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Old 02-10-2016, 08:33 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.

The Great Pyramid: Early Reflections & Ancient Echoes
TestTones, Indiana Jones and the Lost Knowledge of Yore
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Old 02-10-2016, 10:24 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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Old 02-10-2016, 10:42 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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Old 02-10-2016, 10:52 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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Old 02-10-2016, 06:27 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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Old 02-10-2016, 08:58 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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Old 02-11-2016, 06:54 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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Old 02-11-2016, 06:56 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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Old 02-11-2016, 09:59 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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Old 02-11-2016, 02:31 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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Old 02-11-2016, 02:45 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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Old 02-11-2016, 07:24 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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Old 02-11-2016, 07:26 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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Old 02-12-2016, 05:39 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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Old 02-12-2016, 05:42 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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Old 02-12-2016, 04:51 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).
Quote:
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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Old 02-12-2016, 05:03 PM
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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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Old 02-13-2016, 07:51 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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Old 02-13-2016, 10:17 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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Old 02-14-2016, 02:35 PM - Thread Starter
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Quote:
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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.
The ULF Card does show an estimate of the ground plane db for each setup. Once you get a measuring rig, you could perform a close mic response (no eq) of your sub at say 75db, and then do the same measurement (no eq) at your listening position keeping the volume the same (it will end up being above 75db at your LP).

From there, you could calculate your room gain by looking at your close mic curve, and comparing it to your LP curve. The difference would be your room gain at each frequency. Add that number to the ground plane number on the card to approximate max output of your room.
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Old 02-14-2016, 02:47 PM - Thread Starter
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Quote:
Originally Posted by dominguez1 View Post
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?
@MKtheater , comments?
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Old 02-14-2016, 02:51 PM
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Quote:
Originally Posted by dominguez1 View Post
The ULF Card does show an estimate of the ground plane db for each setup. Once you get a measuring rig, you could perform a close mic response (no eq) of your sub at say 75db, and then do the same measurement (no eq) at your listening position keeping the volume the same (it will end up being above 75db at your LP).

From there, you could calculate your room gain by looking at your close mic curve, and comparing it to your LP curve. The difference would be your room gain at each frequency. Add that number to the ground plane number on the card to approximate max output of your room.

_____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
Receiver : Denon x5200
Speakers : Martin Logan Motion 60XT/Motion 40s - HTD Level 2 Tower surrounds
Extra Speakers : Pioneer FS52s/BS22s - Infinity Primus 363s/163s - RBH R5Bi(2pair)/R5Ci
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Old 02-14-2016, 04:45 PM
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Sorry, been busy putting up bass traps and panels. I have to take measurements and stuff but I do believe it is more violent feeling around tune.
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Old 02-15-2016, 04:44 AM
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I connected the LMS-18 to my FP14k and drove it 1ch @ 4-ohms into clipping, with the TermLab in front of the cone.

164.5db @ 14hz with about ~9% THD.
I don't think I'll ever be able to beat this score, like EVER!
I tested the box, 11hz is the peak frequency (3db higher), but the excursion gets crazy so I'm not gonna try it.


I'm pretty sure if your ears were where that meter is, that they would be bleeding and you'd be perma-deaf, or possibly even dead!




I could try bridging my iTech 8000 into 4-ohm, it supposedly does 10kW RMS for ~3 seconds. But I don't want to blow up my stuff, so I won't...

How they reach +180db at the windshield of car comps is beyond me... maybe if you sent 200kW @ 1-ohm @ 70hz into 16 18's and totally annihilated the cones and box!
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Old 02-15-2016, 06:19 AM
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@BassThatHz , does your hzhorn feel more tactile vs other alignments given you are listening at the same spl?

Maybe I misread, but are people saying that ported alignments are more tactile than sealed if played at the same spl and if so, I'm wondering how these large horns compare?
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Old 02-15-2016, 10:23 AM - Thread Starter
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Maybe I misread, but are people saying that ported alignments are more tactile than sealed if played at the same spl and if so, I'm wondering how these large horns compare?
More tactile for ported alignments just around tune...below is the test that supports this hypothesis:

Ported produces more tactile response near tune than sealed test

Here's the summary:
  • We 'feel' sound through Sound Intensity. It is the cause for the shaking of the couch, pressure on our bodies, etc.
  • Sound Intensity is made up of two quantities; 1) Pressure, 2) Particle Velocity
  • Sound Intensity (SIL) = pressure (SPL) * particle velocity (PVL)

In the nearfield, SPL alone does not accurately describe tactile response. IOW, given the same SPL, one sub could 'feel' (greater Sound Intensity) much stronger that another sub. This is demonstrated in this test.

Given the equation above, if SPL is kept constant, then the only way Sound Intensity can be greater is greater PVL. This is just math...

SPL does not have a direction. PVL is directional.

This is easy to test: Put a sub right up against a couch, calibrate to 75db, and notice the tactile response. Turn the sub around so the driver is facing the opposite of the couch, calibrate to 75db, and notice the tactile response. It will 'feel' much less tactile...PVL is directional.

In the ported vs sealed test, it shows that near tune the ported produced more of a tactile response...but why? At first, I thought it might have been because the driver and ported are both producing PVL. However, the driver is barely moving near tune. Thanks to @derrickdj1 for perhaps a better hypothesis:

Outside the tune, the driver is producing sound waves and PVL equivalent to the size of the driver (15in, 18in, etc.). However, near tune, the port is producing the sound waves. The hypothesis is that the port is producing the same amount of PVL as the 15in driver would, but concentrated through the size of the port. Because it is more concentrated, it is more effective at tactile response as that sound wave interacts with other objects. An analogy would be a water hose and an empty bucket: Try and move the bucket when the nozzle is set to wide spray. Now try and move it when set to stream...much more effective when the water is more concentrated.

Again, the above is a hypothesis as to why ported produced more tactile response than sealed near port tune in the test noted above. Is it correct? Don't know...but what we do know in this particular test; ported was more tactile around tune. Other anecdotal evidence of this has been expressed by several folks as well that have had both configurations in their room.

For those that are interested in some of the physics behind PVL etc, below is a math intensive read:

http://www.microflown.com/files/medi..._vibration.pdf
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Last edited by dominguez1; 02-15-2016 at 10:44 AM.
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Old 02-15-2016, 06:59 PM
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@BassThatHz , does your hzhorn feel more tactile vs other alignments given you are listening at the same spl?

Maybe I misread, but are people saying that ported alignments are more tactile than sealed if played at the same spl and if so, I'm wondering how these large horns compare?
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Originally Posted by dominguez1 View Post
More tactile for ported alignments just around tune...below is the test that supports this hypothesis:

Ported produces more tactile response near tune than sealed test

Here's the summary:
  • We 'feel' sound through Sound Intensity. It is the cause for the shaking of the couch, pressure on our bodies, etc.
  • Sound Intensity is made up of two quantities; 1) Pressure, 2) Particle Velocity
  • Sound Intensity (SIL) = pressure (SPL) * particle velocity (PVL)

In the nearfield, SPL alone does not accurately describe tactile response. IOW, given the same SPL, one sub could 'feel' (greater Sound Intensity) much stronger that another sub.
I have heard in-person both LMS's sealed, and horned, and UXL's ported.

IMO, horned is the best of those three, at least within its operating range and if you can tolerate a bit of resonance in your bass between 35-120hz.
It has the highest efficiency and lowest excursion for a given SPL, which translates into lowest distortion, with seemingly end-less headroom.
Its "port" is much larger than a ported box so the air velocity is kept to a minimum for a given SPL, this is important for high SPL ULF. Don't get me wrong it still "chuffs", it moves more air than any other design and the hole is like 10"x24" (at a minimum), up to 20"x30" on a larger design... so if/when you get that whole area chuffing, it is quite violent!

Ported boxes are usually half the size of a horn, usually ~6db quieter and slightly higher distortion and more excursion and earlier chuffing that is more audible.

Sealed is the smallest and quietest, but deepest extending, sealed tends to have the highest distortion between 12hz and 20hz compared to most HT optimized ported or horned boxes. Below 12hz the sealed wins for both distortion and SPL.

IB is like sealed but with horn-like efficiency, it has single digit extension just like sealed, but slightly lower distortion, at the ultimate expense of mid-bass SPL (which is often compensated for, by using an array of cones.)

Bandpass and ISO are mostly a waste of time outside of car-comp's, horrible transient response and larger box than ported, more expensive and harder to build, needs massive EQ; thus not suited for applications where SQ is cared about.
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Old 02-15-2016, 09:18 PM
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I tried bridging the FP14k but the SPL actually lowered!
163.6db which tells me the FP14k clone is not doubling-down on it's power when bridged @ 4-ohm, it is outputting less power and more current (which is a bad thing!)
To find the true limit of the HzHorn @ 14Hz requires something more powerful than the 14k clone.
Either the VPL/CPL are too sensitive or the amp isn't close to the real-deal @ 2-ohms, I didn't want to break my FP14k so I stopped @ 163.6db.

I bet the Gruppen would be a different story, it would be closer to 168db (or more...)
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Old 02-15-2016, 09:50 PM
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Why are you measuring inside your sub? Saying the 14k is not enough for your sub is misleading.
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Old 02-16-2016, 01:11 PM
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Quote:
Originally Posted by DotJun View Post
@BassThatHz , does your hzhorn feel more tactile vs other alignments given you are listening at the same spl?

Maybe I misread, but are people saying that ported alignments are more tactile than sealed if played at the same spl and if so, I'm wondering how these large horns compare?
Power drives TR. You I can increase power by a voltage increase or a more efficient speaker. Where vented/ported systems excel is at the tune, which it should, do to response remaining flat above tune, whereas sealed rolls off. So there's nothing magical about a vented cab, it just has more output down around tune. If you match spl of both systems at a specific freq, say 15hz, they would perform the same. But if you set them with broadband noise the vented will win, again because the sealed system rolls off at a high freq. The sealed must be compensated with a Lo Shelf or LT. Of course that takes more power.
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