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hz numbers on a 15" 2 driver (Read 42951 times)
bassboy
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #210 - 06/06/06 at 22:36:55
 
Bob, I have to admit that I haven't done the calculations on any of the suggestions John and others have posted.  I have full faith that if John says the box is tuned at 19 hz, then it is.  If you chose the right length of port, it should perform as described.

But just if you want to be sure, plug the driver's specs into WINISD (it even allows isobaric loading as an option) and model the suggested box.  Then go to the next tabs and change the box size and port length to your box size and port length.  What you see in WINISD is what you should hear in your room, but with a bit of room enforcement on the low end, and even more for corner placement.

Keep fiddling with WINISD until the curve looks like what you want to hear, it's fun and free.

Try playing with flared ports too, it's good for you.
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« Last Edit: 06/06/06 at 22:38:16 by bassboy »  
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bassboy
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #211 - 06/06/06 at 22:39:40
 
And if you can't find ALL the specs, you have to download the manufacturer's driver specs in pdf, I found out they are all there.
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John in CR
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #212 - 06/07/06 at 01:55:30
 
The bottom 2 chambers of Bob's box nets to about 155L (net of driver and port).  With the 13.5" long 4" port the tuning is just above 19hz, but with that corner placement he's getting an effective length of over 15".  With the isobarik loading, the drivers are acting the same as a single driver in a 310L box.  It's closer to an EBS type alignment but with a small box.  Even though he could lower the tuning, the port would turn into a problem because it would get so long.

So no Bob's box isn't flat to 19hz, but the few db sacrifice for the added shelf of extension is offset by some room gain.  In room, Bob should be pretty flat down into the upper teens even though his layout doesn't give him maximum room boost.


Bassboy,
I'm pretty sure that 95db on 1 watt at 20hz is a pipe dream (excuse the pun).  I think only a giant bass horn or multi-driver rig will do that.
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John in CR
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #213 - 06/07/06 at 02:10:09
 
Bob,

How about if I throw you a real curveball.  If you only connect 1 of the voice coils on your drivers, it is almost identical to the Dayton IB15.  That means you also have the capability of going OB or IB with those drivers and even get the added advantage of fine tuning the sound with RDO (Resistive Damping Operation) using a variable resistor across the unused terminals.

What's on the other side of the wall behind your screen?
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bassboy
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #214 - 06/07/06 at 03:52:02
 
The Tower of Power does 95 db.  My traditional design models at 93 in open space.  With Transflex loading, corner loading and room gain I am hoping for 95 db at 1 watt at least way down low.

I would be thrilled with that level, and I am hoping for that much volume but we'll see.
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Bob in St. Louis
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #215 - 06/07/06 at 12:45:10
 
John, my drivers are Single Voice Coil...

http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=295-130&CFID=4954...

The depth of the surrounding cabinets is about 18", the back of the cabinets are about 1 1/2', slightly less from the sheetrock wall. The thickness of the screen is about 1". The screen is "torsion panel" construction, like a cheap interior hollow core door. The distance from the back of the screen to the wall behind it is right at 30". Currently the space is storage. The screen is hinged at the top, and 'flips up' like a giant car hood. My original plan back there was to put shelving for storing 'stuff', but just havn't gotten around to that particular project. So the 'stuff' is just sitting on top of the cabinets.

So yea, I've got plenty of space back there, cubic feet wise. But that may be irrelevant if were not talking about the correct drivers.

Bob
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bassboy
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #216 - 06/07/06 at 18:26:08
 
Bob, overlooking the DVC issue, the end results are not irrelevant.

The important thing when designing EBS ported is the box and port tuning.  As long as the box and port are tuned to work together, the driver is the only responsible for putting out whatever it can at the requested frequency.

The box will output whatever sound the driver presents it with at the box's tuning frequency.

The problem comes into play when you tune the box and port WAY out of the driver's range, which you haven't.  The cost in that case is sensitivity, because the driver is struggling to make sound way below it's resonance and we've all seen the FR graphs that show heavy rolloff around fs.

I strongly urge you to play with WINISD, you'll learn more there much more quickly than anyone can explain anything.  It's an excellent visual tool that you can experiment with.
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« Last Edit: 06/07/06 at 18:27:15 by bassboy »  
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Bob in St. Louis
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #217 - 06/07/06 at 19:58:24
 
bassboy, I've played with WinISD, it is pretty cool. Somewhere around page 3 or 4 of this thread I mentioned to John, that the program was giving me the message, "this version can't perform that task, you looser". I guess I need "PRO" version?
It is fun to play with though.

Bob
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John in CR
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #218 - 06/07/06 at 20:13:54
 
Bob,

It would be nice to know once and for all which drivers you have.  Back on page one you gave us a link to these, which have 15mm of Xmax (that's almost a 6db difference at the bottom end):  http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=295-190

Let's get on the same page before proceeding.
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Bob in St. Louis
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #219 - 06/07/06 at 20:38:11
 
John, I'm sorry. Your reading post #3 which is the one I said I have Part#295-190 (DVC's)
On post #8 I apologized, corrected my mistake by saying I have Part # 295-130 the single voice coil.

I though about deleting/modifying post #3 so thing like this wouldn't happen. I figured I'd leave it alone since it would "F"-up the 'story line'.  ::)
I didn't think by now, anyone would have gone back that far, or would have read further down and see the correction.

Again John, I'm sorry.
I do sincerely Thank You for the time you've spent with me.

Bob
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bassboy
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #220 - 06/07/06 at 20:54:22
 
Bob, WINISD cannot model the HWK or 6th order bandpass but it does very well with isobaric vented, which is what you have.

I'd go through the motions but I don't post pics so it's meaningless for me to do it.
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John in CR
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #221 - 06/07/06 at 21:20:05
 
Bob,

I think we're back to where you should give a good listen to what you have (drivers in top baffle clamshelled, one bottom port blocked, the other with a 13.5" or so long 4" port.  I think with the top off will be easier to blend with your mains but check it out, since the top on gave you better control over excursion.

Then play some of your DVD chapters with the sound at a good level overall and note whether you're getting pretty good oomph on your LFE's.  Keep in mind that later you can split the drivers up and put each in a box twice the size with the same tuning and get the same sound but +6db in potential.  You can also add a rumble filter at say 15hz which will give you more potential at 15hz and higher.  With only 8mm of excursion, I think you should forget about going lower than 15, but don't worry there's plenty of feel in the LFE's 15hz & up.
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Bob in St. Louis
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #222 - 06/07/06 at 22:28:19
 
John, I don't know where we're at now in the hz department, but I think I'd take the 15hz/rumble filter idea over the +6db gain since I'd have to build two boxes twice the size of my existing one to get there.
I'll take bassboy and your suggestion first. Remove some wires, listen to the mains then slowly add wires/equipment and gentle tweek along the way.

After I do that, I think I'll play with room treatments.
This is cheap/easy, don't laugh if it's a dumbass idea.
Take all of the cushions from the sofa's / loveseat's from upstairs furniture and line my walls with the cushions.

I've got to think that the room is playing into this. Despite how much time/effort I put into the room (with acustics in mind) that it turned out good enough not to need SOME form of absortion/diffusion.
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John in CR
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #223 - 06/07/06 at 23:17:54
 
If you want to see what bass traps might do, haul a couple of mattresses down there too.  Are the recessed areas on the ceiling in front of the seating area reflective or do you have acoustic tiles up there too?

BTW, the rumble filter would be needed with the 2 box approach as well.
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60ndown
Ex Member



Re: hz numbers on a 15" 2 driver
Reply #224 - 06/07/06 at 23:34:03
 
mattresses on the celing? man alive, i laugh at myself sometimes trying to move my hwk and other subs, im sure they weigh in excess of 100lbs and awkward as a dead elephant . but im sure i would collapse into a ball of hyseria trying to fix a mattrress to my celing, bet the wife would love it 2 Roll Eyes
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