Possible New LLT project

[Bob_99]

I have been vacillating for some time now between IB and LLT and so far the one driving point to making me lean toward the LLT are the cold winters here in New England. I can't afford to have cold air pouring down from the ceiling in the dead of winter. In any case, I'm moving my questions from the IB forum to here since I'm leaning in this direction. I'm wondering how putting the LLT on top of the joists with the drivers firing down between them will work. I see no reason it shouldn't but then again, my knowledge of this stuff is pretty limited.

I've been looking at dual IB-Q18 and this current configuration seems to model well in WinISD (can't post pictures):

[ProjectInfo]
Description=
Creator=Bob_99
CreateDate=20080403
ModifyDate=20080404
[Driver]
Brand=Fi
Model=Q18
Manufacturer=Fi Car Audio
ProvidedBy=Bob_99
Comment=
DateAdded=20080402
DateModified=20080402
Qts=0.567482447248976
Znom=4
Fs=23.8690647428854
Pe=0
SPL=89.6895298934095
Re=2.8
Le=0
fLe=0
KLe=0
BL=15.1
Xmax=0.027
Cms=0.00013
Qms=5.73
Qes=0.629862153399143
Rms=8.95131323837812
Mms=0.342
Sd=0.121
Vas=0.26999687715
Dia=0
Vd=0.003267
no=0.00566899329821541
Dd=0.39250730555361
EBP=37.895696088537
numVC=2
Hc=0
Hg=0
SPLmax=0
SPLmaxLF=110.847463269515
USPL=94.2536782904731
alfaVC=0.0039
Rt=0
Ct=0
gamma=44.1520467836257
Rme=81.4321428571429
Mpow=9.02397600047467
Mcost=0
Gloss=0.0161482836666667
VCCon=2
c=343.68275625794
roo=1.20096171470853
Thick=0
Depth=0
MagDepth=0
Magnet=0
Basket=0
Outer=0
Vcd=0
DVol=0
ParState=CCNCENNNEENEECCCEECCNCCENNNCCNNNCCCCNCNNNNNNNNNCC
[Box]
BType=1
Vf=0
Ff=0
Qlf=10
Qaf=100
Qpf=100
Vr=2.04048172574027
Fr=5.50947098159542
Qlr=10
Qar=100
Qpr=100
Vc=0
Fc=0
Qlc=0
Qac=0
Qpc=0
Qiclfr=100
Qiclfc=0
Qiclcr=0
T=293.147777777778
p=101325
phi=0.3
d=1
Med=0
Nd=2
Angle=0
Isobarik=0
alfaVC=0.0039
dTVC=0
Sdfport=0
Sdrport=0.0182414692475099
[VentFront]
Num=1
Shape=1
Fb=0
Vb=0
dia1=0.102108
dia2=0
carea=0
len=0
endcorrection=0.732
crosscalc=1
[VentRear]
Num=1
Shape=1
Fb=5.50947098159542
Vb=2.04048172574027
dia1=0.1524
dia2=0
carea=0.0182414692475099
len=0.76962
endcorrection=0.732
crosscalc=1
[PlotSettings]
Color=33023
Width=1
[SignalSource]
Rg=0.1
P=400
[Filters]
Count=0

I'm wondering if one of the more knowledgeable people on this site could look at this and see if I'm on the right track or sitting at the bus station with a train ticket . If you copy the file, save it in notepad as a text file and give it the appropriate file extension, you should be able to view it in WinISD.

Thanks for any thoughts.

Bob

[Mike P.]

Here's Bob's Dual Q18 modelling.

[Bob_99]

Mike,

I'm not sure how you did it but thanks for posting the image.

Bob

[Mike P.]

Bob_99 wrote:

Mike,

I'm not sure how you did it but thanks for posting the image.

Bob

No problem. I uploaded it to PhotoBucket.

[ccdoggy]

Is that tune a bit too low?

[Bob_99]

ccdoggy wrote:

Is that tune a bit too low?

I'm not sure. The room is a shared space 37'L x 17'W x 9'H. Where should it be tuned?

Let me put it this way, it was the one configuration where everything seemed to be normal. If I changed anything, some other parameter would go wacky. If you have a sense of humor, there's a lot of entertainment value in WinISD as you push down one parameter only to watch another one go beserk.

ANY suggestion is really appreciated.

Thanks
Bob

[Mike P.]

I'n not sure what you mean, Bob. If you raise the tuning to say 13hz, it will affect the cone excursion.

[Bob_99]

As an example, if I raise the tune to 13Hz then the Transfer function magnitude graph develops a peak at the low end of the curve. I'm not sure how to interpret that. After that, getting the port velocity down to something reasonable becomes an issue. If you have the data, can you try to change the tune to see if you're getting the same results?

Thanks.

Bob

[a1161979]

Bob_99 wrote:

As an example, if I raise the tune to 13Hz then the Transfer function magnitude graph develops a peak at the low end of the curve. I'm not sure how to interpret that. After that, getting the port velocity down to something reasonable becomes an issue. If you have the data, can you try to change the tune to see if you're getting the same results?

Thanks.

Bob

How long would the port be for a 5hz tune.... Far too long to be pratical! Have you read Steves LLT Explained thread? From memory when Rodney converted his IB he tuned to 11hz, tunning bellow this is a little pontless, you would be better off with a sealed sub

As for the peak try reducing volume until the graph is flat/rolling of to tuning then heading downwards steeply bellow

Please go read Steves thread here http://www.hometheatershack.com/foru...explained.html and read it from front to back... Twice because it explain in detail everything plus example graphs

[Mike P.]

That peak can look deceiving. It's less then half a db from 20 hz down to 13 hz. Also remember this is without the effects of room gain which will affect the frequency response. Change the tuning to 13hz, change the port diameter to 12 inch, and give it 1000 watts input under the "signal" tab. Port velocity doesn't exceed 26 m/s until 13 hz.

[cixelsid]

Bob_99 wrote:

I'm not sure. The room is a shared space 37'L x 17'W x 9'H.

You're able to create an absolutely airtight space that large? How much is this box going to weigh?

[ccdoggy]

cixelsid wrote:

You're able to create an absolutely airtight space that large? How much is this box going to weigh?

I assume he means that he would be building a box (LLT style) inside of that room with both driver and port into the listening room.

[Bob_99]

Sam

How long would the port be for a 5hz tune

Since the box would be up in the attic, I figured the port could be external to the box so I didn't think the length would be a problem.

Please go read Steves thread here http://www.hometheatershack.com/foru...explained.html and read it from front to back... Twice because it explain in detail everything plus example graphs

I have read and re-read Steve's very excellent article for some time now. I have also looked at numerous other projects that I thought could just be applied to my situation but when it comes down to modelling them, I can't seem to get the specs to agree with published results. I have checked and doubled checked the parameters of the Q18 and the one area that may be problematic for me are the multiple coils. I believe that I am following the Win ISD directions correctly but am not 100% sure.

cixelsid

You're able to create an absolutely airtight space that large? How much is this box going to weigh?

Sorry for the confusion but that's the listening area.

steve

I assume he means that he would be building a box (LLT style) inside of that room with both driver and port into the listening room.

The box would go in the ceiling on top of the room (at the far end between the main speakers). Initially I was going to go with an IB but as I explained previously, decided to check out the LLT design. I figured if I can hide it up in the ceiling, I don't have to worry about size or looks.

Thanks for all the comments.

Bob

[Warmon]

Bob_99 wrote:

...but when it comes down to modeling them, I can't seem to get the specs to agree with published results. I have checked and doubled checked the parameters of the Q18 and the one area that may be problematic for me are the multiple coils. I believe that I am following the Win ISD directions correctly but am not 100% sure.

EBP=37.895696088537

The problem is because of EBP - this driver really wants to be in a sealed box.

[Bob_99]

Thanks Warmon. I questioned the vented box but I seem to recall some projects using it so I tried to go with it. I'll check into more appropriate drivers. I sincerely appreciate your diagnosis.

Bob

[Mike P.]

The database shows both ported and sealed for the Q18, both with excellent results.

http://www.hometheatershack.com/foru...-database.html

[Warmon]

Bob_99, in your search, what you want to look for is a driver with a EBP closer to 100 than 50 and a Qts closer to .30. I lived a few years in New Hampshire, so I understand why you might not want to have an opening in your ceiling.

Mike mentioned the member database. Bill 3 did a dual sonosub with the Q18. From above, you have been looking at the IB-Q18.

[SteveCallas]

Really no pointin using a 5hz tune - I'm a bit confused whether you want to use the FiCar Q18 or the FiCar IB18 driver, which is it? I can post a design that I would personally use myself if you let me know which driver you want to go with.

[Bob_99]

Thank you all for the input. My intention was to go with the Q18 and Not the IBQ18. I'm not sure how I mixed them up but Steve if you could post a design for me, I would be deeply appreciative.


Thanks.

Bob

[SteveCallas]

If getting just one driver, I like something in the neighborhood of ~650 liters with an 8" diameter port that is ~27" long for ~13.5hz tuning.

If getting two drivers, I like something in the neighborhood of ~1800 liters with a 12" diameter port that is ~25" long for tuning ~12hz.

I've heard from a couple Q18 owners that the simulations don't end up with a response that matches the actual response as close as it should, namely due to a faster rolloff below 40hz or so, causing a shallow dip in the region from 20-40hz. I can't confirm or deny that, but what I would do just in case is build your sub in such a way that you could always go back and trim the port length if you needed to, increasing output in the 20hz+ range.

[Bob_99]

Thank you Steve. I am considering two drivers and would there be another driver that you could recommend beside the Fi? Unless the cost per driver goes over three digits, I'm not too concerned. I guess the possibility of the actual response not matching the simulation is of concern to me because I really don't know enough at this point to go in and start changing things after the build is completed.

Bob

[SteveCallas]

The new Maelstrom-X 18 looks really nice at $300 with a pre-order. I would go so far as to call it the new LLT default driver - xbl^2, shorting rings, 33mm xmax with 42mm xmech, and it likes volume. That's about as good as it gets at the moment.

The FiCar IB18 also does well, though I have no idea what it costs since they don't really advertise it.

[a1161979]

SteveCallas wrote:

The new Maelstrom-X 18 looks really nice at $300 with a pre-order. I would go so far as to call it the new LLT default driver - xbl^2, shorting rings, 33mm xmax with 42mm xmech, and it likes volume. That's about as good as it gets at the moment.

The FiCar IB18 also does well, though I have no idea what it costs since they don't really advertise it.

Do you have any enclosure plans for the new default LLT driver yet steve