Thanks, looks interesting too.
I am searching the off axis measurements of the SEOS 8 for DI calculation.
I did find them for the SEOS 10, but not yet for the 8 version.
SEOS-10 - Horns by Auto-Tech
I think some serial resistance can be placed. I have to look in detail.
Overall sensititvity will be not more than 90 dB with the current woofers.
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The 4 Ohm version has a sensitivity of 98 dB at 2 kHz with the waveguide and at 20 kHz we have some benefits of the voice coil inductance.
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Why this obsession with impedance?
Jonasz, the target is to realize an impedance not lower than 8 Ohm and as flat as possible. As a benefit for some tube amplifiers with not a very low output impedance.
Why this obsession with impedance?
That is (was?) part of the design goals as discussed in the open source speaker threads.
This.
Hmm. No.
Edit: YET ANOTHER FACEPLANT MOMENT! My measurements of the SS6600 were with a Monacor WG300, not the WG148. I keep confusing the two. Aaargh! Bottom line: go for the WG148, not the WG300. It may be a bit trickier to fit the WG148 on a Scan tweeter than the WG300 though. The Seas might be easier than the Scans in this regard.
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Did you mount the waveguide flush with the baffle in that test?
Also better to use a large baffle for such measurements.
If you measure a tweeter on a baffle, not flush mounted, there appear diffractions around 5-6 kHz, tweeter of about 10 cm diameter. I have some experience with such things, measuring on IEC baffle. It is very critical for a tweeter.
Also better to use a large baffle for such measurements.
If you measure a tweeter on a baffle, not flush mounted, there appear diffractions around 5-6 kHz, tweeter of about 10 cm diameter. I have some experience with such things, measuring on IEC baffle. It is very critical for a tweeter.
I think you all may need to bend a bit on what you consider to be low impedance ( or "amp-friendly" ).
Personally, I wouldn't dedicate the required cubic space ( where I live ) to a box housing a 15" woofer unless the minimum system sensitivity was 93db ( below that, I just don't see the point ).
Finding a 25mm or 35mm dome tweeter ( worth using ) that has this high a sensitivity will require it to have an impedance that's somewhat lower than 8 ohms ( most likely 4 -6 ohms ).
Perhaps some more polls are in order ( to ask those still following along ) about their preferred tweeter type ( dome, ribbon/AMT or compression driver ? ).
Ok, but if you use the SBA tweeter I linked earlier, 4ohm 96dB, you will with some padding be able to get an 8 ohm load?
I think you all may need to bend a bit on what you consider to be low impedance ( or "amp-friendly" ).
Personally, I wouldn't dedicate the required cubic space ( where I live ) to a box housing a 15" woofer unless the minimum system sensitivity was 93db ( below that, I just don't see the point ).
Finding a 25mm or 35mm dome tweeter ( worth using ) that has this high a sensitivity will require it to have an impedance that's somewhat lower than 8 ohms ( most likely 4 -6 ohms ).
Perhaps some more polls are in order ( to ask those still following along ) about their preferred tweeter type ( dome, ribbon/AMT or compression driver ? ).
Eral, thanks for your feedback
design elements such as size, sensitivity, impedance were implied by previous polls and feedbacks, we may end up with another poll (for tweeter) but things are going well at this point, first we have to see which one fits better before and if we decide on a poll.as for sensitivity, this will be 90+db full space, with simplicity in mind for novice DIYers, finding a suitable driver (mainly woofer) that can have high sensitivity and go that low without breaking the bank or making the design complex (with using multiple drivers and chambers) was not easy and I think team pulled it off very nicely.
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But if we go with a nice compressiondriver it's easy to find 8ohm parts with enough sensitivity...
Once we have two options for driver, and also two options for LF tunning, we should have two options for tweeter.
1) Tweeter + Wave guide
2) Compression Driver + Horn
2 x 2 x 2 = 8 variations
I think two options for the tweeter, CD and dome with waveguide, is the best way to go forward. There will be more people interested to build a Tower XL.
For the dome tweeter choice, my proposal is to take the same one with waveguide as in the Monkey Coffin, if possible.
For the CD tweeter, we have to try to realize a reasonable directivity match with the midrange. Also the acoustical center of the horn tweeter and the midrange should be aligned in the best way. With a passive X-over it is much more complex to compensate for that. So, deep throat CD drivers maybe are not so recommended, probably they are more directive too (I think so).
For the dome tweeter choice, my proposal is to take the same one with waveguide as in the Monkey Coffin, if possible.
For the CD tweeter, we have to try to realize a reasonable directivity match with the midrange. Also the acoustical center of the horn tweeter and the midrange should be aligned in the best way. With a passive X-over it is much more complex to compensate for that. So, deep throat CD drivers maybe are not so recommended, probably they are more directive too (I think so).
Why no AMT? (just wondering)
This really depends on the requirements that need to be filled by the tweeters of the Tower XL and the Monkey Coffin. The two designs have very different midrange drivers, and it would be sheer coincidence if the mid/tweeter x-over would lead to the same requirements. This is how I see this at the moment:
- X-over frequency: for the Monkey Coffin we are currently considering about 2.5 kHz, for the Tower XL is will be bit lower at about 2 kHz for the Tower XL. Not a big difference.
- Dispersion at/around x-over: we don't really know that yet for the Monkey Coffin (have to wait for delivery and measurements of the midrange drivers), and I don't really know what we are looking for in the Tower XL.
- Sensitivity: with the Monkey Coffin we are still aiming for 92 dB/2.83V/1m with an "8 Ohm" rating, but we have bit more flexiblity with the Tower XL 90 dB/2.83V/1m should be okay (as far as I can tell from the recent discussion). This might open up some options that would not work well with the Monkey Coffin.
I'd suggest to leave it to the first builder to choose the tweeter type that suits his/her preferences. I guess since Aatto already ordered the woofers and the mids, he might just go ahead and choose between dome/CD/AMT/whatever he thinks is right. Once we know what to look for (dome/CD/AMT/whatever) we can suggest and discuss specific drivers.
First DI calculations of dome waveguide based on the Pida measurement have shown there is an acceptable directivity match with the AE TD8M. As also such waveguide can be used in the Monkey Coffin, we have to try to keep things common, that was my idea. Because I understand that applying some waveguide with some dome, needs some experienced evaluation.
AMT still is an option, I agree. It is more vertical directional than a dome without waveguide, so expected to have a higher total DI in single hemisphere. Preferred to check it with off axis measurements, how it matches with 8 inch midrange.
Choosing tweeter that someone "wants"... only if the technical picture looks ok too...
AMT still is an option, I agree. It is more vertical directional than a dome without waveguide, so expected to have a higher total DI in single hemisphere. Preferred to check it with off axis measurements, how it matches with 8 inch midrange.
Choosing tweeter that someone "wants"... only if the technical picture looks ok too...
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View attachment 713568
I did find that Leap can also make a driver model with rectangular cone. To be used for ribbon and AMT.
So, I made single hemisphere directivity calculations, meaning horizontal and vertical responses included.
In the plot the calculated DI for the AE TD8M and some different tweeter types.
- AE TD 8M Leap model (green color)
- Dome tweeter without waveguide Satori TW29BN (blue color)
- Dome tweeter with waveguide - Scanspeak R6600 – Visaton WG148 – off axis measurement Pida in enclosure (yellow color).
- CD tweeter with horn 18Sound XT1086 + ND1075 (pink color)
- AMT without waveguide - Leap model – chosen 1inch wide and 3 inch high for this calculation (red color)
- AMT with horn - Beyma TPL-150H - DI curve datasheet (black color) – assumption made, that it is also a single hemisphere curve.
Update of conclusions for a X-over at about 2 kHz with 8 inch midrange AE TD8M:
- Dome and AMT without waveguide: DI dip above 2 kHz, less for AMT, speaker will be less directive between 2 and 4 kHz.
- Dome with waveguide: little DI dip to be expected above 2 kHz. Remark that these off axis measurements are done in enclosure, so DI at 2 kHz and lower will be less.
- CD tweeter with horn, good match, more flat DI above 2 kHz, more directive between 2 and 4 kHz than dome and AMT.
- AMT with horn, Beyma TPL-150H, better match at 2 kHz than dome with waveguide, but more directive above 2 kHz.
So, I made single hemisphere directivity calculations, meaning horizontal and vertical responses included.
In the plot the calculated DI for the AE TD8M and some different tweeter types.
- AE TD 8M Leap model (green color)
- Dome tweeter without waveguide Satori TW29BN (blue color)
- Dome tweeter with waveguide - Scanspeak R6600 – Visaton WG148 – off axis measurement Pida in enclosure (yellow color).
- CD tweeter with horn 18Sound XT1086 + ND1075 (pink color)
- AMT without waveguide - Leap model – chosen 1inch wide and 3 inch high for this calculation (red color)
- AMT with horn - Beyma TPL-150H - DI curve datasheet (black color) – assumption made, that it is also a single hemisphere curve.
Update of conclusions for a X-over at about 2 kHz with 8 inch midrange AE TD8M:
- Dome and AMT without waveguide: DI dip above 2 kHz, less for AMT, speaker will be less directive between 2 and 4 kHz.
- Dome with waveguide: little DI dip to be expected above 2 kHz. Remark that these off axis measurements are done in enclosure, so DI at 2 kHz and lower will be less.
- CD tweeter with horn, good match, more flat DI above 2 kHz, more directive between 2 and 4 kHz than dome and AMT.
- AMT with horn, Beyma TPL-150H, better match at 2 kHz than dome with waveguide, but more directive above 2 kHz.
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