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I’ve been testing drivers in this other thread. I thought it was finally time to share what for.
Reading Jon Marsh’s adventures over at htguide has definitely inspired me here. All credit to Jon. Nothing I’m trying here is an attempt to do anything but piggy-back off his work on the cheap. I really wanted to see if I could design a Duelund three-way for under $200, which admittedly is a fairly arbitrary price point. But I chose it because I think it’s the budget cut-off for lots of the competitions at the get-togethers.
I’m not qualified to expound on the benefits of a Duelund network, although Jon really explains it well if you care to read up. Rather this should probably be classified more as an intellectual exercise for me with the side benefit being, I get to play with and build speakers.
I initially considered two different values of aleph in the Duelund equations, but through various modeling and experimentation settled on aleph = 2√2 (blue), but I then shifted the center frequency down to about 1300 Hz, lowering the crossover points.
Through my driver testing, I settled on the DA215-8 for the woofer, the TG9FD10 for the midrange, and the DX20BF00-04 for the tweeter. The selection of the right midrange is critical here, and the performance of the TG9FD10 is the only reason this is possible.
The midrange driver needs to be small enough to allow for close tweeter placement since the mid-to-high crossover point is fairly high and we don’t want too narrow of a vertical lobe, but also robust enough to play cleanly down to around 250 Hz. The driver should also be as small as possible to achieve the greatest off-axis performance possible since it covers so much of the upper octaves with the tweeter (it is still contributing a couple dB at 6 kHz). Similarly, it is expected to contribute a couple dB at 200 Hz. It basically must be a full-range driver with solid HD performance across its entire bandwidth with no break-up. It is a pretty tall order.
Initially I thought I was going to select the PC105-8 based on my HD testing. I declared it my winner based on its ability to play cleaner, lower. Then I put it in PCD and was slapped in the face by the cone break-up centered around 9 kHz. It made hitting the target low-pass slope damn near impossible without an excessive component count. It really highlighted how smooth an FR response is needed in order to keep the crossover network in line with the budget sensibility.
Note*
This model and testing was with the TG9FD10-04 which drops the impedance to just above 4 ohms at the 150 Hz and 800 Hz dip. I have the TG9FD10-08 on order with the hopes that it measures as well or better and allows a higher minimum impedance at these frequencies so that this can be classified more as an 8 ohm nominal design that any old receiver can power comfortably.
The woofer cannot be any old woofer either. It must be able to play cleanly up to around 1 kHz and not have any excessive break-up until around 3—4 kHz. Even still, a bottomless notch was required to keep everything in line. I had really hoped that the DA215-8 would test well enough in the HD department to make it the right candidate, since it is one of the cheapest 8†drivers out there and integral to hitting the target price point. I’m happy enough with the testing to declare it just that.
I also wanted to do this in a sealed monitor. Form factor is important and floor-standers are not practical for me anymore. I personally feel going below 100 Hz is not as important with most people running subs anyhow. The DA215-8 models reasonably well in around 11 liters which is about all I can afford in my targeted 16†x 10.5†x 11.25†enclosure.
I don’t feel like there is too much to say on the DX20BF00-04 other than the fact that HiFiCompass tested it and it looks fantastic. It has a small form-factor, is easy to mount, and is even recessed a little bit to more closely align the acoustic centers between it and the midrange.
So anyhow, the PCD model above has thirteen (13) components. Four (4) on the woofer, four (4) on the tweeter, and five (5) on the midrange. If you assume an electrolytic capacitor for the woofer shunt and the midrange high-pass only because they are large values, but the rest standard Polypropylene capacitors, the drivers and crossover come in just under $200.
More to come.
Cheers!
Reading Jon Marsh’s adventures over at htguide has definitely inspired me here. All credit to Jon. Nothing I’m trying here is an attempt to do anything but piggy-back off his work on the cheap. I really wanted to see if I could design a Duelund three-way for under $200, which admittedly is a fairly arbitrary price point. But I chose it because I think it’s the budget cut-off for lots of the competitions at the get-togethers.
I’m not qualified to expound on the benefits of a Duelund network, although Jon really explains it well if you care to read up. Rather this should probably be classified more as an intellectual exercise for me with the side benefit being, I get to play with and build speakers.
I initially considered two different values of aleph in the Duelund equations, but through various modeling and experimentation settled on aleph = 2√2 (blue), but I then shifted the center frequency down to about 1300 Hz, lowering the crossover points.
Through my driver testing, I settled on the DA215-8 for the woofer, the TG9FD10 for the midrange, and the DX20BF00-04 for the tweeter. The selection of the right midrange is critical here, and the performance of the TG9FD10 is the only reason this is possible.
The midrange driver needs to be small enough to allow for close tweeter placement since the mid-to-high crossover point is fairly high and we don’t want too narrow of a vertical lobe, but also robust enough to play cleanly down to around 250 Hz. The driver should also be as small as possible to achieve the greatest off-axis performance possible since it covers so much of the upper octaves with the tweeter (it is still contributing a couple dB at 6 kHz). Similarly, it is expected to contribute a couple dB at 200 Hz. It basically must be a full-range driver with solid HD performance across its entire bandwidth with no break-up. It is a pretty tall order.
Initially I thought I was going to select the PC105-8 based on my HD testing. I declared it my winner based on its ability to play cleaner, lower. Then I put it in PCD and was slapped in the face by the cone break-up centered around 9 kHz. It made hitting the target low-pass slope damn near impossible without an excessive component count. It really highlighted how smooth an FR response is needed in order to keep the crossover network in line with the budget sensibility.
Note*
This model and testing was with the TG9FD10-04 which drops the impedance to just above 4 ohms at the 150 Hz and 800 Hz dip. I have the TG9FD10-08 on order with the hopes that it measures as well or better and allows a higher minimum impedance at these frequencies so that this can be classified more as an 8 ohm nominal design that any old receiver can power comfortably.
The woofer cannot be any old woofer either. It must be able to play cleanly up to around 1 kHz and not have any excessive break-up until around 3—4 kHz. Even still, a bottomless notch was required to keep everything in line. I had really hoped that the DA215-8 would test well enough in the HD department to make it the right candidate, since it is one of the cheapest 8†drivers out there and integral to hitting the target price point. I’m happy enough with the testing to declare it just that.
I also wanted to do this in a sealed monitor. Form factor is important and floor-standers are not practical for me anymore. I personally feel going below 100 Hz is not as important with most people running subs anyhow. The DA215-8 models reasonably well in around 11 liters which is about all I can afford in my targeted 16†x 10.5†x 11.25†enclosure.
I don’t feel like there is too much to say on the DX20BF00-04 other than the fact that HiFiCompass tested it and it looks fantastic. It has a small form-factor, is easy to mount, and is even recessed a little bit to more closely align the acoustic centers between it and the midrange.
So anyhow, the PCD model above has thirteen (13) components. Four (4) on the woofer, four (4) on the tweeter, and five (5) on the midrange. If you assume an electrolytic capacitor for the woofer shunt and the midrange high-pass only because they are large values, but the rest standard Polypropylene capacitors, the drivers and crossover come in just under $200.
More to come.
Cheers!
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