2 hz tuning - pros and cons - Page 4

Annnnd what we are telling you is that you will create more problems than make.


BUILD A SEALED ALIGNMENT.


Gosh.

One more point and I guess I might be wrong in even trying to offer this. I find that generally a port is utilized to help the driver in about the same way passives do. You gain a good 1/2 octave below the driver's resonance frequency and then it rockets down. The port not so much, but the port is still just as difficult to design because of size shape and so forth. I know more about passives than anyone I have spoken to because I took the time to actually "see" them in action as I was testing them, not just reading about them and spouting off. That being said, I would expect the port to be somewhat limited in the octaves of improvement that they can achieve. I hope you do not get mad, but I am only saying this because my design is like a port but with out a hole. There are limitations to all designs and it took my actual tests to show me that. I did not believe that a driver could actually excite a passive when on the outside of the cabinet, but it does. At tuning, the driver stops and as I held the passive, it swung like crazy. I would expect the port to act the same. The lower you go, the more air you move regardless of velocity. I can liken this to a 200 mph backpack plower or a 74 mile per hour hurricane. that 2 inch port blowing at 200 miles per hour is still not going to move as much air as the little 74 mph hurricane.

Is that better?

getting the velocity correct still does not account for the huge "slug" of air that has to be moved at full tilt. Mark, Josh, Scott John, Bosso and I and right on this. We may be wrong about your build working or not, but a 2 inch port is too small to work at full tilt in your sub

I will build this and use test it. I have all the gear. I hope I have the skills to actually assemble it correctly so that it will function as designed. One question.

Would you mind if I just allowed the pipe to hang out of the box and not fold it inside, because you obviously know what problems that is going to open up. If you are ok with this. I will start working on it now and as soon as The drivers ship it will be done.

A guy with the same idea as this comes by every year. I'm tired of explaining every little detail. All the important stuff you really need to know has been said already by several members.

We are genuinely trying to help you get whatever you end result is. You say you want to do some odd alignment to remove some port nasties or something? This alignment is creating MORE! Why bother with lower frequence issues when you are creating a 78hz port resonance?!? It's insane. A simple sealed alignment will be smaller by a huge amount and have none of the issues that your alignment is creating all while having the same or better response because you are not making an non-linearities that the port will absolutely create.

This isn't exactly a groundbreaking design. This conversation has been had before. It won't work, it's not worth the effort. You want crazy SPL for the cheap? I was there, man. I build BOTH my LLT's (which measure flat to about 8hz) for $1,200. I specifically designed my system to stretch the extremes of what a vented alignment was capable of doing while at the same time avoiding the bad stuff. It is simply impracticable to go any further. It's been a few years and now I want more SPL and more extension. Where else is there to go than build a proper sealed system? No where. If all you need is 10hz extension and you want to save some bucks and not have to use a bunch of amps? Build my LLT's. If you want lower extension? Go sealed.

Varying Q related to exact geometries are separate from compression effects. Simple fact: A large diameter port that is a fraction of its diameter in length behaves rather differently at tuning than a port that is 5-20x its diameter in length. In general you will also see that real world losses mean that boxes which appear to have very high Q peaks at tuning never have peaks as high as the model.

The fact that we see a bunch of different programs showing different Q to the driver excursion minimum and port velocity points to the Q and loss assumptions I'm referring to. As with any model, the best use always comes from understanding the assumptions it was built on and variables involved. In this case we have at minimum Ql, Qa & % fill of the box to contend with, and then the effects of the end terminations which will all affect the sharpness or Q of the behavior, as well as losses.

It's not that the box won't work, it's that it is unlikely to be demonstrably/significantly better than the same driver in a sealed box of the same or bit smaller size. If you aren't leaving sine waves on for minutes at a time well below 16Hz, more power than the rating is not a problem thermally. For real listening without running hard into clip limits, it's unlikely to ever be a problem. The bigger concerns come down to real world excursion limits in a given box after suspension stiffening, BL drop and mechanical clearances are considered.

Sentence 1, 2 and 3 are all true. I am not off the cuff guessing. I don't know where you got that. Flare it is well known around these parts too. Mark gave you plenty of clues with his hints about comparing smaller systems scaled up in frequency. Your simulations at the beginning of this thread are not accurate or there is some information entered wrongly. Otherwise they bend the laws of physics and the known ways that ports work. I don't know how much more plainly it can be put. You are assuming that no one has experience with this type of design but plenty of people have experience with vented designs and there is reams of data on it. The basics of port operation are well established and will not change just because it is tuned lower than normal. You seem to be claiming that they will. If a 2 Hz tuned system is giving effective gains in performance at 20Hz at 10x tuning then one would expect performance gains from a 20Hz tuned system all the way up to 200Hz. This is not what happens. Bass reflex only gives effective gains over a limited bandwidth. By 2 octaves above tuning the port is not providing advantage anymore.

Basically you do get some reduction in excursion and increased sensitivity by using a port. No one is disputing that. However ports are only effective over a limited bandwidth of about 2 octaves. Also in order to make them effective over that range and remain linear they must have enough port area to cope with the air flow. Ports chuff easier and overload sooner the lower in frequency you go. Smaller ports overload at lower air speeds than larger ports. A 10" port will be much more linear at 25 m/s than a 4" port. If you tune to 2 Hz you can get some gain in sensitivity and reduction in excursion up to about 7-8Hz that is the extent of the bandwidth it will help with. Unfortunately a 2" port just cannot handle the air flow needed in that 2-8Hz range to realize the gains there on paper. This type of system would be much better realized in an IB install with a ton of back space so a large 8 or 10" port that will cope with the airflow can be used and a slightly higher tuning. These reasons are why you don't see builds like this. The super low tuning does not help with any of the content that truly matters and the port size and enclosure volumes needed to avoid noise and compression over the range that the port is effective are huge.

What bandwidth are you trying to realize gains from the port over? Ports only give gains over 2 octaves. 2-4 Hz is an entire octave. Tuning to 2 Hz means all of your excursion reduction and port output is below 8Hz. Is it really worth the trouble to use a tiny port for changes in performance below 8Hz where the content is of limited importance anyway? I would argue no personally. If you want solid gains in output and excursion reduction over the 10-20Hz octave I would suggest tuning in the 8-12Hz range and increase your port area as much as feasible.
Edited by Ricci - 12/10/12 at 4:34pm

10-26-10: Drew_eckhardt
A ported enclosure can be 3dB more efficient at the same size or play a quarter octave lower at the same efficiency.

The same driver excursion will net you perhaps an extra 1/3 octave of extension with a ported speaker.

You'll have higher excursion limited output in the bottom of a ported design's pass-band so you can use smaller + less expensive drivers.

Distortion will also be lower in the bottom of the speaker's pass-band with the port because of the reduced excursion.

Ported enclosure+driver combinations have four poles in their high-pass function for an eventual 24dB/octave roll-off function while sealed ones have just two for 12dB/octave. With sufficiently shallow roll-off room gain (12dB/octave in an infinitely rigid room below its fundamental resonance at 1130 / 2 / the longest dimension) can keep the speaker flat below its roll-off.

Ported enclosures do not load the driver once you get below the port tune, with excursion increasing to what it would be in free air. Where too much low frequency energy is present below the speaker's pass-band you'll have distortion (including midrange IM distortion on 2-way speakers) and may even run the drivers into their mechanical limits resulting in damage (some very nice drivers will bottom the voice coils on the back plate). For a given input level sealed speaker excursion remains constant with decreasing frequency.
Drew_eckhardt (System | Answers | This Thread)


I hope Drew does not mind me posting this here. I hope this helps.

I do not have winisd on my new computer, so I would ask if you could model the sealed version of the same enclosure and then compare the two and post them here. That might help some.

Sorry, I did not read Josh's post. I kind of know his thoughts on this,hence the redundancy.

I will wait for Josh and maybe Bosso on this one.

I haven't used winisd in a looooong time until today. I'm basing that 2 octave effective from measurements. I don't consider the resonances or less than 1dB as effective FWTW.

700 liters with a 2x90inch port mounted external to box. Is that correct? Does the port have to be on the same face as the driver. so it could be wrapped around the box and come out in the same direction as the woofer. Hey, I will get NEO Dan to sketch this for me so that I have something to actually go by that you agree on. If you can do sketchup, then I will follow your plans. As you wish, I will build. I hope you find my building skills up to the task.

Thanks,

Robert

Ever since my dad bought a car when I was a kid I remember something he told the saleman. The salesman told him that the car he was showing him had a V6 and my dad said he wanted a V8. The salesman replied" It acts like a V8. To that, my old man says "I don't want something that acts like a V8, I want a V8. Needless to say, he bought a Crown Vic in short order.

So, I will build the exact thing and let it rip.

Well, I do not even think I will get to the need for the measuring equipment beyond what I have. I think the port will be a non issue and I will see a nice rolloff as in a sealed alignment. Just my thoughts, but I am probably wrong. But, if I do build it and just use the woofer tester on it. The tuning should be really low at least as low as my mic goes? I can easily get a nice microphone shipped to me for little and reduce that problem.

I have aBryston amplifier that is just laying around. I think it can reach fairly deep in the spectrum. Will that help?

Wow. I just read this through and I think you are second quessing yourself or again insulting me and my stuff. I offer to pay and build this thing and you again insult me. Do all the other guys see this or am I just reading this wrong?

I apparently need this written in crayon for me, but why tune so low, effectively eliminating any useful gain from the port? As previously stated by me, the large SLLT designs looked to be effective at boosting the <10hz content, but were tuned more than an octave higher than what you want to do, and used a port large enough to not be problematic. So instead of tuning low enough to push port problems into some mystical realm of 1hz, why not just eliminate those problems?

I do not think that will be an issue. What I think is that as that slug of air is moving into the chamber, it will compress and resist. For the frequencies to eminate, the air has to exit the cabinet. If the volume cannot get out and I do believe a large volume of air will move at the tuning, The cabinet will just act like a sealed cabinet with a leak. I was asking you to model the system as a sealed in order to see what the Fb would be and the F3. Those are around where I think this system would measure. I do not believe this driver in a huge ssealed box can take the power you are going to give it. I think it will fail. I have seen drivers of greater lineage turned to scrap under less demanding situations. 1000 watts to the coil may be fine, but the mechanical limits on this, what may turn out to be an essentially sealed box, may be too much. Easy to find out by powering it up. I do not need measuring equipment to watch the following trailer turn a driver inside out.





http://www.thx.com/consumer/movies/7458473

I have seen it done and it is not pretty. So, if this system will work, it will work one way or the other and should handle anything I throw at it. At least that is what the model says. If I pump Bass I love You through this, it should not hesitate to perform at 1000 watts of input. Afterall, Bass I love You only goes down to about 8 Hertz- More than 1/2 octave over your 5 Hertz guarantee where the port will do most of the work.

I think that the system will see a final tune of a large sealed box and the driver will unload down in the single digits. Just my thoughts.