Stonehenge 1 Tweeter

[Marcs]

Hi everybody, I recently was given a set of Stonehenge 1 speakers. One of the tweeters, model 427-8A does not work. Can anybody recommend a replacement that will be close to the acoustic parameters of the original and will also fit into the cabinet? Thanks!

[badman]

Hi everybody, I recently was given a set of Stonehenge 1 speakers. One of the tweeters, model 427-8A does not work. Can anybody recommend a replacement that will be close to the acoustic parameters of the original and will also fit into the cabinet? Thanks!

I'd check in with Great Plains Audio, and suggest replacing both tweeters, whatever you wind up with. This will likely imply a need for some crossover tweaking or redesign- unfortunately, speakers just aren't a commodity, they're pretty specific in how individual drivers function (which you seem well-aware of).

[Earl K]

Some Older Advice (http://www.audioheritage.org/vbulletin/showthread.php?30847-Altec-Stonehenge-1-s) but still applicable .

:)

[gdmoore28]

Earl, I wonder if Stonehenge owners would benefit from replacing the original tweets with a more modern-designed Titanium dome tweeter? I know there are the originality concerns, but the Stonehenge speakers thus far have not commanded the devotion that Altec fans have to the older "legacy" models. The cabinets are beautiful and definitely deserve preservation, but at this stage it seems to me that a tweet update would not be out of the question. I'm quite sure that a model might be found that will not require cabinet modifications, as well.

What are your thoughts?

GeeDeeEmm

[Earl K]

Earl, I wonder if Stonehenge owners would benefit from replacing the original tweets with a more modern-designed Titanium dome tweeter? I know there are the originality concerns, but the Stonehenge speakers thus far have not commanded the devotion that Altec fans have to the older "legacy" models. The cabinets are beautiful and definitely deserve preservation, but at this stage it seems to me that a tweet update would not be out of the question. I'm quite sure that a model might be found that will not require cabinet modifications, as well.

What are your thoughts?

GeeDeeEmm

Hi GDM,

The "go to" person ( to acquire an appreciation for what these older-style cone tweeters bring to the table versus newer designs ) is Troels Gravensen. (http://www.troelsgravesen.dk/Diy_Loudspeaker_Projects.htm)

Read about his study of the JBL le26 (http://www.troelsgravesen.dk/JBL_LE26.htm).
- I have to imagine the Altec 427-8a has pretty similar strong points going for it .

Finding a modern tweeter that has extended bandwidth, with a low enough Fs & that sports relatively high efficiency / is very tough to find / though not impossible .

The Morel CAT 378 (https://www.parts-express.com/morel-cat-378-1-1-8-soft-dome-horn-tweeter--277-084) should be able to be forced to work in this application ( due to its advertised high power handing ) by implementing a special hi-pass network ( 2 or 3 pole "bump-filter" ) .

Another decent horn/tweeter is this Peerless . (https://www.parts-express.com/peerless-by-tymphany-h26tg45-06-1-silk-dome-tweeter-with-waveguide-6-ohm--264-1386)

- The above suggestions are not "plug-N-play" . They require some design/network expertise .

:)

PS; If I had Stonehenge 1's, I know I'd put a horn/driver combo into the whole section above the woofer ( likely not really what people want to hear at this point ) then re-port the box locating the new port down towards the bottom ( front or back ).
I happen to love the look of those enclosures .

[gdmoore28]

That study on the LE26 is very interesting. I think I'll be keeping an eye open for a couple and do the wave guide modification he suggests.

In connection with the Morel tweeter, you mention implementing a "two or three pole bump filter." I'm not familiar with that term (no surprise). Can you explain?

Thanks for the great info, Earl.

GeeDeeEmm

[Earl K]

Hi GDM,

I'll create within XSim a visual representation for you ( sometime today and then add it into this post ).

:)

[gdmoore28]

That'd be great, Earl. Appreciate you going to so much trouble!

GeeDeeEmm

[Earl K]

Hi GDM,

Here's a pic that displays two different filters ( 2-pole, HP types, both set for 2000hz ) .

You can see that the one labelled "Chebychev Q=1" has a slight rise before ultimately beginning it's roll-off .
- A Q=2 would have more ( & narrower ) rise.

The rise is caused by choosing a tighter ( reactance ) ratio, as made between the individual LC components .
- Increasing the ratio would move the filter from Butterworth towards Bessel and then LR territory .

One can close the gap further ( getting more reactive boost ) at the expense of higher group delay and an lower dip in the impedance ( these are 2 of the big trade-offs that one must contend with )

:)

PS; Please excuse the fact that I got the 2 colors reversed within the impedance pic at the bottom .