[scottw]

Hey,

There have been several examples of people using fairly inexpensive PA drivers to augment the lower frequencies in OB speakers. An example is Martin J. King's Project 7(with Alpha 15A):

http://www.quarter-wave.com/Project07/Project07.html

Even these large PA drivers(15 inch) are designed to go up to a few kHz, although in this application they are only used up to a hundred or so Hz. These drivers also tend to have fairly stiff treated cloth surrounds.

What kind of changes would you expect if you replaced the stiff surround with a more complient foam surround? Increased VAS and Qms? Would the Fs change?

Is the low frequency roll off usually seen on SPL plots of PA drivers related to the stiff surround(without EQ they may start around 150 Hz)?

I'm just wondering if a more complient surround could help a PA driver operate from Fs to around 150 Hz.


Scott

[JohninCR]

I think the reinforced paper surrounds used in pro drivers is part of the mechanical limit on excursion, so you can over-drive them without risking damage.  Accordian surrounds aren't used with drivers having extremely high excursion because they can't hold their form at big excursions, so they aren't used on true subwoofers.  I'm not sure I agree with the statement that they are "stiff".  While some may be, look at the Qms of the Alpha 15 for example.  It has a Qms of 7.23 , which seems plenty compliant to me.  The bottom line is that there's probably very little, if any, to gain, and all you'd end up doing is risk driver damage by driving your driver past its normal mechanical limits, which is quite easy with an open alignment.

I have some cheap high Q 15's with foam surrounds and all you have to do is breathe on them and they bang against the back plate, making them totally useless in an open alignment.  I have a number of different pro style woofers that never have any problems when pushed too hard, since that's what they are designed to handle.

BTW, if you are looking at the LF portion of the Eminence response graphs, it is meaningless.  I talked to one of the techs there who stated that their graphs represent response from 200hz up, because in the bass region the cab and alignment determine response.

[scottw]

Thanks for the reply John. It makes sense that if the surrounds were too complient the speakers would be hitting their limits at low frequency, esp. in an OB.

I was looking for a solution to a problem. Bought a couple fairly cheap 15 inch PA speakers(Knight-made in china) with a Qts ~ 1.0. One of the speakers is OK and the other had way too much glue smeared on the back of the surround when it was made. There is a very obvious complience difference between the two speakers because of the stiff glue pooled up on the back side of the one's surround. Was thinking of trying a refoam kit to try and salvage the project.

Scott

[JohninCR]

I bought 6 of the Warrior 15's.  2 had extra glue sticking in the surround causing a sticking noise I hadn't heard before from a driver.  It took a razor pencil and some patience to get all the extra glue off, but now they all work fine.  Its sounds like yours is more widespread and replacing the surround may be needed.  If so, I'd use an accordian surround.  Did you get those from MusicandSupply.com ?  Won't they just replace the driver?  I was thinking of getting some of the Knights while they are $50/ea, but now I'm not so sure.

Regarding the foam surrounds, I just think they could stretch too far, but the accordian type offers a firm limit on travel.

[scottw]

Yeah, Musicsupplycenter.com actually. And I don't have anything negative to say about them at this point. No response to my first email but email can get lost; and the response when I did get one was to just remove the glue. Well, I sent another email further explaining the situation and waiting for a reply. Guess I should just call them. Worst case, I could buy a recone kit from them for $19 plus shipping.

The Knight 15's aren't bad looking. These are the first PA type speakers I've had my hands on. I was surprised how stiff the cone material was compared to old EV speakers I've had.  Haven't listened to them yet.

Have you measured the Warrior 15's- I was curious how close they are to the stated T/S parameters?

And, you have done some U-baffles- how deep can you go on the sides if you plan to crossover around 150 Hz? (I need to sit down and figure the math out on that.)

thanks,

Scott

p.s. I was just comparing the specs between the Knight 15 and the Warrior 15. A lot of similarities. What is largely different is the VAS and the Qms are much larger for the Warrior. Makes me wonder if the surrounds on the Knights aren't treated/doped more making them stiffer(less complient)?
s

[Maxdd_nj]

I have a pair of the Knight-12s without the glue issues.
I'm still trying to decide what to do with them. I was going to build a pair of 4cu.ft.Aperodic boxes but after some forum reading I really like the idea of OB or maybe the w-baffle/Ripole design. Would the Knight-12s suit either of these designs or am I better off picking up something like the Eminence Delta 15LFAs?
Regards, Max

Knight-12 TSP
FS: 50 hz
VAS: 2.25
SD: 95.033
Qts: 0.64
Qes: 0.665
Qms   : 17.26
BL: 15.47
Re: 6.1
Nominal Ohms: 8
Le (uH): 511.32
Mms: 82.15
X max (inches): 0.25
X mech (inches): 0.5

[mcgsxr]

Maxdd_nj - welcome to AC, and especially, welcome to the Open Baffle Speaker Circle!

From my cursory review of the specs, the FS seems a little high, and the Xmax seems a little low.  I am concerned they don't have a long throw, and with an FS that high, I doubt there would be tons of low bass.

My current OB subs are from Mach 5 Audio - http://www.mach5audio.com/index-2.html USD $53...

And the specs are:

T/S Parameters - MAW-12
(coils connected in series)

Fs = 23.3 Hz
Re = 8 Ohms
Qes = 0.30
Qms = 3.03
Qts = 0.27
Mms = 144 grams
Rms = 6.96 kg/s
Cms = 0.324 mm/N
VAS = 76.6 litres
Sd = 408.3 cm2
Xmax = 13 mm
Cone Diameter = 22.9 cm

It is a dual voice coil sub - I use only 1 VC, so the QTS effectively doubles to 0.54, and with the combination of FS 23.3, and Xmax of 1/2 an inch, they can put out some bass!

[Maxdd_nj]

Thanks for the warm welcome!

mcgsxr, Is that your MAW-12 in the OB w/the b200 in your gallery? Looks pretty quality for that low a price.
The efficiency seems a little low, what do you drive your MAW-12s with and about how big is your room?
Does connecting only one of two VCs have negative effects on a driver?

After looking, I'm thinking about the MAW-15s for OB but will probably end up putting them in stereo (2x) W-baffles/Ripoles.
The H-baffle also looks interesting. Which of these 3 options will mingle best with a single fullrange driver?
Once I build a decent bass system I plan to move my Fostex FE207 to openbaffle (it's doing BR duties now).

Max

[Maxdd_nj]

Not sure if I'm hi-jacking this thread but there's a few things I read on this and other forums that I'm confused about. Maybe someone here can shed some light.

The center opening of a W-baffle or Ripole should be 25 - 30% driver Sd. If drivers xMax (pk to pk) is >10mm the opening should NOT be less than 30% Sd, if xMax is <10, the area should be no smaller than 40%.

I'll use the Knight-12 specs from above as an example...
xMax of .25" (or 6.35mm)
xMech of .50" (or 12.7mm)
Sd of 95.033

Assuming that xMech is xMax Pk to Pk: .30*95.033=28.5099

What exactly do I do with the number 28.5099?
28.5099mm is certainly too small for the opening and 28.5099" is WAY too big.

Please forgive my ignorance. I know I'm missing something, can someone help me understand this?

Thank you,

Max

[JohninCR]

Not sure if I'm hi-jacking this thread but there's a few things I read on this and other forums that I'm confused about. Maybe someone here can shed some light.

The center opening of a W-baffle or Ripole should be 25 - 30% driver Sd. If drivers xMax (pk to pk) is >10mm the opening should NOT be less than 30% Sd, if xMax is <10, the area should be no smaller than 40%.

I'll use the Knight-12 specs from above as an example...
xMax of .25" (or 6.35mm)
xMech of .50" (or 12.7mm)
Sd of 95.033

Assuming that xMech is xMax Pk to Pk: .30*95.033=28.5099

What exactly do I do with the number 28.5099?
28.5099mm is certainly too small for the opening and 28.5099" is WAY too big.

Please forgive my ignorance. I know I'm missing something, can someone help me understand this?

Thank you,

Max

Max,

IME those Xmax numbers on the Knights are probably peak-to-peak, so cut them in half for the more standard Xmax measurement (3mm xmax makes a lot more sense).  Xmech is the mechanical limit and is really only applicable in that you can drive it to twice the Xmax before risking damage.  Pro type drivers typically have a mechanical limit of 2-3 times Xmax.  Xmax indicates the limit where the voice coil remains fully in the gap.  Past that excursion operation is usually much less linear (ie greater distortion).

If you did the math correctly, those numbers are area, so you're looking at minimum openings less than 2.5" wide.

I'm not familiar with the guidelines you quoted, but I'd think with higher Xmax that you would want a larger opening, since more air can be moved.

[Maxdd_nj]

You're right, I misquoted the guideline. The second half of that guideline should read...
"...if xMax is <10mm, the area should be no smaller than 25%." (not 40%)

Since these guidelines are for minimum front-opening width, I wonder how far you can open-up this width before experiencing negative effect. If my 2 rear openings are 4-3/8" wide can I use the same (4-3/8") width for the front opening (or distance between facing drivers)?

Thanks for explaining xMax values.

Max

[JohninCR]

There is no negative to larger in a dipole.  Things change for ripoles though.  With a ripole the pathways are restricted enough that you have to consider the air mass loading with the goal being equal on both sides of the cone for optimum operation.  A benefit, in addition to the reduced size, of a ripole is that this air mass loading results in a significant reduction in Fs, although along with that comes reduced sensitivity.  Note that this happens with almost any manifold alignment at low frequencies, so lightweight cone pro type units aren't the type of driver I'd choose for either W or ripole manifold alignments.

[mcgsxr]

mcgsxr, Is that your MAW-12 in the OB w/the b200 in your gallery? Looks pretty quality for that low a price.
The efficiency seems a little low, what do you drive your MAW-12s with and about how big is your room?
Does connecting only one of two VCs have negative effects on a driver?

Those 12's on the same baffle as the b200 are indeed the MAW-12's.  Exceptional build quality for the $$.  Easily the equal of the $350 Rockford Fosgate woofer you see in other pics, that I bought years ago, for use in a sealed box in my old BMW.

I drive a pair of the MAW-12's with a 300w BASH sub amp.  By using only 1 VC per driver, and connecting the drivers in series, I end up with an 8 ohm load, thus really only using 240w.

Other than the even further reduction in efficiency, I am not aware of any other negative effects on the driver.  I assume that it has less power handling, due to using only 1 VC, but I am not sure.  I am very confident that since each driver is seeing a max of 120w (and I have never run the system FULL volume) that they are safe.

I continue to consider adding another set of MAW-12's, and connecting them all together (4 drivers to the sub amp) to get to the preferred 4 ohm load for the sub amp, and increase the air movement capacity of my system.

I do love my bass!

Mark at Mach5 is really good to deal with, and these drivers are the best bass bargain I have seen.  Period.  Serious drivers, cast basket, great XMAX (the quoted specs are 1 way... these things can bump) nice surround, vented pole piece that does not make noise at high RPM etc.

[Maxdd_nj]

Do you think the MAW-15s are a good fit for riploe configuration?

I think I'm going to put my pair of Knight-12s in a ripole. I know Knights are not suited for it but I got a great deal on them, the enclosure is simple enough to build, I need a project, and I want to play around with adding bass to my system. If I get really good results or see potential (with better drivers) I'll get a quad of the MAW-15s and build a stereo pair of ripoles.

If anyone is interested, here's what I was going to build for my Knight-12s before wanting to try the ripoles...
http://www.maxdd.com/_diyaudio/Maxdd_bass_v4.pdf

Who really wants to build a big box?

Max

[JohninCR]

Who really wants to build a big box?
Max

How about a very small open backed box?
Those Knights are likely to be really good OB bass augmenters.  They won't be close to the MAW's in terms of bottom end potential, but they'll be good up to much higher.  I hate to see you hide those in a manifold.  Say a 12"x12" cube, just large enough to mount the driver on the front and open in the back.  Add a "+" shaped brace and stuff it pretty well, then you've got a nice little U-baffle with an octave better bottom end than an equal depth ripole.  YOu would have to boost the bottom end to flatten the response.  A ripole is flatter on it's own, but it sacrifices sensitivity to do so.  A ripole is kind of like a mechanical Linkwitz transform.

[mcgsxr]

I cannot comment on the whole ripole thing.  I have read about them, and they seem interesting, but I am closer to JohninCR's thoughts around a simple H or U.

The MAW-15 sure looks like a capable driver, but John also makes a good point about how high you want your bass solution to play.  I have been using the 12's from around 100Hz and down, but have played with as high as 150Hz, or as low as 80Hz.

[Luigi]

I'm with John on this one. I have some new B200s up and running now in a smallish open baffle with wings, and support these with a pair of 12-inch open baffle U-tube (heh heh) bass units. These used to be sealed cylinder subs, but I merely removed the end caps. No longer are bass nodes in room an issue, and while there isn't the low end slam of the sealed subs, there's certainly much better extension than before. Fact is, the b200s would appear to work quite nicely on their own. Certainly better than the Fostex FE206Es I was using.

The baffles a friend helped me cook up in a couple of hours, using some scrap 1-inch beech over MDF and 3/4 inch wings of same. Have yet to finish these.

I'd post a pic of the new OBs, but dont know how cos of technophobia. I will try to post them in my gallery later on when I've got a spare day or so to work out how.

[Luigi]

FWIW, I managed to upload a jpeg of my new OB speaker see here

http://www.audiocircle.com/gallery/

Anyone want to let me know how to attach an image to a message here? When I pushed the insert image icon, nothing much happened.

[DanTheMan]

did I miss something?  What is a ripole?

Thanks,

Dan

[Maxdd_nj]

Read this post from the BD-Design forum.
The photos will make things much clearer then I can.
http://forum.bd-design.nl/forum_entry.php?id=11047
Anyone here ever listen to the BD15 bass drivers? Or the Quasar MKIIs ( http://www.bd-design.nl/index.html?lang=en-uk&target=d84.html )?