Multiple ports of varying diameter and length end up creating a single Fb.
Hot Rod 8” 2-Way PA/Studio Monitor
Model the Fb in a simulator, go with a large enough port that does not "blow wind" at Xmax.
Good luck,
Have fun!
Art
Okay, thanks. No sims available from ubuntu, or only ones that crash. I'm using david weems "Designing Building & Testing your own Speaker System" 4th ed and a calculator.Quote:
Originally Posted by indianajo
What if instead of one 4" dia 2" port, I use 3 2" dia ports, 2" long, 4" long, 6" long? Flatten box tuning?
Multiple ports of varying diameter and length end up creating a single Fb.
Hot Rod 8” 2-Way PA/Studio Monitor
Model the Fb in a simulator, go with a large enough port that does not "blow wind" at Xmax.
Good luck,
Have fun!
No 2" plastic pipe floor flanges available anyway @ HD or Lowes. Only 3.5" ID toilet flanges that happen to be 2" long, about the length that the chart on p 64 says is appropriate for 4" ID port, 8 cu ft boxes & 25 hz tuning.
Chart on p 61 says f3 for vbox=vas is 1.0*Fs so with 42hz=fs and 25 hz box, I should get some response lower than 54 hz eminence says is useable. 75 watts max from my M-2600 amp in stereo, should not be overheating any voice coils on a 400 w driver. Nor blowing a lot of wind through the port.
My desire is to reproduce piano notes @ 27 hz, or organ pedal notes @ 32.7 hz. Not many LP's have these notes. They were mastered off LP's after 1964? to avoid knocking the tone arms out of the groove. Some 1950's LP's have them.
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I wonder what the extension possibilities would be with the 8" plus 1" combo...
I've been feeling around for a pair of altec 604's as well...I'm looking for some alternatives to compare to the Axi....I think for the most part the Axi is a high performer but if a coaxial or coentrant design could offer high efficiency but with extension down to ~250hz.....I'd love to hear it lol.
it may be that coming from a PA background i've never quite understood the trend and reasoning behind decreasing/lowering x-over points as to my experience it only succeeds in producing more distortion in the final sonic result....maybe euphonic distortion is preferred over clean reproduction.
I would say that there are differences between using PA components for PA or using them for power HiFi. If large woofers are used up to higher frequencies the signal quality is suffering due to being closer to breakup while one is gaining on the HD performance of compression drivers.
I remember that I only went over 4 Watts approx on my compression drivers when I was listening to veeeeery loud rock (louder than I usually listen and definitely not for long). So I guess fot the intended usage my 650 Hz is definitley the better compromise than 800 Hz or higher.
If I would use my speakers for loud sound reinforcement I would also go for 800 Hz crossover frequency and a box tuning around 40Hz instead of the current 30 Hz.
Regards
Charles
When the crossover is changed for the same two drivers to allow more power rating, the horizontal dispersion is reduced. Look at SP2g speaker spec in post 6940. Crossed over at 1800 hz, the SP2g has horizontal dispersion at 2000 hz of 10 deg. Power rating of that speaker is 500 w continuous due to the heavy use of the woofer. Same two drivers in a SP2-XT, same box frequency (55) crossover of 1200 hz horizontal dispersion @ 2000 hz is 22 deg. Power limit of SP2-XT is now 300 W due to lower power capability of the horn tweeter. Pink noise source in power test.
Prior models of SP2 with 800 hz crossover, same tweeter (woofer not specified but also 15") have 150 w rating.
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Yes, the additonal beaming of the woofers is also one of the reasons for crossing lower and gaining in signal quality at the cost of max SPL.
My compression drivers are specced @ 80 Watts if crossed at 900 Hz and 40 Watts if crossed at the 650 Hz that I am currently using. So far I have never ever used these 40 Watts - not even during short peaks.
Regards
Charles
My compression drivers are specced @ 80 Watts if crossed at 900 Hz and 40 Watts if crossed at the 650 Hz that I am currently using. So far I have never ever used these 40 Watts - not even during short peaks.
Regards
Charles
One way to do this is to have the dimensions of your woofer and tweeter (horn/wg) match.....another way is to lower the XO to a point that neither driver is directional, rather, wide open.
One of the main benefits of lowering the XO is to keep "all" the midrange (and/or treble) on one Axis vs splitting it up...
most of these benefits are first realized in the nearfield. Everyone seems to like unity/synergy/meh...its for the same reason...any XO's to a driver that is off axis with the tops are so low its not as big of an issue.... Optimal CTC spacing becomes a reality when low crossovers are an option.
One of the main benefits of lowering the XO is to keep "all" the midrange (and/or treble) on one Axis vs splitting it up...
most of these benefits are first realized in the nearfield. Everyone seems to like unity/synergy/meh...its for the same reason...any XO's to a driver that is off axis with the tops are so low its not as big of an issue.... Optimal CTC spacing becomes a reality when low crossovers are an option.
well the fact that most of the systems where comprised of three or four and sometimes five way configurations(many horn loaded so efficiency was already better) in order to not introduce issues with beaming or break up to begin with (PA is not always about max SPL some of us cared about quality...) i still favor moving x-over points upwards in order to reduce IMD in the higher frequecy band to reduce perceived harshness regardless of overall throttle.
That will only work in a small number of cases. "Most" horns/waveguides do not have a monotonically falling DI wrt frequency, they have bumps and dips and this will all get baked into the overall DI. The exception is that Marcel showed that he could do a waveguide that had a monotonically falling DI - a fairly unique design. Use that and your good-to-go, almost anything else and this won't work out so well.
Not disagreeing with your aspect...just saying when looking at nearfield and domestic volumes...listening distance is shortened and headroom is not needed as high as a real PA situation....Non of those 3-4-5 way configurations were meant for nearfield were they? I'm attempting to build the "biggest" nearfield full range system. When looking at 1 meter listening distance you'll see that with PA, plenty of headroom is there and not much going on with IMD.
the best IMD is none at all....but when a single diaphragm is required to produce both high and low frequencies (regardless of level) to me there's two ways to reduce it, minimize excursion via level or limit the range of the lower frequencies,no?
let's not lose sight of the fact that we are talking about dropping the x-over point of a high frequency driver ever lower which also reduces the point where the amount of level we can apply also keeps IMD in the domain of good or acceptable performance.
to me it's a point of diminished returns and so long as there's the understanding that it's a compromise do what you will but even at domestic listening levels i've invariably found the sound quality negative.
let's not lose sight of the fact that we are talking about dropping the x-over point of a high frequency driver ever lower which also reduces the point where the amount of level we can apply also keeps IMD in the domain of good or acceptable performance.
to me it's a point of diminished returns and so long as there's the understanding that it's a compromise do what you will but even at domestic listening levels i've invariably found the sound quality negative.
I don't know how far you went with your trials. I would definitley not try to cross a CD intended to be used down to 1.5 kHz at 500 Hz for instance.
I am crossing a driver specified for 80 Watts contiuous when crossed at 900 Hz at 650 Hz in my setup. At this crossover frequency it is still specified for 40 Watts continuous. I guess the manufacturer wouldn't make this specification if it were completely unsuitable for being crossed there.
And I guess there is less FM distortion for instance with this driver reproducing 650 Hz and 10 kHz at once at its xmax of 0.8 mm p-p than my woofers would produce with 30Hz and 900Hz combined at a displacement of +- 5 mm.
Regards
Charles
I am crossing a driver specified for 80 Watts contiuous when crossed at 900 Hz at 650 Hz in my setup. At this crossover frequency it is still specified for 40 Watts continuous. I guess the manufacturer wouldn't make this specification if it were completely unsuitable for being crossed there.
And I guess there is less FM distortion for instance with this driver reproducing 650 Hz and 10 kHz at once at its xmax of 0.8 mm p-p than my woofers would produce with 30Hz and 900Hz combined at a displacement of +- 5 mm.
Regards
Charles
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