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What 15" woofer is better for open baffle?
- Thread starter quorzar
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For an open baffle? Neither, I'm afraid. For low frequencies, you would need a baffle of huge size, to prevent cancelation between the front and rear waveforms. Probably as big as the walls of your room. Audible bass response will require an enclosure of some kind.
I don't know about that. Please see the original Carver Amazing high Qts woofers for example.
Here is a link: https://dynavox.com/12inch-Carver-Amazing-Loudspeaker-Honeycomb-Cone-Woofer-Upgrade and very cheap in quantity!
And another: https://dynavox.com/12inch-Carver-Amazing-Loudspeaker-Honeycomb-Woofer-Driver
Here is a link: https://dynavox.com/12inch-Carver-Amazing-Loudspeaker-Honeycomb-Cone-Woofer-Upgrade and very cheap in quantity!
And another: https://dynavox.com/12inch-Carver-Amazing-Loudspeaker-Honeycomb-Woofer-Driver
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KSTR
Major Contributor
For OB bass, you need EQ anyway. The pretty much dominant parameter is Xmax (linear excursion capability), the more the better. Qts is irrelevant because of EQ but low Qts needs more EQ and hence more voltage headroom of the amplifier. High Qts means low internal feedback in the woofer which isn't exactly ideal when precision is the goal but that of course strongly depends on overall driver execution. Low Fs is also beneficial.
@Inner Space is not quite correct, even without any baffle a 15" can produce 30Hz or even 20Hz, just not with earth-shaking levels... but wait, it can when used really near field where the additional 6dB OB cancellation slope doesn't fully develop. For typical use some baffle (path length) is required and if this is subwoofer duty only consider using a larger H- or U-frame, or one of the folded variants. Path length helps efficiency and hence one should choose the longest path possible that doesn't compromise the upper end of the intended frequency range.
Execpt for the motor strength, both woofers are quite similar overall. I'd choose the first one for its higher Xmax and lower Fs. Bear in mind that the Xmax spec isn't that much standardized so values might not be directly comparable.
@Inner Space is not quite correct, even without any baffle a 15" can produce 30Hz or even 20Hz, just not with earth-shaking levels... but wait, it can when used really near field where the additional 6dB OB cancellation slope doesn't fully develop. For typical use some baffle (path length) is required and if this is subwoofer duty only consider using a larger H- or U-frame, or one of the folded variants. Path length helps efficiency and hence one should choose the longest path possible that doesn't compromise the upper end of the intended frequency range.
Execpt for the motor strength, both woofers are quite similar overall. I'd choose the first one for its higher Xmax and lower Fs. Bear in mind that the Xmax spec isn't that much standardized so values might not be directly comparable.
Speedskater
Major Contributor
Note that the 1994 Carver Amazing used a very unconventional woofer. There were no other replacements and only a small stock of originals.
KSTR
Major Contributor
Oh well, that's not a driver (the one from the first link), that's an insult ;-) It has some significant Xmax, though.
Here's what Peter Aczel had to say about the insulting woofers:
One of the pseudotechnical objection I've heard is
that, well, it's still a high-Q woofer, and we all know that
means underdamped. Wrong. The open baffle acts as an
acoustical short circuit, which lowers the Q analogously to
an electrical short circuit. Or, you could say that instead of
combining a conventional low-Q woofer with a convention-
al high-Q box to produce the desired system Q, the Carver
accomplishes the same thing by combining a high-Q woofer
with a low-Q (and how!) open baffle. The difference is that
the response profile corresponding to the desired Q in the
Carver emerges only after the acoustical cancellation has
taken place, a small distance in front of the speaker; the ex-
treme nearfield measurement still shows the high-Q bump
(obviously, the Don Keele method isn't applicable to open-
baffle systems). Now, the Platinum version of the Amazing
has four 12" woofers per side, a total of eight, and the fun-
damental resonance after break-in is in the neighborhood of
22 Hz, at which frequency the response is still essentially
flat. That combination of air-moving capability and low-
frequency extension results in absolutely majestic, life-size
bass reproduction. No owner of the Amazing will ever need
to bring up the subject of subwoofers. In Mark III and Mark
IV, the acoustically derived equivalent Q is continuously
adjustable on the rear panel from 0.5 to 1.0 (no more resis-
tors to insert, as in Mark II). Another change in Mark IV is
that the woofers and the ribbon all move forward in re-
sponse to a positive-going pulse, thus satisfying one of my
well-known little compulsions.
These speakers didn't require any outboard eq, either.
One of the pseudotechnical objection I've heard is
that, well, it's still a high-Q woofer, and we all know that
means underdamped. Wrong. The open baffle acts as an
acoustical short circuit, which lowers the Q analogously to
an electrical short circuit. Or, you could say that instead of
combining a conventional low-Q woofer with a convention-
al high-Q box to produce the desired system Q, the Carver
accomplishes the same thing by combining a high-Q woofer
with a low-Q (and how!) open baffle. The difference is that
the response profile corresponding to the desired Q in the
Carver emerges only after the acoustical cancellation has
taken place, a small distance in front of the speaker; the ex-
treme nearfield measurement still shows the high-Q bump
(obviously, the Don Keele method isn't applicable to open-
baffle systems). Now, the Platinum version of the Amazing
has four 12" woofers per side, a total of eight, and the fun-
damental resonance after break-in is in the neighborhood of
22 Hz, at which frequency the response is still essentially
flat. That combination of air-moving capability and low-
frequency extension results in absolutely majestic, life-size
bass reproduction. No owner of the Amazing will ever need
to bring up the subject of subwoofers. In Mark III and Mark
IV, the acoustically derived equivalent Q is continuously
adjustable on the rear panel from 0.5 to 1.0 (no more resis-
tors to insert, as in Mark II). Another change in Mark IV is
that the woofers and the ribbon all move forward in re-
sponse to a positive-going pulse, thus satisfying one of my
well-known little compulsions.
These speakers didn't require any outboard eq, either.
Hi, new member here I know this is probably too late but I can confirm what member 'Eurasian' said. I have built some OB towers using the H-frame prinicple and 4 x 15" Goldwood GW-215/4 woofers from Parts-express. I play the organ so required subwoofers to reproduce low frequencies as accurate as possible with no boom. I did a lot of research and I concluded (rightly or wrongly) that OB woofers need the following:
•High Qts•
•High sensitivity
•Low Fs
•Low BL
•Low X-max (linked to high Qts)
•Low frequency response
•45cm (17 3/4") wide box sections for 15Hz bass. It is the surface area which is important.
•17.5cm (7") deep box sections to cut bass off at around 70Hz I think I worked out. The deeper they are, the higher the frequency cutoff.
Armed with this info I found the Goldwood GW-215/4 for just $60 each so I bought 8 of them. I got the 4ohm version so I could make 2 enclosures each side with 2 x 15" in each, wired in series then parallel to give a 4ohm load for the amp. As I had already built some huge 7ft tall OB line array main speakers (copied off a guy on a forum) I wanted a kind of line array H-frame dipole. Woofers face opposite directions but move in same direction together.
I built one cabinet with 2 x 15" in it and tested it with a 32' organ stop and it went all the way down to bottom C which is 15Hz. Astonishing!!! To my ears the response was flat and loud. Later microphone testing proved this to be the case. This is in a 5m x 5m square room. I built the other 3 cabinets as fast as I could, being keen to hear the results. I built them with 2" (50mm) thick baffles and the rest 1" (25mm) MDF. I stacked them to give 4 x 15" wooferd on each side of the room and had only about a foot of space behind them (not ideal in theory). The X-max of the woofers is only 3mm but believe me, this is enough. The bass is huge, clean and fast. They are only rated to 135W each woofer, so just hope they don't blow. I have been running them for 3 years now at high volume with no issues.
I hope this is of use to someone.
See attached photos.
•High Qts•
•High sensitivity
•Low Fs
•Low BL
•Low X-max (linked to high Qts)
•Low frequency response
•45cm (17 3/4") wide box sections for 15Hz bass. It is the surface area which is important.
•17.5cm (7") deep box sections to cut bass off at around 70Hz I think I worked out. The deeper they are, the higher the frequency cutoff.
Armed with this info I found the Goldwood GW-215/4 for just $60 each so I bought 8 of them. I got the 4ohm version so I could make 2 enclosures each side with 2 x 15" in each, wired in series then parallel to give a 4ohm load for the amp. As I had already built some huge 7ft tall OB line array main speakers (copied off a guy on a forum) I wanted a kind of line array H-frame dipole. Woofers face opposite directions but move in same direction together.
I built one cabinet with 2 x 15" in it and tested it with a 32' organ stop and it went all the way down to bottom C which is 15Hz. Astonishing!!! To my ears the response was flat and loud. Later microphone testing proved this to be the case. This is in a 5m x 5m square room. I built the other 3 cabinets as fast as I could, being keen to hear the results. I built them with 2" (50mm) thick baffles and the rest 1" (25mm) MDF. I stacked them to give 4 x 15" wooferd on each side of the room and had only about a foot of space behind them (not ideal in theory). The X-max of the woofers is only 3mm but believe me, this is enough. The bass is huge, clean and fast. They are only rated to 135W each woofer, so just hope they don't blow. I have been running them for 3 years now at high volume with no issues.
I hope this is of use to someone.
See attached photos.
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I have a pair of Eminence Alpha 15s I'm happy to donate to you if you are in central VA
ROOSKIE
Major Contributor
Yes, this is really useful.
I appreciate the time you took to share this.
I was about to go with the exact same woofers and basic design. I am glad I found this today. You post gives the confidence I was looking for in these budget woofers.
I have 1 question. The depth of the box section vs bass cutoff, can you point to info so I can calculate a slightly different bass cutoff?
ROOSKIE
Major Contributor
Actually I found it, I had missed it in Linkwitz's publishing's.
Here it is in case anyone stumbles over here
"
Since the two cones move back and forth in unison, there is little air pressure inside the enclosure b at very low frequencies. When the internal length L becomes half wavelength, there is a sharp resonance of the transmission line between the cones, causing a severe dip and peak irregularity in the frequency response. The two drivers in b can be replaced by a single driver c without loss in volume displacement capability. The latter arrangement, called H baffle, is very practical for dipole woofer construction. It too has a severe resonance because the waveguide of effective length L in front and behind the cone sees large impedance mismatches at the cone and at the open end of the cabinet. The resonance occurs when L = l/4 = 0.25*v/F.
For a baffle of D = 20" (0.5 m) length and with L = 10" (0.25 m) estimated, the resonance peak in the dipole output is at F = 0.25*v/L = 343 Hz. Even when the peak is removed by equalization, the H baffle should only be operated below this frequency. It is a compact baffle for woofer applications and I use it with slightly different driver arrangement for the PHOENIX.
Output equal to a closed box occurs at Fequal = 0.17*v/D = 117 Hz with the 20" path difference D between the positive and negative polarity sources at the H baffle openings.
For a deeper analysis of the H-frame see the Issues in speaker design page." -Linkwitz
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I can’t imagine a situation where low xmax or weak motor are positives. Raw driver LF response doesn’t strike me as meaningful in this century either. Maybe when frequency shaping tools required an MSEE to implement rather than a program and a finger to run on the trackpad it was important.
Basically IMO you always want the least passband resonances, longest throw (assuming inductance is kept low and linear), and strongest motor you can get. System design will get you the rest of the way.
ROOSKIE
Major Contributor
Do you have experience building/architecting open baffle designs?
I ask as I am going to try building some and want to know if you're on point here or not.
Many, many systems (and I know DIY is a real mixed bag of opinions and results)that are purported to be nice use the "Goldwood, Eminence" style 15-18 woofers with lower xmax and higher(.5-.8) or even quite high(1.0-1.5) Q. Some of course use a different approach such as Linkwitz using 10" low Q(.30), Higher Xmax woofers in the LX521, or the GR Research high Xmax options.
The Goldwood and GRS drivers are very affordable and lets face it 3 or 4mm of Xmax on a 15 or 18 is significant air movement, let alone considering using multiples.
(Even if I just consider 2mm the practical limit for these drivers due to potential distortions when driven "hard".)
SB Acoustics came out recently(1yr ago) with a couple of higher Q, High Xmax beefy units for Open Baffle design. They look quite nice.
SB Audience Introduces Bianco 12 and 15-inch Woofers Optimized for Open Baffle Designs
Open baffle loudspeakers are extremely popular for good reason. They can be fitted with large low frequency drivers and they sound "real," in part because open baffles play with room reflections and sound good even off-axis. A big concern though, is control over the bass response, where the...
The main problem I currently see with high xmax woofers is cost as high xmax requires big motors/magnets and typically ends up with low sensitivity so you need several fairly expensive drivers. (Though the low xmax, GRS 15's I picked up are lowish sensitivity as well for an 8ohm, 15" at 87db, but I will get a high q spl bump )
So the advantage of "weak motors" is cost savings when SOTA is not the game.
With the "Goldwood" approach you still need several drivers due to excursion limits but the drivers are inexpensive and one can buy 4huge 15-18" woofers for the price of one high xmax 10 or 12" unit. (except now the SB Acoustics new line is fairly affordable though still pricier)
Very high QTS can help compensate for the acoustic roll off with it's bump and therefore requires less power from the amps and so the xmax advantage of High Xmax/Lower QTS fades as it depends on much more power to accommodate the acoustic fall-off and more EQ boosting. So all the trade offs play out though I have no idea yet what is best myself. I am under no illusions that the GRS drivers are a pound for pound substitute for better units, they are just darn affordable.
I just ordered 4 GRS 15" woofers to play with in basic H frames and they were $125 for all 4 after discounts. That is crazy cheap. (-Unless they sound terrible and then it is just crazy. )If I like them and need more bass, 4 more is $250 total for 8, 15" woofers. The woofer Linkwitz is using in the LX521 cost that per driver (actually $330 or $1320 for 4,10"ers. 8 would be a huge layout of $2640 barring a discount).
Anyway since I am obviously (at least to me) doing this for fun and not SOTA then the $$$ layout is easy to accept for now until I get into Dipole or not. And who doesn't want 8, 15" drivers exposed in their living room??
Amp power is cheap if you are cool with the Monoprice 605030 for testing like I am. That said, the GRS based system won't need much power to play at a pretty reasonable SPL. I should be able to drive all 4 (or 8 if I get crazy) woofers easily with that $100 amp and have room for plenty of EQ/DSP adjustment.
Some other system with robust low qts drivers could require multiple times the power.
To actually know which is better you need to buy and test them.
Linear excursion is the primary limiting factor for producing bass at high SPL, and many manufacturers lazily use the "formula" of voice coil height minus magnetic gap height, divided by 2.
This tells you absolutely nothing useful. Non-linear distortions caused by suspension geometry or motor strength modulation matter a great deal. Only a handful of sources such as Vance Dickason at Voice Coil Test Bench actually measure such driver data.
Linear excursion is the primary limiting factor for producing bass at high SPL, and many manufacturers lazily use the "formula" of voice coil height minus magnetic gap height, divided by 2.
This tells you absolutely nothing useful. Non-linear distortions caused by suspension geometry or motor strength modulation matter a great deal. Only a handful of sources such as Vance Dickason at Voice Coil Test Bench actually measure such driver data.
This is awesome. Can't wait to see what you do for your second post!
My own OB effort is far more modest (and woefully unfinished) but good response to about 40Hz is all I need. It's a basic Linkwitz H-frame built from Martin J King's design using an Eminence Alpha 15A. Sounds really wonderful, though, firing along the room's long axis in support of my Revel M106. Seeing yours has me wanting to build a column of them!
I use an old paradigm sub to extend response below 45 hz.
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