I'm currently enjoying a computer audio system consisting of powerful DSP software, DIY small full-range speakers and a compact desktop subwoofer. It’s a quite lean & compact desktop system for near-field listening with a super wide & flat frequency response.
I’m quite satisfied with the system and would like to introduce my audio trial on this Blog.
- TriggerI started this audio trial approx. 6 months ago. Before that I had not been interested in audio issues at all and satisfied with DENON system compo (approx. 40,000YEN) until I tried a small MP3 player with earphones. It was a kind of cultural shock. It is super convenient because for example I can play LvB symphonies from No.1 to No.9 or Miles Davis from “Birth of the Cool” to “Bitches Brew” in a yearly order without changing CDs. Furthermore, the sound from high quality earphones directly vibrating my eardrums is very clear in whole range including super low-end. Wow, I've immediately recognized that super low must be necessary to really enjoy symphonies.
- Target
Then I started this trial to realize clear & wide-range & direct sound like as earphones as well as that operative conveniences on my desktop, where I’m spending plenty of time for daily translation works.
I bought a small audio computer from ONKYO, downloaded a WAV playback software with powerful DSP functionalities that enable automatic response & phase compensation, built DIY small speakers with 3” full-range drivers and finally integrated a small desktop subwoofer to the system. After playing around and try-and-errors for 6 months, I’ve got a quite sufficient result with the system.
1. LEANAUDIO System Configuration
Here is the current system configuration;
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- Audio Computer
ONKYO HDC-1L; Intel Atom processor 230, 160GB HD
- WAV file Playback Software
Frieve Audio M-Class; Shareware software with powerful DSP, automatic response compensation possible
- Main Speakers
8cm full-range drivers; DIY AUDIO SA/F80AMG, 2.5L sealed enclosures
- Powered Subwoofer
Victor SP-DW-1; 14cm woofer, 30W
- Amplifier
KENWOOD KA-S10; 12W/ch
- Desktop dimension
W 1045 x D 750 mm
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Figure: System overview on my desktop
7.5kg weights on the subwoofer
2. Concept-1: Near-field Listening
As mentioned above, my target is to realize very clear sound field on my desktop, which is comparable to the high quality earphones. Thus I don't like to have any reflections from surrounding room walls. I just want to listen to direct sound waves form the speakers as far as possible.
With full size audio system, in many cases, you suffer with standing wave effects caused by sound wave reflections from every wall ,ceiling and floor in your room. Generally this phenomenon becomes serious in low frequency range (....100Hz) in which the wavelength reaches comparable to the domestic room size.
Here is a simple calculation result. You can see locations of speakers (rectangles red&black) and a listener (circle) in a square room (3.4m x 3.4m, approx) in the right diagram. 
If the speakers generate perfectly flat response down to 20Hz, then the listener at the location will get the actual response shown in the left diagram. The result is indicating that the listener under this specific arrangement will loose 70Hz response quite seriously due to the standing wave influence. For this calculation, reflection factor of each surface is set to 0.7, which corresponds to relatively dead condition. I found this value via a rough comparison with measured data in my room (many books and a bed stuffed in a small room).
Below is the measured response in my room.
Above figure indicates the measured responses in front of a full-range driver on its axial center with two different distances from the front baffle. With the distance of 135cm, you can see a big dip at approx 75Hz and a boosting effect in the range below 50Hz. The response with distance of 40cm looks nearly the driver’s original response.
Here is another calculation result. This time I moved the speakers towards the listener to approx. 30cm distance. The conclusion is clear.
So, this is the advantage of Near-field listening. With the shorter distance to the speakers, you can increase a ratio of Direct / Reflection the more.
Based on the consideration above, I decided to locate the speakers on my desktop nearer to me as far as necessary working space could be maintained.
3. Concept-2: Full Utilization of Digital Signal Processing
Many of traditional audio freaks in Japan seem still rather reluctant for Digital Signal Processing(DSP).
Nowadays, actually 100% of music source is available only in digital format. If thinking in logical way, it must be quite reasonable to perform all necessary filtering and equalization within digital phase because digital filtering offers highest flexibility and accuracy without phase errors.
However, still in the world, many of such processes are done after DAC (digital to analog conversion). For example, most of LCR circuits (e.g. channel divider, some kind of speaker response compensation, tone control of amplifier) and low boost mechanisms (e.g. bass reflex box, resonance boxes), with which phase problems are inevitable, can be partly replaced by DSP.
I’m much interested in comparison of two types of speakers, i.e. one with a simple sealed box with DSP low boost, and another with a bass-reflex box without DSP. Generally, bass-reflex has some problems in low-end range, i.e. larger phase delay, phase reverse thus steep response drop and steep increase of diaphragm stroke. Even with a sealed box phase delay in low range is not avoidable, however DSP can compensate it too.
Now, I’ll introduce powerful WAV playback software Frieve Audio M-Class (Shareware, 3,200YEN !, only Japanese version).
Figure: Overview of Frieve Audio
Its main functionality is playing back of lossless WAV file extracted from music CDs on Windows PC . However, Frieve Audio is outstanding because of its automatic response compensation ability. If you have a microphone for PC, you can make frequency response at your listening position completely flat. As mentioned above, the response can be relatively flatter with the near-field listening style. However, even within 1m distance (actually 85cm in my case), you will still see clear influences of sound reflections.
Using the automatic compensation you can reduce these effects very easily. The system generates a test signal and analyzes the response signal from the microphone at the same time, then calculates necessary equalization factors and also phase compensation factors at each frequency point (max 65535 taps, adjustable).
The internal process is done with 64bit resolution. The resulted factors can be stored permanently and recalled. All calculations and compensations are performed independently for L and R speakers.
Here you can see the effect of automatic compensation at my standard listening position.
Figure: Compensation OFF and ON
First time if you tried the flat response, you might feel unreasonable. However, once you switched off the compensation, you would immediately recognize that you should never switch it off again.
Most of people who tried this compensation are expressing similar experiences in their own Internet threads. Many of them including me use the flat condition as a kind of reference and modify it slightly as preferred. It’s a really useful tool.
4. Concept-3: Satisfactory Low-end Response with Desktop Subwoofer
From experiences with high quality earphones, I have learned the importance of low-end response for really enjoying music. So this is another target, i.e. “super direct low-end sound like as earphones”.
Down to which Hz should the response be flat?
A Japanese audio consultant Mr. Teppei Kado, I rely on his logical and reasonable opinions, indicates his own criteria for “satisfactory speaker” in his own Internet site. According to his opinion, 25Hz(-5dB) should be a guideline. OK, I’ll take it. I decided to integrate a small subwoofer to my desktop system.
I wanted a small powered subwoofer that could be put on my desktop but not on the floor. For such applications, the device should have all sound radiating elements (i.e. woofer and duct) on its front face. Fortunately I found an exactly right one with fairly low price.
Victor SP-DW1
14cm woofer
30W digital amp
approx. 15,000YENWhy I put it on the desktop?
The reason is to catch the sound wave as directly as possible. If you put a subwoofer on the desktop, you can effectively utilize the first reflections (so called wave guide effect) from a desktop and a computer display surfaces just in front of you. Once I tried on the floor setting, but I’ll never do it again. If you put it on the floor, you will have to boost the subwoofer volume more to get the same level of low-end response because of more dispersion, thus you will suffer more reflections from your surrounding walls.
Subwoofer Desktop ConfigurationHow to optimize the subwoofer integration?
At first, adjust volume and cut-off frequency of the subwoofer based on measurements. The result is shown in a figure blow. The cut-off is the lowest (50Hz), the volume is nearly minimum (less than 1/4). It requires only minimum power thanks to above-mentioned desktop configuration. With this minimum setting, the subwoofer's effect can be limited up to approx. 100Hz. 
Then, let’s make it flat by using Frieve Audio software.
Frieve Audio also compensates the phase delay that often be controversial on subwoofer issues.
The low-end of this bass-reflex subwoofer sometimes sounds unstable, how to say, boomy or untidy. To avoid this I had to apply very steep 30Hz digital low-cut filter on Frieve Audio manual equalizer.
Currently I have closed the duct by tightly stuffing felt mats, so now it is more ore less a sealed box. With this modified configuration, I can boost +10 dB from 30Hz to 20Hz without suffering any boomy problems.
Finally I’ve got; 
Red: duct open(low-end cut-off), Black: duct closed(low-end boosted)The difference might look small, however thorough-bass of symphonies sounds definitely different. It’s good. Now I have achieved the criterion of Mr. Kado, i.e. 25Hz/-5dB.
The direct and tight super low-end sound from a desktop subwoofer is quite cool.
Try it!
5. Concept-4: 8cm Single Cone Full-range Drivers for the Main Speakers
Now, the fundamental of “Music Reproduction” is firmly established by “Near field Listening Style”, “Desktop Subwoofer” and “Response Compensation”.
On this basement, the main speakers finally determine the tone character, taste, mood and so on of the total system, which much depends on the listener’s preferences.
As the main speakers, I have selected 8cm(3”) full-range drivers because many of them covers from 100 to 20kHz easily. For me, response below 100Hz is not necessary or even disturbing because of the subwoofer integration. 10cm might be also OK, but maybe less high-end quality. 2-way? I don’t like it for my near-field style. I cannot accept, just mentally, a fact that 3kHz sound wave that has 11.3cm wavelength comes from two different drivers distant each other approx. 10cm. I don’t like to listen it at 85cm distance (again in mentally).
I'm using DIY AUDIO SA/F80AMG that was the highest reputed 8cm driver at that time in Japan. I tried another 3 types of drivers, one from FOSTEX and two from TangBand, then finally selected F80AMG. It’s not so powerful, it’s not so brilliant, it’s not so amusing, however it delivers totally best sound for me. How to say, it’s gentle, accurate, moderate, well structured and stout. I would fully agree the reputations.
DIY AUDIO SA/F80AMG 8cm full-range driverI did say above, “F80AMG
was highest reputed
at that time”.
Because I can no longer believe that's really true.
Just recently the reputation of MarkAudio Alpair is coming up significantly among Japanese DIY builders. I would say "like as the Golden rising sun".
For me the smallest Alpair 5 must be the target, which seems designed as a super wide-range tweeter for combining with a subwoofer or a large driver. It must be the best one in the world for my LEANAUDIO system, I believe.
MarkAudio Alpair 5 Gold
6. Summary 
Finally I’m quite satisfied with the system performance.
The target of this trial was to realize high quality earphones-like sound on my desktop. For that, first of all, influence of sound reflections from walls (i.e. standing-wave effect) was reduced effectively by means of “Near-field Listening Style” and “Response Compensation via DSP”.
On this base, a subwoofer was integrated additionally to fulfill the second target "earphones-like clear & tight super low-end". To achieve this, “Desktop Subwoofer Configuration” and “Optimum Subwoofer Integration via DSP” worked quite efficiently.
I believe above tow requirements, i.e. reduction of standing-wave effects and fulfillment of satisfactory low-end (also high-end of course, but easier) must be the very basic of music reproduction on a 2ch stereo audio system, which should be discussed and fulfilled before any trivial sound fidelity issues.
On this basic structure, 8cm single cone full-range drivers were implemented as the main speakers, which cover 100Hz … 20kHz and determine the total sound character and taste of the system. Although current F80AMG drivers are quite satisfactory for me, I’m plotting to try Alpair 5 in order to further improve detailed clarity in mid-high range.
to be continued....
5) 30Hz
music sources(from left);
music sources(from left);
Base level of each setting is determined so as to 
Calculation results;
