Having discovered that my Home Theatre Processor isn't very good at re-routing LFE to to my main speakers (if at all), I've decided I need a sub of sorts.
My mains are floorstanding transmission line's and their bass response is pretty flat down to about 80Hz, and they still keep going down to 25Hz, albeit quietly (see graph below).
I have 2 spare 12 inch HT300G0 Audax sub drivers that have been sitting in the loft for years, and a couple of spare monoblocs I can use to power them.
My first idea was the set the processor to to output purely LFE below about 80Hz to the sub channel. Then as the sound was to be more for 'effects' than for actual sub bass, I was thinking of mounting a sub driver within each of my sofa's, underneath. There is enough clearance, and my idea was to basically screw a 3ft x 3ft sheet of 18mm MDF to the sofa's frame, cut out a 12 inch hole, and mount the driver pointing downwards. Then I'd just connect up the monoblock and I've got a free-air LFE generating sofa!
But then as always seems to happen, my ideas start developing. Unsatisfied with the potential effort vs. result, I looked into building a proper box.
A sealed box doesn't go low enough.
A vented box has to be very large at 191 litres but produces the deepest bass - flat down to around 30Hz.
A 4th order bandpass is still large at 138 litres, but seems to produce a perfect roll off right at the point where my main speakers start to come alive. However, this box is only flat down to around 40Hz (10Hz higher than a vented box).
Which one do you think is best... And why?
(Pls ignore the white traces)
My mains are floorstanding transmission line's and their bass response is pretty flat down to about 80Hz, and they still keep going down to 25Hz, albeit quietly (see graph below).
I have 2 spare 12 inch HT300G0 Audax sub drivers that have been sitting in the loft for years, and a couple of spare monoblocs I can use to power them.
My first idea was the set the processor to to output purely LFE below about 80Hz to the sub channel. Then as the sound was to be more for 'effects' than for actual sub bass, I was thinking of mounting a sub driver within each of my sofa's, underneath. There is enough clearance, and my idea was to basically screw a 3ft x 3ft sheet of 18mm MDF to the sofa's frame, cut out a 12 inch hole, and mount the driver pointing downwards. Then I'd just connect up the monoblock and I've got a free-air LFE generating sofa!
But then as always seems to happen, my ideas start developing. Unsatisfied with the potential effort vs. result, I looked into building a proper box.
A sealed box doesn't go low enough.
A vented box has to be very large at 191 litres but produces the deepest bass - flat down to around 30Hz.
A 4th order bandpass is still large at 138 litres, but seems to produce a perfect roll off right at the point where my main speakers start to come alive. However, this box is only flat down to around 40Hz (10Hz higher than a vented box).
Which one do you think is best... And why?
(Pls ignore the white traces)
You can adjust alignment with the bandpass, which I'm assuming you've adjusted here.
Vented alignments in subs are so 1995! Passive radiators work better with modern, lower efficiency subs in realistic boxes. If I were you and wanted reasonable box sizes and had a solid budget, I'd probably build a couple of these:
Creative Sound - Product Details
Probably fair to disclose- I've been using CSS stuff for some years and have a light professional relationship, but that's driven by his excellent products. Trios with passive radiators are what I use.
Vented alignments in subs are so 1995! Passive radiators work better with modern, lower efficiency subs in realistic boxes. If I were you and wanted reasonable box sizes and had a solid budget, I'd probably build a couple of these:
Creative Sound - Product Details
Probably fair to disclose- I've been using CSS stuff for some years and have a light professional relationship, but that's driven by his excellent products. Trios with passive radiators are what I use.
Hi,
You should be able to rely on the LFE output rolling off around 80Hz,
so I can't see any real advantage to the bandpass arrangement.
specs are here : http://www.cadaudio.dk/ht300g0.pdf
For subs they are high efficiency, 91dB/W/1m, 94dB/2.83V/1m.
With a high Qts fro vented you end up with boxes a lot bigger than Vas.
something like 120L tuned to 28Hz looks about right to me. Another
option is to fit passive line level low bass boost at the end of the
monobloc leads and use around 60L sealed with low bass boost.
(Or mod the monoblocs feedback loop for a peaking high pass,
say Q=2 (+6dB) at 30Hz for near the same response as vented.)
Vented will go louder at 30Hz than sealed though.
Whilst your sofa's will reperesent a very lossy cabinet, what sort
sort of volume ? Vented still just might work in some fashion.
rgds, sreten.
You should be able to rely on the LFE output rolling off around 80Hz,
so I can't see any real advantage to the bandpass arrangement.
specs are here : http://www.cadaudio.dk/ht300g0.pdf
For subs they are high efficiency, 91dB/W/1m, 94dB/2.83V/1m.
With a high Qts fro vented you end up with boxes a lot bigger than Vas.
something like 120L tuned to 28Hz looks about right to me. Another
option is to fit passive line level low bass boost at the end of the
monobloc leads and use around 60L sealed with low bass boost.
(Or mod the monoblocs feedback loop for a peaking high pass,
say Q=2 (+6dB) at 30Hz for near the same response as vented.)
Vented will go louder at 30Hz than sealed though.
Whilst your sofa's will reperesent a very lossy cabinet, what sort
sort of volume ? Vented still just might work in some fashion.
rgds, sreten.
By the late 1960s passive radiators were in use, while by that time bass reflex was fairly well understood and had been in use for many, many decades, I don’t get the 1995 reference.
A PR occupies less physical space than a large port needed to tune low, but a
BR still provides more output per $$ than PR , has better transient response, how do you define “work better”?
Attachments
I'd go for the big box, but power is nearly free so you could also choose an alignment that lends itself to equalization and correct it electronically. That's what they did with the old Swan project in Speaker Builder, and it's also the idea behind the Bassis(tm) that Marchand sells.
subwoofer equalizer, bass correction equalizer, bass boost
subwoofer equalizer, bass correction equalizer, bass boost
@ judderod
Hi, your 4th order bandpass looks fine on paper, but you will need a LP filter @ the higher Xover f to filter out any garbage. Plus in reality with that in place, that nice looking roll off point @ 80Hz will be affected by the LPF.
Similar to sreten's 120L tuned to 28Hz design, i did this one 150L fb = 30Hz -1db @ 30Hz
Max Power is limited to 118W @ 43Hz
Ave Max SPL = 113dB
Hi, your 4th order bandpass looks fine on paper, but you will need a LP filter @ the higher Xover f to filter out any garbage. Plus in reality with that in place, that nice looking roll off point @ 80Hz will be affected by the LPF.
Similar to sreten's 120L tuned to 28Hz design, i did this one 150L fb = 30Hz -1db @ 30Hz
Max Power is limited to 118W @ 43Hz
Ave Max SPL = 113dB
Well, the '95 thing was kidding around, guess you're immune to my verbal charms
PRs are far more practical in the smaller boxes favored by most current, high Xmax subs. Additionally, they don't have port resonance issues that ports can have, and ports at subwoofer frequencies are often necessarily compromised in terms of cross sectional area by the limited length available. This means that you can often get more output from a PR vs. a vented alignment with a port that had to be undersized to make length manageable.
This is, as I say, particularly an issue with the lower Vas subs that most of us are using in smaller boxes. The more widespread acceptance of multisub setups makes box size more of an issue than ever before, meaning the balance is shifted towards PRs.
The subs I use, for example, use the creative sound trio 12 with an AE speakers 15" passive. To get the same tuning, a 4 ft long 4" dia port would be required- not only impossible to fit in realistic boxes, it'll have significantly less output available before bad port compression and chuffing. More port area? Sure, we'll go to a 10ft long 6" vent!
With higher Vas subs, in 6-8 ft boxes, the balance changes and you have to evaluate each in standalone.
Your Trio 12 has more than double the Xmax and an Fs almost an octave lower than the OP’s Ht300g0 . PR make sense for a super low Fb as you may like with your Trio 12, where a proper vent would be as large as the cabinet, but little sense (cost or SQ wise) for the OPs speaker.Well, the '95 thing was kidding around, guess you're immune to my verbal charms
PRs are far more practical in the smaller boxes favored by most current, high Xmax subs. Additionally, they don't have port resonance issues that ports can have, and ports at subwoofer frequencies are often necessarily compromised in terms of cross sectional area by the limited length available. This means that you can often get more output from a PR vs. a vented alignment with a port that had to be undersized to make length manageable.
This is, as I say, particularly an issue with the lower Vas subs that most of us are using in smaller boxes. The more widespread acceptance of multisub setups makes box size more of an issue than ever before, meaning the balance is shifted towards PRs.
The subs I use, for example, use the creative sound trio 12 with an AE speakers 15" passive. To get the same tuning, a 4 ft long 4" dia port would be required- not only impossible to fit in realistic boxes, it'll have significantly less output available before bad port compression and chuffing. More port area? Sure, we'll go to a 10ft long 6" vent!
With higher Vas subs, in 6-8 ft boxes, the balance changes and you have to evaluate each in standalone.
As it is, the OP’s sim requires such a large box because the Fb at 30 Hz is already too low for the speakers he has, the big box will exceed Xmax at low power.
Even with that 30 Hz tuning however, a decent size port won’t require anything like the port lengths you describe.
Audax Ht300g0 12"
Le: 1.63 mH
Re: 3.2 ohms
Fs: 36.8 Hz
Vas: 2.75 cu. ft.(78 liter)
Qms: 10.39
Qes: .56
Qts: .53
Xmax: 8mm.
CSS TRIO12
Le: 1.63 mH
Re: 3.2 ohms
Fs: 22Hz
Vas: 97 liter
Qms: 6.4
Qes: .46
Qts: .43
Xmax: 20mm.
Your suggestion of PR make sense for your application, not much for the OPs, regardless of the decade
.Art
I'm glad I asked - this forum really is a great place to share thoughts
Thanks for all the advice, and the difference of opinion!
@ sreten
Some interesting ideas there. I've used winISD to come up with the graphs and suggested box volumes. Using a smaller box like you say would be much more practical, but how would I tune it to a certain frequency? I don't see any option to do that in winISD so I guess I need something else.
The other option of using a passive bass boost (I guess this means a HF attentuator?) is a good one, but wouldn't I need a scope and perhaps an SPL meter to tune this properly? (Neither of which I have)
I do like the idea of being able to boost the LF and use a smaller box. But it sounds like I'll quickly get out of my depth. I have no idea how I'd upgrade my monobloc's feedback loop, or even if it has one - they're AB solid state I think.
@ bjorno
The sofa is a 3 seater, and there's a large void that runs up the back, so there's a decent volume in there. However the wooden lining is about 3mm thick so it will resonate like crazy! I thought I could stick some tar sheets/sound deadening to the inside if necessary.
That image you posted looks interesting but is too small to see - have you got a link?
@ Conrad
That's out of my depth, sorry...
@ Zero
Would I definitely need a filter, given that the processor should only be sending LFE signals to the monobloc/s? I was hoping to avoid any additional complications like crossovers, phase, alignment and all those other things I don't fully understand!
Thanks a lot for the graphs. They definitely look feasable. I could make a long flat box that would fit completely under one of the sofa's, and would go up into the lower void slightly. So it would be completely concealed. How much space I've got under there and if I could actually hit 120-150L I don't know yet.
@ weltersys
My thoughts entirely. Thanks.
---
So I think we can agree there isn't really much point going to the extra effort to build a 4th order bandpass.
I'll take a picture of the underside of the sofa tomorrow and post it so hopefully we can decide between gutting out the sofa's void so a ported box can be housed underneath, or just bolting up some wood and a woofer for smiles all round
Thanks for all the advice, and the difference of opinion!
Unfortunately my budget will currently stretch as far as screws, wood, cups of tea and a Sunday afternoon or 2. The real money is being spent on a centre speaker upgrade and a projector, hence I'm trying to make do with loft clutter for the sub idea.
@ sreten
Some interesting ideas there. I've used winISD to come up with the graphs and suggested box volumes. Using a smaller box like you say would be much more practical, but how would I tune it to a certain frequency? I don't see any option to do that in winISD so I guess I need something else.
The other option of using a passive bass boost (I guess this means a HF attentuator?) is a good one, but wouldn't I need a scope and perhaps an SPL meter to tune this properly? (Neither of which I have)
I do like the idea of being able to boost the LF and use a smaller box. But it sounds like I'll quickly get out of my depth. I have no idea how I'd upgrade my monobloc's feedback loop, or even if it has one - they're AB solid state I think.
@ bjorno
The sofa is a 3 seater, and there's a large void that runs up the back, so there's a decent volume in there. However the wooden lining is about 3mm thick so it will resonate like crazy! I thought I could stick some tar sheets/sound deadening to the inside if necessary.
That image you posted looks interesting but is too small to see - have you got a link?
@ Conrad
That's out of my depth, sorry...
@ Zero
Would I definitely need a filter, given that the processor should only be sending LFE signals to the monobloc/s? I was hoping to avoid any additional complications like crossovers, phase, alignment and all those other things I don't fully understand!
Thanks a lot for the graphs. They definitely look feasable. I could make a long flat box that would fit completely under one of the sofa's, and would go up into the lower void slightly. So it would be completely concealed. How much space I've got under there and if I could actually hit 120-150L I don't know yet.
@ weltersys
My thoughts entirely. Thanks.
---
So I think we can agree there isn't really much point going to the extra effort to build a 4th order bandpass.
I'll take a picture of the underside of the sofa tomorrow and post it so hopefully we can decide between gutting out the sofa's void so a ported box can be housed underneath, or just bolting up some wood and a woofer for smiles all round
Hi,
You just change the frequency in the tuning frequency box, the
vent length is recalculated for the default / chosen diameter.
rgds, sreten.
Your suggestion of PR make sense for your application, not much for the OPs, regardless of the decade
Art
Somehow I missed that he already had the woofers.
My PR comments were specific to modern low fs, low Vas subs. As most of us know, higher Xmax tends to drive down sensitivity and Vas and Fs due to the contstraints of building drivers (longer heavier coil)
I'd had a play with changing the tuning frequency, but I'm not entirely sure what I'm aiming for. Is the frequency the resonance of the enclosure?
Is it just a case of fiddling with the frequency and volume until the graph has a nice slope?
@ bjorno I guess those pictures are just for looking nice... 374 thousand watts?!!
On to some pictures...
Underside
Centre section
Left lower void
Up the back
Back (angled)
Looking at these pictures there's a huge volume inside the sofa. Only trouble is some walls are very flimsy, and some walls are just the sofa's foam. No way to calculate anything I guess. How about a big thick sheet that seals off the entire bottom section with the driver in the middle?
Is it just a case of fiddling with the frequency and volume until the graph has a nice slope?
@ bjorno I guess those pictures are just for looking nice... 374 thousand watts?!!
On to some pictures...
Underside
Centre section
Left lower void
Up the back
Back (angled)
Looking at these pictures there's a huge volume inside the sofa. Only trouble is some walls are very flimsy, and some walls are just the sofa's foam. No way to calculate anything I guess. How about a big thick sheet that seals off the entire bottom section with the driver in the middle?
Play with box volume and available space, choose a size that can be built under your couch, then experiment with tunings.
Box tuning is Fb (Frequency of box), or box resonance.
The resonant frequency of the driver is Fc.
An Fb below Fc will have less output compared to one above in a given size box.
Too high an Fb in a small box, and the box will “boom” (a bump) at Fb.
Too low an Fb, and the response will look more like a sealed box.
You need to juggle box size, Fb, output level and excursion to see what the best compromise for your musical taste, available acceptable size, and your driver's parameters are.
Since you have decided against EQ, "a nice slope" would be a flat response.
Art
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IME, If a T-TQWT is built,measured and compared with the HR graphs: Difference's would be near negligible.
I only read 37.5 W at 24 Hz.
, You need to build at least 10000 T-TQWT's to withstand that power.b
Sorry Bjorno I thought you were being silly! I get it now. Thanks for the info.
And thanks for the help Art. I worked with the firgures but couldn't get the frequencies low enough. The room I'm working with seems to have a resonance peak at around 43Hz, and if I was going to the effort to build a proper sub, I'd want it to be fairly flat down to about 20Hz as I can easily hear that low. But it's not possible with the driver I have and the space I've got to work with.
So I went for the sofa sub. http://www.diyaudio.com/forums/subwoofers/202787-lfe-sofa.html
Enjoy
And thanks for the help Art. I worked with the firgures but couldn't get the frequencies low enough. The room I'm working with seems to have a resonance peak at around 43Hz, and if I was going to the effort to build a proper sub, I'd want it to be fairly flat down to about 20Hz as I can easily hear that low. But it's not possible with the driver I have and the space I've got to work with.
So I went for the sofa sub. http://www.diyaudio.com/forums/subwoofers/202787-lfe-sofa.html
Enjoy
Hi,
Good idea..LFE-sofa...Why?...IMO,The submitted picture talks for itself:
b
How can the distance between S3 & S4 be less than 1/2 the diameter of the speaker?
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