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Old 7th June 2012, 07:39 PM   #1
Hrmmf is offline Hrmmf  Denmark
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Default large format midrange driver or...

Hi guys.

So i need a little advice here!

I'm putting together what is supposed to be my last speaker

One important criteria:

I would keep it down to a 3-way.

I'm a little confused about the choise of driver size. Some of you guys are prefering smaller drivers in the midrange, 10" at largest, arguing that larger format drivers, say 15," are not articulate enough, or lack the transient response of the smaller drivers.

Have any of you made a direct comparison between an 8" or 10" vs a 15" in the range up to ~1000Hz.

When i say a 3-way I mean in a sence that I would like the midrange driver to cover 100-1000Hz, crossing over to a pair of tapped horns (~30-100Hz). The awesome Beyma TPL 150 will be doing the high frequency duties.

The candidates are; Jbl 2123, PHL 3451; 18-sound NDA520, AE TD15M.

I know that both 10" dont go anywhere near 100Hz, but is it to much of a comprimise (soundwise) chosing the larger drives to gain the low end extension, thus crossing lower?

Thanks, Thomas
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Old 7th June 2012, 07:51 PM   #2
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The main advantage of smaller drivers is they have wider dispersion such that the frequency response is consistent over a wider range of angles at high frequencies in comparison to a larger driver. You should decide the driver size based upon the polar response you desire, if you are going for a constant directivity (or at least smoothly varying) you should match the directivity of the mid and the tweeter at the crossover frequency. This will result in only one size of driver been suitable (assuming that its behaving as an ideal piston...). The more traditional aproach is just to go for wide dispersion and not attempt to match directivity so you would end up using an 8" mid or smaller.

The larger mids have the additional advantage of smaller excursion for a given SPL which (usualy) results in lower distortion. A speaker such as the Abbey:
Abbey
uses a large midbass and attempts match directivity at the crossover point. You can see from the directivity sonogram that the directivity smoothly narrows throughout the speakers range.
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Old 7th June 2012, 08:03 PM   #3
Hrmmf is offline Hrmmf  Denmark
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Thanks kipman.

I'm actually leaning towards the TD15M from its reputaion. I'm horn loading the beyma with a 30x80 CD horn.

A 15" has an effevtive diameter of ~12.5" which lands the 80 degress dispersion at:
1*10^6/12.5/80 = 1000Hz

I've been told that the TD15M, due to the shape of the cone and the phase plug, this increases its dispersion caracteristics some 10%. As I'm aming for a 1200Hz x-over, this could be a match made in heaven.

-Thomas

Last edited by Hrmmf; 7th June 2012 at 08:07 PM.
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Old 7th June 2012, 10:04 PM   #4
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sounds good how close can you get the acoustic centres of the two drivers though? ideally they should be within 1/4 of a wavelength at the crossover frequency. Worth thinking about.
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Old 7th June 2012, 10:31 PM   #5
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I thought (1) wavelength was fine? 1/4 wavelength is pretty limiting driver wise. Don't see how you could get that close even with a 6" mid @1k.
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Old 7th June 2012, 10:41 PM   #6
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1/4 wl Gives you effectively co-ncident drivers and is a laudable goal. 1/2 w/l would be considered a maximum, but given typical driver selection that is relaxed to 1 w/l to give a chance -- a lot of people don't get near that even. In my last multiway i did meet the 1/4 wl criteria, but that was an MTM with 3" mid-tweet, 2x6.5" at ~350 Hz.

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Old 8th June 2012, 01:02 AM   #7
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I favor 3-way speakers with an 8" to 10" midbass that covers 80-100 Hz to 1000-1400 Hz with a goal of staying under the lambda/2 maximum C-to-C spacing rule. My ears like the coherence and common timbre achieved from keeping the vocal range on one driver. To stay under lambda/4 C-C spacing would likely require a 4-way design to cover 20-20K Hz with low IMD(dopler).

Like Dr. Geddes' Summa speaker with its 700Hz Xover between the 15" woofer and OS waveguide for a correct polar response, I cross my Lambda TD15M speakers with LR4 slopes at ~700Hz to control beaming. Lambda TD10M cross LR4 at 1000 Hz. Tang Band W8-1808 8" cross LR4 at 1400 Hz.

Can a 0.02g Mms ribbon tweeter "perfectly blend" at 1,200Hz with a 70g Mms TD15M midbass?

0.02g Mms, Ribbon tweeter, 98db/watt, 1,600Hz Xover
0.45g Mms, silk dome tweeter, 94db/watt, 1,400Hz Xover

8.1g Mms, Lambda TD6M midrange, 93.5db/watt, 300-2,000Hz Xover

9.3g Mms, Tang Band W8-1808 midbass, 94db/watt, 100-1,400Hx Xover
44g Mms, Lambda TD10M midbass, 94db/watt, 80-1,000Hz Xover
70g Mms, Lambda TD15M(Overhung) midbass, 97.8db/watt, 80-700Hz Xover

104g Mms, Lambda TD15S woofer, 94db/watt, 25-700Hz Xover
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Old 8th June 2012, 01:29 AM   #8
puppet is offline puppet  United States
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Quote:
Originally Posted by Hrmmf View Post
Thanks kipman.

I'm actually leaning towards the TD15M from its reputaion. I'm horn loading the beyma with a 30x80 CD horn.

A 15" has an effevtive diameter of ~12.5" which lands the 80 degress dispersion at:
1*10^6/12.5/80 = 1000Hz

I've been told that the TD15M, due to the shape of the cone and the phase plug, this increases its dispersion caracteristics some 10%. As I'm aming for a 1200Hz x-over, this could be a match made in heaven.

-Thomas
Have you considered using one of John's 12" drivers vs the 15" ? Might be a better match.
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Old 8th June 2012, 01:31 AM   #9
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Quote:
Originally Posted by Hrmmf View Post
I'm a little confused about the choise of driver size. Some of you guys are prefering smaller drivers in the midrange, 10" at largest, arguing that larger format drivers, say 15," are not articulate enough, or lack the transient response of the smaller drivers.
Transient Response, as it's commonly "imagined" has nothing to do with the size of the driver.

However, a larger driver will inevitibly have cone breakup at a lower frequency, which will smear details and in many cases cause harshness. As long as the driver is sufficiently down in level (~24 to ~40+ db) by this point, you're good.

Quote:
When i say a 3-way I mean in a sence that I would like the midrange driver to cover 100-1000Hz, crossing over to a pair of tapped horns (~30-100Hz). The awesome Beyma TPL 150 will be doing the high frequency duties.
Up to 1khz? I'd probably be more comfortable with an 8" or 10" rather than a 12" or 15" cone. I think it will also have a better time of mating to the TPL-150's off-axis response. I know you pointed out that the 15" will be 80 degrees at that frequency, but that doesn't mean the TPL will, even if it's an 80 degree horn. It will lose directivity control higher than that most likely. Perhaps measure the polars to know what you're working with.

Quote:
I know that both 10" dont go anywhere near 100Hz, but is it to much of a comprimise (soundwise) chosing the larger drives to gain the low end extension, thus crossing lower?
I think you DO want more lower bandwidth in this scenario, because tapped horns lack it.

Consider a Seas W26 Nextel FWIW. Maybe roll in a second actively for baffle step.

Also consider using a transmission line or port/ML-TL instead of going sealed. You won't lose anything audible in transient response, and you'll get a nice boost in extension. Bigger box, though.

Last edited by RockLeeEV; 8th June 2012 at 01:34 AM.
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Old 8th June 2012, 03:18 AM   #10
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Quote:
Originally Posted by Hrmmf View Post
I'm putting together what is supposed to be my last speaker.......crossing over to a pair of tapped horns (~30-100Hz). Thanks, Thomas

Dr. Earl Geddes white paper on room modes is a real page turner! With today's digital software crossovers and equalization it is easy to equalize the bass impulse response measured at the listener position, but you cannot equalize room modes. Room modes B nasty. Dr. Geddes recommends adding multiple woofers thoughtfully placed around the room to smooth out the deep bass room modes. Sealed woofers are easier to electronically equalize, and the 6db/octave bass fall-off is a close match to the 6db/octave bass gain from a typical room. A few well respected speaker manufactures now sell a "swarm" of sealed woofers with room mode modeling software to optimize placement.

Can I interest you in a few 15" or 18" sealed woofers? There are great 99db/watt woofers.

If you have the space, there is also some love for Push-Pull-Slot-Loaded sealed woofers which used counter-force to remove vibration and "spit" deep bass from a front slot. The TPL150H tweeter pleated diaphragm "spits", but from different physics.

Wayne at pispeakers.com also has a white paper declaring his love for corner speakers, showing how corner placement increases efficiency, widens the sweet spot, and reduces room modes. You do not need corner horns ala Klipsch, and can get corner benefits from sealed bass woofers + sealed 10" midbass + TPL150H. You get a 90 degree polar response across the full frequency range.

A few alternatives to tapped horns.
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