SB20FRPC30-8 based rear speaker project

[ppataki]

I am venturing into my next project: replacing my truncated line array rear speakers with SB Acoustics SB20FRPC30-8 based loudspeakers

Here are the drivers:

This last picture is to compare the driver with my Markaudio CHR120 in my home office.

The cabinet will be sealed and made of 18mm MDF - to be as eco as possible we will downsize a pair of spare cabinets from one of my previous projects
Cabinet size will be 48 x 33 x 15 cm, listening distance will be ~120 cm

Max power handling will be 65W (xmax limited)

That will produce a max SPL of 97dB at 40Hz at 1 meter for 1 speaker (103dB for 2 speakers)
At 24Hz this is 88.5dB for 1 speaker (94.5dB for 2 speakers)

Impedance:

Group delay:

Construction will hopefully start in a few weeks' time; stay tuned!

 

[ppataki]

Quick update: build is progressing quite well!

 

[ppataki]

Carpentry is finally finished!
The babies are now in my garage so things should speed up from now on....

 

[ppataki]

Some more pictures about the inside:

Used silicone to prevent air leakage (at least those that could potentially occur at the edges)

Then applied vibrodamping sheets

Then felts sheets and then used wad for filling (forgot to take a picture of the latter)

Here is a video about how it sounds - no heavy DSP was applied yet, just some shelf filters to enhance the lows and the highs

New video by Peter Pataki

photos.app.goo.gl

(I would recommend listening with headphones)

I must say I am pretty impressed!! This might actually turn out to be a better driver than my Markaudio CHR120...will see

Next steps: will do some air leakage tests tomorrow and shortly after fixing that I am planning to post some measurements pre and post full correction

 

[ppataki]

So the cabinets are now fully painted (4 layers of ultra-matte white chalk paint) and in their final location, in my living room as rear speakers!

Now let's see the measurements!
(performed at MLP)

This is how the frequency response looks like before/after full DSP correction
I have to quickly add that although it looks as if these speakers can only go down to 40Hz, actually that is totally due to the room and the placement
Here is another measurement I did in my home office (where the video was shot in my above post):

In that room/placement they easily go down to 25Hz at -3dB

Back to the living room, here is the distortion:

Step response:

IR:

Waterfall:

Wavelet:

Overall I am very satisfied with the sound: full, live, detailed sound; I can hear every nuance-effects in the movies and the 'bubble-like' experience (when you feel like you are in a bubble of sound fully immersing you) is extremely cool too!
I can highly recommend these drivers - unbelievably great price/value ratio! I would even go as far as to say that these are one of the best 8-inch fullrange speakers out there

With this I consider this project finished; any comments/questions are welcome

 

[ernestcarl]

I have to quickly add that although it looks as if these speakers can only go down to 40Hz, actually that is totally due to the room and the placement

I find for surrounds it does not matter so much that they reach down so low. In fact, when simply upmixing stereo LR content to MCH, the upmixed, decorrelated surround signals has less issues with causing bass cancellations after high passing around or above 140Hz.

 

[ppataki]

I find for surrounds it does not matter so much that they reach down so low. In fact, when simply upmixing stereo LR content to MCH, the upmixed, decorrelated surround signals has less issues with causing bass cancellations after high passing around or above 140Hz.

Well, actually there is quite a lot of content in movies down to 30-40Hz in all the rear channels (I know since I have run FR analysis on multiple movies), hence my design goal here was to be flat to 40Hz at least.

 

[ernestcarl]

Well, actually there is quite a lot of content in movies down to 30-40Hz in all the rear channels (I know since I have run FR analysis on multiple movies), hence my design goal here was to be flat to 40Hz at least.

Yes, for MCH content there indeed can be… although one can push some of the lower frequencies to a sub as well if using bass management.

 

[TNT]

Can you please also display a distortion graph from the same measurement as above?

//

 

[ppataki]

@TNT As you can see on the FR graph, there is no content below 40Hz hence distortion is skyrocketing there, hence I published distortion data from 40Hz onwards
btw in real-life conditions I am applying a HPF at 40Hz to remove all the content from the incoming signal too

Having said that, I will perform some additional measurements by placing these cabinets in a different (=much more ideal) location in the same room - based on my experience they will go down to 25Hz (0dB) there; distortion data <40Hz will make sense in that case

 

[TNT]

Truly sorry - i missed the distortion graph!!

Was this a calibrated spa mic - was it a 75 dBA? What distance?

Thanks.

//

 

[ppataki]

No worries!

Calibrated UMIK-1 mic
75dB at 1.7m

 

[jamescarter1982]

would you puck this or the fane 15300 tc for sound quality / enjoyment or how would you compare them ?
I understand this driver has a smooth off axis did you find that to be the case
thanks James

 

[ppataki]

would you puck this or the fane 15300 tc for sound quality / enjoyment or how would you compare them ?
I understand this driver has a smooth off axis did you find that to be the case
thanks James

Very hard to answer.....
They are two different animals - I would rather compare this driver to my CHR120 based system in my home office
I would choose this driver over that one because:
- it has a much larger surface area hence cone displacement is smaller to achieve the same SPL
- the air leakage of the SB is smaller (the CHR120 leaks a lot at the dustcap)
- it costs half compared to the CHR120

But if I had to compare the SB with the 15" Fane I would definitely choose the big one - my experience tells me that with full range drivers the bigger the better
Why? For me the bigger ones sound more effortless, they tend to have a way higher sensitivity, much lower cone displacement and hence an overall 'better' sound
Regarding directivity: to be honest I don't care (I know I should but I simply don't) - I am happy to make that compromise - after all I believe that there must be a compromise somewhere at the end of the day

 

[ppataki]

Very hard to answer.....
They are two different animals - I would rather compare this driver to my CHR120 based system in my home office
I would choose this driver over that one because:
- it has a much larger surface area hence cone displacement is smaller to achieve the same SPL
- the air leakage of the SB is smaller (the CHR120 leaks a lot at the dustcap)
- it costs half compared to the CHR120

But if I had to compare the SB with the 15" Fane I would definitely choose the big one - my experience tells me that with full range drivers the bigger the better
Why? For me the bigger ones sound more effortless, they tend to have a way higher sensitivity, much lower cone displacement and hence an overall 'better' sound
Regarding directivity: to be honest I don't care (I know I should but I simply don't) - I am happy to make that compromise - after all I believe that there must be a compromise somewhere at the end of the day

btw if you google this subject of this SB driver vs the CHR120 there is a gentleman in Japan who tried these (+ some others too) and came to the same conclusion as me (i.e. the SB is 'the best' in the 6-8" league)

 

[jamescarter1982]

Very hard to answer.....
They are two different animals - I would rather compare this driver to my CHR120 based system in my home office
I would choose this driver over that one because:
- it has a much larger surface area hence cone displacement is smaller to achieve the same SPL
- the air leakage of the SB is smaller (the CHR120 leaks a lot at the dustcap)
- it costs half compared to the CHR120

But if I had to compare the SB with the 15" Fane I would definitely choose the big one - my experience tells me that with full range drivers the bigger the better
Why? For me the bigger ones sound more effortless, they tend to have a way higher sensitivity, much lower cone displacement and hence an overall 'better' sound
Regarding directivity: to be honest I don't care (I know I should but I simply don't) - I am happy to make that compromise - after all I believe that there must be a compromise somewhere at the end of the day

thanks I remember you saying before that you Don't care about off axis I just wondered if you'd noticed the sb having good off axis performance I like listening to music while I'm walking around and Don't like it if the balance changes alot while I'm moving about the place . was thinking one forward firing and one upwards firing in say 100 litres sealed .
it would require 4 of these to roughly match the sd of the fane ... maybe some kind of mini line array with these could be cool and still quite narrow

 

[ppataki]

thanks I remember you saying before that you Don't care about off axis I just wondered if you'd noticed the sb having good off axis performance I like listening to music while I'm walking around and Don't like it if the balance changes alot while I'm moving about the place . was thinking one forward firing and one upwards firing in say 100 litres sealed .
it would require 4 of these to roughly match the sd of the fane ... maybe some kind of mini line array with these could be cool and still quite narrow

I did an experiment for you: I was walking around in the living room while playing music from the 15" Fane and then I did the same with the 8" SB
There was no noticeable difference, to be honest.....

I would try a Bessel array (using five SB drivers in a sealed cabinet)
This is what you will get in a 95 liter box:

Almost 100dB (=106dB for stereo) at 24Hz at 110W max power

There would be two caveats:
- the total impedance would be 2.28 ohms due to the special wiring of the Bessel array
- the acoustic summation of the drivers would require a greater distance - I cannot simulate that but there are smarter people here who can

Alternatively one could try a normal truncated line array as well using 4 or 6 drivers but again, I am not sure about the required listening distance

 

[jamescarter1982]

I did an experiment for you: I was walking around in the living room while playing music from the 15" Fane and then I did the same with the 8" SB
There was no noticeable difference, to be honest.....

I would try a Bessel array (using five SB drivers in a sealed cabinet)
This is what you will get in a 95 liter box:

View attachment 272332

Almost 100dB (=106dB for stereo) at 24Hz at 110W max power

There would be two caveats:
- the total impedance would be 2.28 ohms due to the special wiring of the Bessel array
- the acoustic summation of the drivers would require a greater distance - I cannot simulate that but there are smarter people here who can

Alternatively one could try a normal truncated line array as well using 4 or 6 drivers but again, I am not sure about the required listening distance

thank you so is that 5 in the 95 litre box ? might be worth buying a few to experiment with they're so cheap and the 15300 tc is no longer available

 

[ppataki]

thank you so is that 5 in the 95 litre box ?

Yes it is

 

[jamescarter1982]

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