FRS 8 M enclosure type for small home theatre - diyAudio
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Old 29th March 2008, 08:30 PM   #1
lithoc is offline lithoc  Malaysia
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Default FRS 8 M enclosure type for small home theatre

Hi,

I have few Visaton FRS 8 M and trying to build a speaker enclosure for this speaker.

Since this driver have good power handling. I'm trying to build this speaker as a small home theater system that cross at 100hz or 150hz.

Here's my problem, I couldn't decide which enclosure to use.
My aim to get more bass out of this small driver on 100hz - 200hz region without speaker over-excursion or burn the voice coil.

My choice:-

1.) Normal bass reflex tune to 120hz(almost same as Fs)
I've read somewhere that vented port tuning frequency equal to speaker free air resonant. It will lower excursion on the speaker and better power handling.

2.) Double basss reflex
I've found FRS 8 M specs are close to Fostex FE83E.
There're some double bass enclosure design.

3.) MLTL - I heard very good review for this design but not really suitable since it's cross at >100hz.

4.) Back Loaded Horn - Again most of the design I found are tuned to lower frequency. But I'm sure this can be tune to higher frequency

5.) Onken design such as Solo 103


Any help is much appreciated.
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Old 30th March 2008, 01:08 PM   #2
hm is offline hm  Europe
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Hello,

look my TROMBONE with two FRS8M, down to 35 Hz.
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Old 30th March 2008, 04:50 PM   #3
GM is online now GM  United States
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This drivers starts running out of Xmax at rated power around 500 Hz, so it will take a horn to get it to the DD/DTS reference 80 Hz XO point. That, or eight of them/channel in ~14.36 L (net) tuned to ~103 Hz just to get to a typical average HT listening level.

GM
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Old 30th March 2008, 04:54 PM   #4
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What about a transmission line? Or is the only option a horn to get to ▒100Hz?
At 8W you get 94dB output per driver, that's why I thought it could do with a TL.

Bart.
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Old 30th March 2008, 05:56 PM   #5
GM is online now GM  United States
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Hmm, the spec sheet says it has a 0.5 mm Xmax, so tuned to ~103 Hz it runs out around 85 dB a half octave up with 8 W and only an undamped TL would give you any real gain, but then its 'ripple' will highly 'color' its mids/HF, so not an option based on its specs since once damped it will have little gain over a sealed box of similar volume (Vb). Not being familiar with the driver I don't know at what excursion it becomes objectionably distorted, but I imagine it's still pretty low since it only has a 5 mm Xmech (hits the backing plate).

Regardless, movies are mixed with 20 dB of dynamic headroom for all but the LFE channel, so add this to whatever average SPL/channel you plan to use to see what the speakers have to be able to reproduce at low distortion.

WRT average SPLs, cinema releases are mixed using the DD/DTS reference of 85 dBC/channel at the listening position using pink noise while made-for-TV movies are spec'd at 79-82 dBC since most folks tend to watch TV at 70-75 dBC. Note that these specs are for USA releases, I don't have a clue if they are universal.

GM
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Old 30th March 2008, 06:50 PM   #6
lithoc is offline lithoc  Malaysia
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Quote:
Originally posted by GM
This drivers starts running out of Xmax at rated power around 500 Hz, so it will take a horn to get it to the DD/DTS reference 80 Hz XO point. That, or eight of them/channel in ~14.36 L (net) tuned to ~103 Hz just to get to a typical average HT listening level.

GM
This is a challenging but fun experiment for me to learn something new.
That's reason it's hard for me to choose a enclosure knowing that small speaker will have over excursion and limited power handling problem.

Interesting articles:-
http://www.zaphaudio.com/audio-speaker18.html

After much googling for few days, my options is down to horn or fonken type enclosure.

I need some back pressure to reduce excursion which fonken is good at but afraid not enough bass for home theater.
Horn have more bass but will cause over excursion easily.

For Horn, reference will be,
http://www.fostexinternational.com/d...pdf/fe126e.pdf
It's tune for 100hz!! but will need to close the port.

For Fonken, reference will be solo 103.
http://www.humblehomemadehifi.com/Solo103.html

I need expert advise on how to tune the box for FRS8M.

Thanks in advance
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Old 30th March 2008, 06:50 PM   #7
Henkjan is offline Henkjan  Netherlands
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I would seriously consider a classic for this driver, either the Needle (also as center) or the Busshorn. and for HT cross them at 150Hz (yes, both designs will go a lot deeper but for HT you need all the dynamics you can get and crossing here will allow for a good transition to the woofer)
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Old 30th March 2008, 06:56 PM   #8
lithoc is offline lithoc  Malaysia
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Quote:
Originally posted by GM
Hmm, the spec sheet says it has a 0.5 mm Xmax, so tuned to ~103 Hz it runs out around 85 dB a half octave up with 8 W and only an undamped TL would give you any real gain, but then its 'ripple' will highly 'color' its mids/HF, so not an option based on its specs since once damped it will have little gain over a sealed box of similar volume (Vb). Not being familiar with the driver I don't know at what excursion it becomes objectionably distorted, but I imagine it's still pretty low since it only has a 5 mm Xmech (hits the backing plate).

GM
Thanks for the fast response. Interesting figure.
Right now, I'm using a buschhorn enclosure for stereo listening. I do not have any measuring tools but I would say the volume from this speaker really sufficient for music.
For movies dynamics, may be I can adjust the DRC or midnight listening mode to protect from damage. Since our comfortable listening SPL is around +/-90db.
If XO at 100hz or 150hz, I think this little driver can be really loud but again no measuring tool.

Well let just build the horn(fe126e minus the port) and let the fun begin.


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Old 30th March 2008, 09:21 PM   #9
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Hello,
FRS8M
the real useful Xmax is 1 mm,
if you want to take a sub you can use a very small bookshelf horn
like my FLUTE-Sat, down to 100 Hz
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Old 30th March 2008, 09:24 PM   #10
GM is online now GM  United States
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Quote:
Originally posted by lithoc

Well let just build the horn(fe126e minus the port) and let the fun begin.
Deleting the port doesn't seem like a good idea to me since it helps reduce the big 3rd harmonic dip it will otherwise have.

GM
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