Hello,
I'm a novice at speaker enclosure design, so please forgive me if this is a dumb question. I'm designing an enclosure for a pair of small (3.5") full range speakers to use in a bedroom/office setting where high volume is not needed. I currently have the speakers in enclosures with a cylindrical port sized to achieve what seemed to be the lowest I could reasonably go without getting huge peaks and valleys in the transfer function curve using an app I found online.
While I like the sound of the current setup. I want to change some things to improve the overall setup and want to try to improve the bass output while I'm at it. Now, I'm looking to construct a multi-chambered enclosure with the full range drivers on each end of the front baffle and a 3" mini subwoofer in the center. To get the lowest bass output I can with a flat transfer function curve with the sub I'm considering, I need a very lengthy port that will take some creativity to build into my enclosure given the size limitations I have placed on it. I'm looking at using a labyrinth port design to achieve this.
After running different port scenarios in my app (single port, multiple ports all of different sizes, lengths, round and rectangular), I've concluded that a single port out of the speaker chamber gives me what I think is the best, flat response until it hits a steep drop off at the low frequency end. The geometry constraints of the overall cabinet makes it challenging to fit the labyrinth port in the box efficiently.
Finally to my question. Is it acceptable to have a single port out of the sub chamber, then Tee it a short ways downstream, then have two runs switch back and forth, terminating in two outlets? Can I count the length of port tubes on each side past the Tee toward the total length of port, or does the Tee somehow reduce the effectiveness of what comes after it.
Thanks for any advice you can give.
I'm a novice at speaker enclosure design, so please forgive me if this is a dumb question. I'm designing an enclosure for a pair of small (3.5") full range speakers to use in a bedroom/office setting where high volume is not needed. I currently have the speakers in enclosures with a cylindrical port sized to achieve what seemed to be the lowest I could reasonably go without getting huge peaks and valleys in the transfer function curve using an app I found online.
While I like the sound of the current setup. I want to change some things to improve the overall setup and want to try to improve the bass output while I'm at it. Now, I'm looking to construct a multi-chambered enclosure with the full range drivers on each end of the front baffle and a 3" mini subwoofer in the center. To get the lowest bass output I can with a flat transfer function curve with the sub I'm considering, I need a very lengthy port that will take some creativity to build into my enclosure given the size limitations I have placed on it. I'm looking at using a labyrinth port design to achieve this.
After running different port scenarios in my app (single port, multiple ports all of different sizes, lengths, round and rectangular), I've concluded that a single port out of the speaker chamber gives me what I think is the best, flat response until it hits a steep drop off at the low frequency end. The geometry constraints of the overall cabinet makes it challenging to fit the labyrinth port in the box efficiently.
Finally to my question. Is it acceptable to have a single port out of the sub chamber, then Tee it a short ways downstream, then have two runs switch back and forth, terminating in two outlets? Can I count the length of port tubes on each side past the Tee toward the total length of port, or does the Tee somehow reduce the effectiveness of what comes after it.
Thanks for any advice you can give.
Hi,
What is the enclosure volume you are looking at? What would be your limit?
What is the brand/model of the 3.5" speaker you are using at this moment? Just to check T/S parameters.
Can you increase the speaker size a bit? Maybe a 4" or 5"?
Do you have the simulation of your current enclosure?
What is the enclosure volume you are looking at? What would be your limit?
What is the brand/model of the 3.5" speaker you are using at this moment? Just to check T/S parameters.
Can you increase the speaker size a bit? Maybe a 4" or 5"?
Do you have the simulation of your current enclosure?
The main parameters of a port are the (effective) cross section surface and the (effective) port length.
In theory it should not make any difference, if you split a section of the port up into two parts. The relevant parameters are still the (total) port surface and the length (parallel parts count once).
In practice splitting up a port reduces efficiency and makes it more prone to noises and turbulence.
If you still have some time left you could use my soon-to-come port optimizer and try to find a geometry that does not need a huge labyrinth.
What stv said.
But there can be an additional factor. I like longish high aspect ratio vents which are often frowned on as they add R to the vent. This can be used to push a reflex owards aperiodic.
Note that when you tune a box “as low as possible” it often does not sound as good higher up.
This is an example of a small box (5 litres) witha 3.5” — this particular box outdid a set of LS3/5A i had restored.
dave
But there can be an additional factor. I like longish high aspect ratio vents which are often frowned on as they add R to the vent. This can be used to push a reflex owards aperiodic.
Note that when you tune a box “as low as possible” it often does not sound as good higher up.
This is an example of a small box (5 litres) witha 3.5” — this particular box outdid a set of LS3/5A i had restored.
dave
Thank you for your reply. I think you confirmed my understanding. Splitting the port works in theory, but from a practical standpoint it could introduce inefficiencies and noise in the system. I will try to avoid doing it.
Thanks for the link to the port discussion. I'll check it out.
Thanks for your reply. The project I'm planning is essentially designing a small multi-chambered cabinet that I will connect to a small tube amp with bluetooth capability. It's essentially a large bluetooth speaker. I'm setting it on top of and will match the plan dimensions of a guitar speaker cab. The head and buetooth amp will sit on top of this cabinet.
The out-to-out plan dimensions of this cabinet are set at 12"x 24". I want to limit the depth to 6". I plan to use 3/4" plywood or sawn lumber for the top, back and sides, and 1/2" plywood for the internal partitions. Given this, the enclosure scenarios and volumes I'm considering are:
- Two ported chambers of 0.286 ft^3, one for each of the full range speakers I have.
- Two closed chambers of 0.124 ft^3, one for each of the FR speakers and one ported chamber of 0.047 ft^3 housing a 3" subwoofer. The subwoofer would be mounted between the two FR speakers and aim the same direction. The remaining volume would be used for rectangular labyrinth port(s) as needed.
- Two closed chambers of 0.124 ft^3 and one ported chamber of 0.234 ft^3 housing a larger subwoofer. The subwoofer would be mounted to the bottom of the cabinet and aim downward. The remaining volume would be used for rectangular labyrinth ports or cylindrical ports with switchbacks if space provides.
Here is a link to the 3" subwoofer I'm considering: Tang Band W3-1876S
I've attached some pdf files of plots and data extracted from the enclosure simulator app I'm using. Looking through this information, I've come to the following conclusions:
- With a vented enclosure tuned as low a possible, the 3.5" FR speakers seem to have significant peaks around 50 Hz and 140 Hz, and a trough in between. It seems better to place the FR speakers in closed chambers to achieve a flatter response, and supplement them with a small subwoofer to improve the bass response of the system.
- The 3" subwoofer I'm considering seems to achieve a flat response curve that supplements the FR speaker response fairly well using a single rectangular port 22" long.
- The SPL plots for the 3" sub seem to indicate that it will not have enough volume to pair well with the FR speakers, and I should consider other options.
- I modeled other subwoofers ranging in size from 4" to 6", mounted in the bottom of the larger chamber noted above. Of the speakers I considered, this one seems to have a flat response, and volume that pairs well with the FR speakers Tang Band W5-1138SMF
- The crossover frequency of 200 Hz would work well for this speaker/subwoofer pair.
This is a ton of information. I realize that you may not have the desire/time to review it. But if you do, I sure would appreciate your thoughts on my conclusions so far and current direction.
Thanks,
Dan
Hi!
Thanks for the information. Good stuff to discuss. 🙂
Let me comment on your conclusions:
With the blue curve of Tang Band W3-1876S, you get -8dB @40hz and -18dB @ 30Hz. In order to have a flat response down to 30Hz, you need to amplify 18dB at 30Hz - it's a lot of differential power. Listening at low SPL (around 75dB for example) it's not impossible.
In order to eq to flat, you need an amplification of 63 times (18dB) @ 30Hz more power than mid/high frequencies. Considering 85dB speaker SPL sensitivity (just to make simple calculations), in order to achive 75dB you need 0.1W @ mid/high and @ 30Hz you need 6.3W. It's possible, but at very low average SPL of 75dB. And being 75dB average, if we consider a normal 1:5 peak/average power, we would be talking about 0.5W peak power for mid/high and 31.5W peak power for bass down to 30Hz. Let's see next option with 5".
With a 20W amp, you could listen up to 4dB more or 79dB in that example.
Considering 82dB SPL of your speakers, you could achieve 76dB flat from 30Hz up.
This is more or less the setup I have for my PC speakers. I use 2 x JBL Control One (modified to sealed) and a software EQ on PC to amplify up to 20dB some bass frequencies. This way, I can listen at around 70 to 80dB SPL and have a flat response above 30Hz using a 20W+20W amplifier.
In summary: I would go with the 2 x 3"FR in sealed chambers (blue line, no peaks) and a 1 x 5"Woofer in a ported chamber (green line).
Adjust the crossover frequency to the best point. 200 to 300Hz seams to be a good start since there is good overlap around it.
It's late now here, check the calculations.
Thanks for the information. Good stuff to discuss. 🙂
Let me comment on your conclusions:
I agree. FR speakers to sealed chambers (red line). If you already decided that you'll have a subwoofer, it's not worth to stretch the FR speaker response.
3" for bass is too small. Even if you can achieve a non boomy response (blue curve), you don't get much SPL below 40Hz.
With the blue curve of Tang Band W3-1876S, you get -8dB @40hz and -18dB @ 30Hz. In order to have a flat response down to 30Hz, you need to amplify 18dB at 30Hz - it's a lot of differential power. Listening at low SPL (around 75dB for example) it's not impossible.
In order to eq to flat, you need an amplification of 63 times (18dB) @ 30Hz more power than mid/high frequencies. Considering 85dB speaker SPL sensitivity (just to make simple calculations), in order to achive 75dB you need 0.1W @ mid/high and @ 30Hz you need 6.3W. It's possible, but at very low average SPL of 75dB. And being 75dB average, if we consider a normal 1:5 peak/average power, we would be talking about 0.5W peak power for mid/high and 31.5W peak power for bass down to 30Hz. Let's see next option with 5".
Now with the Tang Band W5-1138SMF green curve, you get -3dB @ 40Hz and -12dB @ 30Hz. A lot more pressure. So, in order to get a flat response from 30Hz up, you need to amplify 16 times @30Hz. Considering same example, listening @ 75dB SPL with 85dB sensitivy, now you need 0.1W for mid/high and 1.6W for 30Hz. Considering peak power, 0.5W for mid/high and 8W for bass down to 30Hz.
With a 20W amp, you could listen up to 4dB more or 79dB in that example.
Considering 82dB SPL of your speakers, you could achieve 76dB flat from 30Hz up.
This is more or less the setup I have for my PC speakers. I use 2 x JBL Control One (modified to sealed) and a software EQ on PC to amplify up to 20dB some bass frequencies. This way, I can listen at around 70 to 80dB SPL and have a flat response above 30Hz using a 20W+20W amplifier.
In summary: I would go with the 2 x 3"FR in sealed chambers (blue line, no peaks) and a 1 x 5"Woofer in a ported chamber (green line).
Adjust the crossover frequency to the best point. 200 to 300Hz seams to be a good start since there is good overlap around it.
It's late now here, check the calculations.
Don't ever boost a vented woofer below tuning frequency (where driver and vent cancel out)! It will very quickly reach xmax and either make bad noises or even be damaged.
You could tune the enclosure very low and boost the range above tuning, but that's tricky with such a small driver.
Agree with all the rest ron68 wrote!
Sure, these extreme bass boosts (+10, 12, 15dB) must be done with care and are only applicable to very low overall SPL.
I do them, but I listen to very low SPL and very close since they are PC speakers.
In my case, small speakers for PC sound, I decided to seal the boxes for the 2 reasons: control the excursion and get better low bass response (between 30 and 40Hz).
I do them, but I listen to very low SPL and very close since they are PC speakers.
In my case, small speakers for PC sound, I decided to seal the boxes for the 2 reasons: control the excursion and get better low bass response (between 30 and 40Hz).