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Stereo Ported subs port placement and direction.

 

New member
Username: Sq_matters

Knoxville, TN United States

Post Number: 1
Registered: Sep-17
So I have a Car audio system I have built boxes for and made a home audio system. I have two Hertz ML 3800 fifteen inch subs and each with its own Alpine PDX M-12 1200w RMS amp. I had the boxes made to manufactures recommendations. They had four choices of box builds. #1 sealed to save space, #2 sealed for performance, #3 Ported to save space, and #4 ported for performance. I chose ported performance because I read that the sound quality is not affected majorly by using the performance ported enclosure.

So the sub's port is not on the front of the box with the speaker but it's on the side.

The boxes are perfect cubs should be able to point each sub in, up, or out without affecting cosmetics.

All that said I also am wondering how I should position the ports?
Should they be facing away from each other?

Should they be facing up, or in, or one out or one in?

having two ported subs will there be a chance of frequency cancellation should I have gone with two sealed enclosures? If so I can cancel the build and get them to make it sealed.

It's a big room with tall ceilings if that matters
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18454
Registered: May-04
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"The boxes are perfect cubs should be able to point each sub in, up, or out without affecting cosmetics."

Physics should take precedent over cosmetics. The drivers have a spec which tells you how they prefer to be mounted. Do not point the driver up or down unless it is designed for that type of placement.

I have no idea what the specs are for this driver, as with most car audio products, numbers are largely ignored in any consumer oriented media. Contact the manufacturer. If the drivers are mounted facing forward, then your main concern with the port is to minimize interference from a barrier wall. You'll first have to determine the placement of the enclosure before you can decide on anything else.

Do some research with a search engine to begin placing the drivers in the room. Just a simple title such as "How to position a sub" is your start. There are no numbers which tell you this or that with sub placement. There are general rules. Frequency cancellations (nulls) and frequency peaks occur in any sized room. For the most part, once you've got the general placement in mind, you have to walk the room, listen and experiment until you have the performance you prefer.

Do your research and plan on spending several hours finding the placement you feel is best.

Not a scold but in general, car subs have car oriented frequency response anomalies and specs which do not easily translate to their use in a domestic listening room.


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New member
Username: Sq_matters

Knoxville, TN United States

Post Number: 2
Registered: Sep-17
Well, I was never talking about pointing the actual speaker up. only the port.

Also, my question is for two subs one only getting left signal and one only getting right.

The subs, sub enclosures, and amps are all identical.

Again, the ports are on the side NOT the front of the sub box.

So the ports can point in, out, or up.

I don't know if pointing ports (for stereo subs) toward each other will have frequency canceling or not.

I'm not talking about the room or where to put the subs in the room. Just focusing on Port Direction.

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Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18455
Registered: May-04
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"I'm not talking about the room or where to put the subs in the room. Just focusing on Port Direction."



Then focus on what the port is doing. It is a vent for the out of phase waves created by the driver's rearward motion. By its nature, what comes from the vent is out of phase with the front wave created by the driver. That accounts for the basic roll out difference between a sealed and a vented enclosure; the vented system rolls out its bass response at twice the rate of a sealed system due to the omni-directional nature of low bass. Therefore, by using a vented enclosure you are already introducing out of phase wave fronts into the room. How many you add or where they come from is largely irrelevant to your question. Not irrelevant to the sound quality but to your question.

Next, consider what the system is doing, it is loading the room as if the room is another enclosure - which is the correct way to think about the room when it comes to bass response. A pressure wave will be reflected (or absorbed) by the barriers of the room until it has dissipated its energy. Most rooms have very few surfaces which will absorb a wave front so you have to deal with reflections. Reflections cause the peaks and nulls within the room.

If you don't understand how bass pressure waves move within an enclosure, it would pay to learn a bit about the subject. You don't need a PHD is acoustics to know enough to place a sub but knowing what you are hearing and why it exists within a room will be beneficial IMO.



Otherwise, a vented system is simply loading a larger enclosure, the room, with pressure waves. The pressure wave created by the port is out of phase with the front wave created by the driver. There are build techniques which can place both waves more or less in phase with each other but they result in a very large enclosure.

Bass is omni-directional so there will always be cancellations created by the forward/rearward function of the driver unless you create an infinite baffle - which is another description of a sealed enclosure. You don't have an infinite baffle so the direction the port fires is largely irrelevant to the over all room response.

Best performance is still dictated by the basic rules of subwoofer placement.

Additionally, there is no right and left in the subwoofer channel. You haven't said how you intend to hook up what seems to be a kludged together system but bass is mixed into a mono signal beneath about 100Hz. If you sense bass coming from one or the other channel, you are perceiving placement by the upper (harmonic) frequencies which accompany the bass signal.

Bass is mixed into a mono signal and has been since the introduction of stereo recordings - prior to that it was mono by default - and this tradition continues through to today in all source material. You can run individual cabling to your subs but they are still receiving a mono signal.



You don't want to run a subwoofer driver full range or you will introduce more out of phase pressure waves which will create cancellations with the front main speakers (and a center if one is used). You need a low pass Xover for the subs and a high pass for the main speakers. You have not said how you will negotiate this need.

Running your main speakers full range is generally a bad idea since you will be creating more out of phase pressure waves to the room/enclosure. Not only will you have greater comb filtering effects when you do this, you also risk overdriving the main speakers with bass signals. An electronic Xover with adjustable frequency points is the ideal choice for a sub Xover. Many home audio sub amps also include phase controls which can be used to further smooth the in room response.

Kludged systems are generally poor quality systems and car audio is typically not well suited to home audio use. Your amp is another example of this problem but since you haven't asked about the amp, we'll leave that for another thread.

I would tell you to buy a home audio subwoofer with a built in Xover. If your main amplifier/processor doesn't have a sub out, then you are far more likely to have poorer sound quality due to the additional out of phase pressure waves introduced into the room by pressure waves originating from multiple sources in multiple locations. How many subs you have in a room is up to you but each sub you add makes placement more difficult IMO for the average listener .


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Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18456
Registered: May-04
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https://www.google.com/search?rlz=1CAACAY_enUS754US756&q=standing+waves+subwoofe r+placement&oq=standing+waves+subwoofer+placement&gs_l=psy-ab.3..0i22i30k1.12502 .17667.0.18099.20.20.0.0.0.0.271.2368.0j14j2.16.0....0...1.1.64.psy-ab..4.16.236 1...0j0i67k1j33i22i29i30k1.0.U4pFiEQhwws




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New member
Username: Sq_matters

Knoxville, TN United States

Post Number: 3
Registered: Sep-17
I am running a Audison bit one Hd. I have the hertz Mille series 280.3, 700.3, 1650.3, 1800.3. Not one speaker is playing a frequencies of the other. They are all crossed over at an optimual spot. My Rta reads basically flat. All of my crossebets have butter with and linkwitz filters running crossover points all at 4step 24db slope. I have five amps . There alpine PDX f6 all Briged with at 300watts per speaker. And 2 Alpine pdx m12s running 1200w rms to each sub.All gains have been set with my oscilloscope and nothing clipping.
My music runs digitally through a toslink to the processer. I have 4x 500Farid capacitors about 50lbs worth in between my 14.4v 200A power supply to rid any electrical noise. I have sound treatments all over the room to fix problem frequencies. I went from one sub to two and from sealed to ported. I have always used sealed enclosures so I never had to research ports. Look up the speaker I sent you. None of my speakers are normal car audio.

You did not answer the questions about the port direction because you don't know the answer. I was not asking for an encyclopedia of things I understand already but just a answer like ... it does not matter what way the ports face or if they face together there will be an boost in db's or a drop because of major frequency cancellation.

I also want to know shuold I tell the man to make the enclosures sealed these sub slecs are good for either or. If two ports cause problems that two sealed boxes dont I want to know before it's too late thanks for all the assumptions.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18457
Registered: May-04
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Don't get smart, because you're not really. I have given you the answer to your question at least twice and, if you were paying attention, several more times over. It makes no difference the direction of the port in the larger enclosure of the room - just avoid barrier reflections as much as possible.

Sealed enclosures have a less pronounced roll out than do vented enclosures. 2nd order vs 4th. However, since you are not being provided the in room energy of the back wave from a vent, they also give up a few dB of SPL in a typical sensitivity measurement. Knowing how a typical sensitivity measurement is performed would help you make a decision.

Do your research, I am not in the mood for being blamed when your kludged system doesn't suit you. Also, I tend to want to not have much to do with forum members with three posts who insult me.

And, for the record, yes, you do have various drivers outputting the same frequencies at the same time with the Xovers you are using. A digital brickwall filter has the least overlap of any but still is not a complete block of 1,000 to 1,001 Hz. -24dB Xovers give you overlap. It's sufficient to avoid major conflicts but there is overlap. An electronic phase control doesn't completely deal with acoustic phase issues, particularly in a multi-driver system

You might also want to research how much actual RMS/peak power (Volts vs Amps) you'll have from your car amps when you are running them off a 120VAC/15 Amp circuit. Or, have you brought a car battery inside? You sound semi-informed enough to have a scope, maybe you've already got this figured out.

Look, you don't even understand when I explain the basics of subwoofer placement. You aren't interested and you don't seem to comprehend the physics of rooms and pressure waves. I try to give more than enough data to guide any poster along. Some like you want to think you know more than you do.

I'm generally unimpressed.

You're welcome to ask more questions but I simply won't respond to further insults. So play nice 'cause it's still a kludged system that could be made better, IMO, by buying the gear intended for the purpose. But boys will be boys and they will need their toys. And their watts and their 15" subs.

Oh, well. Live and learn.


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Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18458
Registered: May-04
.

Oh, yeah, bass is still mono; https://www.google.com/search?q=lfe+channel&rlz=1CAACAY_enUS754US756&oq=lfe+chan nel&aqs=chrome..69i57.2997j0j1&sourceid=chrome&ie=UTF-8.



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Gold Member
Username: Magfan

USA

Post Number: 3460
Registered: Oct-07
SQMatters:
You said that: "Not one speaker is playing a frequencies of the other."

This is a minor but important point: Crossovers are not a brick wall which excludes frequencies above or below the 'crossover point'. Even with high-slope crossovers, like 24db / octave, you'll still get both speakers playing at the crossover point. The trick is to get them to sum-flat thru that 'region'. As one speaker 'ramps down', the other speaker is getting louder. If both speakers reach the same point, maybe 6db down, at the same frequency, that might not be a bad idea.

I don't know what you are using for crossovers right now, but you might want to check out MiniDSP which is computer programmed and will allow testing of different frequencies and slopes in a short period of time.
 

Gold Member
Username: Magfan

USA

Post Number: 3461
Registered: Oct-07
In re-reading the original post, ::

I'd be REAL careful pointing a port UP. Terrific place for something to DROP. Imagine a 5 year old pouring a SODA down the hole! Or your pet Gerbil deciding to 'nest' in your speaker. Covering in a loose-weave fabric backed by screen would change the port tune only slightly,

I'd point 'em ANYWHERE but 'up'. But that's just me.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18461
Registered: May-04
.

"Even with high-slope crossovers, like 24db / octave, you'll still get both speakers playing at the crossover point. The trick is to get them to sum-flat thru that 'region'. As one speaker 'ramps down', the other speaker is getting louder. If both speakers reach the same point, maybe 6db down ... "


Traditionally, the "crossover frequency" you might see on a spec sheet is the point where both drivers have rolled out/in to a -3dB measurementfor each driver. Summing will bring the level up to roughly flat frequency response at the "Xover frequency". Therefore, even with fourth order filters on both the low and high pass side, there will be overlap between drivers.

The "summing" bit there is somewhat less than accurate in a real world situation due to the nature of driver placement on the baffle, shape and size of the baffle, lobing of the drivers due to the Xover type and the narrowing/broadening dispersion characteristics of dissimilar driver types/sizes. Therefore, measurements should be made taking into consideration several factors and generally "on axis" will give the best measurements, though, not always.

However, most listeners using speakers in a domestic listening room don't pay much attention to these factors - typically aren't even aware of them - and will often times have enclosures mounted far too high or too low or unequal distances from the listening position for the on axis measurement to really matter. If you do not set up your speakers and your listening chair as a technician would a speaker enclosure and a measurement microphone, then there are no guarantees you will achieve decent frequency response from your system. Sometimes that's not a bad thing but generally it is less than desirable. Extremely wide/narrow dispersion systems, bipoles/dipoles can really change the calculations on speaker placement relative to the listening position and to barrier walls.

Throw in a coupla subs and the fun begins!


Due to the frequency doubling of octaves and the nature of combining dissimilar Xover types to achieve a certain end product, this does not mean both drivers will begin their roll out/in at frequencies which are equally distant from the stated Xover frequency. But sharing of similar frequencies certainly exists in any multi-driver speaker system.


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Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18462
Registered: May-04
.

The op lists his equipment here; https://www.ecoustics.com/electronics/forum/home-audio/733420.html#POST2052231

He is using a selectable Xover type controller.


Though I think he's decided he no longer requires our assistance.


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New member
Username: Sq_matters

Knoxville, TN United States

Post Number: 4
Registered: Sep-17
Thanks for the help guys. I do appreciate the responded have more to add later. I'm busy. I have three kids two, three, and four yrear olds and I'm a professor at a college. I hope to continue the discussion when I get some time. Thanks again.
 

Gold Member
Username: Magfan

USA

Post Number: 3462
Registered: Oct-07
3 kids of that age would be considered by some to be a full-time job.

My Maggies have a 1st order and 2nd order hi / low pass with the frequency specified as 600hz. Looking at the slopes, it is clear they are 'asymmetric' but do get the job done. And with panels? the lobing Jan refers to in this case is primarily Left / Right. This means that speaker alignment / orientation is critical to best results.
Some consensus exists, but than again, a few people hold well founded minority opinions.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18463
Registered: May-04
.

You're welcome, hope it was helpful.

And with three small children in the house, I would take leo's cautions about an upward facing port rather seriously. More than one parent has had to fetch a gerbil out of a subwoofer enclosure.


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