FH3-inspired Foam Core Mini Build - Page 6 - diyAudio
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Old 15th March 2013, 08:07 PM   #51
xrk971 is offline xrk971  United States
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Note to self: next time at Lowes, pick up Sureply floor sheathing and can of pecan polyshade Minwax
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Old 16th March 2013, 08:04 PM   #52
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Theyíre finished! Photo below, again with the small Metronomes and Fonkens Prime for comparison.

Only about 10 hrs on the drivers, but they are sounding rather good. Listening to Miles Davis ĎRound About Midnight at the moment. Pretty good sound stage, smooth mids and decent highs. Instruments are well separated (articulated?). The ambiance of the venue is well presented. When listening to NPR news, you can hear the differences in microphones and environments as they change announcers and locations.

Are the Vifa TC9FD as good as the Fostex FF85k? Certainly not! But for less than $12 per driver, Iím plenty satisfied.

I have used BSC on many of my single driver builds, but none is needed here.

And they do produce bass. Got out my trusty Radio Shack SPL meter and Stereophile test CD. In room response at the listening position:

Hz dB
1K 70
200 66
160 63
125 67
100 69
80 68
63 63
50 65
40 62
31.5 51

While they do produce bass, itís not what would call clean, articulate and powerful. I note that the enclosures vibrate rather severely--even the baffle. Not too surprising since they are foam core construction, and the baffle (while plywood) is very thin. I suspect that a proper plywood build would yield better performance and be well worth the time and expense.

Executive Summary: A fine speaker if you listen to jazz or small group type music at moderate SPL. If your favorite is Mahlerís 8th (Symphony of a Thousand), then think bigger, much bigger.

Mr. X: Based on this experience, I would say, donít bother building a Metronome with the TC9FD. The FH3 style enclosure has the characteristics that I like in the Metronome. Probably not surprising, since the acoustic properties are so similar: long, tapered air column with the driver located near the mid-point, port near the floor (and not on the front), and baffle about as narrow as you can get. My thanks for posting the plans for this project!

Cheers, Jim
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Old 16th March 2013, 08:09 PM   #53
xrk971 is offline xrk971  United States
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Jim,
Fantastic build! Looks great and I am glad that you like them. I noticed that you had fewer braces than I did (3 in the triangular section and 3 in the main section), this could be the reason why they vibrate. I don't have any vibration or rattle in mine. Anyhow, thanks for sharing the measurements. Thank you for trying them out and providing a "second opinion".
Congratulations!
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Old 16th March 2013, 08:14 PM   #54
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X,

It's not that the speakers rattle, it's that every surface vibrates when lower freqs are produced at moderate SPL--even the top. More bracing might do something, but I think this is due to the light weight of the entire speaker.

Cheers, Jim
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Old 16th March 2013, 08:23 PM   #55
xrk971 is offline xrk971  United States
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Jim,
OK, yeah they are rather light. If you think having these negates the need building the Mets wit the Vifa's, I will take your advice. Save my foam for another project. I guess your measurements show that the 200 Hz to 500 Hz suck-out was not a problem?
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Old 16th March 2013, 08:37 PM   #56
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X,

I will have to try more measurements to be sure about that, but the way the music sounds, I can't imagine that there is any serious problem with the 200 - 500 Hz region. Voices are well rendered. If something was amiss in that region, there is no way they could sound so good.

Cheers, Jim
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Old 16th March 2013, 08:41 PM   #57
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Oh, I should have explained better. When I say cabinet vibration, I mean that when I put my hand on the box, I can feel vibrations. On my other builds, there is little to no vibration detectable at moderate SPL. (Unless you put your hand in front of the port! :-) )

Cheers, Jim
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Old 16th March 2013, 08:42 PM   #58
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And I have to add: this project has been so successful that I am now considering building the real FH3.

Cheers, Jim
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Old 16th March 2013, 08:50 PM   #59
xrk971 is offline xrk971  United States
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Quote:
And I have to add: this project has been so successful that I am now considering building the real FH3.
This is exactly what Foam Core is for, and this was my feeling too after building these speakers. I want to build the real FH3's in wood with the proper driver. Although a miniature version in 1/4 in ply with FF85WK's may be kind of cute. I couldn't tell if you ended up curving the rear horn mouth outwards?

Quote:
Oh, I should have explained better. When I say cabinet vibration, I mean that when I put my hand on the box, I can feel vibrations.
That is normal with almost all FC speakers - you can feel them vibrate. Didn't you feel the cornu's vibrate too?
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Old 16th March 2013, 09:11 PM   #60
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X,

The Cornu didn't vibrate like these do. Probably because they had little going on in the low freqs. And then there was the hole in the upper bass... For whatever reason, the Cornu project didn't work out all that well. But that's why we use foam core, right?

Even if you add in the cost of the Cornu project to the $24 for the Vifas and $6 for the foam core here, the mini-FH3 is still a great bargain. And a bunch of fun as well!

Cheers, Jim
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