Altec crossovers

[rontec]

I was looking over the mod 19 crossover (n1201-8a) and it seems that c4 (6uf cap) is allowing higher frequencies to pass unattenuated so that the mid frequencies can be attenuated by R3 . If this is true I was thinking of using a similar high band pass cap in both my Valencia's and my 9844's. When using my 19's I don't use any treble or bass boost but with the Valencias or the 9844's I end up cranking up the treble on the amp to compensate for the strong mid range output. It seems that if I use a high band pass cap on the Valencia, then when I turn down the attenuator, it will affect more of the mid frequencies and not so much the higher frequencies.

BTW, this is what I'm trying to do. Tone down the mid freq while leaving the high freq at maximum level. This has probably been covered before but just wondering if anyone has some clarification or some other suggestions. Thanks in advance, Ron

[GM]

Right, as I've periodically posted, all these vintage designs require a period correct high output impedance amp to perform properly, so with more modern amps they require CD horn EQ for best overall performance which at minimum requires a shelving control bypass cap to let the highs through unattenuated.

Set your tone controls to minimum for both bass and treble, shelve the horns as much as it takes to make them sound as tonally balanced to the woofer as you can, set the treble control to flat and try different cap values (I typically used 1 uF to start), finally, bring the bass back up (you may find it needs modest boosting).

FYI, if there's any female listeners, I recommend letting them help set the levels as they tend to have better/more sensitive hearing and found that their audio related complaints tend to fade away if the speakers sound very smooth to them whether they actually measure smooth or not. IME this means a slightly recessed mids similar to the so-called 'BBC dip'.

GM

[rontec]

Thanks GM
I appreciate the explanation and the procedure! I posted this also on the LH Site and got a good link for a ton of info, but your post gives me just what I needed. This should work out well for me!
BTW, I would have entreated my wife or daughter to help in this adjustment, but I think I alienated them from critical listening years ago.

[ZilchLab]

Just use an adjustable version of the bridged-T HF comp filter in Model 19, separately built by Altec as 30923. I have posted adjustable versions for both 8- and 16-Ohm variants elsewhere. It's all of five components to build one.

The PROBLEM with Valencia is that 806 does not have the requisite HF chops to credibly extend the response beyond ~13 kHz, and even there, the attenuated midband is running out of sufficient SPL to balance with the 416 woofer:

[Altec Best]

I thought the 30923/30904 was for matching a medium efficiency woofer to a high effeciency driver like the 411 when using a 416 that may not be needed is that correct Zilch. I just picked up a pair of 30923 with a set of 1285-8B crossovers.

http://www.lansingheritage.org/image...ome/page14.jpg

[ZilchLab]

30923 is M19 HF compensation standing alone, i.e., contoured EQ, way more than simple attenuation, to extend the high frequency response of the compression driver above mass breakpoint when used with controlled-directivity horns or waveguides.

Yes, there is some attenuation at the top, which may be adjusted via varying the value of C1, establishing the upper frequency from which the midband attenuation begins sloping downward toward lower frequencies.

Put it in Spice or mod yours to variable with an L-Pad's terminals 1 & 2, to see how it works....

JBL Technical Notes Volume 1 Number 11

[Altec Best]

Cool Thanks ! :2thumbsup: :thankU: