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Multi-Way Conventional loudspeakers with crossovers

Ribbon Crossovers: Need help...
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Old 14th September 2018, 12:42 PM   #11
lowmass is offline lowmass  United States
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That "ribbon" is really not a ribbon. That tweeter used to be sold by Radio Shack years ago. It is actually a rigid embossed foil strip, sort of like a ribbon, BUT the strip of stiff foil is suspended all around the foil strip by a soft rubbery film material.

I have disected that ribbon , and I have some in use experience with it.

first- its not much good below about 4 k hz so I suspect the crossover may be in this area.
2nd- the 4-6 khz area is an area critical to that "presents" and "crisp" sound your looking for. So if crossed over in this area, the frequency response may have not been handled well here and there may be a large dip in response through the "presents" region.
3rd- The low resistance you are measuring on the ribbon is the DC resistance of the ribbons transformer primary winding. The actual tweeter impedance will be around 8 ohms. so its fine.
4th- This is a very RUGGED "ribbon". I wouldnt worry about burning this one up. The foil is thick and the structure is not a loose fragile foil but a rigidly suspended stiff thick foil strip.

In the end its impossible to tell whats going on here without measuring the freq response of speaker. BUT I suspect the tweeters output is not filling in well in the crossover region.

You may want to consider replacing the ribbon with a real one or a decent dome tweeter. Then have those here help you with a crossover for the whole thing that will get that crossover down around 2-3 Khz.


BTW just as a test I would try changing the polarity of the tweeters. Just a last resort kinda thing. Maybe the crossover is OK BUT there could be a dip in response due to a polarity issue?? Long shot here...

Lastly I would take that 2.2 uf cap And all the resistors in parallel with it and remove them. Just run the 4.2 uf cap. Then listen at lower volumes and see if the sound is more acceptable. That resistor /cap section may be pulling the low end sensitivity down enough to darken the 4 Khz region.

Last edited by lowmass; 14th September 2018 at 12:53 PM.
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Old 14th September 2018, 01:24 PM   #12
Galu is offline Galu  Scotland
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Well spotted lowmass!

Here is the ribbon tweeter in the 1988 Radio Shack Cat (top left).
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Old 14th September 2018, 01:31 PM   #13
Galu is offline Galu  Scotland
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Photographs of the ribbon tweeter are to be seen if you scroll down to post #11 in this forum:


Irish Rose -

Techtalk Speaker Building, Audio, Video Discussion Forum
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Old 14th September 2018, 04:05 PM   #14
lowmass is offline lowmass  United States
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Ha yep thats her. I remember using that tweeter with RS mid dome thats also in some of those pics. The tweeter didnt go low enough and the woofer I had didnt go high enough,so I used the mid dome to fill in.
I suspect same issue the OP is having
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Old 14th September 2018, 06:07 PM   #15
SanJoseMichael is offline SanJoseMichael  United States
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system7:

I've done more research on the drivers.

The woofer is a French Polydax HD20B25VHV. HD series, 20 cm (8 inches), Bextrene cone, 25 mm voice coil diameter, 96 mm magnet, minimum impedance 8 ohm at 150 hz, resonant frequency 26 hz, 86 dB SPL. Normal handling power 30 watts

Ribbon horn tweeter enclosure measures 4 1/4 wide by 3 inches tall. Unmarked but identical to a tweeter used in a DAK-era DBX Soundfield V 4-way. One audio site noted "the ribbon tweeter was made by Pioneer and sold by Radio Shack and others. the transformer is to match the 1.5 ohm impedance of the little ribbon to a load an amp can drive." Radio Shack 40-1390 shows 2500-30,000 Hz frequency range, efficiency at 91dB, impedance 8 ohms, "35 watts music program power" made in Taiwan. Pioneer ART-56F shows 5.7 ohms, made in Taiwan.

Speaker was made by Kenleigh Audio, San Diego, CA, established 1959. The company was involved in audio R&D with products for commercial installations, studio and high end consumer.

chris661:


You are absolutely correct, the caps sum to 1.4 per the formula, about 1.3 measured.

lowmass:

Just saw your posting, after I posted my lastest. I will try 4K as well.

Given that the drivers are good, not great, and they are in cabinets, and that we conclude this crossover design is highly suspect, it's time to try a few crossovers.

Note Radios Shack shipped this with a 1.8uf cap.


Thanks.
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File Type: jpg 20180909_162242.jpg (278.0 KB, 130 views)
File Type: jpg RStweeter.jpg (127.2 KB, 136 views)

Last edited by SanJoseMichael; 14th September 2018 at 06:36 PM. Reason: need to add info
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Old 14th September 2018, 06:55 PM   #16
system7 is offline system7  United Kingdom
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I loved that old 1988 RadioShack catalogue from Galu!

The Golden Age of diy! We knew very little, but enough to have a go... how hard could it be?

I must have got lucky, but I had a good time with a pair of new 8" eminence Alpha 8A I found in a junk shop, and 1.5" Audax TW034 tweeters and off-the-shelf 2.5kHz crossovers I bought in the UK equivalent of RadioShack called Maplin. All in old stripped 25L Wharfedale Linton boxes I found in the street. I added an adjustable port stuffed with drinking straws and fiddled with it till it sounded about right.

This speaker of yours sounds worth rescuing. The bass must be OK. Box is on the smallish side, but should be OK.

What it needs is a new 104mm tweeter and a crossover IMO. I could think of half a dozen ways to do the filter, but will confine myself to two tested designs that might be OK.

First is the KEF style, but works with most 8" basses and tweeters:

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Terrible impedance on that one but actually sounds very good. Might even work with your ribbon.

Second is a Rogers LS5/9 style which uses heavy impedance correction and lets the bass see a very low source impedance:

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

This design is outstanding. I haven't quite decided if I prefer third or fourth order on the tweeter yet. But it's world class sound for a two way. The 39uF and 7.5R is called a Zobel impedance correction, here for a driver around 60 ohms at 10kHz. Your driver might require nearer 15uF and 7.5R. The 89dB tweeter needs to be flat and around 5 ohms DC. But level is adjustable.
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Old 14th September 2018, 07:18 PM   #17
Galu is offline Galu  Scotland
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Quote:
Originally Posted by system7 View Post
I loved that old 1988 RadioShack catalogue from Galu!
The 75W L-Pad Controls and the Fiberglass Insulation shown on that page are installed in a pair of my speakers!

I have a couple of old Tandy (UK name for Radio Shack) catalogues, but here is where you can view all the RS ones:

Radio Shack Catalogs - General Catalogs
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Old 15th September 2018, 12:54 AM   #18
SanJoseMichael is offline SanJoseMichael  United States
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system7: Big thanks, that's the kind of stuff I was looking for. Also, I see the Diana Krall CD in your photo! I use her stuff as test material. New duets with Tony Bennett CD just out, I have not heard it yet. But why did she marry that goofy lookin' Declan McManus fellow? (Saw his first US tour in Long Beach, late 1970's when he was angry and very thin.)
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Old 16th September 2018, 08:44 AM   #19
system7 is offline system7  United Kingdom
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I don't think anything you do to this speaker can make it worse, TBH!

Can we get more detail on this item? I can't read it properly.

Click the image to open in full size.

It is usually possible to splice a known tweeter response onto a known woofer response with satisfactory results. Just how it works.

It's going to be 3kHz crossover.
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Old 16th September 2018, 04:05 PM   #20
SanJoseMichael is offline SanJoseMichael  United States
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Steve,

Tweeter spec sheet photo found on the web, I have not been able to find a better copy of it.

Graph of HD20B25H (from a catalog .pdf) shown below.

Initial tests with just a single 4.2 uF capacitor (about 4,700 Hz) vastly improve the top end on the speaker.
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