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Old 4th August 2006, 07:32 AM   #21
lndm is offline lndm  Australia
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Quote:
Originally posted by infinia
See what design the other guy had in mind.
As far as I know, the guy said put it in a closed box and use it.

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Could work ok but may have to tweek the notch a bit.
I think the LT circuit would be your cup-o-tea.

IMO The best EQ for this is the LT circuit. Rod Elliot has a project of the LT on his web site.
As long as I can trim the hump, I'm half way there. Absolute f3 limits are not crucial.

Phase/delay will still be a problem, not sure whether it will be too bad. I guess the LT would clean that up. Is it just a matter of putting current slope/target slope into the spreadsheet and getting circuit values out?
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Old 4th August 2006, 08:06 AM   #22
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by infinia

A Sealed system (closed box) from Sreten's earlier advise is definitely NOT advisable for higher Qts (> 0.7).

Hmmm...... a contradictive statement that is incorrect.

A higher Q 2nd order alignment combined with a 1st order roll-off
as suggested by E-side gives you a half reasonable 3rd order
alignment that has similar phase and group delay characteristics
to standard 4th order vented alignments, (perhaps better).

Aperiodic vents waste some of the excursion capability. As pointed
out by E-side the 3rd order alignment has some power handling
advantages as it effectively rejects low bass and the excursion
required. Could be a very good choice if the driver has low xmax.

/sreten.
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Old 4th August 2006, 12:45 PM   #23
infinia is offline infinia  United States
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Indm
A good explanation of what the LT equalizer is doing can be read Rods site. Link http://sound.westhost.com/linkwitz-transform.htm
Most people use this technique for getting LF extension in a smallish box at the expense of amplifier and driver power. Should you choose to go this way, you would be using it mainly to control the severe peak.
Download the spreadsheets and use the vaues estimated from a box calculator. I would advise using low gains, just to control the peaking (gains around 6-8 dB). If you choose to build it, hold off on final filter values untill you measure the driver in it's box.
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Old 4th August 2006, 12:54 PM   #24
infinia is offline infinia  United States
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Sreten
Now you're confusing your passive solution of a simple closed box suggested in your first post with eside's active filter solution he suggested later on. I agree with eside solution, it has some merit similar to what the LT does but just not as sophisticated.
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Old 4th August 2006, 03:45 PM   #25
e-side is offline e-side  Netherlands
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Quote:
Originally posted by infinia

Most people use this technique for getting LF extension in a smallish box at the expense of amplifier and driver power.
SPL and power(handling) are usually very important factors for PA speakers and amplifiers. To compensate a 3dB waste of power requires a bigger amp, and a bigger wallet. Especially if cost is an issue, and when cheaper, less sensitive speakers are used, a LT isn't a good option in my point of view.

Also, PA speakers often don't go any lower than 40 or 50 Hz, everything below these frequencies usually isn't worth the required extra Watts.
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Old 4th August 2006, 03:59 PM   #26
infinia is offline infinia  United States
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Quote:
Originally posted by e-side


SPL and power(handling) are usually very important factors for PA speakers and amplifiers. To compensate a 3dB waste of power requires a bigger amp, and a bigger wallet. Especially if cost is an issue, and when cheaper, less sensitive speakers are used, a LT isn't a good option in my point of view.

Also, PA speakers often don't go any lower than 40 or 50 Hz, everything below these frequencies usually isn't worth the required extra Watts.
What you say is true, If you push the LF extension.
Here the LT equalizer is being used for Q correction and should not be a bad trade off if the LF extension is kept within reason. That's why I warn against making the gain any higher than necessary. Not too much different than using a simple HPF if the break points are chosen judiciously.
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Old 4th August 2006, 04:46 PM   #27
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by infinia
Sreten
Now you're confusing your passive solution of a simple closed box suggested in your first post with eside's active filter solution he suggested later on. I agree with eside solution, it has some merit similar to what the LT does but
Hi,

I'm not confusing anything. The principle of my original post (if
you read it all) is the same as E-side's just somewhat simpler.

/sreten.
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Old 4th August 2006, 04:53 PM   #28
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by infinia
Sreten
Now you're confusing your passive solution of a simple closed box
suggested in your first post with eside's active filter solution he
suggested later on .........
Hi,

I'm not confusing anything. The principle of E-sides post is the
same as my original post (it illustrates it, as he's modelled it)
but the my suggested implementation is the simplest (EQ).

/sreten.
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Old 4th August 2006, 06:04 PM   #29
infinia is offline infinia  United States
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Sreten
Sorry but your simple turn the bass down is blindly hopeful at best, still the huge peaking response of a high Q driver results in one note bass. It's not really close to a tuned filter with a target Q as the other poster proposed.
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Old 4th August 2006, 06:46 PM   #30
bjorno is offline bjorno  Sweden
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Indm!

An easy passive cure to lower driver Qts / Qms:


Background from:
/
Small : Chapter 6. DRIVER DAMPING AND VARIATIONS OF THE CLOSED-BOX SYSTEM

6.2. Acoustic Damping of the Driver :

The simplest way to correct a high value of QTS is to apply acoustic damping directly to the driver using a shroud of acoustically resistive material as described in [G1] or [N3]. This effectively adds resistance in series with RAS and leads to a value of QM ( Section 1.5.4 ) lower than QMS. By suitable choice of the kind and amount of damping material, almost any desired value of QT can be obtained regardless of the value of QES or QE. The parameter measurement methods of Section 9.2 may be used to determine experimentally the amount of material needed to meet a particular requirement. Care must be taken that the material remains stationary.
/

My suggestion: Change driver Qms by fitting a 3-4 inch thick cylinder of glass fiber or mineral wool, (1.25 -1.5 lb/ft3 glued Liquid Nail type) to the rear side of the baffle adjusted to completely covering the rear outlets of the driver.

The fibres must be oriented perpendicular to the baffle, also letting air to be passed through without any fibre moving.

Fibre-cylinder inner diameter is equal to the magnet diameter and the latter has also some glue on the surface for fastening the wool securing unwanted fibre movement.

The length of the cylinder is about equal or slightly longer than the formed cylinder outer diameter.

Carefully done this should push Qm down to under Qm=1, resulting in a better driver mechanical system behaviour.

Midband efficiency will drop down a bit, maybe a 1 dB or so and the air column formed in the fibre will add mass causing fs to drop slightly.

Bjorno
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