New Heathkit AS101 owner - First post.

[alancohen]

I moved the speakers around and centered the mic. This seems about what I have:



It's hard to get a quiet room here. I live on a highway and the roads are wet and cars are going by. That's why I'm moving!!

[Earl K]

- A 135 db vertical scale is the geological equivalent of "fools-gold" .

- At some point you'll need to grasp the concept that the idea is to get a trace that is balanced between being "overly critical" & "simple delusional gratification" such as you are now showing ( manipulating the vertical controls will ping pong between the 2 extremes ).

- A "Pro" Range was established as 50db to the vertical ( decades ago ) by the IEEE ( back in the early 60's ) for a certain sized pic .



> ( I think that's enough for now )

[alancohen]

I see what you're saying...I think. Here is the same plot adjusted to a similar range you posted earlier:



This is 3 separate measurements overlaid.

[VolvoHeretic]

I wish there was a way to overlay a keyboard diagram over those traces so that I had a clue what I was looking at.

[Altec Best]

I moved the speakers around and centered the mic. This seems about what I have:



It's hard to get a quiet room here. I live on a highway and the roads are wet and cars are going by. That's why I'm moving!!

Try to run your sweeps at night.When it's quieter.

[alancohen]

Try to run your sweeps at night.When it's quieter.

I will. Now that I've learned a little about using this new toy, I will certainly play with it more. I did notice with the software that just after hitting the Start Measuring button I hear a little pop...almost like a switch being flipped or a turn table needle finding the groove. It does make the level indicators jump. I wonder if this is being recorded in the results.

Sadly, there is no quiet time where I live at the moment. I have this neighbor that thinks he has the coolest sounding motocycle ever. He stripped all the exhaust off and is running straight pipes. He sits at the light in front of my house and just revs it and revs it. Either he just thinks he's cool, or he can't keep it idling because he amputated all the back pressure from his engine. Regardless, it sounds like crap. If I had a little 22 rifle I'd plink a hole in his gas tank.

There is also a rock quarry across the street. From 6AM till 10AM there are huge dump trucks pulling out on my corner full loaded and winding out their gears. Even on Saturdays.

And the traffic runs steady till the wee hours. I guess you get used to it, but it's really noticeable when you try to analyze your speakers!! Last night was rainy so the noise was particularly loud.

I'm hopefully closing on a house in a week or so that is out in the woods and will be much more conducive to quiet audio time. The only noise there will be the crackling of the wood burning stove and the crickets.

[Earl K]

Alan,

> Glad to see you are now measuring things ( having got your Samson USB mic to work with REW ) .

A few things ;

(i) You will still need to acquire a test mic that comes with a unique calibration file ( that is then loaded into REW ) to correct for the mic's deficiencies ( if you want to believe that what you measure is accurate ) .
- Test mics typically use small diameter ( 1/2" & smaller ) , omni-direction capsules .
- I looked briefly at the available Samson USB based microphones and all the ones I saw don't suit the needs for accurate data acquisition ( they're all aimed at the M.I. market having large capsules & bodies ) . Samson USB Mics

- Here's the MiniDSP mic previously mentioned .
- One ( apparent ) weakness ( of this unit ) is the need to have the users computer quite near the mic . Another is the maximum sampling rate of 48K ( which limits HF distortion measurements more than anything ) .



(ii) The exaggerated HF roll-off shown might be there ( or may be less ) . It's all dependent on the linearity of your test mic ( as well as your testing methodology, ie ; whether the mic was pointed directly at horn & was within it's coverage angles ) .

(iii) Display standards ( for test data ) is a bit of a moving target . Much of it is referenced to the older paper print-outs produced by B&K ( who used a 50db vertical axis ) .
- Your latest pic well displays the HF roll-offs ( though the horizontal length of the pic might tend to exaggerate their severity ). See;



vs this one lengthened by 50% ;



> There is a bit of art & craft to data display ( when all is said & done ) .

(iv) For the small cost of making up the Altec 30923 HF compensation network, I would encourage you to do so ( build at least one ) . Insert it just before the compression driver ( you'll likely need to fully turn up the Lpad on the horn ) and then remeasure & take a listen ( you should see & hear that you have reclaimed a lot of missing HF & UHF in that part of the circuit )

[alancohen]

Will do Earl. I'm always a fan of the least invasive (expensive) mods firsts. Can't hurt to try.

Question: What wattage on the resistors? 2W, 5W? And I assume that C-1 is a simple film capacitor?

And I just checked the specs on my Samson Go Mic. It only goes to 18KHz so that could be the reason for the exaggerated HF fall off.

The sample rate of REW is either 44.1K or 48K. Which is better?

And I just ordered the MiniDSP UMIK-1 as recommended. Seems like a pretty good deal for the $75+$20 shpg. The DPA 4007 @ $1925 is a little outside my budget.

[Earl K]

Will do Earl. I'm always a fan of the least invasive (expensive) mods firsts. Can't hurt to try.

Question: What wattage on the resistors? 2W, 5W? And I assume that C-1 is a simple film capacitor?

And I just checked the specs on my Samson Go Mic. It only goes to 18KHz so that could be the reason for the exaggerated HF fall off.

The sample rate of REW is either 44.1K or 48K. Which is better?

> I'd use 5 watts minimum ( 10 watts if you play things loud ).

> A simple 6uF Dayton Polypropylene cap will suffice .

> 48K is slightly better ( and as a habit is better to use for all sorts of software based audio files ).

[alancohen]

I can't seem to find a 6uF Dayton. They have a 6.2. OK?