Flush mounting tweeters on La Scala with new K-77-D?

[DrWho]

Yes, the concept totally makes sense, but as in many things audio, logical doesn't always mean audible. Does anyone know if you can hear the difference between front-and rear-mounted tweeters and is one clearly better than the other?

Discontinuities in the horn cause distortion. I would expect that the original rear mounting would have artifacts very similar to how your voice changes when you cup your hands over your mouth. 3/4" of cupping on your mouth doesn't make a huge difference, but that's because the wavelengths of your voice are too long to notice. At the tweeter frequencies, 3/4" is very significant.

Then of course there are the diffraction effects already mentioned.

Basically, PWK wouldn't have made the change if there wasn't an audible difference. He was very adament about listening to the changes.

[IndyKlipschFan]

Thanks for the input MAS... Makes sense to me too..

Roger

[mr-b]

Some boring (ha!) practical details - I'd appreciate any advice from folks that have done this before.

I looked at routing it out minimally from the front. The issues with that are that it would restrict the unit to a CT125 tweeter. Also on the CT125, it seems that the driver is attached to the horn by 3 philips screws on the front end and they'd be very hard to access and screw in from the front once the horn was fixed in from the front.

So then I decided to look at the Z-bracket option and route out the hole fully.

The positioning of the tweeter horn is restricted in a couple of ways:

1) At the rear, the edge of the driver (circular on CT125) can touch the cab's top panel.
2) The lower edge of the tweeter horn can touch the top of the squawker horn on the motorboard.

So it looks like I have to correctly position the tweeter horn from the rear and then I guess route it out from the rear. Since the cab top panel isn't removable and it's rather a confined dark space, I'm not very confident about my ability to do this properly.

Then I thought that I could position the horn from the back and mark where the screw holes were if they were different from the K77 ones. Then I could drill these holes right through the motorboard to the front. Then I could position the horn at the front and trace the hole cutting outline from there, and then route/drill/cut/bore out the hole from the front.

Thoughts?

[BEC]

The CT125 horn and driver are threaded. The horn simply unscrews from the driver.

Bob Crites

[mr-b]

Cool - back to plan A. ;-)

[Islander]

1) At the rear, the edge of the driver (circular on CT125) can touch the cab's top panel.

On my La Scalas, the CT125s (mounted from the rear in the usual place) were about 1/8" too high for the removable cabinet lids to go back on. The solution was to chisel a 1/4" deep relief, 3" wide and 2" from front to back. The lid is 3/4" thick, like the rest of the cabinet, so I didn't worry about it causing any problems. It's less simple with the usual non-removable top, but if you can see in and mark it carefully, you could do the job with a Dremel tool or something similar.

The very noticeable sound improvement the CT125s give make it well worthwhile to do a little fitting.

[Islander]

The CT125 horn and driver are threaded. The horn simply unscrews from the driver.

Bob Crites

Bob, what type of horn does the CT125 use? Is it exponential, tractix, or something else? Just curious.

[colterphoto1]

even if you can see down the throat of the horn, that is just the direct sound from the tweeter to your ear, a lot of the other sound waves will be diffracting off that 3/4" edge though.

Whether it makes a bit of difference is up to the listener.

[BEC]

Here is what EV had to say about mounting the T-35 (K-77) tweeter back in the old days.

Bob Crites

[BEC]

Then later when EV was building the T-35A (K-77M) the mounting instructions were changed.

Bob Crites

[Islander]

even if you can see down the throat of the horn, that is just the direct sound from the tweeter to your ear, a lot of the other sound waves will be diffracting off that 3/4" edge though.

Whether it makes a bit of difference is up to the listener.

Just this afternoon, I picked up some closed-cell foam (1/8" thick) to put around the tweeter cut-outs to absorb the early reflections and perhaps moderate the diffraction effects. I'll see if I can hear any difference. Perhaps cymbals will be more clear and defined.

[Bofkont]

hello islander,

i just picked up on this 5 year old trail and wondered about the results you heard using the foam. was it any good?

cheers []

[Islander]

Actually, I didn't get around to trying it and instead upgraded the La Scalas to 510 JubScala spec. You can see the K510 tweeter on the speaker in my avatar. In that setup, the K400 mid and K-77 tweeter are no longer used, nor is the speaker's original crossover. All are disconnected, and only the original woofer is used. The new K510 (or much larger K402) horn with K-69 tweeter covers the range of the original squawker and tweeter, and even goes to higher frequencies (19 kHz instead of 17 kHz), while having improved clarity and realism.

It's not a small thing to do, since you need to get a second power amp, a digital processor, and a pair of K510s or K402s, but the sound improvement is well worth the cost.