Ranting of a crazed Audiophile...Vol. 2
Mar 19 '06
The Bottom Line Choosing a conventional speaker...a square wheel!
3-19-06
Ranting of a crazed audiophile vol. 2 (how to choose a square wheel)
This is going to be a tough one! We have previously established that the monopole is not a viable solution for speaker design and yet probably 95% of the commercially available speakers are monopole. Are you sure you want to stay with monopole???
Let’s examine the alternative for a moment. Ok, you have a great new receiver and you want to know what speakers to buy. Ok first off, does the receiver have preamp outputs? You’re going to need these to connect to your external active crossover. By the way, you will not be able to use the internal power amplifiers in your receiver. You’re going to need three or better yet four channels of external amplification for each speaker! A good choice would be to buy two 4-ch amplifiers and set one behind each speaker. Oh, make sure and buy plenty of interconnect cables too because not only do you have one set coming from your receiver’s preamp output to the crossover but you also have four more sets between the crossover and the amplifiers. While you may be accustom to just two wires going to each speaker, you are now going to have at least eight. It’s always better to have an amplifier for each drive unit and since you must have at least two woofers so that one can be reversed to cancel non linearity, you really should have five or more channels of amplification… So after your head spins 360 deg, you say, ‘never mind, sorry I asked…”!
Clearly, despite its short comings, the conventional monopole speaker has an advantage in its simplicity. You buy it, take it home, connect it to your receiver and you’re done! There are commercially available open baffle dipole speakers that do not require the active crossover but these are expensive and in my opinion, defeat their own purpose to a degree. While these retain the simplicity of the monopole, the heavily inductive load created by the required passive crossover, means you need something like a big Krell or other high current amplifier. I don’t think any of these commercially available options would work well with a typical receiver.
Before getting too involved let’s consider the why of it all. Why is the choice of speakers so important? The answer is simply the enjoyment of music! I believe some speaker manufacturers are doing a big disservice to their customers by building speakers that have a very high first impression but deliver only fatigue in long term listening secessions. If you bring home a new speaker system crank it up for a short time on your favorite CD thinking how great it sounds then lose interest, and turn it off to go do something else, you probably have been a victim of such a speaker company.
High levels of harmonic content and other spectral contamination will make a speaker sound very big and full giving the un-calibrated or, “untrained ear” a false first impression. If the system you choose provides an undistorted pure recreation of the original musical event, it will be too captivating to turn off in favor of doing something else. You will find yourself saying, “just one more song”, or “just one more CD”! You’ll be late to bed, late to work… The draw back to a truly good system is that you find you have to not allow yourself to turn it on in the first place! You know you won’t be able to stop listening!
I would like to avoid recommending specific brands in my ranting although I may at times name a few. Likewise, I also want to avoid bashing any particular brand. I will say, virtually all speaker brands sold in mass market electronic stores are in my opinion, not serious attempts at accurate sound reproduction. They don’t call them, “mass market” for nothing! These are for the casual listener that basically just wants to have some noise. Some of these brands may be generally thought of as big name brands by typical consumers but the simple reality is that they serve a different market than the high-end audio world.
While the monopole inherently presents a non uniform radiation pattern to the listening environment, the numerous other factors involved can make a huge difference in the overall sound quality of one monopole relative to another. Many of these are easily measurable with the right equipment but despite this, few if any manufactures publish any meaningful data. This makes the task of the audiophile consumer more difficult.
Another thing I want to avoid in this ranting is all the behind the scenes technical babble involved in speaker design. While this might be interesting to some, when it comes down to making a speaker purchase it probably doesn’t help you much unless you just want to dazzle the sales person. So, I’m going to try to step outside my nature here and write a more practical approach to speaker shopping.
The one big mistake I believe consumers commonly make when choosing speakers is to use a false reference. The two most common false references are one, their existing speakers and two, other speakers in the demo room. None of these are a valid reference! Some hard core heavily opinionated audiophiles (is there any other kind?) believe measurements are generally useless and that only listening test should be used in speaker purchase decisions. This probably stems from the fact that the industry generally makes all the wrong measurements or they make inadequate measurements resulting in data that in no way correlates with sound quality. What these hard core “listening test only” audiophiles don’t seem to take into consideration is that they usually have no valid reference. Most of them use their own existing speakers as a reference either consciously or unconsciously. Unfortunately all this accomplishes is a purchase of new speakers that sound a lot like the old ones.
One problem with listening test is that acoustic memory from short term exposure tends to be very short. If you listen to speaker A today and come back tomorrow to hear speaker B before making a decision, your memory of A has already long passed. Even with a valid reference short term listening experiences are not likely to be of much help. Switching between two possible speaker choices on an interval of a few seconds can be manipulated by small level differences of fractions of a dB. Non linear distortion, which compresses the music material making it sound louder and fuller could lead you to choose the speaker with the most non linear distortion.
The best reference is your own internal long term exposure reference, but first this must be calibrated! If the majority of your listening experiences are at home on your existing speakers, then your internal reference is likely to be far out of calibration. The same is true if your primary listening experience involves any other speakers. The best way to calibrate your internal reference is long term exposure to live acoustic music. Very small venues with performers playing acoustic instruments, an orchestra, or any number of other acoustic performances would all be good choices. In other words, get use to what live acoustic music should sound like when it’s untouched by speakers of any kind. If the performers are selling a CD, buy it and take it with you when shopping for speakers as this can help bring back the memory of the live event.
The idea is to disconnect your reference from all other speakers and their associated distortions. To build a truly useful internal reference takes time because again, acoustic memory of short term exposure is too short to be useful. Also, your reference should be built on averages of multiple exposures to various performances in various venues to average out inherent sonic characters in the venues themselves.
Of course a general writing of how to choose loudspeakers must be considerate of all markets. I would tell you to rap on the side of the cabinet and that if it sounds like a hollow door, don’t buy them but if you’re in the market for a $200 ~ $300 /pair of speakers they’re probably all going to fail this test. This test is important because thin inadequately braced cabinet walls will resonate becoming in effect, an additional speaker cone radiating a distorted version of the music material into the listening environment contaminating the sound quality. A good quality speaker will always be quite heavy as it will be most likely constructed of ¾” MDF if not thicker plus have internal bracing. For my own personal Home Theatre subwoofer, the cabinet walls are 1.75” thick and it is internally braced. I’ve never weighed it but I estimate it to be over 200 lbs. So, with no special equipment you can walk around the show room picking speakers up. You will likely note that in general the more expensive ones are heavier than others of similar size.
I’m not sure how well this will work in the store as it can be very annoying, but if you have a test disk with pure sine wave test tones, you can learn a lot about a speaker’s non linear distortion. It helps if you have had experience listening to low distortion pure tones but even without this experience, comparing speakers in A/B test you will likely find that some speakers have a hardness or harshness to the high frequency tones where other speakers do not.
Contrary to many beliefs, non linear distortion is very audible in the lowest regions of bass. If you have a 20 Hz tone on the test disk use it to evaluate subwoofers. Since most of them can not reproduce 20 Hz, combined with the fact 20 Hz is at the limit of human hearing, you should not hear anything. If you hear a very audible low rumble it is more likely the second harmonic at 40 Hz that you are hearing…distortion! You may also hear a number of other extraneous noises coming from the subwoofer such as wind noise especially if it is a ported subwoofer. The cone and its suspension system can also generate noise. Many subwoofers will have rumble filters built into the crossover so very low frequencies such as the 20 Hz tone or lower may be filtered out before it even gets to the low frequency driver. Assuming that it’s not filtered and you can see the cone moving significantly, you should hear very little sound at or near 20 Hz. Any sound you hear is most likely distortion or some form of extraneous noise and not the test tone you are sending to the woofer.
Some audiophiles believe a single point source to be best approach. These speakers use a single drive unit to reproduce the entire frequency spectrum. Like everything else in speaker design, a balance of trade offs exist here. The advantages of the point source which in my opinion are questionable to start with, come at a very high cost. The argument is that in the case of a multi-drive unit system, phase relationships between the drive units cause addition and cancellation as a function of frequency and location in the listening environment. Also, crossover networks, in the task of dividing the frequency spectrum, induces phase shift or group delay. Well, these things are all true and these are the trade off for some very big advantages to multi-drive unit systems. While many point source advocates may not recognize it, the so called point source really isn’t a point source. To be a true point source, it would need to be a singularity. (Black holes make good speakers???) The cone in a full range driver, due to its diameter, creates similar additions and cancellations as having multiple drivers. Also, at very high frequency the cone stops moving as a piston and begins to enter its break up modes causing large swings in frequency response. This paragraph will get too long if I continue but the yet to be discussed negative aspects of the point source are many.
If you think about what a speaker must do, it’s actually quite a difficult task. It must accurately convert three decades of bandwidth from electrical to acoustical energy. From 20 Hz to 20,000 Hz! The highest frequency produced is 1000 times higher than the lowest! That presents a number of difficulties but the one we will concentrate on here is called, “Doppler distortion”. In the case of the single drive unit system, the theoretical highest frequency produced can be modulated by a theoretical lowest frequency 1000 times lower. This means that 20 KHz tone is first coming toward you, and then moving away at a rate of 20 Hz. Just like an approaching and then passing train, this creates a tonal change in the 20 KHz tone as it’s modulated by the 20 Hz tone. If we were to break this down into two drive units with a crossover frequency of 2000 Hz, the larger drive unit could never modulate its highest tone with a lower one more than 100 times lower. The smaller drive unit could never modulate its highest frequency with a tone more than 10 times lower. This is a big difference compared to the 1000 times ratio of the single drive unit! A three way system with crossover frequencies of 200 Hz and 2000 Hz would divide the spectrum equally so the ratio is never more than 10 to 1. A three way thus is capable of offering a 100 fold improvement in Doppler distortion over a single driver system. The addition of a subwoofer reduces the ratios still further.
All forms of distortion take away from the overall realism of the musical performance. The speaker that jumps out at you over the others in the demo room likely has high levels of one or many forms of distortion. The key is, don’t listen for the speaker that blows you away with its big full loud sound. Listen for the speaker that presents the music in detail. Can you distinguish the individual instruments or individual voices? I’m not talking about can you distinguish the lead vocalist voice from the background singers or hear a triangle, symbol, or similar delicate instrument in the background. Any speaker can resolve these. What I’m talking about is closing your eyes then visualizing the background singers and practically being able to count them! How many are there? Where in the sound stage is each located? You shouldn’t just hear the existence of a triangle in the background you should hear the transit attack of the strike and the lingering ringing. You should hear subtle differences in each strike of the triangle. Sometimes you even hear noises not intended to be in the recording that went unnoticed by the recording engineer. You know, just little background stuff, someone bumping something or what ever.
If you are in the market for inexpensive speakers then unfortunately probably none of the options available will be able to perform well as described above. In fact, all monopoles will have difficulty with reaching this quality level even if you do spend enough money to have bought a small house in my home area of Austin, TX. It’s not just the fact that a monopole has a non uniform power response, it’s also due to other problems associated with “box” speakers such as standing waves in the enclosure traveling back through the cone and cabinet resonance that will only be reduced and not eliminated by rigid cabinet construction.
This ranting is starting to get really long so I’m going to wrap it up. Just remember not to use your existing speakers, other speakers in the demo room, or any other speaker as a reference in your decision. Compare each speaker individually to your long term exposure to live acoustic music and choose the one that seems to immediately spark the memory of being at a live musical event and not the one that jumps out at you as being the biggest and fullest sound.
Enjoy the music!
The Maniac…
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Epinions.com ID:
mthemaniac
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Member: Monte Kay
Location: Austin, TX
Reviews written: 9
Trusted by: 4 members
About Me:
Audiophile, skydiver, traveler...
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