ET Build: Ripole sub & SS 10F/8424 Sphere
Hello all! I am planning a new loudspeaker pair for my home use on my small listening room. Hopefully you can give feedback on what to improve on my plan. All crossover duty will be handled by MiniDSP 2x4 HD. The woofers will be driven with TDA8932s, one per unit. The full range drivers will be driven by NAD 912 amplifier. My listening levels are not very high, so they should manage. Listening height is almost exact 1 meter. Measurements of drivers:
ScanSpeak 10F/8424
Peerless SLS 12
The current plan is to have a pair of Ripole subwoofers producing the 20-250Hz bandwidth. They will have 2x Peerless SLS-12 woofers in them per unit as per the original Ripole plan (attachment 1 & 2). They will be on 20cm legs to adjust the listening height. Nothing special with this, it's a well-proven design good for combating room modes. I am thinking of using 21-25mm BB plywood for the construction, should be very solid to push the internal resonances way up past the operating bandwidth.
From the back of each Ripole sub leaves an axe handle which 38cm upwards from the top of the subwoofer connects to an IKEA Blanda Sphere which houses the ScanSpeak 10F/8424, which will handle rest of the range from (200-300Hz upwards). This is pushing the capabilities of the driver a bit, but I'm fairly certain it will manage. The CTC distance between the drivers would be 58cm, which stays inside 1/2 wavelength of crossover frequency. The sphere itself will be made of the 20cm diameter Blanda Matt bowls, which would mean that the lowest point of the bowl will be 28cm from the Ripole surface and the top 48cm. Center of the SS driver will be 38cm from the surface. They bowls would after damping and bracing equate to around 1,5l internal volume enclosure (attachments 3 & 4). This would mean a critically damped enclosure of quite low Q.
Bushmeister has a good description about the advantages of spherical enclosures in his thread: http://www.diyaudio.com/forums/multi-way/307837-great-balls-prestige.html
The 10F will attach to the enclosure with a bolt and nut, having a 3mm Sorbothane gasket between the enclosure-driver and enclosure-nut. I will break all solid connections between driver and enclosure to minimize vibration transfer between them along with dampening the sphere properly.
Last but not least, a somewhat to-scale drawing of the total system (attachment 5). First time my wife saw them she commented that they remind her of ET, which I kinda agree to
Hello all! I am planning a new loudspeaker pair for my home use on my small listening room. Hopefully you can give feedback on what to improve on my plan. All crossover duty will be handled by MiniDSP 2x4 HD. The woofers will be driven with TDA8932s, one per unit. The full range drivers will be driven by NAD 912 amplifier. My listening levels are not very high, so they should manage. Listening height is almost exact 1 meter. Measurements of drivers:
ScanSpeak 10F/8424
Peerless SLS 12
The current plan is to have a pair of Ripole subwoofers producing the 20-250Hz bandwidth. They will have 2x Peerless SLS-12 woofers in them per unit as per the original Ripole plan (attachment 1 & 2). They will be on 20cm legs to adjust the listening height. Nothing special with this, it's a well-proven design good for combating room modes. I am thinking of using 21-25mm BB plywood for the construction, should be very solid to push the internal resonances way up past the operating bandwidth.
From the back of each Ripole sub leaves an axe handle which 38cm upwards from the top of the subwoofer connects to an IKEA Blanda Sphere which houses the ScanSpeak 10F/8424, which will handle rest of the range from (200-300Hz upwards). This is pushing the capabilities of the driver a bit, but I'm fairly certain it will manage. The CTC distance between the drivers would be 58cm, which stays inside 1/2 wavelength of crossover frequency. The sphere itself will be made of the 20cm diameter Blanda Matt bowls, which would mean that the lowest point of the bowl will be 28cm from the Ripole surface and the top 48cm. Center of the SS driver will be 38cm from the surface. They bowls would after damping and bracing equate to around 1,5l internal volume enclosure (attachments 3 & 4). This would mean a critically damped enclosure of quite low Q.
Bushmeister has a good description about the advantages of spherical enclosures in his thread: http://www.diyaudio.com/forums/multi-way/307837-great-balls-prestige.html
The 10F will attach to the enclosure with a bolt and nut, having a 3mm Sorbothane gasket between the enclosure-driver and enclosure-nut. I will break all solid connections between driver and enclosure to minimize vibration transfer between them along with dampening the sphere properly.
Last but not least, a somewhat to-scale drawing of the total system (attachment 5). First time my wife saw them she commented that they remind her of ET, which I kinda agree to
Attachments
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I've been thinking about the Ripole + full range integration lately. The full range has to go quite low to fill the operating bandwidth. Other drivers I own are
Woofers:
Peerless 830868
Peerless 830869
Seas W15LY001 (would have to buy this)
Tweeters:
B&G NEO3 PDR with the faceplate
ScanSpeak D2010/851300
Would these make a better choice? I'd have to go from full active to half-active, as I plan on running the crossover from dipole to rest of the system with miniDSP. The woofer would go to 9l or 18l enclosure if I stack two 28cm blanda spheres.
Woofers:
Peerless 830868
Peerless 830869
Seas W15LY001 (would have to buy this)
Tweeters:
B&G NEO3 PDR with the faceplate
ScanSpeak D2010/851300
Would these make a better choice? I'd have to go from full active to half-active, as I plan on running the crossover from dipole to rest of the system with miniDSP. The woofer would go to 9l or 18l enclosure if I stack two 28cm blanda spheres.
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I'm mainly looking for better room integration with the Ripole subwoofers. My current setup is Peerless SLS-12 in 70l closed box with SS 10F. It is otherwise fine but in my listening space there is a huge 70Hz null. Very hard to fight against the room modes, must adapt.
The things that I am set on:
1) Ripole or similar subwoofer which helps with room modes (I already got 5pcs of Peerless SLS 12 woofers.
2) IKEA Blanda Bowls for speaker cabinets. I am convinced the sphere is the optimal shape for speaker enclosure (maybe ovoid is better but very hard to DIY). The bowls have 12cm/20cm/28cm outside diameters with 1 cm material thickness.
3) MiniDSP for crossover and time alignment, EQ, etc. between Ripole and rest of the system.
I have nothing aside from the drivers and MiniDSP bought yet, so pretty much full freedom. My listening space is the biggest problem, only a 3,5 x 3m room, very small.
The things that I am set on:
1) Ripole or similar subwoofer which helps with room modes (I already got 5pcs of Peerless SLS 12 woofers.
2) IKEA Blanda Bowls for speaker cabinets. I am convinced the sphere is the optimal shape for speaker enclosure (maybe ovoid is better but very hard to DIY). The bowls have 12cm/20cm/28cm outside diameters with 1 cm material thickness.
3) MiniDSP for crossover and time alignment, EQ, etc. between Ripole and rest of the system.
I have nothing aside from the drivers and MiniDSP bought yet, so pretty much full freedom. My listening space is the biggest problem, only a 3,5 x 3m room, very small.
Hi,
running the dipole sub up to 250Hz is certainly ambitious
In the Sim You can just detect the chamber resonance as a small wobble in the amplitude response ~280Hz.
Even when You notch out the peak perfectly the resonance may still be audible due to its longer decay.
I´d suggest to xover at not higher than 200Hz.
In early 2004 I built a very similar concept I called Drops, featuring the Vifa 10BGS119/8.
I used it combined with a single Ripole made from two 8" Peerless drivers (one of Axel´s original designs under the label of AudioElevation).
I put the Vifas in a small flower vase I bought in a 1€-shop (whereelse could one find such a ugly blue vase anyway?).
Trimmed the opening with a grinder to slush-fit the Vifa basket and milled a hole for the cabling into the bottom and a hole into the side for mounting purposes ... so much for convenience.
The Vifa showed a much smoother amplitude response than mounted to a flat baffle (compare to HobbyHiFi project PicoLino, 4/2001).
It still required a soft notch in the upper midrange to linearize the response ... as almost all FR do.
As the volume of the vase was so small it´d resulted in too high fb and Qtb, I used a large series Cap.
A series cap of appropriate value functions similar to a BR-port.
It equalizes the high Qtb-peak and shifts up the amplitude response below fb.
That way the Vifa could be linearized down to nearly 80Hz in a 1L cabinet and 470µF Cap.
I could have used a active crossover equalizer instead, but I just wanted to try the passive series cap thing anyway.
The bottom of the Vase got closed by a black plastic dome ... originally a egg cup with a opening so that a cable would fit through (the thick Neutrik cables ... which looked a bit weird considering how small the Vase was .... it rather looked like ... well ... ahm ... a sperm.
Mounted it on a stainless steel rod and a concrete garden plate in the shape of a footprint (only 5€ a pcs).
I don´t recall where I crossed the subwoofer but I think it was somewhere around 150Hz.
Sonically the combination of this little fullranger and the dipole woofer astounded everybody who gave it a listen.
Of couse the dynamic limits only allowed rather soft -but mostly sufficient and certainly more than one would have expected- volume levels .... but within this limit it played very neutral, focused and with great staging.
The tiny subwoofer reached down to almost unbelievable 25Hz.
It completed Drops in a way that the combination sounded like a true big system.
I assume Your project will lead to very similar results.
The 12" Peerless will allow for more authority in the lowest registers ... and the FR will rather be the dynamically limiting part here.
You may equalize the FR either with a series cap or with the DSP to reach down to ~150-180Hz .... using 4th order Filters could reduce problems of both, the FR at its lower end and the dipole woofer at its upper end.
Attached are pics of Drops ... not fully completed.
The holding hand just gives an idea how small those thingies really were.
jauu
Calvin
running the dipole sub up to 250Hz is certainly ambitious
In the Sim You can just detect the chamber resonance as a small wobble in the amplitude response ~280Hz.
Even when You notch out the peak perfectly the resonance may still be audible due to its longer decay.
I´d suggest to xover at not higher than 200Hz.
In early 2004 I built a very similar concept I called Drops, featuring the Vifa 10BGS119/8.
I used it combined with a single Ripole made from two 8" Peerless drivers (one of Axel´s original designs under the label of AudioElevation).
I put the Vifas in a small flower vase I bought in a 1€-shop (whereelse could one find such a ugly blue vase anyway?).
Trimmed the opening with a grinder to slush-fit the Vifa basket and milled a hole for the cabling into the bottom and a hole into the side for mounting purposes ... so much for convenience.
The Vifa showed a much smoother amplitude response than mounted to a flat baffle (compare to HobbyHiFi project PicoLino, 4/2001).
It still required a soft notch in the upper midrange to linearize the response ... as almost all FR do.
As the volume of the vase was so small it´d resulted in too high fb and Qtb, I used a large series Cap.
A series cap of appropriate value functions similar to a BR-port.
It equalizes the high Qtb-peak and shifts up the amplitude response below fb.
That way the Vifa could be linearized down to nearly 80Hz in a 1L cabinet and 470µF Cap.
I could have used a active crossover equalizer instead, but I just wanted to try the passive series cap thing anyway.
The bottom of the Vase got closed by a black plastic dome ... originally a egg cup
with a opening so that a cable would fit through (the thick Neutrik cables ... which looked a bit weird considering how small the Vase was .... it rather looked like ... well ... ahm ... a sperm.Mounted it on a stainless steel rod and a concrete garden plate in the shape of a footprint (only 5€ a pcs).
I don´t recall where I crossed the subwoofer but I think it was somewhere around 150Hz.
Sonically the combination of this little fullranger and the dipole woofer astounded everybody who gave it a listen.
Of couse the dynamic limits only allowed rather soft -but mostly sufficient and certainly more than one would have expected- volume levels .... but within this limit it played very neutral, focused and with great staging.
The tiny subwoofer reached down to almost unbelievable 25Hz.
It completed Drops in a way that the combination sounded like a true big system.
I assume Your project will lead to very similar results.
The 12" Peerless will allow for more authority in the lowest registers ... and the FR will rather be the dynamically limiting part here.
You may equalize the FR either with a series cap or with the DSP to reach down to ~150-180Hz .... using 4th order Filters could reduce problems of both, the FR at its lower end and the dipole woofer at its upper end.
Attached are pics of Drops ... not fully completed.
The holding hand just gives an idea how small those thingies really were.
jauu
Calvin
Attachments
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Thanks for the advice Calvin, was hoping you'd comment on the plan as you are probably have the most knowledge about Ripole in these forums.
It sounds like a massive overkill to have 4x Peerless SLS 12 in a small room, or 2 Ripole subs, but I guess you can't go wrong with futureproofing for a bigger listening space These speakers will be strictly for music use, although I might listen to a movie soundtrack every now and then. I got a separate HT setup on my living room.
Do you think I should go with the Ripole plan on my first post or something modified? I contacted my local carpenter, he only has 21mm BB plywood in stock, but that will quite likely suffice. I'll construct and finish the cabinets myself, just want to get the pieces pre-cut
I am currently aiming for 200Hz crossover point at per your advice. I will specify the overall crossovers with in-room measurements, I'm aiming for either 4th order Linkwitz-Riley or Harsch crossover slopes. Harsch would be nice for the phase accuracy, but it puts more stress on the full range as it's only 2nd order high-pass.
Anyhow, looking at the measurements on the 10F, it seems that the 2nd order distortion climbs up almost linearly under 800Hz, whilst 3rd order distortion and 5th order distortion begin rising at around 200Hz. I guess 200Hz is around bare minimum what I'd want to cross this driver.
It sounds like a massive overkill to have 4x Peerless SLS 12 in a small room, or 2 Ripole subs, but I guess you can't go wrong with futureproofing for a bigger listening space
These speakers will be strictly for music use, although I might listen to a movie soundtrack every now and then. I got a separate HT setup on my living room.Do you think I should go with the Ripole plan on my first post or something modified? I contacted my local carpenter, he only has 21mm BB plywood in stock, but that will quite likely suffice. I'll construct and finish the cabinets myself, just want to get the pieces pre-cut
I am currently aiming for 200Hz crossover point at per your advice. I will specify the overall crossovers with in-room measurements, I'm aiming for either 4th order Linkwitz-Riley or Harsch crossover slopes. Harsch would be nice for the phase accuracy, but it puts more stress on the full range as it's only 2nd order high-pass.
Anyhow, looking at the measurements on the 10F, it seems that the 2nd order distortion climbs up almost linearly under 800Hz, whilst 3rd order distortion and 5th order distortion begin rising at around 200Hz. I guess 200Hz is around bare minimum what I'd want to cross this driver.
Hi,
i don't actually know what I could comment more on the concept .... I like it and obviously did quite similar.
With one wooder for each channel the xover can generally be chosen a few Hz higher than with just a single woofer.
With appr. 4-5 times the membrane area compared to the Drops system your woofers allows for much greater dynamic reserves (with nearly the same lower bandwidth limit).
The small FR will very probabely limit first.
Q: is the FR already set, or could there be other options?
I'm thinking for example of those Seas 14cm and 17cm Coax drivers, that may be built into quite small spheres also.
jauu
Calvin
i don't actually know what I could comment more on the concept .... I like it and obviously did quite similar.
With one wooder for each channel the xover can generally be chosen a few Hz higher than with just a single woofer.
With appr. 4-5 times the membrane area compared to the Drops system your woofers allows for much greater dynamic reserves (with nearly the same lower bandwidth limit).
The small FR will very probabely limit first.
Q: is the FR already set, or could there be other options?
I'm thinking for example of those Seas 14cm and 17cm Coax drivers, that may be built into quite small spheres also.
jauu
Calvin
I already own the FR driver. Other choices are the drivers I listed in my earlier post. I prefer to use drivers I already own or can get second-hand for cheaper prices
I personally don't like coax drivers. I can't put my finger on it, but I have never liked their sound. I've heard both expensive (Genelec studio monitors) and cheap (car stuff) coaxial drivers, but I always prefer the non-coax versions.
As of currently, I think I'll build Ripole + Blanda FR spheres on, but I'll make the joint so I can change the spheres later if needed. So Ripole + axe handle will form the bass-stand for the speaker
Question: From the plan, are the drivers surface mounted to the middle chamber? If I surface mount them, should I make front chamber wider?
I personally don't like coax drivers. I can't put my finger on it, but I have never liked their sound. I've heard both expensive (Genelec studio monitors) and cheap (car stuff) coaxial drivers, but I always prefer the non-coax versions.
As of currently, I think I'll build Ripole + Blanda FR spheres on, but I'll make the joint so I can change the spheres later if needed. So Ripole + axe handle will form the bass-stand for the speaker
Question: From the plan, are the drivers surface mounted to the middle chamber? If I surface mount them, should I make front chamber wider?
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Another question: if I go for the plan of 8cm wide front chamber (drivers surface mounted) but change the rear chambers to 12cm width to accommodate the whole driver (no hole on the sides), how much the performance would change from the simulated on the first picture? I assume the first one is with magnets protruding from the sides? I am very new to open baffle dynamics so please bear with me
Hi,
the front chamber beeing much smaller dominates the response by far.
Increasing the back chamber width to 12cm results in almost negligible differences.
Sim says the Fb will rise by ~0.3Hz and chamber resonance will sink by ~5-6Hz.
The Peerless basket is made from steel and features a rather thin outer rim.
Theres no requirement to sink in thie basket into the mounting wall, but You may if You wish.
jauu
Calvin
the front chamber beeing much smaller dominates the response by far.
Increasing the back chamber width to 12cm results in almost negligible differences.
Sim says the Fb will rise by ~0.3Hz and chamber resonance will sink by ~5-6Hz.
The Peerless basket is made from steel and features a rather thin outer rim.
Theres no requirement to sink in thie basket into the mounting wall, but You may if You wish.
jauu
Calvin
Dipole bass is definitely different than monopole bass and the room interaction is different. With the dipole being directional that is what changes the room interaction.
If you put your dipole woofers in the wrong spot you might get a worse response than a monopole in the same position hard to know without trying it.
Another thing that I would build in to your design is the ability to angle the woofer part independently from the Full range. Dipole woofers change their interaction with the room by angle. It doesn't really matter which way you point a monopole sub but a dipole one it can.
It is quite easy to listen to a bass track that covers the modal range or noise to see which angle gives you the most even response. I have done this myself with LX521 and it is much better to be able to angle the woofers to get a more even bass response.
Below 50 Hz dipole woofers really lose output so if you want a lot of sub 50Hz output 4 x 12" woofers is not huge.
To compare the 2 x 10" woofers I have per side have a Volume displacement of 1016 cm3, the 2 x 12" SLS have 867cm3.
You might find that you could combat your 70Hz issue by putting the 4 woofers in small sealed boxes and spreading them out in your room. You could use two under the full range due to the crossover but the other two could be spread out.
In a sealed box the SLS could be pushed higher than 200Hz to relieve the 10F steeper slopes would probably help. Byrtt has a 10F FAST that use some pretty high slopes and he seems to like it.
If you put your dipole woofers in the wrong spot you might get a worse response than a monopole in the same position hard to know without trying it.
Another thing that I would build in to your design is the ability to angle the woofer part independently from the Full range. Dipole woofers change their interaction with the room by angle. It doesn't really matter which way you point a monopole sub but a dipole one it can.
It is quite easy to listen to a bass track that covers the modal range or noise to see which angle gives you the most even response. I have done this myself with LX521 and it is much better to be able to angle the woofers to get a more even bass response.
Below 50 Hz dipole woofers really lose output so if you want a lot of sub 50Hz output 4 x 12" woofers is not huge.
To compare the 2 x 10" woofers I have per side have a Volume displacement of 1016 cm3, the 2 x 12" SLS have 867cm3.
You might find that you could combat your 70Hz issue by putting the 4 woofers in small sealed boxes and spreading them out in your room. You could use two under the full range due to the crossover but the other two could be spread out.
In a sealed box the SLS could be pushed higher than 200Hz to relieve the 10F steeper slopes would probably help. Byrtt has a 10F FAST that use some pretty high slopes and he seems to like it.
Alright, thank you. Ordered the plywood pieces today according to these measurements.
This is a good point I hadn't considered. I will make the woofers separate and have the full range at stands.
I currently run the SLS 12 in a 70l closed box with the 10F crossed at 350Hz. Here's my build:
http://www.diyaudio.com/forums/full-range/294135-hi-end-full-range-project-15.html#post4909284
in a small room like yours
I would do 10F + 8" 2 way mains nearfield (perhaps LX mini style)
and add sub/subs at 70-80hz
sub option 1: 4x monopole 12SLS placed randomly around the room (small sealed enclosure)
sub option 2: 1x ripole nearfield with 2x15" proaudio drivers (12SLS not ideal for ripole)
I would do 10F + 8" 2 way mains nearfield (perhaps LX mini style)
and add sub/subs at 70-80hz
sub option 1: 4x monopole 12SLS placed randomly around the room (small sealed enclosure)
sub option 2: 1x ripole nearfield with 2x15" proaudio drivers (12SLS not ideal for ripole)
I have the two Peerless 8" drivers and two different tweeters. I was thinking I'll maybe do a 2-way monitor of them later on (similar sphere builds) which I can compare to 10F speaker. The stand will have a bolt mount so I can change the speaker on top of it easily.
4x woofers could work, but SLS 12 wants a large enclosure. My room is small and the missus also has an arts and crafts table and shelf there, so space is limited.
On the suitability of SLS 12 to Ripole, I believe Alex Ridtahler originally designed this with the driver aforementioned. Should work.
4x woofers could work, but SLS 12 wants a large enclosure. My room is small and the missus also has an arts and crafts table and shelf there, so space is limited.
On the suitability of SLS 12 to Ripole, I believe Alex Ridtahler originally designed this with the driver aforementioned. Should work.
You can put them in whatever enclosure size you like and use a linkwitz transform or other EQ to adjust the response.
The downside to using a smaller box is that you will need more power to drive it back to the same level as the bigger box.
If you go dipole/ripole you still need a lot of EQ to offset the dipole roll off probably 15dB or more.
I don't mean to try and sway you either way just point out that a small box or dipole both need a lot of EQ.
The slight downside to the SLS12 in a dipole arrangement is that the x-max is not huge. That is what limits them somewhat below 50Hz.
If you turn a dipole woofer up loud with any sub 30 Hz content you will really see those cones move
Hi,
The displacement volume of a pair of SLS12 is 2x540cm²x1.6cm=1728cm³ if displacement is calculated as VC-length minus height of gap.
If You add 25% as many manufacturers do then it increases to 2160cm³.
Quite a bit more than two 10"ers
The SLS-Drivers typically don´t require so much lowbass-eq, rather expect 3-6dB.
Under lucky circumstances they might not need any bass lift at all.
These could be small room, short listening distance, etc.
BTW. I found the dipoles the only cabinet style in which the SLS sound very well.
In CB or TML they just sound boring and slow to my ears.
jauu
Calvin
That´s wrong ... in a Trump-style WRooONnnG
The displacement volume of a pair of SLS12 is 2x540cm²x1.6cm=1728cm³ if displacement is calculated as VC-length minus height of gap.
If You add 25% as many manufacturers do then it increases to 2160cm³.
Quite a bit more than two 10"ers
That may apply to many dipoles, but is not neccessarily so.
The SLS-Drivers typically don´t require so much lowbass-eq, rather expect 3-6dB.
Under lucky circumstances they might not need any bass lift at all.
These could be small room, short listening distance, etc.
BTW. I found the dipoles the only cabinet style in which the SLS sound very well.
In CB or TML they just sound boring and slow to my ears.
jauu
Calvin
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Hi,
That´s wrong ... in a Trump-style WRooONnnG
The displacement volume of a pair of SLS12 is 2x540cm²x1.6cm=1728cm³ if displacement is calculated as VC-length minus height of gap.
If You add 25% as many manufacturers do then it increases to 2160cm³.
Quite a bit more than two 10"ers
That is the funniest thing I have seen for some time
My calculation used Sd x x-max (from manufacturers spec sheets)
Peerless 830669 Sd 522.8cm2 / x-max 8.3mm 0.83cm
522.8 x 2 x 0.83cm = 867cm3
You have used Sd x 2x x-max which I don't think is right.
But if I had used your formula on my 10" drivers
Seas L26RO4Y Sd 363cm2 / x-max 14mm 1.4cm
363 x 2 x 2.8cm = 2032cm3 so you see that ratio is the same, my two 10" drivers have a lot more x-max which overcomes the reduced amount of Sd.
If I then added 25% I get to 2541cm3
Whichever calculation method you choose the 2 x 10" woofers with 14mm x-max have more Vd than 2 x 12" with 8.3mm x-max.
Can you find someway to disagree with that? Fake news maybe?
Do you have a dipole that does not rolloff like all others?
Do you have any measurements to confirm this?
The 15dB I quoted is very close to the amount of EQ used in the Linkwitz LX521 I use to compensate the woofers back to a flat response.
I don't mean to derail Mayuri's thread, I only posted some information based on my own experiences to help and felt the need to respond to the above.
As Calvin was so adamant that the calculation I used was so wrong I had a think about it because I would prefer to know if I have misunderstood something.
So here is a fictional example with simple figures to make the maths easy.
If we have one woofer with Sd of 500cm2 and 10mm (1cm) x-max it's Vd is
500cm2 x 1cm = 500cm3.
If we then add another woofer the same we will double the Vd which would be 1000cm3.
So if we use the calculation I showed
500 x 2 x 1 = 1000
If we use the formula Calvin showed
500 x 2 x 2 = 2000
To me that confirms I had it right.
We can compare the Vd figures quoted to Small's graph for SPL vs Vd in a sealed enclosure that. If two Peerless 830669 woofers had a Vd of over 2000cm3 then they would be able to produce a peak spl of nearly 117dB at 30Hz which does not seem likely.
At 867 it goes down to about 110dB peak which seems about right.
So here is a fictional example with simple figures to make the maths easy.
If we have one woofer with Sd of 500cm2 and 10mm (1cm) x-max it's Vd is
500cm2 x 1cm = 500cm3.
If we then add another woofer the same we will double the Vd which would be 1000cm3.
So if we use the calculation I showed
500 x 2 x 1 = 1000
If we use the formula Calvin showed
500 x 2 x 2 = 2000
To me that confirms I had it right.
We can compare the Vd figures quoted to Small's graph for SPL vs Vd in a sealed enclosure that. If two Peerless 830669 woofers had a Vd of over 2000cm3 then they would be able to produce a peak spl of nearly 117dB at 30Hz which does not seem likely.
At 867 it goes down to about 110dB peak which seems about right.
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