# 4x SB34NRX75-6 subs



## Ride154 (May 14, 2016)

Hi Guys n Gals,
There is a possibility that I can get an nice deal on 4 Sb Acoustics subs, the *SB34NRX75-6.*
I recently saw a thread on (i think) ASR on dual opposed subs configurations.
The steady cabinets sound ideal for 2 beautiful home made sidetables next to the sofa with the 4 subs in it.
But I'm a bit of a noob when it comes to doing the math if the output of the 4 subs will be sufficient.
I don't have an amp yet but I would like to power the 4 subs with a Hypex FA 502.
The cabinets will be 136 liters on the outside and approx 40 x 40 x 84 cm's so they nicely besides the couch.

Below the specs of the amp
Output power in 4 at < 0,1% THD+N:Ω
FA502: 2x 500 Wrms
BTL 1 kW @ 4 /1.2 kW @ 8Ω Ω 

So can some one give me a hand with the following questions
Will there be enough output?
How to wire the 4 subs?
SB says they are 4 Ohms, so i thought to wire each cabinet to 2 or 8 ohms and then between the cabinets back to 4 ohms and use Bridge mode on the amp.
How much power will each subs get?
Will the cabinets sturdy enough with 25 mm plywood/mdf?
Will the need bracing on the inside?

The specs for the subs are here
https://sbacoustics.com/wp-content/uploads/2020/02/12in-SB34NRX75-6.pdf

The 4 subs will complement 4 modified Scandyna Minipods with SB tweeters and mids.
They are still a work in progress but the tweeter will be the* SB26ADC-C000-4 *and the mids* SB15NBAC30-4.*
Each is powered by a Hypex FA 252 amp and there is one in each corner of my living room which is 6 x 7 meters.

Hoping to hear from you and greetings from the Netherlands, Menno.


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## mrexcitement (Jan 23, 2019)

According to winISD you should have about 100db at 13.5hz and around 120db at 50hz , so yes plenty of output , you can wire them exactly as you mentioned , so each cabinet is either 2 ohms or 8 ohms and then parallel or serial connection to end up with a total 4 ohm load , each sub would see about 115wrms.

Even with 25mm mdf or plywood I would be adding internal bracing , you need the boxes to be as solid as possible and resonance free for best performance , you can never have too much internal bracing.

I am very much a fan of SB Acoustics , very good value for money with exceptional performance , my main speakers are these SBA-761


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## Ride154 (May 14, 2016)

Thx for your reply!
Can you please explain how you get to 115 wrms per sub from 2x500 or 1x1000 wrms?
Did I mention that the cabinets will be closed and not vented?
In car audio terms 115 wrms is nothing for a sub or have I been using the wrong subs al those years?

Those are beautiful towers!
I've seen those before at Troels site.
Did you build them yourself?


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## mrexcitement (Jan 23, 2019)

Yes I did build them myself , I used 25mm MDF so I had to change the dimensions slightly but kept the internal dimensions the same , very very nice sounding speakers , in fact the best I have ever listened too , I also changed the tweeter to the new textreme tweeter , the midrange is superb , vocals and guitar sound like they are in the room with you.

Yes the calculations were for a sealed box , personally I'm not a fan of sealed for sub duty , I always use ported as it's more efficient and just sounds better too me.

Oops sorry should have checked the amp more thoroughly , i'm not familiar with it.

So it would be about 250 wrms per driver but at those watts but you will be exceeding xmax ( maximum linear cone excursion ) as at the 115w I originally calculated for it was just reaching xmax of the drivers , they only have 11 mm xmax , as a comparison the drivers I just used in my sub build have 27 mm xmax.

You can still do it , just be carefull at high volumes and low frequencies.


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## Ride154 (May 14, 2016)

One day I will attemp a diy like yours but not here yet.

Sorry for all the questions but why does SB state 200 W as rated power handling for the sub if it can handle 115 W?
In car audio land most would say double the power for the amp what is max rated for the sub.
Or does the sub with this size of the box max out at 115W?
I already use hypex amps for the minipods, the FA252, that's 250 for the mid and 250 for the tweeter.
I can limit each channel to a max wattage, so i have the tweeter channel maxed out at 50 at the moment.
But I never have the amp higher than -24 dB and it can go to +18 dB.
At -30 dB I'm afraid I will blow something and is already ridcoulessly loud, so I would never use the full potential of the amp.

Or are you saying that I will have enough with one FA252 at 2x250W?

What sub did you use that has an xmax of 27!?!


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## mrexcitement (Jan 23, 2019)

The rating they state is the thermal rating , as in what rms wattage the voice coil is able to sustain without melting , cone excursion is dependant on the box size and whether it's ported or sealed.

The main reason they specify double the wattage is too guarantee you will have clean watts always being fed too the speaker , when an amp is driven into clipping it can burn out the voice coil very quickly even if the driver is rated for a lot higher wattage , when an amplifier is driven into clipping it is basically feeding a dc voltage to the voice coil , speakers are designed for ac only and dc fries voice coils.

Yes one FA252 would be enough and stay within the limits of the cone excursion of the driver , you can go above xmax but the distortion increases , to have the best sound quality you want to stay within xmax.

Here is my driver and build Dayton audio HE high excursion , I would have thought you would have seen this as it's in the same section as your posts.


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## Ride154 (May 14, 2016)

I did see that coffin sized box but didn't look at who's it was.
That is huge!

Thx, that clears it up.


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## dumdum (Feb 27, 2007)

You need to forget car audio subs that are generally over engineered and use 3” coils and people send them way more than rated…

try putting 250wrms into the subs full send and I suspect I know the results… definitely don’t clip them… but in reality you won’t need 250wrms per sub, I have four sealed tens from 450wrms and never use full power even on movies 👍🏼

as for 115wrms, that’s down to your box design, it’s likely too big and/or tuned too low


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## Ride154 (May 14, 2016)

dumdum said:


> as for 115wrms, that’s down to your box design, it’s likely too big and/or tuned too low


At the moment I was thinking 40 x 40 x 85 cm's external.
On the outside that would be 136 liters but with 25 mm plywood/mdf the inside is 98 liters.
I could make the 85 cm shorter and the box smaller.
Could you advice on the ideal internal volume for a dual opposed box?
I thought there is not much tuning to be done on a sealed box besides the volume?


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## mrexcitement (Jan 23, 2019)

Ride154 said:


> At the moment I was thinking 40 x 40 x 85 cm's external.
> On the outside that would be 136 liters but with 25 mm plywood/mdf the inside is 98 liters.
> I could make the 85 cm shorter and the box smaller.
> Could you advice on the ideal internal volume for a dual opposed box?
> I thought there is not much tuning to be done on a sealed box besides the volume?



It would be best if you learn to use winISD then you can experiment with different drivers and box size and see the results for yourself.

Click on New Project to start , then beside the driver selection drop down box click on new to enter the driver into the database , on the general tab enter Manufacturer and brand , same for both eg SB Acoustics then the model number for Model , click on the parameters tab up the top to go to the page where you enter the driver parameters.

The key to winISD is the order you enter driver parameters , I always do it in this order and it always works.

Qes
Vas
Qms
It will calculate Qts
Fs
Re
Sd
Xmax
Pe

The rest of the parameters it will calculate for you , only enter the parameters I listed , the rest need to be calculated , this is where so many people go wrong and have issues with using winISD , I have been using it for years with the above order of entering parameters.










Green is the parameters I entered and blue is what winISD calculated , this is for the Dayton Audio RSS390HE-22

Once your driver parameters are entered then click save and if you entered everything as i listed it will then have a popup allowing you to save , if it comes up with an error , double check that you only entered the parameters I listed , once saved it will be in the driver database for you to choose when starting a New Project.

Click on New Project and chose the driver you just entered in the drop down box , select ported or sealed , let it chose the rest and it will give you the optimum box size for the driver you have chosen , you can change the volume and tuning (if ported) to suit your requirements afterwards and see the effects.


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## Ride154 (May 14, 2016)

I tried Winisd a couple of times but always ended up with errors.
As I see in your description I probably filled in to many fields so thx for clearing that up.
And how do I calculate for a dual opposed box?
Is that like a normal box but with 2 drivers and therefore twice as big?
I read in a thread that dual opposed are 2 drivers in a box the size normaly for one driver and also doubles the output?
Tomorrow I will show my calculations and hoping you can explain a bit more.
I really would like to know how to read the needed rms, xmax and as you said the [email protected]
thx


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## dumdum (Feb 27, 2007)

Ride154 said:


> I tried Winisd a couple of times but always ended up with errors.
> As I see in your description I probably filled in to many fields so thx for clearing that up.
> And how do I calculate for a dual opposed box?
> Is that like a normal box but with 2 drivers and therefore twice as big?
> ...


What do you mean by dual opposed? Isobaric where the drivers are face to face? Or two drivers on opposite sides of the enclosure to each other?

perhaps draw what you mean…


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## mrexcitement (Jan 23, 2019)

Ride154 said:


> I tried Winisd a couple of times but always ended up with errors.
> As I see in your description I probably filled in to many fields so thx for clearing that up.
> And how do I calculate for a dual opposed box?
> Is that like a normal box but with 2 drivers and therefore twice as big?
> ...


Yes your box is just 2 drivers in a sealed cabinet , so select 2 drivers instead of 1 after clicking on New Project.

Whenever you add more drivers then the recommended box size just doubles for each additional driver from the recommended size for a single driver box. 

If you do the order I said then you shouldn't have any errors , and yes that's the mistake most make is entering too many parameters.


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## Ride154 (May 14, 2016)

dumdum said:


> What do you mean by dual opposed? Isobaric where the drivers are face to face? Or two drivers on opposite sides of the enclosure to each other?
> 
> perhaps draw what you mean…


like so, magnet to magnet ... stole this pic from the parts express forum








dual opposing subwoofers vs dual push pull design, thoughts? - Techtalk Speaker Building, Audio, Video Discussion Forum
I just googled for a pic but didn't read it yet but looks interesting
Will read soon


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## dumdum (Feb 27, 2007)

Ride154 said:


> like so, magnet to magnet ... stole this pic from the parts express forum
> View attachment 359659
> 
> dual opposing subwoofers vs dual push pull design, thoughts? - Techtalk Speaker Building, Audio, Video Discussion Forum
> ...


That doesn’t make the enclosure any different to side by side. Power handling will be the same give or take, and it may cost you a tiny amount of spl depending on orientation in the cabin


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## Ride154 (May 14, 2016)

mrexcitement said:


> The key to winISD is the order you enter driver parameters , I always do it in this order and it always works.
> 
> Qes
> Vas
> ...


This is some good stuff, finally got some results, great.




































But now offcourse ... more questions 😄

yellow line 98 ltrs
green line 130 ltrs
blue line 251 ltrs
pink 98 ltrs vented
all dual subs.

What is the differance between max spl and spl? the lines are very close together
As is looks only the blue line comes above the 22 mm xmax, what did I do wrong here? that box is 251 ltrs
Earlier you spoke about 11 mm Xmax but SB says 22









In the last 2 pic I added a 98 ltr vented box
What is happening with the excursion on the vented box? it goes all the way down to 2 at 18 Hz
And where can I read back about the 115 wrms needed?
Adding a vent looks promising


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## Ride154 (May 14, 2016)

hmm maybe not ... Port air velocity goes of the charts


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## mrexcitement (Jan 23, 2019)

Xmax is one direction , they state 22mm p-p which is peak to peak (both directions) so it's half of that which is 11mm xmax.

If you right click on the graph screen and select options you can change the scaling for each graph.

With a ported cabinet the cone excursion is at minimum at the port tuning frequency.

Max SPL uses the xmax as the limit , I just look at the SPL chart which uses the power you specified and I don't bother with the Max SPL chart


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## dumdum (Feb 27, 2007)

You have tuned to 18hz, you simply won’t get a decent port length in at that freq… if you tune it higher, say 25-30 you will then push the dip in excursion higher to match the higher tuning freq and also reduce excursion above that freq as well to hopefully bring it below 11mm one way (xmax) 👍🏼 and you will still be able to play into the 20’s until excursion runs out 👍🏼


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## Ride154 (May 14, 2016)

got it ... also added the mid in the minipod and the filters
looks promissing
but what do you guys think about port velocity for both drivers?
Will flared ports on both ends eliminate chuffing etc?
yellow = closed box 98 ltrs
cyan = ported box 98 ltrs
white = mid in 5 ltr minipod
low and highpass filters @ 80Hz


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## mrexcitement (Jan 23, 2019)

The general recommendation for port velocity is too keep it under 17 m/s, although the box I just built and I designed is 23 m/s , you need to change the scale like I mentioned so you can see the highest values.

Also depends on how hard you will push the subs as the port velocity is at the power level you specified and if you aren't going to be using that level then you can get away with a higher port velocity.

My understanding of flared ports is it needs to be quite a large flare to have any real effect and again it depends on the max wattage you will be feeding your sub , I didn't bother with the box I just built and my old subs never had any flares and I never heard any chuffing.


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## Ride154 (May 14, 2016)

Thx you both helped a lot!


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## mrexcitement (Jan 23, 2019)

Ride154 said:


> Thx you both helped a lot!



Glad to help out a fellow audio enthusiast.

Cheers

David


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