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Hi all,
After Bing and I practically hijacked Huskerduck's thread over in the AV Chalet, it occurred to me that we should start two new threads here in DIY, (at least two!) to discuss tweaks and mods to the 281 Adire design (generally, cabinet related), and the concept and designs behind the small speaker project I'm working on now, for now just called the M8. Flashy name, huh? You can tell I'm not in marketing, in spite of the things they've made me do over the years at Infineon.
The M8 is being developed to fill a need for a relatively compact bookshelf sized (not placed!) speaker, for several friends, and also my own use. Somehow, I just couldn't see building another pair of SLAM Klones for the bedroom....
Why an 8" two way, of all things? This is not normally a promising configuration; heck, even a lot of 6-1/2" or 7" two ways leave something to be desired.
Let's consider the goals I had. Yours may be similar, they may be different, but discussing illuminates the points.
1. Fairly wideband response at SPLs up to 100 dB at 1 meter. These speakers are designed for rooms like bedrooms, study's, and living room apartments. They don't have to pump dB's at vanishingly low distortion like a SLAMM or Whisper. Wideband means 30 Hz to 30 kHz.
2. Compact- relatively. No more than 50 liters or so external volume. Stand mounted for flexibility; that way floor distance, side wall, and rear wall can all be optimized independently for smoothest bass in room.
3. Highly uniform axial response and power response- (averaged total room response) which requires either a dipole design (not practical at this size) or wide polar response throughout the frequency range. That becomes a tough nut, particularly with a typical two way.
4. Reasonable bill of materials, with upgrade potential. Baseline, and upgrades, depending on means of "customer/constructor".
5. Minimal driver and cabinet resonance. Drivers must be operated largely in pistonic range, and cabinet should be stiff and inert to the highest degree feasible within size and weight constraints.
First, it's a two way, because building a quality three way crossover is literally twice as expensive. Also, there are some very real issues about interaction between upper and lower crossover points that makes developing a three way bandpass a real bear; they must be at least 3 octaves displaced.
For a two way, the crossover frequency could first be dictated by the diaphragm sizes and their radiation patterns. For an 8" two way, the ideal crossover is in the range of 1-1.5 kHz. For the tweeter, the issue becomes LF power handling. Not many tweeters have much of it! High sensitivity is an asset, because this eases power handling if the tweeter is padded down 5-6 dB relative to the woofer. My favorite tweeters, it seems are all 92-93 dB efficient.
Selecting drivers is both simple and frustrating. Simple, in that to achieve reasonable LF output in a smallish box, a ported system should be used, which dictates driver Q and some other characteristics. Frustrating, in that once you start looking for drivers this wideband without breakup modes, you'll find its a very narrow field.
Two alternative mid-bass drivers were selected for the M8; the "baseline" choice being the Focal 8V4211, the upgrade being the Eton 800/37.
For the tweeter, the MBTT1 is the "baseline" choice; a 1" titanium dome, I have experience modifying it, and have used it for years. It has also been used by Avalon Acoustics and others.
The enclosure design is roughed out, using a Woodstyle 123REV cabinet as the basis and cosmetic shell.
I'll flesh this out and update as time permits during the weekend.
When finished, complete plans will be available in PDF form for those interested, along with documentation of the measured performance, including MLSA (quais-anechoic) and in room RTA averaged response.
Best regards,
Jon
Earth First!
_______________________________
We'll screw up the other planets later....
After Bing and I practically hijacked Huskerduck's thread over in the AV Chalet, it occurred to me that we should start two new threads here in DIY, (at least two!) to discuss tweaks and mods to the 281 Adire design (generally, cabinet related), and the concept and designs behind the small speaker project I'm working on now, for now just called the M8. Flashy name, huh? You can tell I'm not in marketing, in spite of the things they've made me do over the years at Infineon.
The M8 is being developed to fill a need for a relatively compact bookshelf sized (not placed!) speaker, for several friends, and also my own use. Somehow, I just couldn't see building another pair of SLAM Klones for the bedroom....
Why an 8" two way, of all things? This is not normally a promising configuration; heck, even a lot of 6-1/2" or 7" two ways leave something to be desired.
Let's consider the goals I had. Yours may be similar, they may be different, but discussing illuminates the points.
1. Fairly wideband response at SPLs up to 100 dB at 1 meter. These speakers are designed for rooms like bedrooms, study's, and living room apartments. They don't have to pump dB's at vanishingly low distortion like a SLAMM or Whisper. Wideband means 30 Hz to 30 kHz.
2. Compact- relatively. No more than 50 liters or so external volume. Stand mounted for flexibility; that way floor distance, side wall, and rear wall can all be optimized independently for smoothest bass in room.
3. Highly uniform axial response and power response- (averaged total room response) which requires either a dipole design (not practical at this size) or wide polar response throughout the frequency range. That becomes a tough nut, particularly with a typical two way.
4. Reasonable bill of materials, with upgrade potential. Baseline, and upgrades, depending on means of "customer/constructor".
5. Minimal driver and cabinet resonance. Drivers must be operated largely in pistonic range, and cabinet should be stiff and inert to the highest degree feasible within size and weight constraints.
First, it's a two way, because building a quality three way crossover is literally twice as expensive. Also, there are some very real issues about interaction between upper and lower crossover points that makes developing a three way bandpass a real bear; they must be at least 3 octaves displaced.
For a two way, the crossover frequency could first be dictated by the diaphragm sizes and their radiation patterns. For an 8" two way, the ideal crossover is in the range of 1-1.5 kHz. For the tweeter, the issue becomes LF power handling. Not many tweeters have much of it! High sensitivity is an asset, because this eases power handling if the tweeter is padded down 5-6 dB relative to the woofer. My favorite tweeters, it seems are all 92-93 dB efficient.
Selecting drivers is both simple and frustrating. Simple, in that to achieve reasonable LF output in a smallish box, a ported system should be used, which dictates driver Q and some other characteristics. Frustrating, in that once you start looking for drivers this wideband without breakup modes, you'll find its a very narrow field.
Two alternative mid-bass drivers were selected for the M8; the "baseline" choice being the Focal 8V4211, the upgrade being the Eton 800/37.
For the tweeter, the MBTT1 is the "baseline" choice; a 1" titanium dome, I have experience modifying it, and have used it for years. It has also been used by Avalon Acoustics and others.
The enclosure design is roughed out, using a Woodstyle 123REV cabinet as the basis and cosmetic shell.
I'll flesh this out and update as time permits during the weekend.
When finished, complete plans will be available in PDF form for those interested, along with documentation of the measured performance, including MLSA (quais-anechoic) and in room RTA averaged response.
Best regards,
Jon
Earth First!
_______________________________
We'll screw up the other planets later....
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