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Hmm, all the traditional short horns except the original A5 (A110) have an audible amount of throat distortion ('honk') and why I'll never go back to an 825, 210 or similar in a high SQ system, though damping the vent is still desirable to smooth out its overall response.
GM
There are a few of these boxes loaded with 416s on Fleabay now; minimum bid is 8.5K; they come with 511 horns and 288 CDs.
If you bothered to read the forum you'd see they have been discussed at length....Quote:
Originally Posted by robertbartsch
Darn it GM, why do you have to go saying things like that when I can't fit my 110 though the front door! ;-)Quote:
Originally Posted by GM
I thought the "honk" was only a high frequency horn thing...... not that I've ever heard it. It's something that I hear about on other boards, which may be because I was using a 1500hz crossover frequency with on 511B.Quote:
........amount of throat distortion ('honk') and why I'll never go back to an 825, 210 or similar in a high SQ system, though damping the vent is still desirable to smooth out its overall response.
GM - Could you please explain more about damping the vent - I'm not sure what you meant by this because I was going to block off the front vent and put a port in the rear so that I could use the wall for bass loading. The reason why I'm toying around with this box is that it places the 511 horn at ear height which I thought might make it better suited to near field listening as what would be expected in the home environment.Quote:
Originally Posted by GM
One last question, the modified A7 box is about 180 litres in volume, about 40 or so litres smaller than the Model 19, would increasing the size to about 220 litres help. I've noticed that most people say that the 416-8B works best in about a 7 cubic foot box (200 litres) does this apply when it's horn loaded.
Well, it's got its own problems due to its parallel walls.......:(Quote:
Originally Posted by Audio_by_Goodwill
No, anytime there's a pinched throat, there's 'honk' and by 'throat', I'm referring to the horn's initial expansion. If you XO high enough to flatten/'jump over' its BW, then it's less/not audible, which in the 511/1500 Hz XO's case it's mostly already rolled off, so any 'honk' would be reduced to a minor peak in the response at most. The other option is to omit this part of the intitial expansion such as the Tractrix flare does for a given mouth frequency or 511E by the simple expedient of being physically whacked off, with the trade-off of course being less horn loading.
Unfortunately, with an 825 or similar it would have to be low passed down around 110 Hz, so not practical from both an efficiency POV and the large horn required to blend to it, i.e. in both cases the horns have been relegated to some form of waveguide (WG) status, so better to design a WG that best meets the needs of the app rather than 'making do' with existing components.
GM
Greets!Quote:
Originally Posted by altec-man
Damping the vent is about lowering its high Q peak (narrow BW) to a lower Q one (lower peak, ergo wider BW) and since its harmonic structure's amplitude is tied to the fundamental's (remember, a vent is a half WL resonator, so has a harmonic at every 5th), they will decay away faster same as stuffing an open pipe, so while its acoustic efficiency is reduced, its HF BW's ability to comb filter with the driver's direct radiation is reduced and if critically damped, then in theory it's reduced enough to be inaudible during playback.
If the vent is relocated to take advantage of boundary loading, then it seems reasonable that a higher damping density is required to offset the gain to keep those pesky harmonics from being spread around the room like an echo, so it becomes a 'chasing your tale' scenario. Instead, better to tune the vent while well away from the wall, then add a scrap of damping material to the wall that's large/dense enough to attenuate ~only the vent's harmonics to have your 'cake and eat it too'. Not many 'free lunches' in audio, but this is one of them.
While the rule-of-thumb (ROT) is to put the tweeter at ear level, this assumes that it will be flat on-axis, which is rarely the case due to the XO's impact on it due to delay, so is only true if you get it phased right with the woofer's output centered at the XO's BW.
Then there's personal preference as to what vertical sound-staging you prefer. Since we normally listen to music/watch a movie at the cinema where the HF sound source is above us with the bass line pounding our chest/face for max cerebral impact, I prefer speakers that replicate this 'feel', so for me, even the A7's height is marginal and why I was an early adopter of tower/column/TL/MLTL, et al cabs and a more uniform power response than traditional horns could give me. Traditionally, either angling the horn as required and/or choosing the appropriate slope order XO to steer the beaming HF to the 'sweet spot' and/or adding a super-tweeter were the only options due to the need for extreme efficiency and/or a height placement limitation such as in a living room.
FYI, the M19 is ~9.427333209 ft^3 (266.952348 L) net as best I can tell short of filling one up and measuring its contents, which is about the minimum for decent bass output from the 416-8B, so not sure where the ~7 ft^3 'optimum' comes from other than a basic T/S max flat calculation, though a bit large for the 416-8C in later units and about right for it. Never having compared them I don't know how audible the difference may be in a typical room (if any), especially if Altec increased its stuffing density to compensate which would be one explanation why I've seen photos of M19s with fiberglass insulation ~blocking the vent as oppose to the early unit's obviously lined internal walls 'look'.
Bottom line, up to a point of diminishing returns, 'bigger is better' (BIB) rules when it comes to the amount of LF gain BW, but by the same token any size can be critically damped with the trade-off being decreasing LF gain BW proportional to decreasing box volume (Vb).
In the case of such a wide BW driver as the 416, there's another consideration since as the Vb decreases, the stuffing density must increase and at some point it acoustically mass loads the driver's diaphragm enough to begin audibly damping its HF response. There may be some math to calc this point, but IME (limited) a 1.5 lb/ft^3 stuffing density using 'faceless' R-19 fiberglass insulation was the limit before my compression loaded converted 210's 'honk' and Qtc had been reduced as much as practical, which also coincided with the point where its adiabatic to isothermal conversion started measurably reversing, i.e. Fb progressive dropped with increasing stuffing, then began increasing again with increasing stuffing density. I haven't had the chance to research further or read anything in the meantime to indicate whether this is a good ROT or just coincidence in my case, so Caveat Emptor.
GM
GM
So what you are saying is that to dampen the 816 satisfactory would also reduce it BW efficiency, making it behave more like a closed box.
So I suppose the 825 is the best compromise being that it's physically larger making it easier to dampen. As I'm using the N1201-8A do I still need to put fibreglass behind the woofer and how much fibreglass would you need to dampen the 825 effectively, I've also reduced the port size to 75 sq inches. I have had a look of an A7-X for reference, there was no damping behind the woofer and not much else where, was this the norm.
Again, 'satisfactory' depends on the things I discussed, but yes, anytime you add damping you're trading acoustic efficiency for increased smoothness/'faster' transient response and what works for you in your app doesn't de facto work for others to the same degree and yes, a critically damped vented alignment winds up being a leaky closed box alignment with extra gain which will blend better to a typical room's gain curve than a T/S max flat alignment that box programs usually auto calculate.
What the 825's size gives us is tuning flexibility and is only the best compromise as long as the driver's specs and the signal chain driving it are close to what it was designed/voiced for, so if driven with a very low output impedance a lot of EQ is required to flatten it out plus a higher power handling driver with more LF protection for the same peak SPL level of performance.
?? Normally, we only want to attenuate any eigenmodes (standing waves) in the cab so that they won't audibly modulate the driver which is usually done by lining at least one of any parallel surfaces with 1" acoustic fiberglass insulation or a similar rated material. Critical damping is done at/in the vent(s) and can be done with any type/number of porous materials. For your app where cosmetics isn't an issue, insulation material between two pieces of wire mesh is fine and makes it easy to tune. If you use a cloth such as the expanded knit I normally used, then it must be stretched tight enough to force a smile from a Parris Island DI.
Yes, for the majority of prosound apps, acoustic efficiency is pretty much everything since at the average SPL levels desired combined with the far-field minimum listening distances (movie screen or not), any box induced distortion other than horn 'honk' is so far down in the noise floor it's completely indistinguishable from ambient noise at any human perception level AFAIK. In a cinema app, the screen's induced distortion further masks it. Not so in a typical HIFI/HT app unless your average listening SPL is at a hearing impairing large concert 'live' level. Even at DD/DTS/THX reference levels I notice and can be distracted by box distortion, though from experience I know I'm in a small minority group as most folks prefer a certain amount of it, i.e. an 'accurate' alignment sounds too 'analytical'/'dry'/'sterile' for them.
GM
GMQuote:
Originally Posted by GM
What you are suggesting is aperiodic loading e.g. the same principle Goodmans used back in the 50 & 60's (I had a pair of old Warfedale Airedales which used the same principle also). They always used to advertised this way of loading by saying that the enclosure could be made smaller and produce the same bass extension as in a larger enclosure. Would you still use this principle for the 825, I'm using a 10 watt 300B SET to power the A7's when I have finished all the mods.
Has anyone thought of modifying the throat shape of the 825/816 to reduce the honking by a phase plug/waveguide.