Crossover Roadshow

[CECAA850]

Have either of you done an A/B with and without charging the circuit?

No. Don't plan to either.

OK, both crossovers are done, Overall, I give them .

The bass is no longer lean, it's nice and fat as it should be. Part of my issue was only having one speaker hooked up and the other part was my source material. Took a little trial and error to figure it out but that tells me that the speakers are accurate.

The ear bleed mids are about 80% less than before. The mids are still slightly forward but not much more than the other 2 pair of heritage I own. I believe that they'd be about perfect if I had them in a decent room.

Highs are sharp and accurate as they should be.

These speakers will be fed by a few different things over the next 2 months. I look forward to listening to the changes as they occur. I typically obsess over any flaw that I perceive as I build and change a system till I get it to a point that I'm happy with it. The speakers and crossovers are at that point now. Time to move on.

Thanks Dean!

[Thaddeus Smith]

These speakers will be fed by a few different things over the next 2 months.

what happens in 2 months?

[CECAA850]

These speakers will be fed by a few different things over the next 2 months.

what happens in 2 months?

Fodder for a new thread

[Marvel]

The batteries that speakerfritz put in mine are still good, and he sent them to me in April of 2011. They are Duracell Alkalines dated Mar. 2015.

Bruce

[Deang]

So if you don't connect the battery to the charge-coupled B2 network, you still have a stock Cornwall B2 network, just with capacitors in series, correct?

Yes. Think of it as two independent circuits tied together. The biasing cicuit doesn't need to be active for the crossover to work.

Keep in mind that once you charge the batteries, they will likely stay that way for some time -- even without the battery in the holder. So, doing the A/B thing is kind of tough, because you would have to short out all of the caps to drain them.

So, that's a good idea. Start without the battery, listen for a while, and then add the battery.

I have some links on my website that are probably worth looking at. It's very hard to find negative comments related to this. It's like I told Bob, everyone cuts a corner or two on their crossovers, so why implement something that requires you to double the parts, double the size of those parts, and add batteries -- just so you can add a line in your sales brochure that people will either not understand or care about.

I agree that all loudspeaker companies sometimes stretch the truth regarding the benefits of some kind of new technology or implementation. But I just don't see any point in adding something like this if you know it does ABSOLUTELY NOTHING.

[djk]

"I to am interested in what happens when there is no battery... do they revert to passive?"

Yes

"Also, would you need to install some king of continuity jumper inplace of the battery?"

No

"Have either of you done an A/B with and without charging the circuit?"

The cheaper the caps, the better the improvement. The biggest difference will be heard in the silence between the notes, it's a deep black rather than a dingy gray.

[mike stehr]

I received the parts today to make the charge-coupled Cornwall B2 networks...my GF Miss Barb is gonna be bummed out when she has to listen to the TV speakers for awhile.

[CECAA850]

Update:

I finally had time to peel the speaker cloth and cut the new openings in the grill to match the larger horns. It still blows my mind that the old owner never did this. Now I'm waiting on some of that fancy Madisound speaker wire that Dean recommended. It should be here today. A new pre-amp should be here this week for this system also. I probably won't have time to mess with it till I get back from the gathering in Hope.

[Deang]

A buck a foot is not "fancy". : )

[CECAA850]

I said fancy, not expensive

[CECAA850]

Actually, I normally pay about .30/ft at Monoprice so I guess they ARE expensive

[Deang]

Would it be too much to ask, when reviewing these crossover to list the horns and drivers being used, as some may not be suited for the crossovers being used.

For instance I see a lot of Cornscala's out there that have the Selenium D-405 driver coupled to the JBL 2380 clone horn. This combo is not compatible with a 6k crossover because the D-405 start to roll off around 4K, and it has a rated SPL of 111. This is going to use a bit more attenuation than the K-55, and requires a different crossover point. For this combination, ALK offers a 400hz-4khz crossover option.

SPECIFICATIONS

Nominal impedance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 W

Minimum impedance @ 3,450 Hz . . . . . . . . . . . . . . . . . . . . . 6.3 W

Power handling

Musical Program (w/ xover 800 Hz 12 dB / oct)1 . . . . 200 W

Musical Program (w/ xover 1,200 Hz 12 dB / oct)1. . . 250 W

Sensitivity

On horn, 2.83V@1m, on axis2. . . . . . . . . . . . . . . . . . . 111 dB SPL

On plane-wave tube, 0.0894V3 . . . . . . . . . . . . . . . . . . 113 dB SPL

Frequency response @ -10 dB . . . . . . . . . . . . . . 400 to 20,000 Hz

Throat diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 (2) mm (in)

Diaphragm material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Titanium

Voice coil diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 (4) mm (in)

Re . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8 W

Flux density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.70 T

Minimum recommended crossover (12 dB / oct). . . . . . . . . 800 Hz

Dave

Dave,

I don't know of any Cornscalas that have been with the D405TI driver you have posted the specs for. Several hundred have been built with the phenolic diaphragm version.

Bob Crites

I missed this.

Using the phenolic version of this driver on the 2380 horn, the correct crossover points are 500/5000. 400Hz is too far below the fc of the horn. The spec sheet for the horn recommends 500Hz. And yes, there is a 500/5000 version of the Roadshow Crossover (SuperX). To be honest, I'd rather build something simple using them big fat paper in oil cans.

Mike just sent me an email of his rebuilt B2s. He hasn't put the batteries in yet, choosing instead to listen for a week or two.

Edited March 26, 2014 by DeanG

[CECAA850]

He hasn't put the batteries in yet, choosing instead to listen for a week or two.

That's a great idea.

[Guest David H]

Mike just sent me an email of his rebuilt B2s. He hasn't put the batteries in yet, choosing instead to listen for a week or two.

Not a bad idea. I built battery biased type E2 for my Heresy's, and although they sounded very good, I dont know that I can hear a difference with or without the battery.

Keep in mind I am a skeptic, therefore my not hearing an improvment doesn't mean there wasn't one.

Dave

[mike stehr]

I spotted Dean conversing on a thread about a inductor mod/tweak used, connected in series on the midhorn after the autoformer.

To my ears it seems to attenuate the midhorn in a slight manner, without sucking the life out of it like a resistor or L-pad might do.

I'm stuck in a small abode, and have always listened near-field because I have no choice.(12'X 14')LR, with the speakers 7' apart, and the listening position 7' back. About two feet out from the corners, each toed-in slightly. So you have limited SPL listening near-field, without the horns spitting in your face.

I had a pair of inductors the same value (.39mH) as the mod or whatever...once I confirmed the value with Dean I installed them.

When I installed the .39mH inductors, I swapped in some oil caps for the midhorn and tweeter, (2uF Cornell-Dubilier and the stock Aerovox 3uF cap) with a 22uF Jantzen cross-cap for the woofer.

I like things laid-back a slight bit, but it was overkill for the tweeters. The 2uF CD oil caps made the tweeters dead and dull, but by this time Dean offered up some parts for this project, and I just lived with it until the parts arrived.

I had no problem with the stock Aerovox 3uF cap for the midhorn, using the .39mH inductor. Smooth, with no shout. Better than a 3uF Sonicap I had used for a long period of time...to my ears.

Once I finished the project, and installed the crossovers, I hooked up a Marantz/Heart tube output CDP as the source. Directly connected to one of my Magnavox 6BQ5 SEP console amplifiers.

The first thing I noticed was a tighter stereo image and separation. I attribute this to the tighter tolerance Dayton caps. (1-2%?)

The bass seems nice and strong...and tight as a Cornwall can get without major cabinet mods I guess. Not much difference using a Bi-polar 'lytic over a film type cap in that position from what I can tell.

I couldn't find anything objectionable sounding about the networks, or the speakers. Things sound great...other than that slight metalized polypropelene "plastic" kind of sound. But it's not objectionable, just noticed.

These networks maybe have two hours of use. So they may settle-in a little more given more time. In a week or two I'll install the batteries, and see if it may rectify the slight tizz/harshness of the caps.

As said, it's slight and not objectionable.

These are late '82 or '83 Cornwalls, with the K51V midhorn drivers, Crites woofers, and CT125 tweeters.

Mike

[Deang]

Mike just sent me an email of his rebuilt B2s. He hasn't put the batteries in yet, choosing instead to listen for a week or two.

Not a bad idea. I built battery biased type E2 for my Heresy's, and although they sounded very good, I dont know that I can hear a difference with or without the battery.

Keep in mind I am a skeptic, therefore my not hearing an improvment doesn't mean there wasn't one.

Dave

If you start with the batteries in, and then remove the battery, you are still listening to a charge coupled crossover. This is why Mike hasn't put the batteries in yet. To hear the crossovers without the charge, you have to discharge, or short them out first. Edited March 26, 2014 by DeanG

[Guest David H]

If you start with the batteries in, and then remove the battery, you are still listening to a charge coupled crossover. This is why Mike hasn't put the batteries in yet. To hear the crossovers without the charge, you have to discharge, or short them out first.

Absolutely correct. I used them charged and fully discharged. The bridge type battery bias network will even work with the battery shorted.

Dave

Edited March 26, 2014 by GotHover

[Deang]

I didn't say anything about shorting the battery, though I did mention shorting the caps as a method of draining them. Discharging using a resistor (200K/10 watt) or the test leads from the meter is probably better. Whether using the method popularized by JBL, or the bridged method, either will allow the crossover to work without the battery in play.

I can't find a reference regarding the "bridge type" method anywhere. I'm curious where Speakerfritz got the idea. In the thread where he introduced the network and the schematic, Dennis said, "I'm not sure this is the best way to do it. In use there is a very low impedance from X to Y (X to ground of less than 0.1Ω, and Y to ground of less than 1Ω)."

With the bridge type method, notice that the negative side of the battery doesn't connect back to the common connection on the network.

Presuming the bridge type method even works, if you started with the batteries in the networks, and then pulled and discharged them, there's still a decent chance you ended up listening to them charged anyways -- because the longer a capacitor remains charged, the harder it is to keep it drained.

Dielectric Absorption relates to a thing called memory effect. In practical terms, this means we can discharge a capacitor, but it will almost immediately begin to charge back up on its own without any applied voltage. This is called "voltage rebound", and the longer the capacitor has a charge on it, the faster the charge returns. So, we can discharge and get a zero reading on the voltmeter, but by the time we get the networks back into the speakers and going again, we still end up hearing the effects of DC biased capacitors in the networks.

"What playing around I have done with initial application of a battery to a biased circuit (that has not been previously powered up) is that it takes about 3-5 seconds for the soundstage to change. I have tried to measure the voltage level in that time period and it seems that several volts is all that is necessary to accomplish 90% or more of the improvement. Once a circuit has been energized, it is nearly impossible to return it to zero. You have to individually short out each cap and leave them shorted for a while or else they will creep back up somewhat. If you replace the battery with a short and play the system for a while, the caps will start to bias themselves, although not to anywhere near the same degree." -- Greg Timbers

http://www.lansingheritage.org/images/jbl/specs/home-speakers/1993-k2-s5500/page10.jpg

http://www.lansingheritage.org/images/jbl/specs/home-speakers/1993-k2-s5500/page11.jpg

http://www.lansingheritage.org/images/jbl/specs/home-speakers/1993-k2-s5500/page12.jpg

Edited May 10, 2014 by DeanG

[djk]

Single capacitors (as in a coupling cap in a preamp) have higher distortion with a DC bias on them.

The increase in distortion is dependent on the internal symmetry of the construction of the capacitor.

Using two of the same caps hooked head-to-head with DC bias reduces the distortion, and can be even lower than with no DC bias.

[Guest David H]

I didn't say anything about shorting the battery

What a coincidence, neither did I.

I merely stated the bridge type will operate even if the battery is shorted. Shorting out the battery would be silly.

Dave