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Old 11th September 2013, 08:35 PM   #1
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Default Couple of questions about ports

Have a few questions about adding ports to a speaker box.

Is it okay to port/tune the sub box at 40Hz , given that the speaker
bottoms out around 30Hz, and the receiver bottoms out at 40Hz ?

Or is it even necessary for a port ? I mean does the enclosure have a natural
resonance in that frequency range ?

The manufacturer suggests a similar design 2.25 ft3 with a 70mm port 65mm length.
My box is right around 2 ft3

- a well-constructed box 13.5" wide X 19.5" deep X 18" deep ,
made of 3/4 plywood. I understand this is not the greatest material
for sound, but it is very tight construction . Built it myself.
Used this box for years with a Nippon america NHW-1035
(can't get specs all i remember is 250 watts, 92dB, 8ohm, 35Hz, 10")
-and it seems to resonate around 40-60 Hz without a port.

- Now for the driver-
I want to put a Peerless 850136 8" woofer into the box.
It's 150 watts, 8 ohm, fs 28 , qts 27 , 89.5dB 2.83V 1M, (more specs if needed).

-That is the driver, now for the receiver-
My receiver is a panasonic scht-290 that goes 40-20k Hz .It's a 5.1 with a sub
channel, and the receiver has buttons to adjust the frequencies and dB
that the subwoofer gets. Not a lot of power, but adequate for my listening.

My speakers are all home built - L and R fronts are Aura NS6 255 8A with Audax tweeters,
the center and rears are Celestion Neodymium 5" with Mylar tweeters
(Pyramids in rear and Goldwood in the center).
All the drivers go 89-90dB and so i thought the Peerless 8" would be a good fit .

Has a fine mids - highs for my tastes, I am not really into loud music or lots of bass,
most of the time i prefer the 'flat' sound from a CD without adding tone.
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Old 11th September 2013, 09:24 PM   #2
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To be honest, I can't figure out what answer you would like. Just remember once you cut a hole in the box, that is it, you cannot reverse it or wish it away.

You closing paragraph seems that you are satisfied with the sound, so why ask if it is okay to add a port? If you are currently using a sealed box then a ported box present a totally different sounding speaker. Your speakers are almost entirely responsible for your system's characteristic sound.

Will it be better? - there is no such thing as better or worse, only different. Whether you like and live with the result depends entirely on your expectation. However, it would seem that you do not know what to expect and probably the reason for asking someone else to make the decision for you.

If you are happy with what it sounds like don't do it. If you want to change the drivers this is a better choice, if you don't like what you hear the process is reversible. Cut a hole in the box, it is stuffed!
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Old 12th September 2013, 03:10 AM   #3
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Quote:
Originally Posted by Nico Ras View Post

If you are happy with what it sounds like don't do it. If you want to change the drivers this is a better choice, if you don't like what you hear the process is reversible. Cut a hole in the box, it is stuffed!
Thank you for the reply. Let me see if I can clarify my question a little better.

The reason i am confused about adding a port is per
"manufacturers suggestion of a ported enclosure."
With an xmax of 4mm i don't think it is necessary to add a port. (?)
Normally, i would just install the new ( never been installed ) driver without a
port and accept whatever results i get.

The other question is, would adding a port tuned to 40hz add to the load
on my receiver ? This may sound a little funny, but i have to ask.
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Old 12th September 2013, 03:52 AM   #4
sine143 is offline sine143  United States
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Xmax of 4 mm is not a lot for an 8

The fs of 28 does not really mean, 'the speaker bottoms out around 30hz'

assuming those are tye outside dimensions of your speaker box, its actually more like 2 cubic ft internal vol. there is nothing wrong with plywood. in many ways it is superior to other manufacturing materials, unless its utter shite plywood.

put the 8 in the box. my gut feeling is that the box is too big for an 8 with only 4mm xmax and an fs of 28 in a sealed configuration, but i cant speak for your tastes. throw the sub in there and let her rip. if younlike it, sweet, no work for you. if you dont, port it as per the manufacturers suggestion (although your box is too small).

you are absolutly sure the reciever rolls off below 40hz? thats wierd. With a hipass at 40hz i cant see much advantage for a sealed sub. also, does it hipass (locut) the non subwoofer outs?
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Old 12th September 2013, 05:19 AM   #5
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Quote:
Originally Posted by sine143 View Post
...you are absolutly sure the reciever rolls off below 40hz?
I think it is much more likely the 40-20k spec is for the POWER output rating, not the frequency response. Only a real piece of cr@p would roll off at 40 Hz frequency response these days.

As for the port, the Bazooka car subwoofer company always tuned to 40 Hz. Why? Because that is the lowest note on a bass guitar, and "you don't need any lower," and inventor Dave Prophit told me God sent him a dream about it, so how can you argue with that?

WELL, that's all true technically, but the Bazookas were always really muddy and boomy. Powerful, but not nice sounding. The high tuning has a poor effect on the time response.
--> If you pretty much like your sound now, but wanted to add a port for a bit more low end and less excursion, I'd tune more like 30 Hz.
Hard to say more without looking a simulation.
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Old 12th September 2013, 07:23 AM   #6
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Quote:
Originally Posted by head_unit View Post
As for the port, the Bazooka car subwoofer company always tuned to 40 Hz. Why? Because that is the lowest note on a bass guitar, and "you don't need any lower," and inventor Dave Prophit told me God sent him a dream about it, so how can you argue with that?
Somewhere before the turn of last century the amount of five string bass guitars with a low "B" at 31.5 Hz started to equal the amount of four string basses with a low "E" at 40 Hz.

For home use, I'd agree with a 30 Hz (or so) tuning, for most PA use, around 35, for cars, the cabin gain is enough that sealed will often be near flat and 40 Hz Fb will boom like a bazooka in a dumpster.
But some guys like that...
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Old 12th September 2013, 03:14 PM   #7
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Peerless 850136 8" - CSX217H - 217 WR 33
First you don't get to much of a woofer/sub from such a sealed enclosure 2ft³ = 56.634L.
In a br close to 31Hz tuning works better. I would not use it because only a miracle will give it LF extension (or in a very small room).
You will get to 30's Hz at ~F3 nothing else below that. It can work for a speaker (that was done). Not so nice if you r building a sub.
You want to use your existent box sealed, starting from scratch (56L), use this one driver Dayton Audio RSS210HF-4.
Or Morel CAW 938 (better in a bigger box).
Dayton Audio RSS210HF-4 8" Reference HF Subwoofer 4 Ohm 295-456
Morel CAW938 9" Cast Frame Woofer 297-086
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Old 12th September 2013, 03:23 PM   #8
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Quote:
Originally Posted by head_unit View Post
... inventor Dave Prophit told me God sent him a dream about it...
You are using ""Prophit, ""God, ""dream and ""inventor words all in the same phrase what makes me believe you are not in a loudspeaker forum right now and/or what he told you comes not from a veridical prophet or technician.
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Old 12th September 2013, 05:58 PM   #9
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Quote:
Originally Posted by sine143 View Post
Xmax of 4 mm is not a lot for an 8

The fs of 28 does not really mean, 'the speaker bottoms out around 30hz'

assuming those are tye outside dimensions of your speaker box, its actually more like 2 cubic ft internal vol. there is nothing wrong with plywood. in many ways it is superior to other manufacturing materials, unless its utter shite plywood.

put the 8 in the box. my gut feeling is that the box is too big for an 8 with only 4mm xmax and an fs of 28 in a sealed configuration, but i cant speak for your tastes. throw the sub in there and let her rip. if younlike it, sweet, no work for you. if you dont, port it as per the manufacturers suggestion (although your box is too small).

you are absolutly sure the reciever rolls off below 40hz? thats wierd. With a hipass at 40hz i cant see much advantage for a sealed sub. also, does it hipass (locut) the non subwoofer outs?
Thanks for your advice! I plan to give it a listen before changing anything.

Would you (or anyone else) have an opinion of how this 8" woofer would
sound in a box that is .7 ft3 (around 19-20 litre) ?
. I like the smaller size, although it would require a port
about 14" inches long to get 38Hz.

I don't know exactly what bass frequency the receiver can achieve, i only have the
pdf manual with a specs page..which says 40-20000 100 watts @ .9 thd .

The receiver has a low freq. cutoff which you can adjust 50 100 150 or 200Hz.
What it does is send those freq below the cutoff to the sub, the other speakers
only get frequencies above the cutoff point.
My usual setting is 100hz and sometimes 50Hz sounds better because my
front L/R have a port tuned to 100Hz.
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Old 12th September 2013, 06:20 PM   #10
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Quote:
Originally Posted by head_unit View Post
I think it is much more likely the 40-20k spec is for the POWER output rating, not the frequency response. Only a real piece of cr@p would roll off at 40 Hz frequency response these days.

As for the port, the Bazooka car subwoofer company always tuned to 40 Hz. Why? Because that is the lowest note on a bass guitar, and "you don't need any lower," and inventor Dave Prophit told me God sent him a dream about it, so how can you argue with that?

WELL, that's all true technically, but the Bazookas were always really muddy and boomy. Powerful, but not nice sounding. The high tuning has a poor effect on the time response.
--> If you pretty much like your sound now, but wanted to add a port for a bit more low end and less excursion, I'd tune more like 30 Hz.
Hard to say more without looking a simulation.
LOL! Yes, that is the power rating specs, you are correct.

Within the last year i have updated everything except the sub.
that is why i am changing the subwoofer driver. The Peerless i plan to
(at least try it once) use is old stock (a great price) because i couldn't
commit myself to a $150-$200 subwoofer at this time.

The LOL worth repeating for the dave prophitt quote.. thank you!

Bass isn't my favorite part of music listening; it just completes the project.
I usually keep it turned down, and the listening room is only 15' x 12' ..
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