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Old 5th October 2007, 04:32 AM   #1
ro9397 is offline ro9397  United States
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Default Variovented divider panel + more

The two intended sealed subs will also serve as monitor stands. Active sub low-pass xo will be about 70 Hz. Prior testing w/ these 10s resulted in a twice-confirmed anechoic f3 of 40 Hz; got 30 Hz f3 in two different rooms. Will probably add about +3 dB EQ around 20 Hz.

Each sub will house two sealed 10s. I propose to install one 10” to the front baffle per normal fashion. The other 10” will be installed on the rear panel.

Considering the approximate 70-Hz xo, is it worth the effort to invert the rear-panel-mounted 10" with its basket exposed facing outward & its input polarity inverted to cancel uneven distortion products related to cone direction? Would really appreciate personal listening experience on this point. Cosmetic impact is irrelevant.

A respected room acoustics professional suggested the two 10s be isolated w/ a divider panel rather than normal compound loading. He also suggested the divider panel be "porous". Each driver requires only about .8cf. Would appreciate comments on using one Parts Express variovent to achieve the recommended porosity on the divider panel. The vent would be located just below the front 10". Per Parts Express recommendation the pathway would be kept clear between the vent & both 10s.

After my search there appears little to no consenus for variovents in general. What about also adding one Parts Express aperiodic vent to the rear panel just below the rear-mounted driver? Again, all paths would be kept clear between the divider vent, the rear-10 & the rear-vent.

Thanks for your consideration.
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Old 6th October 2007, 09:54 AM   #2
bjorno is offline bjorno  Sweden
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Quote:
...A respected room acoustics professional suggested the two 10s be isolated w/ a divider panel rather than normal compound loading. He also suggested the divider panel be "porous". Each driver requires only about .8cf. Would appreciate comments on using one Parts Express variovent to achieve the recommended porosity on the divider panel.
Hi,

It is impossible to answer any of your questions as you have left out the most important clues, the driver data, your stand internal dimensions and a clear picture of suggested internal damping.

Quote:
...Per Parts Express recommendation the pathway would be kept clear between the vent & both 10s.
No uses of this assert useless you give more information and the box type is established.

Is it a third or forth order system you are targeting or an intermediate?

Possible examples: Leakage-Damped (+Absorption?) Closed-Box System or a combination of: Damped-Vent System, Leakage-Damped Vented-Box System (ARU), Absorption-Damped, Damped-Box- Damped-Vent (Aperiodic) System, Double-Cavity Vented-Box System.

A simple picture could help, like: 1(1)

b


1(1)
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Old 6th October 2007, 05:26 PM   #3
ro9397 is offline ro9397  United States
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Quote:
Originally posted by bjorno


Hi,

It is impossible to answer any of your questions as you have left out the most important clues, the driver data, your stand internal dimensions and a clear picture of suggested internal damping.

Many years ago (long lost, at least at this moment) Ken Kantor tested the 10s & gave me the T/S parameters. The best I can recall now was that they were unsuitable for a vent & a sealed .75cf box would yield a 40 Hz f3. If memory serves the Qts was .49, fs 28 Hz & that is unfortunately the best this guy can do till I start cleaning up after the latest move. Sorry can't do more, except to mention carbon/poly cones, foam surround, 40oz magnet, 2.5" vc, stamped steel basket, made I believe by Gefco in the '80s (19, not 18!).

I want to finally use these speakers because I've heard them before, they sound as good as I've heard down to their effective 30 Hz in-room cutoff, I've got four of 'em, & they work in a small sealed enclosure. I prefer the sound of sealed overall & the size matches well w/ the 9.5" wide main speakers.

The commercially made main speakers have an optional sub that is 31.5" in height. I assumed that would be a good height for my sub/stands. Between the sub & main speaker I intend to place a 1.25" thick MDF isolation platform lined above/below w/ 1/8" thick blue E.A.R. Isodamp.

I'm intending to use all 1.25" MDF: outer dimensions HxWxD 30x11.5x16, w/ the mentioned vertical divider panel seperating the front/rear 10s. I was hoping the variovents on the divider & rear panels would minimize any negative impact of the internal dimensions being a bit far from Golden Ratios.

Please let me know if there's any other info that would be appropriate.

Quote:
No uses of this assert useless you give more information and the box type is established.

Is it a third or forth order system you are targeting or an intermediate?

Possible examples: Leakage-Damped (+Absorption?) Closed-Box System or a combination of: Damped-Vent System, Leakage-Damped Vented-Box System (ARU), Absorption-Damped, Damped-Box- Damped-Vent (Aperiodic) System, Double-Cavity Vented-Box System.

A simple picture could help, like: 1(1)
b
1(1)
Sorry the rest is way over my wittle head...To summarize I'm wanting the best performance from two 10s in a sealed system. I'm definitely willing & able to just put the two 10s in a simple compound system & forget the divider. In that case, the above dimensions are very close to a perfect Golden Ratio. I'm curious how much difference the GR dimensions make for the intended bandwidth.

Thanks again!
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Old 7th October 2007, 03:13 PM   #4
Ron E is offline Ron E  United States
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Variovents do nothing to ameliorate box ratios, and box ratios are unimportant for low frequency duty. Using a variovent in the divider between the independent sealed boxes will do no harm, but neither it nor the divider is necessary. Putting a variovent then on the rear enclosure and not the front does not make sense unless you are trying to get different response from the front and rear woofers.

Your initial request seems clear, but since then you mention vents and sealed and aperiodic and compound. The mashup of terms has me unsure of what you are actually proposing. Perhaps a simple drawing is in order.

Making subs with 1.25" MDF walls is certainly your prerogative, it is your back.... IMO bracing is more efficient/effective than thick walls, and good plywood is stiffer and lighter.
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Old 7th October 2007, 11:42 PM   #5
ro9397 is offline ro9397  United States
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I know you guys are way over my head on this stuff so I appreciate the patience very much, believe me.

I am big & strong, but what heck, I work out almost daily & honestly don't need the extra labor. I WASN"T looking forward to hussling 175 lb sheet of 1.25" MDF around.

For the inside dimensions 28.5x9x13.5 I'm indebted to hear recommended plywood types & thickness, & also some general minimum recommended ideas for bracing.

So am I correct that, for the approximate 75 Hz maximum xo pole I can do pretty much any dimensions?

Finally (I hope): I put one 10 on the front & one on the rear....how much audible benefit inverting the rear w/ basket exposed & the input polarity inverted to match phase w/ the front? Has anyone done audio tests for this?

Thanks a ton!
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Old 8th October 2007, 01:50 AM   #6
ro9397 is offline ro9397  United States
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Two corrections below:

Quote:
Originally posted by ro9397
inside dimensions 28.5x9x13.5

26 x 9 x 13.5 (H x W x D) Accounting for 1.5" tall spikes for concrete slab floor (thank goodness!), plus my math was off by one inch...

Quote:
for the approximate 75 Hz maximum xo pole I can do pretty much any dimensions?
For the approximate 75 Hz maximum xo pole, is it correct that minimum negative impact will result by straying from Golden Ratio dimensions?

Quote:
Thanks a ton!
No corrections there!
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Old 8th October 2007, 10:47 AM   #7
bjorno is offline bjorno  Sweden
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Quote:
I was hoping the variovents on the divider & rear panels would minimize any negative impact of the internal dimensions being a bit far from Golden Ratios.
I don’t think this is an important issue considering it’s a sub HP filtered at 70-80 Hz? Use this standing wave calculator and you will find no standing wave modes below 250 Hz or about 1.5 octaves above 80 Hz when using your suggested box volumes:

http://vikash.info/audio/standing_wa...7&threshold=20

Quote from another forum:

Quote:
2005:The company who manufactured the REV 3 10 inch drivers has been located at last!!!
"Gefco" in Chicago… The owner's name is Brian Geffort. Gefco 101 Pine St Grayslake, IL 60030 (847) 223-8171
Is the 10” REV 3 the driver you have? Your data is still incomplete, at least the driver sensitivity and Re is required to make any prediction trustworthy.

Quote:
The best I can recall now was that they were unsuitable for a vent & a sealed .75cf box would yield a 40 Hz f3. If memory serves the Qts was .49, fs 28 Hz…
Looks like to be a driver intended for a closed box (maybe a car driver?), heavy magnet and weight of the cone?
The use of variovent on front or the rear would severely restrict the possible LF output below fc, the low frequency cut-off then equalizing at 20 Hz would be a bad idea if x- max also is low.

Good internal bracings (even inter driver magnet to magnet bracing) and homogenous volume damping if a closed box is chosen would result in much better performance than if equipped with internal dividers or variovent types as your intended boxes gross volumes are chosen to be on the smaller side.

Here are a couple of closed box simulations based on above information, with one driver, two and bipole variants and if your supplied data is close to the reality, only the absolute SPL, the real impedance values should vary as Re, Sd, BL, Qmd, Qes are estimated with no guarantee to be the real data of your drivers: 1(4)-2(4) and 3(4)+4(4) = bipole

Quote:
So am I correct that, for the approximate 75 Hz maximum xo pole I can do pretty much any dimensions? Finally (I hope): I put one 10 on the front & one on the rear....how much audible benefit inverting the rear w/ basket exposed & the input polarity inverted to match phase w/ the front? Has anyone done audio tests for this?
The answer is yes and if the rear diver were mounted with the basket and magnet facing out the only impact on the polar would be if crossed over at a much higher frequency (midrange and above) than for a sub, there is almost no difference at all when crossed over at 70-80 Hz.

More impact has the physical inter driver distance, the inter driver phase depending on polarity and if one of the driver is pre-filtered, the box size (baffle step and the diffraction) and the room placement for this case.

Quote:
For the approximate 75 Hz maximum xo pole, is it correct that minimum negative impact will result by straying from Golden Ratio dimensions?

Your suggested box is too small for any mayor or noticeable impact but if the volume goes up, lets chose 250 L (8-9 cu ft) or above where some of the internal distances reaches lengths of 1m (about 40”) or above and a shallow LP filter is used (6dB/12 dB) for the XO, then the standing wave at about twice the crossover frequency would be heard only 6dB/12 dB down (but rather blameless if a 24 dB filter is used) and an internal Golden Ratio of the box would be an improvement.

b

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Old 8th October 2007, 10:48 AM   #8
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2(4)
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Old 8th October 2007, 10:50 AM   #9
bjorno is offline bjorno  Sweden
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3(4)
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Old 8th October 2007, 10:52 AM   #10
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