Desktop Sub, I'd like your feedback.

[roadsterdriver]

Hi,

I am designing a desktop system. My hope is that It will provide a nice musical experience while seated at the desk and also be "OK" while seated in the middle of the room. I live in England, so my office is 6'X9'!

There are a lot of constraints on this project. First one is 5" foot print for the sub. It is after all, a desktop system ie small than a "bookshelf" system.

My first idea is to use two 2" "subs." in a ~5" cube. One down firing the other rear firing. The idea being that the rear firing sub would extend the bass using a horn-like effect with the back wall (TB 2" subs have a free air res of 90Hz).

The second idea is to use a 4" sub, down firing, in a roughly ~5"x5"X12" box, but this is already starting to get too big for the desktop.

I'd like to hear what you guys think about these ideas. Looking forward to your more learned and experienced input.

I'll put my right left speaker ideas in another thread.

Thanks!

 

[roadsterdriver]

OMG Subwoofer Calculations!!!

I'm working on designing a desktop subwoofer. I had no idea how complicated this can be!!!

I have a basic idea to design a true desktop system, as in SMALL.

For the sub I was considering using two Tangband 2" subs in a ported box. One down firing and the second rear firing to take advantage, hopefully of extending the bass by wall placement. I live in England and have a 6'X9' office. Rooms are small here, usually. I was also hoping for a 5" foot print, no larger.

I would like to build something that will be musical while seated at desk and "OK," while seated in the center of the room.

However, I did a Vb calculation for only one driver and got 4.59 cubic feet!!!

Is this correct?

Qts = .31
Vas = .31L

I'm totally new to this. Be gentle

Thanks!

 

[edjosh23]

A 5" footprint... does that mean that you're going to put the sub on the desk rather than the floor?
With an fs of 90Hz and low efficiency I would go with a larger driver. With 2x 2" you can get 86dB/w but with a larger driver you can get down to about 55Hz with the same spl if not higher.

Josh

 

[roadsterdriver]

Yes, thanks.
After doing a few calculations, which Iwill post in another thread, I have decided to go with a 4" driver....I think.

and yes, sub on desk...I think...

 

[Brian Steele]

Hi,

I am designing a desktop system. My hope is that It will provide a nice musical experience while seated at the desk and also be "OK" while seated in the middle of the room. I live in England, so my office is 6'X9'!

There are a lot of constraints on this project. First one is 5" foot print for the sub. It is after all, a desktop system ie small than a "bookshelf" system.

If you expand your limitations to include a sub that can bolt on below the desk, you'll increase the number of possible options significantly - like a TL or a TH with one of those square TB 4" drivers.

 

[edjosh23]

I think you should place the sub on the floor below the desk.
Its good to keep your desk clutter free and with the the possibility of building a cabinet larger in volume your sub can go much lower and louder.

Josh

 

[roadsterdriver]

quency

"Subwoofer" is really a misnomer here. I'm thinking of it more as a bass augmenter which will probably have quite a high crossover point considering the mains will be 3" drivers.

I think a fair amount of the bass coming from this "sub" will be relatively directional due to a highish crossover point. So, I wanted to have it near and more or less on the same plane as the mains.

I'm only theorizing here.

Thanks for your ideas.

 

[roadsterdriver]

Subwoofer Calculations. Help!

Considering a box for my desktop subwoofer.

Tangband 4" Sub

Vas 4.84L
Qts 0.28

Using online calculator Vb = 1.45L or a roughly 4.6" square box.

That seems very small. Is this correct?

(I haven't got to tuning and porting yet)

I'm totally new to this. So, go slow.

Thanks.

 

[GM]

Is this viable? http://www.diyaudio.com/forums/showthread.php?t=146639

GM

 

[roadsterdriver]

Haha, that's really cool!

But, no, it's not an option for me.

Definitely "outside the box!"

 

[keantoken]

I can see a possible issue here:

There is a good possibility (IMO) that the woofer will find the resonant frequency of something on the desktop. Since it's directly on the desktop, there will be more vibration than if placed somewhere else. This can cause random objects to rattle.

I suggest putting some very rubbery feet on it (go to Petco and look at the fish air pumps for inspiration), though this could just have the effect of shifting the resonance (or giving the woofer box resonance of its own).

If you place two speakers on opposite sides of the box which are electronically in phase, you can cancel most of the vibration.

- keantoken

 

[kipman725]

what about something straped to the bottom of the desk, a long thin tube sub like:
http://www.visaton.com/en/bauvorschlaege/subwoofer/alto_genesis_sub/index.html

 

[roadsterdriver]

The bolting to the bottom of the desk idea is intriguing. I'll keep it in mind.

Meanwhile, off-topic, I can't seem to find some of my posts. Is every single post moderated? Do they often delete posts or do we just wait until they get to them? Just curious...new here.

Thanks.

 

[edjosh23]

Which 4" Tang Band subwoofer are you looking at?
It is recommended that the enclosure not be square due to standing waves.

Josh

 

[roadsterdriver]

Which 4" Tang Band subwoofer are you looking at?
It is recommended that the enclosure not be square due to standing waves.

Josh

Yes. Thanks for that. I was only using the cube reference to point out how small the box volume calculation came to.

Is that the correct Vb?

 

[kipman725]

Which 4" Tang Band subwoofer are you looking at?
It is recommended that the enclosure not be square due to standing waves.

Josh

my understanding was such that standing waves could only devlop if the longest dimension of the box was at a wavelegnth the sub would be playing at. Therfore for all but very large enclosures this was a non issue.

 

[Salas]

The bolting to the bottom of the desk idea is intriguing. I'll keep it in mind.

Meanwhile, off-topic, I can't seem to find some of my posts. Is every single post moderated? Do they often delete posts or do we just wait until they get to them? Just curious...new here.

Thanks.

Yes. We examine them, and if they are not spam or offending, we approve them, until you will be registered members. After that, bad posts get either reported by members or we bump on them, and we take action if needed.

 

[GM]

It is recommended that the enclosure not be square due to standing waves.

Cabs that are acoustically small for the intended BW are considered to have a ~uniform particle density, so there's not enough acoustic energy to excite them enough to matter and adding damping finishes them off to well below its noise floor, ergo its shape and where the driver and vent (if used) is located on it is irrelevant.

For example, loosely stuffed (or lined) with a 100 Hz/2nd order XO, the cab's dims shouldn't generate any eigenmodes below ~ the XO's Fh -24 dB point or ~100*2^(4/2) = 400 Hz or ~13560/2/400 = ~17" (~2.84 ft^3 gross) to ensure a minimal amount of damping can handle it, so for many of today's 'sub' designs a cubic solution is acceptable.

GM

 

[keantoken]

The bolting to the bottom of the desk idea is intriguing. I'll keep it in mind.

Instead of bolts, magnets might work if you're lucky enough to have a metal desk. Though I would worry about magnets and computers near each other. Maybe put hooks on each side so you can strap it on with bungee cords.

- keantoken

 

[edjosh23]

Cabs that are acoustically small for the intended BW are considered to have a ~uniform particle density, so there's not enough acoustic energy to excite them enough to matter and adding damping finishes them off to well below its noise floor, ergo its shape and where the driver and vent (if used) is located on it is irrelevant.

For example, loosely stuffed (or lined) with a 100 Hz/2nd order XO, the cab's dims shouldn't generate any eigenmodes below ~ the XO's Fh -24 dB point or ~100*2^(4/2) = 400 Hz or ~13560/2/400 = ~17" (~2.84 ft^3 gross) to ensure a minimal amount of damping can handle it, so for many of today's 'sub' designs a cubic solution is acceptable.

GM

Thanks GM for the explanation.

Josh