no, way before my time. My father had something really nasty. Warfedale E30s in the window alcoves,
on their sides. But at least I inherited his Koncrete Kenwood turntable when he gave up on vinyl
I would really encourage you to try and check them out sometime. I feel the same as you about ports,
but these are very different, and have quite excellent bass.
I had W60Ds as a teen, kits from Radio Shack. I quickly traded them in.
They do need a good solid-state amplifier. My 70s era HK-430 receiver does really well with them
in my video system, especially since I bypassed the preamp circuit, running directly into the power amp.
Stands about a foot high work well. http://p10hifi.net/planet10/TLS/downloads/TedJordanAperiodic.pdf
http://www.seas.no/index.php?option=com_content&view=article&id=475:seas-a26-kit&catid=66&Itemid=365
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A port only uses 1 resonance effect, given its name by Helmholz. How well they work is a matter of design and execution. Sealed and ported each have their disadvantages. Flabby and poorly defined bass is not innate to ported speakers but to poor engineering.
As to definition:
a well done BR has lower distortion at low frequencies than a sealed enclosure with the identical driver (Linkwitz boosted to get the same frequency extension). The reason is that the cone of the BR speaker moves much less at low frequencies than the same speaker in a sealed enclosure. The port takes over at low frequencies and ports can be made surprisingly clean, distortion wise. Also noise wise. A bass driver flapping 1 cm both ways will produce a lot of mechanical noise, likely more than a well done port with the same acoustic output.
The only thing worse in a ported speaker is more phase shift, double that of a sealed enclosure. Not that much of an issue imo. People get upset because of 'long group delay', but that might be because they don't understand that concept very well.
What about waterfall plot decay time? Doesn't resonance mean somewhat more prolonged damped ringing, as compared to very rapid damping of a small sealed enclosure?
If there is some ported design with a very quickly damped waterfall, I would like to take a look at the graph, if possible.
Jan,
An article for your reference (pretty sure you already know this stuff):
Understanding Impedance Curves & Phase Angles | Audioholics
Also very curious to know if the actual flatenning of impedance really helps...
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Waterfall's are good for delayed resonances. Even in headphones I see resonances popping up milliseconds after the initial signal. Speakers and headphones do not act like resistors, capacitors and inductors since there is a time delay between a transient moving a voice coil and that wavefront propagating through the cone. Electrostatics are a little better but even there parts of the frame will react when the vibrational energy gets to them.
Waterfall's don't necessary show non-minimum phase and phase is easier to see with a Bode plot, especially if time corrected. There still is a lot of controversy on what phase behavior is audible.
Waterfall's don't necessary show non-minimum phase and phase is easier to see with a Bode plot, especially if time corrected. There still is a lot of controversy on what phase behavior is audible.
Taking waterfalls at the low end requires linearizing of phase, so it is not that easy to take those kinds of measurements. If you don't linearize phase, the BR waterfall looks worse than sealed waterfall for the mere reason that the former has more phase shift. This creates a measurement artefact.
Okay, maybe, depending. It would be helpful to see a detailed analysis including estimation of the magnitude of likely artifacts. Is there some reference material you could point to?
Like Mark I'm not sure I follow. Both types have major phase shifts around the resonance. BR has two closely spaced but I don't see how that would affect a waterfall plot in ways that are not valid. Taking waterfall plots of woofers is borderline impossible. You need a very large space with low background noise. And for 20 Hz one cycle is 50 mS, to see if there is stored energy decaying you need possibly 500 mS of time to look at to see decay over 10 cycles. That would translate into 500'. I could see doing this in something like the Roman Colosseum if the floor were flat and solid. I doubt you could rent it for this purpose anyway.
How about the guys up at the old WPPS power plant cooling tower near Olympia?
http://nwaalabs.ipower.com/index.html
"The largest reverberation chamber is 738 cubic meters in size and can accurately measure frequencies down to 25Hz. It is also the second quietest room in the world with a background level of -15 dBA."
possibly big enough
Cheers
Alan
http://nwaalabs.ipower.com/index.html
"The largest reverberation chamber is 738 cubic meters in size and can accurately measure frequencies down to 25Hz. It is also the second quietest room in the world with a background level of -15 dBA."
possibly big enough
Cheers
Alan
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People have done LF waterfalls in anechoic chambers. I guess if some people who are serious about building amps go out and buy expensive distortion analyzers, serious speaker builders might need to do something equivalent.
This brings out another issue though, which is if time domain response is hard to measure, it is one more reason why design for good time domain performance might be given less attention than it otherwise could benefit from.
Between measurement difficulties and not being able to model and visualize time domain performance during design, what should we expect? Not surprising if it were to suffer in the process of optimizing designs for what is more easily modeled and measured: frequency response.
I heard a story that the poor man's way to measure was to take a speaker out in the middle of a field on a quiet, windless day, and set it up on top of a ladder pointing straight up (with a mic suspended above it)! Of course, ground reflection would still be there...
This brings out another issue though, which is if time domain response is hard to measure, it is one more reason why design for good time domain performance might be given less attention than it otherwise could benefit from.
Between measurement difficulties and not being able to model and visualize time domain performance during design, what should we expect? Not surprising if it were to suffer in the process of optimizing designs for what is more easily modeled and measured: frequency response.
I heard a story that the poor man's way to measure was to take a speaker out in the middle of a field on a quiet, windless day, and set it up on top of a ladder pointing straight up (with a mic suspended above it)! Of course, ground reflection would still be there...
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Yes done by friends in the 70's. There also is the repeat play and record loop into unintelligibility thing that was popular then.
A another way is to place the speaker flat on its back out in a large parking lot when it is empty. Placing the mic flat on the surface too. That'll work well.
I think Mark Gander wrote a paper about that.
Edit: Gander, Mark R., “Ground-Plane Acoustic Measurement of Loudspeaker Systems”, Journal of the Audio Engineering Society, Vol. 30, #10, October 1982
Jan
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Demian,
You can rent an empty arena on an off day for $5,000!
Loudspeaker on the ground aimed up with a microphone above is often done. A bit rarer is loudspeaker on a tower.
Other folks have used an aircraft hanger.
Of course I get to play in stadiums. One "consultant" specified a microphone level cable (incorrectly) and then tried to use a spool of it to extend the range of his measurement microphone. He the blamed the results on the loudspeaker manufacturer.
I just did a demonstration where the audio power amplifier received the signal via 4,000 feet of cable. Rate capacitance 34 pF per foot and DC resistance of 17 ohms per 1,000 feet. Source impedance around 200 ohms and the audio power amplifier input impedance greater than 10,000 ohms.
I used a repeat coil. A piece of audio hardware that is virtually unknown these days.
You can rent an empty arena on an off day for $5,000!
Loudspeaker on the ground aimed up with a microphone above is often done. A bit rarer is loudspeaker on a tower.
Other folks have used an aircraft hanger.
Of course I get to play in stadiums. One "consultant" specified a microphone level cable (incorrectly) and then tried to use a spool of it to extend the range of his measurement microphone. He the blamed the results on the loudspeaker manufacturer.
I just did a demonstration where the audio power amplifier received the signal via 4,000 feet of cable. Rate capacitance 34 pF per foot and DC resistance of 17 ohms per 1,000 feet. Source impedance around 200 ohms and the audio power amplifier input impedance greater than 10,000 ohms.
I used a repeat coil. A piece of audio hardware that is virtually unknown these days.
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