Paper-In-Oil Capacitors?? Wooden Horn?

Quote:

---

Originally Posted by DerekTheGreat

It uh, "..really ties the room together."

115dB sensitivity. Whoa. And here I thought anything over 100 was impressive. How did you build the horns? Response down to 20hz? What kind of bass driver feeds the horn?

---

When I first built the bass horns about 20 years ago they were primarily lath and cement/stucco construction with some brick/block work in the backchamber portion. While messy, the lath and cement is a pretty easy way to shape a big horn and the density is a big help too.

When I re-worked the room for the Cogent system I demoed the original cement mouths and reconfigured them a bit with the new hardwood mouths. The wood is a Brazilian species called Garapa and it is extremely dense and hard.

Drivers since the beginning have been JBL K151 alnico 18". Since I added the active low-pass and EQ to boost the 20-30Hz range I've been worried about over excursion. I have a pair of Gauss 4882 driver waiting to be installed which have greater power handling a double the excursion of the K151s.

eso

Quote:

---

Originally Posted by DerekTheGreat

115dB sensitivity. Whoa. And here I thought anything over 100 was impressive.

---

When I built my 103dB+ system I took a page from the Cogent crew and used magnet wire to feed the Audax tweeters. Only milliwatts are required. Past 100dB efficiency it is a different world. It is a simple augmented single driver setup, nothing fancy, but the First Watt F1J ten watt transconductance amp would be enough to drive a dozen of them.

Quote:

---

Originally Posted by Ducatista47

When I built my 103dB+ system I took a page from the Cogent crew and used magnet wire to feed the Audax tweeters. Only milliwatts are required. Past 100dB efficiency it is a different world. It is a simple augmented single driver setup, nothing fancy, but the First Watt F1J ten watt transconductance amp would be enough to drive a dozen of them.

---

Who organised the amp?

eso,

RE post # 16

"I've been worried about over excursion. I have a pair of Gauss 4882 driver waiting to be installed which have greater power handling a double the excursion of the K151s."

I don't know where you took the excursion numbers for the JBL K151 and Gauss 4882, but if you compare apples with apples ( i.e. Xmax, linear displacement) then the JBL has 2.5 times the cone travel capability of the Gauss, as per the JBL TS table and Gauss spec sheet.

Gauss 4882: .040" = 1 mm vs JBL K151: 2.54 mm. So your concern might have to be the other way around.

Richard

Hmm... internet is a funny place... along with old spec copy. JBL had a long published Vas zinger for the 145 woofer.

Also found: 4882A 18" 400W 8 102dB 28Hz 22.0 0.24 0.165" 0

from a different source... .165" is closer to 4mm which makes more sense to me than 1mm for a "400w" 18" driver. Perhaps the .040 was decimeters.
Plug some numbers into a simulation... at 400w (the smaller of the various quoted power handling figures), you'd run out of steam at ~250Hz. reasonably ported OR sealed.
Gauss put these in ~6ft3 ported cabs for bass guitar and even in Karlson enclosures.

So guessing a typo somewhere or something funny like it was -designed- to distort way before Xmech (which seems very unlikely).

An audiomart listing showed the following ... who knows where those numbers came from ... shrug (fwiw... the rest of the TS parameters hung together)

Cetec / Gauss 5181 Bass Guitar Bottom
1 - 4882SX driver
Slot-Loaded
400 Watts RMS
102 db
8 ohms
40-4000 Hz
37 1/4" H x 24" W x 20" D
100 lbs.

Cetec / Gauss 18" Bass Speakers / Woofers / Sub-Woofers / Sound Reinforcement Drivers.
Model #4882SX
8 ohm.
Patent no. 225,069.
Doped suspension surround.
Field-serviceable voice coils.
Develeoped by Bart Bingham and Ed May
Vas [Liters]; Equivalent volume = 430 liters
Qts; Total Q-factor = .2416
Qes; Electrical Q-factor = .27
Qms; Mechanical Q-factor = 2.3
Fs [Hz]; Resonance Frequency = 33 Hz
Approximate minumum power for nominal EQ accuracy = 20 watts rms.
Max Power [W]; Maximum input power = 400 watts rms, 800 watts program, 1600 watts peak.
xmax [mm]; Max excursion from center = 1mm
Moving mass [g]; Weight of moving parts = 107.24 grams
Disp area [m2]; SD, Effective piston area of cone = .119 m^2
Re [ohm]; DC resistance = 6.7 ohms nominal.
Z; Impedence of coil = 8 ohms dynamic, nominal.
L [mH]; Inductance of coil = 1 mH
Bl [Tm]; Magnetic strenth = 23.49 Tm
Weight = 25lbs each.

Quote:

---

Originally Posted by Ian Mackenzie

Who organised the amp?

---

I do love the F2J (thank you!) but as all but three of the original F1s were eventually converted to F1Js by Nelson Pass, I was on the lookout for a used bargain. It came from another geezer who chose his speakers poorly and felt his F1J did not "have enough power". I bought it for half price. Usually earlier used First Watts go for at least full new price or better, at least a few years ago when I last checked. It worked out so well I took my subwoofer out of the system.

So what do you listen to these days, how is your headphone rig working out?

RE post # 20

No material discrepancy or shenanigan in my view.

Not unusual for a large driver to have limited excursion capability, specially when its destined to horn loading as indicated on spec sheet attached (e.g. older 2220A/B/C).

Very high sensitivity (102 db) was priviledged here, not very low bass (btw remember Eargle's phrase i posted recently regarding high efficiency vs LF bandwidth being sacrificed).

At .24 Qts of 4882 is low, one may wonder if the driver would effectively make it down to 30 hz and with lots of output, personnaly i doubt.

As shown Xmax is what it is i think. The .165" (4 mm) is identified as Maximum excursion, which i understand as being Xlim, commonly known as the limit before driver damage. So one might think got another 3 mm in stock, great lets go. Not really. At Xmax (1 mm) you're already at 10% driver distortion (see note 1). Turning up the volume distortion increases even more, continuing such sooner than later the user will be "swimming" in distortion even though the driver hasn't given up mecanically yet...

Now put that in parallel with the fact that horn lovers usually appreciate the device's low distortion.....

Richard

Note 1: John Eargle, Loudspeaker Handbook, 2nd ed, p.64

Thanks Richard,

Having the actual spec sheet with full info does help!

Still makes me wonder about the Cetec-Gauss 5180 bass guitar cab though.
Looks like a 6ft3, perhaps 55Hz tuned cab (guessing from pics and dimensions), which would be severely displacement limited below 200Hz (vs midband).
Perhaps in that application, some audible distortion was acceptable or even welcomed, ala "It just worked".

Always appreciate good info and learning (sometimes by being corrected) :)

Best regards,

-dave/grumpy

Dave,

Had no intention at all of correcting you, but rather add more info and showing the OP the 4882 idea might not be the nirvana he was expecting. Honestly i feel bad for the guys who purchase drivers, maybe not consulting here ahead of time, then finding out from someone the cruel reality. Sometimes i try to help them "making it work" with a software modeling for example, however cone travel capability i can't add any to this, simply impossible. Then hinted K151 he also had was better on that aspect. Nevertheless he remains the boss of his own project.

Yeah full specs do help, but did mention post #19 i was looking at the Gauss spec sheet, having most of the Gauss stuff.

RE Perhaps in that application, some audible distortion was acceptable or even welcomed, ala "It just worked".

You're right, in fact Eargle mentions this with regards to MI drivers where some "distortion may indeed be sonically beneficial" (p. 25). Obviously he's talking about sound production drivers, not sound reproduction ones.

Richard

As l recall those drivers has dual spiders and were notably tougher than their JBL counterpart.

One way of assessing the peak displacement is to model the horn and driver in Hornresponse software. Some dimensions on the mouth, the throat, rear chamber, horn length Z, the number of segments and r factor.


http://www.hornresp.net/