Archive for April 2008

WinISD Accuracy and Subwoofers

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To those of you who plan to use WinISD for predicting subwoofer maximum SPL.

Be weary of using WinISD to predict maximum output. WinISD can be a great tool for predicting speakers at small amplitudes, but it is a little naive concerning the non-linearities that occur with high amplitudes.

WinISD makes all of its predictions based off of T/S parameters, which are small-signal specifications and they are not always scaleable to larger power levels. You hope they don’t change in order to use them as an indication of performance, but they are better used for on deciding on box size and box type.

It’s also important to remember two different speakers with the exact same T/S parameters can have extremely different parameters at a given X-max. With small drivers it isn’t that big of a deal since X-max isn’t a big factor, but high excursion drivers are a different story. It’s safe to say that frequency response changes with power output especially for lower frequencies and WinISD doesn’t model the changes since it models in an ‘ideal’ world.

By ideal I mean WinISD assumes that a driver won’t suffer from power compression and more generally assumes that a driver’s response won’t change as additional power is applied.

Take a look at AV Talks Tests and Ilkka’s Tests. You’ll notice that every one of the tested drivers suffer from power compression at lower frequencies and the lower you go the greater the problem becomes. As Keith Yates puts it, “Power compression is the audio equivalent of getting shortchanged.” WinISD does not give you any indication of when your design is going to get shortchanged, which makes it very hard to compare to subwoofers that are already tested.

Another important piece of WinISD that is missing is that it doesn’t indicate how THD levels relate to SPL and frequency. For example, WinISD may show a maximum ouput of 114dB at 40Hz, but it won’t tell you how much distortion exists at that SPL level.

Further reading on high amplitude scenarios: here


Written by syntatic

April 28, 2008 at 8:44 pm

Posted in audio

Impedance Matching

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As I’ve moved further into software development consulting, I’m becoming more aware of the role that empathy plays in all client relationships. When a client calls because disaster has struck their software, it is imperative that I match their level of concern. If my level of concern doesn’t match their level then I’ve failed as a consultant. I can deliver software on time. I can estimate projects accurately. I can have technical mastery. If I can’t be in their shoes and convey that state to them then I’m not developing a long-term relationship. Genuinely share in their work by staying on the same page.

Impedance matching isn’t solely about the words that you say or write. Your overall attitude and tone of voice matter too. Additionally, it’s important to recognize the form of communication used has implicit levels of concern and care. Impedance matching is the act of meeting your clients social attitude, orientation and behavior to maximize communication transfer and minimize problems with the client.

In my realm of work receiving messages often occur via instant message. Unfortunately, instant messages are easy to overlook and relay little context. Receiving a message that says “the server is down” can mean hundreds of different things. Most of them require a simple reply, “I’ll take a look.” Receiving a message that says “SERVER!! DOWN!!” means that the instant messaging needs to stop. While the client is choosing to use instant message the amplitude of the conversation is far beyond any instant message can convey appropriately. Pick up a phone, their impedance demands it.

How I communicate over instant message changes drastically with each client. Most of the time, I think it is best to adopt whatever format the client uses. If they write in complete sentences with capitalization and punctuation then I meet that formality. I let them set the stage for professional communication.

As consultants we want our clients to have positive feelings about us. We want the work to be collaborative instead of adversarial. We need to bend our thoughts and actions to meet theirs. As consultants it is our job to be in their shoes and earn their trust.

Written by syntatic

April 28, 2008 at 8:32 pm