Open baffle subwoofers - do they work?

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#2
Yes, it does, but be aware that you will need really BIG drivers to get reasonable bass extesion/loudness. I would say that 15 inch in an open baffle is comparable to, let's say 8 inch in closed.

What u get is total lack of 'boxiness'...I used such a config something like 8 years ago with ElCheapo 30 cm drivers.
For my former, small 20 sq meters room it was simply impressive.

For me there are two options to get true bass - open baffle and
'bag end'...well they're totally different but..as U say..they're simply and ellegant (maybe the latter is not so simple).

Greetz,

Spherion
 
#5
Spherion-

Getting rid of the boxiness is the reason I was considering building 27 cu. ft. (sorry, don't know metric equivalent offhand) infinite baffle boxes to hold two 15" JBL woofers.

Can I possibly get the same sound pressure levels with the open baffle setup if I dust off the Hafler 500 watt boat anchor to power them and will they go as low?

Both seem like ways to negate the back wave cancellation, but the open baffle would take up a lot less room and material.


Also, I'm curious. Is there a lot of interest in vacuum tube and vintage gear in Poland?

Peace

Lee
 
#6
Hello Lee, if you look at the third image in the page you linked above you will see a line labeled "Dipole EQ." This line represents about 10dB of boost from 100 Hz to 30Hz, which is necessary to compensate for the progressive cancellation of the front and back waves as frequency gets lower. Excursion requirements of the woofer/s increases accordingly, as Spherion says one large woofer on an open baffle "equals" one much smaller woofer in a sealed box.

The amount of compensation depends on how large the baffle is. Anyway open baffle is not the best choice if high output level at low frequency is the goal 🙁

JohnR
 
#7
Well, the pressure level actually depends on the size of woofer
and displacement (Xmax)...well...what are the parameters
of these 15 JBL's ?

What is the size of you room?
How deep do U want to go? 40 Hz, 30 or...?

To be honest...I like bag end subs but I'll never go for one.
Open baffle is good idea - the only real problem is size/amount
of woofers in comparision to pressure level they produce.

Get me some info 'bout these JBL drivers...

Greetz,

Spherion
 
#9
JohnR said:
Hello Lee, if you look at the third image in the page you linked above you will see a line labeled "Dipole EQ." This line represents about 10dB of boost from 100 Hz to 30Hz, which is necessary to compensate for the progressive cancellation of the front and back waves as frequency gets lower. Excursion requirements of the woofer/s increases accordingly, as Spherion says one large woofer on an open baffle "equals" one much smaller woofer in a sealed box.

The amount of compensation depends on how large the baffle is. Anyway open baffle is not the best choice if high output level at low frequency is the goal 🙁

JohnR
Click to expand...

Yep, when there's a compensation in the range below 100 Hz
please bear in mind the fact that Xmax requirements simply
skyrocket. 15" driver would be theoretically enough but the key
is how it will behave under some specific conditions in open baffle
(large excurions etc). The other thing is how would your amp
behave on such a load...hmm..Hafler...there things used to have
decent bass quality.

Subjetively, I feel that there's nothing like good closed cabinet, with really good driver. The problem is, considering, for example
15" ATC SM375 driver, we would need a 'little' more than 150
liters (I don' remember by heart) - the thing is that with this size
of cabinet you HAVE to make some walls slanted to avoid
standing waves. This is one of the reasons for 'boxiness'.
Staning wave : Vofsound / 2 * distance between planes.

btw. There is some interest in tube gear in Poland. Especialy DIY'ers. I feel it has grown since last ten years (that much I can
remember, I am only 22 🙂 )
Unfortunately, the problem for us here are components and customs. Got OPA627 from TI shipped and these idiots at cusoms
wanted me to translate the invoice...wonder what will happen
if I buy some AD1853 or sth like that 😉
 
#10
John-

These are only for a small room and I'm not at all looking to crack the plaster. I'm more concerned with quality than quantity. 500 watts of amplifier should be enough, I'd think.

Spherion, here's some specs on the woofers-
http://www.lansingheritage.org/html/jbl/specs/pro-comp/2235.htm
They should be able to handle about anything I throw at them.

I get usable response below thirty cycles on my Altecs, maybe even as low as twenty cycles and would sure like to go that low on any subwoofer....

Lee
 
#11
They look serious, indeed 😉
If your room is less than 40 sq meters go for open baffle
if you want quality.
8.5 mm Xmax plus really BIG B*l factor plus JBL's
magnet technology will cut the mustard.

btw. Where did U get them? Is it possible to get these drivers at
reasonable cost?

Greetz,

Spherion
 
#12
Spherion-

I bought these over ten tears ago in Chicago.

I don't know if they are still available.

They are very similar to the 2225 series but have softer surrounds, a little better efficiency, and reach down a little lower in frequency response.

I searched eBay out of curiousity and couldn't find any 2235's, but did see these and a few others at similar prices---

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=23794&item=928628554

As I recall, a JBL Professional Products dealer quoted me 450-500 dollars on the 2235's.

I paid much less for mine.

This might be worth trying.

I did build two 5 cubic foot boxes for these, but they're so heavy they're a pain to move around.

Lee
 
#14
Xmax= maximum linear excursion

Serious companies like JBL usually state the one-way (i.e. peak)value (or they specify if it is one-way or p-p).

I have two pieces of the newer 2226, for these they state a linear x-max of 7.8 mm and a maximum excursion before damage of 40mm peak-peak, which is quite a lot for a P.A. driver of this generation. I assume the model has been introduced about 5 to 7 years ago.

BTW: There is a German company producing dipole subs:
http://www.audioelevation.de/frameSet.htm
The even got a patent on this one, what for I can't imagine since it isn't differing that much from the Linkwitz design 😕

Regards

Charles
 
#15
The nice thing about open baffle is that it doesn't take very long to make a prototype...

Just get 2x4 or 4x4 ft plywood and cut a hole. Remember that for flat bass you will need to equalize the bottom end but this will give you an idea of the sound 🙂

JohnR
 
#16
I think it will depend on your volume needs. 8mm is not a huge amount of Xmax for a sub driver, compared to something like the Stryke AV15 with 28mm or so. The low Q also means you will need to start any EQ earlier. And you might want to check for noises from pole vents.

The Linkwitz site has a download of an Excel calculator which will give you an idea of how much bass you will actually get. I'll try to post a link.


Steve
 
#17
Open Baffle Needs high Qts

If you remember about ten or twelve years ago Bob Carver was selling an open baffle sub. It had (kerrekt me if I am rong) three twlves per side and (of course) included amplifiers. Carver's trick was to use high Qts drivers. No, I mean REALLY high Qts-like 2.6 or so. This fully compensated for the inevitable open baffle cancellation. High Qts generally indicates lower BL product and/or stiffer suspension. Since Carver designed the drivers for subwoofer use, they did not have stiff suspensions. Instead, they had wimpy magnets! Carver bragged about this, claiming that this helped keep driver cost down!. He forgot to mention that this also made the drivers horribly inefficient. With the three 12's they only managed (if I remember correctly) about 85dB/W/M !
So they put BIG wire in the VC's and about 1KW amp per sub! I could'nt help but think that there has to be a better way to skin that cat!
And I think it is this: If you use a pro sound driver, as recommended in the previous posts to this thread, you will find that you will have a 'surplus' of driver sensitivity and efficiency. Typically a JBL 18 inch woofer will have something like 100dB W/M. Of course the Qts is way too low for an open baffle. If you start with, say a lead guitar speaker (really just a huge mid/full range driver) with a stiff suspension and high(er) Qts,rather than a woofer, then add weight to the cone to lower the resonance and further raise Qts you might just get Qts into the ballpark. When you have Fs where you want it, then gradually add resistance to the woofer circuit (use BIG resistors and don't touch them while running!) to get Qts where you want it. Okay so you are squandering the efficiency of the driver with dead weight and wirewound resistors but so what? You'll have your open 'unboxed' sound, and when guests walk around the back they will see those nice big magnets! And since your room is small you will never run into any excursion limits. I would be suprised if you use more than +/- 3mm.
I personally do not believe there is any relationship between boxes and the 'boxy' sound. Some of the most 'open' sounding speaks, including subs, that I have ever heard were in boxes.

Jimbo
 
#18
Jimbo-

A most thought provoking response.

Maybe I'd be better of with the 2225 JBL's. They are musical instrument drivers.

I'll have to bone up on speaker parameters again to understand some of your points, but thanks for presenting them in a logical and understandable fashion.

I hate it when people deliberately talk over your head and don't consider that everyone isn't as knowledgable as they might be!!

Thanks!

Lee
 
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