Panel vent vs port(s)?

**mah** · February 19th, 2009, 11:45 PM

Do they have differing audio qualities? Are there applications where one is preferred over the other?

GM · February 20th, 2009, 03:29 AM

Depends, yes, though this gets fairly involved technically, so the relatively simple answer is that if using a TL, MLTL or similar alignment where the cab loads the vent enough to shorten it WRT a standard calculated length, then a a simple baffle thickness reflex vent is fine. For all other alignments a ducted port vent system is preferred since it controls the driver better at resonance, i.e. a higher Q/faster decaying port resonance for 'tighter' bass and why the Onken is so popular.

All that said, many Altec, PA driver alignments typically require a large vent area just to be baffle thickness and since an equivalent ducted port must have a larger vent area which causes its own organ pipe 'coloration', it's normally best overall to use the reflex vent in a HIFI/HT app.

GM

**Mike Gibson** · February 20th, 2009, 12:02 PM

As far as technical differences I haven't a clue. The only comparison I've ever made was between the Altec 846A Valencias I have and a pair of 846B Valencias. The A model has the vent alongside the horn and the B model has a ducted port. I prefer the A model but then I'm old, nearly deaf and have lived with the A's for over 40 years so YMMV.

GM · February 20th, 2009, 01:35 PM

I'm curious as to in what way you perceive it different/better? WRT 'deaf', how 'deaf'? I mean I'm trying to get a 'feel' for how us older folks into HE HIFI/HT perceive subtleties. The few folks I know around my age either are satisfied with whatever comes out of their stereo TVs, car radios, phones and/or wear hearing aids, so no help there.

My comparison of the two was only at the time the 846B first arrived at the distributor, so obviously had much younger ears and it was enough of an improvement in controlling the woofer at high power that it convinced me ducted port was the way to go when practical. The first 500 Hz 'clones' I built were owned by a Ga.Tech student and I remember them filling an outdoor frat party with a far more balanced, smoother, bass line than their EQ'd A7s.

GM

**westend9** · February 22nd, 2009, 02:58 AM

Here's my take on age and hearing: The difference I hear in sound, even when focusing on barely perceptual differences, is in detail. At one time I sold stereo gear and hence, taught myself how to listen for differences in presentation between speakers, amps, etc.. I am also a life-long musician.
I don't think my hearing was necesarily any better than average but I do know I was able to differentiate small, subtle differences in sound. Now, I am still able to hear the differences but really need to concentrate to hear those differences. Also, the high-end of frequencies, as most folks, is greatly diminished. Perhaps what I can barely hear now, compared to what was easy when younger, is the harmonics.
I'm not an audiologist so lack the vocabulary to convey exactly what I'm hearing/not hearing but for lack of better words, I'd call it shaded or somewhat muffled, or absent of detail.

Originally Posted by GM

I'm curious as to in what way you perceive it different/better? WRT 'deaf', how 'deaf'? I mean I'm trying to get a 'feel' for how us older folks into HE HIFI/HT perceive subtleties. The few folks I know around my age either are satisfied with whatever comes out of their stereo TVs, car radios, phones and/or wear hearing aids, so no help there.

My comparison of the two was only at the time the 846B first arrived at the distributor, so obviously had much younger ears and it was enough of an improvement in controlling the woofer at high power that it convinced me ducted port was the way to go when practical. The first 500 Hz 'clones' I built were owned by a Ga.Tech student and I remember them filling an outdoor frat party with a far more balanced, smoother, bass line than their EQ'd A7s.

GM

GM · February 22nd, 2009, 12:29 PM

Yeah, this is my problem also and why I'm so curious what differences Mike's hearing that makes him prefer the 846A's simple reflex with its somewhat more 'muddy' bass line over the somewhat more tightly controlled 846B's. Now if both were tuned much lower, then the differences get lost in the room's high noise 'floor' and our increasing hearing acuity loss with decreasing frequency. Indeed, here the reflex can be superior due to its minimal port depth, i.e. no pipe harmonics.

GM

**westend9** · February 22nd, 2009, 10:39 PM

I'm curious, as well but I was the little guy who took the clocks and toasters apart, too.

**Mike Gibson** · February 22nd, 2009, 11:10 PM

To me the A sounds more like live music. As to whether or not it does to anyone else I don't know. The B had bass that sounded controlled if there is such a thing. It sounded like a speaker to me. Like I said I've had mine for a long time and maybe I wouldn't recognise good bass if I heard it. Or wouldn't like it.

One thing I have noticed is since they have been actively crossed they are not anywhere near the same speakers sound wise. I don't have the expertise or vocabulary to explain it well. This is as good as it gets

**scharron** · February 24th, 2009, 07:52 PM

Hi Guys,
since a lot of you understand the acoustic physics of these animals much better than I, I have a question related to the op. has anyone ever done an accurate measurement of how much you would have to close down the opening around a 511 thats mounted in the port of an inverted A7? It seems like there is agreement on 75 sq inches, but how does that relate when the filler boards are removed and the horn is inside? I have both utility and magnificents and wonder if they could be made to sound even better than they do?
thanks to all,
scott in nc

GM · February 24th, 2009, 11:21 PM

Well, only the narrow filler board should be omitted...... Anyway, the 75"^2 port should tune it to ~ 42 Hz, so unless someone has already measured a 511-in-port you'll have to experiment with increasing the lower filler board's width to see if that's all that's required, though I don't recommend going higher than the bottom of the 511's lip. If you want to go lower, then the woodworking gets a bit more involved.

If they were mine though, for lowering tuning/increasing bass SQ, instead of doing any woodworking I'd just experiment with tacking thick enough pieces of backless fiberglass insulation to fill the area between the horn and side walls out to, and over, the side wall flanges along with another strip to do likewise between the horn and inner top plate, then the inside of the filler board if still more damping is required. This way they can easily be brought back to stock if desired and anyway, these areas need some damping to minimize the various HF reflections.

GM