To line or not to line walls?

bcodemz

Member
2014-02-21 1:19 am
I'm building a small 3 way speaker, and the woofer has about 2L of net internal volume after subtracting for drivers and walls. The woofer handles 40-300Hz. I'm wondering, should I line the walls with 1/4'' or 1/2'' wool felt? Would it be effective for frequencies 300Hz and below? What I'm worried about is that the wool felt will absorb the rear waves and reduce the efficiency of the passive radiators. Even though for vented enclosures should only be lined and not stuffed, I feel like in such a small space 1/2'' lining would be taking up significant amount of space inside that it would be like stuffing a cabinet.

If 1/4'' or 1/2'' felt won't do much to absorb the 300Hz and below sound, I may consider just having a bare wall so the passive radiator can have maximum efficiency.
 
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Hi, I remember having seen the same question in another thread :rolleyes:
1) if the speaker is enclosured, there is no rear wave: it's just chaotic movement of particles of air, just pressure.
2) I had the same question some months ago, but just a flash. I put the wf and the pr in the box with no stuffing at all, saying to myself that if I would be hearing something wrong, I'd add some felt < real felt> in the vicinity of the wf.
Never happened. Best project in my life :cheers: ( big bass from a 5 1/2 wf and 7 pr )
 

bcodemz

Member
2014-02-21 1:19 am
2L and it is getting to 40 Hz?

Hard to build a box that will fit anything larger than a 4" at that volume. And it will be extremely inefficient.

2 litres is the territory of 3" FRs.

dave

Yes, 4'', with a lot of EQ. It's actually 3.5L, but once you subtract the volume taken up by the driver and the passive radiator themselves, the net volume is just around 2L.
 

bcodemz

Member
2014-02-21 1:19 am
Hi, I remember having seen the same question in another thread :rolleyes:
1) if the speaker is enclosured, there is no rear wave: it's just chaotic movement of particles of air, just pressure.
2) I had the same question some months ago, but just a flash. I put the wf and the pr in the box with no stuffing at all, saying to myself that if I would be hearing something wrong, I'd add some felt < real felt> in the vicinity of the wf.
Never happened. Best project in my life :cheers: ( big bass from a 5 1/2 wf and 7 pr )

Yes, but this is a different question on the viability of felt. The other thread was on the effectiveness of different absorptive materials.

So I take it that the felt didn't do anything for you?
 

bcodemz

Member
2014-02-21 1:19 am
Not a good idea at all to EQ a vented speaker below its tuning, unless you are decreasing the output.

dave

No worries buddy, I got that covered. There's a very strong 48dB/oct high pass filter applied.

I've built the speaker already (and it sounds stunning), except I stuffed it. Now I know why I haven't destroyed the 2 passive radiators yet because the stuffing was reducing the PR's efficiency. I'm just planning on building an improved version now knowing that stuffing is bad for vented enclosures.
 
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bcodemz

Member
2014-02-21 1:19 am
What drivers are you using? Pictures?

The high pass filter needs to be just below the tuning frequency which is very unlikely to be 40 Hz.

The stuffing does not decrease the sensitivity.

dave

Tuning is at ~46Hz. A high pass at 45Hz was killing too much output around 45Hz, which is very important for a lot of music. The 40Hz high pass sounded and measured better.

Here's the thread.

http://www.diyaudio.com/forums/mult...-sounding-small-speaker-ever.html#post4693812

In the other thread people were saying stuff decreases the efficiency of the port/PR, and I think it is true, because it would explain my real world experience vs simulations of woofer/PR excursion, as well as explaining why the impedance sweep showed a nearly flat curve near the tuning frequency when there should be a pronounced V shaped curve near the tuning. Currently the woofer is working a lot harder than it should because of the stuffing, which I'd like to avoid/minimize.
 
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Without hearing it, best sounding small speaker might be a stretch… it would be interesting to hear them. Where are you located?

I have SS 10F and it is good, but we have a couple drivers that out-perform them (and cost a little less). Particularily in terms of clarity & detail... and you have an XO above the ¼ wavelength C-C spacing of mid-tweeter, that will cause lobing at a minimum... and the analog sections of the miniDSP are going to limit performance.

My model shows a nicely shaped response with (uneqed) with a bit less than 1 dB peak at ~190Hz, F3 of ~98 Hz, F10 ~61 Hz. To get to 40 Hz you'd need about 13 dB of boost… looks doable althou xmax looks to limit you to about 75 dB before exceeding it. I wouldn't have guessed that.

It is amazing to hear a 2-2.5 litre box with hi fidelity output. Our uFonken family stun a lot of people when i play them in the big room.

Used below 300 Hz, it is questionable whether airspace damping is going to do much, but i'd play it safe and line them with 12mm cotton felt. Not a good idea to use stuffing in a reflex enclosure.

dave
 

bcodemz

Member
2014-02-21 1:19 am
Without hearing it, best sounding small speaker might be a stretch… it would be interesting to hear them. Where are you located?

I have SS 10F and it is good, but we have a couple drivers that out-perform them (and cost a little less). Particularily in terms of clarity & detail... and you have an XO above the ¼ wavelength C-C spacing of mid-tweeter, that will cause lobing at a minimum... and the analog sections of the miniDSP are going to limit performance.

My model shows a nicely shaped response with (uneqed) with a bit less than 1 dB peak at ~190Hz, F3 of ~98 Hz, F10 ~61 Hz. To get to 40 Hz you'd need about 13 dB of boost… looks doable althou xmax looks to limit you to about 75 dB before exceeding it. I wouldn't have guessed that.

It is amazing to hear a 2-2.5 litre box with hi fidelity output. Our uFonken family stun a lot of people when i play them in the big room.

Used below 300 Hz, it is questionable whether airspace damping is going to do much, but i'd play it safe and line them with 12mm cotton felt. Not a good idea to use stuffing in a reflex enclosure.

dave

Yeah the next speaker is going to fix all that. Much closer CTC by cutting off the frames, XO at 1/4 wavelength, miniDSP 2x4 HD with digital input to avoid DA and AD and linear phase crossovers.

Outdoor ground plane measurements actually show a F3 of 68Hz, and only 9dB of boost was needed to achieve F0 at 45Hz, F3 at 42Hz. I'm guessing I need even less when the stuffing is taken out. Maximum 1 meter clean output is ~89dB from 40-50Hz, 91-94dB from 50Hz-100Hz. Another ~2dB can be eeked out if distortion is disregarded. When placed in a room I can get several dB more output.

I'd love to know which drivers you think are better than the SS 10F, especially for clarity and detail, which is what I'm looking for. I'm located in Toronto. I'd like to know more about the uFonken speakers.
 
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Much closer CTC by cutting off the frames, XO at 1/4 wavelength, miniDSP 2x4 HD with digital input to avoid DA and AD and linear phase crossovers.

Hard to get close enuff at 3000 Hz for ¼ wl XO, you'd need to get C-C down to 1.13". Isn't that miniDSP called the nanoDSP?

I'd love to know which drivers you think are better than the SS 10F, especially for clarity and detail, which is what I'm looking for.

The treated versions of our FF85wk and probably the Mark Audio Alpair 5.2. They also have better HF than the 10Fs and you might be able to toss the tweeter completely.

I'm located in Toronto.

Too far to bring them to diyFEST in Aug… althou we have had attendees from further away.

I'd like to know more about the uFonken speakers.

Lots of pics in this thread: http://www.diyaudio.com/forums/plan...nken-gallery-pictures-only-3.html#post3067777
The link takes you to the post with my personal pair of uFonkenSET.

The rectangular version with the same volume is more compact (but doesn't quite disappear as well) and their is a smaller one (and an even smaller one in development)

uFonkenFamily.gif


dave
 

bcodemz

Member
2014-02-21 1:19 am
Hard to get close enuff at 3000 Hz for ¼ wl XO, you'd need to get C-C down to 1.13". Isn't that miniDSP called the nanoDSP?

I'm crossing a lot lower, at 1700Hz.

On a side note, I wonder why the CTC of 1/4 wavelength at crossover frequency is emphasized. For most builds it is physically impossible to do. I don't know of any other way to achieve CTC that's 1/4'' wavelength with any driver combination without modifying the drivers themselves. In my case I'm using an exceptionally capable tweeter that can (and has to) be crossed exceptionally low just to a tiny 3'' midrange driver, and that's only possible by cutting off the frame of both the tweeter and midrange so I can achieve a CTC of 2''. Most tweeters have 4'' faceplates that automatically exceeds 2'', and most midranges are much bigger than 3''.

The treated versions of our FF85wk and probably the Mark Audio Alpair 5.2. They also have better HF than the 10Fs and you might be able to toss the tweeter completely.

What did you do to treat the drivers? How does it compare to the 10F for midrange duty?

I don't think I'll be ditching the tweeter, I need the off axis response.

Too far to bring them to diyFEST in Aug… althou we have had attendees from further away.



Lots of pics in this thread: http://www.diyaudio.com/forums/plan...nken-gallery-pictures-only-3.html#post3067777
The link takes you to the post with my personal pair of uFonkenSET.

The rectangular version with the same volume is more compact (but doesn't quite disappear as well) and their is a smaller one (and an even smaller one in development)

dave

Beautiful looking cabinets!
 
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I'm crossing a lot lower, at 1700Hz.

2" now.

On a side note, I wonder why the CTC of 1/4 wavelength at crossover frequency is emphasized.

It is the frequency at which the drivers appear coincident (ref Danley). That allows a 1st order XO to essentially give phase coherent behaviour and lobing disappears.

For most builds it is physically impossible to do.

That is why all my XOs tend to be <400 Hz.

I don't know of any other way to achieve CTC that's 1/4'' wavelength with any driver combination without modifying the drivers themselves.

We have achieved it in a number of builds. That and simple XOs get rid of most of the evil inherent in XOs.

What did you do to treat the drivers?

I have been treating drivers to improve their performance since the late 70s. EnABL really jumped things up a notch.

Middle of this page has a generic discription of the treatment. planet_10 hifi | drivers

How does it compare to the 10F for midrange duty?

I don't know. We only use them as mid-tweeters. I do have customers who very happily use them as mids.

I don't think I'll be ditching the tweeter, I need the off axis response.

I'm not a big fan of dome tweeters… partially because you have to XO them so high and partially because something just sounds off. I would not write off the dispertion of the little FRs… the ¾" dustcaps go a long ways to keeping the off-axis good. Getting rid of that XO has big positive benefits.

Beautiful looking cabinets!

Most of the uFonkenSET pictured are by Bernie in solid wood… as well as sounding really good they are art-pieces.

dave