# SB20FRPC30-8 based rear speaker project

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#### ppataki

##### Addicted to Fun and Learning
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

##### Active Member
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

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#### ppataki

##### Addicted to Fun and Learning
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

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#### ppataki

##### Addicted to Fun and Learning
@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:

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)

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#### jamescarter1982

##### Active Member
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

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#### ernestcarl

##### Major Contributor
@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:

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.

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#### ppataki

##### Addicted to Fun and Learning
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

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#### MontyGibbon

##### New Member
...felts sheets and then used wad for filling...

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?

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#### ppataki

##### Addicted to Fun and Learning

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

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