Use of large pro driver as OB-feasible?? - diyAudio
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Old 16th April 2007, 09:32 AM   #1
terry j is offline terry j  Australia
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Default Use of large pro driver as OB-feasible??

Hi every body

I originally posted this question in the Ariel thread, which on hindsight was a totally silly thing to do as it understandably got totally overlooked so here it is all on itís lonesome.

Tiny bit of background. Iíve only ever heard two dipole speakers, one was the Alon 4ís and the other the Orions. To be honest, they didnít do it for me, BUT the dipole bass on the Orions I thought was very nice indeed.

So, it has got me thinking about converting my sealed bass to dipole. I use an 18 inch PHL sealed in about 110 litres. It doesnít go deep naturally, with appropriate eq I can get it flat to thirty hz then it drops like a stone.

Now, I also happen to have four peerless 10ís a la the orions, but there is no point in going dipole with the tens as in the orions and then using the phlís as a sub to go under them because they wont!! Ha ha.

I have a set of plans (from shinobiwan) that uses the four peerless as a sub to the high teens (I think) so I can use that for the bottom octave and a half, if I can turn the PHLís into a decent dipole bass unit from 50-60 hz up.

7030 parameters

HIELE-SMALL PARAMETERS: TYPICAL (QC LIMITS)
Resonance frequency
Fs 34(Ī5)
DC Resistance 5.5(Ī0.5)
Mechanical quality factor Qms 4,8
Electrical quality factor Qes 0,41
Total quality factor Qts 0,38
Mechanical suspension compliance Cms 115
Effective piston area Sd 0,128
Equivalent Cas air load Vas m3 ,260
Max linear excursion Xmax Īmm 8,0
Linear displacement volume Vd 10-3.m3 1,024
Reference efficiency 0 % 2,5
Unity load volume Vas.Qts2 10-3.m3 41,4

Iím wondering if my real problems may lie in how high I want the bass unit to go. I donít really want to take my mids lower than 300 hz, and so for all I know that may be the problematical area for running a dipole bass.

Does the fact that it will only be a single driver mean that vibration will be a huge issue??

All help will be appreciated, but I certainly donít expect others to design it for me ha ha, your help will be more like in the way of links etc.

Iíve waded thru Seigfrieds site once or twice now, it gets easier each time but I dare say it will take a couple more times yet before my old Pooh Bear brain gets it all.

The actual xover implementations and eq that might be required are reasonably easy for me, it will be in a fully tri-amped deqx system. Although with the addition of the four driver sub, it will be in effect a four way setup, but will probably run the sub with a piece of behringer kit rather than an extra deqx!!!!

I will leave the mid and high as it currently exists, and just go for the dipole bass. The other option is too simply hack off the back of my existing sealed box and measure what happens, ie a version of suck it and see. The depth of the box is only about 300 mm, so in effect I suppose there wouldnít really be much separation of the front and rear signal.

Hope I have given enough info that someone doesnít have to ask for much more, and I hope Iíve done it without boring the hell out of you!!!

Thanks a lot

terry
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Old 18th April 2007, 07:33 AM   #2
Pano is offline Pano  United States
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Hey Terry - funny you didn't get any responses to this. So I'll bump it.

I haven't ever heard the PHL drivers, but they get good reviews.
No surprise that your 18" drops like a stone under 30Hz, at least that's what I would expect in OB, don't know about sealed. Still, that's pretty decent, you know. Do you really need that 20 to 30 Hz range? Or are you just not happy with the low end below 60?

You don't say what your mids are (or did I miss it?). A lot of good 18s will play pretty high, it's only beaming that becomes an issue. With that deqx you should be able to get out of the 18 real fast, if need be.

The Q of the driver is a little low for OB, but you may be able to make up for that with lots of power and EQ, a la Linkwitz

From what some OB users have told me, the single 18 can be a vibration problem. Sometimes they "walk" if you play them hard. I don't play my single 15s that hard, so mine stay put.

Let us know what progress you make.
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Old 18th April 2007, 07:34 AM   #3
terry j is offline terry j  Australia
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OK, probably bored the hell out of you all ha ha. No, more likely that only those who helps themselves get help-and fair enough too I say.

To that end, just been to the local hardware and grabbed some roughed up gyprock (drywall I think you call it) for nix, and have decided to simply mount the woofers and then by measuring see what happens. Suck it and see indeed.

Anyway, will get started soon and post the measurements so others may learn something. It will probably confirm what some already know, but at least for me I will have learnt something.

will keep you informed.

isn't it always the way!!! post something and then find that someone has just posted ha ha.

Just to clarify, the 30 hz is the phl's in a sealed box, and eq'd to the max. I intend to see how low they go OB, and am not fussed if they only go as low as say 50 hz as I can put a sub under them.

The mids are also phl, will have to look up the number if someone is interested, but it is their dedicated - no compromise mid. If you can put any stock in marketing language!

The tweeter is the cabasse dom 40.

yes, will certainly keep any interested people up to date.

The bass is very tight and certainly visceral, just the way I like it!!
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Old 18th April 2007, 05:22 PM   #4
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Hi. Two words: Linkwitz transforn. If you want bass from that driver below 30Hz, OB is not the way to go IMO. That PHL is perfect for LT, just needs lots of power. Your box maybe a little big for it, but easily corrected.
It's what I use, and I'd never go back.
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Old 18th April 2007, 06:37 PM   #5
Rudolf is offline Rudolf  Germany
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You could build a "ripole" with that PHL driver. You can expect Fs to fall into the mid 20 Hz. But you should be aware of dipole bass limits in rooms.
There have been some ripole threads in the subwoofer division of this forum.
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Old 18th April 2007, 09:03 PM   #6
Paul W is offline Paul W  United States
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If you are satisfied with 50Hz, with appropriate EQ, you should be okay.

I'd be more concerned about the 300Hz top end you want. Look for the drivers 1st breakup frequency...you may see the impedance curve "wiggle" at that point. Ideally, XO no higher than 1/5 that frequency, but 1/3 should be okay with a steep slope and a notch filter. This will minimize harmonics exciting the cone breakup.

7030 Mms is fairly low, so you may not have a big problem with vibration...though I can't imagine too much baffle mass for big cones.

Here is the BMS 18N850 in a 15" felt-damped U-baffle. Because of the baffle it doesn't need much EQ at 50Hz. However, Mms is high so even the 1.5" baffle is not heavy enough to prevent vibration. 1st breakup is just over 1k so I haven't tried it above 200Hz.

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Old 18th April 2007, 10:30 PM   #7
ttan98 is offline ttan98  Australia
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Paul,

I notice you build the U frame woofer based on the 15" frame, you be able to advise me which sort of parameters one shuld be looking at in order to build a U or even H frame woofer.
example
Qts should be medium high around 0.4 or higher?
and what about other parameters?

thanks...
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Old 19th April 2007, 12:19 AM   #8
Paul W is offline Paul W  United States
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ttan,
These two guys have forgotten more about dipoles than I'll ever know...great reading which should answer any questions you have.
Paul

S Linkwitz site
John K site
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Old 19th April 2007, 12:49 AM   #9
terry j is offline terry j  Australia
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Wow, thanks guys. Nothing for a day or two, I wake up and all of a sudden there is heaps!!

mml2, currently they are in a sealed unit (not sure my first post was all that clear?) and as you say, eq'd heavily. But being big pro drivers they can certainly handle the power. From memory in the sealed box the Fb of the box is something like 70 hz, so an awful lot of eq is used to make it go lower.

Once they get put into an OB situation, they will I'm sure still require heavy eq. Those duties will be handled by the deqx unit. As I mentioned I'm not that fussed how low they end up going because I can throw a sub in under them.

BTW, if the sub only goes up to (say) 50-60 hz, will a single sub be sonically noticeable?? or should I split the single sub (four drivers) into two stereo subs of two drivers each and make it a true four way rather than three way plus sub.

Rudolf thanks for your suggestion, have come across ripole before. Will have to go and do a bit of looking up later (need to get some work done) but from vague,vague memory a ripole has two drivers??? As I say I need two go and have a look.

Paul, thanks. Interesting you should mention the upper frequency as the potential problem, I wondered if that might be the case as well. My measuring techniques at the moment are limited to frequency sweeps. Would the breakup frequency you mention be evident in that??

For my education, what is the effect of going higher than i/3 breakup frequency, does it simply leave a hole in the response for example? Bear in mind that the deqx can measure and correct the measurement, so any problems in the frequency domain I'm not to fussed with, but as you can tell the finer points of these interactions are a bit beyond me at the moment.

If I need to bring down the mids a bit I can I suppose, as the deqx would allow me to put say a 250 db/octave slope on them, which would cut out just a little of the LF energy methinks.

The potential vibration problem I guess would be minimized the higher I cut them off, but of course the first goal would be to have them go as low as possible.

Really appreciate everyone's responses, will post some measurements soon and we can all have a look see.
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Old 19th April 2007, 06:18 AM   #10
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I won't consider dipole for anything under 50 Hz. It is a job for a sealed sub. I believe dipole advantage is from 50Hz-80Hz up to the dipole peak at, say 500Hz.
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