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Old 5th February 2009, 06:50 PM   #1
Sumba is offline Sumba  Sweden
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Default Small subwoofer using Peerless 830946

Hi all DIY gurus

I have an idea of building a small vented subwoofer using the Peerless 830946 6.5" SLS driver.

http://www.tymphany.com/datasheet/printview.php?id=355

The aim is to assist my studio monitors in the low frequencies so the sub doesn't need to play that loud.

I have done some simulations in BassBox 6 with a 12.3L box tuned at 45Hz which give me a F3 of 42Hz but I'm not sure if I done it right

So to put it short, I need your expertise

Can I get a good response down to ~45Hz with this driver in a small vented box?
Any other issues with the idea?

Cheers
Sumba
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Old 6th February 2009, 03:55 AM   #2
GM is offline GM  United States
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Greets!

Yes, and no. I mean it wants a tiny box volume (Vb), so it will need a long vent folded up inside it.

I don't have BB6, but an F3 below Fb with a relatively low Q motor (if the published specs are reasonably accurate) means strong peaking at Fb, so not a good alignment. Better would be around 8 L net for solid output to 45 Hz with a ~40 Hz F3. Looks like a 5.08 cm dia. vent x 38.1" long and if it 'chuffs', then you'll need to experiment with different vent stuffing densities to find the least amount required to damp its noise.

Anyway, plug these numbers into BB6 to see if it suits you.

GM
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Old 7th February 2009, 05:52 PM   #3
Sumba is offline Sumba  Sweden
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Thanks for your reply GM.

38.1" long vent sound like quite a mission to accomplish

But you mentioned vent stuffing which I am not familiar with but I guess it's there to reduce air speed through the vent, correct?
And if so, would stuffing the vent reduce the required length and is there some sort of formula to calculate it?

Since this project isn't required to play loud due to it being a mid field monitoring system I'm not sure if the air flow will be large enough to produce noise.

Lots of questions but it isn't supposed to be easy is it?

Cheers
Sumba
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Old 7th February 2009, 11:00 PM   #4
bjorno is offline bjorno  Sweden
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Sumba, This simulation may help:

b

1(1)
Attached Images
File Type: gif 12.4l_box_peerless 830946-sls-damped port.gif (57.8 KB, 1166 views)
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Old 9th February 2009, 03:10 PM   #5
Sumba is offline Sumba  Sweden
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Quote:
Originally posted by bjorno
Sumba, This simulation may help:

b

1(1)

Thanks bjorno, your simulation looks a lot like mine so I guess I've done something right

I think I will go somewhere in between in terms of box volume and try around with different tunings until I find what I like the most.

Cheers
Sumba
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Old 9th February 2009, 04:17 PM   #6
GM is offline GM  United States
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Quote:
Originally posted by Sumba
Thanks for your reply GM.

38.1" long vent sound like quite a mission to accomplish

But you mentioned vent stuffing which I am not familiar with but I guess it's there to reduce air speed through the vent, correct?
And if so, would stuffing the vent reduce the required length and is there some sort of formula to calculate it?

Since this project isn't required to play loud due to it being a mid field monitoring system I'm not sure if the air flow will be large enough to produce noise.

Lots of questions but it isn't supposed to be easy is it?

Cheers
Sumba
You're welcome!

Ugh! I normally use Imperial and forgot to change the length to 'cm' also, so I meant 38.1 cm (15") which normally means the vent would be a folded up open ended 'TL' in a small cab.

Anyway, correct and the math required to accurately calculate the effect of stuffing on airflow is well beyond my math skills, so without simming using software designed to do so as bjorno has done it's a 'stuff to taste' either by ear or doing impedance sweeps to find the best in-room response WRT the BW around/at Fb.

No, probably not.

No, truly high performance speaker design is no trivial pursuit.

GM
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Old 9th February 2009, 04:19 PM   #7
tinitus is offline tinitus  Europe
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I would consider this one...goes straight to 30hz in relatively small BR

http://www.bmm-electronics.com/Produ...roduct_ID=5864
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Old 9th February 2009, 09:24 PM   #8
bjorno is offline bjorno  Sweden
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Quote:
I would consider this one...goes straight to 30hz in relatively small BR
Well, I usually try to stay on topic but if Sumba had asked for a down to 30 Hz sub that also ‘doesn't need to play loud’ in a 12.3 L box, then I had posted this simulation instead: See picture 1(1).

If he wants to build this 'Tapped (folded) box’ I must agree with GM: s statement:

‘truly high performance speaker design is no trivial pursuit’

It would be a challenge to fold this design suggestion into a compact internal volume of 12.3 L while still keeping the airways dimensioning/ acting accurate as shown in the simulation.

The port or slotted duct if 40 cm^2 would have the dimensions of 2.2 cm x 18.2 cm = about 40 cm^2 and if the port dimensioning is to be considered reliable at 20 Hz too, this area must be provided both in front and at the rear side of the driver.

The driver magnet has to be countersunk and sealed into one of the dividing walls…etcetera, etcetera.


b

1(1)
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File Type: gif peerless 830946-30 hz-sub.gif (75.9 KB, 1024 views)
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Old 16th February 2009, 06:42 PM   #9
tb46 is offline tb46  United States
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Hi Sumba,

Thanks for bringing the little Peerless to my attention :-).

I agree with GM's suggestions, as to the vent (duct) take a look at this construction:

Regards,
Attached Images
File Type: jpg peerless_830946_45hz_12.31l.jpg (88.9 KB, 943 views)
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Old 17th February 2009, 07:32 PM   #10
Sumba is offline Sumba  Sweden
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Quote:
Originally posted by tb46
Hi Sumba,

Thanks for bringing the little Peerless to my attention :-).

I agree with GM's suggestions, as to the vent (duct) take a look at this construction:

Regards,

Hi tb46 and thanks for your suggestion.
I will be building several different boxes with different approaches and fiddle with different tunings and vents and one will be a folded vent like that.

The Peerless is indeed a interesting little driver and it will be great fun to play with it
I've just finished soldering the chipamp to the project, an Amp9 from 41Hz.com.

While waiting for the Peerless driver I built a ~6 L sealed box to an old 6½ driver I had laying around just for fun.
I don't know anything about the driver though other than it came from a Audio Pro passive subwoofer with 2 of those in a push-pull configuration.
The end result was rather surprising, it played a lot cleaner and nicer than I thought it would considering it probably costs next to nothing so I'm gonna take the opportunity to learn how to construct a linkwitz-transformer
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