Surround Speaker Design for a Small Home Theater - Page 4 - AVS Forum
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post #91 of 99 Old 02-26-2014, 02:11 AM
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Klipsch RB-75
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post #92 of 99 Old 02-26-2014, 07:36 AM
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Looks great Mike!

I want to run an idea by you. I'm sure you've read the recent conversations about excursion in the LF portion of a coax upsetting the frequency response in the HF region. Are you happy with the trade-off this speaker represents in that regard? I don't know enough about these designs to say confidently, but I feel like cabinet volume, extension, and sensitivity could be manipulated to minimize excursion at reference and maximize HF fidelity. So, I guess the first issue is do you think the HF is refined enough when the bottom end is pushed hard? And related, do you have any concerns about being able to drive them to reference in your space? (would you be willing to give up two or three dB sensitivity?) If that is possible (I think it would need more volume) any ideas what that would dso to the native FR and how that would influence your opinion on the final result? (sorry - too many questions)


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post #93 of 99 Old 02-26-2014, 02:23 PM
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Quote:
Originally Posted by HopefulFred View Post

... I feel like cabinet volume, extension, and sensitivity could be manipulated to minimize excursion at reference and maximize HF fidelity...

Other than porting vs. sealed, the only way to lower excursion is to raise the XO freq and/or limit output.

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post #94 of 99 Old 02-26-2014, 06:12 PM - Thread Starter
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Quote:
Originally Posted by HopefulFred View Post

Looks great Mike!

I want to run an idea by you. I'm sure you've read the recent conversations about excursion in the LF portion of a coax upsetting the frequency response in the HF region. Are you happy with the trade-off this speaker represents in that regard? I don't know enough about these designs to say confidently, but I feel like cabinet volume, extension, and sensitivity could be manipulated to minimize excursion at reference and maximize HF fidelity. So, I guess the first issue is do you think the HF is refined enough when the bottom end is pushed hard? And related, do you have any concerns about being able to drive them to reference in your space? (would you be willing to give up two or three dB sensitivity?) If that is possible (I think it would need more volume) any ideas what that would dso to the native FR and how that would influence your opinion on the final result? (sorry - too many questions)

Fred, I've been considering your thoughtful post all morning. My thoughts have ranged from "I don't have the ears to discern such differences", to "I don't listen loud enough for that to happen", to "I'm not knowledgeable enough to answer intelligently." Since I've never let my lack of intelligence prevent me from wading in and offering an opinion or an intelligent sounding response, I'll give it a shot:

I am familiar with the discussion you mentioned and it makes a lot of sense to me ( whether I can hear it or not ). That was part of the reason why I went with the V10 over the V8 and also why I went sealed rather than ported. It is also why I am crossing my surrounds over to my sub at 120 Hz. With regards to trade offs, my selection was primarily driven by price sensitivity. mad.gif

Noah has already addressed the factors impacting woofer excursion, and I have not pushed these speakers hard enough yet to determine what if any bad habits they may exhibit when pushed. They sounded a little nasal in my test enclosures which were smaller and unstuffed, but the finished speakers sound similar to my Cheap Thrills, but not quite as open and precise.

I run out of amplifier before the V10s run out of response, so I can't answer how they perform at their limits.

I'm not sure I understand the last part of your question. I don't have a calibrated mic or SPL meter, so I'm not sure if they play at reference levels or not.

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post #95 of 99 Old 02-26-2014, 07:20 PM
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Quote:
Originally Posted by mhutchins View Post

...why I went sealed rather than ported.

If Fb and XO freq are suitably chosen, excursion will be greatly reduced for the same output.

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post #96 of 99 Old 02-26-2014, 07:31 PM - Thread Starter
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Noah, I don't understand how less excursion at a given frequency can result in the same SPL, just by changing the box volume. Can you explain how that works, using small words.

Thanks,
Mike
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post #97 of 99 Old 02-26-2014, 07:41 PM
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Thanks for your thoughts Mike. I didn't imagine that I could tell the difference and know if excursion was interfering with high frequency fidelity, but I had to ask. Are you running Audyssey or similar? If so, then I guess the question is do they distort or sound ragged (whatever that sounds like) at 0dB master volume? I wouldn't think they would sound that way, with power handling of 400W and 95dB sensitivity they should be running pretty easily to reference in your space with probably less than 50W.

I think Noah is explaining what I was thinking about (thanks Noah!). I was, in my naivety, seeing (in my head) the max SPL graphs where varying Qtc changes max output. I was hoping that a higher Qtc would result in higher output with less excursion. I think there's no way this can be, but I still don't see how output can be higher with the same power. (Wait, yes I do - I think - once the box volume gets big enough relative to the driver, the air-spring gives the cone resonant reinforcement - increasing excursion for the same power at that frequency.) At any rate, what I see from Noah's explanation is that only by getting the output from the port can the excursion be limited without sacrificing SPL. That is to say: with a sealed box, the only sound radiator is the cone, and the cone excursion is the only thing that can influence SPL. Ports and passive radiators produce their own acoustic output, at the expense of group delay and unmanaged cone excursion below tuning frequency. (I'd love to be corrected if this is wrong smile.gif )

Edit: I hadn't seen Mike's last post before I posted this - this is not intended as a response to Mike's question of Noah.


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post #98 of 99 Old 02-27-2014, 01:54 PM
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Quote:
Originally Posted by HopefulFred View Post

At any rate, what I see from Noah's explanation is that only by getting the output from the port can the excursion be limited without sacrificing SPL. That is to say: with a sealed box, the only sound radiator is the cone, and the cone excursion is the only thing that can influence SPL. Ports and passive radiators produce their own acoustic output, at the expense of group delay and unmanaged cone excursion below tuning frequency.

You got it.

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post #99 of 99 Old 02-27-2014, 01:58 PM
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Quote:
Originally Posted by HopefulFred View Post

Wait, yes I do - I think - once the box volume gets big enough relative to the driver, the air-spring gives the cone resonant reinforcement - increasing excursion for the same power at that frequency.

It occurs at all box volumes, just the resonant freq at which it occurs changes.

Also note that output/efficiency increase only around this freq, as volume decreases there's a faster rolloff at the low end.

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