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Old 2nd August 2006, 11:42 AM   #11
AndrewT is offline AndrewT  Scotland
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Hi,
I think the high Q will dominate the sound.
The effect will probably sound like a boom box with all bass notes sounding like they were of the same frequency.

I tend to concur with the other posters, High Q speakers were never intended for use with a cabinet.
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Old 2nd August 2006, 11:51 AM   #12
lndm is offline lndm  Australia
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Hmmm, I am fearing that.

On the other hand, if I make the baffle any smaller I'll just create a dip in the response, larger, a peak. I do still have the option of the aperiodic enclosure. I suspect that the overshoot may slightly compensate the apparent levels for adding a variovent after the fact. At least I hope so. Am I being reasonable?
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Old 2nd August 2006, 09:00 PM   #13
forr is offline forr  France
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With an amp with some negative output resistance, you can easily divide the Qe by 2, at least.
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Old 3rd August 2006, 03:16 PM   #14
infinia is offline infinia  United States
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Quote:
Originally posted by forr
With an amp with some negative output resistance, you can easily divide the Qe by 2, at least.
Come on Forr
Yes, maybe if you could stabilize it, But NOT practical! I would definitely NOT recomend it, except if you want to spend alot more time working on amplifier development. IMO More of science fair projects.
Best solution if going for an active solution, would be a Linkwitz Transform circuit. It's well documented as a working solution to Q and Fs problems besides.
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Old 3rd August 2006, 06:39 PM   #15
sreten is offline sreten  United Kingdom
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Hi,

Corner mounting will bump up the response such that BSC is not needed.

Aperiodic vents aren't really appropriate for PA speakers.

E-sides suggestion is easily implemented by upping the input
capacitor value of the power amplifier - or can probably be
approximated by knocking back the bass tone control.

TBH quality wise getting reasonable bass balance is not that
diificult as long as you don't want / need real bass extension,
the highish q point simply defines the lower limit when Eq'd back.

Quality wise the real issue is getting an overall good balance
with decent dispersion and low distortion across the range.

/sreten.
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Old 3rd August 2006, 09:32 PM   #16
infinia is offline infinia  United States
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Quote:
Originally posted by sreten


Aperiodic vents aren't really appropriate for PA speakers.

/sreten.

A Sealed system (closed box) from Sreten's earlier advise is definitely NOT advisable for higher Qts (> 0.7). Aperiodic (vario) vents will make a a bad situation tolerable at higher spl's. IMO They are very useful for weak motor drivers. Whether or not this driver fits that bill is not known. Otherwise use open back type cabs.
Or even better use an active solution via a LT circuit. Not too hard to implement. A PCB is available on a currently running group buy on this forum as we speak.
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Old 3rd August 2006, 11:33 PM   #17
forr is offline forr  France
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About negative impedance

Infinia
---Yes, maybe if you could stabilize it, But NOT practical! ---

You have to stabilize it if you want to nullify the voice-coil DC resistance a la Stahl. However dividing it only by 2 is very easy, you can do it with only three resistors around the power amp. Qt is then less than 0.7, a more manageable value than 1.3.

I have not made simulations of a Linkwitz transform with this precise speaker which has a Qt of 1.3, but previous attempts with high Q's failed.
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Old 4th August 2006, 12:53 AM   #18
infinia is offline infinia  United States
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Forr I Haven't read the AES papers in a long time. AFAIK pwr amp should be configured as a current source (AB w collector outputs). Small resistor samples the current at output return then applies neg feedback with trickey compensation network in feedback loop. A stability analysis would be required. IMO this technique needs a special dedicated pwr amp for woofer only.
I can simulate LT circuit if poster is interested in going active. This way he can use "off the shelf" voltage mode power amp.
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Old 4th August 2006, 02:02 AM   #19
lndm is offline lndm  Australia
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The equipment I have to work with was purchased on the advice of 'the guy at the other end of the line' , and this is a not for profit organisation so what we have is all we have.

There is one 2ch power amp that will do well if we don't need to go active, and there is a mixing board which seems to have three fixed EQs per channel. Not sure whether the bass controls are centred or tone control shaped.

There is a reasonable chance I could apply passive EQ at the input to the power amps.

I am feeling that the power response will be more important here than the on axis response. Because of this, I feel I need to take the baffle step with a grain of salt, rear wall loaded or not.

I am concerned with the cancellation effects and placement difficulties I may encounter with an open baffle. I am concerned that a closed box would ensure overshoot and ringing in the bass. I am wondering whether EQ will make this tolerable.
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Old 4th August 2006, 03:16 AM   #20
infinia is offline infinia  United States
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Quote:
Originally posted by lndm
The equipment I have to work with was purchased on the advice of 'the guy at the other end of the line' , and this is a not for profit organisation so what we have is all we have.
See what design the other guy had in mind.
Hopefully you'll get all the credit when all your work pays off

Quote:
Originally posted by lndm
There is one 2ch power amp that will do well if we don't need to go active, and there is a mixing board which seems to have three fixed EQs per channel. Not sure whether the bass controls are centred or tone control shaped.
With just 3 tone controls most prob not where you need them to be.


Quote:
Originally posted by lndm
There is a reasonable chance I could apply passive EQ at the input to the power amps.
Could work ok but may have to tweek the notch a bit.
I think the LT circuit would be your cup-o-tea.

Quote:
Originally posted by lndm
I am feeling that the power response will be more important here than the on axis response. Because of this, I feel I need to take the baffle step with a grain of salt, rear wall loaded or not.
Most likely if you couldn't control the placement
Quote:
Originally posted by lndm
I am concerned with the cancellation effects and placement difficulties I may encounter with an open baffle. I am concerned that a closed box would ensure overshoot and ringing in the bass. I am wondering whether EQ will make this tolerable.
Yes they can cancel where you want them, but they add in phase at a central frequency as well. IMO The best EQ for this is the LT circuit. Rod Elliot has a project of the LT on his web site.
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