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Old 2nd February 2002, 08:54 PM   #21
Ron is offline Ron
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Lightbulb Collective wisdom rules

Hi All,

OK, now that everyone knows F3 to me is a function key on the keyboard......

I appreciate all the input and the heads up regarding wiring my (cheap) amp in parallel. I believe I will try to utilize both voice coils, as my understanding is I will effectively gain almost double the power? In addition all of the Shiva's specs seem to based on parallel wiring of the voice coils.

Primarily because I am such a complete neophyte, I'am leaning towards a sealed box due to the simplistic ( really ..? ) nature of the endeavor, and the notion that I will achieve greater fidelity. That is to say I haven't a clue as to judge the length, or tuning aspects of a port.

By using a low Q alignment of 0.5 it would appear to me from the Shiva specs, that I should get the best performance, since box size is of no consequence to me. I simply build a net volume box of 178 liters, stuff it with polyfil of 1.5 pounds per cubic feet, and I'am set... right? The quality of construction, and attention to detail, should be the deciding difference.

Although most of you, if not all, had more knowledge of the subject than I when you built your FIRST box, I'am curious as to specically what you would build if you only had a Shiva, my lack of knowledge, and it was your first attempt all over again? Primarily, would it be sealed or vented?

I'am seriously tempted to build whatever the collective wisdom suggests here. Hey, I can always take the driver out and start over! In any event I will begin building something this next coming Saturday. When finished, I will let you know how I think it turned out. Purely subjective of course, I have absolutely no way to actually measure anything, other than my perceptions.

Again, Thanks for sharing,
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Old 2nd February 2002, 10:12 PM   #22
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ok the easiest way to utilise both the channels of a stereo amp with a shiva is to feed each voice coil from it's own channel of the amp... you'll get twice the max power going into the speaker but the 3dB increase in headroom is unlikely to make much of a difference... if you've got the extra amp channel free you might as well use it, just dont expect much higher output ... just my opinion. Also, an enclosure of Q=0.5 will generally give very tight bass but the tradeoff is that you get less low bass.
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Old 3rd February 2002, 04:06 AM   #23
Ron is offline Ron
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Question amp confusion

Quote:
Originally posted by AudioFreak
ok the easiest way to utilise both the channels of a stereo amp with a shiva is to feed each voice coil from it's own channel of the amp... you'll get twice the max power going into the speaker but the 3dB increase in headroom is unlikely to make much of a difference... if you've got the extra amp channel free you might as well use it, just dont expect much higher output ... just my opinion.
Hi,

Or is it Gooday Mate?

The amp I was planning to use is an existing plate amp (120 W)from a KLH 10 inch subwoofer. This obviously is not the best in the world (IMHO). I presently feed it thru the pre amp out (L & R) outputs of my Denon A/V Rec'vr. I Was thinking of doing the same with the new Shiva box. Does the above still apply? Or are you speaking of feeding the new box and driver via a cup and inputs directly with the power being supplied by the Denon? Such as speaker level, then to the mains from the sub? Won't I get close to the doubling of power of the plate amp ( 230 W +/- ) simply by virtue of the parallel wiring of the voice coils? Or, am I even more confused then I know?

BTW...

Have a brother in law professor, visited Australia ( quite extensively ) for a year, he still raves about it. Only two places, I myself would like to see, Australia and New Zealand.

Best Regards,
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Old 3rd February 2002, 04:50 AM   #24
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Ok my mistake Ron,

Yes you can just wire the 2 voice coils in parallel and see what happens. This wont always get twice the power or anywhere near it because the amp may have current limiting or the power supply may simply be unable to supply that much current but if you dont mind the chance of blowing the output/driver stages of the plate amp up then go ahead.

I wouldnt suggest you run the sub thru the main (Denon) amp outputs.... it would mean just another passive x/over to bounce around and it probably just aint worth it .... (incase you cant tell, i rather prefer active x/overs )

Just take it slow and follow the suggestions i made in my 1st post in this thread.

p.s. it is indeed G'day Mate.
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Old 3rd February 2002, 05:42 PM   #25
Ron is offline Ron
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Smile Plate amp

Quote:
Originally posted by AudioFreak


but if you dont mind the chance of blowing the output/driver stages of the plate amp up then go ahead.

Hello,

I have come to the conclusion that your original advice regarding wiring the voice coils is right on. Why would I want to possibly risk blowing the only amp I have at present. Especially on theories I don't understand. It seems to pump the 10 inch KLH driver pretty well with a single voice coil. Also I think I read something regarding the Shiva that with one coil shorted or open, the 'braking' effect is enhanced. 120 W should be plenty of power for what I need anyway.

Thanks for being persistent. I can get on with it, without having to worry about the amp frying, or worse, blowing my new driver!
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Old 4th February 2002, 11:36 PM   #26
ucla88 is offline ucla88  Tahiti
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Quote:
Originally posted by mgoedeke
BTW F3 referenced to 100 Hz isn't fair either, because you'll want to reference the F3 of the system to its rated efficiency.

not too make too much out of this, but for a sub, i think this is entirely fair, as i noted previously. look, if you're crossing over your driver at 60, 80, or 100 hz in an active configuration, then why not reference the f3 to the peak value between 0 and 60, 80, or 100? why "punish" the driver by comparing its f3 to its peak efficiency at 200 hz when your sub will be down 24 db and you're going to raise the output level on your sub anyway?

now you do get a dropoff off the rated efficiency-so in this sense the manufacturer is trying to have it both ways i suppose.
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Old 5th February 2002, 07:53 AM   #27
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ucla88 said:

"Mainly, i think the difference is explained by this quote in the white paper--


Note that the frequencies are referenced to the peak output of the system, not the nominal output. Thus,
increasing any peak in the output frequency response, e.g. increasing the Q of a sealed box, can result in a
higher actual F3, not a lower F3. We choose to use this reference (peak versus nominal) because for higher
Q systems, the nominal output is not achieved until several hundred Hertz (>200 Hz). We believe this is
not applicable to subwoofers. As such, the F3 should be referenced to the highest value below 100 Hz.

is this fair? for a sub, i think so. if you were building a 3-way system and crossing over the shiva above 100 hz then their published f3 doesn't apply."


.... um - still doesn't explain it. First - they say "frequencies are referenced to the peak output not the nominal output" - here migth be my misunderstanding but.... ok - so we 10 fold the power - now we are up 10dB - but surely thats the same F3 Hz, just 10dB higher??? (ie. relatively speaking the F3 is the same - just louder - the frequency response curve has moved up uniformily 10dB). Maybe this is were voice coil inductance and impedance variations play a part as power increases.....

Increasing the Q raises the F3 - yup - have no problem with that.

Also - say the theoretical params are out by 5% over a DUMAX result - still doesn't count for 14+Hz difference...

I think its marketing going into overdrive again - or Thiele and Small have an error in their theory that Adire need to point out to them.

Dave.
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Old 5th February 2002, 02:02 PM   #28
ucla88 is offline ucla88  Tahiti
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Quote:
Originally posted by Dave Bullet


.... um - still doesn't explain it. First - they say "frequencies are referenced to the peak output not the nominal output" - here migth be my misunderstanding but.... ok - so we 10 fold the power - now we are up 10dB - but surely thats the same F3 Hz, just 10dB higher??? (ie. relatively speaking the F3 is the same - just louder - the frequency response curve has moved up uniformily 10dB). Maybe this is were voice coil inductance and impedance variations play a part as power increases.....

Dave.
my kingdom for two or three graphs...

i still don't think some of you understand what is the concept behind adire's quote. i think adire's point is exactly that it is NOT the same f3 if you pick a different reference level. let's say the driver doesn't hit it's reference efficiency until 200hz, say 90 db. say the output is 87 db at 35hz. this is the f3. fair enough.

BUT, you are crossing your sub over at 100hz, where the output peaks at 88.5 db. thus, the effective 3 db point in my system would be 85.5 db, and this would occur at 25hz.

yes, the whole curve is shifted up, but only so the output level matches the rest of your system.


anyway, these numbers are conjecture. i haven't run the simulation, but i'll put it to the test bench soon with my sealed tempest.
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Old 6th February 2002, 07:41 AM   #29
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Thanks ucla88. Using numbers makes it easy to see.

I now understand.

Cheers,
Dave.
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Old 6th February 2002, 02:24 PM   #30
ucla88 is offline ucla88  Tahiti
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hey, no problem dave.

took me a bit to figure out what they were doing as well.


remember all, you don't get something for nothing. doing this requires more power because in this particular system, the system sensitivity is lower.
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