SB20FRPC30-8 based rear speaker project

[ppataki]

so this would raise the q above 0.707 ? I worked out a 45/50 litre box would be ideal for this driver do you notice any difference in using a smaller box like this ? I have a project for a friend would be handy to be able to put a couple 15s in a smaller than the ideally suggested 300 litre box

No, this is with Q=0.707
The reason why the cabinet became this 'small' is that I assumed that the cabinet would be heavily filled with damping material (cotton wad)
If that is not the case then you would need a 137 liter box

Generally speaking smaller box = (much) more amplifier power needed to reach peak SPL (but with wad filling we can 'trick' the driver to 'think' that it is in a bigger box)

My 15" Fanes are in a 65 liter box with heavy filling so I could reach max SPL with 100W/channel
In a 300 liter heavily filled box only 20W would suffice for the same

 

[jamescarter1982]

No, this is with Q=0.707
The reason why the cabinet became this 'small' is that I assumed that the cabinet would be heavily filled with damping material (cotton wad)
If that is not the case then you would need a 137 liter box

Generally speaking smaller box = (much) more amplifier power needed to reach peak SPL (but with wad filling we can 'trick' the driver to 'think' that it is in a bigger box)

My 15" Fanes are in a 65 liter box with heavy filling so I could reach max SPL with 100W/channel
In a 300 liter heavily filled box only 20W would suffice for the same

so if you made the box smaller without heavily filling with wadding would that raise the q of the system or just raise the f3 point. this information could be really helpful I just need to make sure I understand it correctly thanks

 

[ppataki]

so if you made the box smaller without heavily filling with wadding would that raise the q of the system or just raise the f3 point. this information could be really helpful I just need to make sure I understand it correctly thanks

Smaller box with less wad filling will raise the Q value, yes
But if you use DSP to correct the FR you really do not need to worry about the Q value...
You just need to worry about having enough amp power to compensate for the small box size and for the heavy DSP correction

 

[ppataki]

@TNT
As promised, I am sharing my experience with these speakers when moved to another part of the same room
Actually I moved them to where my 15" loudspeakers normally are - that is a much better location acoustically speaking

Here is how they compare when measured in the rear vs in the front:

Clearly, in the front position they shall go down well below 30Hz

Actually here is the corrected curve:

-3dB point is at 22Hz

Now let's see the distortion graph:

To me at least this looks pretty good down to 24Hz (that is where I would apply a HPF)
This was measured at 75dB, 260cm from the microphone

When listening to it (with some low shelf and high shelf filters to taste), this is how they sound:

New video by Peter Pataki

photos.app.goo.gl

New video by Peter Pataki

photos.app.goo.gl

New video by Peter Pataki

photos.app.goo.gl

And you can find here the whole mdat file: https://drive.google.com/file/d/13LyxpPVmqNyLQgZGX7KXAmOLbb3fQfvu/view?usp=sharing

I must say that I am simply blown away.....IMHO these speaker is the price/value champion in the full range category; I have never seen/heard anything like this before (in the up to 8" range)

 

[jamescarter1982]

definitely going to get myself some of these . what size box have you got these in again pls . been reading last night about reducing box size and igs effect on q going from 0.707 to 1 pretty much halves the box size so if this isn't audible then might as well use a smaller enclosure

 

[ppataki]

definitely going to get myself some of these . what size box have you got these in again pls . been reading last night about reducing box size and igs effect on q going from 0.707 to 1 pretty much halves the box size so if this isn't audible then might as well use a smaller enclosure

Just refer to my first post: https://audiosciencereview.com/foru...b20frpc30-8-based-rear-speaker-project.41687/

 

[ernestcarl]

@TNT
As promised, I am sharing my experience with these speakers when moved to another part of the same room
Actually I moved them to where my 15" loudspeakers normally are - that is a much better location acoustically speaking

View attachment 274238


Here is how they compare when measured in the rear vs in the front:

View attachment 274245

Clearly, in the front position they shall go down well below 30Hz

Actually here is the corrected curve:

View attachment 274240

-3dB point is at 22Hz

Now let's see the distortion graph:

View attachment 274241

To me at least this looks pretty good down to 24Hz (that is where I would apply a HPF)
This was measured at 75dB, 260cm from the microphone

When listening to it (with some low shelf and high shelf filters to taste), this is how they sound:

New video by Peter Pataki

photos.app.goo.gl

New video by Peter Pataki

photos.app.goo.gl

New video by Peter Pataki

photos.app.goo.gl

And you can find here the whole mdat file: https://drive.google.com/file/d/13LyxpPVmqNyLQgZGX7KXAmOLbb3fQfvu/view?usp=sharing

I must say that I am simply blown away.....IMHO these speaker is the price/value champion in the full range category; I have never seen/heard anything like this before

How have you set up the rears... mounted directly against the rear wall or corners? If you don't mind, a photo or diagram of your rear setup configuration would be appreciated as well.

 

[ppataki]

How have you set up the rears... mounted directly against the rear wall or corners? If you don't mind, a photo or diagram of your rear setup configuration would be appreciated as well.

Hi @ernestcarl
The photos have already been shared a few posts ago: https://audiosciencereview.com/foru...based-rear-speaker-project.41687/post-1504326

They are mounted on the side wall, basically in line with my ears

 

[ppataki]

This is how the room looks like with my 4.0 setup

This wide-angle photo is distorting like hell; in reality the front ones look much bigger and the rear ones look much smaller

 

[MontyGibbon]

...felts sheets and then used wad for filling...

Really interesting thread. Thank you.

From later posts, I gather the wadding is important to achieve the desired frequency response. Can you provide a little more insight about the extent to which you packed the wadding?

 

[ppataki]

Really interesting thread. Thank you.

From later posts, I gather the wadding is important to achieve the desired frequency response. Can you provide a little more insight about the extent to which you packed the wadding?

The wad helps the driver 'see' the cabinet bigger than it is hence it increases low-end extension
I have filled the cabinets heavily but paying attention that it shall not get in contact with the diaphragm on the inside

Actually more important than wad is the DSP correction - that is the most important factor in linearizing the response of the driver and applying further low-end extension if needed

 

[diyhobby]

This is how the room looks like with my 4.0 setup

View attachment 274555

This wide-angle photo is distorting like hell; in reality the front ones look much bigger and the rear ones look much smaller

are you using a subwoofer or the Fr 8" is giving enough basss

 

[ppataki]

are you using a subwoofer or the Fr 8" is giving enough basss

At the time this photo was taken I was not using a sub
The sub channel was downmixed to the 15" fronts
The rear channels were handled by the 8" SBs with a high-pass filter at 40Hz (no bass redirection whatsoever)

In my current system (see my signature) I do have a sub but only the fronts are redirected (below 80Hz) the rears are not (the 40Hz HPF is still applied)

 

[WohnW]

The wad helps the driver 'see' the cabinet bigger than it is hence it increases low-end extension
I have filled the cabinets heavily but paying attention that it shall not get in contact with the diaphragm on the inside

Actually more important than wad is the DSP correction - that is the most important factor in linearizing the response of the driver and applying further low-end extension if needed

@ppataki Peter, it's over year since you published your findings on SB Acoustics SB20FRPC30. I would like to know if you sustain your positive opinion on this driver one year later? I recently bought this speaker and I am highly impressed. You showed performance in 23 liter enclosure (in quite surprising, flat front-rear shape). I am considering to make more "classic" shape like 250mm wide X 330mm deep (towards wall behind) and 480mm tall that brings me to 39 liters. SEALED, but not much damping material. Just 25mm thick, self adhesive, trapezoid shape acoustic foam. It's gonna be 18mm plywood not MDF, so rigidity of enclosure is gonna be higher. I would like to ask you to share your valuable opinion on such concept. Perhaps you have some advices that will make me to change design assumptions?
Thanks in advance

 

[ppataki]

@ppataki Peter, it's over year since you published your findings on SB Acoustics SB20FRPC30. I would like to know if you sustain your positive opinion on this driver one year later? I recently bought this speaker and I am highly impressed. You showed performance in 23 liter enclosure (in quite surprising, flat front-rear shape). I am considering to make more "classic" shape like 250mm wide X 330mm deep (towards wall behind) and 480mm tall that brings me to 39 liters. SEALED, but not much damping material. Just 25mm thick, self adhesive, trapezoid shape acoustic foam. It's gonna be 18mm plywood not MDF, so rigidity of enclosure is gonna be higher. I would like to ask you to share your valuable opinion on such concept. Perhaps you have some advices that will make me to change design assumptions?
Thanks in advance

Hi @WohnW
A lot of things have happened since last year
I am now using totally different speakers both in my living room and in my home office

But to answer your question: it is a definitive YES
I am still saying that you cannot buy a better price/value ratio 8" full range driver - period. This driver is easily worth at least 3 times the money that is costs...
I sold the rear pairs to one of my acquaintances who is using them as rear speakers in his new DIY home cinema system where the LCRs are also using this same driver + I have another acquaintance who also built his whole HT system using these drivers. Both of them are raving about the quality - and that is for a reason.
Last week I went to the first to calibrate his system with Dirac Live - it was a jaw-dropping experience I can tell you. I have heard systems that cost literally a 100 times more and they did not sound this great.

The other pair that was in my home office got bought by a guy who called me several times afterwards, saying how incredibly great these speakers were

With regards to the design: using a sealed cabinet is the way forward, definitely. Forget about ported boxes (all the above mentioned systems are also using these drivers in sealed cabinets)
If you put these drivers in a 39 liter box you will literally need only a handful of watts to drive them to xmax - so basically any amp will be able to drive them.
Nowadays I use vibrodamping sheets (4mm thick) and 10mm thick felt in my cabinets. And then for filling material I replaced wad with melamine foam - I would strongly recommend those, watch this.
Also for a cabinet with this size I would consider adding some bracing - at least one towards the middle
Good luck! I am sure you will love the sound (use Dirac Live or equivalent though to tame the response)

 

[WohnW]

Hi @WohnW
A lot of things have happened since last year
I am now using totally different speakers both in my living room and in my home office

But to answer your question: it is a definitive YES
I am still saying that you cannot buy a better price/value ratio 8" full range driver - period. This driver is easily worth at least 3 times the money that is costs...
I sold the rear pairs to one of my acquaintances who is using them as rear speakers in his new DIY home cinema system where the LCRs are also using this same driver + I have another acquaintance who also built his whole HT system using these drivers. Both of them are raving about the quality - and that is for a reason.
Last week I went to the first to calibrate his system with Dirac Live - it was a jaw-dropping experience I can tell you. I have heard systems that cost literally a 100 times more and they did not sound this great.

The other pair that was in my home office got bought by a guy who called me several times afterwards, saying how incredibly great these speakers were

With regards to the design: using a sealed cabinet is the way forward, definitely. Forget about ported boxes (all the above mentioned systems are also using these drivers in sealed cabinets)
If you put these drivers in a 39 liter box you will literally need only a handful of watts to drive them to xmax - so basically any amp will be able to drive them.
Nowadays I use vibrodamping sheets (4mm thick) and 10mm thick felt in my cabinets. And then for filling material I replaced wad with melamine foam - I would strongly recommend those, watch this.
Also for a cabinet with this size I would consider adding some bracing - at least one towards the middle
Good luck! I am sure you will love the sound (use Dirac Live or equivalent though to tame the response)

Hi @WohnW
A lot of things have happened since last year
I am now using totally different speakers both in my living room and in my home office

But to answer your question: it is a definitive YES
I am still saying that you cannot buy a better price/value ratio 8" full range driver - period. This driver is easily worth at least 3 times the money that is costs...
I sold the rear pairs to one of my acquaintances who is using them as rear speakers in his new DIY home cinema system where the LCRs are also using this same driver + I have another acquaintance who also built his whole HT system using these drivers. Both of them are raving about the quality - and that is for a reason.
Last week I went to the first to calibrate his system with Dirac Live - it was a jaw-dropping experience I can tell you. I have heard systems that cost literally a 100 times more and they did not sound this great.

The other pair that was in my home office got bought by a guy who called me several times afterwards, saying how incredibly great these speakers were

With regards to the design: using a sealed cabinet is the way forward, definitely. Forget about ported boxes (all the above mentioned systems are also using these drivers in sealed cabinets)
If you put these drivers in a 39 liter box you will literally need only a handful of watts to drive them to xmax - so basically any amp will be able to drive them.
Nowadays I use vibrodamping sheets (4mm thick) and 10mm thick felt in my cabinets. And then for filling material I replaced wad with melamine foam - I would strongly recommend those, watch this.
Also for a cabinet with this size I would consider adding some bracing - at least one towards the middle
Good luck! I am sure you will love the sound (use Dirac Live or equivalent though to tame the response)

Dear Peter, thank you for taking time to answer my questions. I am using DSP. I am using EL84 tube single ended amp => around 4W. So far I found it more than enough to drive my current speakers with sufficient volumes (hovewer my current are 94dB effective). Do you think such amp will be good as well for SB Acoustics?
Additionaly I would like to focus at damping material for the moment - I have very good experiances with 20 mm thick special self adhesive acoustic foam (see picture please). Do you think it's good idea? Do you think I need bitumic damping layer underneeth, having in mind my construction is going to be plywood not MDF => way stiffer?
And finally - one thing makes me courious - you are not the first person who mention that closed cabinet is a way to go, BUT if you loot at WinISD or Basta simulation they seems not to confirm this opinions. If to believe WinISD it will roll down already at 60Hz (Basta shows more-less the same). Is it realistic to get 40Hz with not excessive DSP support?

 

[ppataki]

Dear Peter, thank you for taking time to answer my questions. I am using DSP. I am using EL84 tube single ended amp => around 4W. So far I found it more than enough to drive my current speakers with sufficient volumes (hovewer my current are 94dB effective). Do you think such amp will be good as well for SB Acoustics?
Additionaly I would like to focus at damping material for the moment - I have very good experiances with 20 mm thick special self adhesive acoustic foam (see picture please). Do you think it's good idea? Do you think I need bitumic damping layer underneeth, having in mind my construction is going to be plywood not MDF => way stiffer?
And finally - one thing makes me courious - you are not the first person who mention that closed cabinet is a way to go, BUT if you loot at WinISD or Basta simulation they seems not to confirm this opinions. If to believe WinISD it will roll down already at 60Hz (Basta shows more-less the same). Is it realistic to get 40Hz with not excessive DSP support?

This is where things start to get a bit complicated....

Cabinet size, cabinet type (sealed or ported) and power need are all related
Without going much into the details, first check my post in this same thread about the design simulations that I did.

There you can see that when this speaker is put into a sealed cabinet of approx. 14 litres the xmax in the low-end will be reached with 65W of power. This means that whatever happens you will get a max SPL of 97dB at 40Hz at 1 meter for 1 speaker (103dB for 2 speakers) with this configuration (or 88.5dB at 24Hz) + room gain!
For 39 liter the max. input power will be 10W to reach xmax at 20Hz so your 4W amps might not be able to drive these speakers fully, especially if you apply DSP that will elevate the low-end. But definitely give it a try, it might work.

Regarding sealed vs ported: sealed boxes can go down to 0Hz in any room, theoretically speaking (there is a great thread about that here on ASR by René - Acculution.com)
These speakers in my living room could easily go down to 24Hz when placed correctly/strategically - see that here
You might need to apply some low-shelf filter to help with that though - this is why 4W might not be enough at the end of the day
If you were to use a ported cabinet you might not need that shelf filter and less power will be enough - but your speakers will not go that deep, they will have a much worse phase response (and hence impulse and step response), a much worse impedance response and a much worse group delay response
Speaker design is all about compromise...

Regarding the damping - I use the vibrodamping sheets since they will make the cabinet resonate less and they will make the cabinet more 'soundproof' (=they will minimize the sound coming through the walls - since sound shall only come through the drivers and not the cabinet). So this is not only about rigidity but these other factors that I just mentioned.
Stuffing the cabinet with wad or melamine foam is needed again for a different reason: for the driver to 'see' the cabinet bigger - the stuffing will act as if the cabinet got bigger --> the driver will go deeper since more excursion will be enforced
And since a 480mm cabinet is not small I would also add one bracing close to the middle to further reduce resonances
I hope this helps