Building a sub (kinda big)

[Haaspac]

amp - Strassacker: Speaker Building, Components

sub - Strassacker: Speaker Building, Components

building instructions - Strassacker: Speaker Building, Components

I have all the stuff except for the MDF. Is there anything we could do to really jazz it up or just follow the directions to a T?

Thoughts, suggestions, comments?

My dad and I have our work cut out for us it seems.

 

[Haaspac]

Sorry, on the building instructions link, just scroll down to the very bottom and click "building instructions"

 

[TLS Guy]

amp - Strassacker: Speaker Building, Components

sub - Strassacker: Speaker Building, Components

building instructions - Strassacker: Speaker Building, Components

I have all the stuff except for the MDF. Is there anything we could do to really jazz it up or just follow the directions to a T?

Thoughts, suggestions, comments?

My dad and I have our work cut out for us it seems.

I have found the T/S parameters of your driver. It is not a sub driver but an instrument speaker, which Monacor are known for.

The driver has a very poor xmax and the published graphs look optimistic by my dead reckoning.

The idea of series resistances to change Q for different cabinets is a very bad one and wasteful.

I will model that driver later, when I get a chance and work out the optimal cabinet and true specifications.

At first glance this does not look like a good project. Subs of European origin are not usually anything to get enthused about.

 

[GranteedEV]

The driver has a very poor xmax and the published graphs look optimistic by my dead reckoning.

13mm of xmax is plenty for an 18" driver, especially one that will be vented. It's comparable to a 12" subwoofer with 31.5mm of xmax, except that 12" sub would be much less efficient too - probably 8db less efficient. That's the difference between 400 watts and around 2400 watts!

The idea of series resistances to change Q for different cabinets is a very bad one and wasteful.

Agreed. Better to equalize these things actively rather than try to convert the extra efficiency up to into heat just to get a higher Q.

Anyways I modelled this driver up. I think it's a pretty good driver but tuning it correctly requires a very long and also large port, which will limit your upper bandwidth to around 80hz or so. This is because these is a port resonance at around 150hz.

You will also need to equalize its frequency response if your room is not favorable with respect to room gain. Due to its low qts is starts to roll off very early. Referenced at 80hz, its F3 appears to only be 43hz or so. Not really a problem as long as you realize that its F6 is below 20hz! This is something that good room interaction could be agreeable with.

Woofer displacement curve shows a tuning frequency at about 18hz. With 400 watts input xmax is not even approached until 15hz:

Frequency Response graph shows SPL with 400 watts input to be above 114db above 20hz. You can see the effect of the low QTS (or more accurately - the high midbass efficiency) on the response above 40hz. What this will actually sound like will depend on your room and the crossover used to integrate this sub to the main speakers

.

The box modelled had internal dimensions of 36 inch x 22 inch x 23 inch. It also has a large 40 inch long vent with 410cm^2 of cross-section area. The vent alone will take some considerable real-estate NOT including the size of the box. I would do a 22 inch x 2.9 inch slot vent and fold it around the outside of the box to get the 40 inch length. The large port helps keep vent speeds very low, even at 400 watts:

 

[Haaspac]

Ok I read what you guys wrote and I pretty much don't understand a word of it. What I get from it is, TLSguy says its a mediocre sub, and GranteedEV says its probably pretty decent.

So my next questions is, do I just build the box as the instructions show on the webpage, or do I ask one of you very nice and very knowledgeable scholarly gentlemen to draw me up a new/better box and build that one? I can build anything, I just need a blueprint.

 

[GranteedEV]

do I just build the box as the instructions show on the webpage, or do I ask one of you very nice and very knowledgeable scholarly gentlemen to draw me up a new/better box and build that one? I can build anything, I just need a blueprint.

I didn't really examine the box with instructions. What I modelled was what I found to be a very good box for the driver. Making a blueprint out of that should be pretty straightforward if you're interested.

 

[TLS Guy]

I have done two models of your sub.

I have done two vented alignments, one 3.412 cu.ft and the other 7.197 cu.ft.

As I suspected, since this is a high sensitivity low Q driver, it has poor bass extension. However, it does have high output as a consequence.

It is impossible with ported loading to get the 3 db roll off point below the mid 40 Hz range. So the specs do guild the Lilly.

The larger extended bass alignment does give you another 10 db of output at 20 Hz, so there is an advantage in the larger cabinet.

I modeled both coils in parallel. I do not know the diameter of the supplied ports, but the ports I specified give a vent velocity of 18 m/sec for both designs, with a length that will fir in the box. This really is the minimum port area or you will have port chuffing.

If you want a sub with a lot of output and pretty tight, as driver Qt is low, then this will fit the bill.

There is an inverse relationship between bass extension and flux density and therefore sensitivity.

This driver would make an excellent horn loaded sub, but then it would be really big!

I can't make my files small enough to load, without going to the work of putting them on my website. The upload limit for this site is way too small.

But here is the raw data.

Smaller box.

Name: SPH-450TC
Type: Standard one-way driver
Company: Monacor
No. of Drivers = 1
Dual voice coils = parallel
Fs = 20 Hz
Qms = 2.97
Vas = 480 liters
Cms = 0.22 mm/N
Mms = 305 g
Rms = 12.7 kg/s
Xmax = 12.9 mm
Xmech = 19.35 mm
P-Dia = 397.3 mm
Sd = 1250 sq.cm
P-Vd = 1.613 liters
Qes = 0.27
Re = 1.85 ohms
Le = 1.1 mH
Z = 2 ohms
BL = 16.2 Tm
Pe = 700 watts
Qts = 0.25
no = 1.37 %
1-W SPL = 93 dB
-----------------------------------------
Box Properties
Name:
Type: Vented Box
Shape: Prism, square (optimum)
Vb = 3.412 cu.ft
Fb = 28.89 Hz
QL = 6.478
F3 = 43.09 Hz
Fill = minimal
No. of Vents = 8
Vent shape = round
Vent ends = one flush
Dv = 2 in
Lv = 21.37 in

Larger box.

Name: SPH-450TC
Type: Standard one-way driver
Company: Monacor
No. of Drivers = 1
Dual voice coils = parallel
Fs = 20 Hz
Qms = 2.97
Vas = 480 liters
Cms = 0.22 mm/N
Mms = 305 g
Rms = 12.7 kg/s
Xmax = 12.9 mm
Xmech = 19.35 mm
P-Dia = 397.3 mm
Sd = 1250 sq.cm
P-Vd = 1.613 liters
Qes = 0.27
Re = 1.85 ohms
Le = 1.1 mH
Z = 2 ohms
BL = 16.2 Tm
Pe = 700 watts
Qts = 0.25
no = 1.37 %
1-W SPL = 93 dB
2.83-V SPL = 99.87 dB
-----------------------------------------
Box Properties
Name:
Type: Vented Box
Shape: Prism, square (optimum)
Vb = 7.197 cu.ft
Fb = 21.98 Hz
QL = 5.652
F3 = 44.71 Hz
Fill = minimal
No. of Vents = 8
Vent shape = round
Vent ends = one flush
Dv = 2.25 in
Lv = 21.85 in

 

[GranteedEV]

Two 4 ohm voice coils in parallel would give a 2 ohm load. I modelled in series for a nominal 8 ohm.

 

[Haaspac]

A large cabinet is no big deal, I imagined I would be building a refrigerator sized box anyway. My towers are 96liters each, I'm guessing the sub would be over 200liters easy. Could the two of you swap prints and see what would work best? When you say vented, do you mean a rectangular slot vent and toss out the bass reflex tubes I have or use them? I can probably get you a diameter and length of the 8 tubes after work today if they will be used.

 

[TLS Guy]

Two 4 ohm voice coils in parallel would give a 2 ohm load. I modelled in series for a nominal 8 ohm.

It changes impedance and sensitivity, but nothing else.

Name: SPH-450TC
Type: Standard one-way driver
Company: Monacor
No. of Drivers = 1
Dual voice coils = series
Fs = 20 Hz
Qms = 2.97
Vas = 480 liters
Cms = 0.22 mm/N
Mms = 305 g
Rms = 12.7 kg/s
Xmax = 12.9 mm
Xmech = 19.35 mm
P-Dia = 397.3 mm
Sd = 1250 sq.cm
P-Vd = 1.613 liters
Qes = 0.27
Re = 7.4 ohms
Le = 4.6 mH
Z = 8 ohms
BL = 32.4 Tm
Pe = 700 watts
Qts = 0.25
no = 1.371 %
1-W SPL = 93.52 dB
2.83-V SPL = 93.86 dB
-----------------------------------------
Box Properties
Name:
Type: Vented Box
Shape: Prism, square (optimum)
Vb = 3.412 cu.ft
Fb = 28.89 Hz
QL = 6.478
F3 = 43.17 Hz
Fill = minimal
No. of Vents = 8
Vent shape = round
Vent ends = one flush
Dv = 2 in
Lv = 21.37 in


Name: SPH-450TC
Type: Standard one-way driver
Company: Monacor
No. of Drivers = 1
Dual voice coils = series
Fs = 20 Hz
Qms = 2.97
Vas = 480 liters
Cms = 0.22 mm/N
Mms = 305 g
Rms = 12.7 kg/s
Xmax = 12.9 mm
Xmech = 19.35 mm
P-Dia = 397.3 mm
Sd = 1250 sq.cm
P-Vd = 1.613 liters
Qes = 0.27
Re = 7.4 ohms
Le = 4.6 mH
Z = 8 ohms
BL = 32.4 Tm
Pe = 700 watts
Qts = 0.25
no = 1.371 %
1-W SPL = 93.52 dB
2.83-V SPL = 93.86 dB
-----------------------------------------
Box Properties
Name:
Type: Vented Box
Shape: Prism, square (optimum)
Vb = 7.197 cu.ft
Fb = 21.98 Hz
QL = 5.652
F3 = 44.64 Hz
Fill = minimal
No. of Vents = 8
Vent shape = round
Vent ends = one flush
Dv = 2.25 in
Lv = 21.85 in

 

[TLS Guy]

A large cabinet is no big deal, I imagined I would be building a refrigerator sized box anyway. My towers are 96liters each, I'm guessing the sub would be over 200liters easy. Could the two of you swap prints and see what would work best? When you say vented, do you mean a rectangular slot vent and toss out the bass reflex tubes I have or use them? I can probably get you a diameter and length of the 8 tubes after work today if they will be used.

The larger box works best. If you look at the data the port tubes are specified.

The air vent velocities are acceptable in both my models.

I don't know the inside diameter or length of your tubes, or is they are flared or not.

For maximum bass output you need the larger box as output is significantly greater below 40 Hz with the larger extended bass alignment. You will get away with an extended bass alignment with this driver as it is very low Q.

There is no point making the box bigger. My larger design maximizes the bass output of that driver. That is the limit of what is possible with that driver with reflex alignment.

Now remember you have to add the volume of air, your braces, the port volumes and the amp displacement have to be added to my box volume for your final volume. Half the internal surface of the box should be lined with Polyfill.

If you PM me your Email I will send you the files with the graphs.

Are you going to use the coils in parallel or series?

 

[Haaspac]

Sorry about being kinda absent from the discussion for a few days, I have been very busy. TLSguy I looked at those files but I'm not really sure how to take those numbers and graphs and design a box around them. I appreciate the help, and the numbers and graphs look impressive, I just don't have skills to design a box around that information. The DIY stuff I did before was from Visaton where I just bought the stuff and built everything from instuctions, so I am very new to this "design and build a sub box from scratch" stuff.

 

[GranteedEV]

Sorry about being kinda absent from the discussion for a few days, I have been very busy. TLSguy I looked at those files but I'm not really sure how to take those numbers and graphs and design a box around them. I appreciate the help, and the numbers and graphs look impressive, I just don't have skills to design a box around that information. The DIY stuff I did before was from Visaton where I just bought the stuff and built everything from instuctions, so I am very new to this "design and build a sub box from scratch" stuff.

You just want some blueprints? When I get time tommorow i'll try to do that for you. Can you post the dimensions of the vents that you already have? I don't know if they'll work or not but we can give it a shot.

 

[TLS Guy]

You just want some blueprints? When I get time tommorow i'll try to do that for you. Can you post the dimensions of the vents that you already have? I don't know if they'll work or not but we can give it a shot.

That is really nice of you. I have so many irons in the fire right now, I do not have the time for blue prints.

I did Email the OP the two designs I did as pdfs. I have also carefully explained how you get the Vt from Vb

He has not got back to me on the port dimensions, he did say, that although there are 8 tubes, they join together to make four ports.

When I get the dimensions of the ports, I will rerun the designs, and check tuning and vent velocity. Vent velocity is already at the top end with 8 ports, so a slot vent may well be required to stop chuffing.

 

[GranteedEV]

That's my concern too. I'm very confortable however with the slot vent I highlighted in post number 4.