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Hi i wonder which are the main audible differences with a port placed on the front or on the back of a bass reflex speaker
Which is the rationale behind the two options ?
What do you think is the better solution ?
I noticed that many high end speakers like Wilson Audio, Rockport have ports on the back.
Actually also many mini monitors like Kef ls50
Maybe this is indeed the way to go ?
Thanks a lot.
Kind regards,
bg
Edits: 12/07/14Follow Ups:
This thread discussed this also
Hi and thanks a lot for the very interesting link
But the more i think about this and the more i do not like both ports and passive woofers
I cannot explain why but i much prefer the acoustic suspension design
Of course i should select the right woofer for the right cabinet.
But i would me more comfortable with this solution.
No problems at all due to possible interactions between the woofer emission and the port emission ... much simpler
I could even used a bigger 15" to compensate for the lower emission on the very bass.
I think that a DIY solution could be also viable.
Thanks again for the link.
Kind regards,
bg
Edits: 12/09/14
I like the ports in the front and above the woofer which sits on the floor. This way the air flow energizes the room. However the said woofer is usually 15" crossed below 400hz and the port is 6" by 12".
With mini monitors where the port is tuned above 50hz, front or back is hard to say.
Hi and thanks for the helpful advice
I am quite set on the satellite + plus arrangement
There are many good midi/mini monitor around that could work as nice satellites
My main doubt is about which part of the spectrum send to the satellites
I understand that woofer size does matter also in this regard
For instance i would cross a 4" woofer satellite at around 200 Hz
and a 8" woofer satellite at around 100 Hz
and quite sharply also
So in the case of a 8" woofer satellite the bass woofer should cope only with freqs from 100 Hz down ... something like a 12" would be perfect
Thanks again.
Kind regards,
bg
Hey Beppster,
If you're going to cross at 100-200 Hz, you'll want two "subs", not just one. As an added bonus, you can set the "satellites" on them, avoiding the cost of stands.
High quality 12" woofers will be just fine. I'm going to use 15" woofers, just because I'm that kind of guy and I like to "crank it" sometimes. :) Although, I'm still torn between the JBL woof at $500 each, and a couple of others such as the Eminence, which are much less expensive. This issue will be resolved soon.
:)
Hi !
yes of course ... one for side
I have some principle
1) no common speakers between L and R. To keep them the more separate as possible
2) to give to L and R signal the same "treatment". For instance i like the mono amps perfectly identical, speakers perfectly identical ... mirroring speakers leave me uncomfortable.
So yes one identical satellite and one identical bass for each channel.
But the real question is ... should be better 100 or 200 Hz ?
Most of high end designs are in between.
Thanks again.
Kind regards,
bg
"But the real question is ... should be better 100 or 200 Hz ?"
It depends upon the specific speakers. Although, I'd prefer to keep it on the lower end, thinking about not putting a crossover in the middle of the trombone range. Trombone players need all the help they can get.
:)
Hi and thanks for your valuable reply
Just to be sure to understand rightly, you mean 100 Hz ?
Seriously i am convinced that the statement of 4 ways minimum to cover rightly the all audio spectrum, with conventional drivers, is very right
So a 3 ways is always a compromise
But i am always wondering about the best solution for midrange range
I know, for instance, of speakers with exceptional sound relying on big dome midrange crossed with the woofer at around 5-600 Hz
And i could think to build a satellite with a dome mid and tweeter.
It would be also nicely compact.
Then i see instead many high end designers preferring a big cone midrange
But usually crossed at around 120-150 Hz
To get the mid down to 100 i need a very robust driver, like a good 8"
I guess that at 100Hz the signal is still very powerful
Last thing i would want is distortion in the lower midrange
As i said this is a fundamental design choice
I think i will go with a bigger satellite in the end and cut it at 100 Hz as you recommend
Thanks a lot again.
Kind regards,
bg
Edits: 12/11/14
On back is best, not from a bass performance standpoint but for both chuffing sound if too small port and midrange bounce back from interior walls.
As example from Stereophile's measurements of Opera Callas speaker. The red curve is port. 800 hz area.
Hi and thanks for the advice
these speakers by the way look pretty weird ... 5 tweeters ???
i could see them in an array ... like some old Infinity speakers ...
But the case is different i think
Kind regards,
bg
Either the port tuning hasn't been designed properly or one is operating the speaker beyond its design limits. I can crank my PSB Image bookshelfs too loud levels in excess of 90db without port chuffing.
Sometimes the trade off of enclosure size vs port diameter has to be focused on enclosure size.
Engineer "I can make the speaker the size you want, but if I put in the large diameter port, I'll have to increase the size 25%"
Bean Counter "Make it the size I want"
Engineer "Okay, then I'm forced to use a smaller diameter port, okay if I put it on the back to reduce the chance of hearing the chuffing?"
Bean Counter "Yeah that is a cleaner look anyway"
I understand what you are getting at but the design is still flawed or incorrect if the port chuffs. Its too bad that bean counters dictate incorrect designs.
Unless I missed it, the answer here is "I dunno".
;)
Audible differences - but usually the room modes will mask the differences. At the port resonance the output is 90 degrees out of phase with the woofer. Depending on the tuning - the woofers output has probably dropped well below that of the port (or passive radiator output.
If you use a rear port - and the loudspeaker is placed with the port very close to a wall (less than the port diameter - is a good rule of thumb) then the base tuning could be effected - unless it was compensated in the tuning of the speaker. Side and front port openings alleviate this.
Many, including Linkwitz, and others (myself included) think ported woofers and subwoofer just make the response of the loudspeaker in the room (due to the room modes and various phases of the output radiators) and their impulse responses less predictable.
Ported speakers use the reactive energy that is stored in the cabinet to extend the bass lower without requiring more drivers or power. This also reduces the distortion of the loudspeaker system. My choice is to use more woofers - always two sealed subwoofer cabinets or more and usually two woofers per sub cabinet in a push pull arrangement (to also reduce distortion). Place the subwoofers at the sides or center front and back of the room - not in the corners - to reduce the amplitudes of the room modes.
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
Hi and thanks a lot for the very valuable advice
Your words " ported woofers and subwoofer just make the response of the loudspeaker in the room ... and their impulse responses less predictable " are enough for me to avoid ported speakers, front or rear is no difference at all.
It is always possible to design a good sealed and powerful bass speaker
I will lose maybe something in the bass .. but control is also important and also the placement in the room.
I do not want to have an overwhelming bass at all.
Thanks again.
Kind regards,
bg
All Audio Note speakers are designed for near wall or corner placement and all have rear ports. Except the AN K which is Acoustic suspension/sealed although they still recommend it for corners.
Even the AZ two and Three floorstanders which apparently are a must for corners have a huge hole at the top of the speaker (it's a horn transmission line).
Granted - generally what has been stated is true but there are exceptions.
Hi and thanks for the very interesting information
I listened to AN speakers and liked them a lot
So it all depends in the design but there is no on principle a better option
Good to know. Thanks again.
Kind regards,
bg
if the speaker designers did their job properly. There will be no difference in sound when in a free air environment. Front ported speakers have one advantage over their rear ported cousins when it comes to placement. You can put front ported speakers closer to boundaries such as walls than you can with rear ported speakers. My PSB Imahe suite of speakers are all front ported while my PSB Alpha suite are rear ported.
Hi and thanks and message received
If the design is ok non problem with both the solutions
Thanks again
Kind regards,
bg
The sound coming from a port covers a very narrow band width at a frequency so low the bass is omnidirectional. The box is literally invisible to the port. You cannot locate the sound coming from the port. So unless the rear port is close to a reflecting surface which will reinforce the port sound there is no difference bass wise. However if there is resonances at higher frequencies in the box(and there always are but the magnitude varies speaker to speaker) a rear port will weaken the affect as these sounds come out from the port.
Hi and thanks for the helpful explanation
It seems to me that the rear port is preferable in the end
If i had to place the speakers very close to the wall i would put some acoustic panels on them to neutralize the reflections
Thanks a lot.
Kind regards,
bg
bg-
this is my preference;
I do not like side-port(s) nor side -firing woofers in a speaker.
Hi thanks for the helpful reply and i agree completely with you
I do not like especially side firing woofers
I do not listen by the side
I much prefer frontal woofers
I do not know what has started this "lateral" design
I do not know if bass are directional or not or from what freq thay start to be directional
In the doubt i prefer woofers firing to the listening spot, just to avoid this kind of issues
Thanks again
Kind regards,
bg
Edits: 12/07/14
"I do not know what has started this "lateral" design."
It allows for a narrower frontal width which can improve midrange/treble dispersion.
Hi and i see
But every time i listened to a speaker without direct firing woofers ... i did not like the sound.
The first time that i remember was with these ones here depicted
I did not like them in the bass
Kind regards,
bg
The port actually acts like another low frequency driver and is similar in principle to a passive radiator. Low frequency drivers tend to not be directional, but can be affected by their proximity to obstructions. Unless the speaker is designed to be placed near a back wall, the location of the port will have only a minor effect on the bass and some manufacturers have offered speakers in more than one port configuration.
Hi thanks for the kind explanation
But so the port adds bass and the speaker goes lower ?
I mean placing far from a wall a speaker ported on the back and one same crossover and drivers but sealed ... will the ported go deeper in the bass ?
Kind regards,
bg
You're welcome.
Ported speakers typically produce more bass than sealed ones. The port creates a volume of 'trapped' air with a particular mass. Above a certain frequency, the port produces very little output and the box acts like a sealed box. At the port resonance, the port actually inverts the back-wave of the speaker and adds it to the front wave. Below that frequency, the port simply becomes a hole in the box which allows the back wave to cancel out the front wave.
For this reason, a ported enclosure will extend deeper in the bass, then drop off quickly whereas a sealed enclosure will roll off earlier and more gently. Designing a good ported enclosure requires careful speaker/enclosure/port matching to get the best behavior from the speaker.
Hi and thanks again
So now i understand why the rear port is so popular
Now that i have googled better i see almost all rear ported speakers today
In the past they were all in the front baffle
It must work for sure seeing how common it is
Thanks again
Kind regards,
bg
In my opinion, the rear port is largely a cosmetic decision. The port can also produce some undesired wind turbulence noise which is another reason to move it to the back. Turbulence is also the reason modern ports are flared or have other exotic opening shapes.
HI and thanks again
But i am quite sold more in general on bass reflex because i see speakers of unbelievable high quality adopting this arrangement
So i think it must work very good
And i also prefer a sharp cut in the bass instead of a slow slope ...
Thanks again.
Kind regards,
bg
If you require accurate bass best to avoid reflex and go for transmission line speaker.Due to very good review in Hi-Fi News I bought KEF R500 reflex speakers HFN said the bass was very good, when I tried the speakers at Home there was hardly any bass compared to my TL speakers unless the KEF's were played at a far too high volume level,KEF port at rear my TL speakers port in the front not that think port position makes much difference.
Edits: 12/07/14
Besides PMC who else currently uses transmission lines?
Acoustic Zen. I am considering them myself.
Hi and thanks for the valuable advice
You say " not that port position makes much difference "
This is what i was wondering
Maybe it is just a practical reason because there is little space on the front baffle to make a hole
Much easier on the back
Transmission line speakers are very rare today
I read indeed great things about them but i do not think i have ever heard one personally.
Thanks again
Kind regards,
bg
If the speaker is to be placed inside a cabinet or furniture or if it is to be placed close to the wall behind it, then a rear port is a bad choice. Otherwise, it should make no difference in use.
Hi and thanks a lot but i am not sure to understand rightly what is the reason of the port on the back
Does it improve the low freq response ?
Kind regards,
bg
beppe61,
Employing a port on the rear allows the manufacturer to build a smaller speaker than an identical front ported example.
Al
Hi and thanks and this is what i wanted to hear
That at the end of the game is mainly for practical reasons but the effect is identical.
Good to know. Issue closed.
Thanks again.
Kind regards,
bg
Air moving out of front port creates cancelation with next driver above. Don't believe me? Try using an appropriate sized post em note over port and the difference is not the bass but the midrange.
I disagree with your assertion. Its all about the bass and not the midrange as easily shown by the frequency response curves. The black trace is a sum of the blue trace which is the driver and the red trace which is the port. Look how far down the amplitude is at 1Khz ..
Hi and thanks. Interesting.
If i understand rightly the bass port adds to the midrange ?
this i did not know. I was thinking that the main effect was in the bass actually.
Good to know.
Kind regards,
bg
No it is almost always a BASS port. The air coming out of a port is designed to resonate at a particular bass frequency. At the upper end of the frequency response the air in the port moves diametrically opposite to the low end response of the driver above (Midrange in a three way, tweeter in a two way). Temporarily blocking such a front port will reveal significant detail in the range of the crossover.
Using a post em note allows the paper to flap when large bass dynamics are present, but blocks lower velocity air movement which causes cancelation.
Above tuning frequency, port in phase with bass, below tuning frequency out of phase (that is the port resonance, not the midrange leakage from the back of driver to wall to port exit, which might be what you are trying to explain)
Very rare that port will interact with tweeter as they are at least one but usually well over three octaves away from tweeter xover point.
In a two way system?
About the worst/highest of significance port measurements I've seen or done show the midrange leakage through port in the 700 to 800 hz. So a xover of 2k to 3.5k (fairly typical of speakers), that is the one to two octaves.
And with good number having 400hz to 500hz that then approaches 3 to 4 octaves. So even with fairly shallow 12db slopes your looking at 36 to 48 db down for tweeter output at the interaction point of the port leakage to the tweeter
Now interaction with midrange, that can clearly have an affect. Another thing is port exhibiting resonance (not leakage), that resonance will ADD to the output (see the graph I posted in original response of the Opera Callas).
So with all that going on, for most speakers setups in rooms, the port on the back is the chosen design.
Hi and thanks for the valuable explanation
i think i have understood better now
Kind regards,
bg
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