The Metronome

frugal-phile™
Joined 2001
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Steve,

The Metronomes are also quite interesting.... and not really a TQWT (in a strict sense). I can't remember whether we discussed it here or on the full-range forum. Because it tapers in both directions the taper is not linear, but quadratic. It does make for a very elegant looking speaker.... have you posted drawings anywhere?

dave

PS: always nice to see the "Made on a Mac"
 
planet10 said:
Steve,

The Metronomes are also quite interesting.... and not really a TQWT (in a strict sense). I can't remember whether we discussed it here or on the full-range forum. Because it tapers in both directions the taper is not linear, but quadratic. It does make for a very elegant looking speaker.... have you posted drawings anywhere?

dave

PS: always nice to see the "Made on a Mac"

Dave

The plans for the speaker can be downloaded from here

Steve.
 
frugal-phile™
Joined 2001
Paid Member
Here is a graph of the actual taper of the metronoe.

dave
 

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frugal-phile™
Joined 2001
Paid Member
Steve Cresswell said:
There's a slight curve on the taper... Does this mean it has an element of horn behaviour involved with it ?

A Voigt can already be thot of as a form of conical horn. Here the taper is quadratic, as opposed to linear.

Normally a classic receipe Voigt has little chance of being close to optimal, but you have added a twist -- this has been discussed, but yours is the 1st i've seen actually built.

http://www.diyaudio.com/forums/showthread.php?postid=569253#post569253

I've sent the data off to Scottmoose to see if he would be so kind as to model it for us.

dave
 
frugal-phile™
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Hi Dave -interesting design. Did you get my email?

Hugz -First port of call you need is Martin King's TL alignment tables. Necessary line length varies depending on taper.

Generic example lifted from Martin's tables: assume a 40Hz cut off. A straight line requires an 84in line. A TQWT with a 1:3 taper ratio requires 102.9in length. And a reverse tapered line with a 3:1 taper needs a 66.8in length. Providing you keep this basic principle in mind when you design, you're fine. If not, as Martin points out, you're in trouble. His tables are free to download, and provide ~optimum driver offsets for each rough geometry too. The quadratic flare will affect the spread of resonance, but it won't make much difference to the final cut-off IMO, though I speak under correction. Mass-loading should work in the same fashion as it does for a staight taper.
 
Hey Scott

It would be interesting to have a look at those sims to see if they do really cut off as sharp as I hope they do.

They seem to integrate well enough with my sub but sometimes I get a slight honk on records with a strong upper bass content such as some Motown and Atlantic/Stax stuff from the 60s.

It is not enough to be annoying and no speaker is perfect but I'd like to get some insight into a way of maybe getting rid of it.

Steve
 
frugal-phile™
Joined 2001
Paid Member
Steve,

I'm away from my home 'puter at the moment. I have a chart that shows the as built, modified to an ML-QQWT, and one lengthened to reflect the length needed to actually have the box resonate at a 1/4 wl of the Fs.

I've hesitated to post it so far because the straight taper equivalents are perfect duplicates, something i didn't expect, and therefore deserve a triple check.

The as built QQWT shows a roll-off at ~100 Hz with strong ripple -- a broad peak at the bottom, a deep null at about 400 Hz, and then another broad peak (plots only go up to 1k). The bottom peak could offset baffle step, the null is narrow enuff that it might be unobjectionable, but the upper peak indicates a lot of mid-range energy coming from the bottom which might colour the mids a bit -- this is into the region of floor bounce and other room effects so may well be swamped by other things.

The ML-QQWT exhibits much, much smoother response, with almost an extra octave on the bottom, the lengthened QQWT looks like the shorter one, but with everything shifted lower in frequency.

Scott also mucked about a bit with a bipole FE126 in an ML-QQWT and it looks quite good. Certainly an alternative to having to build a horn.

dave