Some Design Questions

[coolkhoa]

I've taken a look at speakerbuilding.com's Esquire design. I think its crossover is unnecessarily complicated (4th order Linkwitz-Riley) for those particular drivers (Vifa P13 and D27).
That said, I think the design proposed by planet10 (5 mfd cap in series with tweeter) is too simple. I believe the tweeter needs some attenuation courtesy of a resistor, and maybe both drivers can get the help of a Zobel.

Please discuss.

[coolkhoa]

planet10?

[Timn8ter]

Just a thought, not really a recommedation but, I wonder what a 1st order series at 3 or 3.5 Khz would sound like? Something like .30mH, 11.5uF, and a L-pad of 11 ohm parallel, 6 ohm series.
Opinions?

[coolkhoa]

Why series?

[Timn8ter]

There was a very long thread on this not too long ago and I don't want to start that here. The one definite advantage to series is, if you want simple, no Zobel is needed as the series XO will "correct itself" with impedance changes in the woofer. The argument for parallel is, if you know for sure where you want your XO point, it gives you more control of the roll-off points. Other than that both networks give you virtually the same results. I've been using extended bandwidth drivers in my designs and the 1st order series XO has served me well.

[rabbitz]

Yep. We discussed this combination quite a bit and there's some info on this in the "Wiki" under Vifa P13/D27 project.

x. onasis has been actually building this combination as an exercise and did report his findings on the 5uF cap. I sent him a 1st order series xo to try.

Crossover 3225Hz
Zeta = 1
Resistor in series = 10ohm
Capacitor = 3.3uF
Inductor = 0.7mH (low DCR less that 0.4ohm)

These were calculated at the impedance at the crossover frequency and not the nominal values. This is a suggested starting point and like all series xo's, subject to fine tuning.

x. onasis are you out there buddy??? Any comments???

This is the thread:
diyAudio reference speaker project

[Timn8ter]

Is the single series resistor somehow preferable to the L-pad configuration?

[weeghel]

It can help sometime, yes. Vance dickason discusses this in the LDC, paragraph 7.60 (I own the 6th edition). The damping with a single resistor (on the driver side) is frequency dependent, so you can use this to your advantage.

[Jay]

SMALL BOOKSHELF ESQUIRE

Esquire is a small speaker. The enclosure doesn't help much in the low frequencies. The solution is to take away the sensitivity out of the drivers by adding resistance, or by high order steep filtering such that when it is driven hard, the drivers survive. IMHO, complex filtering is even more acceptable in small bookshelves, especially when the amplifier is the standard high wattage bipolars.

WHY SIMPLE CROSSOVER

We build audio system for one reason, to enjoy the music (not necessarily low NSR, low THD, or high price tag). IMHO, sonic is the most important factor for audio enjoyment. Build a Gainclone, short signal path (low FB) preamp and a fullrange (TL) speaker. Quality parts won't make you broke either. Tell me if you can't enjoy the music. So if you want to build a speaker, think first if you can take the filtering components out of the sytem as much as possible. The crossover is like a medicine, it is a poison, you need it to cure something, but if you don't have to consumme then don't.

Fullrange drivers are designed for no crossover. Try it first. If you think there's something that you cannot live with (usually the striking mids), then use ordinary drivers, but think of the simplest crossover possible first. Only 1 cap for the tweeter, or simple series crossover.

THE DIRECT COUPLED VIFA P13WH

P13WH is doable for direct coupling. You get the sonic, that's the good news, but you will have to overcome the problems. Because it will be too sensitive, you will not get enough lows, so you need the enclosure to support the bass section. Small bookshelf is not an easy option, not only because you will not have decent bass but the resonance/bump due to the enclosure is not easy to overcome. If the highs from P13WH is not enough, then the 4.7uF plus a tweeter may be used to extend the treble, but you have to be prepared with reallignment of the tweeter position.

THE SIMPLE SERIES X-OVER

Simple 1st order series has similar problem in bass area, and it has even more problems. Basically, if you can get away with only 1 inductor and 1 capacitor then you will have a very good speaker. But if there are problems that you have to overcome due to WRONG driver selection, then adding compensation circuits (notch and series resistor) results in more damaging effect than using them in parallel crossover (L-pad is often a big no) .

To get away with simple series x-over, you need a smooth drivers that do not have bumps around rolloff frequency (because the rolloff will not be steep), you need tweeter capable of handling higher power and lower resonance point. And you need a tweeter that is not too sensitive compared to the woofer (to avoid series resistor). And probably you need a low wattage amplifier. Even so, you will still get problem when you drive the speaker hard enough. The most common problem is the midrange: you get a shouting woofer, you get frying tweeter (so low DCR inductor is mandatory), or simply lose control of the midrange (Choosing a high "zeta", that is to attenuate mid frequencies, may avoid midrange problem but you loose the mid details that is very good and necessary for good imaging).

WHAT I WILL TRY TO DO TO BENEFIT FROM SERIES X-OVER

May be not a good idea to you that rely on dificult-to-use design tools. But designing a 3-way is always a headache for me and it seems that 2-way is never enough (trade of between lows and mids).

The first thing is the correct drivers. The selection of L and C values are such that they form a "2nd order" filter for each individual driver that will expose the potential of each drivers. Usually, 8uF to 12uF suitable for 6 to 8 inch woofers. The L is around 1mH to 1.8mH. The x-over will be too low, but the tweeter will be protected by high zeta and a 4 to 5 inch midwoofer.

Basically, it will be a parallel of 2 speakers, where each speaker uses series x-over, except that for the smaller speaker the tweeter is replaced with a resistor or a cheap tweeter without a cone or dome.

What do you think? And how about the enclosure "strategies"?

[coolkhoa]

Jay,

Do you think 1st order Butterworth (6dB/6dB) is appropriate for these drivers? Or should I let the woofer reproduce its full range and stick with a cap on the tweeter?