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Old 17th February 2014, 09:17 PM   #41
Speakerholic
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Quote:
Originally Posted by conanski View Post
Response is somewhat peaky with the Cubo so it will require more EQ to flatten. There are 2 driver loading options too, frame out or cone out and each one produces a slightly different response. I have not had a chance to measure it cone out but my ear tells me that config produces a smoother response.. in my listening room at least. I noticed both the cubo and reflex box have a similar peaky response when I measured them originally so obviously the room is affecting things.
Good to know! I'll take this into consideration when I do further research. It looks like it will come down to reversing the cone cone pair in my current sub or building a cubo-something. Building a cubo will give me a fallback to my current sub. In my situation where I can't be caught without a working sub, this is a very important consideration.
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In one thousand years, will they still be called the Thiele Small parameters?
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Old 19th February 2014, 02:49 PM   #42
Zero D is offline Zero D  United Kingdom
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Lightbulb Re - Isobaric enclosures

@ Thetwinmeister

Hi, fs is NOT halved ! It along with many other T/S's remain the same. It's Vas that's halved

Quote:
The two drivers operating in tandem exhibit exactly the same behavior as one loudspeaker in twice the cabinet. The cabinet is defined as the space behind the rear driver. The volume of air between the speakers has no acoustic function so that the saved space is less than 50%. All other aspects are unchanged like resonant frequency and maximum SPL. The new driver will have the same resonance frequency, Qts, distortion, excursion etc. as one driver with the same applied signal https://en.wikipedia.org/wiki/Isobaric_loudspeaker
Anyway, i'm following your thread with interest. All the best with your endeavours
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Old 19th February 2014, 04:03 PM   #43
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Hi Zero D, it's good you pointed this out. It's high time I tested the drivers empirically with my DATS in parallel, series, and individually to shed some light on this question. Prior to building my isobaric sub, I read similar articles about isobaric and believed Fs did not change.

Perhaps it doesn't change, perhaps it does change a little but isn't halved. I should have confirmed with test equipment by now what my ears have observed-- parallel has the least LF extension, series has greater extension, and discretely driven seems to have the greatest extension.

I could be imagining things however, so I reserve the right to change my opinion. So far no direct A/B tests have been performed on this. I will have the time to test the drivers next week. Until then!
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In one thousand years, will they still be called the Thiele Small parameters?

Last edited by Thetwinmeister; 19th February 2014 at 04:08 PM.
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Old 19th February 2014, 04:59 PM   #44
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Your right, FS would not change. I stand corrected. I was going off memory!
I posted some WinISD plots using the same size box. Notice the SPL@1watt takes quite a hit going isobaric.
Attached Images
File Type: jpg fr.JPG (148.6 KB, 51 views)
File Type: jpg spl.JPG (129.7 KB, 47 views)

Last edited by Joseph Crowe; 19th February 2014 at 05:01 PM.
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Old 20th February 2014, 03:30 AM   #45
Zero D is offline Zero D  United Kingdom
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@ Thetwinmeister

I agree that there could be a shift in fs. Variations in drivers T/S, & Volume of the shared enclosure, being just 2 possibilities that spring to mind !

@ Joseph Crowe

We've all done it from time to time I thought it best to point it out ASAP so others reading it too are clear on this.

Regards
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Old 24th February 2014, 03:06 AM   #46
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Driver testing is still in the future, in the meantime I have a couple of updates from my latest escapade.

Yesterday night I provided reinforcement for three college bands from two states in a praise and worship night, one of the groups being my regular guys. (None of these bands are professional if anyone had that idea, but this fact allows great liberty.) I was able to test the upper limits of my entire system from source to speaker. Even my soundboard was pushed heavily.

Sub: My dual pair isobaric sub performed fantastically on both 4-string bass guitar and kick drum mic'ed with a Sennheiser e902. Currently I have each of the 18" Dayton PA460-8 drivers discretely amplified utilizing two Behringer iNuke NU1000 amplifiers. I choose discrete amplification over something like wiring the pairs in parallel for two 4ohm loads and setting each amp in bridged mode because the former sounds so obviously superior to the latter I immediately wrote it off as even an option. At one point I pushed these amps so hard I said to myself "well, I did purchase the extended warranty..." but thankfully not only did they hold up but performed flawlessly even when I asked too much of them. I suppose I really need higher powered amps, my sealed isobaric is hungry.

Ah, you noticed those 18" drivers cost less than $100 each? Partly I wanted to prove (read: find out) that (if) two drivers half the cost of a single when coupled in a pair could outperform the single driver. Mostly it was due to budget considerations and an unwavering desire to go isobaric. I have lived to not regret my choice. Whether two of those are better than a given $200 driver (take your pick) is something I have yet to discover. Immediately, I take note the $200 driver has more xmax and is more sensitive.

Not a note from the bass guitar was missing or lacking, even at considerably high SPL. Another notable thing; I never passively noticed distortion at any level! Whether I would have picked up on it if I had purposefully listened for it is another thing however, I did not have time to do so. Even if I did, I'm not sure I would know how to evaluate with apparent distortion levels seemingly so low! My faith in this design concept has been fully reinvigorated. I may focus on perfecting it rather than attempting alternate designs from scratch.

The bass guitar required no EQ, however I had to EQ the kick drum substantially. I suspect this is due to two things: The kick drum my drummer uses is sealed. No traditional hole to mic. I might be doing it wrong. Secondly as I have mentioned before, the radio labs "stick on" sub crossover I am using doesn't have a very nice sounding rolloff. I believe it is due to these two reasons, and not a fault in the e902 microphone, that the kickdrum required heavy EQ to sound right. With EQ, the kick was powerful and sounded good, matching the rest of the kit well.

I am considering a balanced miniDSP to replace the radio labs until I can afford a driverack or equivalent Behringer. To those reading this in the future: The balanced miniDSP costs a dinner out more than the radio labs sub crossover. Consider your options wisely.

Mains: I don't think I have the crossover right. However, much better news is that somehow I am no longer hearing distortion from the Dayton D250P-8 compression drivers as I was before. In fact, even the tone is a little different. Where as before it was slightly warm, now it seems cold almost to be described as hollow. I do not have an immediate explanation for this other than pointing my finger at burn-in and shrugging my shoulder. Unfortunately I did not have my SPL meter with me, so all I can say it was loud, really loud, much louder than I've ever pushed the speakers before, and I never heard distortion. (From any driver at that!)

About the almost-hollowness; it's more welcome than distortion. I still would like to improve upon these drivers, however the necessity is less pronounced now. I may end up choosing to wait and purchase a driverack or similar before replacing something that already works. For information sake, the mains are run from an NU1000DSP amp with a HPF @ 80hz.

Mics: Unrelated to the thread, but I have to throw this in here. Subform appropriate! The venue allowed us access to two Sure Beta 58a microphones. Among other configurations, one of the bands had 4 vocalists simultaneously during a song. After my two Sennheiser e935 mics were utilized, I mic'ed the remaining vocalists with a Beta 58a throughout the performances. I have used the Beta 58a in the past, but never in direct comparison to an e935. Both are excellent microphones, both have great clarity, both stand up well in really loud environments, both cut through the mix, both have high gain-before-feedback, and both EQ well. However, putting aside as much prejudice as I can, I admit to find the e935 notably superior in all of these aspects. (With appropriate vocalist-related EQ applied to each, respectively.) I love the Sennheiser e900 series!


One of the musicians and lead singers came up to me afterwards and estimated I had $10,000 invested into this system. I don't know whether he knew a lot about PA system pricing, but his gesture made me smile. If you can't tell from my Dayton subs and Behringer amps, it's a lot less than $10,000. Although the mics are nice. Can't be awesome without those guys.
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In one thousand years, will they still be called the Thiele Small parameters?

Last edited by Thetwinmeister; 24th February 2014 at 03:29 AM.
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Old 24th February 2014, 11:14 AM   #47
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500 watts seems to be the magic number for mains. It's terrifying at first using that much power into modest sized speakers but you quickly realize they handle it fine. (Crossed over) and if your continuously listening for any signs of clipping.
Good job on sound!

Did you ever get a chance to measure your mains using the Dayton reference mic? It will reveal a lot. +/-3 dB is my rule. I had 3 dB bumps in the midrange that once fixed sounded 10 times better.
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Old 25th February 2014, 02:05 AM   #48
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Quote:
Originally Posted by Joseph Crowe View Post
Good job on sound!
Thanks!

Quote:
Originally Posted by Joseph Crowe View Post
500 watts seems to be the magic number for mains. It's terrifying at first using that much power into modest sized speakers but you quickly realize they handle it fine. (Crossed over) and if your continuously listening for any signs of clipping.
Where did you get 500 watts? Is that from empirical experience? I've used as little as 75 watts for live sound reinforcement (on a different pair of speakers) for a small audience with no real headroom issues, although mixing is honestly a little tighter. The NU1000DSP puts 150w into 8ohms. With the LTA's sensitivity of 97.7db, that works out to 123.2db at 3 feet. 500w increases that to 128.5db.

Mathematically, that's only 5.3db more. I have no experience mixing more than 150 watts, so I can only speak from mathematical terms to say 5.3db doesn't seem like much more for a 350 watt increase. 75w turns out to 120.2db.

Does 5.3db really make that much of a difference? Then again, going from 75w/120.2db to 150w/123.2db did afford noticeable breathing room. Only being a 3db increase.

Quote:
Originally Posted by Joseph Crowe View Post
Did you ever get a chance to measure your mains using the Dayton reference mic? It will reveal a lot. +/-3 dB is my rule. I had 3 dB bumps in the midrange that once fixed sounded 10 times better.
I'm still looking forward to it! I haven't procured an adequate testing space. It's kind of silly though, I already have all the equipment I need to test and flatten the speaker's frequency response, (NU1000DSP) but I just haven't done it yet. I need to get my tail on that project!
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In one thousand years, will they still be called the Thiele Small parameters?
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Old 25th February 2014, 11:29 AM   #49
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Quote:
Originally Posted by Thetwinmeister View Post
Thanks!



Where did you get 500 watts? Is that from empirical experience? I've used as little as 75 watts for live sound reinforcement (on a different pair of speakers) for a small audience with no real headroom issues, although mixing is honestly a little tighter. The NU1000DSP puts 150w into 8ohms. With the LTA's sensitivity of 97.7db, that works out to 123.2db at 3 feet. 500w increases that to 128.5db.

Mathematically, that's only 5.3db more. I have no experience mixing more than 150 watts, so I can only speak from mathematical terms to say 5.3db doesn't seem like much more for a 350 watt increase. 75w turns out to 120.2db.

Does 5.3db really make that much of a difference? Then again, going from 75w/120.2db to 150w/123.2db did afford noticeable breathing room. Only being a 3db increase.



I'm still looking forward to it! I haven't procured an adequate testing space. It's kind of silly though, I already have all the equipment I need to test and flatten the speaker's frequency response, (NU1000DSP) but I just haven't done it yet. I need to get my tail on that project!
Oh sorry, I looked up the spec on the Behringer and it said 500 watts, however that's at 2 ohm! I had to dig very deep to see what the rating was for 8 ohm, 160 watts. I was thinking this was similar to what I've been using (Crown XLS-2500) at 440 watts per channel at 8 ohm. It was just my experience that bumping up in power produced a system that could play shockingly loud and clean. Depends on many factors of course.
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Old 25th February 2014, 05:14 PM   #50
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Originally Posted by Joseph Crowe View Post
Oh sorry, I looked up the spec on the Behringer and it said 500 watts, however that's at 2 ohm! I had to dig very deep to see what the rating was for 8 ohm, 160 watts. I was thinking this was similar to what I've been using (Crown XLS-2500) at 440 watts per channel at 8 ohm. It was just my experience that bumping up in power produced a system that could play shockingly loud and clean. Depends on many factors of course.
That does make sense, having higher headroom with ~500w would equate to lower THD vs squeezing every last watt out of a lower wattage amp. Amplifier upgrades are in my future, for sure! One day I would like to upgrade to Crown all around.
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