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Old 10th March 2012, 05:58 AM   #11
mdocod is offline mdocod  United States
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Hello Silent,

Any time you double the number of drivers, you gain 3dB efficiency. In the real world, when you double up drivers, you are forced to contend with various real world wiring options. Going from 1 to 2 drivers gives you the option of doubling or halving resistance, which will either halve or double power consumption. You still get the 3dB efficiency benefit either way, but the voltage requirements change to reach the same output levels.

Series wiring cuts power in half, that's -3db, but doubling of drivers is +3db, result is 0db change, half power. Parallel wiring doubles power, that's +3db, plus the doubling in drivers, another +3db, that's +6dB. Each system is equally efficient [sort of, but nevermind].

If you start wiring woofers in parallel, it's important that you have an amplifier that is comfortably driving the new load. Some are better than others at this. The amp I use is rated by the manufacture for 4 ohm or greater, but is actually very well composed down to below 2 ohms. Some amps are rated more honestly than others. Some are over and some are under rated.

Implementing BSC properly is probably not just a matter of padding down the tweeter. Many passive designs, especially half-way implementations, deal with BSC by selecting crossover points and slopes to "build in" an acceptable rise through the bottom end based on speaker baffle width, and intended room placement. In your case, I suspect that your 2-way x-over point will be too high and too steep to double as an effective BSC implementation [I could be wrong because I don't know enough about that tweeter or your crossover]. You may need to do this passively on the woofer section, and then pad down the tweeter to match.

I can't make driver recommendations for 2 reasons: 1. I don't really have any good feel for the drivers available where you are, and 2. There is a lot of evidence to suggest that when a thread starts going down the road of "picking drivers" it is unlikely to ever get anywhere.

The logical course of action is to make your intended application more well known, then folks may be able to make some suggestions. Pick a set of drivers and move forward, don't let an endless sea of driver options complicate the issue, pick a driver with response characteristics that will be easy for you to utilize for your x-over intentions. Ideally speaking, pick a driver with respectably low distortion (look for 3rd party testing and reviews) within it's price class. I don't recomend spending hundreds or thousands on drivers unless you have enough experience or testing equipment or expertise to actually take advantage. I would not personally bother with a 6" driver costing more than $50 because I know there are plenty of great drivers in this size class below that price point, and I do not have the ears or testing equipment or listening environment for a more expensive woofer to make a positive difference.

Best of luck,
Eric

Last edited by mdocod; 10th March 2012 at 06:10 AM.
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Old 10th March 2012, 06:11 AM   #12
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Sensitivity is always a good thing (all else being equal) but in your case is not really an issue at all.

It's worth noting that you are choosing a mid for a 4-way, and bsc is unlikely to be handled by the mid. The above contributors might give you different advice if they knew that.
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Old 10th March 2012, 07:06 AM   #13
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An M-T-M may not be the best sounding topology for a high’ish efficiency RAAL design. If both the M-T and M-M spacing requirements of less than one-half wavelength are not met, there will be audible lobing.

You may find a T-M-W or T-M-WW topology with a high’ish efficiency 8” midbass crossed LR4 at 1,600Hz (the RAAL standard) will deliver superior sound to an M-T-M using two 6.5” midranges. The T-M will need to be mounted as close together as possible, and this might make a separate T-M box plus separate W(or WW) box the best option to get edge diffraction reduction and vibration isolation. Measurements of RAAL ribbons in a T-M topology have shown less lobing than estimated from the using the center point of the RAAL ribbon in simple calculations.

To maintain 94db/watt down into the bass will require a 98-100 db/watt BIG woofer, or two large woofers wired in parallel to gain 6db from 2*area times 2*power from the lower parallel-woofer resistance load.

From Biro Technology paper on MTM spacing

Biro Technology

fx = c/2 * |{[(L cos [theta])^2 + (d + L sin [theta])^2]^1/2
- [(L cos [theta])^2 + (d - L sin [theta])2]^1/2}^-1|

fx is the lowest frequency of total cancellation in Hz, [theta] is the vertical displacement (ranging from -90 deg. to +90 deg.), d is the vertical separation between the high-frequency driver and one low-frequency driver, L is the distance from the plane of the drivers to the on-axis design point, and c is the velocity of sound. For a given d, as [theta] increases in magnitude, fx decreases. Clearly, if d and [theta] are sufficiently large, it is possible that fx will occur at a frequency where
Clearly, if d and [theta] are sufficiently large, it is possible that fx will occur at a frequency where the output from the high-frequency driver is negligible, and the system response at that frequency at that listening angle will effectively drop to zero.
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Old 10th March 2012, 07:20 AM   #14
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Thanks Hypertune its hard to know what is relevant and what's not. I think it is this sea of driver choice that mdocod mentioned that is clouding my judgement. I am looking to buy the best driver I can afford to do the job and the problem is there is just too much choice.

I have even been looking at the $900 each Accuton drivers. I would really like some advice on drivers, but it seems like such a subjective topic that most people don't know how to go about answering it. Definately would help if I knew the right questions to ask, but it comes down to different expectations.

I want the best sound possible but that is hard to determine because no one driver is best at everything. Until I get the dongle for the DCN28 software I won't know what I can and can't adjust in the digital crossover.

I would have actually thought there would be a few drivers that stood out from the rest in a few of the catagories to narrow down the choice. I really don't even know how to define what I am looking for, seems I almost need to blow through a ton of cash trying everything to know what I like.

Perhaps I should go back to my original idea of using the ScanSpeak illuminator drivers since I know first hand how well the Revelator series works. I did like the idea of the AudioTechnology drivers as from what I read they were less coloured than the paper drivers, and to me I guess that is one of my key criteria, I want to hear the music as intended.

I want low distortion, I want clarity, then I want some more, and then some more, but how to put that into terms that can help with a recommendation I don't know.

I was thinking along the lines of the 140-15D Raal tweeter a 6" a 10" and what ever I need to achieve house shaking base for the sub cabinets, which of course will rarely be used for music, so I need full frequency from the first three drivers.

The drivers in the pics are the ones I want to use, I guess I should ask is this a bad match?
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File Type: jpg Raal.jpg (148.8 KB, 123 views)
File Type: jpg AudioTechnology.jpg (238.8 KB, 122 views)
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Old 10th March 2012, 07:26 AM   #15
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Ok if I understand you correctly LineSource what your saying that the Raal tweeter is so flexable / efficient that I should be jumping straight to an 8" instead of mucking around with MTM 6".

Putting the tweeter and the 8" in the same cabinet close together won't be an issue as that was kind of what I originally had in mind early on.

Would I need one or two 8"? and then maybe the 12" KAP?
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Old 10th March 2012, 07:43 AM   #16
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Just dawned on me since I have chosen a tweeter capable of going fairly deep into the bass teritory, perhaps I should be looking to turn this back into a 3 way... otherwise I am trying to cram 3 drivers into a fairly narrow band.
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Old 10th March 2012, 07:39 PM   #17
mdocod is offline mdocod  United States
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Silent,

I'll try to put this as gently as I can.

Ignoring the issues that you don't understand doesn't solve them.

Throwing big money at low value high cost boutique drivers solves absolutely nothing- in fact, it often complicates things for an amateur builder as many of them are actually harder to work with than value oriented but well made drivers.

There is no magical secret combination of perfect drivers. We're not holding out on you here.

Going from an MTM with 6"s to a single 8" REDUCES over all driver spacing issues, which allows you to use a more sensible x-over point on the RAAL without as much or theoretically no detectable lobing. I'm not sure where you're getting this "my tweeter selection is so elite I didn't even realize how amazing it was I guess I can use an 8" wow it's dawning on me" revelation. You're interpreting what LineSource was trying to tell you in complete reverse of the intended point. I assume that you didn't understand part of what was being said so you simply ignored the part that didn't make sense, hoping that the issue would solve itself. LOOK UP LOBING.

The RAAL looks like a good candidate for the top end of a wide bandwidth 3-way system, yes.

Last edited by mdocod; 10th March 2012 at 07:57 PM.
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Old 10th March 2012, 09:58 PM   #18
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Thanks mdocod I have no issues with you telling it as it, is in fact it prefer when people are more to the point, it is easy to work out what their point is.

You dont know what you dont know, and I have already learned a lot since joining this forum, but the simple fact is I will never have the understanding of math to interpret the forumlas the way many of you guys do, so I have to learn by what I pick up by reading, and yes I probably did miss the point being made, because of the bits I didn't understand, but at the very least I am one step further forward knowing there is this issue of lobing that needs to be considered.

Unfortunately I sometimes find it difficult to translate the text into a meaning, that is why I probably learn better from visual that I do written (but incredably hard to see sound waves).

Please don't get me wrong I am not trying to be ellitist by saying what I have is better than anyone elses. If that was the case I would have that set of gold speakers costing nearly 7 million dollars in my place.

We all have different budgets and sound equipment is probably my biggest joy, so I will sacrifice a lot to get the best, but unlike most things in life where the best is often more expensive, that doesn't necessarilly seem to hold true for drivers.

So I probably need to let go of price and try find what suits my taste rather than budget based on what I read.

The epiphany I had was more around the range of how far the modern tweeter will go into bass territory, not the specific one I selected (after all I only paid for it, not built them so nothing to be over joyed about for me).

The last set of speakers I built in the late 90's I crossed the Polk Audio tweeters over quite high in comparison (long time ago but vaugley remember setting up the passive crossover somewhere around ~4 - 5kHz) so what was a revelation to me, has probably been common knowledge to you for some time.

I suspect that perhaps the little information that is in my head is well out of date, and that is why it comes as a surprise. Instinctively I still want to try get the bass higher up in the frequency range to help out the tweeter, is this wrong?

Raal suggests a low pass crossover at 1600Hz with a 4th order Linkwtiz-Reily configuration and this would seem like a very sensible place to start since the person who made it recommended it. As I say there is a strong temptation is to cross the 8" (or whatever combo) higher to try help out the tweeter, is this being counter productive?

Or alternately crossover with a 1st order configuration to let it taper off more gently to go higher up the range. My gut says I should crossover with a fairly high order to stop the bass wandering out of its comfort zone.

I guess one of the great benefits of using the active crossover is I can alter the crossover order without ever having to get the soldering iron out, so I can test combinations to my hearts content for nothing.

Anyway I appreciate the advice and I am trying to learn as best I can, so please don't stop trying to get it through my thick head.
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Old 10th March 2012, 10:32 PM   #19
Lusk is offline Lusk  Australia
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Out of the AT units you have selected above it would be best to go a C-Squenze than a flexunits for the midrange maybe like 15H 521206SDKM or if you want a lager midrange 18I 520613SD

For woofers what enclosure are you going with sealed or ported?

For 10" woofers.
Sealed l would go Qty 2 x 10A 772510 KAP
Ported Qty 1 x 10C 772510 KAP

also maybe check this diyérs site.

http://www.digitalroomcorrection.hk/Site/Welcome.html

Last edited by Lusk; 10th March 2012 at 10:43 PM.
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Old 10th March 2012, 11:00 PM   #20
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Hi Lusk... It would appear based upon my tweeter selection that it would now make more sense for me to going three way instead of the four way I was planning on when the thread started.

So not so sure if I would look at the 10" as the bass driver as it was suggested as a main speaker woofer, not the definative sub frequency driver.

Going three way means a bit of a juggle around. I could still do a two way with a seperate bass unit, or maybe try squeeze the third driver in the same box.

I don't want to go back to having a seperate powered subwoofer like I currently do, I want to try achieve the full spectrum of sound for each side.

So if I went with a tweeter, an 8" and maybe a 12" - 18" depending on what works.

I am partial to the idea of building the bass in its own cabinet purely to optimise the cabinet design that would work best with a bigger driver of low frequency.

But at the same time I want the mains to be able to produce 90-95% of the frequency range, so should I be listening to music that doesn't require deep bass I could simply leave that amp / speaker off.

I would use my the 2 channel RB-1092 amp I was using to power my Sonus Faber Cremona's for the sub frequencies, as it really is overkill to use it on anything less than a passive speaker where all drivers are driven off it.

At 1000w @4ohm (500w @ 8ohm) per channel it really is a little over the top to power the tweeter or the mid woofer.

For the woofer I was actually thinking of possibly building a TL box for them...

Edit:
Just realised that what I wrote there sounds contridictory...

If I build the sub frequency drivers in a seperate box and power it seperately, as it will be because I am using a active digital crossover. I am effectively building 2 sub woofer boxes... what I meant by that is I don't want to go back to the arrangement I currently have with a limited main speaker with a seperate subwoofer and it be virtually impossible to get the balance right because of the different crossover slopes.

Using the digital crossover I want the crossover network to function as one speaker even though I plan to build in two seperate boxes.

Last edited by Silent Screamer; 10th March 2012 at 11:17 PM.
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