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post #3991 of 4009 Old 02-10-2016, 09:33 AM
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The Helmholtz resonator reference reminded me of Tom Danley's trip to the pyramids to measure the sound inside using a microphone and an accelerometer.

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post #3992 of 4009 Old 02-10-2016, 11:24 AM - Thread Starter
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Quote:
Originally Posted by 3ll3d00d View Post
Since the driver is barely moving at this point, isn't it more likely that a port produces greater pvl per SPL than a driver? If we assume the driver doesn't contribute in the ported system, you could test this by applying a bandpass filter to a sub so as to coerce it into the same FR as the port has alone. Compare the tr results when playing a sine wave (or noise band limited to the port output passband?) and see which one wins.
I believe I've already performed this test as documented in post 5 below:

http://www.avsforum.com/forum/113-subwoofers-bass-transducers/1488059-your-home-theater-ulf-score.html#post23676274

The results support the hypothesis as I recorded more Tactile response with the vibration meter with the ported design.

But you're right, it could be because the port is contributing more pvl per spl compared a sealed design at those frequencies. I don't understand the physics enough to explain why if that was the case, but definitely a possibility.
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post #3993 of 4009 Old 02-10-2016, 11:42 AM - Thread Starter
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One other note about pvl...

It is directional. That being the case, subs where the port fires up or down or a different direction than the driver, may not be able to optimize tactile response...above tune, the driver produces the lion share of pvl, but near tune the port does. If they aren't firing the same way, you may lose TR.

Directionality is an easy one to test...for those with nearfield setups, turn your sub so that the driver is facing in the opposite direction of your seating...Tactile Response will drop significantly even if calibrated with the same spl.

Of course boundaries could also come into play, and perhaps dual opposed boundary loading might be a sweet spot as I know @coolrda experienced a difference when he went DO behind his seating...
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post #3994 of 4009 Old 02-10-2016, 11:52 AM
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Quote:
Originally Posted by dominguez1 View Post
But you're right, it could be because the port is contributing more pvl per spl compared a sealed design at those frequencies. I don't understand the physics enough to explain why if that was the case, but definitely a possibility.
I wonder whether different port configurations behave differently too? e.g. 1 big port vs 3 smaller ones.
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post #3995 of 4009 Old 02-10-2016, 07:27 PM
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Think of a port similar to a flashlight. For example a fluorescent flashlight and a large panel fluorescent light that are equal in lumens. which is brighter? Up close the small beam of the flash lights may appear brighter but, further back at 30 or 40 ft., the panel appears brighter.

At the port, working at max there is more intensity along a focus path. This should lead to higher PVL. Just throwing around a possible explanation. A model for testing would be needed to validate this.
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post #3996 of 4009 Old 02-10-2016, 09:58 PM - Thread Starter
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Quote:
Originally Posted by derrickdj1 View Post
A port of similar to a flashlight. For example a fluorescent flashlight and a large panel fluorescent light that are equal in lumens. which is brighter? Up close the small beam of the flash lights may appear brighter but, further back and 30 or 40 ft., the panel appears brighter.

At the port, working at max there is more intensity along a focus path. This should lead to higher PVL. Just throwing around a possible explanation. A model for testing would be needed to validate this.
Interesting hypothesis...I think that has merit.

In the research that I've done, there was some mention that the diameter of the driver had a greater impact on TR in the nearfield sound field. In the example with the ported design, if the driver is 15in, it's producing 15inches of pvl, so to speak. When near tune, the pvl of the 15in driver is concentrated through the diameter of the port, thus producing a concentrated pvl wave producing more TR (think of a water hose going from spray to stream).
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post #3997 of 4009 Old 02-11-2016, 07:54 AM
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Well, after several weeks of reading to get to this point all I can say is what a great thread you started! Thanks, it's taught me so much! Perhaps then you can add me to your list? It's my first attempt at DIY but was well worth it in the end. Do I qualify for inclusion in the 5Hz club?







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post #3998 of 4009 Old 02-11-2016, 07:56 AM
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Quote:
Originally Posted by dominguez1 View Post
Interesting hypothesis...I think that has merit.

In the research that I've done, there was some mention that the diameter of the driver had a greater impact on TR in the nearfield sound field. In the example with the ported design, if the driver is 15in, it's producing 15inches of pvl, so to speak. When near tune, the pvl of the 15in driver is concentrated through the diameter of the port, thus producing a concentrated pvl wave producing more TR (think of a water hose going from spray to stream).

This is how I think of it as well. Usually 18 inch drivers have 8 inch round ports for large DIY subs, at least that is what I use and used in the past. That 8 inch port is tiny compared to the driver yet the same spl is being produces at port tune and in my case more due to rom gain. It makes sense but who knows because it is too simple for all of this.
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post #3999 of 4009 Old 02-11-2016, 10:59 AM
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I was curious to see how many db's I could register on my TermLab, so I put it 5ft deep into my HzHorn and played a 14.5Hz sinewave @ 1/4 power (~1000watts).
The subwoofer was only moving 4mm's out of 80!
I got 145.1db @ 14.5Hz with ~8% THD. (I was too afraid to try a higher frequency like 70Hz, the SPL would have killed me. )


I wouldn't be surprised if the SPL was 180-190db directly in front of the cone with full power.
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post #4000 of 4009 Old 02-11-2016, 03:31 PM
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Good thing you don't live near anybody, that was a mini tremor in the area, lol.
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post #4001 of 4009 Old 02-11-2016, 03:45 PM
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@BassThatHz - can you run it at full-tilt and measure from the MLP? Please setup your camera outside as I'd like to see your theatre space crumble

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post #4002 of 4009 Old 02-11-2016, 08:24 PM
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https://drive.google.com/open?id=0Bw...WNIZFZxdlBFM1E
I have an old recording of what my theater sounds like 100ft away, as recorded by a UMIK-1.
This was with 12 sealed subs at 1/2 power. (I didn't have a horn back then, still pretty loud though...)
The mic was set to clip at 96db (which it did), in hind sight I probably should have set the UMIK to clip at 120db instead.

I tried to live as far out of town as possible, while still maintaining high-speed internet.
So unfortunately I do live near some people, there are about 9 houses within 80-150ft, and another 15 houses 3-500ft away.

The only way to obtain 40+ acres around here is to say goodbye to HS internet, and have a 20-50mile to get the nearest big store. Basically you'd be in farm-type land driving in cow poop every day, just to get away from everyone.

Because of the mountains, most people are living in the valleys in between, so you have chains of homes stretching all the way until the HS internet ends, so like 10 miles in any given direction (copper cable lines mostly.) The homes continue on like that 20-30 miles in any direction (just with no HS internet).
They are slowly installing fiber, so that's good, but the first rollout is only to the high density areas, the rural areas will be without for several more years... only LTE with huge lag.

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post #4003 of 4009 Old 02-11-2016, 08:26 PM
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The amp is rated for 4kW x2 or 7kW x1 @ 4-ohm. Which would be another 6-8db.

I lose about 10-25db from 4-5ft inside the horn to the horn-mouth,
the sub is ~7ft away from the LP in which I lose another 6-15db.

So I'd be lucky to reach THX at 14.5hz at the LP with one 18". (Still one of the loudest single-cone boxes in the world though...)
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post #4004 of 4009 Old Yesterday, 06:39 AM - Thread Starter
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Quote:
Originally Posted by Ringnut View Post
Well, after several weeks of reading to get to this point all I can say is what a great thread you started! Thanks, it's taught me so much! Perhaps then you can add me to your list? It's my first attempt at DIY but was well worth it in the end. Do I qualify for inclusion in the 5Hz club?







Wow, that's really impressive for just two subs!...of course the are lmsu's...so guess I shouldn't be surprised. Nice amp as well.

Congrats on the response as well...welcome to the 5hz club.

I'll get you in the next update.
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post #4005 of 4009 Old Yesterday, 06:42 AM - Thread Starter
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@BassThatHz

That is sick...that's probably my favorite frequency from a TR perspective...can't imagine what it feels like at 145db!!!
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post #4006 of 4009 Old Yesterday, 05:51 PM - Thread Starter
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Quote:
Originally Posted by dominguez1 View Post
Interesting hypothesis...I think that has merit.

In the research that I've done, there was some mention that the diameter of the driver had a greater impact on TR in the nearfield sound field. In the example with the ported design, if the driver is 15in, it's producing 15inches of pvl, so to speak. When near tune, the pvl of the 15in driver is concentrated through the diameter of the port, thus producing a concentrated pvl wave producing more TR (think of a water hose going from spray to stream).
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Originally Posted by MKtheater View Post
This is how I think of it as well. Usually 18 inch drivers have 8 inch round ports for large DIY subs, at least that is what I use and used in the past. That 8 inch port is tiny compared to the driver yet the same spl is being produces at port tune and in my case more due to rom gain. It makes sense but who knows because it is too simple for all of this.
I'm pretty convinced that this how it works...

Take for example your setup MK. You've basically got a 8x18in array of PVL...that since you've ported at the 6hz tune, is compressed through two large ports. Prior to the port, you had sealed.

You had mentioned this before, but just wanted to confirm. Is there more Tactile Response around port tune compared to your sealed at the same SPL?

Is there a way for you to measure via VibSensor ported vs sealed around tune?

Anecdotaly, I've experience this before in different rooms in the past, when I was running just sealed vs a buddy of mine's ported setup...in his room, there seemed more 'pressurization' (Tactile Response) around port tune compared to mine, and I never understood why.

@notnyt also has mentioned this before going from 8 sealed LMSUs to 8 Ported LMSUs...

Also remember, that room gain does not likely produce any PVL as it is not 'mechanically' created by the driver (which derives the PVL). Perhaps this is the reason we typically don't 'feel' the single digit effects as we do in the higher frequencies because it is mainly made up of room gain (that naturally lacks any PVL). (***Note, I do believe room gain adds a 'pressure and weight' to the room, just not a Tactile Response like pant leg flapping....if that makes sense.)

The room gain effect could be overcome by a huge house curve down low so that the driver is working hard to produce that very low PVL. However, most don't have the displacement to be able to get such a curve...

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post #4007 of 4009 Old Yesterday, 06:03 PM
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[MENTION=7958592]145db!!!
Speaking of dB, would it be possible to incorporate max possible dB levels at the LP in this Score Card?

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post #4008 of 4009 Old Today, 08:51 AM - Thread Starter
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Speaking of dB, would it be possible to incorporate max possible dB levels at the LP in this Score Card?
Hmmm, I know others have brought this up before. I avoided it in the past just to avoid the SPL war debate, but perhaps I should revisit?

Maybe I include it in the ULF card as commentary as opposed to a sortable field, just to give additional color about their HT ULF experience. It would be totally optional and wouldn't effect their overall score. If you did include something, you'll need proper proof like @BassThatHz provided.

Personally, I wouldn't participate just because I don't like risking my equipment, and I think the ULF score does a good job of giving a general idea of what my ULF experience is. However, certainly others could if they wished!
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post #4009 of 4009 Unread Today, 11:17 AM
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Quote:
Originally Posted by dominguez1 View Post
Hmmm, I know others have brought this up before. I avoided it in the past just to avoid the SPL war debate, but perhaps I should revisit?

Maybe I include it in the ULF card as commentary as opposed to a sortable field, just to give additional color about their HT ULF experience. It would be totally optional and wouldn't effect their overall score. If you did include something, you'll need proper proof like @BassThatHz provided.

Personally, I wouldn't participate just because I don't like risking my equipment, and I think the ULF score does a good job of giving a general idea of what my ULF experience is. However, certainly others could if they wished!
Well, what I was thinking that it could be a calculation based on subs, room, etc. - just like the UFL card is. While I agree that this card gives a great idea of how our ULF experience is, I don't exactly know how that translates into dB levels. It's just some gear that I have yet to invest in because I'm still investing in subs and other equipment. In the end, my comfortable dB level is something I could find out myself, but I was just curious if some math could be used to give some insight.

But I am like you, I would opt out if it mention actually pushing our gear to those levels. I over-buy so I don't have as much risk hurting anything, and if I (or the content) gets a little excessive, I'm usually protected because of headroom and power handling.

I agree that some "proof" is always nice to see. I love seeing pictures and what not. But I bet there are posts in this thread that are not accurate.

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