Generic: How BIG for mid duty driver - diyAudio
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Old 20th August 2014, 04:09 PM   #1
koja is offline koja  Canada
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Default Generic: How BIG for mid duty driver

This thread originally started as my inquiry into speaker measurements but quickly evolved into another interesting discussion, thus I overhauled this first post and moved my questions elsewhere:

so, for those "who like it BIG" the NEW TOPIC is:

>Does the size and mass of the cone driver matter when it comes to mid duty?

>Does a large and heavy cone sound "lazy" and lack "attack" subjectively (for example a 12 incher if used up to say 1kHz)?

How about the difference between the same large size drivers but one meant for bass and the other exclusively declared by manufacturer as "mid duty" (like those from PD for vocal stage monitors for example)?

...and more questions are wellcome if along these lines

Bask in difference of opinions and enjoy .

Last edited by koja; 22nd August 2014 at 02:38 AM. Reason: minor
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Old 20th August 2014, 04:46 PM   #2
gedlee is offline gedlee  United States
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I would not use the DAC output, I'd add an amp. The DAC may want a more stable higher impedance load. The amp will buffer this.

Choose the highest level that is well within the "safe" range of the drivers. This will yield the best SNR.

Measuring near resonance on any woofer is tricky. Just be careful or the data won't be very good.

Only ever use a system that does a transfer function from voltage to SPL. "Blind" measurements of just SPL can have too many unknown errors.

Check out HolmImpulse.

I live in Novi, just across the river from you, you could come and see how I do things sometime. I am only 1/2 hour from the border (on a good day!)

Last edited by gedlee; 20th August 2014 at 04:48 PM.
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Old 20th August 2014, 05:20 PM   #3
koja is offline koja  Canada
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Earl, thanks for the pointers. I hope others chime in as well since I am not looking forward to damaging any drivers (been there, done that, paid for it )

off the topic: I was actually over at your place last year. for that matter, right now two of your B&C 12inchers are getting boxed up for sub duty . I also auditioned your system and you got me hooked on managing spk directivity; this for the open stage feeling (i.e. no room) and for not being able to localize the speakers. I think others probably experienced the same when commenting about SL's speakers and the music "not being attached" to them. after this OB project (which is my own "design"), I will try and merge those subs with LX521 top. I want to see if my expectations are right. p.s. the only reservation I had to your design was that you used a large (really bass driver) for lower mid duty to keep the dispersion angle down, whereas the real challenge is to do it with drivers of the right size for the job. on the other hand, the "beef" I have with SL/JK designs is that I have low wattage (pass) amps; thus my own attempt to design a wider OB (before surrender? ).

Last edited by koja; 20th August 2014 at 05:22 PM.
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Old 20th August 2014, 07:15 PM   #4
gedlee is offline gedlee  United States
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Quote:
Originally Posted by koja View Post
p.s. the only reservation I had to your design was that you used a large (really bass driver) for lower mid duty to keep the dispersion angle down, whereas the real challenge is to do it with drivers of the right size for the job.
I can measure the polar response problems at crossover when one uses a "smaller" mid-woofer. I do not measure any problems of this sort, or any other for that matter, when I use the larger drivers. You'll excuse me if I stick to quantifiable objective evidence for my designs rather than unsupported dogma about using "too big a midrange driver".

We had this exact same conversation over in another thread and it turned out that there wasn't a single shred of evidence to support the claim. Only unsupported opinions.

My evidence is clearly shown for all my designs on my web site. As I clearly show, there is no problem using a "overly large" driver for the midrange, as long as it is the right driver. The right ones are rare, but they do exist.
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Old 21st August 2014, 12:48 AM   #5
a.wayne is offline a.wayne  United States
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What is an overly large midrange, could you quantify Earl ....?



..
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Old 21st August 2014, 01:25 AM   #6
gedlee is offline gedlee  United States
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I would suppose that the dogma would claim that a 15" should go no higher than 300-500 Hz, a 12" no higher than 500-700 Hz and a 10" no higher that 700-900. But that's just a guess since I don't buy into the whole concept of cone weight as being a factor for anything audible. Its size matters since that determines it directivity and that is audible. How well the cone is made, its termination, etc. are the important factors in its high frequency response. Mass doesn't even play a role.
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Old 21st August 2014, 01:27 AM   #7
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If you had a 12 inch woofer that crossed over to a 1 inch dome tweeter at say 3kHZ, you could adjust it so the on axis frequency response was relatively flat, but off axis it's highly likely that the response would roll off from about 600HZ on up to the 3kHZ crossover point, where it would abruptly jump back up to being about level with the 200HZ area of the woofer, because the dome tweeter is very likely to have a much wider dispersion at 3kHZ than the 12 inch woofer.

In the case where the upper frequencies are being delivered by a horn with controlled directivity, the abruptness of the dispersion change at the crossover frequency could be made to be minimal, at the expense of high frequency off-axis dispersion. The "power response" or "room response" would have a significant rolloff at high frequencies, because the off-axis emissions would bounce around the room and eventually add to the direct signal at your ear.

Last edited by Bob Richards; 21st August 2014 at 01:36 AM.
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Old 21st August 2014, 02:04 AM   #8
gedlee is offline gedlee  United States
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Hi Bob

I think that you have that wrong.

With a controlled directivity waveguide (CD) one can perfectly match the polar pattern of a large woofer at the crossover to that of the "tweeter". Since the "tweeter in this case has CD then its response does not "fall off" off axis, it is flat. The forward "beam", if you will, is narrow, but that is exactly what is desired to avoid early reflections.

This is clearly demonstrated on my website for the NS-15 (for example) where at 20 degrees off axis - the design intent because of toe-in - the Directivity Index (DI) is perfectly flat meaning that the direct field and the reverberant field will have exactly the same frequency response along this axis.

A subtle fall-off of the power response towards 10 kHz is intended because this is more like sound in nature where the falloff due to air absorption is ever present. a flat power response will always sound bright.

Last edited by gedlee; 21st August 2014 at 02:06 AM.
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Old 21st August 2014, 05:00 PM   #9
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Quote:
Originally Posted by gedlee View Post
Hi Bob

I think that you have that wrong.

With a controlled directivity waveguide (CD) one can perfectly match the polar pattern of a large woofer at the crossover to that of the "tweeter". Since the "tweeter in this case has CD then its response does not "fall off" off axis, it is flat. The forward "beam", if you will, is narrow, but that is exactly what is desired to avoid early reflections.

This is clearly demonstrated on my website for the NS-15 (for example) where at 20 degrees off axis - the design intent because of toe-in - the Directivity Index (DI) is perfectly flat meaning that the direct field and the reverberant field will have exactly the same frequency response along this axis.

A subtle fall-off of the power response towards 10 kHz is intended because this is more like sound in nature where the falloff due to air absorption is ever present. a flat power response will always sound bright.
I agree with what you're saying here. I'm not sure I'd want the directivity to be that narrow (matching a 15 inch woofer at roughly 1kHZ ?). The sweet spot would be better (less room reflections) but outside of the sweet spot I'd expect it to be more compromised.

Choosing directivity is a game of tradeoffs. If you want it to sound balanced and relatively full range everywhere in the room, the DBX Soundfield speaker designed by Mark Davis back in the early 1980's is the opposite extreme and sounded very good when I heard it, anywhere in the room.

It seems that the worse case is when a room has one major reflection creating comb filter effects. If the room has enough reflections, they all pretty much average out. Most typical living rooms will still have problems in the 80HZ - 300HZ area where there may only be one or two effective reflections.

If a room is substantially acoustically problematic, then controlled directivity could be a valuable asset.
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Old 21st August 2014, 06:19 PM   #10
gedlee is offline gedlee  United States
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Hi Bob

Again I have to disagree.

With an total 90 degree pattern (+- 45 degrees) and a toe-in of 45 degrees, the entire room is covered by the directivity of the speaker and all seats get the same flat and smooth response because of CD. What is avoided are the walls - they are outside of the coverage angles and as such to not generate early reflections - only late lateral reflections that are the best for the feeling of spaciousness.

My rooms are always quite reflective because I want them to sound spacious and this does that. But early reflections cause degraded imaging. By using a highly directive CD speaker I can achieve both good imaging AND good spaciousness. To my knowledge there is no other simultaneous solutions to these two major problems. Usually a designer goes for one or other - I go for both.

So you would call my rooms "acoustically problematic" because they don't fit the traditional dogma of room acoustics - highly reflective walls, etc.. But yet, all being custom built, these rooms acoustics are precisely what I intended. There are no compromises made for aesthetics, etc.. It is an entirely different paradigm.

Below 300 Hz. is an entirely different problem that directivity has no effect on, so I am not talking about that situation.

Directivity is not so much a tradeoff as it is a compromise. High directivity at lower frequencies requires very large speakers. How large one is willing to use is usually the compromise.

And actually my techniques yield an incredibly wide sweet spot, not a small one. Almost the entire room has good imaging and timbre.

Last edited by gedlee; 21st August 2014 at 06:22 PM.
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