Hello All,
After building Zaph Audio SR-71's and being very impressed with them, I am going ahead with a vented TMM design built around the Dayton RS225P-8A and either the Dayton RST28F-4 1-1/8" fabric dome or the HiVi RT2C-A planar isodynamic tweeter.
My first puzzle is whether to keep the woofers acoustically isolated from each other or not. I'm concerned that if the output of one differs from the other even slightly, then not isolating them may cause interactions that degrade the sound. I've searched extensively by myself for advice on this and found little to no mention of the benefits of either route so thought I'd see what the very skilled folks on this forum have to say. I modeled each design in WinISD and see that using one vented enclosure results in a smaller box, 62 liters vs. 80 liters if each is isolated (each design tuned to 35Hz). My preference is a smaller box, but not if that results in reduced sound quality.
Any data or thoughts would be greatly appreciated.
After building Zaph Audio SR-71's and being very impressed with them, I am going ahead with a vented TMM design built around the Dayton RS225P-8A and either the Dayton RST28F-4 1-1/8" fabric dome or the HiVi RT2C-A planar isodynamic tweeter.
My first puzzle is whether to keep the woofers acoustically isolated from each other or not. I'm concerned that if the output of one differs from the other even slightly, then not isolating them may cause interactions that degrade the sound. I've searched extensively by myself for advice on this and found little to no mention of the benefits of either route so thought I'd see what the very skilled folks on this forum have to say. I modeled each design in WinISD and see that using one vented enclosure results in a smaller box, 62 liters vs. 80 liters if each is isolated (each design tuned to 35Hz). My preference is a smaller box, but not if that results in reduced sound quality.
Any data or thoughts would be greatly appreciated.
That Planar tweeter likes to be xoverd at 2.7-3kHz. If you ask me, this is very high for an 8" 2-way in most cases. Another thing about it- it's HUGE in diameter. This can wreak havoc on center to center distance. That said, I've seen and heard it done with an Audax Aerogel 8" woofer, and that worked out okay. I'm just not sure if the RS225P will meet it alright. The RST28 will likely reach it, but 8" 2-ways are never easy.
I recommend you attempt it one of these ways:
1- use a waveguide on the tweeter
2- start the tweeter rolloff shallow and early to combat the directivity mismatch at the xover point to the 8" driver.
3- Use a larger widerange or tweeter so that it is easier to do.
As to the TMM and isolate/not, I wouldn't worry about it. The area they move more together is in the bass range, and they won't fight each other in that range as the load is split evenly between the drivers. The upper one just happens to play higher into the midrange is all if you go 2.5-way. If you go straight 2-way TMM, then nothing differs between them at all.
I recommend you attempt it one of these ways:
1- use a waveguide on the tweeter
2- start the tweeter rolloff shallow and early to combat the directivity mismatch at the xover point to the 8" driver.
3- Use a larger widerange or tweeter so that it is easier to do.
As to the TMM and isolate/not, I wouldn't worry about it. The area they move more together is in the bass range, and they won't fight each other in that range as the load is split evenly between the drivers. The upper one just happens to play higher into the midrange is all if you go 2.5-way. If you go straight 2-way TMM, then nothing differs between them at all.
Thanks. If the planar tweeter needs to start at 2.7-3kHz then I won't use it. I was considering it based on the specifications listed at Dayton Audio, which state a frequency response starting at 1.7kHz. That being said, the stated specs for the RS225P-8A are 30-7,000Hz, which sure seems questionable.
As for the advice on the woofer isolation, many thanks. That keeps my cabinet size small and puts a limit to my overthinking.
As for the advice on the woofer isolation, many thanks. That keeps my cabinet size small and puts a limit to my overthinking.
Limey,
Something is wrong with your model- whether the dual driver box is separated into two chambers or is a single one, the net volume occupied should be the same. There will be a small difference in gross volume due to the additional port and cabinet walls added.
Splitting the boxes does offer an advantage if you consider the use a 2.5 way crossover (often preferable), as well as stiffening up the box and reducing any cone intermodulation effects.
Hi,
Zaph himself did measurements on exactly that question, my takeaway is that while there is a very slight difference, it's too small to matter.
http://www.zaphaudio.com/commonenclosuretest.html
One other little advantage that 2 separate ported chambers offers is some extra in-room lower bass tuning flexibility.
If you understand room gain and boundary re-enforcement or if on occasion you just come across material that is extra heavy in the bass, and you port each driver individually, you have the ability to stuff just a single port in each speaker and thereby reduce the bass response down to somewhere between a ported and sealed response. On certain occasions, that could be advantageous.
If you understand room gain and boundary re-enforcement or if on occasion you just come across material that is extra heavy in the bass, and you port each driver individually, you have the ability to stuff just a single port in each speaker and thereby reduce the bass response down to somewhere between a ported and sealed response. On certain occasions, that could be advantageous.
Many thanks to all for the advice. Interesting to see the comment about two separate ported chambers. In the mid-80's when I was about 30 I built a pair of speakers using Dynaudio drivers, back when they sold drivers to the public. The design I used came from a magazine called Speaker Builder, which was a paper magazine since this was prior to the internet. The box design called out two shallow ports flush with the back panel, each one filled with dense cloth material. I think the box design was supposed to be in between ported and sealed, as JReave mentions above. I still have the Dynaudio woofers. 10" I think, with cast Magnesium frames.
I just checked the Swan's website, and they suggest a crossover point >3kHz, so Parts Express spec seems wrong. Can you suggest a planar tweeter which reaches down to 2kHz? I'm leaning towards a ribbon/planar because I understand that they have narrow vertical dispersion, which is what I think I need in order to minimize reflections from the ceiling and floor. I also attached the RT2C response curve. It does appear about 5dB down at 2kHz.
Attachments
No need to isolate the woofers
They will share the same airspace and same port.
This guarantees tuning will be the same,
and a larger volume, allows shorter port length for same port area.
So its possible to have very good port velocity and not have extremely
long ports. Better not to overthink, but it has been tried.
Having built a few test boxes with separated/shared applications.
Shared space seemed preferred
Check the FRD files that Dayton includes with the drivers.
The RS225P does go to 7K but 5K more realistic.
But exhibits the usual uneven pattern a 8" would have that high.
Smoother transition is around 800 to 1,600 K
GRS PT6816-8 Planar extends to midrange capabilities.
Believe Fs is around 350 Hz
RST28F is a nice sounding soft dome.
Resonant frequency is around 700 Hz
with the usual rule of thumb crossover Min is 1400 Hz
with a 2nd order.
Looking at the 8" response, 3rd order wouldn't hurt
and keep the soft dome safer crossed low.
They will share the same airspace and same port.
This guarantees tuning will be the same,
and a larger volume, allows shorter port length for same port area.
So its possible to have very good port velocity and not have extremely
long ports. Better not to overthink, but it has been tried.
Having built a few test boxes with separated/shared applications.
Shared space seemed preferred
Check the FRD files that Dayton includes with the drivers.
The RS225P does go to 7K but 5K more realistic.
But exhibits the usual uneven pattern a 8" would have that high.
Smoother transition is around 800 to 1,600 K
GRS PT6816-8 Planar extends to midrange capabilities.
Believe Fs is around 350 Hz
RST28F is a nice sounding soft dome.
Resonant frequency is around 700 Hz
with the usual rule of thumb crossover Min is 1400 Hz
with a 2nd order.
Looking at the 8" response, 3rd order wouldn't hurt
and keep the soft dome safer crossed low.
Actually, even-order electrical networks protect tweeters more than odd order. This is due to the coil being across the tweeter.
yes understood.
It was more the large response peaks of the 8" speaker is likely hard to tame if crossed high.
Taking a quick glance at the FRD
It was more the large response peaks of the 8" speaker is likely hard to tame if crossed high.
Taking a quick glance at the FRD
Played around with the RST28F crossed @ around 1600 kHz
seems to work alright with the 8"
Tossed in basic baffle step compensation.
My Simulated response wont be flat below 400Hz because it includes the 6dB compensation in the low end.
seems to work alright with the 8"
Tossed in basic baffle step compensation.
My Simulated response wont be flat below 400Hz because it includes the 6dB compensation in the low end.
WhiteDragon, that is very kind of you. I had downloaded Xsim the other day and was going to have my first crack at crossover design. Now I have some guidance! You guys are great. I've pretty much ruled out a ribbon or planar tweeter and will probably go with the RST28F, or perhaps the Peerless DA32TX00-08 which also seems to work well down low. Time to buy parts and start work!