heresy center channel testing part 2

[Dan308]

Well this took a while to get all the parts and pieces together but here it is. The drivers I ended up with are a

T-35 tweeter

Atlas PD-4V squawker

2 Peerless 8" 12ohm drivers

E-Type crossover

After glueing, screwing and sealing the box, I installed the woofers in holes that were slightly too big. I made some gaskets for the first test. seemed to seal ok. I'll come up with a better solution later. My first impressions are mixed. The woofers sound surprisingly good. Lots of good base as my B&K 507 crosses over to the sub at 60hz. the tweeter is nice and sharp. The upper mids are fair. The 2 woofers are parallel to present a 6ohm load. I am going to put a different coil on the woofers to keep the crossover point at 700hz. I have some questions about the mid and tweet crossover points. I've asked but seem to get no information, so here goes.

1. stock E-Type xover points are 700/7000 I would like to put new caps on this.

a. I've been told the T-35 won't safely go that low (6000) and the PD-4V won't go that high (6000). And I've been told it will.

b. Here is a copy of my xover. will this work? If not what are the correct values?

c. if the squawker and tweeter connections are changed on the autoformer, what caps are needed to keep the xover points the same on the 1,2,3,4 tabs?

d. should the xover point be 7000 or 6000?

Should I go with a Type AA instead?

the speaker

[Guest " "]

manufactures data for the pd-4v (early k-55) shows 85hz to 7000hz

[Guest " "]

manufactures data for pd-5vh (present k-55-X) 100hz to 4100hz

[Guest " "]

based on your tap settings (4x for tweet, and 8x for mid) for 700 and 6000 (Heritage k-77 are xovered as low as 5000hz) (BTW, your schematic is very simular to a cornwall type B xover).

[Guest " "]

here's a 2nd order ...since your woofer and tweet is 2nd order.....but I would recommend using a 1st order xover....your on the right track...enjoy

[Guest " "]

what we don't know is the SPL rating of the woofers....you might wind up dipping lower on your tap settings. Here's the cornwall type B

[Dan308]

wouldn't that be a 16ohm mid on tap #2 @ 8x = 128ohm mid?

The woofers wired parallel and double surface area should be 91.5 + 3db +3db = 97.5db

Wouldn't going 2nd order on at least the high pass protect the tweeter better at high volume levels?

[Guest " "]

Dan, 11 ohms is the average impedance for the Atlas PD drivers. The SPL gain of two parallel 91.5 db drivers is 3db total so the new spl for the pair is 94.5, but, you should check the response curve of those 8" drivers because as cone size shrinks, the usable SPL within your targeted bandwidth 60hz - 700hz will dive. Most driver SPL's are computed at 1000hz, and what you need to look for is what the variance is from 30hz to 700hz. If it's -10db (very likey), your effective SPL would only be 84.5 for the parallel pair. Some additional useful info, the area of 2 8" woofers is 80% the area of a 12" woofer. You can increase the effective cabinet volume using some poly fill stuffing. This chart is an example. If you have the spec's for the woofers you can gap analysis how close you are from the optimum volume for the drivers and use poly fill to increase or decrease the effective volume. That will help tweak the bass. And yes 2nd order offers some protection, but only an additional 6db cut, it's not bullet proof. And since the t-35 horn can reproduce down to 3500hz on rolloff, you mike like the sound of a first order network better (like the type A). Another advantage of first order is that since the rolloffs are very wide, it makes for a more forgiving crossover in terms of precise calculations of crossover points.

[Dan308]

so for the 1st order, would the autoformer take the place of the L-1 coil or do I need to add that?

[Guest " "]

so for the 1st order, would the autoformer take the place of the L-1 coil or do I need to add that?

you would have to add it......it's simular to the P-trap discussed on this forum as an add on to the AA...

[Guest " "]

so for the 1st order, would the autoformer take the place of the L-1 coil or do I need to add that?

you would have to add it......it's simular to the P-trap discussed on this forum as an add on to the AA...

[Guest " "]

there was an error on the earlier 1st order xover....this one is correct...for L2 the impedance difference between tap 2 and tap 3 is 2x so for that part of the xover the tweeter is seen as 16 ohms.....C1 placed in between tap 3 and the tweet sees the tweeter impedance as 8 ohms.

[Dan308]

Here is the new crossover. Testing today.

[Guest " "]

really nice layout Dan