port help

[ameuba10]

im looking to build a new set of bookshelf speakers primarily for ipod use in my bedroom. i have a set of peerless 830875 6 1/2" woofers paired with a vifa's bc25sc06 1" tweets crossed at 4.5khz. right now theyre in a prefabbed sealed enclosure thats a little too small for woofers. so i would like to build a pair of ported boxes. freq response for the peerless woofers are 20-6.5khz with Fs: 48.1hz. im thinking about tuning the port to 37hz. Vas: is only .62cu. ft. this would actually be my first set of boxes that i build myself so i would like a little help on dimensions, especially the port. the ports are something that i am unfamiliar with. any help is appreciated!

 

[annunaki]

im looking to build a new set of bookshelf speakers primarily for ipod use in my bedroom. i have a set of peerless 830875 6 1/2" woofers paired with a vifa's bc25sc06 1" tweets crossed at 4.5khz. right now theyre in a prefabbed sealed enclosure thats a little too small for woofers. so i would like to build a pair of ported boxes. freq response for the peerless woofers are 20-6.5khz with Fs: 48.1hz. im thinking about tuning the port to 37hz. Vas: is only .62cu. ft. this would actually be my first set of boxes that i build myself so i would like a little help on dimensions, especially the port. the ports are something that i am unfamiliar with. any help is appreciated!

4.5Khz seems like a pretty high x-over point for a 6.5" woofer.

As for venting, you will need the T/S parameters to model the response. Without those it is a shot in the dark. Sealed enclosures are very forgiving, vented enclosures are definitely not if they are misaligned with the woofer.

 

[ameuba10]

T-S Parameters
Resonance Frequency fs 48.1 Hz
Mechanical Q factor Qms 2.67
Electrical Q factor Qes 0.45
Total Q factor Qts 0.39
Force factor Bl 8.4 Tm
Mechanical resistance Rms 1.88 Kg/s
Moving mass Mms 16.6 g
Suspension compliance Cms 0.66 mm/N
Effective cone diameter D 13.3 cm
Effective piston area Sd 139 cm2
Equivalent volume Vas 17.6 ltrs
Sensitivity (2.83V/1m) 88.6 dB
Ratio BL/√(Re) 3.3
Ratio fs/Qts F 124

 

[highfigh]

im looking to build a new set of bookshelf speakers primarily for ipod use in my bedroom. i have a set of peerless 830875 6 1/2" woofers paired with a vifa's bc25sc06 1" tweets crossed at 4.5khz. right now theyre in a prefabbed sealed enclosure thats a little too small for woofers. so i would like to build a pair of ported boxes. freq response for the peerless woofers are 20-6.5khz with Fs: 48.1hz. im thinking about tuning the port to 37hz. Vas: is only .62cu. ft. this would actually be my first set of boxes that i build myself so i would like a little help on dimensions, especially the port. the ports are something that i am unfamiliar with. any help is appreciated!

You could always use the info from the Tymphany site.

http://www.tymphany.com/datasheet/appview.php?id=12

 

[TLS Guy]

T-S Parameters
Resonance Frequency fs 48.1 Hz
Mechanical Q factor Qms 2.67
Electrical Q factor Qes 0.45
Total Q factor Qts 0.39
Force factor Bl 8.4 Tm
Mechanical resistance Rms 1.88 Kg/s
Moving mass Mms 16.6 g
Suspension compliance Cms 0.66 mm/N
Effective cone diameter D 13.3 cm
Effective piston area Sd 139 cm2
Equivalent volume Vas 17.6 ltrs
Sensitivity (2.83V/1m) 88.6 dB
Ratio BL/√(Re) 3.3
Ratio fs/Qts F 124

This is from the Tymphany website for that driver.

Vented box of 12 liters (0.45cf); F3 of 53Hz; 2" port by 5.6" long

Here is the data Sheet for that driver.

That driver can not be crossed over at 4.5 kHz, that is way beyond the cone break up modes. crossing over at 4.5 kHz will make a very nasty speaker in deed.

That unit needs to crossover at 2 kHz.

It is very similar to the 830874, that I did a design for. NASP

That design uses a SEAS tweeter, so you would have to use that tweeter if you use that crossover.

The crossover is the heart of the speaker, so you are wasting your time building anything until you get the crossover issues sorted out.

 

[annunaki]

T-S Parameters
Resonance Frequency fs 48.1 Hz
Mechanical Q factor Qms 2.67
Electrical Q factor Qes 0.45
Total Q factor Qts 0.39
Force factor Bl 8.4 Tm
Mechanical resistance Rms 1.88 Kg/s
Moving mass Mms 16.6 g
Suspension compliance Cms 0.66 mm/N
Effective cone diameter D 13.3 cm
Effective piston area Sd 139 cm2
Equivalent volume Vas 17.6 ltrs
Sensitivity (2.83V/1m) 88.6 dB
Ratio BL/√(Re) 3.3
Ratio fs/Qts F 124

Unfortunately these parameters are useless without xmax specifications. However, I did find the specs for the 8 ohm driver here hopefully these are correct:
https://www.madisound.com/store/manuals/peerless/830875.pdf

When I do some modeling here I get a .500 ft^3 enclosure tuned to 49hz with two 2" vents with flanged ends 12.58" long. It will require at least two 2" vents to keep the vent velocity below 17m/s.

37 hz is probably bit too deep as you may start running into some excursion issues.

 

[TLS Guy]

Unfortunately these parameters are useless without xmax specifications. However, I did find the specs for the 8 ohm driver here hopefully these are correct:
https://www.madisound.com/store/manuals/peerless/830875.pdf

When I do some modeling here I get a .500 ft^3 enclosure tuned to 49hz with two 2" vents with flanged ends 12.58" long. It will require at least two 2" vents to keep the vent velocity below 17m/s.

37 hz is probably bit too deep as you may start running into some excursion issues.

You are not going to get 12.5 inch vents in a small 0.5 cu.ft bookshelf speaker. I would use 1 vent as suggested by Tymphani. A vent velocity of 30 M/sec is acceptable especially if the port faces the back. This is not a sub, and most small speakers have vent velocities in this range.

He has a much more pressing issue with the crossover.

The other issue is he won't gain much over a sealed alignment. His driver is really intended for sealed and the 830874 for vented.

The sealed enclosure has an F3 of 85, but the rolls off 12 db per octave, so actually the sealed has greater low bass output. At 40 Hz the output of vented or sealed is pretty much a wash.

I'm sure his speaker sounds as if it does not have lick of bass, as he is listening to the shouty break up mode and not much else.

 

[ameuba10]

the tweeters that im using have a freq response starting at 1.5khz, so is it ok to cross around 2khz? i see that crossing lower seems to be a unanimous first solution

 

[TLS Guy]

the tweeters that im using have a freq response starting at 1.5khz, so is it ok to cross around 2khz? i see that crossing lower seems to be a unanimous first solution

You can't use that tweeter with that woofer. You have to buy different tweeters. That Vifa unit has an Fs far too high for your application and is starting to roll off at 2 kHz. Use the SEAS tweeters in my design and you can build my crossover.

 

[highfigh]

im looking to build a new set of bookshelf speakers primarily for ipod use in my bedroom. i have a set of peerless 830875 6 1/2" woofers paired with a vifa's bc25sc06 1" tweets crossed at 4.5khz. right now theyre in a prefabbed sealed enclosure thats a little too small for woofers. so i would like to build a pair of ported boxes. freq response for the peerless woofers are 20-6.5khz with Fs: 48.1hz. im thinking about tuning the port to 37hz. Vas: is only .62cu. ft. this would actually be my first set of boxes that i build myself so i would like a little help on dimensions, especially the port. the ports are something that i am unfamiliar with. any help is appreciated!

That tweeter and x-over point would be OK if you were making a true 3-way with a 4" to 5-1/4" mid-range. You generally want the -3dB of the high pass to a driver to be at least 1-1/2 octaves above the Fs but these 6-1/2" drivers don't go to 4.5KHz without problems. That rise above 2KHz would make for some pretty nasty-sounding mid-range and it's right in the area where human hearing is most sensitive. It's best to let drivers work in their comfort zone and not try to make them do something they aren't capable of.

The Seas tweeter would be a much better match. Sure, it's more money but the results will be far better. Using components that won't/can't work as intended will waste money, time and lead to frustration.

 

[caper26]

most speakers ar XO'd at 2-2.2 kHz for a reason!

 

[ameuba10]

thanks guys! noobs have to start somewhere... well ima cross at 2khz, and build a larger box tuned to 45hz. box dimensions are 8"x10.75"x17.5" using 3/4" mdf. inside will be lined with peel and seal, and then maybe a polyfill or some other foam. still working on vent dimensions now though...

 

[TLS Guy]

thanks guys! noobs have to start somewhere... well ima cross at 2khz, and build a larger box tuned to 45hz. box dimensions are 8"x10.75"x17.5" using 3/4" mdf. inside will be lined with peel and seal, and then maybe a polyfill or some other foam. still working on vent dimensions now though...

You don't want a larger box. The manufacturer's specified box is optimal. You will only loose performance by over sizing the box. Build the optimal box, or use the one you have. You need new tweeters and crossovers first.

 

[annunaki]

You are not going to get 12.5 inch vents in a small 0.5 cu.ft bookshelf speaker. I would use 1 vent as suggested by Tymphani. A vent velocity of 30 M/sec is acceptable especially if the port faces the back. This is not a sub, and most small speakers have vent velocities in this range.

He has a much more pressing issue with the crossover.

The other issue is he won't gain much over a sealed alignment. His driver is really intended for sealed and the 830874 for vented.

The sealed enclosure has an F3 of 85, but the rolls off 12 db per octave, so actually the sealed has greater low bass output. At 40 Hz the output of vented or sealed is pretty much a wash.

I'm sure his speaker sounds as if it does not have lick of bass, as he is listening to the shouty break up mode and not much else.

Agreed on the crossover, but vent velocities above 17m/s begin to adding compression at the vent. Understood that this is not a sub, but this can begin adding coloration to the sound. If one plans to use the speakers at moderate to higher volumes even a small amount of time, I would suggest not to exceed 26m/s at a maximum.

Also a 1" x 6" slot vent at 11" long will accomplish the same thing which will not add much to overall dimensions to accommodate. This keeps vent velocity just below 17m/s.

And when one has complete control over such factors, why compromise?

 

[ameuba10]

well the box that they are in are some bookshelf speakers that i just did a speaker swap on. so they arent enclosures made for them.

 

[TLS Guy]

Agreed on the crossover, but vent velocities above 17m/s begin to adding compression at the vent. Understood that this is not a sub, but this can begin adding coloration to the sound. If one plans to use the speakers at moderate to higher volumes even a small amount of time, I would suggest not to exceed 26m/s at a maximum.

Also a 1" x 6" slot vent at 11" long will accomplish the same thing which will not add much to overall dimensions to accommodate. This keeps vent velocity just below 17m/s.

And when one has complete control over such factors, why compromise?

Obviously a slot vent is the best solution. However the Tymphani alignment is pretty typical for off the shelf ported bookshelf speakers.

 

[ameuba10]

so i believe that i was making this box 10x harder than it needed to be. using the winisd program i came up with the following dimensions...

W: 11.5"
H: 17.5"
D: 7.5"

.65 cuft total


now i have two port options...

option 1: 1 port 2.25" diameter, 4.87" deep resulting in a port velocity of .08
option 2: 2 ports 1.25" diameter, 3.11" deep resulting in a port velocity of .06

im sure these options are just about the same but does anyone have opinion of which option to take? also, is there an audible difference of the port location? say forward or rear facing?

looking at the spl graphs from both the woofer and tweeter, i believe that i would like to crossover at 2.8khz. it looks to me that that would be a good compromise on both parts. it should also follow the rule of thumb by not crossing below twice the tweeters Fs, in this case 1350hz*2=2700hz.

any input greatly appreciated!

 

[TLS Guy]

so i believe that i was making this box 10x harder than it needed to be. using the winisd program i came up with the following dimensions...

W: 11.5"
H: 17.5"
D: 7.5"

.65 cuft total


now i have two port options...

option 1: 1 port 2.25" diameter, 4.87" deep resulting in a port velocity of .08
option 2: 2 ports 1.25" diameter, 3.11" deep resulting in a port velocity of .06

im sure these options are just about the same but does anyone have opinion of which option to take? also, is there an audible difference of the port location? say forward or rear facing?

looking at the spl graphs from both the woofer and tweeter, i believe that i would like to crossover at 2.8khz. it looks to me that that would be a good compromise on both parts. it should also follow the rule of thumb by not crossing below twice the tweeters Fs, in this case 1350hz*2=2700hz.

any input greatly appreciated!

Your box is badly miss tuned. You are getting no advantage by making your
box larger than the optimal box. I have run it on Bass Box pro, and the tymphani calculations are right on. If you over size it, although you have a few Hz lower F3, the roll off starts higher. You also greatly increase vent velocity and you will have to use a slot vent and not a port.

For your 0.65 cu.ft enclosure a 2" port with two flared ends would be 7.2" long with a vent velocity of 48 m/sec, which is totally unacceptable.

Your two vents 1.25" dia would be 5.9" long with a vent velocity of 37 m/sec which is also unacceptable.

The next issue is that your box is far two wide. To minimize diffraction and irregular response, your box needs to be as narrow as possible.

Your crossover is still too high. It is right at the break up mode. Crossovers are not brick wall, and you need to get your crossover point well below the breakup mode. It needs to be around 2 KHz and at least third order, so as not to excite the breakup mode. You absolutely need a different tweeter.

If you PM me your Email, I will send you a full set of graphs for your box alignment.

 

[highfigh]

This would work better with that woofer-
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-1026&FTR=264-1026&CFID=4482332&CFTOKEN=83545677

I'm using them with the 830874 and even with a thrown-together crossover to keep from roasting the tweeter with pink noise, the response is ridiculously smooth when I measured it outside, away from the ground plane. Fs is lower, at 1KHz, too.

 

[ameuba10]

im sorry, i think that was my dyslexia kicking in there on my interior volume. its .56cuft not .65cuft. i believe that i have finally come up with my final dimensions...(ODs)

H: 17.5"
W: 7.5"
D: 11.5"

2.25" round port 6" deep for a port velocity of .08
port will be rear facing right behind the tweeter

tweeter will be changed to Vifa's BC25SG15-04 so i can achieve a smoother frequency band and an easier crossover point of 2khz.

crossover will be 2nd order Butterworth as shown.

C1: 15uF
C2: 6.8uF
L1: .45mH
L2: .09mH

i hope i got it this time...