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-   -   Enclosure for high Q driver (http://www.diyaudio.com/forums/multi-way/83982-enclosure-high-q-driver.html)

lndm 31st July 2006 03:01 AM

Enclosure for high Q driver
 
I have a friend with a 15" driver and he wants to use it for public address and light music, and to mount it near a bricked ceiling corner. I have measured 44Hz and Qts=1.3.

I could use some suggestions on what enclosure type to use. I am hoping not to need to resort to active EQ, though the corner boost with the high Qts concerns me.

sreten 31st July 2006 10:51 AM

Hi,

Seems to me your only option is a sealed box and knocking back
the bass EQ knob somewhat. The high Q in box will then control
the effective bass extension. More common than you think, see :

http://www.partsexpress.com/projects...oys/index.html

:0/sreten.

infinia 31st July 2006 12:56 PM

I have use drivers with higher Qts and it is not possible to get lower system Q unless with active solutions. With passive solutions an IB would give Qs=Qts at best. Smaller boxes with produce Qs even higher than that.

Some options to consider
1) aperiodic vents for weak motor drivers (ie acceleration Bl/mms)
2) Open or semi-open back enclosures for stronger motor drivers (like the old guitar combo amps)

e-side 31st July 2006 07:53 PM

Looks like a suitable driver for open baffle, although such an 'enclosure' has some disadvantages when used for PA.

Also, according to the author from the alpha-TL article any driver's suitable for alpha-TL loading. You could run some simulations if you're interested in TLs

mashaffer 1st August 2006 01:20 AM

I couldn't find anything on "alpha tl" but out of curiosity i modified the parameters of a 15" pro woofer to equal the limited specs that were given above and ran some simulations. The results were interesting. This hypothetical driver shows a huge bump of 6 to 7 dB in a rather large closed box (about 4dB IB) So OB is the obvious usage but not too practical for PA.

So I tried a few things in TL and was able to get a sim that showed broad ripple of about 2dB over the range from just under 30Hz to about 80Hz with sensitivity of around 105dB/W. But get this. The pipe cross sectional area was 8000 cm^3. :bigeyes:

An interesting thing to play with but I wonder about the accuracy of simulations when such way out sizes are needed. It would be interesting to have the complete parameters of the driver for further play.

mike

lndm 1st August 2006 01:53 AM

I like the idea of a lossy box of some sort, even if I'll need to resort to a little EQ.

I've loosened the driver up a little and fs has dropped to 37Hz. Haven't remeasured Qts but working with 1.2 till I do. Added mass Vas measured 122l (4.3'^3).

Edit: This driver has a fairly light paper cone for its size (in my experience), adding 147g of mass reduced fs from 37 to 26.5Hz. Suspension seems a little stiff (pleated doped cloth) and magnet is approximately 15cm*2cm.

Ron E 1st August 2006 02:16 AM

Adding mass raises Q and reduces sensitivity. Not the right direction, IMO.

Either apply EQ or live with the high Q. If you will be playing rock/pop people will probably like the extra punch.

e-side 1st August 2006 09:58 AM

According to WinISD Pro a 100 L closed box with an (active) 1st order HP filter at 85 Hz gives pretty nice results. F3 at ~50 Hz, max dip/peak is 0,32 dB.

For PA (at higher volumes) excursion is an important factor, so you might reduce box size even more to gain more power handling.

infinia 1st August 2006 12:52 PM

Quote:

Originally posted by lndm
I like the idea of a lossy box of some sort, even if I'll need to resort to a little EQ.

I've loosened the driver up a little and fs has dropped to 37Hz. Haven't remeasured Qts but working with 1.2 till I do. Added mass Vas measured 122l (4.3'^3).

Edit: This driver has a fairly light paper cone for its size (in my experience), adding 147g of mass reduced fs from 37 to 26.5Hz. Suspension seems a little stiff (pleated doped cloth) and magnet is approximately 15cm*2cm.

Yes. An aperiodic vent is a resistive loss term in an otherwise closed box system. IMO it is a variable depending on pressure in the box. Also adding mass might help things here as well. Your cone mms is most likely around 50g, so I would not add more than 100% depending on suspension and possible reduction of Xmax and sensitivity. EQ as required for source and placement.


<edit>oops just noticed it was a 15" so mms would be a little higher than 50g, you can estimate by looking at similar drivers with known T/S.

lndm 2nd August 2006 11:29 AM

2 Attachment(s)
OK, I was tossing up whether to go with a box much smaller than Vas and deal with the consequences, or make one closer to Vas. I began to sim the baffle step and luck kicked in. I chose a box as large as Vas and used the two largest dimensions for the front.

The red curve is from 'The Edge' baffle sim, the blue is the box response (it is plotted where it is for better visibility), and the green is the resultant. :cool:


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