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Multi-Way Conventional loudspeakers with crossovers

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Old 14th May 2008, 12:11 PM   #11
pjpoes is offline pjpoes  United States
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Oh forgot to add, Orca did finally get back to me, and I can get replacement domes for the tweeters, so its possible. None the less, I found out what the problem was. They were "damaged" in shipping, the coils were out of alignment. I dismantled them and found ferrofluid on the back of one of the domes. I cleaned the two domes, carefully reassembled them, used a cross hatch torquing method, and finished final reassembly. Using this method I was able to fix the problem. The domes both measure around .15 mh of inductance, around 6.8 ohms dcr, and have an fs at around 1000hz. The impedance rise looks normal and smooth now, everything seems good. The midbass drivers needed to be worked in a little, and then securely clamped durring testing. After my testing in the lab I realized that you really should test the drivers in a near anechoic room with somewhat controlled atmospheric conditions. The lab I was in used the 12'x12' anechoic chamber with controlled temperature, humidity, etc. The driver was securely mounted by its motor assembly area. Through this method, I managed roughly equally good results with all the methods of testing. The Fs still is too high compared to that spec sheet you show, but its close enough. The Fs is like 44hz and 46hz for each of the drivers respectivly, and thus my Vas and mms are a little off, but I've been told its fine, average the two if it makes me feel better.
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Old 14th May 2008, 12:49 PM   #12
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About the high order xover read what I've said to Simon.
http://www.diyaudio.com/forums/showt...18#post1505718
unless you go the Duelund (DK) way with extremely expensive parts that you can't afford.

As soon as you have a graph for tweeter output in frequency, post it (only found one for the Focal TC120td).
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Old 17th May 2008, 03:40 PM   #13
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In fact FOCAL 6 W 4254 shows a high BSC (~9dB) between 100Hz and 1KHz. As you said earlier about a 12dB BSC, not that much but very close, for the driver to be used as a mid-woofer. Unless you add a subwoofer. I will re-check with Edge/Basta! software next to confirm.
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Old 17th May 2008, 09:58 PM   #14
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Don't confuse driver roll off + the effects the room has for BS. You cannot get more then 6dB by nature of how BS works, if there is more then this, look elsewhere for the cause.

I should also add a rising driver response can offset this too.
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Old 17th May 2008, 10:25 PM   #15
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At 9" cabinet width, part of what looks like baffle step is actually a diffraction peak centered at around 1100 Hz with a slope that happens to blend into the baffle step slope.

Modeling a 9" wide baffle in The Edge showed slighty higher peaking than measured in cabinets 10" wide and 1.25" roundovers. but the center frequency matched. If you want to cross high you'll need to notch that out, or deal with a 3-4 dB hole in the response above 1300 or so to the crossover.

I used the same drivers (actually -TD5), but used a high order elliptical active filter (~LR8 initial rolloff) to cross at 1400 Hz. This sounds much better to my ears than the original 2400 Hz LR4 crossover with appropriate notch filters.

As an M-T it feels like the single woofer trying to get down to 80 Hz is the limiting factor at high levels rather than the tweeter being pushed too hard. I haven't measured distortion, though.

Hope this helps.
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Old 18th May 2008, 12:40 PM   #16
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FOCAL 6 W 4254-BSC on Edge @570-600mm/24"

We can look at a BSC of ~7dB in this case.

Quote:
Originally posted by BobEllis
Modeling a 9" wide baffle in The Edge showed slighty higher peaking than measured in cabinets 10" wide and 1.25" roundovers. but the center frequency matched. If you want to cross high you'll need to notch that out, or deal with a 3-4 dB hole in the response above 1300 or so to the crossover.
Not if you take advantage of that in your xover, roll off. You don't say how high. It seems that at 2KHz it's clear.
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Old 18th May 2008, 12:41 PM   #17
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FOCAL 6 W 4254-BSC on Edge @~850mm/35"

In ths case I am more inclined for an ~8dB BSC, not including any woofer of course (or room-gain), and counting with xover frequency at around 2K.
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Old 18th May 2008, 01:54 PM   #18
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Quote:
Originally posted by Inductor
Not if you take advantage of that in your xover, roll off. You don't say how high. It seems that at 2KHz it's clear.
Right- I think that's part of the reason why my high order low XO version sounds better than trying to cross to that curve at 2500 like the Focal/JMLab Micro Utopia I was semi-cloning.

The peak extends a little higher than I remembered it, but it has been years since I looked at it.

You can make a passive Cauer-Elliptic filter - See the HT Guide diy forum for some examples of the topology. It's typically one part per section more than a LR4 XO, so they tend to be expensive. They can be modeled in Speakare Workshop.

Actively it is a fourth order filter with a notch about an octave outside the passband to get an 8th order initial rolloff. The response bounces back up to net out at 4th order, but if you keep the bounce >50db down, life is good.

PJPOES -

As for commercial speakers not having BSC, did you know that you can impliment BSC without adding components? Model a textbook crossover and then double the low pass section's first inductor value. You'll see a shelving effect.

The exact increase you need to match the compensation you want varies by application. Other component values will need to be changed to maintain the same XO frequency and corner shape but you'll get the idea. You can reduce your component count and increase your net sensitivity (the separate BSC inductor will add its own losses, not just distortion) while saving money.

And, yes, you'll want BSC if you plan to have your speakers out in the room. The closer they are placed to the rear wall the less you'll need, but even backs against the wall you will usually need some. Without it, your speakers will sound bass shy and thin in the lower midrange.
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Old 20th May 2008, 02:55 AM   #19
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Thanks guys, I would like to make clear though, I have no real problems with BSC, I just wondered why I didn't see it more in commercial designs. Maybe they do as you say Bob, but I have, as I said, some schematics that have no BSC. My JmLabs Electra 905's have no BSC, I can show you the schematic sometime if you want. Those were what, like 2200 dollars a pair new, and I consider them bookshelf.

By the way, the enclosure isn't planned yet, I have drivers, some measurements, and some drawings. As I mentioned, I don't have room right now to build my own, so I must rely on others to build them for me. I'm awaiting a quote on a few designs we came up with. This was really meant as a temporary holdover, and chance to play with the midbass drivers, until I can afford and have time to do my final penultimate design. Or should I say, start to severe and expensive DIY nervosa. I've been building some speakers using the Scan-speaker revelator midbass drivers and various tweeters, and I keep thinking I would like try this with the Focal tweeter. Only thing is, I don't feel like the midbass is clearly better than the focals, its just different. Better bass, better dynamics, I think it has lower measured distortion, but it just doesn't sound as clean to me. More importantly though, I think nothing does microdynamics like focal drivers, which is why I like them so much myself.

Bob I would be curious to know what you think of the crossover. Sounds like you feel a 10" wide baffle would be good, a different BSC scheme to match, but otherwise, seem ok? I mean, there are only so many 4th order setups you can do really. I heard you mention LR4 a few times, I didn't model those after LR4, but after tweaking the slopes I may have inadvertently ended up at that. I think they match Butterworth better though. They are also steeper than 4th order. The resistor I have from inductor to ground and cap to ground removes crud in the crossover region and increases the slope slightly.
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Old 20th May 2008, 12:04 PM   #20
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You've gone the extra mile with the tweter notch. I have tried with and without and have no clear preference.

As for the BSC in your 1st post, the norm is to place the L//R on the source side of the filter. As it is now, you've added a bit of variable impedance to your filter load.

You know by now, I'd cross it lower.

You may end up with a 2nd or 3rd order electrical filter and get to a fourth order electrical rolloff.
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