Q&A # 30 - September 23, 1997
Staff
Q What's the difference in performance between a ported and closed box design of a speaker? Is one better than the other? Most are ported.
A A closed box, sometimes called acoustic suspension, is simply a sealed
cabinet. The air in the cabinet stays there when the driver cone moves into the box, increasing the internal air pressure, and when the driver cone moves out of the box, decreasing the internal pressure. This creates a
shallow slope which is a second order rolloff (12 dB/octave). A ported
enclosure is tuned to a particular frequency by adding a port (or tube) with
a given length and diameter for that given frequency. The port allows air
to pass in and out of the box. This creates a much steeper slope which is a
fourth order rolloff (24 dB/octave). For a given box size, the ported
design will give slightly lower bass extension compared to the same box size
of a sealed enclosure. One criteria a speaker designer looks at when considering
a closed box vs. a ported design is the driver's Qts, or the total Q.
Q is the ratio of reactance to resistance (in a series circuit) or
resistance to reactance (in a parallel circuit). The whole point of fitting a driver to a
particular box volume is to control the response characteristics of the
combination. Here, Q describes the resonant magnification in speaker boxes.
It represents the degree to which the electrical, mechanical, and pneumatic
circuits of the woofer/box combination interact to control resonance.
If the
driver Qts is 0.4 and above, a closed box is recommended, and anything below
that, a ported configuration is appropriate.
There are good points and bad points for both types. Although the
ported design allows a speaker to go lower for a given box volume, it
also contributes to other undesirable sounds such as port "chuffing" (the air whooshing in and out of the port).
Ported systems are typically more efficient (~ 3 dB) and have higher
power handling compared to a similar driver in a closed box.
Q I have recently installed my system using the Harman Kardon AVR 80 along
with the Bose Acumass 10 speaker system. I find that the system for home
theater is terrific. However when listening to CDs, the speakers
don't deliver enough bass unless I really crank it up. The highs and
midrange levels sound excellent. I guess I need to add a subwoofer??? Would
you agree? Is this common using Bose speakers?
A Bose systems are designed for people who like compact, modular setups. The speakers are small, and the woofer uses small drivers too (usually about 6"). This lets you install the entire system in a very inconspicuous manner. That's what they are built for. However, a lack of deep bass is common with these Bose packages. A good subwoofer would, indeed, help. Since your Bose system is small, the Sunfire subwoofer would fit in nicely (an 11" cube), and would give you all the bass you are missing now. Set the low pass crossover to about 60 - 70 Hz at the start, and adjust it from there.
Q I am thinking of getting one of those Mega-changers which are currently
available in the market, specifically the Sony CDP-CX255 or CDP-CX270.
However, I have heard that there are complaints on the changer mechanism,
i.e., from slow response to getting jammed up.
I would really appreciate it if you could give your opinion on these
changers and whether or not the alleged complaints are true. I sure would
not want to spend hard-earned money on something which I will regret later
on. Thank you for taking time to answer the question.
A I have taken a look at some of these mega-changers, and, frankly, I have a feeling that jams are common. That is the price for the convenience. Personally, I would never buy one, but that is just me. The manufacturers are really pushing them though. In any case, I would suggest getting a carousel type changer, such as the Sony CDP-CA8ES. I just bought one for my wife's office, and it is easy to use, you can put 5 CDs in at one time, change the CDs while one is playing, and the carousel-type changer is a proven, essentially bug-free technology. The "juke box" style of changer just begs for trouble, in my opinion.
Q This is all the way from BANGLADESH.
I intend to install a Home Theater system at my home on a 50/50 music/movie
entertainment basis. To get an idea of what should be the components &
brands for my dream system, I have thoroughly read all the Q&A sessions of
your wonderful web site, right from # 1 to # 29. I am immensely grateful
to you for educating me with your very descriptive answers to all the varied
questions that have been forwarded to you. From the knowledge gathered from
you, I have already decided that I shall purchase B&W DM602 speakers all
around front & rear, matched with CC6 center speaker and AS6 or Sunfire True
subwoofer. Now, my question is, what should be the ideal power output in
WRMS per channel in 5 channels of the Power Amplifier to match these
speakers perfectly, given my room size 16'x16'x10'H. I am eagerly awaiting
your answer at the earliest.
A Watching movies requires lots of power, especially if you like action films. Since you will have a set of excellent full range speakers in the front and rear, you will probably get AC-3 someday. So, I would suggest a minimum of 100 watts rms/ch rated into 8 Ohms. Something like the Adcom GFA-7000, Carver AV-705, or Rotel RB-985 would do nicely.
Q In terms of Toshiba TV video performance, can you tell me which is a better set? The
advantage of the F80 over the G60 is the 3DYC comb filter (the G60
has a digital comb filter), and the advantage of the G60 over the F80 is
its component video inputs (the F80 has S-Video). I am planning to
purchase a DVD player with component video outputs. However I do watch
a lot of cable television.
A If it were me and DVD was most definitely in my future, I would go for
the model with the component inputs. The overall quality of cable is
rather poor, and their comb filter should do an adequate job. When the
time comes for you to throw in a DVD, you will be most happy
with the component video.
Q Do you know of any plans for a DSS system to have component video
outputs? If yes, then would there be a way to switch between two
component video sources, namely the DSS system and a DVD player with
component outputs?
A I WISH they would hurry up and add them! MSB Technology was advertising a souped-up DSS receiver for around $3,000, which has component video outputs.
They (MSB) are the only ones that I am aware of who are offering it. From
what I have gathered, the mass market manufacturers might start adding the outputs in the future, but
the cost will probably be over $500.
In the PRO world, component switchers are common. They will be coming
soon in the consumer world. The Meridian 861 will offer this in the
future, and Entec (Monster Cable) will offer a component version of
their A/V switcher as well. These should become more
common among all manufacturers. If you look back to
when the first S-VHS machines came out, very few TVs had video signal inputs other than the antenna, and
very few products had switching capability.
Q Should I use a coax or S-Video cable for a direct connection between
a Pioneer 99 LD player and a Barco 701 (with internal line doubler)?
I know that Barco 701s' comb filter is not "3D" like Pioneer 99's, but
since most of the video in not in a static mode, perhaps the Barco's 2D is
superior to the Pioneer's.
A I have not seen the comb filter in the Barco 701. If you have access to "A
Video Standard" or "Video Essentials", you should put up the color bar test
patterns and/or the Snell & Wilcox test pattern. This will allow you to see
which comb filter is doing the better job. The Pioneer might be the better choice.
Q There are some items which you may or may not know about Meridian. As a
Meridian dealer for a long time, I feel I must share with you some
inaccuracies about your answers to the following questions that you
received from one of the Q&As!
Original question to Secrets: "I'm looking for suggestions in three areas:
1) I'm not sold on the 562V due to price and lack of video flexibility
(no composite to S-Video, no composite). Plus it seems overkill for
audio right now when I only need to mix two analog channels into the 565.
Any suggestions? Is there even a decent low-tech (high audio-quality)
solution, even if it means I have to get up and walk across the room to
switch between analog sources?"
Reader's response to Secret's answer: 1A: This gentleman should NEVER use a product which tries to switch
from
composite to S-Video and visa versa. Reason, When changing a composite to S, it
actually can not break up the Y/C signal correctly therefore diminishing
the chroma output making the picture darker than was intended to be. For
any reasonable video quality, tell him to always go with a straight video
signal! The 562v, as you know has 6 composite and 2 S-Video inputs which he can run
separately to his TV and have no problem. Does he understand this issue? It makes no sense to me!
Secrets' original answer: "Meridian has a new version of the 565 called the 561 . . ."
Reader's response to Secrets' answer: This product my friend has been shelved and will not be released any
time
soon. So please refrain from telling people that certain products are
available which are not.
If you are not using the 562V, you will have to plug the analog input
directly into the 565, bypassing the 518 altogether. The 518 only has
digital inputs, so you could plug your Sony DVD into there.
Addressing the 518, the person who posed the original question CANNOT use the 518 for any reason with a
Sony DVD player unless he 1: gets the new software just released (1.4) 2: It will ONLY
reduce jitter, and nothing else in the 518 will be of any use to him in
this case. In his case he either does not buy a 518 without the 562v or
he can use the 518 in between the 562 and 565. This way he can still
receive the largest benefit from the 518 with his LD player and use the
noise shaping curves and bit enhancement features. DVD will use any
feature on the 518 Except for jitter reduction!
He should really buy an LD player with a digital output because of
DTS! The 565, as you know, is still the greatest processor out there, and DTS is
unbelievable in the 565. This way he can use the 518 as a Digital Pre amp
and not use the 562. I think that makes the most sense.
A Regarding 1A:
At some point in the video chain, the composite signal must pass through a
comb filter. In the past, either your TV or your source (LD player) had to
do the work. Whichever component did the best job was the one you wanted to use.
Well, a third option was introduced a while back by Audio Alchemy with
their VRE 1.0 outboard comb filter. This box was better than any LD player
or TV on the market. Audio Alchemy is no longer around and the VRE is gone,
but Faroudja has stepped in with their VP-100 outboard comb filter, and
Camelot is gearing up to distribute the Crystal Vision 1 (from the same team
who built the VRE) comb filter. Both of these are much better choices and
*CAN* improve the overall quality of a VCR or LD player. **REMEMBER** with
DVD there is no need to go through a comb filter because the source is
already separate so always use the S-Video or component out of your DVD
player.
Regarding the 518 with a Sony DVD player:
I have been using the Sony DVD player with the 518 (Software Revision 1.2) since May, 1997, and it DOES work. I have encountered one issue with the Sony and Meridian
and it only occurs on Columbia Tri-Star titles, not Warner. When I put in a
Columbia title, I must re-select my source; otherwise the sound is muted. I
spoke to Meridian and there is no Version 1.4 for the 518. So please refrain from telling our readers that certain products are available which are not. Version 1.21 has been
released which deals with some DTS issues.
As far as the 518 dealing with jitter, that is exactly what I want it
for. Most DVD players are terrible when it comes to jitter, and anything that can be done to reduce the jitter is a move in the right direction.
Q I would like to know where I can get some reviews of DSS dishes.
A When DSS first hit the market, most A/V magazines reviewed all the
products available. Now the focus has moved on to DVD. I can tell you that
the overall quality from DSS is common among all the receivers. The major thing that differentiates them are the "features". I have used the Sony DSS
receiver with a digital output (their 2nd generation) and it was fantastic.
I have also used the 1st and 2nd generation of the RCA receivers and found
them to be a little slow (the interface). RCA is now introducing their 3rd
generation DSS with an improved interface, but I have no experience with it.
Theta is offering an upgrade for Sony receivers that they claim will
improve the performance. They replace the single power supply with a
dedicated one for Audio and Video. They also had a reclocking device to cut
down on the jitter. At some point I hope to send mine in for the mod, but
this will be down the road. When I do, I will publish the findings here in
Secrets.
Q I own a small company that manufactures speakers. I can't afford the exhibitor prices of the large shows. Why don't you guys do a show that is affordable for everyone?
A We are planning to do that. We will call it something like "The Consumer Home Theater and Hi-Fi Show". It will probably be a cost plus arrangement (our actual costs plus a small amount to make sure we don't go in the hole) that will make it very inexpensive compared to some of the other shows. I already have the convention center information and am moving forward. Companies that are interested should contact me ([email protected]) to get on the list for info when it becomes available. I feel that shows need to be vehicles for communicating, not just big money makers in themselves. Our magazine is based on that principle, and so will our show.
� Copyright 1997
Secrets of Home Theater & High Fidelity
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