Yes, there is merit in all you have said. I have used test tones, sweeps, etc. already; just not with a microphone or measuring tools. Having said that; as a former musician; I have a very keen ear for what sounds right. Many of my family and close friends are also musicians; practicing even now. I am also a retired Engineer and Technician so I know and fully understand the value of valid testing and measuring. I asked my brother to listen critically to several test tracks while I made changes to my woofer X/O. He isn't technical at all so had no clue what I was up to. He is one of the current musicians I mention though and he and I both agreed on the exact same set-up as sounding the "most real" and "natural".
It has been 20+ years ago but I once had a calibrated microphone and access to very high quality, laboratory grade electronic test and measurement equipment. What I am JUST NOW getting into is all of the free and in-expensive software packages and tools available "these days".
I will do some "blind A/B/X" testing with these musicians; I will know what is going on but they will not. This takes MY personal bias out of the equation entirely!
Cheers!
It has been 20+ years ago but I once had a calibrated microphone and access to very high quality, laboratory grade electronic test and measurement equipment. What I am JUST NOW getting into is all of the free and in-expensive software packages and tools available "these days".
I will do some "blind A/B/X" testing with these musicians; I will know what is going on but they will not. This takes MY personal bias out of the equation entirely!
Cheers!
We know doing it the other way has problems. Technically nothing 'hits' the stuffing because the driver is already up against it. Its effect would be continuous, simply a different load.33Polkhigh said:
This is going to give you two half length pipes. The full length mode won't eventuate. There will still be modes like before, they will be pushed up in frequency.
Sobering to have a show of hands when younger guests are by for who can hear tones at 10kHz, 11 kHz, and so on.
Or try this excellent website (results nicely match* my Can. Hearing Society audiology tests):
Online Hearing Test & Audiogram Printout
B.
* "nicely match" doesn't mean "pleasantly revealing"
If anyone is interested; check out my latest project "3 1/2 way with sub...". My woofer chamber is NOT filled with stuffing on purpose. Felt on the walls...YES; large foam pyramids...YES; stuffing/fill is only in the lower chambers and accounts for about 50% total. Again, mic and interface on the way; I am convinced I am 85% to over 90% fine tuned to the best possible "compromise" but will keep going...retired with nothing better to do has it's MANY benefits...Speaker builder, musician and Technician OVER 50 years; Engineer over 45 years...did NOT just fall into this crazy hobby by accident or yesterday!
I've been advocating this sort of structure or rather structures for a while now (..I even did a design for a member quite some time ago for a sand-damped subwoofer box that had not only the center absorber, but also two rear corner absorbers). Principally you need to keep absorption OFF of the interior walls.
Most of what's subjectively *disliked has nothing to do with standing waves and their reduction, rather it's the restrictive change in the driver's mechanical compliance under normal use (..not simply mechanical compliance as a singular value, but rather a far more complex interaction with driver motion and the box's interior that is of course transient with dynamic changes with reproduced music).
Timely, Veritasium has a recent video on Turbulence. Note that "fluid" in this case is the air inside the box:
YouTube
The center of the box has much higher air velocity than at the cabinet's interior panels. The compliance of the driver however primarily couples to those walls - it "spreads-out", and you can see from the video what is occurring.
Here is a discussion I had with another member with his fullrange driver in-pipe, stuffing and no stuffing:
https://www.diyaudio.com/forums/full-range/75940-fostex-fe-108ez-project-2-a-2.html#post874667
Note that not all drivers have such different subjective results with stuffing (on cabinet interior walls or not). It depends a lot on the driver's mechanical nature and particularly its surround in relation to the driver's excursion under operation.
This is particularly critical to the subjective result of tweeters. (..lower excursion under typical use, the more critical it is). (..and the other area is the profile of the diaphragm - trying to decrease damping while still maintaining a good result.)
*reflections going through the cone diaphragm are another source of dislike, mostly as freq.s increase. So here in particular it's good to have that absorber behind the driver, though again away from interior surfaces including the driver. Suspending a "sheet" of ultratouch insulation in the cabinet does a great job (..as an alternative to using a "dowel"/cardboard-tube and wrapping it like a paper-towel/toilet paper roll). Again of course, keeping the stuffing for the absorber off of interior surfaces.
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Here's the impedance of a 4x15" line array consisting of two separate modules.
The 400Hz bump is driver's own upper surround/cone edge resonance, not cabinet's. Above picture is a simulation of standing waves inside the cabinet using Vituixcad (no modes near 400Hz).
You can see there is very small bump at the 160Hz which is the lowest cabinet resonance. If I connect only one of the woofers the lowest ~160Hz mode is greatly amplified. But with dual drivers it smoothens out almost completely because their acoustic center is at the pressure minimum of said mode and driver's don't excite it.
The cabinet is lined with only 2cm thich acoustic felt on top/bottom/back and sides have only one layer/1cm, so it doens't do anything really for the lowest mode. If damping material were to be used to tame the 160Hz resonance, it would need to be VERY thick like 20cm at least. It would greatly affect the box's air spring also.
With only lining the box the box's air spring and compliance stays "non-lossy" ie. you get high impedance peak at the system resonance (which I want). Choosing a driver with high Qms/low Rms (low friction) would be in vain if the lossy air spring's friction would dampen it anyway.
Minimum damping for the maximum effect, just enought to adequately kill the box but leave the air spring as non-lossy as possible if one wishes to get that tactile, dynamic, easy to breathe and "sensitive" at low spl bass quality imo.
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Great inputs here from everyone! Take a look at my photos; not the best but then you will get a better understanding of what I'm trying to describe. As I said, maybe elsewhere?, blocking my Aperiodic "flow resistor" vent seems to muddy the bass; making it less defined. Having the mic and measuring software will allow me to confirm or disprove what my ears are telling me. Again. maybe elsewhere; the felt damping is only glued down on some woofer chamber walls and the removable (side) panel. All other felt, stuffing/fill and foam pyramids are just shoved into place and held by friction and compression. This gives me many options for box treatment. This is the main reason I wanted a removable panel. I never mentioned this but the photos show it; I used 2 inch wide rubber strips; 1/8 inch thick as a sealing gasket on the removable panel. There are about 18 screws holding this in place; I seriously doubt I have any flex or movement here because I added cleats or wood blocks for these screws so I am not affixing the panel to the MDF itself. Should it become necessary; I can always increase the screw size for a tighter fit.
My thread is "3 1/2 way with sub..." I have done horns, vented (we called it bass reflex growing up) and closed box designs plus a few hybrids. I have never done a TL of any kind. I used to do mostly large BR designs with low tuning; these days it's mostly smaller closed boxes. My 3 1/2 way is the first time at using an Aperiodic vent.
I know from acoustics studies we sometimes need to do short bursts, chirps, gated measurements, etc. Continuous tones can be misleading; same with slow seeps.
WHAT DO YOU GUYS RECOMMEND FOR BEST TESTING FOR ROOM MODES; STANDING WAVES, PEAKS, DIPS, ETC.??? Is REW sophisticated enough to "sniff" these things out? I have never used it before; looking forward to new discoveries here!
Cheers!
My thread is "3 1/2 way with sub..." I have done horns, vented (we called it bass reflex growing up) and closed box designs plus a few hybrids. I have never done a TL of any kind. I used to do mostly large BR designs with low tuning; these days it's mostly smaller closed boxes. My 3 1/2 way is the first time at using an Aperiodic vent.
I know from acoustics studies we sometimes need to do short bursts, chirps, gated measurements, etc. Continuous tones can be misleading; same with slow seeps.
WHAT DO YOU GUYS RECOMMEND FOR BEST TESTING FOR ROOM MODES; STANDING WAVES, PEAKS, DIPS, ETC.??? Is REW sophisticated enough to "sniff" these things out? I have never used it before; looking forward to new discoveries here!
Cheers!
I guess the only way to preserve a driver charactar is to use a infinite baffle, driver rear output freely guided to another room as far as i know. 2nd best, response wise would be a very large closed box with the right amount acoustic damping inside, i guess it would be a necity to use a large amount, preferable mineral wool of a quite a low density.
Anything else would alter the driver natural response and introduce resonances
Anything else would alter the driver natural response and introduce resonances
A friend of mine planned infinite baffle woofers when he built his house. The woofers are wall mounted and the backs go into another room or chamber, effectively infinite baffle. The rest of the system is horns.
He seemed pleased with it, but even though I helped a lot with measurements and crossovers, I never got to hear it.
He seemed pleased with it, but even though I helped a lot with measurements and crossovers, I never got to hear it.
I can say too much stuffing doesn't sound like an infinite baffle, so whatever is going on its not the best. Though it doesn't seem to affect a subwoofer as much. We generally like to hear uniformity. Its possible that too much stuffing that is all the same becomes too effective at some frequencies relative to others. So it sounds disjointed
I posted about the idea of a "musical cabinet" in another thread. Basically no attempt is made to attenuate the back wave. So it is allowed to radiate back out. But what makes it musical is a lack of specific resonances. So the cabinet isn't boxy sounding. But how fast the sound radiates out and what the cabinet is made of and the panel resonances would all come into play. In fact a "musical cabinet" is more complex overall.
This cabinet sounds to me like it has musical qualities. YouTube
Here is another one that sounds nice, not sure if the builder posts here, YouTube
Obviously though its easy to hear the room or something else and think its the cabinet.
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Yes this kind of a cabinet can sound nice, requires fine tuning and/or luck to get it right.
Not the cabinet type for maximum oomph and tight bass with electronic music, it requires a heavy cabinet. But it might be very good for subjectively satisfying "music bass" with acoustic instruments. I have done a lossy enclosure (15mm plywood + bitumen) once and they were quite good subjectively! Hifi and especially speakers is a form of art in the end and there is no right and wrong.
If chosen to go down the uncolored, tight bass etc. road instead, I have begun to appreciate mdf more than before. I have always used 15-22mm birch plywood, which is very stiff and lighter compared to mdf, but 25mm mdf which I chose to my lates project, makes a much less "expressive" cabinet than my previous plywood cabinets. Mdf cabinet sounds dead and weights a ton. Plywood cabinets have a specific tone if they are not braced to death and because they weight much less they dont seem to produce quite as tight bass as a heavier cabinet. Mdf is also quite lossy, maybe it does not radiate/pass "through" it the back wave/sound as much as a more rigid and less lossy panel, who knows. Nevertheless mdf cabinet sounds "silent".
But if used "a low Qms, rubber surround, aluminum cone" etc. nightmare bass drivers, then maybe I would not put it in mdf cabinet. Plywood cabinet might give it subjectively "livelier" sound which the woofer inherently lack, and might work better in plywood cabinet? It a balancing act. Just came to my mind when I watched those videos
. Regarding the videos, big room has a big room's sound. I like bigger rooms, sounds organic and there is natural "blacker backround" to sounds as early reflections are delayed more.
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Is it that it's important to keep absorption off of the interior walls, or that it's much more important to damp the center of the box?
You can vary the density of the stuff so that the change in acoustic impedance is less abrupt... or just stuff the entire box.
Morel has a "musical cabinet"... I think if it is done EXACTLY; it might work OK; I think overall though; it is BEST to just have the drivers do what they do in their designed range and try to suppress anything that is NOT supposed to be there by whatever means! Funny; if you study acoustical musical instruments and have played them then you know that the body plays a SIGNIFICANT role in the overall sound...Stradivarius is the obvious extreme example of this! Was it the shape, the wood, the glue??? We may NEVER really know for SURE!!! Cheers!!!
Friction absorbers does not work in pressure zones so it is not effective to place absorption materials onto interior walls, but for structural reson it can be a good thing to stuff the space between two walls with absorption materials, this to prevent the material to move which can cause non linear behavior
I do it to dampen the walls from vibrating. Not the same as fill or stuffing; that serves another purpose. My foam pyramids serve yet another purpose to help break up back pressure waves so they are not so uniform. I am using all 3 techniques. From what I understand, the stuffing or fill can effectively appear to the woofer as an increase in box volume for one.
And this:
get stuffed [English]
Off of the walls.. well unless you have a very thin diaphragm where the interior cabinet reflections present as significant spl through that diaphragm, and mostly at higher freq.s..
Of course having the absorber in the center of the cabinet absorbs a fair amount of those reflections off of the walls.
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