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Multi-Way Conventional loudspeakers with crossovers

How to deal with high Qts
How to deal with high Qts
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Old 15th June 2018, 04:11 PM   #11
Fast Eddie D is offline Fast Eddie D  United States
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Back in the day, high Q speakers were all there was. No computer sims either.

I used to have a nomogram to determine cabinet volume. You would measure free air resonance, then resonance in a small specified volume box. Each size driver required a test box of different volume. Then you plotted the points and drew a line through them. The intersection with the line on the nomogram indicated optimum enclosure volume.

You had to adjust port length with impedance measurements from frequency sweeps. For bass reflex, "double hump" impedance is optimal, with both "humps" being equal in peak impedance. You could extend the bass by making the lower frequency "hump" bigger.

This worked great! I built 3 or 4 pairs of speakers with this procedure and they were all pretty good; one was monstrously great (15" 3-way).

The beauty of this relatively simple procedure is that you don't need to depend on T/S parameters. You are measuring the actual speaker yourself. Typical parameters provided back in the day were resonance, frequency response, and power handling. Q? Vas? What's that? I never even heard of that until I started building again around 8 years ago.

I wonder if anybody does this any more. I'd provide a link if I had one.
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Old 16th June 2018, 03:31 PM   #12
Pano is online now Pano  United States
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How to deal with high Qts
Sounds like you were choosing box volume by Vas, then tuning by looking at the peaks.
We still do that, don't we?
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Old 16th June 2018, 04:18 PM   #13
Fast Eddie D is offline Fast Eddie D  United States
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Quote:
Originally Posted by Pano View Post
Sounds like you were choosing box volume by Vas, then tuning by looking at the peaks.
We still do that, don't we?
Yes, that is what the procedure addresses.

I didn't know anything about Vas. Nobody I knew used T/S parameters like we use them today.

Today "we" use computer simulations, which saves building test boxes. But I think field measurements are more reliable than manufacturer's claimed specifications.

This was 1974. I was in high school. I didn't have a lot of money. I grew up working class. I'm glad my father didn't see my hobby as a waste of time and money. Maybe nowadays they would consider it neglect to allow a minor to work with a hot iron, lead, and acid. It was a different time.
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