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Old 30th September 2009, 03:43 AM   #1
Borat is offline Borat  United States
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Default a way to test enclosures for "deadness"

take two enclosures facing each other and screw a single driver into both of them at the same time so all of the output of the driver on both sides is going only into the enclosures themselves.

you can rotate the enclosures around a bit so their front baffles are exposed and can radiate sound into the room.

now play your music. you will hear what your enclosure is contributing to the mix.
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Old 1st October 2009, 10:47 AM   #2
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$40 worth of accelerometer and interface electronics will allow you to measure it which will bring more useful results.
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Old 1st October 2009, 02:13 PM   #3
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Quote:
Originally Posted by Brett View Post
$40 worth of accelerometer and interface electronics will allow you to measure it which will bring more useful results.
I'm sorry, but I think it is incorrect to say that any measurement is "more useful" than what you HEAR.

Measurements are not significant compared to how a speaker sounds to the listener, right? The main purpose of a speaker is for listening to, or for being measured?

Sure, measurements are useful for designing speaker systems, and for marketing, but, I think how the speaker sounds trumps any measurement.

In the end, listening tests (measuring with our ears) is the most important type of measurement when completing a speaker design, I think successful speaker companies and DIY enthusiasts have all learned this, or will eventually.

EDIT: Though, I do think that cabinet design is extremely significant and vastly overlooked by both most speaker companies and DIY folks. And, that an accelerometer (or other means of measuring enclosure resonances/transmission) should be part of the tool set of anyone hoping to design anything more than a mediocre speaker system.
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Last edited by critofur; 1st October 2009 at 02:20 PM.
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Old 1st October 2009, 03:28 PM   #4
timpert is offline timpert  Netherlands
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I have to agree with Brett here. What you propose will give indeed some form of "residual" signal, but you simply don't know what the residual consists of. Assuming the two speakers are wired in reverse phase, and facing each other, the signal you still hear doesn't come from the cabinets alone. Any mismatch in the driver's transfer characteristics, crossover electronics, cabinet construction and such, will manifest itself as an additional "leaked" signal with a crooked frequency response, hard to discern from cabinet vibrations by casual listening.

It all depends on what you consider useful. If you want to know whether a system sounds right to you, by all means listen. But if you want to spot a potential issue and deal with it, by all means measure. Because your intention seems to be to assess cabinet vibrations, the casual test you describe just isn't going to nail them.
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Old 1st October 2009, 03:47 PM   #5
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Quote:
Originally Posted by timpert View Post
I have to agree with Brett here. What you propose will give indeed some form of "residual" signal, but you simply don't know what the residual consists of. Assuming the two speakers are wired in reverse phase, and facing each other, the signal you still hear doesn't come from the cabinets alone. Any mismatch in the driver's transfer characteristics, crossover electronics, cabinet construction and such, will manifest itself as an additional "leaked" signal with a crooked frequency response, hard to discern from cabinet vibrations by casual listening.

It all depends on what you consider useful. If you want to know whether a system sounds right to you, by all means listen. But if you want to spot a potential issue and deal with it, by all means measure. Because your intention seems to be to assess cabinet vibrations, the casual test you describe just isn't going to nail them.
Maybe I misunderstood the OP's intent when he said: "take two enclosures facing each other and screw a single driver" - what I thought when I read that is that you use a total of ONE driver for both cabinets. Doing it that way would avoid the problems that you mentioned, so long as there is a good seal between the two facing speakers.

I would add: use some form of gasket between the two speakers, also, rotating the cabinets by 90 degrees would allow more of the front panels to be exposed, which seems important to me as the front baffle is generally the most important one since it faces the listener and resonanace/transmission there would most likely be more audible, though, I suppose the combined output of two larger side panels could be more significant.

One thing I am certain of - this is an interesting and useful experiment...
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Last edited by critofur; 1st October 2009 at 04:06 PM.
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Old 1st October 2009, 05:42 PM   #6
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Quote:
Originally Posted by critofur View Post
EDIT: Though, I do think that cabinet design is extremely significant and vastly overlooked by both most speaker companies and DIY folks. And, that an accelerometer (or other means of measuring enclosure resonances/transmission) should be part of the tool set of anyone hoping to design anything more than a mediocre speaker system.
This is correct. I don't want to 'hear' the enclosure at all, and measuring it is the way to get the most accurate results. Keep trying different designs until you get no significant response from the enclosure itself.
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Old 1st October 2009, 05:44 PM   #7
Borat is offline Borat  United States
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Quote:
Originally Posted by critofur View Post
Maybe I misunderstood the OP's intent when he said: "take two enclosures facing each other and screw a single driver" - what I thought when I read that is that you use a total of ONE driver for both cabinets. Doing it that way would avoid the problems that you mentioned, so long as there is a good seal between the two facing speakers.

I would add: use some form of gasket between the two speakers, also, rotating the cabinets by 90 degrees would allow more of the front panels to be exposed, which seems important to me as the front baffle is generally the most important one since it faces the listener and resonanace/transmission there would most likely be more audible, though, I suppose the combined output of two larger side panels could be more significant.
yes that's what i meant. the front baffle is important because it is most directly energized by driver's vibration.

since cone moving mass is usually an order of magnitude higher than airload mass most vibrational energy will not come from sound but from the driver itself and transfer directly to the baffle.

accelerometer will provide a different kind of information. neither one is "better" than another. both is better than either one alone. accelerometer may help you zoom in on a trouble spot that requires bracing but it won't tell you what your cabinet sounds like.
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Old 1st October 2009, 06:17 PM   #8
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Quote:
Originally Posted by Borat View Post
yes that's what i meant. the front baffle is important because it is most directly energized by driver's vibration.

since cone moving mass is usually an order of magnitude higher than airload mass most vibrational energy will not come from sound but from the driver itself and transfer directly to the baffle.

accelerometer will provide a different kind of information. neither one is "better" than another. both is better than either one alone. accelerometer may help you zoom in on a trouble spot that requires bracing but it won't tell you what your cabinet sounds like.
Any energy imparted physically to a baffle glued to the rest of the enclosure will transfer effectively to the rest of the enclosure.
It appears we are talking about very different things, because I don't want the enclosure to have any sound at all.
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Old 2nd October 2009, 01:02 AM   #9
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Originally Posted by Brett View Post
Any energy imparted physically to a baffle glued to the rest of the enclosure will transfer effectively to the rest of the enclosure.
It appears we are talking about very different things, because I don't want the enclosure to have any sound at all.
to have no sound from enclosure at all is great in theory but not practical.

in practice the resources put to eliminating enclosure contribution completely would be better put to use elsewhere.

for example i think most people over-brace and under-stuff speakers. then they have a completely dead cabinet that howls like a wolf through the port.
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Old 2nd October 2009, 05:17 AM   #10
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Quote:
Originally Posted by Borat View Post
take two enclosures facing each other and screw a single driver into both of them at the same time so all of the output of the driver on both sides is going only into the enclosures themselves.

you can rotate the enclosures around a bit so their front baffles are exposed and can radiate sound into the room.

now play your music. you will hear what your enclosure is contributing to the mix.
Great idea..the only problem i can thinkn of is that in a vented system(ported qwtl tl whichever) you are also going to hear whatever spurious output there is from the vent also.

n ice idea though and a more tangiable result that acc. displacment and velocity resutls than youll get using a velocimeter or accelerometer
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