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_djk_ View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2007 at 10:05am
Post #87
"I'm interested in hearing more about dimensioning the cavity."

It's mainly a plenum to mount the drivers in, I generally make it as small as I can and have it all fit together properly.

"To go that high, I think you'll need to eliminate the parallel panels inside the cavity to avoid resonances, including the driver mounting panels. The opening would be taller and wider than the panel at the back."

The parallel resonance is high enough to be out-of-band. The dominant one is the depth, and the height, if close to the same dimension.

The mounting of the magnet structure of the one driver in the face of the other driver cone makes it very irregular in any event. Wayne Parham makes a horn with push-pull 12s. Wayne investigated push-pull mounting after a discussion we had on AA years ago. He says it makes a very audible difference compared to traditional mounting (as in) the Lab-12. Wayne used corner blocks to reduce cavity volume, mainly because the cavity in-between the drivers and the main horn affects the response of a bass horn a lot in the bottom octave (try it in McBean), not because of higher frequency modes.

I use parallel walls in the mounting plenum area. It does the job, is simple to build, and is strong. An easy way to shape the rear cavity corners is to use 703 fiberglass, trim to fit around the frame with an electric carving knife. If you do this, and make the cavity as shallow as possible (only large enough for mounting purposes), it should yield maximum bandwidth. Remember, we are not trying for a bandpass type resonant cavity.

The EV MTS1 is worth a mention. The cavity on this was paralled walls and push-pull mounted 15s, but instead of the plenum mounted at a right-angle to the front of the cabinet, it was horizontal and hung at an angle, maybe 45°. You would see the front of the plenum and look at the front of the woofer cone of the top driver (at an angle to you), and just a part of the magnet structure of the lower woofer (also at an angle to you). It looked a bit more complicated to build, but it must of had the mid-frequency response because it was mated to a HF compression driver at 500hz. I no longer can find a clear photo (of the plenum) of this product, although the data sheet is archived at EV.

"In the case you mention the speakers are still mounted in a box of some type??? Not like the open baffles with similar cavity? "

You can make it work with any type of loading suitable for your drivers. Mine have mostly been vented, and I use a regular box volumes and port tunings. Sealed volumes work well too. Wayne Parham uses a horn. Linkwitz uses open baffle, as long as you can live with its limitations that's fine too.

"I don't have room for bass horns."

Most people don't. For peoples' with size limitations this is a very good option. I have a friend that has twelve of the 31hz PPSL enclosures that I designed and had the drivers custom made for. My brother built them. For the total bulk of the system, a horn would have been better, but you can't use just one small bass horn. One of the PPSL will eat any bass horn of similar bulk in the bottom octave. The tapped-horn from Danley might be an exception, but it doesn't have the bandwidth that you can get out of the PPSL, and driver requirements and cabinet details are a bit sketchy at best.

"I am looking for something to mate to a horn like the Oris or the Pi or one of the other horns of this frequency range that have been covered in the forum. "

It should work very well in this application.

I use some custom drivers that will do 31hz to 200hz in a 15 cu ft (gross) box that are about 104dB/2.83V in their passband. This could be a 30" cube form factor for minimum footprint size, although virtually any shape and size can be made to work within the limits of the T/S parameters of the drivers you choose.

Various other box combo's tried:

Dual 8s shielded for a HT system (28hz)
Quad 12s for a car stereo (31hz)
Dual 12s for portable DJ use in a 2' cube form factor (40hz)
Dual 18s for dance club install in a 3' cube form factor (28hz)

Except for the dual 8 design, these were all for rot-your-face-off levels and trade-offs were made for maximum bass extension and minimum size.

The friend mentioned above with twelve dual 15 PPSL boxes used to work for JBL, and now only uses JBL for HF. Steve started out with eight, and only used all eight one gig (not counting a rave). Later he added another four, and has the ability to do multiple jobs of various sizes. Steve only takes one PPSL into small clubs, and seldom does four (two per side). Twice last year three per side were taken out, both were college home-coming dances, one being in a 4,500 capacity auditorium (festival seating, ie: standing room only).

Another sound company about 20 miles away has a similar modular system. A link-up for a huge show may be in the works.

Horn loading is employed above about 150hz (100hz~250hz) depending on requirements.


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Disco Stu View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Disco Stu Quote  Post ReplyReply Direct Link To This Post Posted: 18 January 2008 at 4:15pm
Originally posted by _djk_ _djk_ wrote:

If you run them at an angle, they work better this way:





is that your box design djk?

From your own experience if someone was going about a design like the one in the photo what drivers would you use and how big would you make that kind of manifold front chamber? Does the angle matter? Im talking subwoofer for live use so probably doesnt need to go above 140Hz and would be more interested in using Neos 12 or 15 if possible.

Stu

Edited by Disco Stu - 18 January 2008 at 4:20pm
All you need to know is:
Sensitivity + Power Handling - Power Compression = Max Output

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Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 19 January 2008 at 11:24am
That's someone else's design, it's actually a dipole! I always make mine with parallel motor boards (like the thumbnail sketch above), but this method looks pretty good too. I would probably put a brace front and center in the manifold. I am a little concerned about the strength of the angle joints, I would want to use splines in them for maximum strength.
 
"From your own experience if someone was going about a design like the one in the photo what drivers would you use and how big would you make that kind of manifold front chamber? "
 
It's mainly a plenum to mount the drivers in, I generally make it as small as I can and have it all fit together properly.
"Does the angle matter? "
 
No, but I would probably not build them with an angle. If I did I would probably try 60°.
 
"Im talking subwoofer for live use so probably doesnt need to go above 140Hz and would be more interested in using Neos 12 or 15 if possible."
 
If you were in the USA I would suggest the Eminence 151269, about 13lbs and 9.1mm x-max for $USD 65.  You will need to examine what drivers you can obtain locally and choose accordingly. Ideally, for minimum box size and maximum bass extension you want a Qts=0.312 and an Fs of the desired cut-off frequency.
 
If I had the money I would try four of these and a pair of Crest CA18; one box per side, one amp per side. I think the box would end up the same size as my dual 15 boxes, and have the same F3, but be able to handle 3KW for 135dB from one per side (about what three per side of my dual 15 boxes do).
 
 
 


Edited by _djk_ - 19 January 2008 at 11:32am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Disco Stu Quote  Post ReplyReply Direct Link To This Post Posted: 19 January 2008 at 6:11pm
So djk from what I have read

1) There is no increase in efficiency over a regular box with this design however because of the way the driver is loaded it means the cabinet can be made smaller than a standard reflex with lower distortion. Is this correct?

2) Both drivers in your plan are wired the same i.e. firing in the same direction?

3) Can you give me any more info about your box, if I were modelling this in WinISD or BB6 should I use a standard reflex with a push pull configuration or something else?

4) You said if I went with the 21SW B&C I could get around the same volume from the box as your double 15 of the same configuration. How is this so?

Stu
All you need to know is:
Sensitivity + Power Handling - Power Compression = Max Output

My acts:
www.myspace.com/thebowiexperience
www.myspace.com/scheisseelektronisches
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_djk_ View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 20 January 2008 at 4:43pm

"1) There is no increase in efficiency over a regular box with this design however because of the way the driver is loaded it means the cabinet can be made smaller than a standard reflex with lower distortion. Is this correct? "

The PPSL boxes are just an ordinary B6 reflex alignment. The B6 is the optimum trade-off between size, efficiency, and bass extension. The PPSL cabinet is exactly the same volume as a straight relfex box for the same driver, plus the volume for the plenum. On my dual 15 boxes the plenum adds about 1.5cu ft net for both drivers, so if you need 4 cu ft per driver for a B6 you will need 4+4+1.5=9.5 total vs 4+4=8 for an ordinary box. The extra 1.5 cu ft allows for dramatic distortion reduction, these boxes have less distortion than bass horns (unless you run them PP like Wayne does)! The main advantage is that one or two of these per side will eat any conventional horn box (with the exception of a Danley tapped horn).

"2) Both drivers in your plan are wired the same i.e. firing in the same direction? "
 
No, the driver whose magnet you can see in the plenum has to be wired up backwards to keep cone motion in phase.

"3) Can you give me any more info about your box, if I were modelling this in WinISD or BB6 should I use a standard reflex with a push pull configuration or something else? "
 
(going from memory here as this computer doesn't have BassBox on it) You can model it in BassBox v6 under assisted reflex Q=1.93 (the default Q) with Faux set to Fb (when using a Qts=0.312). Try a volume of about 4.1 times the Vas total for the drivers.

"4) You said if I went with the 21SW B&C I could get around the same volume from the box as your double 15 of the same configuration. How is this so? "
 
The B&C 21 neo has a very low Vas and Qts and is not really that efficient (95dB), so it will work in the same sized box as the typical 15 but give hugh output because it has twice the cone area and twice the x-max of a typical 15. I don't think it is practical because of the cost, both of the drivers, and the bigger amp required. Two per side of my dual 15 boxes will have the same output, with only $500 in driver cost vs $2800 and $800 in amplifiers vs $3000.
 
There is also the matter of stacking, two per side gives me a 4' high base for the mids and highs to stack on; one per side would require scaffolding of some sort. The last problem is that of powering those huge 5KW amps, they are not going to run from a couple of wall outlets like the smaller amps will. My big system that has a distro hooked to the mains would benefit in size from the B&C 21 drivers, but it only goes out about five times a year, requires the straight truck anyway, and would never return the cost of investment.


Edited by _djk_ - 20 January 2008 at 4:49pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 20 January 2008 at 5:14pm
Efficiency comparison (ignoring power compression):
 
Two B&C 21 at 95dB/W/1M gives a system of 98dB/W/1M. With 3KW input power (34.8dBW) that gives 132.8dB for one cabinet, plus another 3dB for the cabinet on the other side of the stage (135.8dB). Total amplifier power required is 6KW, this will draw over 50A at 240V on program material with dance music type high duty-cycle bass (droning sweeps).
 
Four 15 at 95dB/W/1M each gives a system of 101dB/W/1M. With 1.5KW input power (31.8dBW) that gives 132.8dB for two cabinets, plus another 3dB for the cabinets on the other side of the stage (135.8dB). Total amplifier power required is 3KW, this will draw only 2x25A at 120V on program material with dance music type high duty-cycle bass (droning sweeps) so you can power it from two wall outlets (one per each side of the stage on different breakers).


Edited by _djk_ - 20 January 2008 at 5:38pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Disco Stu Quote  Post ReplyReply Direct Link To This Post Posted: 20 January 2008 at 9:04pm
Originally posted by _djk_ _djk_ wrote:

Efficiency comparison (ignoring power compression):
 

Two B&C 21 at 95dB/W/1M gives a system of 98dB/W/1M. With 3KW input power (34.8dBW) that gives 132.8dB for one cabinet, plus another 3dB for the cabinet on the other side of the stage (135.8dB). Total amplifier power required is 6KW, this will draw over 50A at 240V on program material with dance music type high duty-cycle bass (droning sweeps).

 

Four 15 at 95dB/W/1M each gives a system of 101dB/W/1M. With 1.5KW input power (31.8dBW) that gives 132.8dB for two cabinets, plus another 3dB for the cabinets on the other side of the stage (135.8dB). Total amplifier power required is 3KW, this will draw only 2x25A at 120V on program material with dance music type high duty-cycle bass (droning sweeps) so you can power it from two wall outlets (one per each side of the stage on different breakers).


Not ignoring power compression the 15s should win out

Anyway thanks very much for the info its very interesting, so you were saying that the Vas is one of the most important specs before since it dictates the total size of the box, what other specs apart from Qts=0.312 are relevant. Whats the tolerance in the Qts spec?

Stu
All you need to know is:
Sensitivity + Power Handling - Power Compression = Max Output

My acts:
www.myspace.com/thebowiexperience
www.myspace.com/scheisseelektronisches
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Disco Stu Quote  Post ReplyReply Direct Link To This Post Posted: 20 January 2008 at 9:30pm
What about the following?

Eminence Kappalite 3015LF?

OR

http://www.bluearan.co.uk/menu/index.php?id=BMA115NDW&product=Beyma_115NdW_15!dquote!_700w_AES_8_Ohm&browsemode=category

http://www.eminence.com/pdf/kappapro-15lf-2.pdf

Also worth investigating 12s since I can get higher sensitivity using more smaller drivers but cant find many Neos atm!

Stu
All you need to know is:
Sensitivity + Power Handling - Power Compression = Max Output

My acts:
www.myspace.com/thebowiexperience
www.myspace.com/scheisseelektronisches
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Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 20 January 2008 at 10:53pm
The Beyma is L`170 with VAT even in Europe.
The Eminence is only $104 in the USA, about L`118 with VAT in Europe.
 
The Eminence is 3dB more efficient and has a higher x-max. Being 3dB more efficient they would play as loud with 350W as the Beyma would with 700W.
 
I think I'd rather have the Eminence, they look good in BassBox v6 with 4 cu ft per driver ported to 40hz (F6 point).
 
"Vas is one of the most important specs before since it dictates the total size of the box"
 
In general, box size is proportional to the square of the Qts times the Vas, and the useable low end is roughly Fs divided by Qts times 0.312
 
From the above we can see that the lower the Qts, the smaller the box size AND the lower the Qts the less bass we get. The two formulas have an intercept at a Qts of 0.312, so the optimum trade-off of box size, efficiency, and bass response for a vented speaker is with a Qts of 0.312
 
Efficiency is Fs^3*Vas (in cu ft)*0.000'00277/Qes. The answer is in %No, 1%=92dB, 2%=95dB, 4%=98dB, etc.
 
    Posted by djk (M ) on July 25, 2005 at 00:55:59
    A 2 cu ft 2nd order sealed box with an F3 of 30hz can only be 0.18% efficient (84.55dB).
    A 2 cu ft 4th order vented box with an F3 of 30hz can only be 0.36% efficient (87.56dB). 
A 2 cu ft 6th order vented box with an F3 of 30hz can only be 0.90% efficient (91.54dB).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Disco Stu Quote  Post ReplyReply Direct Link To This Post Posted: 20 January 2008 at 11:56pm
I see, well the Eminence is nice and cheap which is why I liked it but the Vas is quite high so I thought it may not work. Cant see much else available that will work well!

So a couple more questions while I think of it, did you try different heights to the plenium, is it just a case of as small as possible or is there a range for a 15" that works well?

Also, you had the port in your design at a different place to the drivers, would it also work to use the plenium as the port?

Thanks

Stu
All you need to know is:
Sensitivity + Power Handling - Power Compression = Max Output

My acts:
www.myspace.com/thebowiexperience
www.myspace.com/scheisseelektronisches
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Post Options Post Options   Thanks (0) Thanks(0)   Quote da_audio_don Quote  Post ReplyReply Direct Link To This Post Posted: 22 January 2008 at 9:25pm
http://www.eaw.com/info/EAW/Loudspeaker_Product_Info/Current_Loudspeakers/FR250z/FR250z_PHOTO.jpg
 Speaking of push-pull designs, I was thinking of coming up with my own version of of the EAW FR 250z. Am I hurting myself with me desire to have my baffles straight instead of angled and model it as a regular vented enclosure??
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Post Options Post Options   Thanks (0) Thanks(0)   Quote darkmatter Quote  Post ReplyReply Direct Link To This Post Posted: 30 September 2009 at 2:39pm
Looks like this driver might work:
 
No idea on price though, I imagine it's pretty high.
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