HiVi M8n - a true bargain

[RonS]

Thanks Jon. I look forward to receiving the details

Cheers,
Ron

[Daryl Furkalo]

The LCR LF zobel with the D2904 is 68uF + 2.0 mH (can be high DCR) + 5 ohms net. By 5 ohms net, I mean that the DCR of the 1.8 MH inductor plus the resistor should equal 5 ohms. Most likely you can buy a 1.8 MH air core inductor with about a 1 ohm DCR, and add 4 ohms in series. For example, the 2.0 MH "standard Inductor" line at PE is 1.07 ohms.

Regards,

Jon

Jon,

This would replace the 700uH + 136 uF + 4 ohm circuit on the Zobel circuit for the XT25? Just want to be certain. Thanks a lot for the information.

Regards

[Ten 99]

Jon,

I sent you a PM regards to the PDF files.

Thanks,

Chris.

[Dennis H]

Jon, a bit off topic but what is your favorite 7" that can be crossed at 2500 Hz, LR4? Would it be the Eton you used in your monster project? Or maybe one of the Focals?

[JonMarsh]

Jon,

This would replace the 700uH + 136 uF + 4 ohm circuit on the Zobel circuit for the XT25? Just want to be certain. Thanks a lot for the information.

Regards

Yes, that's correct-a-mundo!


~Jon

[JonMarsh]

Jon, a bit off topic but what is your favorite 7" that can be crossed at 2500 Hz, LR4? Would it be the Eton you used in your monster project? Or maybe one of the Focals?

That would be the SEAS W18EX001. Or, if you prefer, the lower sensitivity version.

The X1 Kones were the last speaker I did before I really started getting rabid about the whole cone breakup thing. In fact, they kind of drove that, because although the particular Eton's I used look pretty good out to 5 kHz, doing some snooping re close mic measurements and the impedance curves, after I wasn't fully getting the sound I hoped for, revealed some more subtle problems, with cone modes that manifest as dips, associated with energy storage.

IMO, there are few or no other 7's you could probably get away with that. Mind you, I'm being a stickler about applying my personal criteria- other's would argue you can make a good speaker even if the cone isn't pistonic in the operating range- I disagree. Everyone is entitled to an opinion, of course.

The SEAS G18RNX/P might work; the plots look good, but I'd like to see ETC data and some close mic scans at center, mid cone, and edge before making a call. It has a very suspicious looking blip in the impedance curve at about 800Hz, though it looks pretty smooth above that.

For example, the Focal 7W4411 has modes at 1400 Hz and 2800 Hz.

The Vifa XT18WH08 has modes at 300 Hz and 1200 Hz.

The Revelator 7" has a nice mode (well, not NICE!) at 800 Hz, like most ScanSpeak 7" and 8" drivers- it's practially a signature thing for them, becuase they design the cone to have a rising response above 700-800 Hz, so that with a simple low pass function you can get typical baffle step plus a zero in the response to come out of it ~ 800 Hz, while the network keeps rolling off. Ouch, for $225, you'd think we could do better!

The carbon fiber-paper ScanSpeaks do the same thing to a lesser degree, but the 18W8545K is still not a driver I'd use to 2.5 kHz, (look at the peak at 3 kHz), and it has modes at 800 Hz and 3.2 kHz.


Now, if I was thinking budget speaker and a crossover like you propose, I'd look closely at the Peerless HDS without the phase plug. There's a friend back east I may build something like that for, with the Seas T25C without ferrofluid.

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Low in energy storage and distortion, trade off is toward Xmax, so with a couple in an MTM, you can get some reasonable LF out. Of course, I'd cross them over lower; heck; why not a Millenium or SS9800 at 1500-1800 Hz? I've got a design like that on the digital drawing boards, too. At the lower crossover frequency, the driver blend for an MTM is much better.

But then, maybe I might use M6N's if I can get hold of them anywhere, just out of "nostalgia"? :W

Regards,

Jon

[Dennis H]

Thanks, Jon. I was thinking about a high-SPL 3-way where you might need to cross high to keep from overloading the tweeter. So the mid might cover somewhere between 200 and 400 on the low end (depending on floor bounce) and 2500 on the high end to something like the Millennium.

Just a thought experiment - through wall, IB, (2) TC Sounds 12", W18EX, Millennium, all LR4 acoustic, adjust the Fc's for best in-room high-SPL response at a 15' sweet spot. Active crossovers so sensitivity isn't an issue.

[Al Garay]

If you are going up to 2500, why use the Millenium? You can use the Seas Excel T25CF 001 (non Millenium) which according to Dennis Murphy is identical to the Millenium if you are crossing over high.

But, I think if you are following the gospel according to Jon, you would want to use the low crossover point afforded by the Millenium or the SS9800.

So many choices.

Al

[Dennis H]

2500 (maybe 2000 at the lowest) is how high you need to cross the Mill for a "high SPL" system according to my calcs. The Seas 001 only has 1/2 the Xmax and the 9800 only has 1/5 the Xmax so they aren't really contenders for that application (IMO). I know the latest fad is crossing them low but it looks to me like you're going to hit Xmax limited distortion if you do that. Crossing an octave higher buys you 12dB more clean sound.

[Al Garay]

This is good learning.

I don't understand the role of xmax for tweeters. If it is critical, wouldn't the Accuton C23-6 with xmax of 1.2 be the best?

Al

[Dennis H]

Tweeters are just like any other driver. If everything else is equal, the one with the larger Xmax will give you more SPL at low frequencies. Of course, everything else isn't equal when comparing different models and brands so Xmax is only one factor in picking the best one for your application.

[JonMarsh]

Thanks, Jon. I was thinking about a high-SPL 3-way where you might need to cross high to keep from overloading the tweeter. So the mid might cover somewhere between 200 and 400 on the low end (depending on floor bounce) and 2500 on the high end to something like the Millennium.

Just a thought experiment - through wall, IB, (2) TC Sounds 12", W18EX, Millennium, all LR4 acoustic, adjust the Fc's for best in-room high-SPL response at a 15' sweet spot. Active crossovers so sensitivity isn't an issue.

I think that's a very reasonable idea, Dennis - depending on the driver height you use, 350 should be about right (per Roy Allison's boundary studies), the TC2+(s) should be at the floor boundary, and the tweeter not too far above ear level seated. I'm guesing you're talking about doing the whole thing in wall (like a studio monitor built in flush); this certainly kills any worries about BSC comp. Only down side is you don't get the usual LF boost below 100, because everything is boundary loaded.

What sort of SPL are you shooting for in this thought experiment?

One last point, for a "point source" speaker, to avoid beaming and flare effects in the crossover region, at 2500 Hz my "loosey-goosey" recommendation is that the center to center distance of the drivers is no more than 5.25". (13570/Fx) My "tight@ss" recommendation is that the outer boundary of the radiating drivers at crossover be no more than 5.25", which at that frequency is clearly impossible. But this tells you where a 7" woofer starts to beam. :W

At 1250 Hz you can double those distances, which explains why I went to a lot of trouble to develop an 8" two way crossed over with steep slopes at 1250 Hz. And why our recommended MTM configuration has the woofers scrunched up together with the tweeter offset. But it's not a high SPL system, of course- but within the limits, it sounds pretty nice. Great on and off axis curves through the crossover region, too, which is pretty important to overall in room sound, especially if you're not sitting locked in the sweet spot.

And it does seem to be hard to directly compare tweeters from different mfr's just on specs. I've built a system with the C23-6, and I found it a pain to work with, and the best large baffle curves I could get with my B&K mic wasn't nearly as good as what they publish- unlike what I get measuring a Focal TC120, for example, which correlates very well with the factory curves.





Which brings me to another thought- crossing over at 2500, I'd also look at the TC120TD5 tweeter- except that I'm hearing Focal is pulling out of supplying drivers to anyone external, DIY and otherwise. It's a very good tweeter in the $80 range if you don't need to go low- one of my favorites. It's much flatter (in my measurements) than the C23-6.

However, the Focal's are not "forgiving", being more on the analytical side of things- first rate source gear and electronics are suggested!

Regards,

Jon

[Dennis H]

What sort of SPL are you shooting for in this thought experiment?

I dunno, it would be a combined multichannel music and HT system so pretty loud. THX calls for 105dB transients. I'm just kicking ideas around in my head. The best wall to mount a screen has the garage on the other side so IB speakers look like a natural. If my calcs are right, including baffle loading, distance to the seats and contribution of the mid, the Millennium at Xmax would give me about 105dB crossed at 2000 and 110dB crossed at 2500. It would be nice not to have to drive it to Xmax. If I were to start tearing out walls, I'd probably do an acoustic ceiling too (tile plus a foot of fiberglass in the attic for bass trapping) so, with heavy carpet, vertical polar response wouldn't be a huge deal. Standing only puts you about 10 degrees off axis at the most.