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Old 21st January 2004, 02:08 AM   #1
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Default Please help with 5" midbass recommendation

Can anyone help me sort through the different 5" midbass options available? I'm basically looking for the best sounding driver that is usable *off-axis* up to about 4kHz with a 2nd order filter. Bass response isn't all that important. So far, I've nailed it down to:

Focal 5W4211 (5W3211b) - seems like a pretty good choice right now. Does anyone know if the magnetic shielding on the 3211b has an effect on sound quality? Do the W cones sound substantially better than the polykevlars?

Audax HM130CO - less expensive driver. Does it sound as good? I read a post from Al Von Schweikert that stated the stock version of this driver were actually no better than +/- 3dB in response.

Morel MW144 - supposedly an upgraded version of the MW142. Anyone with experience with this particular driver?

Can anyone suggest other good 5" drivers that might meet my criteria?

Thank you so much for your help.

Derrick
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Old 21st January 2004, 03:43 AM   #2
michael is offline michael  Australia
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I have a few suggestions, dont know if you will like them but there is the peerless 850488 that i have heard many good things about, and also the Vifa p13. These are i think not as high end as the ones you have suggested but they are very well received.
I just thought of it, if you do not mind a complex crossover the Seas excel W15 magnesium driver is supposed to have some of the lowest distortion and highest detail available.
There is also the Scan Speak 5" revelator.
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Old 21st January 2004, 08:38 AM   #3
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Default Re: Please help with 5" midbass recommendation

Quote:
Originally posted by ThyroidAblation
Can anyone help me sort through the different 5" midbass options available? I'm basically looking for the best sounding driver that is usable *off-axis* up to about 4kHz with a 2nd order filter. Bass response isn't all that important....
...Can anyone suggest other good 5" drivers that might meet my criteria?...
I think you're right in wanting a good off-axis sound, especially since the "on axis" sound is inevitably just a small part of the sound we end up hearing. But you'll only get so far with "soft" (paper, fibre, polymer...) materials. These materials like to flex and oscillate, and produce fatiguing resonances. If you run a polymer cone at 4kHz, imagine the cone-breakup with invisible surface-ripples all over it. These designs rely on self-absorption with rubber surrounds and the softness of the cone material. When listening away from the speaker's "axis", different parts of the speaker cone are at different distances from the listener, and you get "lobing" etc from constructive and destructive interference patterns (aka: generic mish-mash of sound).

What you really want is a speaker with a very hard cone material like metal or ceramic. These cone materials have all of the same problems as above or even worse, but occurring at much higher frequencies after the tweeter takes over. I can think of 2 types of speaker that do it that way: Accuton and Seas. Seas with their "Excel" drivers with magnesium alloy cones, and Accuton with their ceramic cones.

Not too long ago I bought a pair of C94-8 7-inch midwoofers from Accuton and haven't regretted it despite the hefty price-tag. Smooth and crystal clear. As for off-axis performance: these babies can really fill the room with glockenspiel before the tweeters even kick in . Possibly their only downside is their relatively large cone area - it requires a top quality large box to absorb the back-wave well enough to stop box-reflections/resonances from exiting through the cone. A 15L sealed box is what I made and, picky as I am, it's still not big enough despite the T/S parameters pointing towards a tiny 4.2L. With speakers like these you will seriously hear the improvement on paper/plastic cones. You'll see how the mediocre midrange of other speakers can mask other problems like inadequate damping of the box and panel vibrations.

What are you planning anyway? If it's a 3-way system then Accuton's C79-6 is what I'd go for (in fact I think will get that one when I decide to make a 3-way loudspeaker). If it's a 2-way (plus subwoofer I assume?) then take your pick out of the bigger Accuton speakers or the Seas speakers. For some reason the specs for the 5" Accuton speakers don't look as good as the 7" one I chose, and with Seas speakers you may have to use a notch filter to get rid of the high-frequency spike in the response (there goes that 2nd order XO!...)

CM
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Old 21st January 2004, 10:41 PM   #4
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The W15 does indeed sound magnificent, dont forget about the new w15CH, either way you can use it up to 4k. If by 2nd order you are refering to an electrical filter of 2nd order this can be tweaked to get 4th order acoustic, use a good res trap and youll be doing fine. 2nd order (acoustic!!) @ 3.5khz with a res trap, with me sounded brilliant so I think 4k would also sound fab.
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Old 22nd January 2004, 03:39 AM   #5
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Thank for everyone's reply. The drivers would be mounted in custom fiberglass kickpods, aimed 30-45 degrees off the listening axis, and mated to a subwoofer at about 80Hz. With the 4kHz tweeter crossover restriction, it's been hard to find midbass speakers that perform well off-axis up to that frequency.

Unfortunately, the cost of the Accuton's and the Scanspeaks are prohibitive. Right now, the Focal 5W's look like they do fairly well up to 4kHz and are amenable to my existing 2nd order active filters.

I'd really like to consider the Seas Excel's because I've heard such great things about them. I've checked out some of 5th element's posts, and it looks like you've used them successfully with 2nd order filters along with an LCR/notch filter to get roughly 4th order rolloff? And you've had no problems with that nasty cone resonance around 8kHz? That's a big concern of mine because most of the "kit" designs all use 2nd-order + LCR filters and tend to cross over about an octave lower! What exactly makes the Excel's so good? The freq response graphs don't even look all that linear, and distortion apparently goes up to like 3% at the resonance freq.

Thanks again!

Derrick
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Old 22nd January 2004, 10:55 AM   #6
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Quote:
Originally posted by ThyroidAblation
I've checked out some of 5th element's posts, and it looks like you've used them successfully with 2nd order filters along with an LCR/notch filter to get roughly 4th order rolloff?
Not exactly but yes 2nd order can be used to get 4th order roll off with this driver at that frequency. I have used many different xover frequencies with the w15 one of which was @ 3.5khz. This was 2nd order overall.

If you look again at the SEAS data sheet you will see that the peak in distortion is not where the resonance occurs but at 3k. I dont know why this is. But between 200 and 2000hz the distortion figures are very low, this is also measured at 96 dB and not with 1 watt. The distortion peak extends from say 2-4.5k, most "notes" within music are between 200 and 2k. The excels do have lower distortion then other drivers within certain frequency bands, important bands, also the metal cone as seas says prevents all kinds of break up within the most important parts. If someone else can provide a better explanation I would be greatful.
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Old 23rd January 2004, 12:25 PM   #7
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Quote:
Originally posted by 5th element
If you look again at the SEAS data sheet you will see that the peak in distortion is not where the resonance occurs but at 3k. I dont know why this is. But between 200 and 2000hz the distortion figures are very low, this is also measured at 96 dB and not with 1 watt. The distortion peak extends from say 2-4.5k, most "notes" within music are between 200 and 2k. The excels do have lower distortion then other drivers within certain frequency bands, important bands, also the metal cone as seas says prevents all kinds of break up within the most important parts. If someone else can provide a better explanation I would be greatful.
At the resonance peak the movement of the edge of the cone is delayed by 180 degrees from the movement of the voice coil, hence the cone flexes and stores energy like a spring to produce loud ringing. Some of the sound will cancel out, but the cone vibrations increase drastically as the effective mass of the cone drops close to zero (just look up resonance). At half that frequency the phase delay should be only 90 degrees. However, it's actually more complicated than that, because as the cone accelerates parts of it are under tension and others under compression, and these properties change depending on the direction that the cone is accelerating in (inwards or outwards?).

When parts of the cone lag other parts of it (near the first breakup frequency or above it), this changes the effective mass that the VC has to push or pull. The distortion isn't caused by the lagging effect itself, but because the cone is stronger in one direction than the other. Therefore the acceleration will be non-linear, because the changes in mass are non-linear. Even without looking at actual measurements I can tell that the distortion should be mainly even-harmonic distortion (plus associated IM). At low frequencies the THD will increase due to the non-linear magnet-motor and spider, and somewhere in between the distortion will drop to very low levels because of both low peak-to-peak distance and low cone-flexing.

A couple more things: I don't think these distortion levels would be particularly noticeable, other things are bigger deciding factors on how good a speaker sounds. At the cone breakup and above is the problem area, and it can be easily seen on waterfall plots as long decay times, whereas it usually can't be seen on frequency response plots. Again it's obvious that with plastic/fibre cones the same problems occur but at lower frequencies and to a worse extent because they flex more.

CM
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Old 23rd January 2004, 01:31 PM   #8
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I've got a pair of Focal 5kx mids I've never used sitting in my living room. They were the Utopia line equivalent before the utopia's were released. I just talked to a Focal rep 2 months ago and she told me the usable range of them is 50 to 8000. 30 degrees off axis they are good to ~5000.

The main difference from the 5kx and the 5w is the utopia is very laid back, while the Xpert is more forward. I found the utopia's too dull for my liking. The Xperts were just perfect. Just in case you are wondering, I was thinking about competing in SQ so the ones sitting in my living room were my spares. If you are interested, I would let them go pretty cheap. They easily compare with what you posted above.

Email me at Punch150hd@netzero.net if you are interested.
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