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Old 5th January 2013, 12:35 AM   #31
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This article Center Channel Speaker Design Additional Considerations — Reviews and News from Audioholics is probably worth a read. something like that in figure 4 might be a good compromise.

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Old 5th January 2013, 12:49 AM   #32
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Quote:
Originally Posted by sreten View Post
Hi,

Its very unlikely your speakers have significant output below the port tuning
frequency to "dump" energy into the room, with an 80Hz 2nd order L/R high
pass you will have a 6th order roll-off in the bass, and if anything going to
sealed boxes will increase bass below 60Hz due to the 4th order roll-off.
I guess I shouldn't have said anything about the room. My reasoning for building new speakers is that I want the experience and I want the ego boost that comes with successfully designing and building a set of good speakers. I HATE the KEF C1 bookshelf speakers I have. I know from experience that no amount of bass trapping or dial fiddling with crossovers will change their small size and overheated tweeter sound. They need to be replaced. I've listened to other speakers in the same room and they sound MUCH better. My room comments are probably dead wrong. As I said I have done precious little to work out the room acoustics. Partly because I've been changing furniture. Here's why:
Two weeks ago I bought a soft comfy cloth sectional and hated it so I sold it. It took 5 days to get rid of. Today I purchased a couch, love seat and chair made from what feels like Italian leather-- if ONLY... A month ago I didn't have an Omnimic to measure the room, now I do. Two weeks ago I didn't know how to measure a room, now I have a basic idea. Now that my environment is more stable (I still have a coffee table and ottoman to indulge in) I can begin to understand why I hear what I hear in the room.

As for significant output below port frequency it's a moot point. I don't really care if it does or not but something is exciting the room and it's happening at a frequency too low to be the tweeter. It's not the speaker that's the issue anyway, it's the room. I couldn't possibly fix the LF rumble by altering the speaker. I need to reduce the resonances in the room by both absorption and changing the acoustic shape of the room some way. I do need help and I do need to measure the room both acoustically and physically so I can understand which dimension waves are building and what objects/walls are perpetuating the buildup. But let's do it in a different thread, K?
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Old 5th January 2013, 01:26 AM   #33
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Building because you want to is the best reason.
With the room try the cheap fixes first, my beloved was amazed at how much difference the wall hanging made and she is an interior designer ( but obsessed with looks first as most women are ) where function is usually subservient to visual appeal
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Old 5th January 2013, 01:38 AM   #34
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Originally Posted by Siggma View Post
Are you always this forgiving of newcomers questions? Sheesh. If there are so many links to MTM designs why not post one, or would that destroy your reputation (with me anyway) as 48 hours of stubble?
For anyone coming here 'hat in hand' and when they don't get a quick response, pop off with a comeback similar/same to your 2nd post, you bet your sweet bippy!

I don't catalog links to info I have zero interest in, but am well aware that they've been 'beat to death' ad nauseum over the years here and on other web forums, so know that there's plenty of knowledge to answer most anyone's Qs for those willing to do a bit of due diligence to find them.

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Old 5th January 2013, 01:51 AM   #35
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Originally Posted by Siggma View Post
Now that my environment is more stable (I still have a coffee table.........
There should be no reflective surfaces between the speakers and listening position.

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Old 5th January 2013, 01:48 PM   #36
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Originally Posted by Ahmad_tbp View Post
i m not sure if I don understand what you r saying because of my english or because of my lack of knowledge , or because you r wrong
anyway , i m not an expert by all means but from what I know you gonna need one crossover for whole system , I mean you have to connect your woofers in parallel and connect them to your designed crossover , again means you have to see the paralleled woofers as one single unit ...!
I have to admit I didn't read as much as I probably should have before posting but what I was looking for is how to calculate the final gain of two mid woofers in a single enclosure vs a single driver in half the volume. I can't seem to find it anywhere. I recall reading that in some situations two drivers sharing the same enclosure volume will net an increase in output compared to a single driver. I've googled dual speaker, dual driver, etc and I can't seem to find it.

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first , if my memory serves me right you gonna end up with +6db in sensitivity of paralleled woofers ,and you don need to find a tweeter to have the same sensitivity , if you r worried about difference in sensitivity of drivers (your parallel woofers and your tweeter) you don need to double the tweeters either , you need an L-pad (driver attenuation circuit ) to equalize the different driver sensitivities (if there is any!),
The issue is not parallel wiring gain, it's acoustic coupling gain . The woofer is rated 90db 1w/1m and the tweeter is rated 91db 2.83v/1m. Both are "over" rated to some extent. It looks like the woofer is right about 90db over the range I'm using it. If dual woofers nets me 91db I should be fine. If it's more I may not be able to use a 91db tweeter.
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Old 5th January 2013, 02:06 PM   #37
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Originally Posted by Siggma View Post
I have to admit I didn't read as much as I probably should have before posting but what I was looking for is how to calculate the final gain of two mid woofers in a single enclosure vs a single driver in half the volume. I can't seem to find it anywhere. I recall reading that in some situations two drivers sharing the same enclosure volume will net an increase in output compared to a single driver. I've googled dual speaker, dual driver, etc and I can't seem to find it.
Try 'mutual acoustic coupling' to get the higher math, though this should suffice for the typical novice:

Ripped from Electro-Voice documentation:

When a common signal is applied, a 6-dB increase in maximum acoustic output occurs. The cones “mutually couple” and act as one cone with twice the area (therefore twice the efficiency) and twice the power capacity. The additional cone area provides 3 dB more output and the additional power capacity accounts for the remaining 3 dB.

Specifically, mutual coupling occurs at frequencies whose wavelengths are longer than one-quarter the center-to-center distance between the cones. The highest frequency at which mutual coupling occurs is calculated from the following equation:

f = 3,000 / DMAX

where DMAX (inches) is the distance between the cones, and f (Hz) is the highest frequency at which coupling occurs. When DMAX is greater than one-quarter wavelength, or at frequencies much above f even when closely spaced, the increase in acoustic output is limited to the 3-dB power-handling increase.


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Old 5th January 2013, 02:24 PM   #38
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Originally Posted by Soundtrackmixer View Post
Actually, this is a no on all counts. I am just trying to make sense of your argument for building new speakers. The reason you gave does not make much sense. If you want to build new speakers, great. But the reasoning you use for doing so just is not sound at all.
The thread and question is about MTM designs. I apologize if I shared more than I intended regarding my choices or my room. I wasn't really after a treatise on how to design MTM or fix my room or why I've chosen to replace the sats. The reason I'm replacing them is twofold and simple, I don't like them and I want to build my own. I don't like the metal dome tweeter and they have a ported sound, which I don't like. I made a mistake in purchasing them because I didn't do my homework. I'm trying to prevent the same mistake again. I haven't worked on the room because I've been changing furniture and rearranging things. Some of the issues become apparent as I move furniture around, others are a little more tricky.

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Did it ever occur to you that the reason the tweeter sounds harsh, and the bass sounds muddy, is because you have not treated the room? Bare walls can make a speaker sound harsh, especially at higher levels. Corner resonances can be taken care of with bass traps.
Yes it occurred to me. That's why I've listened to more than one speaker in the same room. The harshness isn't in the reflections, it's coming directly from the tweeter and it follows the tweeter. I do know the difference between reflected harshness and sibilance. Granted the room has a large effect on how a speaker will sound but in this case it's definitely the tweeter. I did not say it was a "bad" tweeter or that it will sound that way elsewhere or with different equipment but on my Yamaha surround processor in my small room it sounds harsh and annoying. It's bad enough that a simple mp3 recording with a computer mic would pick it up.

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Since KEF did not invent small room acoustic issues, then your comment on this is nonsense. The issues you mention are small room acoustical issues. You can build another speaker, and if you do not address the acoustics of the room, you will end up with acoustical issues that will play out differently than your current issue. You cannot build your way to getting good acoustics in your room via the speakers. You are going to have to address the room, or you will not be satisfied with the sound of any speaker you create.
I have no illusions that a new pair of speakers will fix the problems I'm having. I have done almost nothing to correct room acoustics. Did it occur to you that I know nothing about correcting a room? You've come off like I deliberately misled you or that my inexperience is somehow wrong. You focused on the room and how wrong I am without asking a few basic questions like "What have you tried?" or "Do you have any measuring equipment?", or even easier, "Why do you think the speakers are the problem?". You've made this personal and I don't understand why.

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Had you have just stated that you wanted to build a MTM speaker system and need advice, you would not have gotten a response from me. But your excuse for wanting to do so was so off the wall, I had to respond. I am done - good luck with your project.
That is the most immature thing I've heard here yet. Sounds like you stopped by to try to boost your ego by telling me I'm wrong.
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Old 5th January 2013, 02:26 PM   #39
Siggma is offline Siggma  United States
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Quote:
Originally Posted by GM View Post
Try 'mutual acoustic coupling' to get the higher math, though this should suffice for the typical novice:
Thank you! Thank you! I knew it was here somewhere.

Quote:
Ripped from Electro-Voice documentation:

When a common signal is applied, a 6-dB increase in maximum acoustic output occurs. The cones “mutually couple” and act as one cone with twice the area (therefore twice the efficiency) and twice the power capacity. The additional cone area provides 3 dB more output and the additional power capacity accounts for the remaining 3 dB.

Specifically, mutual coupling occurs at frequencies whose wavelengths are longer than one-quarter the center-to-center distance between the cones. The highest frequency at which mutual coupling occurs is calculated from the following equation:

f = 3,000 / DMAX

where DMAX (inches) is the distance between the cones, and f (Hz) is the highest frequency at which coupling occurs. When DMAX is greater than one-quarter wavelength, or at frequencies much above f even when closely spaced, the increase in acoustic output is limited to the 3-dB power-handling increase.


GM
Wow, so I can shape the FR by how far apart I mount them... Excellent, thank you again.
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Old 5th January 2013, 02:31 PM   #40
Siggma is offline Siggma  United States
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Quote:
Originally Posted by GM View Post
For anyone coming here 'hat in hand' and when they don't get a quick response, pop off with a comeback similar/same to your 2nd post, you bet your sweet bippy!

I don't catalog links to info I have zero interest in, but am well aware that they've been 'beat to death' ad nauseum over the years here and on other web forums, so know that there's plenty of knowledge to answer most anyone's Qs for those willing to do a bit of due diligence to find them.

GM
Not all of us have been here "over the years"... To me this thread is "due diligence". Sometimes I can't remember what to ask for. Plus, the more dialogue on an issue, the more discovery.

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