Help needed for home made

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I haven't really given this much thought, but some off-the-shelf crossovers are in the right ballpark:

HW 3/130 NG - 8 Ohm | Visaton

Not a million miles away from where you want to be! :D

Falcon Acoustics do some KEF and Cambridge crossovers too:
Crossovers, Networks, Filters, LS3/5a, KEF, RAM, Celef from Falcon Acoustics.

Now do those measurements and simulating I asked for. The Visaton W200S, W170S and G20SC drivers will be similar for simming purposes. This is serious engineering, not messing about. I will help you up to a point, but it's your project.

The readings I have after a bit of trying to work out why the multimeter was buzzing was this;

Top 101
Mid/bass 067
Bass 228

Does this sound right? There was some jumping around with numbers to start with but I think that's it...
 
John, in order to measure the dc resistance of the drivers you have to disconnect them from the crossover network - did you do this? Also make sure you have selected a low resistance (ohms) scale on the mutimeter. The dc resistance of the B139 should be around 6.5 ohms.
 
My capabilities are that I can do some soldering if following instructions but don't really understand the terminology or what the components are about.

Budget would hopefully not exceed £200, time is not limited apart from around normal working hours.

I am running the speakers from a Nad C370.
That's perfect - it has the ability to be used as an integrated amp or to split into pre + amp. With a Y shaped cable, you can run the pre into 2 amps (itself and one other). I have a NAD 3020i which I sometimes use this way.

So my question is, is there much of a difference with your suggestion and just putting a passive low pass filter in line with the Keff?_

The amp suggestion gives:


  • Sharper filter (18dB per octave). A passive with a single inductor is 6dB per octave.


  • Adjustable filter - just turn a dial to move the crossover point. With passives, you have to buy more parts / rebuild to tweak the crossover point.


  • modifiable gain - if you want more bass, just turn a dial. With passives, if you want more bass, you have to add resistors to pad down everything that isn't bass.


  • Lower inductance. Some people claim that a direct connection amp-woofer is better for this reason, but I glaze over at the explanation for this :)
Negatives are


  • Cost - but still < 50% of your budget. And the cost of passives can blow out if you find that you need different values / need more parts.


  • Risk that Parts Express won't pack it properly / your postman will chuck the parcel extra hard, requiring a return or refund (but PE are good with this).


  • Crossover point can't be higher than 150Hz with this particular amp.
 
I got this going on a 28cm wide baffle. Looks alright to me.

Just a question of getting the levels right for the B139 and a 6" midbass and 1" tweeter. The bafflestep frequency is 500Hz.
 

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That's perfect - it has the ability to be used as an integrated amp or to split into pre + amp. With a Y shaped cable, you can run the pre into 2 amps (itself and one other). I have a NAD 3020i which I sometimes use this way.



The amp suggestion gives:


  • Sharper filter (18dB per octave). A passive with a single inductor is 6dB per octave.


  • Adjustable filter - just turn a dial to move the crossover point. With passives, you have to buy more parts / rebuild to tweak the crossover point.


  • modifiable gain - if you want more bass, just turn a dial. With passives, if you want more bass, you have to add resistors to pad down everything that isn't bass.


  • Lower inductance. Some people claim that a direct connection amp-woofer is better for this reason, but I glaze over at the explanation for this :)
Negatives are


  • Cost - but still < 50% of your budget. And the cost of passives can blow out if you find that you need different values / need more parts.


  • Risk that Parts Express won't pack it properly / your postman will chuck the parcel extra hard, requiring a return or refund (but PE are good with this).


  • Crossover point can't be higher than 150Hz with this particular amp.

I can see the advantages and disadvantages of this. For me I think the disadvantages outweigh the advantages. Also this would involve cutting another hole in the back of the speaker box for another terminal.
I do like the idea of it being fully adjustable though.
 
I got this going on a 28cm wide baffle. Looks alright to me.

Just a question of getting the levels right for the B139 and a 6" midbass and 1" tweeter. The bafflestep frequency is 500Hz.

Steve, I have been away with work and not had the chance to re-do the readings yet but what you have in the graph is looking good and I like the idea of crossing at 500hz.

I have attached a pic of the Ditton crossover which looks quite basic. I could only see the value of the bigger Alcap which is 93-8340.
The Keff has SP1044 written on it.

I will get the driver values this weekend and do the SIM. A question I have is will I need to measure the internal box sizes and if so, how does that work with the fact I have a box within a box for the Keff?
 

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I got this going on a 28cm wide baffle. Looks alright to me.

Just a question of getting the levels right for the B139 and a 6" midbass and 1" tweeter. The bafflestep frequency is 500Hz.

Steve, I have done the SIM but it certainly doesn't look like yours. I'm not sure what has happened but the input data is correct with the drivers and resistance value. The enclosure details are correct but something is not right.
Is there a way on here of sending you my project so you can have a look over it?

Regards,
John.
 
Here it is, big John!

Anything you want to change, just mark it in red and let the optimiser in the extras menu play around with it. It usually gets it right. Or better.

Steve, the graph seems to show 3 drivers but only 2 doing anything. Even the crossover is only showing 2 drivers on it. I have tried the optimiser but still not getting anywhere. Even the 2 drivers are crossing just above 2000.
See pic.
 

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A friend is helping me to get the SIM sorted.

A question I have is, when the SIM is looking good, I presume it will give me a wiring diagram of the crossover needed. Will this be accurate to build from or is there another process as this was based partly on some drivers from the program?
 
Unzip 3 way classic folder downloaded from here.
Place 3 way classic.BPJ in projekte folder.

Start boxsim and load project file 3 way classic from file menu.
To view crossover go to amplifier menu and select edit crossover network.

Voila.

By default, Boxsim displays the default project loaded.
When finalising a crossover, you enter convenient nearby preferred values which are easily obtained at suppliers and reoptimise around them.
 
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I am having a dilemma with what frequency to cross the bass with the mid.
On one hand, knowing the bass is 20 to 1000hz, makes me want to crossover at about 500hz.
On the other hand, knowing the mid is a mid bass capable of clean lower frequencies, I am thinking maybe crossing about 300hz.
Any advice here would be appreciated.
 
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On one hand, extending the mid down to 300Hz rather than 1kHz puts a crossover in a less sensitive region. Not that a crossover has to be a problem but, sometimes they are just short of perfect.

On the other hand, try measuring (with a ruler) the direct and floor reflection distances to see which drivers are affected by which modes.
 
As much as I have looked into active crossovers, this seems to be a complicated affair especially having to use multiple amps or inferior AV amps.
I am working on getting the passive crossover sorted with a friend helping me with the SIM program.

A dilemma i have at the moment is this;
If I am going to the expense of getting some passive crossovers made, do I go ahead with using the cabinets I already have with the Ditton 110 mid and top and Keff B139 bass which are amazing sounding speakers, or do I make a new set of speakers still using the Keff B139's with the ProAc Response Two s as a mid and top.

Any thoughts on this would be much appreciated...
 
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