suitable dipole mid-woofers

[smak]

after sucessfully completing my dipole sub-woofer project (w-frame using pyle 15" drivers) i'm itching to swap my mediocre cabinets with maybe a nice plate glass or acrylic dipole replacement.

I already have a pair of horn tweeters laying around which i'd really like to make use of.. they're labeled foster 025N47 and have a min crossover listed at 5k. My sub is great from about 100hz down, so basically i'm looking for something that will do well from 100hz-5khz.

i'm at a loss as to which woofer to use though. I was considering linkwitz's mini-dipole prototype choice (vifa P21) but it seems to take the more difficult route of forcing a conventional driver to respond well in a open baffle as opposed to choosing something which will respond well naturally. i'd like to avoid eq alltogether if possible.

i've heard ciare make a great low cost driver that would suit my needs but they dont seem to be avaliable in north america. I'm located in canada.

any ideas out there?

[Sjef]

Supravox makes suitable 8"drivers for use in an open baffle. They work very well in combination with a fostex horn tweeter.

To reach 100Hz you will need a relatively big baffle, can look very nice in acryllic though, see the various open baffle projects on the forum.

Are you using the subs without any eq ?? Hardly unbelievable. I'm also using a w-baffle with 15"drivers and defenitly do sound a lot and than a mean a LOT better with eq.

The fact that Siegfried Linkwitz is using small baffles for the low/mid range and a relativly low crossover point between mid and high has every thing to do with the desired off-axis response, not with the fact of having a small baffle.

I have been experimenting a lot with open baffle and as a conclusion of all my experiments I can tell you that Siegfried Linkwitz isn't such a stupid guy after all, if only I had believed him right away would have saved me a lot of trouble.

[static]

Hi All

for some reason my first reply did not make it through, so i will repeat myself (if the first reply do appear though dont be surprised)

smak:
I'm sorry I dont have the answer for your question about the woofers, but I have a question though.
Where in Toronto did you get those 15'' Pyle?
I am a beginner in the whole dipole thing so decided to experiment with it a bit. I needed a sub to extend my mains and got on the topic of dipoles - got fascinated.
Couple of days ago I've got a couple of 12'' Pioneer TS-W34C car subwoofers (Qts: 0.64, Fs: 29Hz - i know not the best for the application) they were quite cheap on sale @ Futureshop, so I got them.
I dont expect much from them, so if I can get the 15'' Pyles for reasonable price, I'd return these.
Can you drop me an email? Mine is ababkin_NOSPAM_@yahoo.com (remove _NOSPAM_)

Sjef:
What configuration H or W would you say is better?
I too thought that the reason Linkwitz used small baffles was in pursuit to get a smaller overal box. Since size is not much concern to me - I was going to make the baffle and walls bigger. So you are saying that you tried that and it didnt work out? (that is size does not equal more/lower bass, because as far as i understood - the bigger the baffle the lower is the 6db/oct rolloff starting point)
Also i was wondering about the optimal proportions of the H, or W for that matter, configurations. I think I read somewhere that the 'wings' (baffle folds) should not pertrude to far, as it would create undesirable turbulence and so on.
I've been reading dipole related stuff for days nonstop now, so no wonder it all gets fuzzy to me now

Any input appreciated
Thanks
Alex

[Nuuk]

Sjef - my sanity is at stake here! I have been trying to locate suitable drivers for dipole bass units for ages but can't find anything I like this side of the Atlantic. What do you use and where did you get them?

And what do you use for the mid/top in your system?

[Sjef]

Nuuk:

I'm using a pair of JBL 2205H 15" PRO woofers each side in a relativly very small w frame baffle. It measures 40*44*44cm, couldn't get it any smaller. The woofers only just fit into the cabinet.

These are very old woofers wich came out of an old PA system from the mid-seventies. They where quite expensive those days but I had them for free, they where just lying around at my job. didn't expect much of them, didn't know what to do with them, any enclosure would have become way too big with these drivers. So I tried the W baffle. Never would have thought it would stay in my system, but I like it, a lot.

When you look at the specs of these drivers anyone would say that they are not suitable for open baffle. They have a resonance freq of 31Hz with a Q of 0.31 and a max excursion of 4mm Together in the W-baffle they have a resonace freq of only 16Hz due to the air compression in the cabinet, Q stays at 0.31

Because of the low Q and the baffle properties I get a roll-off at 100Hz with 12dB/oct. That has to be compensated for with an active eq. For anyone who's worried about the sound pressure capability, here is a comparison list

Lets compare it with a 10" subwoofer with a Xmax of 10mm in a closed box (very common these days)

maximum achievable sound pressure

2*15"/4mm open baffle

[Nuuk]

Well, it looks as though I may have to settle for a lower Qts and a bit more EQ!

That would open up the options a bit for sure! Back to the search.....

[Sjef]

Sorry, something went wrong in posting.

The comparison table of maximum sound pressure

2*15" Xmax 4 mm in my W-baffle

25 Hz = 83 dB
35 Hz = 92 dB
50Hz = 101 dB
71 Hz = 110 dB
100 Hz = 119 dB
141 Hz = 128 dB
200 Hz = 137 dB

1*'10" Xmax = 10mm !!!in a closed box

25 Hz = 88 dB
35 Hz = 94 dB
50 Hz = 100 dB
71 Hz = 106 dB
100 Hz = 112 dB
141 Hz = 118 dB
200 Hz = 125 dB

Be very aware of the difference in Xmax.
I have made this comparison because with this two differnet arrangements you will get aprox. the same enclosure size
Off coarse 2 15"drivers in a closed box can deliver much more sound pressure but in my case that would be a closed box of aprox. 500 liters, so that's not a fair comparison, is it.

[static]

Sjef,

Can you please answer my questions posted by me earlier?
If I am going to use 12'' subs with Fs: 29Hz and Q:0.65, will Fs go lower at all in H configuration? or only in W ? Do you have pics of your dipole? What kind of eq are you using?

Thanks
Alex

[ThorstenL]

Konnichiwa,

Originally posted by Nuuk
Sjef - my sanity is at stake here! I have been trying to locate suitable drivers for dipole bass units for ages but can't find anything I like this side of the Atlantic.

You may have looked long, but obviously not very hard... ;-)

There is plenty od Pro-Audio and interestingly Car Audio stuff around that lends itself to the topic. Okay, cheap or next to free they ain't, but good driver usually never are....

Sayonara

[Sjef]

Static:

I did not say that you won't get any further low end extension with a bigger baffle. That's defenitly true. The bigger the baffle, the further the extension, quite simple.

What I meant to say is that it's not only the low end extension. It's also about the desired off-axis response.

I'm using a PHY-HP 8" wideband unit as a midrange. This is a sort of tweaked out version of the Supravox unit that Thorsten uses in his baffle, it's got more or less the same properties. This in combination with a imitation (and actually improved) version of the famous DECCA/Kelley DK30 ribbon horn tweeter. Mine comes from Jordanow.

I have tried many sizes of baffles. Also tried about the same size baffles as Thorsten. That worked pretty well and I have listened to it for a long time, thinking it was one off the best speakers I have ever had. But when you measure the off axis response, the Phy started to roll off at a little above 1 kHz, not much off full range outside off the sweetspot I would say. With a smaller baffle this rolloff point was extended to a little above 2 kHz. So instead of more low end extension you get a wider dispersion at the mid's.

Tried to combine this with a tweeter crossed at 9kHz, the natural endpoint of the Phy. Worked pretty well indeed, but you will still here the units playing seperatly. Why??

Measuring again under 30 degree angle showed the problem. There was a strange dissorder in dispersion. The Phy starts to beam at 2kHz, but at 9kHz (the crossover point) it start to disperse again. That's not good for room integration.

Changing the crossover point to 2,5kHz cured this problem very nicely. Thank you again Mr. Linkwitz !!! Couldn't get any lower because of the horn resonance of 1kHz from the tweeter.

At the low end I have tried to compensate the Phy down to 100Hz. The small baffle starts to roll off towards the low end at aprox. 300Hz. That did not work out very good. First of all, I was a little short in amplifier power. The Phy is powered with a 8 ? (maybe even less, never measured it) watt SE 300B amp. Second, the Phy doesn't like to move that much. So I moved the crossover point to 200 Hz. That right on the edge for the subwoofer. The W-baffle has a very strong resonce at 270Hz, but with steep filters and an extra notch filter it's possible.

So I use the Phy only from 200 Hz to 2,5kHz ? Yes. The Full range mafia will kill me for this !!! I'm gonna be thrown out of their church I guess. But hey, it's still a pretty good midrange.

All the crossover points are now right on the edge off the problematic area's of the drive units. This is possible for me because I'm using Linear Phase digital crossover and freq, phase and time correction with a slope of 90db/oct. (I'm really starting to love my DEQX unit) This combination as it is now simply NOT possible with 24 db/oct crossovers. You will get colouration of the woofers resonance. Also colouration of the cut-off frequency off the horn tweeter, and a colouration of the Phy moving too much.

As you can see, there are many many ways that lead to Rome.