This project came about due to the need for a high quality small speaker for music and home theater
Design Goals
Driver alignment
After doing some research on the web for about a year finally convinced that an MTM(mid-tweeter-mid) configuration will satisfy my requirements. There are some advantages that an MTM has over the usual TM and TMM alignments.
Choice of Enclosure
The low frequency cut off of the enclosure is planned to be around 45Hz as this will allow a smooth transition to the subwoofer in case of a HT use. There is another advantage of crossing to a sub at this frequency, due to the non-directional nature of sound at these low frequencies, there is more freedom to position the sub to blend -in and become invisible sonically.
I was confounded between floor standing(tower) and stand mount(mini-monitor) options. Few months of research helped in deciding in the favor of a stand mount . Here are the reasons for this conclusion.
For ease of construction a ported enclosure is chosen, decided to go with a forward firing port since it allows the speaker to be kept closer to the back wall useful for small rooms and HT use
Drivers
Of all the drivers I had collected these years, I am planning to use two of my favorites - 5.25 paper composite midbass drivers and low Fs silk dome tweeters manufactured by Peerless India. That would make this project cost effective and 100% Indian as well
. These midbass drivers are very similar to the ones used by GR-Research M-130 which is also manufactured by Peerless India. Here is a quick comparison.
The Silk dome tweeters have an Fs of 880Hz and can be easily crossed around the intended crossover frequency around 2500Hz. So my expectation is that these two drivers are good candidates for building a cost effective system of high quality.
Driver pics
First I am planning to test these drivers in a set of experimental enclosures with 3 variations of front baffle with different driver alignments. This is basically to check the vertical dispersion effects and tweeter offset (Dappolito configuration). A pc based active xover is going to be used to determine the final crossover frequencies and slopes.
The test mules (enclosures) have already arrived from the carpenter. So this weekend is reserved for Diy
Design Goals
- Less demanding on the room size and better integration in smaller rooms.
- Should provide well balanced sound output suitable for music and good power handling and dynamics for home theater use.
- Easy integration with sub woofers should cross at a frequency suitable for a good 12 sub to take over
- Small footprint and WAF
- Match the quality and finish of speakers that cost much more.
Driver alignment
After doing some research on the web for about a year finally convinced that an MTM(mid-tweeter-mid) configuration will satisfy my requirements. There are some advantages that an MTM has over the usual TM and TMM alignments.
- Compared to a TM, MTM with the same drivers will have better power handling and dynamics and can go louder as well all good traits for a HT speaker
- MTM design will have roughly the same horizontal dispersion as a TMM or TM design
- The MTM will have a narrower vertical off axis response, compared to TM and TMM. This can work out well for small rooms and cramped spaces as it minimizes the effect of floor and ceiling reflections.
- MTM has a symmetric dispersion pattern and coherent phase and amplitude characteristics when the listening position is at the tweeter level this is something difficult to achieve with TMM or TM designs.
Choice of Enclosure
The low frequency cut off of the enclosure is planned to be around 45Hz as this will allow a smooth transition to the subwoofer in case of a HT use. There is another advantage of crossing to a sub at this frequency, due to the non-directional nature of sound at these low frequencies, there is more freedom to position the sub to blend -in and become invisible sonically.
I was confounded between floor standing(tower) and stand mount(mini-monitor) options. Few months of research helped in deciding in the favor of a stand mount . Here are the reasons for this conclusion.
- Cabinet resonance problems are comparatively less in a short stand mount enclosure. They are cheaper to make, brace and finish.
- With a proper stand, stand mount can be positioned in axis with the ears, this has some good sonic benefits as indicated before. Even though they increase the overall cost, I think this cost escalation does not outweigh the flexibility.
- Simulations did not yield significant low frequency extension to a floor stander compared to stand mount.
For ease of construction a ported enclosure is chosen, decided to go with a forward firing port since it allows the speaker to be kept closer to the back wall useful for small rooms and HT use
Drivers
Of all the drivers I had collected these years, I am planning to use two of my favorites - 5.25 paper composite midbass drivers and low Fs silk dome tweeters manufactured by Peerless India. That would make this project cost effective and 100% Indian as well
. These midbass drivers are very similar to the ones used by GR-Research M-130 which is also manufactured by Peerless India. Here is a quick comparison.- The M-130s have been lauded for their midrange clarity that accounts to the curvilinear cone structure that allows smooth roll off into the higher frequencies and a paper composite cone which provides smoother breakup modes. These features make the crossover design easier. The Peerless India Standard line (SL) drives I am using for this project also has the same cone.
- Both have polycarbonate frames. This does not transmit vibrations into the front baffle like a metal frame. The difference of GR- Research drivers is that the frame shape is suitable for surface mounting.
- The GR research drivers seems to be having smoother high frequency response . But till 2.5Khz they are almost identical with each other.
- The SL driver seems to have lower Fs than the GR research drivers.
- The SL drivers have an impedance of 4ohms against 8ohms and 16 ohms versions of M-130. This means that these drivers need to be in series for an effective impedance of 8ohms. This results in an overall sensitivity of 88dB(ie: the sensitivity of a single driver) which should be sufficient for driving them with a medium power amplifier.
The Silk dome tweeters have an Fs of 880Hz and can be easily crossed around the intended crossover frequency around 2500Hz. So my expectation is that these two drivers are good candidates for building a cost effective system of high quality.
Driver pics
First I am planning to test these drivers in a set of experimental enclosures with 3 variations of front baffle with different driver alignments. This is basically to check the vertical dispersion effects and tweeter offset (Dappolito configuration). A pc based active xover is going to be used to determine the final crossover frequencies and slopes.
The test mules (enclosures) have already arrived from the carpenter. So this weekend is reserved for Diy
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