2245H Sub-Woofer Project

[Val]

Last year I bought a new-old-stock 2245H off the bay. Next week I will begin construction of a sub-woofer box. I will build it to match the speakers that I built a few years back (pictured here) with the help of this forum (http://audioheritage.org/vbulletin/s...ead.php?t=7140).

My wife, now completely converted to vintage JBL sound, has agreed to a 12.8 cubic feet box as long as it is aesthetically pleasing. The idea is this: get rid of our existing 20 year old entertainment center, build a low and wide sub, build a matching equipment rack to ride on top of the sub and top with a new 46" (or bigger) LCD TV. Everybody wins.

I've got it all penciled out. The sub will be made of 1" MDF and have external measurements of 64"W x 23"H x 19"D. This yields 12.8 cu ft internal. I'm planning on using 2 each 4" ports. WinISD calculates 3.22" long tunes to 30 Hz and 5.26" long tunes to 26 Hz. Once I get it built I'll play around with tuning.

My biggest concern is that the long and narrow shape of the box will have standing wave issues at certain frequencies. I do plan to brace the heck out of the box.

I'll scan in my sketches soon.

I welcome design comments and suggestions.

[4313B]

The idea is this: get rid of our existing 20 year old entertainment center, build a low and wide sub, build a matching equipment rack to ride on top of the sub and top with a new 46" (or bigger) LCD TV.

Been there.

My biggest concern is that the long and narrow shape of the box will have standing wave issues at certain frequencies.

Calculate the frequency of the lowest standing wave and if it is an octave or two above your crossover frequency then it should be "ok".

Alot of subs are cubes which is a total no but they do it anyway because it is minimal material and they cross them over low enough for the standing waves to be reasonably attenuated.

[duaneage]

You could use staggered walls inside the box to add bracing and break up the dimensions to prevent standing waves. Do some testing with loose boards and a signal generator to find the best place to put them.

[Val]

Been there.Calculate the frequency of the lowest standing wave and if it is an octave or two above your crossover frequency then it should be "ok".

Currently I'm running a cheapo Sony AV receiver (STR-DE595) which has a sub-out. I have looked but cannot find the sub-crossover frequency.

Looking at it another way, and, if I have my math right, the frequency of the wave that fits in the 62" internal width is 217Hz. Halving that is about 109 Hz. Which could be a problem as I imagine the sub crossover is higher than that.

[Val]

You could use staggered walls inside the box to add bracing and break up the dimensions to prevent standing waves.

If I put in two staggered walls then certainly there would be shorter wave lengths between the walls which is good. But doesn't the wave travel the "S" shape around the staggered walls and so a longer wave length is created?

[Loren42]

I ran your numbers through BassBox Pro and did not get the same port length you cited for 30Hz.

However, the real problem is not port length, but vent speed. Two 4" vents yield a vent speed of almost 30 m/s. That is almost twice the maximum speed you should design for.

Using a 12.8 cubic foot internal volume you should use two 6" diameter vents (internal diameter) that are 6.624" long. I would flare both ends.

The cabinet is tuned to 30 Hz and has an F3 of 30.52 Hz. Vent speed is a comfortable 12 m/s.

If you choose a 26 Hz Fb, then the ports will be 11.18" long and the F3 will be 30.99 Hz.

The standing wave is not likely to be a real issue if you stuff the box correctly. Rock wool is a cheap and effective tool to cut standing waves and internal coloration.

One thing you do not want to do is electronically assist this box below the Fb. Plots show that with 300 watts applied your cone excursion exceeds xmax at about 24 Hz for the cabinet with an Fb of 30 Hz and xmax is exceeded at 20 Hz for the 26 Hz tuned box.

300 Watts is not a lot of power, but your SPL level will be at 112 dB at those frequencies when you reach xmax, which should rock very well. However, any frequencies lower than 20 or 24 Hz will be much worse as far as exceeding xmax. A low cutoff filter may be a good idea.

Last year I bought a new-old-stock 2245H off the bay. Next week I will begin construction of a sub-woofer box. I will build it to match the speakers that I built a few years back (pictured here) with the help of this forum (http://audioheritage.org/vbulletin/s...ead.php?t=7140).

My wife, now completely converted to vintage JBL sound, has agreed to a 12.8 cubic feet box as long as it is aesthetically pleasing. The idea is this: get rid of our existing 20 year old entertainment center, build a low and wide sub, build a matching equipment rack to ride on top of the sub and top with a new 46" (or bigger) LCD TV. Everybody wins.

I've got it all penciled out. The sub will be made of 1" MDF and have external measurements of 64"W x 23"H x 19"D. This yields 12.8 cu ft internal. I'm planning on using 2 each 4" ports. WinISD calculates 3.22" long tunes to 30 Hz and 5.26" long tunes to 26 Hz. Once I get it built I'll play around with tuning.

My biggest concern is that the long and narrow shape of the box will have standing wave issues at certain frequencies. I do plan to brace the heck out of the box.

I'll scan in my sketches soon.

I welcome design comments and suggestions.

[4313B]

The nice thing about the B460 or 4645 (2245H version tuned to 25 Hz, not the 2245H version tuned to 30 Hz) with the BX63/BX63A is that one only needs 8 cubic feet tuned to 25 Hz to get rock solid response to 25 Hz and the low cutoff filter is built right in.

[Loren42]

The nice thing about the B460 or 4645 (2245H version tuned to 25 Hz, not the 2245H version tuned to 30 Hz) with the BX63/BX63A is that one only needs 8 cubic feet tuned to 25 Hz to get rock solid response to 25 Hz and the low cutoff filter is built right in.

That is an electronically assisted cabinet?

[grumpy]

... electronically assisted alignment, yes.

[4313B]

Yes, all you do is take a typical 12 dB/octave high pass cutoff filter and skew the Q so it has a bump at the tuning frequency of the vented box.

B460

What's the cost? A reduction of enclosure real estate by four to six cubic feet and a few more electronic parts in the form of a BX63/BX63A resulting in a shift in alignment from quasi-third order to quasi-fifth order yielding increased group delay which most people couldn't care less about anyway.

[Val]

I ran your numbers through BassBox Pro and did not get the same port length you cited for 30Hz.

However, the real problem is not port length, but vent speed. Two 4" vents yield a vent speed of almost 30 m/s. That is almost twice the maximum speed you should design for.

Using a 12.8 cubic foot internal volume you should use two 6" diameter vents (internal diameter) that are 6.624" long. I would flare both ends.

The cabinet is tuned to 30 Hz and has an F3 of 30.52 Hz. Vent speed is a comfortable 12 m/s.

If you choose a 26 Hz Fb, then the ports will be 11.18" long and the F3 will be 30.99 Hz.

The standing wave is not likely to be a real issue if you stuff the box correctly. Rock wool is a cheap and effective tool to cut standing waves and internal coloration.

One thing you do not want to do is electronically assist this box below the Fb. Plots show that with 300 watts applied your cone excursion exceeds xmax at about 24 Hz for the cabinet with an Fb of 30 Hz and xmax is exceeded at 20 Hz for the 26 Hz tuned box.

300 Watts is not a lot of power, but your SPL level will be at 112 dB at those frequencies when you reach xmax, which should rock very well. However, any frequencies lower than 20 or 24 Hz will be much worse as far as exceeding xmax. A low cutoff filter may be a good idea.

Thank you for running those numbers on bb and recommending the low pass cut off. What is the advantage to flaring the port ends?

[Val]

Yes, all you do is take a typical 12 dB/octave high pass cutoff filter and skew the Q so it has a bump at the tuning frequency of the vented box.

B460

What's the cost? A reduction of enclosure real estate by four to six cubic feet and a few more electronic parts in the form of a BX63/BX63A resulting in a shift in alignment from quasi-third order to quasi-fifth order yielding increased group delay which most people couldn't care less about anyway.

I've spent a fair amount of time reviewing the B460 information on this site. Seems like a cool box. The BX63s seem to be a bit hard to come by though. This post has got me asking myself what that extra 4 cu ft buys me? My understanding is that the 2245H, with such a large vas, likes a big box. The way I see it is I need less (or no) eq if I go with the larger volume. Does that make sense?

[4313B]

I've spent a fair amount of time reviewing the B460 information on this site. Seems like a cool box.

Or 4645 if the B460 box is too much hassle to clone.

The BX63s seem to be a bit hard to come by though.

They are pretty easy to build DIY if someone has the time and a nice hobby box to put the parts in. I built a few in some Niles switch boxes back in the day.

This post has got me asking myself what that extra 4 cu ft buys me?

Less floor space that might not be an issue if you have it to burn.

My understanding is that the 2245H, with such a large vas, likes a big box.

It likes a seven to fourteen cubic foot box. The larger the box and the lower the tuning the more excursion limited it becomes. Probably not an issue in a home environment but JBL had problems with them in the SR arena (hence the rise of the 2242H).

The way I see it is I need less (or no) eq if I go with the larger volume. Does that make sense?

If you have the room to burn. I personally put my foot down at ten cubic feet.

[Loren42]

Thank you for running those numbers on bb and recommending the low pass cut off. What is the advantage to flaring the port ends?

Port flares reduce vent noise and chuffing and they also reduce compression, which can lead to some distortion artifacts.

It isn't most critical thing you need to do when designing a cabinet, but if you can flare the port is simply adds a little more overall quality to the system.

Parts Express sells an ABS port kit (you will need two):

http://www.parts-express.com/pe/show...number=268-354

I think Madisound does the same.

[Valentin]

there are cad plans for the B460 in this site so you would only need to go to cnc place

here are the ones i did



i did two of them in mirror image