Supreme Home Theater Hall - Where Decor Meets Acoustics

Originally Posted by Dennis Erskine

This will likely be long; but, first, there isn't anything wrong with the use of 1" dome tweeters. They are like any other "tool" ... they must be appropriate to the task. One other preface ... pro speaker companies publish the polar radiation plots of their speakers. Pros must know the radiation characteristics of any speaker so it can be used in an appropriate application for the specific speaker. Consumer speaker companies do not, will not, or simply have never done the measurements...scary thought eh? (I think they rely on marketing hype and a lack of consumer education to sell their stuff ... there are still some very excellent consumer speaker manufacturers who really do care.)

Here are some basic principles. Sound will decay in air. Generally, you can figure on a six dB loss for each doubling of the distance between the listener and the speaker. That being said, high frequencies decay faster than low frequencies...by a lot.

Given that, as you move further from the speaker, you'll experience a decrease in SPL. In addition, you'll experience a greater loss in the high frequencies than the mids and lows. What are then some of the practical considerations?

First, when you have multiple rows of seating, you want a greater distance between the first row and the speakers than with a single row of seating. The reason is that overall loss of 6dB for every doubling of the distance ... the purpose is to reduce, as much as possible the difference in SPL between each row. Second, we have the problem that as we move further from the source, the high frequency loss is greater than in the mid and low frequencies. For accurate reproduction we therefore need to increase the high frequency output of the speakers to compensate such that when given a flat 20Hz to 20kHz input signal, you get a flat response at the seating location.

Let's look at a fundamental difference between a true studio monitor and a typical consumer grade speaker. The designer of the studio monitor has very specifically designed that speaker with the expectation the listener (mix/sound engineer) will be listening in the near field of the speaker. If you were to measure the FR of a true studio monitor at 1 meter (maybe less for some monitors), you should see bascially a flat response to 20kHz. If you were to do the same with a speaker designed for consumer use, you should see not a flat response; but, a rise in output above 10kHz to 20kHz. The amount of this rise would tell you what the speaker designer thought would be the typical listening distance by consumers purchasing that speaker. Because of that rise in high frequency response, if you were seated closer than expected, the speaker would sound overly 'bright' and you're likely not going to like it.

So now, let's consider speakers designed for large rooms. You'll find they use any number of techniques to compensate for the HF rolloff in air. These would be in the form of wave guides, compression drivers, and horns. All of which have the singular purpose of increasing HF energy from the speaker. In this case, if you were seated closer to the speaker than its designed intent, you'd find it harsh and bright (this is one reason I suspect many dislike horns ... ala Klipsch and others ... simply because they are too close to the speaker). Have you ever had a consumer electronics sales person tell you not to buy the Klipsch speaker because your seating distance is six feet? Nah. In fact, they'll try and sell you the bigger one because it is totally awesome, dude.

So, how does this align with 1" dome tweeters? There are very, very good 1" dome tweeters on the market and they do an excellent job of accurately reproducing high frequencies; but, within the physical constraints of the tweeter and its engineering design. When over driven, they will distort, overheat, and blow out (as would any other driver when driven beyond its design limits). Unaided, they are not high output devices.

Once you get beyond 8 to 10 feet that tweeter cannot keep up with the mid/lf drivers, to overcome the in air decay over distance. Your solution ... turn up the volume. The response is distortion and blown drivers. It really isn't the 1" dome tweeter's problem, it's the problem with the sales person's lack of knowledge and the fact the speaker selected doesn't match the application it is being asked to accomplish.

In the end, with multiple rows we need:
1. more distance between the speakers and the first row to reduce row to row SPL differences;
2. we need to overcome the loss in energy over distance (which is now greater) to compensate for that greater distance; and,
3. we need even more HF energy to compensate for its high decay rate over distance.
We're talking about some serious output/amplification/speaker out put issues here.

The designed capabilities of the speaker(s) must be matched to the engineering requirements of the space and seating distances and once you get beyond about 10' and you have more than one row of seating, that 1" dome tweeter (and the speaker you were sold *before* the room was designed) simply won't cut it. There's nothing wrong with the tweeter. The problem is you (and/or your HT 'expert') are trying to move a ton of coal with a wooden tea spoon.

How many times have we seen: "Hey guys I just bought the following gear (list of "stuff") and will be building a home theater in my basement. I have two difference places I could put it ... need your help." At this point, he is likely beyond help. How many times have you seen an "experienced, we know our s**t" home theater company with here's the list of stuff, let's design and build this thing?.

Oh, well. There's more to this room design thing than dimensions, isolation clips, and fuzzy stuff on the walls.