MJL21193 said:
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.
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.
soongsc said:
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.
ShinOBIWAN said:
Looks like we are of the same mind.
ShinOBIWAN said:
http://www.diyaudio.com/forums/showthread.php?postid=1489182#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
MJL21193 said:
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.
planet10 said:
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
peufeu said:
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?
MJL21193 said:
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 )
An externally hosted image should be here but it was not working when we last tested it.
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.
chrisb said:
Thanks Chris,
The drivers are fairly cheap, so I may build a pair and see what I have been missing. I have a number of projects happening right now that will need to be finished first.
Also, as i sit here now, there are 3 pairs of speakers staring back at me, two more pairs down in my basement, a pair in my "lab" and a pair in my shop. There is a general consensus that I already have enough speakers.
Oh, I didn't mention the ones on the back deck.
Lately, since it has been brought to my attention, I have been turning the idea around in my head about a pair of Summa type speakers, with B&C drivers. I've been wanting to try the B&C's for a while, and the prospect of turning a tractrix waveguide mold is luring me.
The listening test for MDF was talked about last year, in the other thread. Don't take this the wrong way but you can't expect me to take that as conclusive proof of an audible difference. Too many variables.
My challenge would be for Dave to consistently single out which speaker (built be me, with the drivers measured and matched) is made with MDF. This is the only way I'd accept it.
Yes, there have been volumes said, but there are volumes said about other irrelevant subjects here also. I, for one, try to make my posts concise and to-the-point, without a lot of technical doublespeak designed to veil the absence of substance.
MJL21193 said:
A graph help? This graph is in units of pressure. It takes energy to excite a panel resonance. If the energy is not at the frequency of the panel rersonance it won't excite that resonance.
The excercises in this thread have reminded me that the 4 AES Loudspeaker Anthologies should be in an serious speaker builders libraries.
dave
Attachments
Re: Re: and???
That's nothing more than the pressure in the box for constant radiated power for given box volumes. I don't see how that's relevant to your statement here:
"An analysis of the braced comparison -- remember the energy available to excite a resonance is inversly proportional to the SQUARE of the frequency".
That doesn't help the situation directly. As for being inversely proportional, it also indicates that it takes less box pressure to attain the same radiated power, so the fact that the box pressure for a given radiated power drops as frequency rises simply means that it will take less box pressure, hence less panel vibrational movement to attain the same output from a resonating panel. The only important point is that if the resonant frequencies are raised, they may be more easily damped, since most damping materials are more effective at higher frequencies.
If you have some other point of which we're unaware, I don't see it. Raising resonances above the passband of the driver/XO used isn't new, IIRC that was one of the points Gedlee (or someone in the thread) made early on.
Dave
planet10 said:
That's nothing more than the pressure in the box for constant radiated power for given box volumes. I don't see how that's relevant to your statement here:
"An analysis of the braced comparison -- remember the energy available to excite a resonance is inversly proportional to the SQUARE of the frequency".
That doesn't help the situation directly. As for being inversely proportional, it also indicates that it takes less box pressure to attain the same radiated power, so the fact that the box pressure for a given radiated power drops as frequency rises simply means that it will take less box pressure, hence less panel vibrational movement to attain the same output from a resonating panel. The only important point is that if the resonant frequencies are raised, they may be more easily damped, since most damping materials are more effective at higher frequencies.
If you have some other point of which we're unaware, I don't see it. Raising resonances above the passband of the driver/XO used isn't new, IIRC that was one of the points Gedlee (or someone in the thread) made early on.
Dave
planet10 said:
That's fine. It's what you have been saying all along. Crystal clear to me now and I have to say I was a little dense about it before. I gave you endless argument, when I did not properly see what it was you were saying. I will re-program myself to this approach, as it's clearly a better way of building to control resonance.
Re: patronizing c^&%
If you think so.
More a definition TMM -- something to define a frame of reference for all those lurking and trying to learn something.
This basic stuff is applicable to any box. For a woofer you can target just getting the panel resonances out of band. ie if you are XOing a woofer @ 200 Hz, the XO is removing available excitation energy.
dave
auplater said:
If you think so.
More a definition TMM -- something to define a frame of reference for all those lurking and trying to learn something.
This basic stuff is applicable to any box. For a woofer you can target just getting the panel resonances out of band. ie if you are XOing a woofer @ 200 Hz, the XO is removing available excitation energy.
dave
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