Something Glowing This Way Comes

General discussion for all questions based in the home audio/video world.
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Mike S.
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Postby Mike S. » Thu Jul 06, 2006 1:26 am

'JimJ[VT wrote:']Was just reading this...



While a good tester to measure transconductance is a cool thing to have (and something I probably need to acquire in the future), are VTVM's really needed anymore now that we have DMM's with relatively high input impedances? I've used vacuum-based GDO's before, and I wouldn't wish that on my worst enemies...:)



No, it's probably not really needed. It may be good to use to compare to a DMM I guess.....
I got a Hewlett Packard 400H, it's a pretty decent old piece of lab gear. It's made to hold it's tolerance within 1, 2% with tube emission loss up to 75% if I recall. Granted it's kind of a novelty item, it does have it's purposes.

A VTVM and a signal generator is nice to have for finding out the vent tuning of speaker cabinets, peaks, etc. Though you could probably do the same with a DMM I suppose.
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westend
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Postby westend » Fri Jul 07, 2006 4:07 pm

Me glow too!!:) Layfayette LA-212 through Large Advents is a good match. Listening to FM with Pioneer TX-7500. If the speakers were better this would approach Hi-fi.
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Postby Mike S. » Sat Jul 08, 2006 3:23 pm

I bet the Lafayette doesn't sound bad with the Advents.
Maybe upgrade the capacitors in the speakers, they just use cheap bi-polar electrolytics. (I hoarded some tweeters from a trashed pair of "The Advents".)

Homebrew speakers. Yeah, really butt-ugly, but good sound for cheap.

The woofers are Lafayette "Criterion" branded japanese 10" drivers, pulled from the Criterion 100B speakers. Criterion was the house name for Lafayette, which were just a crummy line of speakers ala "Kubuki". Which more or less competed with the likes of Sansui in the late sixties.

Steel stamped basket, 2 inch voice coil, a alnico magnet with a paper cone and treated rolled paper surround. Fs is around 50, 60 Hz, depending on the driver....

The original Criterion 100B enclosures were around 1, 2 feet in volume with a oversized port. They had no bass.

In the 3 and half foot volume cabinet tuned to 35 Hz with tons of polyfil, the cheap little 10" is rather impressive. It goes way below it's free-air roll-off in the cabinet, around 36, 37 Hz.
Clean tight bass with tube amps, with good upper mid-bass and midrange. The 10" is a bastard woofer......
They do have a bit of dryness in the midrange, a dammar treatment may help...

The JBL 075's are capped-off with 4 uF GE "Pyranol" oil caps, with a 0.39 uF russian military teflon bypassed across it. Padded with a either a .47 or 1 ohm resistor.

These speakers aren't bad for 2-way, they work like headphones with images spinning to and fro, and behind.....

The Klipsch Cornwall's sound bigger, and are way more sensitive, but they don't image like these.
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Postby JimJ[VT] » Sat Jul 08, 2006 3:52 pm

Looks cool :)
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westend
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Postby westend » Sat Jul 08, 2006 8:21 pm

I bet those do image well and I'm gonna lay it off to the excellent crossover and the JBL tweeter. You can't discount the older woofers, either. There are a lot of sleepers out there. I've got the parts for new crossovers for the Advents. Maybe I'll whack them together, tonight. The tube thing is cool. I'm hearing info in the mid range that wasn't there before, lol.
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Mike S.
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Postby Mike S. » Sun Jul 09, 2006 1:28 am

westend wrote:I bet those do image well and I'm gonna lay it off to the excellent crossover and the JBL tweeter. You can't discount the older woofers, either. There are a lot of sleepers out there. I've got the parts for new crossovers for the Advents. Maybe I'll whack them together, tonight. The tube thing is cool. I'm hearing info in the mid range that wasn't there before, lol.


Heh.....wait until you hear a good single-ended triode amp. Although that little 6BQ5 PP integrated is probably rather close sounding with a little more power.

A audio buddie and I went in on some of these cheap-assed little 2-way crossover networks:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5780366350&rd=1&sspagename=STRK%3AMEWA%3AIT&rd=1


The center frequency is 3 kHz from what the seller claims. I'm using them now. The high pass section didn't seem too special, making the JBL 075's sound a little dull. The low pass section seems to work pretty good with the woofers.
I'm now just using the low pass section of the cheap passive network, and the 075's capped off with the GE 4 uF oil cap, padded with a .47 ohm resistor.

Seems to sound pretty good that way, using a old Mitsubishi DA-R15 receiver.

Today, the same audio friend and I were comparing the Lafayette/Criterion 10" in a 4 foot cabinet on one side, with a JBL 2235 15" in a 4 foot cabinet on the other side. Both woofers were vent tuned to around 35, 40 Hz.
He was using a pair of Selenium D405's with some sort of CD horns for midrange for each side, and either a JBL 075 type of bullet tweeter, or a Selenium (300?) slot tweeter.
A vintage Mitsubishi dual-mono pre and power amp was used.

The D405 driver is huge, really huge.....80 watts RMS or something like that.
Excellent horn midrange once padded down, they dig down deep.
http://www.partsexpress.com/pdf/264-244.pdf


The JBL 2235 had a little more punch, with the deeper bass more noticed. And a little more richer bass than the Lafayette Criterion. And of course can handle gobs more power.
But the JBL was just a little more boomy, proper cabinet tuning may help that however.

Considering the fact the cheap japanese driver is a 10", it could do 75% to 80% of what the JBL does.(In a vented 4 foot cabinet) And the JBL 2235 is not a cheap driver, they are a expensive industrial woofer.
I've watched this guy go through many many singles and pairs of woofer drivers, some rather cheap, some rather spendy indeed. (Fostex, JBL, etc..)
And the cheap Lafayette Criterion 10" always get compared to the others, and they always hold their own within their limits.

You never know......me and this guy like these woofers, but other folks may think they suck. Different tastes, etc.....
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Postby westend » Sun Jul 09, 2006 3:27 pm

Yeah, the Lafayette vintage gear always seems well built. Here's one to get your Lafayette bass goodness on: http://cgi.ebay.com/ONE-NICE-LAFAYETTE-15-SPEAKER-ALINICO-8-OHMS_W0QQitemZ130003625077QQihZ003QQcategoryZ50597QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
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Mike S.
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Postby Mike S. » Mon Jul 10, 2006 2:17 am

That doesn't appear to be a bad Utah 15" driver, the magnet looks pretty good sized. You never know until you actually have the woofer to listen to.

I was using a pair of Realistic/Utah 12" coaxial drivers with a wizzer cone. The cone tweeters were unhooked 'cause they sucked. They didn't do too bad with a external tweeter, but the little 10's do much better.

The trick is getting a woofer (or semi-fullrange) that will cruise down low as you can, and still cruise on up through the midrange to the upper midrange. With good clean tight midbass and midrange that does not go ragged, common with paper cone full-range drivers when pushed.....

The full-range should extend as high as possible, actually, but a full-range driver that does 20 Hz to 20 kHz doesn't exist.

IME's, I've never really like the sound of a full-range driver without some sort of tweeter on top for some added "air". The driver always seemed dull, and the tweeter added some life.

The Lafayette/Criterion is only a semi full-range driver I suppose, they are pretty much done by 8kHz.

In the pics, one 10" is stock, with the paper cone and treated rolled paper surround.
The other has been modded with a pleated fabric surround, it dropped the fs to around 50 Hz.
The audio friend pawned it off on me to use and abuse to break it in, it's still a little stiff and needs to be beat on for awhile. He said it did seem to sound a little less lively than before.
I noticed that the surround is fabric, and will leak air through it if not treated with the type of glue suited for the purpose.
(I suppose I should hook it up and try to kill it....)

The ultimate garbage woofers......
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westend
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Postby westend » Wed Jul 12, 2006 5:55 am

Have you ever used "Mod Podge" or any other acrylic on the surrounds or cones? Man, we are hijacking this thread far out, lol.
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Postby Mike S. » Wed Jul 12, 2006 3:21 pm

westend wrote:Have you ever used "Mod Podge" or any other acrylic on the surrounds or cones? Man, we are hijacking this thread far out, lol.


I haven't used puzzle glue on any sort of cones. I've heard of folks using thinned Elmers and paper to repair a damaged cone. I would think the stuff dries kinda stiff, and you want it flexible. Especially with a surround.
You get too much glue on a cone, and it will throw off the fs and other parameters, overdamped. Same with a surround, you don't want to restrict it's movement.

I've repaired some drivers with mild cone and paper surround damage with Alene's stretchable fabric glue. It works well and is flexible.

For the driver that has the untreated fabric surround, we were thinking of using a thin coat of glue for bicycle tubes. It just needs to seal the surround from air leakage, and remain flexible.

Here, this kinda keeps things on topic......:cwm12:
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