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New Large Advents...need some help


Guest echesky

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Guest echesky

I owned a pair of New Large Advents that I traded in a pair of Small Advents for in April of 1978. I really liked the way the NLA’s sounded in the ‘normal’ position of the tweeter control switch. Being a college kid at the time I periodically blew a tweeter because the Sherwood 7910 receiver used to power them had one of two settings…off or full blast (rated at 60w RMS @ .1 THD 20-20K…actually tested at 75w RMS at those specs by an electrical engineer where I worked at the time). In 1983 I blew a woofer right before the warranty went out and the newer woofers had round magnet structures…so I opted to get another to have a matched pair of woofers. I also ‘upgraded’ to the newer soft dome tweeters. In time those tweeters got blown, too. Over time I tore-down the speakers and discarded the cabinets, blown tweeters and x-over networks…keeping only the woofers. The woofers were re-foamed by me in the early 90’s with surrounds bought from Parts Express…easy to do and worked great. I have since built new, solid as a rock, cabinets out of ¾” MDF and covered them in plastic laminate and built acoustically transparent grilles for them…they look quite nice. When I built new boxes the tweeters were centered above the woofers at approximately the same distance they were originally. FWIW, what was ‘up’ with the ‘off-set’ placement of the tweeters in the original speaker?? I did take the time to record what the values were for the original x-overs…for the most part. There were resistors on the tweeter switch/crossover which I did not record the values for. I went to a local electronic shop and used an inductance meter to measure the original woofer inductance coils: .3 mH. The capacitors were labeled at 13 uF. Now I am trying to re-set-up a decent (read ‘killer’) pair of NLA speakers. I bought a pair of the orange ‘ferro-fluid’ ‘fried egg’ tweeters off of ebay as originally equipped in the NLA’s. Using a simple digital ohmmeter the tweeters measured at 2.4 ohms each. The Advent (Jensen ?) woofers I have measured at 4.7 ohms each. I realize that once a speaker is put under a load that the resistance value does increase. Potentially considering slightly elevated resistance loads with power applied I hypothetically ‘assumed’ the tweeter to be 4 ohms and the woofer 6 ohms. That would make the x-over points at ~3300 Hz for the tweeter and ~3000 Hz for the woofer…per the x-over network design chart in 'Building Speaker Enclosures' by David Weems (distributed by Radio Shack). I then went to the 'Loudspeaker Design Cookbook' by Vance Dickason to figure new crossover networks and opted for the second order (12 dB) Linkwitz-Riley formulas which ended up with a .47 mH coil and a 3 uF capacitor for the woofer and a 6 uF capacitor and a .37 mH coil on the tweeter…’crossing’ at 3500 Hz and the tweeter being wired in reverse polarity. The speakers are now somewhat lacking in the midrange area…they basically sound ‘dead’ or ‘muddy’. I’m thinking I need to simply go with a 6 dB slope on the woofer to ‘bring it up’ a bit and then for the tweeter…I’m dumbfounded?? I have read that the orange ‘ferro-fluid’ ‘fried-egg’ tweeters crossed at 1500 Hz as built by Advent ‘back then’. Yet…when I look at the newer tweeter specs I got from them (Advent/Jensen) long ago, the response for the tweeters is 3500-23,000 Hz. Typically, I like to use Solen 400 volt capacitors, 18 gauge coils and 16 gauge oxygen-free copper wires to wire the insides of speakers.

Bottom-line…Without using a three-way switch on the tweeters…’normal’ position is good for me…what can I do to get these guys sounding like they used to without using inordinate amounts of equalization circuitry to make up for any shortcomings?

I’m not looking for rocket-science here…just a simple solution to a simple problem.

Any and all help would certainly be appreciated…thank you for your time!

Yeah…BTW…I do try to use all settings of the volume control these days…older and wiser. I still would like to ‘crank them up’ on occasion though.

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Guest russwollman

Wow.

I replaced the orange tweeters with the newer style black dome tweeters purchased from Layne Audio. And I replaced the caps with poly caps. Also built Pete B's BSC circuit (in an earlier post on this board) and use that in the processor loop of the preamp. Finally, I had some mods done to my NAD 2600 amp and 1700 preamp, which were well worth the cost. Maybe most important of all, I live in the basement of an extremely solid old building, so most of the walls are backed with earth.

The sound is glorious. Friends smile when they hear this Double Advent system. And I've stopped fooling around with equipment—except that I want to have my cheapo Sony SACD player modified someday, but the cost is—GULP!

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Guest gkentsmith

It would seem to me that you are looking for a simple solution to a very complex problem you have created for yourself. If what you want is the sound you remember from the New Advents, buy another pair, upgrade the crossover components if you really think it's necessary, using the same values, and then FUSE them. Problem solved.

Kent

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Guest echesky

I can't see where I made this a complex problem. Two Advent drivers in a professionally built 1.65 cu ft enclosure that just need a crossover design...simple to me.

I have found a source for the specs for the original crossover network. I plan on building them with modern, higher quality components rather than what was used initially by Advent. I think I'll even go back with the three-way switch on the tweeter.

Fusing is a good idea until I get to the fact that the fuse 'wire' is tiny as compared to the rest of the wire guages in the box's wiring. The volume control is a far better idea IMO.

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  • 3 months later...
Guest sbalfour

>I owned a pair of New Large Advents[...] Over time I tore-down the

>speakers and discarded the cabinets, blown tweeters and x-over

>networks…keeping only the woofers. [...] I have since built new,

>solid as a rock, cabinets out of ¾” MDF [...] I did take the time

>to record what the values were

>for the original x-overs…for the most part. There were

>resistors on the tweeter switch/crossover which I did not

>record the values for. original woofer

>inductance coils: .3 mH. The capacitors were labeled at 13

>uF. Now I am trying to re-set-up a decent (read ‘killer’)

>pair of NLA speakers. I bought a pair of the orange

>‘ferro-fluid’ ‘fried egg’ tweeters off of ebay as originally

>equipped in the NLA’s. Using a simple digital ohmmeter the

>tweeters measured at 2.4 ohms each. The Advent (Jensen ?)

>woofers I have measured at 4.7 ohms each. I realize that once

>a speaker is put under a load that the resistance value does

>increase. Potentially considering slightly elevated

>resistance loads with power applied I hypothetically ‘assumed’

>the tweeter to be 4 ohms and the woofer 6 ohms. That would

>make the x-over points at ~3300 Hz for the tweeter and ~3000

>Hz for the woofer…per the x-over network design chart in

>'Building Speaker Enclosures' by David Weems (distributed by

>Radio Shack). I then went to the 'Loudspeaker Design

>Cookbook' by Vance Dickason to figure new crossover networks

>and opted for the second order (12 dB) Linkwitz-Riley formulas

>which ended up with a .47 mH coil and a 3 uF capacitor for the

>woofer and a 6 uF capacitor and a .37 mH coil on the

>tweeter…’crossing’ at 3500 Hz and the tweeter being wired in

>reverse polarity. The speakers are now somewhat lacking in

>the midrange area…they basically sound ‘dead’ or ‘muddy’. I’m

>thinking I need to simply go with a 6 dB slope on the woofer

>to ‘bring it up’ a bit and then for the tweeter…I’m

>dumbfounded?? I have read that the orange ‘ferro-fluid’

>‘fried-egg’ tweeters crossed at 1500 Hz as built by Advent

>‘back then’. Yet…when I look at the newer tweeter specs I got

>from them (Advent/Jensen) long ago, the response for the

>tweeters is 3500-23,000 Hz. Typically, I like to use Solen

>400 volt capacitors, 18 gauge coils and 16 gauge oxygen-free

>copper wires to wire the insides of speakers.

>

>Bottom-line…Without using a three-way switch on the

>tweeters…’normal’ position is good for me…what can I do to get

>these guys sounding like they used to without using inordinate

>amounts of equalization circuitry to make up for any

>shortcomings?

>

>I’m not looking for rocket-science here…just a simple solution

>to a simple problem.

>

>Any and all help would certainly be appreciated…thank you for

>your time!

Oh, my, oh, my! Did you get full Thiele-Small parameters for your

drivers before you tried to design a crossover? Going by dead

reckoning as you did is problemmatical, especially if you try to

use the manufacturers specs (they lied). The actual crossover on

the New Advent is around 1800hz. The tweeter has strong response at

least down to resonance at 1900hz. The woofer voice coil is a

lossy 1.43mH inductor; it has astonishing impedance of over 21 ohms

at 3000hz! So that .3mH inductor doesn't do what you think it does.

The woofer apparently isn't rolled off by a filter, and what does

that mean?

Your missing resistors are a series 1.5ohm in the decrease circuit,

and a series 1.0 ohm pad.

The 13uF capacitor isn't a high-pass filter - it's more like half

of a notch filter, but we don't see the series inductor to complete

it. It does NOT roll off the tweeter at 3300hz, because that's

well up on the resonance hump and output is still rising rapidly.

The midrange is lacking in your 2nd order filter design because

the tweeter has been cut off very high, and the woofer's response

extended well beyond it's beaming frequency, and even beyond its

natural rolloff (due to rising inductance). You are asking a woofer to reproduce frequencies for at least an octave beyond 3500hz,

because even with a 2nd order filter, the acoustic output of the woofer (should) contribute audibly to the frequency response well

beyond the crossover point. The woofer doesn't have dispersion

in the midrange, so it sounds wooden. It has very attenuated

response around the crossover point, so the lower treble probably

sounds "thin" as well.

There are more questions than answers here, and your understanding of

the crossover is just beginning. Advent's own crossover was designed

to create an auditory illusion, a particular kind of impressionistic

sound - it isn't even close to being a flat response. With ferro-

fluid tweeter resonance of 1900hz, it's just barely feasible to create a coherent 2-way with it. The New Advent was a 'Hail Mary' play, not

an analytically correct design.

Since you're basically mod'ing, the rest of this thread, if any, goes

in the tweakers and mod'ers forum. See you there.

Stuart Balfour

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  • 1 month later...

Disregard the previous post. After writing it I did some research in the discussion archives and found the answer to my question. However, I can't believe they actually created a design incorporating foam stuffing for an AS speaker! Highly unique and unusual.

It's all about the music

Carl

Carl's Custom Loudspeakers

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