The French Bulldog - Tang Band W6 PR micro-sub

[justwill]

All,

This is my first design, rougly based on RJB's Cerberus sub. Let me know what you think.

In brief

Tang Band W6-1139SIF $50
Dayton SA70 $60
Dayton SD270 PR, with 190g mass added to the cone $25
12" cube gross (could use the PE prefab .67 cu ft cabinet)

Total cost ~ $170
F3/6/10 at 32/28/25
99 db



Design Goals

The idea was to design a small, low-budget, good looking sub that could fill out the bottom end of my Overnight Sensation MTMs. This sub will be used almost exclusively for music, and I'm an apartment dweller, so I wasn't after 25hz at 110SPL. I just wanted a clearer bottom octave, and to feel some bass. The Cerberus, with its combination of Tang Band W6-1139 and Dayton SA70, seemed to fit the bill, but that vent....it just seemed like something I didn't want to deal with. Other builders reported chuffing problems, and the 2" port looked pretty cramped in that box. I probably made too much of those challenges, as RJB's designs are well regarded and lots of folks have built the original Cerberus with no problems. Still: one obvious solution to the port problem is to use a PR. Plus, hey, it would be fun to design this around a PR.

With the help of Wolf, fastbike1, jonpike, and others, I modeled the W6 in a .55 cu ft box (the net volume of a 12" cube after subtracting amp and driver) with the SD270 10" PR, with 190g mass added to the cone. This tunes the box to 32.5hz, yielding F3/F6/F10 of 32/28/25. Models at 99dB with 70 watts, without excursion issues (once the 20hz highpass on the SA70 is factored in). So I won't be powering the neighborhood block party, but it should be enough for my needs.

Construction

It's a tight squeeze to get the driver, PR, and amp in this little box, and I had to position the amp and driver off center. But everything fits comfortably, with the PR on the side, the driver down-firing, and the amp on the back.

I wanted to dress up this little box. I built it out of 3/4 birch ply, with a douglass fir frame around a ply panel for the front. The ply panel is glued into the grooves on the frame, which eliminates potential rattling. I'm happy with how it looks: I really like the added detail of the frame on the front.

I painted the box with "French Gray" milk paint. I really love milk paint, both for its ease of application, non-toxicity, and deep, streaky color. I topcoated it with a couple coats of dewaxed shellac, which deepens the color and provides a real smooth surface (FWIW, this was my first time top-coating milk paint with shellac. I'll return to wax or oil in the future - the shellac was difficult to level in this application). I finished the base in shellac.

Hopefully I'm not being presumptuous in renaming a modified design, but I call it the French Bulldog. The name is an homage to RJB's "Cerberus" designation - Cerberus was a hellhound in Roman mythology. Mine is painted in french gray, and maybe it's not from hell, but a small, short-legged, apartment-friendly companion to my stand-mounted Overnight Sensations.



Listening Impressions

Sounds good! The French Bulldog does exactly what I want: it fills out the bottom end and makes my system sound much bigger and fuller. On one of my favorite tracks - Kort's "Invariable Heartache" - I can really hear the low double-bass plucking along, where it was muddy and undefined before. The French Bulldog goes plenty loud and low for my modest living room. I cranked it up the other day, and thought "woah, that's too loud" before I ever reached excursion limits or ran out of watts.

One final thought: I called PE today, and asked them whether the high level inputs on the SA70 simply passed the full-range signal through the plate amp to the speakers, or if it actually high-passed the signal to the speakers, thereby taking the low frequencies away from the OS MTMs. The tech told me that it's a pass-through. I'd like to be able to remove bass duty from the mains, thereby freeing them up for midrange clarity. Any thoughts on how to best accomplish this? Should I just connect an 80hz low pass crossover from the output of the plate amp to each speaker? Is it even worth my money, or should I just be happy as is?

Thanks for reading!

Justin

[evilskillit]

Re: The French Bulldog - Tang Band W6 PR micro-sub

Looking great! I'd love to have one of those as part of my PC speakers setup.

A few things. 1: The pass through on the plate amp can change the frequency response of the speakers but not in a good way. Someone once measured the difference and it wasn't pretty. But now I can't find the article so unless someone else knows what I'm talking about and posts the link you'll just have to decide whether or not to take my word for it.

2: As far as high passing your mains what are you using as a source? If you're listening from a PC you can probably do a 2.1 setup with your soundcard and high pass the mains. Otherwise you'll need either a home theater receiver that can do this, or some sort of DSP solution like a Mini-DSP. Being able to high pass the mains when a sub is involved is ideal but if you can't do it you'll probably still enjoy them just as well.

Edit: Ah, here it is. I found it. Go here and scroll down and read the part that says "Use an active crossover!"

http://www.zaphaudio.com/audio-speaker18.html

Double Edit: But the SA70 manual says this, so I guess it's just a pass through and doesn't matter.
"3.) High-Level Outputs
Speaker level passthrough outputs using spring clip type jacks to permit connection with bare wire. Used to connect from the
subwoofer amp to pass signal from the full range amp on to the main L/R speakers. Signal is only present on this output if
the high level input is also used. The signal to the L/R speakers is not filtered. The impedance “seen” by the full-range source
amplifier will be that of the connected speakers only"

[thekorvers]

Re: The French Bulldog - Tang Band W6 PR micro-sub

An NP capacitor in series with your Overnight Sensation MTM's will work. Depending on where you want to high-pass, 200 - 1,000 MFD should work. Experiment!

[thekorvers]

Re: The French Bulldog - Tang Band W6 PR micro-sub

Looking great! I'd love to have one of those as part of my PC speakers setup.

A few things. 1: The pass through on the plate amp can change the frequency response of the speakers but not in a good way. Someone once measured the difference and it wasn't pretty. But now I can't find the article so unless someone else knows what I'm talking about and posts the link you'll just have to decide whether or not to take my word for it.

2: As far as high passing your mains what are you using as a source? If you're listening from a PC you can probably do a 2.1 setup with your soundcard and high pass the mains. Otherwise you'll need either a home theater receiver that can do this, or some sort of DSP solution like a Mini-DSP. Being able to high pass the mains when a sub is involved is ideal but if you can't do it you'll probably still enjoy them just as well.

Edit: Ah, here it is. I found it. Go here and scroll down and read the part that says "Use an active crossover!"

http://www.zaphaudio.com/audio-speaker18.html

Double Edit: But the SA70 manual says this, so I guess it's just a pass through and doesn't matter.
"3.) High-Level Outputs
Speaker level passthrough outputs using spring clip type jacks to permit connection with bare wire. Used to connect from the
subwoofer amp to pass signal from the full range amp on to the main L/R speakers. Signal is only present on this output if
the high level input is also used. The signal to the L/R speakers is not filtered. The impedance “seen” by the full-range source
amplifier will be that of the connected speakers only"

The impedance peak problem John Krutke (Zaph) mentions is specific to his design using the HiVi B3S. This problem is not necessarily the case with every design as he states so himself.

I suggest the O.P. experiments some. Maybe it will sound horrible, maybe it will sound pretty good. Who knows? Either way it will be a good learning experience for him.

[justwill]

Re: The French Bulldog - Tang Band W6 PR micro-sub

Thanks for the interest.

I'm using a T-amp to power the mains. No internal crossover capabilities. And I'm hesitant to spend $100 on signal processing. Which leads me to...

An NP capacitor in series with your Overnight Sensation MTM's will work. Depending on where you want to high-pass, 200 - 1,000 MFD should work. Experiment!

Sorry, I'm really a novice at electronics terminology and theory. Can you draw or explain what it means to put a cap in series in this context? Does it mean to put the cap between the sub amp and positive input on the speaker terminal? And I'd love to experiment, but how would I decide a starting value? What happens to the crossover frequency as cap value increases or decreases?

[thekorvers]

Re: The French Bulldog - Tang Band W6 PR micro-sub

Thanks for the interest.

I'm using a T-amp to power the mains. No internal crossover capabilities. And I'm hesitant to spend $100 on signal processing. Which leads me to...



Sorry, I'm really a novice at electronics terminology and theory. Can you draw or explain what it means to put a cap in series in this context? Does it mean to put the cap between the sub amp and positive input on the speaker terminal? And I'd love to experiment, but how would I decide a starting value? What happens to the crossover frequency as cap value increases or decreases?

NP stands for Non-Polarized. The leads will not be marked + and - like a standard capacitor will. That means that the cap is not directional and rated for AC and it does not matter how (in which direction) you hook it up. A standard cap is rated for DC, the leads will be marked + and -. It can only be hooked up one way, according to polarity.

[thekorvers]

Re: The French Bulldog - Tang Band W6 PR micro-sub

Does it mean to put the cap between the sub amp and positive input on the speaker terminal?

Exactly. Go from the terminals "To Speakers - High Level Out" on the plate amp to your speakers. Put one cap in series with one of the leads.

[thekorvers]

Re: The French Bulldog - Tang Band W6 PR micro-sub

What happens to the crossover frequency as cap value increases or decreases?

The impedance of a capacitor is inversely proportional to the frequency. What that means is that impedance becomes smaller as frequency increases. So higher frequencies are passed more easily.

It also means that a higher value capacitor will pass AC easier than a lower value capacitor as the impedance of the higher value capacitor is smaller. So to lower the x-over frequency we need to increase the size of the capacitor.

The formula is: Z=1/2πfC where

Z = Impedance in Ohms
1/ = 1 divided by
π = 3.14
f = frequency in Hz
C = Capacitance in Farads

I hope this all makes sense.

Lessons to continue tomorrow.

[Wolf]

Re: The French Bulldog - Tang Band W6 PR micro-sub

Looking great! I'd love to have one of those as part of my PC speakers setup.

A few things. 1: The pass through on the plate amp can change the frequency response of the speakers but not in a good way. Someone once measured the difference and it wasn't pretty. But now I can't find the article so unless someone else knows what I'm talking about and posts the link you'll just have to decide whether or not to take my word for it.

2: As far as high passing your mains what are you using as a source? If you're listening from a PC you can probably do a 2.1 setup with your soundcard and high pass the mains. Otherwise you'll need either a home theater receiver that can do this, or some sort of DSP solution like a Mini-DSP. Being able to high pass the mains when a sub is involved is ideal but if you can't do it you'll probably still enjoy them just as well.

Edit: Ah, here it is. I found it. Go here and scroll down and read the part that says "Use an active crossover!"

http://www.zaphaudio.com/audio-speaker18.html

Double Edit: But the SA70 manual says this, so I guess it's just a pass through and doesn't matter.
"3.) High-Level Outputs
Speaker level passthrough outputs using spring clip type jacks to permit connection with bare wire. Used to connect from the
subwoofer amp to pass signal from the full range amp on to the main L/R speakers. Signal is only present on this output if
the high level input is also used. The signal to the L/R speakers is not filtered. The impedance “seen” by the full-range source
amplifier will be that of the connected speakers only"

The 70W plates I've had all have jumper wires where that cap would be positioned. If you want to HP them out, you can just use a 150uF as is normally installed there.

Later,
Wolf

[justwill]

Re: The French Bulldog - Tang Band W6 PR micro-sub

The impedance of a capacitor is inversely proportional to the frequency. What that means is that impedance becomes smaller as frequency increases. So higher frequencies are easier passed.

It also means that a higher value capacitor will pass AC easier than a lower value capacitor as the impedance of the higher value capacitor is smaller. So to lower the x-over frequency we need to increase the size of the capacitor.

The formula is: Z=1/2πfC where

Z = Impedance in Ohms
1/ = 1 divided by
π = 3.14
f = frequency in Hz
C = Capacitance in Farads

I hope this all makes sense.

Lessons to continue tomorrow.

Good; thanks! That's exactly the explanation I needed. I think I get it. So if I follow you right, and I want to high pass the monitors at, say, 80 hz (is this too high?), I calculate:

C=1/4*6.28*80=.000497, or a 500uF cap?

Above, I'm using the impedance of the sub driver/amp. Should I be calculating with the impedance of the speakers? In which case I'd calculate:

C=1/6*6.28*80=.000333, or a 330uF cap.

The 70W plates I've had all have jumper wires where that cap would be positioned. If you want to HP them out, you can just use a 150uF as is normally installed there.

So if I follow thekorvers right, that yields a high pass frequency of 1/(4*2*3.14*.00015)=265hz or 1/(6*2*3.14*.00015)=176 hz? That seems high, right? or should I be trying to cross the sub that high up? Or did I just mess up the equation?

[justwill]

Re: The French Bulldog - Tang Band W6 PR micro-sub

The 70W plates I've had all have jumper wires where that cap would be positioned.

Later,
Wolf

Hmmm...my amp has a big plastic case around any electronics, which would mean I'd have to disassemble it to get at the jumper wires. Is there any reason to prefer wiring the cap internally?

[fastbike1]

Re: The French Bulldog - Tang Band W6 PR micro-sub

Hi pass to mains aside, a nice job on the box. The legs, frame detail and color all work well.

Nicely done.

[justwill]

Re: The French Bulldog - Tang Band W6 PR micro-sub

Hi pass to mains aside, a nice job on the box. The legs, frame detail and color all work well.

Nicely done.

Thanks for the complement. All told, I'm pretty happy with how it looks. Nothing's perfect, I see the flaws, yada yada. But I like it.

And I should say again, thanks, fastbike and Wolf, for all your help along the way.

[Wolf]

Re: The French Bulldog - Tang Band W6 PR micro-sub

Good; thanks! That's exactly the explanation I needed. I think I get it. So if I follow you right, and I want to high pass the monitors at, say, 80 hz (is this too high?), I calculate:

C=1/4*6.28*80=.000497, or a 500uF cap?

Above, I'm using the impedance of the sub driver/amp. Should I be calculating with the impedance of the speakers? In which case I'd calculate:

C=1/6*6.28*80=.000333, or a 330uF cap.



So if I follow thekorvers right, that yields a high pass frequency of 1/(4*2*3.14*.00015)=265hz or 1/(6*2*3.14*.00015)=176 hz? That seems high, right? or should I be trying to cross the sub that high up? Or did I just mess up the equation?

I just stated what is normally there. Remember that this is a 6dB/octave rolloff, the caps usually measure a little higher (say 160-170uF). The OS are an 8 ohm design aren't they?

Later,
Wolf

[justwill]

Re: The French Bulldog - Tang Band W6 PR micro-sub

I just stated what is normally there. Remember that this is a 6dB/octave rolloff, the caps usually measure a little higher (say 160-170uF). The OS are an 8 ohm design aren't they?

Later,
Wolf

Ah, I see. Can you recommend a frequency at which to high pass the mains?

I have the OS MTMs, which, from the diysoundgroup page, I thought was a 6 ohm design. But after a little bit of digging, I came up with this thread, which suggests 4 ohms. So that at least clears up the question of what value to plug into the equation.