Multiple Small Subs - Geddes Approach - Page 154 - diyAudio
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Old 9th January 2013, 12:39 AM   #1531
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Quote:
Originally Posted by gedlee View Post
Not so for the short term "thermal modulation". The copper does begin to heat "instantaneously" as the current passes through it. I had this discussion with my physics advisor and he agreed that the heating would occur on a time scale of that of the speed of light. Of course the "temperature" lags the "heating" by a time rate that depends on the thermal capacity of the material. This is exactly why more copper yields a lower rate of temperature change than less copper for a given current.
Have you tried testing the power amplifier voltage rails during the period of 'thermal modulation'?

A higher efficiency driver is unloading the amplifier power supply also so I am thinking out loud that the thermal modulation of a lower efficiency driver should be evaluated together with its impact on the amplifier power supply?

Improved dynamics is one of the advantages presented for SMPS with high power and tightly regulated output and proper use of amplifier decoupling capacitance.
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Old 9th January 2013, 02:25 AM   #1532
gedlee is offline gedlee  United States
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Nothing that the speaker does should ever affect the amplifier - or its a poor design.
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Old 9th January 2013, 02:49 PM   #1533
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Originally Posted by weltersys
One can certainly EQ anything flat at a low enough level, but if one actually wants high SPL low frequency, there are many useful specifications which will separate the wheat from the chaff.

Relevant specifications for a sub are frequency, phase, and impedance response, sensitivity, harmonic distortion at rated power, and power handling.


Quote:
Originally Posted by gedlee View Post
Phase? Really?

THD - you should know that I think this a completely useless specification.

Frequency response - you mean the response in a free field that has absolutely nothing to do with its response in a real room?

Impedance - sure, that's relevant, I can do that.

Power handling is what the driver manufacturer says it is.

You are quite correct that its the EQ capability that "will separate the wheat from the chaff" which is why I use drivers with headroom to spare. EQ is not going to be a problem in any small room.
Knowing the subwoofers phase response in the intended crossover band will help in deciding whether the sub can be phase aligned with the mains without use of DSP, or the extent of DSP that will be needed.
Of course, if one uses more than 2 subs not in close proximity to the mains, phase alignment is not really possible anyway.

While the distortion a good sub will produce in it's linear range is not a problem, your suggestion that "EQ is not going to be a problem in any small room" is an invitation for gross distortion.
Apply the 2000 watts the 12TBX100 is rated for at twenty to thirty Hz and tell me whether you don't notice the distortion more than the fundamental tone.

Stating a frequency response of "approx. 45-120 Hz" and a sensitivity of "TBD" is almost worse than no information at all. Is the response -3 dB at 45 Hz, or -10 as is often the case for manufacturers who don't bother with a response curve?
What happens above 120 Hz, a smooth roll off, or a rolloff and then a bunch of horrible out of band junk that will chew up several parametric EQ bands to fix?

Obviously each room has it's own problems, but knowing what the sub's raw free field response is certainly useful in making an informed decision rather than relying on a manufacture's claim that "this sub can take whatever is required".
If one's requirement is 120 dB at 25 Hz or lower in "any small room" (whatever that is), and knows a 95 dB sub that handles 2000 watts is -24 dB at 25 Hz, even if it does not flap like a strangled goose at 2000 watts we know it will only make 104 dB (excluding power compression), some 14 dB short of the goal.

And what if 104 dB at 25 Hz is adequate for a user, without a frequency response curve at a known distance and input voltage we have no idea whether we need 20 or 2000 watts to achieve it.
And of course, knowing the impedance minima will inform our decision as to what type of amp can supply the voltage needed to achieve the desired SPL.

Your decision to not post any specifications of what your sub can do, then your response dismissing specifications does not inspire any confidence in the performance claims for your product.

Cheers,
Art
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Old 9th January 2013, 03:33 PM   #1534
gedlee is offline gedlee  United States
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Originally Posted by weltersys View Post
Of course, if one uses more than 2 subs not in close proximity to the mains, phase alignment is not really possible anyway.
Thats really the point, I do not recommend ever using just one sub so everything that I say assumes at least two or more - likely three. That makes a lot of difference, which is why I said that EQ in any small room is not a problem. It almost always will be with one of some other subs, just that with three of mine it isn't.

Although "phase alignment" at modal frequencies is kind of a joke really - it is swinging all over the place with both frequency and location for both the sub and the mains. Do you "align" at one spot at one frequency? Any phase setting will do that at some frequency and location.

Quote:
If one's requirement is 120 dB at 25 Hz or lower in "any small room"

Your decision to not post any specifications of what your sub can do, then your response dismissing specifications does not inspire any confidence in the performance claims for your product.
120 dB at 20 Hz! You achieve that regularly do you? Kind of insane as far as I am concerned.

I am not trying to promote my subs - they are a bad business for me. I sell them because customers ask what kind of subs that they should use with their mains and I tell them - "I know of no good subs for a decent price", but I know that three of my subs will satisfy anyone. I don't think that I need to specify any more than that.

When they buy the subs from me then I provide a setup service as well which ensures that no sub is ever overloaded. No one has complained yet.

My lack of specifications is almost by design - I only want to sell mains, but I will sell subs if I need to.

Last edited by gedlee; 9th January 2013 at 03:37 PM.
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Old 9th January 2013, 05:12 PM   #1535
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Originally Posted by gedlee View Post
Do you "align" at one spot at one frequency?

120 dB at 20 Hz! You achieve that regularly do you? Kind of insane as far as I am concerned.
Earl,

I phase align subs to mains using pink noise, microphone placed equidistant between the sub and mains, ground plane outdoors (if possible), using Smaart.

Funny, yesterday I turned up the stereo "loud" while I was vacuuming, (I wear hearing protection when vacuuming) and it was less than 100 dBC, about 90 dBA.
It "only" takes 90 dBA , the OSHA 8 hour permissible level, to sound as loud as 120 dB at 20 Hz.

When testing a pair of my Lab 2x12" in "step down" mode I have listened to them producing over 120 dB at 20 Hz.

I don't regularly listen to subs at 120 dB at 20 Hz, but there are many on the forum that do.

I'd agree that level is kind of insane, though when I was providing "sound by the pound", 120 dBC was not uncommon at the house mix, people up close to the speakers were getting way more than that.

That was back in the 1990s, before it was common for car subs to hit well over 120 dB at 20 Hz, now people seem to expect that kind of level.

Just worked on a 2300 seat church install, fourteen B&C 21" woofers with about 5000 watt potential for each cone using bridged Lab Gruppen amps.
Insane, but the church brings in about one million dollars a weekend.

That is more than my company grossed in a year when I was deploying over a million dollars in sound and lighting gear.
Might have to review what is insane...

Art
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Old 9th January 2013, 05:25 PM   #1536
gedlee is offline gedlee  United States
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Home theater and Pro are different worlds, especially for subs. I've been in both. Pro is all about SPL and HT is all about sound quality. Sound quality is all that interests me. I leave the SPL games for others.
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Old 9th January 2013, 05:40 PM   #1537
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Originally Posted by gedlee View Post
Home theater and Pro are different worlds, especially for subs. I've been in both. Pro is all about SPL and HT is all about sound quality. Sound quality is all that interests me. I leave the SPL games for others.
The professionals I generally work with requiring live sound reinforcement are quite concerned with sound quality.

I'm glad I seldom work with pros who are only concerned about SPL.

As far as "different worlds", there are different sized venues requiring a different amount and type of gear to achieve the same SPL and sound quality required for a home theater.
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Old 9th January 2013, 06:17 PM   #1538
gedlee is offline gedlee  United States
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Based on the last few examples of Pro setups that I witnessed, sound quality is not even a consideration.

The size of the venue is more than a minor consideration. It tends to dictate designs with serious compromises.
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Old 9th January 2013, 11:41 PM   #1539
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Originally Posted by gedlee View Post
As expected people are confusing thermal compression with thermal modulation. they are related but distinctly different effects.
*****************
Thermal compression is also, for the most part, independent of the current voice coil temperature, while thermal compression is completely dependent on the current voice coil temperature. Thermal modulation acts in addition to thermal compression and is essentially independent of it.
*************
This discussion should not really be in Subwoofers. But I was asked here.
I think that we have a typo here.
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Old 10th January 2013, 12:04 AM   #1540
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If all pro sound companies took sound quality seriously I wouldn't have a job =). There are many large companies with large rigs and large egos who's systems almost always sound like garbage( I won't name names ) but as Art said, there exist pro sound companies who are concerned with quality( not many in California ). How we define quality is another matter. Some just don't know what quality is, don't understand the inherent non-linear behavior of their equipment, or go deaf by the time they start to figure things out.

I think many will agree there are nuts in both the hifi and pro sound camps. IMO pro sound has a tougher job having a much larger listening area in which to keep the system aligned. I have a great deal of respect for both Earl and Art having learned much from both you. Can we not accept that these "different worlds" both contain the good, the bad, and the insane?

-Matt
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