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Which Qts to look for, for a Ripole?
Which Qts to look for, for a Ripole?
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Old 23rd June 2015, 08:45 AM   #1
stijn001 is offline stijn001  Netherlands
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Which Qts to look for, for a Ripole?
Default Which Qts to look for, for a Ripole?

Hi I'm planning to try out a ripole woofer design. I've shortlisted two drivers

The Eminence:
- KAPPA PRO-15B with a Qts of 0.31
- Delta 15B with a Qts of 0.62

The Monacor SP-382 PA, is used in Ripole designs I come across and has a Qts 0.75, but not the right impendance for me.

I need 16Ohm drivers to keep the total at a resonable level, otherwise I shortlisted these Eminence drivers for the following reasons:

- They are well reviewed,
- High efficiency +/-100dB
- Papercone and surrround, similair to the full-range driver they will augment.
- Affordable
-They have a reasonable midrange, so cone break up will be well out of the way after filtering.

I'm planning to filter very low at about 100Hz first order with a single coil.

Any suggestions?

I've used the Wavecor Excellsheet to calculate Sd and it estimates a possible 43Hz..
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Old 23rd June 2015, 09:46 AM   #2
Calvin is offline Calvin  Germany
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Hi,

both drivers have only a very limited excursion limit, which makes them rather useless for Ripoles.
Eminence alternatives with proper set of parameters could be the Kilomax Pro 15A, the Definimax 4015LF or the LAB 15.
With the size of the front chamber You can tune the resonance frequency and Qt a bit.
the smaller the chamber the lower the Fb.
In extreme You can achieve Fb of up to 15Hz lower than the Fs.
My experince is, that larger drivers allow for lower Qts without he need of equalization/bass boost.
Between 0.35 and 0.5 seems optimal to me for 15"er.

jauu
Calvin
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Old 23rd June 2015, 10:09 AM   #3
stijn001 is offline stijn001  Netherlands
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Which Qts to look for, for a Ripole?
Thanks Calvin,

Thanks for pointing this out, I didn't know excursion was that critical. De Kappa Pro does 13.2mm XMax, where as the Definimax does 15.5mm XMax.

I like the look of the Definimax and know Nelson Pass used one with great success in a dipole, something I took inspiration from. However I need a higher impedance.

Any more suggestion?
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Old 23rd June 2015, 11:23 AM   #4
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Calvin View Post
Hi,


Eminence alternatives with proper set of parameters could be the Kilomax Pro 15A, the Definimax 4015LF or the LAB 15.
With the size of the front chamber You can tune the resonance frequency and Qt a bit.
the smaller the chamber the lower the Fb.
In extreme You can achieve Fb of up to 15Hz lower than the Fs.
My experince is, that larger drivers allow for lower Qts without he need of equalization/bass boost.
Between 0.35 and 0.5 seems optimal to me for 15"er.

jauu
Calvin
Hi,

I don't what your talking about regarding tuning of a ripole.
Or what box arrangement with Fb the above applies to.

rgds, sreten.
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Old 28th June 2015, 06:42 AM   #5
Calvin is offline Calvin  Germany
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Hi,

well, the thread is about Ripoles and my post deals with Ripoles
In case You´re unfamiliar with Ripoles ....
They are variants of Dipole Basses.
They are characterized by comparatively very small open chambers for the front and backside of the driver diaphragm.
They comprise a Dipole of folded Baffle style.
Using two drivers facing each other, two of the chambers may be joined into one chamber that both drivers use at the same.
This way the more commonly known 2-driver-3-chamber structure develops.
Due to their smallness the chambers add a serious dynamic load to the drivers which leads to the lowering of Fs and raise of Qts.
The smallest chamber shows the greatest effect and depending on the driver parameters Fs may sink by up to 15Hz.
With larger dimensions as for e.g in the folded dipoles after S.Linkwitz or plain open baffles the driver´s Fs and Qts remain rather unchanged.
So, driver parameters shall differ between a small and a large folded dipole.
While verylow Fs and Qts drivers are suggested by SL (12"/20Hz/0.2), the drivers for a ripole may preferrably be of medium Fs and medium to high Qts (15"/25-35Hz/0.35-0.5).
One finds the parameter set 35Hz/0.35 in many Pro-audio drivers.
Fortunately over the last years more and more drivers occur with raised excursion capability.
Beyma 15LX60, FaitalPro 15FH500 and 15FH520, BMS 15N850, Eminence LAB15, RCF 15 LP200AK, and some more.

As with all dipoles, the wavelengths within the working range are lareg compared to the baffle dimensions, hence they suffer from acoustic phase cancellation.
The effect is that for same SPL the excursion of the diaphragm is larger than with other cabinet styles, hence the need for longthrow drivers (requirement to move more air volume).
Larger sized drivers and/or Arrays of drivers allow to trade membrane excursion against membrane area.

jauu
Calvin
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Old 28th June 2015, 07:08 AM   #6
TBTL is offline TBTL  Germany
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A ripole is a dipole with added mass to the cone in the form of air. A longer chamber length results in a larger added mass. A smaller cross section does the same, because it forces the air to move faster.
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Old 28th June 2015, 09:31 AM   #7
stijn001 is offline stijn001  Netherlands
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Which Qts to look for, for a Ripole?
Thanks guys.

Calvin, I had a look at your website, you make some great looking audio gear. You obviously know your stuff.

I think the Eminence Kappa Pro 15B is the best compromise I will find in 16Ohm driver.

What do you guys think about trying to cross-over @ +/- 100Hz with just a single coil., is this feasible (I'd rather not go the Bi-amp route)? I understand this large a coil will impact dampening, but how critical is this at these low frequencies? How liniear can I expect the Ripole to stay below 100Hz, I've not found any measured data on this. Any pointers would be apprecaited.

I'm planning to integrate the Ripole front slot into a large baffle, so hopefully this will deal with accoustic shortage better.
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Old 29th June 2015, 09:11 AM   #8
Calvin is offline Calvin  Germany
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Hi,

Your hint regarding using a coil reminded me of something I miussed saying.
A Ripole implemented properly features a passive EQ network.
This consists of a series inductor with a copper resistance of 0.3-0.6 and a parallel RCL network.
Whereby only the ohmic part of the inductor is required for the notch filter to work on.
The inductive part could be omitted with, but it performs a very welcome lowpass functionality.
The slight raise of the Qts due to the series ´resistance´ counters for the losses of the inductor ... so efficiency won´t be affected -> no loss of SPL.
Inductors with higher dc-resistance are quite cheap.
See for example the I-Kern inductors at Intertechnik.de (pic below).

Without that circuit its just a small folded dipole.
The network comprises a lowpass and a notch filter to cope with the chamber resonance (typically ~200-300Hz, depending on the cabinet dimensions).
Besides increasing Qt slightly, the Fs drops even more.
The impedance response also drops in value and the minimum, somewhere between 100-200Hz, should be watched if teh amplifier can drive that load safely.
It is not a necessity to use highohmic drivers and to connect the drivers in parallel ... the series connection of 4-ohmers works well also.

jauu
Calvin

ps.
Quote:
I'm planning to integrate the Ripole front slot into a large baffle, so hopefully this will deal with accoustic shortage better.
This will change to whole dimensioning.
It is to understand that the cabinet already is a baffle, just a folded one.
Attached Images
File Type: jpg I_Kern_Spule.jpg (4.7 KB, 589 views)
File Type: gif Ripole Subwoofer Filter - principal schematics.gif (23.8 KB, 591 views)

Last edited by Calvin; 29th June 2015 at 09:14 AM.
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Old 29th June 2015, 08:21 PM   #9
stijn001 is offline stijn001  Netherlands
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Which Qts to look for, for a Ripole?
Thanks Calvin, some great tips. The 200-300Hz notch filter is a great idea, do you still think I need it if my LPF is at 100Hz, using a single 25-27mH transformer inductor?

I’m planning to use a single driver, so putting them in series is not an option. Keeping the total (three way) system impedance at a reasonable level is a main concern. Efficiency is less of a concern.

I don’t quite understand why putting the Ripole into a baffle is a concern. Doesn’t it just make the total effective baffle bigger thereby reducing the effect of acoustic shortage even more, which should be a good thing. I thought the key to the Ripole design is the slotloading in combination with the baffle effect of the rear chamber (compared to the Dipole).

This is the inductor I was thinking of:
Audio Tschentscher | Lautsprecherreparatur | Lautsprecherentwicklung | HIFI - High End Trafo Spule Audio-Tschentscher, Feron Trafospule 27,00 mH, Produktion Audio Spul
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Old 30th June 2015, 11:19 PM   #10
zobsky is offline zobsky  India
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Quote:
Originally Posted by Calvin View Post
Hi,

both drivers have only a very limited excursion limit, which makes them rather useless for Ripoles.
Eminence alternatives with proper set of parameters could be the Kilomax Pro 15A, the Definimax 4015LF or the LAB 15.
With the size of the front chamber You can tune the resonance frequency and Qt a bit.
the smaller the chamber the lower the Fb.
In extreme You can achieve Fb of up to 15Hz lower than the Fs.
My experince is, that larger drivers allow for lower Qts without he need of equalization/bass boost.
Between 0.35 and 0.5 seems optimal to me for 15"er.

jauu
Calvin

Well said, .. don't underestimate swept volume when selecting ripole drivers. They need it.
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