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I want to bi-amp Lowther DX3's in Azura 204 horns and Altec 414's in mini Onken enclosures. The DX3's will be driven by my 2A3 Paraglow II's while the 414's will be driven by an undetermined sand amp. My preamp, a Foreplay III, has two outputs, so I thought one signal could go into an active crossover system feeding the sand amp. The other signal would go directly to the DX3's allowing them to roll off naturally so as to not put anything between the tube amp and the speakers.
Am I missing something? Does this make sense? Is it possible to just use the crossovers for the woofers? I'm thinking of buying a cheap active crossover like an old Furman or Dod which has variable crossover points so I could experiment with different values initially, and then go for a tubed xover at a later date, when resources and knowledge are at a higher level.
I'd appreciate any recommendations for an active crossover and suggestions for what a good crossover point to start at for the Azura 204's would be.
Thanks
Bryon
Follow Ups:
Some very helpful ideas - I have thought about the Welborne Labs xover kit as it has high quality components but Ron is apparently moving his business at the moment and his website isn't accepting new orders - maybe later. The Marchand options look good as well. Both of these options require a bit more knowledge than I have about which crossover point is the best for the Azuras and the room.
So I've decided to go with a Furman TX-3 that a fellow inmate offered me [Thanks Benjamin] and play with the crossover points until I get a handle on the points which work for my system and then go with either a tube crossover , or the Welborne labs kit.
thanks again everyone for the helpful suggestions
Bryon
I use Welborne labs crossover set to 200hz with 204 Azura and Altec 414 in BR.
I tried 2nd order passive line level crossover Oris/Bert approach but found with Welborne get much cleaner bass.
Rafal
Agree w/this recommendation except I cross over at 100 hz due to using a combination front horn/BR enclosure.
Jim D.
i have no horns yet but may get soon
the azura 204.
i have some aer with high Qt and some
38 cm. xo around 200 Hz.
For the time being, what works best
is a digital filter for the bass
with steep slopes. 48 or 96 db/oct
i run the aer full range.
with lowthers avoid any kind of filters
between them and the amps.
Use a steep filter for the bass.
By experience passive with a cascade
of LR to get 18DB slopes (orys filters)
sounded muddy and yielded a poor bass
integration.
good luck and let us know.
Vince
There is nothing good to be had by trying to force the paraglow and lowthers to handle much below 100 hertz (really anything lower than the horn's cutoff IMHO). So you really need two crossover points, a high pass to the paraglow/lowthers, and a low pass to the sand amp/414's.
Marchand sells a very low cost solution if you don't mind doing a little soldering and building your own "box". Look at the XM1. Their power supply is adequate but you could build something a lot better from scratch. If looks matter you can consider the XM9. Marchand is a lot better than the options you mention. If you really hate the idea of op amps on the lowthers consider the XM46, a passive line level crossover. But it is a very tough load for a tube based preamp. I'd ask Paul Joppa's advice (a step down transformer after the foreplay is one way for example).
Russ
Russ makes an excellent point. The Lowther drivers should not be run full range as they try to reproduce the bass, it will muddy the midrange through the doppler distortion, and force the amp to work harder than it needs.
However, instead of a separate crossover device which will reduce the transparency of the midrange, simply size the capacitor(s) in your amps to serve as high pass filters.
Retsel
F= frequency in hz
R= resistance in ohms
C= capacitance in farads
I did some online research and found this formula to determine the size of capacitor to use as a high pass filter in the Paraglows.
I was surprised at the values I ended up and as I am not overly competent in these matters, thought I'd appeal to those who are.
The DX3's are 16 ohm drivers but actual resistance is more like 10 ohms. Which value should I use for R? Can I ignore the supposedly small level of resistance that the output RCA jacks and speaker cable add?
If I want to aim at a cutoff 200 hz and I use 16 ohms, the capacitor value works out to .202uf so I can parallel a couple of .10 uf caps to get there.
If I use the actual resistance of 10 ohms, the capacitor should be in the neighbourhood of a .33 uf cap.
Is this the right formula to use for this purpose? Is my math even close to being correct [it's been nearly 40 years]. Am I missing anything obvious [or not so obvious?]
thanks again for your input
Bryon
I would determine the value experimentally since what the capacitor sees is the impedance at 200 hz not the nominal impedance of the driver. Also this impedance is seen "through" the transformer.
Before sizing and investing in all that money for the V-caps, I would make one more change (if you have not already). I would wire your output transformer as an autoformer, instead of the conventional parafeed setup that you have now. To do this, search this and the Bottlehead forum for autoformer and parafeed and you will read the instructions for how to make the conversion. This change provides a noticable improvement in transparency.
Once you make the change to the autoformer setup, try a capacitor in the 0.2 range (if you are like me, you have these sitting around) and see where the Lowther starts to roll off (measuring their output using a test CD). You can then ratio the 0.2 capacitor value appropriately to derive the crossover point at 200 hz.
Do you also have a coupling capacitor in this amp (the capacitor between the driver tube and output tube)? If so, you can size this smaller as well to have a second order crossover at 200 hz. This will also save you money with the V-caps if you plan on replacing these as well.
Retsel
Sounds like a good idea - I know you can increase the bass by increasing the value of the capacitor and so I guess the inverse would hold true as well.
The question is what value to use. The Paraglows came stock with 2.0 uf caps and I actually increased them to 3.3 to get improved bass. How much lower do I have to go? 1 uf? .47 uf? I was thinking about getting teflon v-caps for my Paraglows and this could be an unexpected savings as the price of the v-caps increases proportionally and significantly as the cap value increases.
thanks for the input
Bryon
Why not try the passive line level x-over that BD-Design use on their Oris horns?
Frode
Hi Bryon
If you can DIY Welborne lab is selling a crossover Kit specifically designed for Oris (and the like)It is active bass with passive hf (or you can run lowther directly)It is designed for onken like solution. I heard DX3 in Azura 204 horn and its OK although I think with the time you will lack hf extension and integrating any tweeter with such a big horn is a bitch. rEgards, L
not sure they still sell the xo kit.
????
This is a subject that can have almost religous conotations, with various belief systems having different opinions.
However, I think you wil likely do better using some form of active crossover that allows using a high pass on the subs -
IMHO, if you have digital sources - the best way is to use a digital crossover that has digital in, then let the crossover do the filtering.
Even so, there are a number of ways of going about it.
Would hate to say one is better than another, however, digital is clean and allows the variable settings to try how things sound.
While tubes and HE do not normally make you think of digital - if that is your source, why would it matter - you're just using the DACs in the Crossover rather than your CD player
Thanks for the input - I haven't looked into a digital crossover at all, although it might be a way to approach dialling in the crossover if a digital crossover was available cheaply.
I listen to vinyl about 98% of the time, so I'm a bit hesitant about introducing a digital element in the crossover. I'm not sure how much impact it would have if it were just operating at <200 hz, so it might be worth trying in order to determine the correct xover points.
thanks
Bryon
PS
Your crossover points will depend a good bit on the slopes you use.
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