A shilling request for a bit of simple 2-way crossover help...

[Apfelsauce]

As I've sort of eluded over the past few threads I've started, I built a new pair of two-ways over the last several weeks. I've been listening to them concertedly for about two weeks, and am not quite satisfied. Part of this is the cabinet, which will be remedied.

But another part is the crossover, and I'm not electrical-engineeringly smart enough to know how to proceed. Can I ask for a little blind help? I'll tell the board the drivers I used, cabinet volume and approximate dimensions, and port tuning, and the board can collectively "design" for me what it thinks would be the ideal crossover? Then I can compare this to mine - and spill the beans on what I did, of course - and proceed accordingly? I'd appreciate it, and would like some advice uncoloured by what I have done so far...

So, here's the details:

1x SB Acoustics SBX12NRXF25-4 ~3.5" mid-woofer.

1x Vifa DX25SG0504 25 mm soft-dome tweeter (shielded, because these were on sale).

...in a 10.85 L ported cabinet, internally about 4.5" x 30" x 6", with a 2" x 11" flared port and generous bracing and industrial packing felt.

So, if you were going to design a SIMPLE (second order, say) crossover, what would it look like? It's currently crossed over at 2650 Hz, but I'm not wedded to that number; in fact, I have sufficient leeway on either side of that number for a first-order filter, but I wasn't sure how to accommodate the various polarity issues that attend first-order filters. If whatever hypothetical filter the board comes up with diverges significantly from the one I'm currently running, I'm content to start all over with something else entirely. So be bold!

Anyway, discuss... And thanks!!

[Apfelsauce]

Bump! OK, so here's what I did... (As best I can in words, because I drew the schematic on paper!)

Tweeter (noted below as 1), Vifa DX25SG05-04; woofer (noted as 2), SB Acoustics SB12NRXf25-4. Roughly in order from terminal to driver...

C1 7.51 uf (in series), C2 7.51 uf (in parallel); L2 .48 mH (in series), L1 .48 mH (in parallel). "L=pad" on the tweeter, R2 2.11 Ω in series on the negative, R3 3.59 Ω in parallel. Impedance EQ, in series in parallel on the woofer, C3 6.91 uf, R1 6.25 Ω.

Does that make sense? I would find that very hard to interpret... I can scan my drawing, I suppose, or see if I can find a javascript schematic-drawing tool.

Right now I feel like there's something just not...right. The highs seemed a bit muffled at first, so I bypassed my 2.11Ω resistor on the tweeter negative. Now they seem almost bright. I'm not equipped to do any real testing, and my ears are of dubious objectivity... Would anyone care to chime in and tell me what he or she would do? I'd appreciate it!

[AllenB]

It sounds typical for a "no measurement" crossover. Start by changing the polarity and messing with the L-pad. Keep in mind that the way you alter the L-pad can affect the Q of the tweeter filter and give you more or less lower treble.

[AndrewT]

A shilling was a twentieth part of a pound. It is no longer legal tender in the UK.
I believe Austria also had schillings, but they spelled it differently.

[AllenB]

I read that a little fast and thought you wrote Australia. Of course we had shillings, got them from you guys.

[Apfelsauce]

Originally Posted by AndrewT

A shilling was a twentieth part of a pound. It is no longer legal tender in the UK.
I believe Austria also had schillings, but they spelled it differently.

I speak, read, and write English, thanks.

shill - 4 dictionary results
shill   
[shil] Show IPA
Slang .
–noun
1.
a person who poses as a customer in order to decoy others into participating, as at a gambling house, auction, confidence game, etc.
2.
a person who publicizes or praises something or someone for reasons of self-interest, personal profit, or friendship or loyalty.
–verb (used without object)
3.
to work as a shill: He shills for a large casino.
–verb (used with object)
4.
to advertise or promote (a product) as or in the manner of a huckster; hustle: He was hired to shill a new TV show.

[Apfelsauce]

Originally Posted by AllenB

It sounds typical for a "no measurement" crossover. Start by changing the polarity and messing with the L-pad. Keep in mind that the way you alter the L-pad can affect the Q of the tweeter filter and give you more or less lower treble.

Can I ask which part "sounds typical" - the crossover itself, or the fact that the results were less than ideal? (Or both?) I'm not well versed enough in electrical engineering to start experimenting, at least not with even a general idea of what might cause what results, etc.

I bought all the parts from Solen in Québec, and they offer a free crossover design service; I just sent them an email, and can, I hope, still take advantage of this service. I'm interested to see whether their "professional" design looks significantly different from my amateur mucking about...

[AllenB]

Firstly, what you are basically after is a response that is even at all frequencies. Some of these crossover design services (I'm noting this one is free) will design you a crossover based on the sound that radiates directly forward from the speaker, although there is a lot more sound that actually comes out of a speaker and it isn't all the same. I don't think you should worry about that yourself just yet but you shouldn't automatically consider this 'professional' one as ideal, either.

The "no measure" crossover usually consists of picking a crossover frequency more than an octave above the tweeters resonance, choosing a filter order (like second order), doing impedance compensation on the woofer, using the same cap and inductor combination for the tweeter and woofer based on text book formulas, and using an L-pad on the tweeter with reversed polarity.

There is nothing inherently wrong with this except the likelyhood of errors if it is based on guesswork. The main problems you'll have are that the drivers response is not flat to begin with and has phase variations. The same could be said about the impedance which means the crossover may or may not work quite as intended. Usually you'll be moderately close.

Tweaking by ear is not very easy but will bring you to a reasonable result. Measuring then tweaking will bring you to a better result. Measuring all things before you start should bring you very close.

A real crossover does not always use the same order filter for the woofer and tweeter. It does not always produce the same acoustic effect as the filter order suggests should happen. It does not typically use impedance compensation in woofer circuits, and the capacitor/inductor that is sometimes found will have strange looking values that happen to work well. Tweeters can be crossed over closer to their resonance when done properly. L-pads may use only one leg of the 'L'. etc.