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Old 30th March 2008, 09:22 PM   #1
FE3T is offline FE3T  Norway
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Default Help, need to simulate Excursion limit

I have 2 pairs of subbass drivers i plan to use in my living room
but i have no program suitable for simulating how much i can feed them before they reaches xmax
can anyone help me out?

12" (RFR 2215) 35-50L sealed

15" (RFR 2215) 85-120L sealed

Plan is to run atleast a pair of the drivers powered with a Hypex DS 8.0 on each. (530Wrms@8ohms)
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Old 30th March 2008, 09:30 PM   #2
GM is offline GM  United States
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http://home20.inet.tele.dk/kou/ubmodel.html

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Old 30th March 2008, 09:58 PM   #3
FE3T is offline FE3T  Norway
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Thanx for the link, but i must do something wrong here.
the output graph doesent look anything close to what WinISD predicts. and the powerhandling suggested here are about half of what i already have ran into the 15" without audible distortion
and about a third of rated powerhandling (380 Watts versus 1000Wrms)
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Old 30th March 2008, 10:49 PM   #4
GM is offline GM  United States
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You're welcome!

Well, for one, I'm not a fan of WinISD, which isn't known for its accuracy and WRT Unibox, it works fine for me. In the speaker design tab you can input anything in blue, then click the graphs and/or frequency response plot update and view the various results in the 'closed', 'vented', etc., tabs, plus there's a 'compare' tab to compare your sealed, vented, PR, BP designs.

Maybe you would find subsim's presentation more to your liking: http://www.geocities.com/f4ier/newsubsim.htm

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Old 31st March 2008, 12:46 PM   #5
bjorno is offline bjorno  Sweden
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1(2)
Quote:
...i have no program suitable for simulating how much i can feed them before they reaches xmax...
Hi ,

As expected, the 12 and 15” Rockford car drivers performs very similar when compared (See the plots 1(2)-2(2).) in the suggested boxes: 50L respective 120L, only covering the Mid-Bass octave (40-80 Hz) down to 40 Hz at most.

The Low-Bass octave (20-40Hz) would probably be possible in a car compartment and for this reason you ‘could’ call these drivers subs but not in a room where the Sub-Octave (10-20 Hz) would be 12 –24 dB down.

Quote:
… without audible distortion…
When arbitrary drivers with typical no distortion data or Dumax report given, operating at x-max and beyond, audible noise/artefacts is often heard at much lower input powers than given advertised ‘highlighted’.

Power compression resulting from non-linearity is heard long before reaching x-max and not to forget the accompany driver distortion.

In case when unknown or car drivers stating exaggerate power capabilities are thrown in here to this forum, I chose to use a derated x-max*, that allows x-max to be reached at 1 Hz as a prerequisite, thus the input powers are also de-rated accordingly.

The 12” driver is then good for 158W Rms and the 15” 126W at max and the headroom power requirements for suitable amplifiers can be relaxed to more reasonable numbers.

*About 50% down from f-3dB counted for the 12” driver and the 15” too.

Somebody agree?

b

1(2)
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File Type: gif rfr-2212-closed_box.gif (50.9 KB, 84 views)
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Old 31st March 2008, 12:47 PM   #6
bjorno is offline bjorno  Sweden
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2/2)
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File Type: gif rfr-2215-closed_box.gif (50.8 KB, 80 views)
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Old 1st April 2008, 03:09 AM   #7
GM is offline GM  United States
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Quote:
Originally posted by bjorno

Somebody agree?
Unless their quality has slipped in recent years, Rockford-Fosgate drivers are quite good and don't start compressing until above ~half power, so with a little room gain both these drivers should have no trouble in Vb = Vas cabs tuned down in the teens without exceeding Xmax or audibly compressing on 'only' 530 W, though if tuned to Fs or below a TQWT would be preferable due to the long vents required.

That said, there's still a lot of junk in car audio, so when in doubt it's indeed wise to use a conservative power and excursion rating for a HIFI or HT app with 1/4 power a good rule-of-thumb.

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Old 1st April 2008, 03:10 PM   #8
FE3T is offline FE3T  Norway
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These drivers arent actually "recent" they are from 97-98 and are also refered to as the Punch Power DVC series.
They where the top models before RF released the Power HX2.

And even if i know that power ratings from caraudio manufacturers are seldom accurate, i do actually belive RF made some pretty rugged drivers when they came upp with these.

With a 4" voicecoil, 116 OZ magnet and a vent in the polepiece large enough to fit a beer can.
they should be able to handle some abuse.

The 12" have been used in my home for quite some time now, powered by 2x120Wrms each (one stereo amp per woofer) in 35L sealed boxes, and to me it seems like the amps are the limiting factor sofar (2 Technics SE-A900SM2).

One of the 15" drivers was used in my car for some years in a 71L sealed box, powered with a 500Wrms mono block (RF Power 500M) and also in this case i didnt find the limit of the driver

Ps the drivers seems to be able to handle some serious excursion in free air without making mechanical noise, like breathing or flapping
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Old 2nd April 2008, 06:48 PM   #9
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Rockford fosgate is pretty much horrible now (been awhile since I have delt with car audio), but those power dvc woofers are fairly rare now and very impressive. Even with todays drivers!

Dan
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Old 2nd April 2008, 07:09 PM   #10
GM is offline GM  United States
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Bummer, I assume Jim's no longer in control then.........

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