. Is a path 1/2 or (oh my god) the full wavelength a feasible thing?

I have never heard of using a passive radiator at the end of the TL line. Has this been tried?

Would the Peerless 10" subs (831727) I have now be OK firing down from the ceiling or are other subs made differently (and for this direction of firing)?

Finally (at least about subs) since I have a lot a flexibility about where the driver & mouth of the line would be; would it be a good or bad thing to have the sub drivers mounted near the front of the room and the mouths of the line directly over my sweet spot chair?

Now for the mains:

From what I've read spheres seem the best enclosure (not feasible for me) and and uneven triangle with sloped side walls 2nd best (fits in the room).

I'd like to have the speakers on the wall at the ceiling corners. The cabinets would be constructed with the drivers angled down & in to my listening chair.

Would this placement be a horror or could it work?

Thanks again, I look forward to hearing from everyone & hope someone else finds an answer to a question they might have.

 

[ralph-bway]

Additional Info

I should have added that the den this is all happening in is 18' long x 11' wide with an 8' ceiling.

Also I have this wonderful deal with my wife. I can do whatever I want in the den, but have no say in the rest of the house, or access to the credit cards, or check signing. All in all a fair deal.

 

[roddyama]

Hi Ralph,

Welcome to the forum. The TL in the attic is a great idea (a good winter project, I'd hate to be up there in the summer ). Planet 10 (one of the forums peace keepers ) is the TL guy. Hopefully he'll come pay a visit to provide some guidance in this regard.

WRT the main speakers in the ceiling, I only caution you that you will limit your placement options. Getting a pair of speakers to work in a room can, at times, be very difficult. This can become an impossible situation if the speakers are locked in a fixed position. I have always like to have my speakers a couple feet away from the front wall. It tends to add to the image depth. I think I would stick with floor placement.

What! No That's no fun.
Rodd Yamas***a

 

[jgwinner]

Even better than a TLine, If you are going to put subs in an attic, use an Infinitely baffled" setup. You just put the 'back' end of the sub so that it radiates inside your attic. This is essentially a 'perfect' enclosure - see Cult of the Infinitely Baffled Gallery There's a forum as well.

 

[planet10]

I would like to install TL subs in my attic where I would have virtually no size constraint considerations.

Good idea. I plan on building some in the ceiling area of my shop (12' ceilings) firing into the listening room (there is a convienient split-level right behind the speakers).

Everything I've read about TLs is to have a path 1/4 of the wavelength of the Fs you're looking for. Is a path 1/2 or (oh my god) the full wavelength a feasible thing?

No matter how long you make it, once you close one end of the pipe and open the other you have a quarter-wave resonantor. It is actually better to have a line a little short than too long.

I have never heard of using a passive radiator at the end of the TL line. Has this been tried?

Shahinian does this in some of their models.

Would the Peerless 10" subs (831727) I have now be OK firing down from the ceiling or are other subs made differently (and for this direction of firing)?

That would probably work fine -- i don't recommend firing it down thou, you will decrease its lifespan at minimum.

Finally (at least about subs) since I have a lot a flexibility about where the driver & mouth of the line would be; would it be a good or bad thing to have the sub drivers mounted near the front of the room and the mouths of the line directly over my sweet spot chair?

My 1st reaction was no, but i'm giving this some thot. Usually the terminus and driver are approximately equidistant from the listener. Your lines are going to be 12-13' long (for the Peerless). I personally like to get the terminus tucked right up next to the driver.

Now for the mains:

From what I've read spheres seem the best enclosure (not feasible for me)

Better than spheres are half elipsoids that taper away at the back (ie a teardrop is an example) The B&W Nautilus are a good example.

uneven triangle with sloped side walls 2nd best (fits in the room).

Anything with non-parallel walls.

I'd like to have the speakers on the wall at the ceiling corners. The cabinets would be constructed with the drivers angled down & in to my listening chair.

This is where i was thinking the woofers would load into the room. Probably not an ideal place for mains. That said one of the fellows on the FR Forum has a set of open baffles he has cut so that they fit into the rooms corners and reposrts good results. An open baffle is big thou and his drivers are not actually in the corners -- imagine 2 sheets of plywood trimmed to fit up in the corners.

As Rodd says, better placement is usually out in the room and some flexibility to play with position is almost certainly a reuirement to getting the best sound.

Would this placement be a horror or could it work?

Likely the former

dave

 

[ralph-bway]

Thanks

Thanks for the input guys, and you got me thinking (this is where my wife usually says oh-oh).

John - thanks for the link to IB, it's very interesting but seems be overpowering.

Rodd - I figured since the mains would be rolling off at 80hz the bass boost if at all present could be compensated for. I didn't realize I would be hurting the image depth.

Dave - You made some points that raised some questions for me.

I've looked around at your site & Subwoofer DIY and could use the wave length for 22hz.

How many degrees of downward tilt (if any) is possible without accelerating the demise of a driver?

You said you prefered a shorter rather than longer line. Why? I thought the advantage of a longer line was that it didn't have to be dampened as exactly as a shorter line.

I thought if the rear radiation from the driver has to travel 12-13' before exiting the terminus and the terminus is equidistant from the listener doesn't this put the signal from the rear of the driver significantly delayed from the front of the driver signal, or is trying to get both signals there at the same time helping phase cancelation?

Thanks again everyone.

 

[planet10]

Re: Thanks

I've looked around at your site & Subwoofer DIY and could use the wave length for 22hz.

speed of sound divided by the frequency, in this case 1130/22=51.4'

How many degrees of downward tilt (if any) is possible without accelerating the demise of a driver?

Just mount the driver in the regular orientation.

This version doesn't consider that you will probably need an offset to kill the 1st harmonic.

You said you prefered a shorter rather than longer line. Why? I thought the advantage of a longer line was that it didn't have to be dampened as exactly as a shorter line.

An ideal line is 1/4 the Fs, a shorter line can be given a bit more damping, you can't do anything about a line that is too long (ie you can't speed up the speed of sound (well you could fill it with liquid, but that is probably impractical)

I thought if the rear radiation from the driver has to travel 12-13' before exiting the terminus and the terminus is equidistant from the listener doesn't this put the signal from the rear of the driver significantly delayed from the front of the driver signal, or is trying to get both signals there at the same time helping phase cancelation?

The terminus output derives from the out-of-phase back radiation of the driver -- you need the delay to bring it into phase with the front.

dave

 

[ralph-bway]

Design

Dave that drawing is elegant in it's simplicity. What are the 1st harmonics? What taper ratio have you found successful?

 

[jgwinner]

I don't understand this at all - why not just go with an Infinitely baffled sub? My understanding is that transients are near perfect (no resistance to the cone moving), and output is high as you don't have to wory about the dipole wave cancelling anything. Is there something the extra complexity and extra hole's of the TL give you?

 

[navin]

Dave,

the driver and the TL end in the same mouth. does not seem kosher to me.

taper I have found that works is 1.25Xsd at the begining to 0.75xSd at the end or 1.5Xsd at the begining to 1xSd at teh end.

cheers

 

[planet10]

I don't understand this at all - why not just go with an Infinitely baffled sub? My understanding is that transients are near perfect (no resistance to the cone moving), and output is high as you don't have to wory about the dipole wave cancelling anything. Is there something the extra complexity and extra hole's of the TL give you?

An infinite baffle can be very good. The system will have the Q of the drivers (pretty much) so you want to limit your choice of drivers with Q=0.5-0.7 unless you want to use EQ.

The TL can use a lower Q driver, and you have the potential to recover some of the energy from the back of the driver. A TL is tuneable. It can range from a 4th order system were efficiency is maximized, to a system with 2nd order system (terminus output is reduced). In all cases the driver resonance is damped for flatter impedance curves.

There is also weather to consider.

dave

 

[planet10]

the driver and the TL end in the same mouth. does not seem kosher to me.

You have to be a bit careful but it isn't a problem.

taper I have found that works is 1.25Xsd at the begining to 0.75xSd at the end or 1.5Xsd at the begining to 1xSd at teh end.

A better rule of thumb (based on systems designed with King's or Augspurger's sw) are 3 Sd for straight pipes, 3:1, 4:1 for tapered TLs, and 1:5, 1:6 for voigt pipes (with a restriction at the end of the pipe). Actually Sd has nothing directly to do with the enclosure cross-section. Vol = f(Vas). Since the optimal line length = f(Fs), that gives us a cross section. The driver can be placed along the line so that the resonances from the 2 linelets mostly cancel the 1st harmonic The graph shows the unstuffed line response -- all the peaks and valleys are from the rotating phase of the terminus. The stuffing and the line geometry are used as a Low Pass filter to try and kill all but the fundemental resonance and remove the ripple.

dave

 

[peterr]

ralph-bway,
Interesting project! I did something similar but on a much smaller scale. I built a TLsub inside the space of a doorway we did no longer need. Soon to be featured on planet10's website. The design was heavily influenced by the articles of Martin King. (to be found on planet10's site) He has written software to simulate the behaviour of your TL design. It was a great help to come to something that really works. The best advice I can give you is to download it and just play around with it for a while. You then develop a far better grasp of what you will need to do. It may turn out that what you need is a lot smaller then you expect (thats what happened to me, eventhough it is still about 400 liter ) Who knows, you may even keep some storage!
Anyway, good luck

 

[ralph-bway]

Dave & John

Hi guys, please clarify something for me. I've been under the impression that to get the most accurate & natural bass TLs were the way to go. IBs would be much easier to build, install & maintain than a TL and are very attractive in that regard. Thanks for the help & I passionately hope I'm not starting a clan war (well at least not a bloody one).

Best Ralph

 

[jgwinner]

Don't look to me for an answer

I haven't done as much research into IB's as I wanted, mostly because for me the only area I could install an IB is behind our listning position and about 8' UP. We have a cathedral ceiling but the client 'tilts' down to the front of the home theater. The area behind the seating area has a small attic above it. We were going to put the couch facing the OTHER way in which case they would be perfect for the front channel, but I'm not sure I like the idea of the sub woofer being behind and high above our heads.

For the rear channels, I think it's not good positioning either.

Anyway, the long and short of it is that Dave probably knows much more about TL's than I know about IB's so I can't give a good comparison. I would say to read up on the links I provided for the answers, or post in the IB forum.

Yep, this is all confusing

 

[planet10]

Anyway, the long and short of it is that Dave probably knows much more about TL's than I know about IB's so I can't give a good comparison.

Here an IB would be an ideal thing to try out.

People build TLs because you can get away with a smaller box.

Choose your drivers carefully. I like to use them in push-push pairs(4-10s instead of 2 -12s, 4-12s instead of 2-15s sort of thing).

a couple possibilities:

Do you have any problems in the attic with weather, small mammals or birds, or members of the six-legged majority?

dave

 

[Oz_Audio]

Dave,

Wounderful stuff, this has realy got the grey matter going.

I like your first design, the TL in the roof. I have 2 Peerless XLS 12" and I think they may work. 2 TL for stereo bass, one on each side of the roof directly above the TLb's.

Size is not a problem so the department of war and finance will be OK.

How long would you make the TL? (I do not have MathCad to use your software).

Mark

 

[ralph-bway]

IB design

Dave this all brings up another question I've had.

It would seem that if sub driver or or port were pointed at the listening area the output would be more pronounced than where the sub driver or port were firing up or down or whatever and the listener was getting the reflected output. If this is true what about mounting the sub drivers on the back wall and venting the rear radiation up to the attic & the great beyond?


About my attic conditions:

No two, four, six, or other legged homesteaders.

I am on the shore, but humidity doesn't seem to be a problem in the house or attic (nothing seems to rust up there as opposed to any tools I PREVIOUSLY left out in my shed).

I have three exhaust fans up there on a themostat so heat and humidity are not problems.

Thanks again, Best
Ralph

 

[planet10]

How long would you make the TL? (I do not have MathCad to use your software).

What are the Peerless specs?
There is a link to MathCad explorer on my site. (and lets call it Martin's software -- i only provided the venue).

dave

 

[planet10]

Re: IB design

It would seem that if sub driver or or port were pointed at the listening area the output would be more pronounced than where the sub driver or port were firing up or down or whatever and the listener was getting the reflected output. If this is true what about mounting the sub drivers on the back wall and venting the rear radiation up to the attic & the great beyond?

At sub frequencies there is no directionality -- it won't care how it gets out to you.

The little box on the wall, venting into the attic is one that crossed my brain, but i was saving it for later. It will work fine. It will all come down to what is most appropriate to fit into the structure of your room.

dave