hey everyone!
Ive decided to build a new speaker.
Drivers will be:
18" woofer. Woofer choice not made!
Audax pr170mo or PHL 1120
Hivi Rt2Ha
Ala Geithain arrangement: https://www.kmraudio.com/geithain-rl901k-pair.php
The box will be about 180L.
Ill be upgrading this thread as i go!
Ive decided to build a new speaker.
Drivers will be:
18" woofer. Woofer choice not made!
Audax pr170mo or PHL 1120
Hivi Rt2Ha
Ala Geithain arrangement: https://www.kmraudio.com/geithain-rl901k-pair.php
The box will be about 180L.
Ill be upgrading this thread as i go!
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Interesting. It seems difficult to predict where to put a crossover.
Be careful with the 1st order crossovers - don't forget driver excursion unfortunately doubles every octave below the (high pass) crossover frequency. Until resonance, that is, and then the potential for problems may get even worse:
In the case of the tweeter, main resonance may well be damped by ferrofluid, so excursion won't suffer further excursion problems, and below the resonance frequency, excursion will actually be attenuated at a rate of a net halving per octave. So, a highish resonance frequency is beneficial, provided the tweeter is ferrofluid-damped. But, anyway, most tweeters suffer from significant distortion anyway, without adding to it by requiring it to cover, in effect, unnecessarily low frequencies.
But the midrange driver won't be mechanically damped, which means its cone will flap around at resonance (the impedance presented by its crossover capacitor will be too high to afford much electrical damping). This situation can be helped by adding an RC Zobel damping circuit in parallel with the driver, and by critical choice of resonance frequency. The R may need to be able to dissipate some power. But a pretty unsatisfactory situation, all in all.
My advice: go for at least LR2.
In the case of the tweeter, main resonance may well be damped by ferrofluid, so excursion won't suffer further excursion problems, and below the resonance frequency, excursion will actually be attenuated at a rate of a net halving per octave. So, a highish resonance frequency is beneficial, provided the tweeter is ferrofluid-damped. But, anyway, most tweeters suffer from significant distortion anyway, without adding to it by requiring it to cover, in effect, unnecessarily low frequencies.
But the midrange driver won't be mechanically damped, which means its cone will flap around at resonance (the impedance presented by its crossover capacitor will be too high to afford much electrical damping). This situation can be helped by adding an RC Zobel damping circuit in parallel with the driver, and by critical choice of resonance frequency. The R may need to be able to dissipate some power. But a pretty unsatisfactory situation, all in all.
My advice: go for at least LR2.
The intended tweeter is a sealed planar, and no FF.
I don't know how a Zobel will help at midrange Fs unless cap is huge in value. Without this, the circuit will only affect inductive rise in its stopband. Parallel resistor will do the trick cheaply,, but needs power handling.. Best bet is an LCR targeting Fs to bring it down.
Yes, more slope will likely be needed, and a chamber for the midrange so it does not flap from woofer air movement due to proximity.
Yes, the Zobel C is there to allow the R to damp the cone resonance, and needs to be sized accordingly. An LCR version could work better in that respect, but might negate the phase advantage of the 1st order crossover, so ultimately self-defeating.
The LCR part of the Zobel is aimed at making the impedance simpler, and impedance phase with it. It won't necessarily turn into a problem.
Well, that's true - though some fine tuning would probably be necessary. The main idea is to allow a high resonance frequency driver to be used, which would minimise the excursion disadvantages of the 1st order crossover (but additionally will make for a driver with high sensitivity/excursion, so a win in that respect too).
I am planning a three way with 18" woofer myself. But IMO a coaxial mid/tweeter makes more sense. A crossover below 200hz brings everything within 1/4 wavelength.
That would be a rather low crossover frequency for a small OB midrange assembly - or for a small sealed midrange enclosure - why not a somewhat higher frequency? Though you can't really go too high, as the bass driver will be breaking up (which is another reason not to go for a 1st order crossover).
If you look at my post history, youll see that the speaker i use now its basically the same thing in terms of slope/design and drivers used (apart from the 18" woofer). Therefore, I know those drivers can tolerate 1st order
Series XO 1st order:
The whole crossover contain no resistors to lower sensitvity, only two Inductors and two Capacitors.
The reason I always prefer series networks for 1st order crossovers, is that due the use of "shunt elements" at frequencies where the driver impedance is approximately resistive means the drivers inductance and LF resonances do not require compensation networks.
This is totally independent from all the articles all over the net where debunkers try to prove that there is no difference between series and parallel network. This case is only true for resistors, not for real drivers. A parallel type crossover would require both voice coil inductance and driver LF resonance to be compensated, making the parts count very large, especially for the midrange.
In effect, the planar Tweeter is a resistor, the midrange will need RC "Zobel" to compensate the voice coil inductance and at least one RLC "Trap" to compensate the impedance "humps" at low frequencies to make it behave like a resistor. The Bass Driver would need a RC "Zobel". Then an equivalent parallel crossover will work broadly equal. The series network does not need these compensation elements and is super simple.
Midband sensitivity is around 95dB/2.83V/1m with around 6 Ohm impedance.
Xo points about 350hz/1500hz
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Well OK, though do check the tweeter's specs, as I had a quick look and they seemed to be talking about a crossover frequency of 3kHz, 2nd order.
I do like the idea of the 18" driver and concentric mid/treble. Crossing at 350Hz, there's a lot of scope for unwanted box effects, so do pay attention to, for instance, bracing, internal baffles and wall lining (with thick felt).
I do like the idea of the 18" driver and concentric mid/treble. Crossing at 350Hz, there's a lot of scope for unwanted box effects, so do pay attention to, for instance, bracing, internal baffles and wall lining (with thick felt).
ill make a 1.5'' long tube filled with fiber behind the midrange driver for sure.
Ive seen a couple of speaker companies using those tweeter in a 1st order xo quite low.
I think the hivi rt2ha specs are for commercial applications? if I were to use those speakers in a over 105db setting, probably the hivi would struggle, not at 85 db average!
Well that and the assumption that the public at large will abuse it for various reasons/ways, but the driver's ~94 dB/m with its ~2nd order roll-off + 1st = ~18 dB/3rd acoustic XO seems plenty good enough for us ~1%ers that 'have a clue' what its actual limitations are.
If I got thinking right what happens as the mid woofer is brought in front of the bass box the backwave of the mid dipole reflects from the boundary which would suck out more bass and cause interference above. If this is right then it would be good to keep the main speaker box as small as possible so that the lows of mid back side would not reflect that well from the box and go around instead. So bafflestep as high as possible and /or crossover as high as possible to have as little dipole mid bass reflect from the box (bass woofer) as possible.A quick check on the effects of the enclosure size and the "open baffle" mid, using "edge":
The PR170MO will be -3dB @ 300Hz due to limited baffle size.
The fear is that -3db point on the dipole mid goes octave up as result when it is brought in front of the bass woofer. Also its acoustic high pass would be 1st order already from dipole config and now perhaps even more. Add 1st order electic filter and its 3rd order acoustic slope as result. Geithain has very small baffle, not much bigger than the bass woofer, perhaps a coinsidence or perhaps it has to be 🙂
Also the construct in front of the bass woofer will make some acoustic lowpass so perhaps size and shape would benefit prototyping a lot, or copy what Geithain has done.
Interesting project, it'll be very interesting to see how prorotype measures.
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I'm just speculating on it and suspect there is some prototyping agead to get the acoustic filters play nicely together.
Bafflestep is seen on the edge screenshots posted. if speculation is true and xo is at 300Hz the baffle support and reflection is still strong here and it will result some destructive interference for the mid, possibly making the electrical xo hard, possibly its nothing to worry about. Takeaway is that its better to have the structure work for the system and not against it which might take some prototyping to get tuned right. Size of the mid baffle, distance from bass woofer cone, attenuation on the back, possibly even the size of the main box plays a stake. In the end the acoustic responses show where the good crossover points are.
Bafflestep is seen on the edge screenshots posted. if speculation is true and xo is at 300Hz the baffle support and reflection is still strong here and it will result some destructive interference for the mid, possibly making the electrical xo hard, possibly its nothing to worry about. Takeaway is that its better to have the structure work for the system and not against it which might take some prototyping to get tuned right. Size of the mid baffle, distance from bass woofer cone, attenuation on the back, possibly even the size of the main box plays a stake. In the end the acoustic responses show where the good crossover points are.
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Geithain xo are around 500hz. I therefore am optimist that this sort of design can work.
their mid-HF baffle is actually not as small as it could be... not sure why
I suspect it is sized to adjust the acoustic slopes to work together, lowpass for the woofer and highpsss for the mid perhaps.
Given secon thought to the mid back side reflection from the vass wpofer, perhaps it is just what doctor orders if it happens where the main diffraction hump of the woofer is, which perhaps compensates. Anyway, after you build and messure then you'll see how the system plays out 🙂
Given secon thought to the mid back side reflection from the vass wpofer, perhaps it is just what doctor orders if it happens where the main diffraction hump of the woofer is, which perhaps compensates. Anyway, after you build and messure then you'll see how the system plays out 🙂