The Boominator - another stab at the ultimate party machine

[DunkH]

Hi Guys,
I have built my own mini boominator.



Here is the build thread.

http://www.diyaudio.com/forums/showt...71#post1939971

[Love Below]

Saturnus

If I may ask, where have you found your HP10W4 speakers?..

[Havoc08]

Originally Posted by Saturnus

Indeed I have found the HP10W in 4 Ohms, it's called the HP10W4. But I also need 4 channels as I'm going to use an active x-over to drive the tweeters and the woofers separately.

Saulty, to answer you question most thoughroughly. I'd like you to make 3 mp3, one each with a 60, a 80 and a 100 Hz sinus wave. Now take a speaker you know is capable of playing those at fairly loud levels outside and put in the middle of a grassfield. Stand back 4-5 meters and play the mp3s. Then you'll know why it's completely redundant going lower than roughly 100Hz for semi-loud applications outdoors.

I'm going to use a amp9 with a active crossover too, although with two fullrange sats and a DVC sub.

Originally Posted by mor2bz

I really like this boominator. I can't stand loud music, but if you are going
to listen to loud music, outside is the place to do it.

I have read that sealed boxes really do not give up anything in bass to ported, it is just that they do not go as low or drop off so quickly below F3. And the
boxes can be about half the size. Maybe we have given up too quickly on the
sealed box?

You're right in what you're saying about the F3 and the steeper rolloff, but as far as I remember the ported box gives +3dB vs. sealed because of the inverted phase sound is being let out also and not just converted to heat as in a sealed box.

I might be wrong so someone comment please .

The sealed box has lower latency than a ported and not as high phase shift. It is often regarded more accurate and "faster" than a ported speaker (although IMO because of the many faulty port constructions making one note bass, port noise, being used below the Fs etc.).

For outdoor use I believe ported has been used to gain the most dB @ 1watt, but maybe saturnus has a better answer?

[saulty]

Completed my version of the boominator. Still waiting on my Sure 2*100 though.

Despite the lack of an amp, I did have a few sessions with a full size HT receiver to really see what it is made of. I ran into some limits at the very high end that I'd like your advice on.

When pushing it in the 105-108db range, certain music selections with heavier bass seemed to distort (Rap music). I believe I was pushing the speakers past their excursion limits (xmax=2mm). Turning it down a notch for these selections kept them operating normally.

Here is what my cone displacement looks like at my current current tuning.

It is hard to see in this image, but anything past the 2mm is slightly greyed out so at this power output I would be pushing past the limit in the 100hz range then again at 50hz. I have no idea which frequency was causing the problem, but potentially both.

And SPL response:


I don't have any high pass filters or other crossovers. Just the woofer and Motorolla Piezo. Bumping up the tuning frequency to 75hz or 85hz seems to help with the spike at 100hz but I hit xmax much sooner at the low end.


Should I be tuning a little higher and adding a high pass filter to protect the woofers from anything below 60-70hz? I hate to do this cause this only poses a problem when playing at absolute extreme volumes. At normal listening levels, it doesn't have any problem with excursion. Am I missing something else here?

More details about the woofer and enclosure.

Driver Properties
Name: GW-1058
Type: Standard one-way driver
Company: Goldwood
Comment: Pro series
No. of Drivers = 1
Fs = 43.4 Hz
Qms = 2.696
Vas = 2.249 cu.ft
Cms = 0.359 mm/N
Mms = 37.39 g
Rms = 3.79 kg/s
Xmax = 2 mm
Xmech = 3 mm
P-Dia = 212.1 mm
Sd = 355.4 sq.cm
P-Vd = 0.0707 liters
Qes = 0.459
Le = 0.282 mH
Z = 8 ohms
BL = 10.83 N/A
Pe = 180 watts
Qts = 0.392
no = 1.093 %
1-W SPL = 94 dB
-----------------------------------------
Box Properties
Name:
Type: Vented Box
Shape: Prism, square
Vb = 22 liters
Fb = 65 Hz
F3 = 66.89 Hz
Fill = minimal
No. of Vents = 1
Vent shape =
Vent ends =

[Saturnus]

Bumping the tuning frequency to 80Hz and adding a high pass is what I do and would do in your case. Actually the high pass filter is just selecting the right input capacitor on the amp so it's not a major issue. Cut-off at around 50-60Hz is fine.

[saulty]

I could use some help on the cap selection. Which input cap would correspond to a 50-60 cut off? I'm a bit clueless when it comes to this.
Would it be in addition to the 2.2uf caps already on the board or replacements for them?

[Saturnus]

That's pretty easy to calculate actually.

fc = 1 / (2 x pi x F x Z)

fc = corner frequency
F = capacitance in Farads
Z = input impedance in Ohms

It's definitely replacing the 2.2uF capacitor as that's way too big.

As far as I can see the sure boards have 22K to 47K Ohm input impedance, set by the gain switches. If we assume you want the 22K Ohm option for best performance with an mp3player (especially iPods) the replacement input capacitor should be 0.15uF (which puts it in the realm of ultra high quality low voltage SMD capacitors*) for a 48Hz cut-off.

*As a side note I have always had great difficulty in understanding why people would want to chose very large (and noisy) high voltage capacitors made for speaker filters as input capacitors when the needed voltage range would hardly ever be more than a few volts.

[saulty]

Thanks Saturnus. I've been thinking about making the amp portion of this somewhat modular so I could take it out and use it with a different set of full range speakers indoors. In this case, could I move the high pass function between the amp and the speakers rather than modifying the amp directly?

And if so, is it true that I'd use the same formula but solve using an impedance of 8 ohms rather than 22k ohms?

[Saturnus]

Originally Posted by saulty

Thanks Saturnus. I've been thinking about making the amp portion of this somewhat modular so I could take it out and use it with a different set of full range speakers indoors. In this case, could I move the high pass function between the amp and the speakers rather than modifying the amp directly?

And if so, is it true that I'd use the same formula but solve using an impedance of 8 ohms rather than 22k ohms?

Well, yes and no. Theorically it's possible but it would make the cap much much too big to be practically possible, ie. 680uF for 50Hz cut-off.

But you say full-range speakers, right? Why do you think they wouldn't benefit from the same cut-off? I use a 50Hz cut-off on my Fostex 207Es to keep cone excursion acceptable below the back loaded horn cut-off.

Any full-range speaker is a non-closed cabinet, ie. ported, horn loaded, infinite baffle etc etc will benefit from the same cut-off to limit cone excursion.

[saulty]

After a whole lot of reading on Passive Crossovers, Capacitor and Coil Calculator, your response makes a lot more sense. I get it. I'll go your route with an input cap.
You mentioned not to mess with the higher voltage caps and to stick with lower voltage SMD ones. I also assume a lower Tolerance is better?
Do any of these make more sense than the other?
Capacitors from Allied Electronics
It doesn't seem like the lower voltage ones come in a 5% tolerance.