Juice out great sound from budget 5.1 home theatre speakers, DIY modifications mercury IXA 660
Now a days, budget 5.1 home theater speakers are available all over the internet and in the local market too. More often these budget 5.1 systems sound good for watching movies and games. However, the sound quality is inferior for music listening.
I am going to show you how i modified my budget 5.1 speakers for a quality sound
Here is my 5.1 speaker system Mercury IXA 660 (roughly 65 watt rms) with 25 watt rms subwoofer (5 inch) and 5x8watt rms satellite speakers (2.75 inch).
A quick index of the modifications made:
Problems with cheap 5.1/2.1 speakers
The problem with these speakers is that, the lower mid range or mid bass frequencies are of inferior quality (boomy bass).
Muddy sound (causes listening fatigue) due to sound coloration in higher mid range frequencies (above 700 hz). This is because of the smaller size satellite speaker enclosure (as a cost saving strategy in manufacturing).
1. Subwoofer crossover frequency change to 107hz:
The subwoofer low pass filter circuit had a fourth order sallenkey filter.
R1= R2= 10k ohm
C1= C2 = 0.1 uf
I just replaced 0.1 uf capacitor with a 0.15 uf polyfilm capacitor to get a low pass cutoff at 107 hz.
2. Subwoofer interior lining with foam
The subwoofer was probably build assuming the EBS (extended bass shelf) alignment. So ringing is noticed @ 60 hz (driver's resonance inside the box)
As per my understanding EBS alignment deliver boomy bass (@ 100-125 hz).
EBS alignment works well for crossover frequencies below 90 hz (or 80 hz THX recommended). For highter crossover frequencies, the sound becomes boomy in the midbass region (100- 120 hz).
The subwoofer interior wall was glued with packing foam material. The end result is some deep lower frequency extension (below 60 hz)
3. Port tuning to 45 hz
The internal volume of the subwoofer was found to be around 0.3873 cubic.feet. So i added a 1.7 inch port, around 5 inches in length (taken from a old creative pc speaker). This gave a port tuning around 45 hz. I tried different dimensions using PVC pipes and finally settled with this.
The 5 inch subwoofer has difficulty producing notes below 60 hz. However, I am lucky enough that there is no unloading of driver till 40 hz. But below 40 hz the driver began to unload. So i added a first order high pass filter (cutoff frequency - 40hz) for driver protection below port tuning.
The spl gain achieved through port helped in normalising the frequency response in the range 40-60 hz.
4. Tuned enclosures for satellites (front and center channel)
Small enclosure size is the reason for all that muddy and highly colored sound.
I made an attempt to constuct 3 enclosures using paper card board (daily sheet calender board). I glued foam in the inner wall of the enclosure to avoid sound coloration due to standing waves).
The enclosure dimensions are as below.
Factory made enclosure dimensions 3.5 X 4 X 5 inches (All speakers)
New dimensions 4 X 5 X 7 inches (Front and Center)
Temporarily i wrapped the enclosure with gift packing paper for cosmetics.
5. Open baffle rear speakers
Open baffles really make wonders to the sound.
I wanted a small open baffle. I was just playing around with some boring mathematics (I am allergic to mathematics) and finally arrived at something new and interesting. It is λ/32 baffle.
My satellite speakers has a -3dB rolloff point around 110 hz. So i wanted a baffle that rolls off at 120 hz. I calulated λ/32 for 120 hz, which is around 7 inches. (Coming soon in a different post)
I chose H-frame alignment for open baffle. Below are the dimensions.
Height: 7 inches. Width: 4 inches. Depth: 8 inches.
Since my satellite speakers have high sensitivity, open baffle alignment sounded good with good spl.
I love these small 2.75 inch satellites. It can go till 110 hz (-3dB rolloff) without effort. Below that the spl rolloff is significantly high. It can play till 60 hz (@ -10 dB). For protection, i set the crosseover @ 98 hz.
The mid bass (100 to 200 hz) is not heavy. But for listening it sounds neutral, punchy and clean.
Sound waves reflected from the back walls, triggered noticeable boundary interference.
Here is the transient response of the satellite (you can see how boundary interference affects your bass.)
High sensitivity 2.75 inch satellite speakers still delivered some punchy mid bass. The imaging of the mid bass however is poor. Might be upsizing the front speakers help with better imaging.
Good listening levels from 55dB to 72dB (15 feet listening distance) with minimum distortion. My listening room dimensions are 20x8x10 feet.
Summary:
I am going to show you how i modified my budget 5.1 speakers for a quality sound
Here is my 5.1 speaker system Mercury IXA 660 (roughly 65 watt rms) with 25 watt rms subwoofer (5 inch) and 5x8watt rms satellite speakers (2.75 inch).
A quick index of the modifications made:
- Subwoofer crossover frequency changed from 160 hz to 107 hz
- Subwoofer interior lined with foam
- Port tuning changed to 45 hz, Initially it was around 110 hz
- New tuned sealed enclosures constructed for 3 satellite speakers (front and center)
- Open baffle speakers for rear channel
Problems with cheap 5.1/2.1 speakers
The problem with these speakers is that, the lower mid range or mid bass frequencies are of inferior quality (boomy bass).
Muddy sound (causes listening fatigue) due to sound coloration in higher mid range frequencies (above 700 hz). This is because of the smaller size satellite speaker enclosure (as a cost saving strategy in manufacturing).
1. Subwoofer crossover frequency change to 107hz:
The subwoofer low pass filter circuit had a fourth order sallenkey filter.
R1= R2= 10k ohm
C1= C2 = 0.1 uf
I just replaced 0.1 uf capacitor with a 0.15 uf polyfilm capacitor to get a low pass cutoff at 107 hz.
(Sorry for poor quality photos. shot in mobile)
2. Subwoofer interior lining with foam
The subwoofer was probably build assuming the EBS (extended bass shelf) alignment. So ringing is noticed @ 60 hz (driver's resonance inside the box)
As per my understanding EBS alignment deliver boomy bass (@ 100-125 hz).
EBS alignment works well for crossover frequencies below 90 hz (or 80 hz THX recommended). For highter crossover frequencies, the sound becomes boomy in the midbass region (100- 120 hz).
The subwoofer interior wall was glued with packing foam material. The end result is some deep lower frequency extension (below 60 hz)
 |
| Foam glued to inner wall of subwoofer |
The internal volume of the subwoofer was found to be around 0.3873 cubic.feet. So i added a 1.7 inch port, around 5 inches in length (taken from a old creative pc speaker). This gave a port tuning around 45 hz. I tried different dimensions using PVC pipes and finally settled with this.
The 5 inch subwoofer has difficulty producing notes below 60 hz. However, I am lucky enough that there is no unloading of driver till 40 hz. But below 40 hz the driver began to unload. So i added a first order high pass filter (cutoff frequency - 40hz) for driver protection below port tuning.
The spl gain achieved through port helped in normalising the frequency response in the range 40-60 hz.
4. Tuned enclosures for satellites (front and center channel)
Small enclosure size is the reason for all that muddy and highly colored sound.
I made an attempt to constuct 3 enclosures using paper card board (daily sheet calender board). I glued foam in the inner wall of the enclosure to avoid sound coloration due to standing waves).
The enclosure dimensions are as below.
Factory made enclosure dimensions 3.5 X 4 X 5 inches (All speakers)
New dimensions 4 X 5 X 7 inches (Front and Center)
Temporarily i wrapped the enclosure with gift packing paper for cosmetics.
5. Open baffle rear speakers
Open baffles really make wonders to the sound.
I wanted a small open baffle. I was just playing around with some boring mathematics (I am allergic to mathematics) and finally arrived at something new and interesting. It is λ/32 baffle.
My satellite speakers has a -3dB rolloff point around 110 hz. So i wanted a baffle that rolls off at 120 hz. I calulated λ/32 for 120 hz, which is around 7 inches. (Coming soon in a different post)
I chose H-frame alignment for open baffle. Below are the dimensions.
Height: 7 inches. Width: 4 inches. Depth: 8 inches.
Since my satellite speakers have high sensitivity, open baffle alignment sounded good with good spl.
I love these small 2.75 inch satellites. It can go till 110 hz (-3dB rolloff) without effort. Below that the spl rolloff is significantly high. It can play till 60 hz (@ -10 dB). For protection, i set the crosseover @ 98 hz.
 |
| transient response of the entire system |
The mid bass (100 to 200 hz) is not heavy. But for listening it sounds neutral, punchy and clean.
Sound waves reflected from the back walls, triggered noticeable boundary interference.
Here is the transient response of the satellite (you can see how boundary interference affects your bass.)
 |
| Satellite speaker transient response |
High sensitivity 2.75 inch satellite speakers still delivered some punchy mid bass. The imaging of the mid bass however is poor. Might be upsizing the front speakers help with better imaging.
Good listening levels from 55dB to 72dB (15 feet listening distance) with minimum distortion. My listening room dimensions are 20x8x10 feet.
Summary:
- The sound stage got better
- Bass is clean and punchy (not boomy at all)
- No more listening fatigue at average levels (55dB - 72dB at 15 ft listening distance)
- Great ambience from open baffles.
- Good bandwith (flat from 47hz to 13khz at @ -3dB)
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