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Old 25th April 2008, 03:15 PM   #241
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Quote:
Originally posted by MJL21193
Hi Ant,
The Dutch tests were presented by Dave earlier in this thread, but he focused on the braced results, not the raw unbraced panel results. Not knowing the exact details of the bracing used, I didn't see the value of those, and went with (as you have done) the raw panel results.
There is some correlation between my amateurish results and these ones. Both show approximately equal resonance frequency for each material, and they both show the plywood to resonate louder than the MDF for the same input energy.


The braced results don't particularly favour birch ply or MDF the unbraced results relate to your own tests.

Going back to the braced results; both MDF and BB are still OK. Its swings and roundabout when you look closely at the graphs. Some level differences and more or less stored energy depending on where you look. I think the differences here are in the audibility spectrum but not to extent where you could easily dismiss one or the other ie. Birch is no good, only use MDF.

Quote:
The reality is that even my tests were hedged - claims are that differences can be detected from listening in a normal position and not with your ear 1/2" from the side of the speaker.
A more realistic test would be with the mic in the listening position. I don't need to wonder what the results of THAT test would show: no difference at all.
Indeed, even with isolated measurements its difficult to distinguish a clear and realistic advantage so given a room and all its attendant colourations I fully believe any differences disappear.

I think there's more pressing decisions to be made other than material selection. Build it good and strong, thoroughly brace and top it off with other tricks like lead sheet etc. And your good to go.
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Old 25th April 2008, 03:37 PM   #242
tinitus is offline tinitus  Europe
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And the question again.."will you be able listen/hear the difference between various kind of bracing"...or measure it from listening position
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Old 25th April 2008, 03:55 PM   #243
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by tinitus
And the question again.."will you be able listen/hear the difference between various kind of bracing"...or measure it from listening position
If the original box vibration has a longer decay time that the drivers, then you can here a difference if the bracing increases decay rate faster than the driver. So it really depends on driver performance, and enclosure size, etc. Not really a simple answer.
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Old 25th April 2008, 04:58 PM   #244
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Quote:
Originally posted by soongsc

The more I dig into cone vibration, the more I know about why and when EnABL works. Let's not let the EnABL argument spread spread.
The idea behind Enabl seems to be solid - cone resonances, but the treatment of it by this process is very doubtful. There is also the issue of the audibility of an effective treatment, as the "noise" produced by these resonances would be very tiny indeed. Compared to the gross output of the driver itself, any backwave treatment from the vent (if equipped) and the enclosure walls (if allowed to resonate due to ineffective bracing), this noise source would be swamped.

Quote:
Originally posted by ShinOBIWAN

I think there's more pressing decisions to be made other than material selection. Build it good and strong, thoroughly brace and top it off with other tricks like lead sheet etc. And your good to go.

Looks like we are of the same mind.
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Old 25th April 2008, 05:33 PM   #245
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Quote:
Originally posted by ShinOBIWAN
The braced results don't particularly favour birch ply or MDF the unbraced results relate to your own tests.
http://www.diyaudio.com/forums/showt...82#post1489182''=

An analysis of the braced comparison -- remember the energy available to excite a resonance is inversly proportional to the SQUARE of the frequency

dave
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Old 25th April 2008, 06:04 PM   #246
peufeu is offline peufeu  France
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Quote:
Originally posted by MJL21193


The idea behind Enabl seems to be solid - cone resonances, but the treatment of it by this process is very doubtful. There is also the issue of the audibility of an effective treatment, as the "noise" produced by these resonances would be very tiny indeed. Compared to the gross output of the driver itself, any backwave treatment from the vent (if equipped) and the enclosure walls (if allowed to resonate due to ineffective bracing), this noise source would be swamped.
I would say, depends on the frequency.
At 100 Hz, yeah. Cone is pistonic anyway.
At 1000 Hz (consider a two-way), stuffing will absorb lots of the backwave, not much will come up from the vent. The panels could resonate. But, breakups and cone reasonance are likely to come into play more at those higher frequencies. Also if the cone isn't pistonic but rather chaotic, beam pattern will be affected, etc.
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Old 25th April 2008, 06:08 PM   #247
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Quote:
Originally posted by planet10


http://www.diyaudio.com/forums/showt...82#post1489182''=

An analysis of the braced comparison -- remember the energy available to excite a resonance is inversly proportional to the SQUARE of the frequency

dave
Okay... now what? Are you gonna actually DO some calculations and show that this statement has any actual relevance to your position? Or is this meant as an engineering statement for the uninformed the masses?

John L.
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Old 25th April 2008, 06:11 PM   #248
dlr is offline dlr  United States
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Quote:
Originally posted by planet10


http://www.diyaudio.com/forums/showt...82#post1489182''=

An analysis of the braced comparison -- remember the energy available to excite a resonance is inversly proportional to the SQUARE of the frequency

dave
I'm not sure what you're implying. The energy that excites the panel is whatever energy is supplied by the driver, but that alone is not the whole story. The energy is a function of the sound pressure applied to the panel excluding direct contact of driver to baffle to side wall. If the driver's output is a flat line for SPL (it won't be on the rear side, of course), then the energy originally output from the driver is equal at all frequencies.

If you're thinking E=1/2(mV^2) for a panel vibration, you've got the cart before the horse. The energy of the resonance is not due just to the energy available (that in theory is equal at all frequencies), it is the energy available minus the energy loss in the panel, i.e. internal damping, in the most simplistic analysis. The measurements shown reflect the varying degree of damping within the various panels plus other factors. Keep in mind that resonances take a finite amount of time to reach an equilibrium. The CSDs shown are for the case of the FR being the point of equilibrium with a time-continuous signal and the subsequent decay rate after that signal is suddenly stopped. At that point the resonance ridges show the speed at which the panel dissipates energy in the bandwidth represented.

The panel will react differently at every frequency, related to the dimensions of the panel, the material's mass and damping properties and also the distribution of the sound pressure wave as it impinges the panel, since it's unlikely to be uniform across the panel interior side, especially for a wall in a box. This distribution will be different for every driver, every box with differing baffle dimension, every case of different driver mounting position on the front baffle, every case of differing internal damping materials used, even different densities and distributions of damping material in the box. Ports will even alter it to some degree.

In the end, there's not a simple way to consider the energy transfer from driver to box wall.

Dave
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Old 25th April 2008, 06:13 PM   #249
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Quote:
Originally posted by peufeu


I would say, depends on the frequency.

Agreed, but the Enabl process has not been proven to do this. Anyhow, there are already enough threads devoted to Enabl (what is the latest count: 4? 5?), do we need it here too?

Dave, the inversely proportional thing sounds impressive. Can you please explain it to us who are not math majors?
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Old 25th April 2008, 07:04 PM   #250
chrisb is offline chrisb  Canada
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Quote:
Originally posted by MJL21193



This is the one you would chose? I don't think I'd have much trouble with it - I have put together a few fairly demanding boxes in my time.
What driver is this designed for?

You would attain God-like status in my eyes IF you could tell which one was made from MDF. I would erect a shine in your honour and travel throughout the country in my 1972 Dodge Monaco wood panel station wagon, with loud hailer on the roof singing your praises!

Well, I might not go that far, but it would shut me up once and for all.

John:

I'm not sure if your question (i.e. which for which driver/s was this designed ) has yet received a reply - the answer is specifically, Fostex FE127E and CSSFR125. A couple of other drivers have been tried as well (Hemp FR4.5 and FE126, at least) but they don't work as well as the previously mentioned units.

I've built over half a dozen pairs of these cabinets, predominantly for the Fostex. My current “daily-driver” is a pair constructed of Teragren ¾” bamboo plywood, with EnABL'ed FE127E.

As is no secret to you, we're big fans of BB ply, but you may have missed the discussions of how we arrived there. Several years ago, we did in fact built 2 pairs of the same enclosure design from MDF and BB plywood.

Specifically the design was a bipole MLTL using CSS FR125 on the face and WR125 on the rear. (the 2 pair in the left-most photo - the stunningly gorgeous VG fir pair with tweeter were constructed by Scott Dunn )

Click the image to open in full size.

These were demo'ed in a non scientific manner at a DIY get-together; only the guy moving the speakers around (me, mostly) knew which was which. Of those actively listening to the comparison, most definitely heard a difference between the two, but there was no consensus as to superiority of one over the other. For some of us, however, the BB ply had a "life" and more nimble articulation of lower mid-bass.

Since that time, the only cabinets I've built from MDF have been the occasional "sub"woofer box. I guess you could say that my mind is made up on the subject as well, in my case it's based on the above experience.

While I recall volumes of bandwidth expended by all on the MDF vs BB debate, throughout all the polemics and technical buzz-speak with which I quickly tire, I can't recall if you mentioned ever actually repeating this exercise?

The little box design in Dave's post is certainly not the most elaborate enclosure I've built either, you might want to entertain yourself with a pair.

In the next production batch of this enclosure, I'm very tempted to build one pair from MDF, just to recalibrate my ears and thinking.

Thanks to all who've participated in this thread, there may well be some revisions to the bracing plan. As there are several pairs of this enclosure on hand, it shouldn’t be difficult to identify sonic differences resulting from both the material and bracing revisions. However, it's not likely that any rigorous technical measurements of enclosure resonances will be taken any time soon.

FWIW, I'll freely admit that I'm a big fan of the suspension of disbelief, and of surrendering to the potential of emotional connection with what the composer / performer is trying to make.

With respect, for me there are many other impediments to that than whether my choice of drivers, enclosure materials, speaker wire or (take your pick...) doesn't align with any particular current scientific theory - in over 40yrs of listening to music and the associated bloviations, I've the pendulum swing in more than 2 simple directions.
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