open baffle

Smokeyone said:
Is the bass likely to be any good.............

Typically bass is very good -- no box to add its signiture, but getting it to go low is a challenge.

I know Peter says he is getting good bass from his dipoles despite their small size.

The attached nomograph gives an idea of the physics.

dave
 

Attachments

  • infbaffle-width.gif
    infbaffle-width.gif
    14.7 KB · Views: 815

Smokeyone

Member
2002-06-21 7:48 pm
More Questions

Thank you both for your replies. I am tempted to go ahead with the Linkwitz prototype complete with passive crossovers especially after reading Peter's comments. However the TL design page is very interesting and unless I have missunderstood the graph it is technically impossible to get deep bass out of an open baffle unless it is door size.

A sideways question might be how do the new, very expensive,
high tech looking speakers from large firms bring out the bass in a box the size of three pkts of cigs or the size of a peperback.

Thanks

Smokeyone
 

diypole

Member
2002-10-01 6:14 pm
Vermont
I have built the w-frame subs that go with the pheonix, and have in room response well below 30hz. These are built with 4 madisound 1252dvc's. Since I built these, Peerless has come out with the xls subs, which Linkwitz now recommends, and which should give +3db over the madisound(which are no longer available).
I beleive Peter is getting the in room response he says he is, as it correlates well with many others who have found that (in room) dipole bass response does not perfectly follow thoery. I am satisfied with the spl I can acheive, but the real advantage of dipole bass is that room modes are excited far less than with monopoles, and the increased definition is readily apparant. There are null planes on all sides of a dipole woofer, which make it moderately directional, and provide better power matching with midrange. All in all, about 1/3 less power is put to the room according to Linkwitz.
Right now I am getting unequalized response before rolloff to ~300hz with two Peerless 10 inch csx in a mtm configuration with a 7" x 2" planar magnetic on a baffle that is 13" wide by 3.5" deep with 3/4" thick sides, crossed at 1000hz 24db/oct passive(for now). This corresponds to a 43" round trip, or 1127feet per second divided by a 3.58 ft baffle gives 314hz supported before rolloff. I can then equalize these to cross with the dipole sub around 100hz(still experimenting), but you see why you need 2 10" woofers with 9mm x-max, as air must be shoveled to fight rolloff. While this may be a 'po mans pheonix, it does have some advantages in it's own right.
I am very happy with the sound. No matter what level you want to play them at, you will not strain to hear detail. Soundstaging of live performance is magnificent, with uncanny depth. If you build the pheonix, you might consider doing what I am going to do next; a stacked w frame with Peerless xls similar to this http://members.tripod.com/jimmcdougall/id31.htm

Should make scary dipole bass. regards, Jason
 

Smokeyone

Member
2002-06-21 7:48 pm
Phoenix grand

Thanks for the advice. How are you coming along with the Phoenix Grand....around ten feet high I would guess....

I have actually been looking at the Phoenix prototype which is on the Linkwitz page link at the bottom under prototype.

This uses a passive crossover and I am not penny pinching but multi amps would be just too costly. From the advice given I think I should be happy but am wondering if there are any ways to improve on the Linkwitz design, maybe better quality drivers etc.

Smokeyone
 

diypole

Member
2002-10-01 6:14 pm
Vermont
If you can afford the drivers Mr. Linkwitz has designed for, there is no way to improve. IMO Siegfried Linkwitz is on the cutting edge of Loudspeaker design. A retired engineer, having been involved in the feild for years, and having no other design considerations other than absolute reference to unamplified sound, he has been extremely generous with knowledge many would refrain from publishing due to monetary interest.
To quote "The typical box speaker, whether vented, band-passed or closed, is omni-directional at low frequencies and becomes increasingly forward-directional towards higher frequencies. Even when flat on-axis, the total acoustic power radiated into the room drops typically 10 dB (10x) or more between low and high frequencies. The uneven power response and the associated strong excitation of low frequency room modes contributes to the familiar (and often desired :-( ) generic box loudspeaker sound. This cannot be the avenue to sound reproduction that is true to the original."
S. Linkwitz@ http://www.linkwitzlab.com/rooms.htm
My project is coming along great, thanks. I am only building stacked subs like the one on the link, not the whole system. With the stacked subs, it will just be tall enough to put the listening axis of my MTM at ear level. I am finding the MTM main panels to be very satisfying with the subs off though. As a 2 way dipole they are covering from 13khz to below 100hz very nicely(listening to Natalie Merchant live on broadway now). Kind of like a huge dipole bookshelf speaker-lol.
Active cross with amplifiers hooked directly to drivers makes a big difference though. Once I sell the passive versions I am building(3 ordered), I will make myself an active one. You may consider buying kits from Marchandelec.com, I find them a unique value. You could probably go active for less than $300. Oh well, doubt you'll regret building the pheonix.
regards, Jason
 

dc

Member
2001-12-26 9:04 pm
NYC
diypole,

I started a thread last week about dismantling my Phoenix and making box speakers with the drivers (all Scan-Speak). Since then, I've added some damping material to the insides of the midrange and the sound improved dramatically. I'm ordering parts now to change the woofer to mid XO to 24dB/octave. I'd also like to double-up on the woofers (8 more Peerless?).

Are you using the Scan-Speak or Seas drivers? SL lists changes to the XO for the Seas drivers on the page for people who bought PCBs, now. If things continue to improve after adding some woofers, I might try my hand at a 4-way with Seas drivers. The Seas 8" SL recommends as well as the Seas 10" that was discussed on the dipoles forum are less efficient than the Scan-Speak, but several have reported better sound. I could then use the Scan-Speak drivers in a pair of Orions...

There are several excellent drivers that I don't believe have been tested - Triangle midranges, Lambda Acoustics dipole drivers.... These are more expensive, but may make a great soeaker even better.
 
I'm currently assembling the parts for a modified super-Orion/Beethoven. The main tower is a taller Orion style array using the Seas Millenium, 2 x SEAS W22 mids and two Focal 10L6411 aluminium woofers and the dbx Driverack PA digital crossover/EQ.

The woofer towers are (at the moment) going to be two of the new Stryke AV15 drivers (23mm Xmax), which should give the equivalent of about four of the Peerless 12 inch drivers, EQed with a Behringer Feedback Destroyer.

Once this is finished I'll work on surrounds, but probably two ways with passive crossovers.


Steve