New Heathkit AS101 owner - First post.

[Earl K]

That makes perfect sense, Earl, but it might not be a good option in my case. The amp(s) I plan on driving my HFs is a pair of 1W 300B OTL monoblocks. At 1W I need as much of the efficiency that a HF CD can afford. If I'm toning down the mids almost 14dB then I think I'm shooting myself in the foot.

FWIW, once I build the 300Bs I will have 3 amps available for tri-amping. That would allow me to boost the above 14KHz range through a tweeter without muting the 800-14Khz mids through the 811.

But that might defeat the gloriousness of the 300Bs by chopping them off at 14Khz and not allowing them to reach higher. And I'm not building 4 300Bs!!

I think the 802-8Gs might be the answer. It will allow the 300Bs to play all the way up, I won't be disturbing the imaging by adding another component and I'll be able to maintain the high efficiency Altec horns are known for.

A couple of things to make note of ( before you pull the trigger on any new drivers or tweeters ) .

(i) You're repeating verbatim ( as if it's somehow gospel , info that can't be substantiated ) that your current drivers are somewhat flat out to 14K .
- I can assure you they are not flat out to 14K / ( almost 15db down at 14K compared to 1K, is not my definition of the word "flat" ) .
- I guess the message contained within this Zilch graph ( that I posted earlier ) simply didn't register with anyone here .
- The existing curve ( on your 811/806 combo ) won't be that much different from the following red trace .
- If you want to use tweeters, you'll want to cross-over in the 6-8K region ( if you go with a raw 811/806 response ) .
- Here's that graph again ;



(ii) If you do get some 802-8G drivers, you'll need to tone down the mids 10 or 11 db to be somewhat flat out to 14K ( according to some testing that I just did with a 802-8T loaded with a 34647 diaphragm / I'll post pics sometime later today ) . The 806 requires even more midrange attenuation .

(iii) I'd suggest you get some measurement gear before buying anything like other drivers or tweeters.

- FWIW, REW is still free & it works well on a Mac ( under some strict conditions that dictate what sort of external soundcard you can use ).

- Also, a USB based test-mic is in the works ( from the MiniDSP people ) which will come with a unique calibration file ( for each & every device sold ) making the mic useful for measurement purposes. It'll be @ $100.00 ( from what I've read ) making the entry cost for getting serious data, cheap as Borscht !

[alancohen]

That is certainly a sober recommendation, Earl.

I have a USB-based Samson Go Mic. It might do the job well enough. I also have a Macbook Air. I downloaded REW, but I don't have the patience at the moment to set it up or figure out how to use it. Can these programs play a pink noise signal through the headphone output and record it back though the USB mic?

[Earl K]

<<<<<<<snip>>>>>>>
Can these programs play a pink noise signal through the headphone output and record it back though the USB mic?

Yes ! ( REW has a great signal generator built into it )

[Alien_Shore]

I did some horn compares that you might find interesting:

Here is a modern HF driver (B&C DE250) on three different Altec horns:


And here is the same driver compared to an Altec 802D on an Altec 511B horn:


All of these are "barefoot" driver measurements (no XO, EQ, etc.)

I also have some 902 and 802-8G graphs here somewhere....

[Earl K]

Alan,


Here's the pic I promised .

My apologies for it's "clutter" ( hopefully the message doesn't get lost in the info ).



The red and teal colored traces shows an 802 ( on a Radial horn ) with a 2-pole HiPass ( similar to the AS-101 values ) coupled with the HF portion of the 30923 "Equalizer Network" . I'd say this network offers 10 to 12db midrange suppression .

[alancohen]

I think I got REW working a little. Here is what I got:

[Earl K]

Put that file into a 60-70 db vertical scale, apply 1/6 ( or 1/12 smoothing ) & then repost the graph.

[alancohen]

Huh???????

[alancohen]

OK...found it I think:

[Earl K]

- A couple things to check out ( to investigate the "suckout" between 800 hz & 1600hz ) .

(i) Replace the horn driver with a single 8 ohm resistor & run another trace ( to see ho high up that woofer is working ) .
(ii) Do the same with woofer ( replace it with a single 8 ohm resistor ) and capture a sweep of the horn circuit on it's own ( to see how low it's going ) .
(iii) Switch the polarity of the horn circuit and then capture a sweep of the horn & woofer together ( to see if the stock polarity is actually "adding" within the crossover region ) .