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Old 15th January 2007, 08:53 AM   #111
Scottmoose is offline Scottmoose  United Kingdom
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Yeah, positioning close to a rear wall frequently obviates the need for baffle-step correction, as the room is giving a helping hand. Plus, when Steve mass-loaded them, I suggested he used a nominally flat alignment to further help a little with this.

BTW the site Dave links to is his new one for a few different frugal designs, which is, I believe, why the regular 'al' spelling is used. It's not live yet, but should be soon. Might need to replace the comma though to get to it... ;-)

www.frugal-horn.com
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Old 15th January 2007, 11:29 AM   #112
gychang is offline gychang  United States
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Quote:
Originally posted by Steve Cresswell


Scott's opinion is that providing the speaker is not too far out into the room then you should be able to get away without a BSC circuit.

Steve

mine will be against the wall (not in corner) on wooden floor, will try without a BSC circuit.

gychang
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Old 15th January 2007, 11:32 AM   #113
gychang is offline gychang  United States
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Quote:
Originally posted by Scottmoose

www.frugal-horn.com

will be checking for more info on the metronome.

gychang
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Old 22nd January 2007, 12:28 AM   #114
lousymusician is offline lousymusician  United States
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Default A new Metronome is born!

If this is not the first Metronome built for the Hemp Acoustics FR8, at least it's the first posted here! The second is in the garage awaiting glue. The wood is birch veneered ply (not true Baltic birch, but a decent enough 11 ply with minimal voids). It has yet to be sanded, let alone finished.

I've got it hooked up, and I'm listening to the right channel of Norah Jones' "Come Away With Me' as I type. At first blush, I'd say that it's indeed a bit smoother through the mids than the same driver in the quick'n'dirty BR box (left channel seen in the background) in which it has been breaking in. That's just what I was looking for when I started this build. Bass is just a bit lighter weight, which I had also expected. So far, so good. I plan on adding some spiked feet when I finish them, the tall enclosure is a bit wobbly on the carpet.

Many thanks to those who had the inspiration for the Metronome, and refined and published the design work. Gentlemen and scholars, each and every one!

More to come,

Bill
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Old 22nd January 2007, 12:48 AM   #115
planet10 is offline planet10  Canada
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The Metronome
Vanyou post some more pics (for me to swipe for the web page)

dave
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Old 22nd January 2007, 12:55 AM   #116
gychang is offline gychang  United States
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Default Re: A new Metronome is born!

Quote:
Originally posted by lousymusician
If this is not the first Metronome built for the Hemp Acoustics FR8, at least it's the first posted here! The second is in the garage awaiting glue. The wood is birch veneered ply (not true Baltic birch, but a decent enough 11 ply with minimal voids). It has yet to be sanded, let alone finished.

I've got it hooked up, and I'm listening to the right channel of Norah Jones' "Come Away With Me' as I type.
Bill

Bill, looks good, mine is in the works, cut all the wood to dimensions but have to put them together. Yours look classy. Are u planning on using BSC circuit?

gychang
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Old 22nd January 2007, 02:39 AM   #117
lousymusician is offline lousymusician  United States
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Default Re: Re: A new Metronome is born!

Quote:
Originally posted by planet10
Vanyou post some more pics (for me to swipe for the web page)

dave
Let me get the pair up and finished, and I'll try to get some decent looking pic's. Might have to clean up my room, too! What file size/resolution suits you?


Quote:
Originally posted by gychang



Bill, looks good, mine is in the works, cut all the wood to dimensions but have to put them together. Yours look classy. Are u planning on using BSC circuit?

gychang
Thanks, GY. I've been using a 1.0 mH coil paralleled with 9.5 ohms and a 2uF cap in the BR boxes. I'll live with that for now, and decide on whether to change the network once I get them positioned well in the room and see how they sound. I suspect it won't change a lot.
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Old 22nd January 2007, 02:56 AM   #118
planet10 is offline planet10  Canada
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The Metronome
Default Re: Re: Re: A new Metronome is born!

Quote:
Originally posted by lousymusician
Let me get the pair up and finished, and I'll try to get some decent looking pic's. Might have to clean up my room, too! What file size/resolution suits you?
As big as possible. I can do the rest from there.

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Old 22nd January 2007, 09:50 AM   #119
Steve Cresswell is offline Steve Cresswell  United Kingdom
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Default Re: A new Metronome is born!

Quote:
Originally posted by lousymusician
If this is not the first Metronome built for the Hemp Acoustics FR8, at least it's the first posted here! The second is in the garage awaiting glue. The wood is birch veneered ply (not true Baltic birch, but a decent enough 11 ply with minimal voids). It has yet to be sanded, let alone finished.

I've got it hooked up, and I'm listening to the right channel of Norah Jones' "Come Away With Me' as I type. At first blush, I'd say that it's indeed a bit smoother through the mids than the same driver in the quick'n'dirty BR box (left channel seen in the background) in which it has been breaking in. That's just what I was looking for when I started this build. Bass is just a bit lighter weight, which I had also expected. So far, so good. I plan on adding some spiked feet when I finish them, the tall enclosure is a bit wobbly on the carpet.

Many thanks to those who had the inspiration for the Metronome, and refined and published the design work. Gentlemen and scholars, each and every one!

More to come,

Bill
Nice work Bill.

This is what I've been waiting for.
It's great to see a bigger one built and sounding decent.
I know that the FE108ESigma version sounds good of course, but until someone else actually built one of the larger versions, all we had was the theory and math to go on.

As we know only too well sometimes the math does not always predict what the speaker will sound like.

In this case it proves just how refined Martin's TQWT computer modelling software really is.
It makes one confident that the smaller original Metronome design is indeed scalable for different drivers.

Thanks for proving the concept Bill

Steve.
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Old 23rd January 2007, 04:34 AM   #120
lousymusician is offline lousymusician  United States
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Default Re: Re: A new Metronome is born!

Quote:
Originally posted by Steve Cresswell


...In this case it proves just how refined Martin's TQWT computer modelling software really is.
It makes one confident that the smaller original Metronome design is indeed scalable for different drivers.

Thanks for proving the concept Bill

Steve.

Thanks, Steve. I don't think Martins worksheets are dependent on this one speaker for validation, the past experience of many other builders (armed with better measurement tools than my old ears) have already proven their worth. All I did was trust the math.

Pondering about this design for several weeks, and the responses to a question from Panamaniac several pages ago, have led me to ask myself a question - since they look so similar, when does a bass reflex box become a mass-loaded quarter wave resonator? I think I have some kind on an intuitive answer. If I may rave for a moment, I'd like to expound for a moment and give the real experts a chance to give me a reality check.

Thiel and Small described the workings of a BR box some decades ago. Their work only adressed one resonant property of the encosure, that of the mass of air working as a spring against the driver and the air mass in the port. I have no reason to doubt their math, since it has been a good predictive tool for thousands of speakers. But, it is a simplified case of what is really happening.

In a real rectangular BR box, there is not only the fundamental air mass resonance that T & S described, there are also standing resonances that can form between opposite parallel walls, and other more complex modes besides. The port cannot control any of those resonances, as in a usual (somewhere between cube and pillar shaped) box those resonances are all well above the ports frequency.

The higher frequency resonances can only be controlled with damping materials in the box. To much damping will affect the BR action, so te designer is left with a balancing act between the proportions of the box and the amount and location of damping in the box to control resonances. Sometimes the balance can work well, other times it may not.

Now, take that basic BR box and stretch it into a tall, skinny pipe. At some point, the the resonant freq. along the long axis of the box will drop to the point where it is as low as, of even lower than, the air mass-port frequency that T & S analyzed. Reducing the CSA so that the total volume is a bit less than that of a T/S designed box would raise the air mass resonant point, further tipping the balance towards the QW resonance. With the length and cross sectional area properly sized, the 'organ pipe' resonance becomes dominant, and we've crossed the transition to QWR territory. Instead of locating the port anywhere we want, and tuning the air mass resonance with it, we can locate it in the end of the line and tune the pipe resonance with it.

Why bother? Well, unlike the BR, we have at least dealt with one of the box resonances, and damped it effectively. Also, by making the box so thin, the other panel-to-panel standing wave fequencies have been moved higher, to a frequency where they can be more effectively damped with a little stuffing (as will be higher harmonics of the fundamental resonance). Since we're not depending on the air-mass resonance to excite the port, the stuffing won't completely kill the bass response. The result should deliver a cleaner, less peaky midrange response. My gut tells me that a classical BR could maybe produce a little more bass, but that it would be harder to keep it as well defined.

Now, enter the Metronome. Like a straight QWR, it should have good control of the lowest bass resonance. Its long walls are not parallel, so there are fewer strong high frequency standing modes to excite. With the open end at the big end of the taper, its line length is longer than that of a straight QWR. What might in other cases be a liability becomes a virtue, as the length allows the driver to sit up at a convenient height for the listener, while still being at a good nodal point in the line. The panels are all very narrow, so they can be stiff without needing to be excessively thick, and without complicated bracing. The narrow baffle should help the speaker 'disappear' in the room (at the cost of maybe needing more baffle step correction). Plus, they just plain look cool , and have high WAF.

On the minus side, the tapered panels are a PIA to cut.

To me, that's a darned attractive set of virtues! Well worth the cost of a couple of sheets of plywood and some time in the shop to try them out.

Man, do I want to get the second one built!

Sorry that went on so long. Allow me to don my Nomex long johns now.

And Steve - !
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