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Old 20th April 2013, 12:33 PM   #41
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Fine. But if i choose to paralell both the two drivers and the voice coils, will it give louder SPL?
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Old 20th April 2013, 12:52 PM   #42
OllBoll is offline OllBoll  Sweden
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Quote:
Originally Posted by superlian View Post
Fine. But if i choose to paralell both the two drivers and the voice coils, will it give louder SPL?
Yes, I think so. Only at the lower frequencies though since the le is very low on those drivers and so after the impedance peak at fs it converges to 8 ohm per coil. You'd have to be careful not to exceed xmax though, but except at 40 hz and below that shouldn't be an issue if I remember correctly.
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Old 20th April 2013, 03:56 PM   #43
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OK.

Now i am finally playing with them in 8 ohm configuration.

They sound very dynamic, open, clean and the bass is deep and has slam. I can hear details with drums etc i never had heard before. It is fun to listen.

This is definitely high end. I am very satisfied. THX John keep up the good work
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Old 22nd April 2013, 06:15 AM   #44
AcuVox is offline AcuVox  United States
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Default Dipole Selection

Quote:
The lower the Qe (or Qes), generally the more detail - all else equal.

... It's often the case that a much lower Mms for the same driver diameter with a higher Qes is overall more detailed than a much higher Mms driver with a lower Qes.
I look for low Le, specifically Le/Re. The Le is the limiting factor on high frequency extension and "jerk", the third derivative of displacement. Since pressure is proportional to acceleration, this is necessary for good transient response and integration with the midrange driver.
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Old 22nd April 2013, 12:05 PM   #45
Tytte71 is offline Tytte71  Norway
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Quote:
Originally Posted by AcuVox View Post
I look for low Le, specifically Le/Re. The Le is the limiting factor on high frequency extension and "jerk", the third derivative of displacement. Since pressure is proportional to acceleration, this is necessary for good transient response and integration with the midrange driver.
I have some problems understanding/accepting that low Le in itself is important for transient behavior. It is true that Le limits the upper frequency, but when the driver is bandwidth limited by a XO the Le value should not matter. Fourier's law will apply to the system.
However, I believe Le(x) can be of importance - variation of Le vs displacement. The speaker will show off different transient (bandwidth) behavior with different sound pressure levels or for that matter, dynamic in a recording. In this context low Le may be beneficial as %-age variations in Le vs. displacement have lower influence on the XO filter/end result.
Or I might be wrong...
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Old 24th April 2013, 08:19 PM   #46
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The wiring of the VC in series with drivers in parallel will give an 8ohm overall impedance. At 8ohm you only need to deliver about 100W to the pair of woofers at 25hz to reach Xmax and about 150W at 30hz. Above those frequencies the efficiency goes up due to the baffle so you shouldn't need to apply more power than this. As long as your amplifier puts out that amount of power, that is the method I would choose.

In regards to inductance, it is linear inductance with respect to excursion more so than low inductance that is the issue. The issue though is that high inductance is usually an indication that nothing is done to linearize inductance. The other issue is back EMF created as the VC moves through the gap. As the VC is energized it becomes an electromagnet that moves or modulates the permanent flux field. The more windings there are, the stronger this electromagnet is and the more flux modulation there is. Reducing both Le(x) and Le(i) are critical. Addressing only one is less effective.

A voicecoil is like an inductor. An iron core inductor can have the same windings as in an air core inductor, but magnitudes higher inductance. This is what happens in a typical voice coil. If you measured the inductance sitting on a bench it would be very low. Putting it around the pole makes it become an iron core with the pole as the core.

The full copper sleeve put on the pole then lowers the inductance back down to that of an air core. It makes the VC a much weaker electromagnet reducing Le(i) and gives perfectly linear Le(x) as well.

Compare the Le(x) results for the TD12M here:
https://sites.google.com/site/driver...ers-td12m/le-x

to the Le(x) for drivers that do not address this issue like the GPA/Alted 414 here:
https://sites.google.com/site/driver...altec-414/le-x

You can see the Altec is a very reactive load where the impedance curve changes wildly with excursion. The TD12M however doesn't do that at all. This is the case for all the TD woofers. The Dipole and LO woofers have the additional advantage of the underhung motor with a nice flat Bl curve as well. This further makes them ideal for open baffle use.
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Old 27th April 2013, 07:41 PM   #47
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I have now 20-30 wonderful hours with the Custom AE LO15 and i have only one comment: THX John They sound fantastic. In a 10 year HiFi perspective this is one of very few "best buy" in my world (together with some First Watt gear).
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Old 30th May 2013, 03:53 PM   #48
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I have now wired both the voice coils and drivers in paralell and i got more SPL. It sounds good
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Old 30th May 2013, 03:59 PM   #49
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This is my bass amp a Musical Innovation 2x50 Watt class A made by mr Roar Malmin.
It has 2x500VA and 200.000 uF.

The active crossover (First Watt B4) is at 160hz Linkwitz Riley 24db. I dont use any kind of EQ.

John, do you think a higher crossover point will provide more slam in the midbass?

Click the image to open in full size.
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Old 6th December 2013, 08:06 PM   #50
JackG3 is offline JackG3  United States
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Quote:
Originally Posted by ScottG View Post
-2 LO15's then per side, OR a different design.

The very best bass you'll get is in the NEAR-FIELD (..if only one sub positioned very near and just behind your head with the appropriate delay for proper summing.)

It will give you these properties (assuming you sit right next to them):

1. substantially more "efficient" at lower freq.s regardless of design, but particularly well suited to a dipole/ripole/cardiod.

2. substantially more linear - with less influence from standing waves.

3. greater tactile sensation (..upper bass "punch", and lower bass "slam"). It also allows the use of drivers that have these qualities that might otherwise be a poor choice for a more typical application.

The common aesthetic I mention for such a "sub" is an "end-table" behind your listening chair or sofa, OR if stereo and only using a chair - a pair of side tables to the left and right of the chair.

Figure about a 2 foot distance to the closest "edge" of the driver (or closest driver) - the closer, the better.
Sorry, a bit OT and old but I found this thread searching on dipoles and joined just to vehemently agree with this post. Inspired by Martin King's wonderful write-ups and John Reekie's article on nearfield dipole subs I decided to give it a go and am glad I did. I'm just using a simple H-frame for an Alpha 15A per Martin's dims in the nearfield it's the best bass I've experienced. I have a very difficult, small, cinderblock room which is a modal nightmare. With this thing bringing up the rear, though (see pic), it's incredible. I get excellent depth (below 40Hz or so, anyway, which is fine for my music) along with a punch and bass-drum-head-thwak-in-the-chest that I haven't experienced before. It's...awesome. FR at my seat is utterly flat in the upper bass and ringing is negligible. It's crossoved over at 80Hz, 24dB/oct via my Denon 4310. If I have it to the side I can somewhat place it but if it's directly behind, all bass is solidly placed up front.

Click the image to open in full size.

So now I'm drooling over an AE Dipole 15, of course, so see how much better things can get.
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