Designing Open Baffle speakers...

[Sumanta]

@ Sumanta
I do not have the skills to design a tapered TL line and all my designs in TL has been straight line. Also i do not follow the classic TL design approach where the driver is tuned to the resonance freq. I tune it much higher than resonance. This keeps my line shorter but thicker due to increased cross-section area. Also there need not be any off-set required in this design.
If you have the 12 FRX driver, i would suggest you the measure the Fs, Qts and Vas of the drivers before I design and publish as in my experience the published and measured values vary from 5% to 15% depending totally on your luck. I will post one design based on the published parameters for the discussion today for the 12 FRX.

A quick calculation gave me the following dimensions with the published parameters for the 12 FRX

H = 36", W = 21", D = 21". Cross-section area = 390 sq.inches. Terminus preferably at the bottom - hence needs stands for escape of LF. Tuned at 80Hz.
Will need to add 7KG of polyfill stuffing for the odd harmonics with damping coefficient of 1.89 pounds/cubic feet.

Since Vas of this driver is very high (105 Liters) it will give too high, punchy and deep bass which could shake everything in the room. Recommended for outdoor use or may be OB loading.

Cheers,

Superb Hari!
Thank you so much!
Now other can use these dimensions and make their own big boy TL speakers. thanks again.
As you already know I go more with my ears than with measurements and I do not own measurement instruments either.
There is another driver of Ahuja which is a 12 incher and having double power handling capability. I think that will be even better performer.

I will make a TL if such a situation comes in future.

I have a special liking on Ahujas you know.

Hi, sorry to highjack the thread, but i have a similar requirement.

I'm using a pair of philips HiQ speakers in an open back (not sure if this is the right term - It's a stock Sony Cabinet with a perforated back covered using some sort of felt)

the sound quality is amazing, but there is nothing below 100 Hz. I'm not planning to squeeze anything out of it using any TL or eq, but rather, try to build a woofer that can take care of the lows (<100 hz)

Looking for cheap high sensitivity woofer, I came across the Pioneer TS W304R & the ahuja L12 MB200. What sort of enclosure would be advisable? I was interested in something like an H baffle, but due to space constraints, I would need to keep them pretty close to a wall, plus am not sure how/where to design an H baffle.
a vented box is the backup plan (both drivers have recommended vented box plans) but any advice on choice & design for an open enclosure would be appreciated
Thanks!

Hi,
If you can not place your speaker(s) 3' away from the front (listener's) wall, then even your mid and high will not give you the required imaging, rest assured the lows too.

If you can, then you probably can make a Ripole (folded baffle) design that I am happy with. It is compact (that is one of the key reason for my selection of this design. You can also choose to use a combination of slot loaded open baffle design and Ripole design which I feel is even better to have best of both designs. Means, having the benefit of decreased value of Fs of driver as well as increased SPL on the front end of the driver.

Make sure SPL of the low frequency driver is around 10dB higher than the mid & high drivers reproduction level SPL.

 

[greenhorn]

Hi,
If you can not place your speaker(s) 3' away from the front (listener's) wall, then even your mid and high will not give you the required imaging, rest assured the lows too.

Imaging is not critical, but the lows are important - I'm thinking of going for a U frame instead of an H frame

If you can, then you probably can make a Ripole (folded baffle) design that I am happy with. It is compact (that is one of the key reason for my selection of this design. You can also choose to use a combination of slot loaded open baffle design and Ripole design which I feel is even better to have best of both designs. Means, having the benefit of decreased value of Fs of driver as well as increased SPL on the front end of the driver.
Make sure SPL of the low frequency driver is around 10dB higher than the mid & high drivers reproduction level SPL.

the philips are already at 93db. I am not sure i can get 103dB subs + the enclosure at my budget (<10K for the whole setup) - I think at this point i might as well give up and go for an active sub

 

[Sumanta]

Imaging is not critical, but the lows are important - I'm thinking of going for a U frame instead of an H frame



the philips are already at 93db. I am not sure i can get 103dB subs + the enclosure at my budget (<10K for the whole setup) - I think at this point i might as well give up and go for an active sub

I have that same Philips driver for my OB set up, the lows are produced by Ahuja AS 15 drivers.

I attain required benefit of SPL by having active system only. I achieved that with separate amps for separate frequency ranges.

I am waiting (for long now) for a good active cross over (DIY) to make it work better.

It worked best when I played with true active by having Pc-foobar-DSP-amplifiers-speakers.

 

[soundnovice]

Imaging is not critical, but the lows are important - I'm thinking of going for a U frame instead of an H frame



the philips are already at 93db. I am not sure i can get 103dB subs + the enclosure at my budget (<10K for the whole setup) - I think at this point i might as well give up and go for an active sub

imaging is not critical!!!???
the whole point of having open baffle speakers is open, imaging, soundstage etc. flat response you can get with closed or even ported boxes also. however you can say 'pinpoint imaging is not critical'!!

your listening levels can not be 93dB! in a normal room usually it never crosses 85db. having active setup would be helpful as sumanta suggested. playing with volume knobs until you are satisfied with the sound.

 

[greenhorn]

I liked OB because of the non boxy sound, I'm not a big imaging fan - I usually drop the needle and roam around the room listening to it, so imaging is a bit pointless.

By 93dB i meant sensitivity - the full rangers are 93db/1W@1M. getting a sub driver with 100+db efficiency is tough - as it would be needed if i was planning to hook them up passively , not that i was planning to play it at those levels

so yes, active is the way to go.

 

[Sumanta]

imaging is not critical!!!???
the whole point of having open baffle speakers is open, imaging, soundstage etc. flat response you can get with closed or even ported boxes also. however you can say 'pinpoint imaging is not critical'!!

No, I realize, the primary point to me now also is to get non boxy and natural(ish) sound. And many stereo recordings do not have quite a wide spread zone system imaging at all anyway.

Bonuses are of-course imaging, less room interaction (room treatment gets level level of importance), low cost of making and many other things.

Listening more records than CDs at home anyhow enable me to enjoy non pixelated smooth analogue imaging of the system as a whole.

Records now complement OBs.

 

[soundnovice]

later you will like OB/dipoles for imaging also. most of these aspects you will get anyway in an OB speaker.
as Sumanta mentioned, and as many of the experts including SL, recommend min.3 feet distance from rear wall. this is min. space required for 'breathing'. what would happen if not maintained can only be found by trying it out.

 

[greenhorn]

I have that same Philips driver for my OB set up, the lows are produced by Ahuja AS 15 drivers.

Any reason why you chose the 15" drivers? after comparing, i saw that the 15" have some 3dB more sensitivity than the 12", but adding 2x the power was cheaper than paying 2x for the 15" drivers, especially if you're going active.

I attain required benefit of SPL by having active system only. I achieved that with separate amps for separate frequency ranges.

My philips HiQ are driven by an NAD 3020 at 25x2W RMS, and I was planning to use my SMSL SA 98E (with an upgraded PSU) to send 2x100W to the woofer

I am waiting (for long now) for a good active cross over (DIY) to make it work better.

Eight Audio - Active Sub-Woofer Filter with Phase, Gain & Freq. Adj.

this is what I was planning to use - it has a 55-160Hz range (good enough since the philips do well till around 100hz) these are 2.1 boards, so I was planning to use a pair.

 

[Sumanta]

later you will like OB/dipoles for imaging also. most of these aspects you will get anyway in an OB speaker.
as Sumanta mentioned, and as many of the experts including SL, recommend min.3 feet distance from rear wall. this is min. space required for 'breathing'. what would happen if not maintained can only be found by trying it out.

Human brain can differentiate a sound from the same but delayed one only when it is timed 6 mili second or more delayed. That delay happened between sounds of front and back of a driver when the rear sound travels a total (3 + 3) 6 feet by reflecting from the front wall. Hence that 3 feet distance is necessary.
Plus the reflecting sound reverse its phase at the time of reflection. It helps.

Some brands sell OB confirming that 2 feet is enough but I felt 3' is well worth the compromise.

Any reason why you chose the 15" drivers? after comparing, i saw that the 15" have some 3dB more sensitivity than the 12", but adding 2x the power was cheaper than paying 2x for the 15" drivers, especially if you're going active.

15" isn't double the price, it costs 1800 a piece, only. Plus I control them with separate amplifier, so I have full control over effective SPLs of drivers.

My philips HiQ are driven by an NAD 3020 at 25x2W RMS, and I was planning to use my SMSL SA 98E (with an upgraded PSU) to send 2x100W to the woofer

Have two amps so have full control.

Eight Audio - Active Sub-Woofer Filter with Phase, Gain & Freq. Adj.

this is what I was planning to use - it has a 55-160Hz range (good enough since the philips do well till around 100hz) these are 2.1 boards, so I was planning to use a pair.

Thank you! How you are planning to send signals to individual amplifiers. Where the separations will happen?
Plus I want 24 dB/octave slope. My earlier active setup confirmed it as the best @ 180~200 Hz range.

Edited to add last sentence of the last paragraph.

 

[greenhorn]

15" isn't double the price, it costs 1800 a piece, only. Plus I control them with separate amplifier, so I have full control over effective SPLs of drivers.

oh! the prices online are very different - I should check out prices in ritchie as well.

Thank you! How you are planning to send signals to individual amplifiers. Where the separations will happen?

I'm in the process of building a CNC phono preamp. the output of that will go to these filter boards, each running as mono for each channel
regardless, I have two plans for running the setup

1 - I'm not sure about the quality of the network, so was thinking I'd send the low passed signal to the amp driving the woofers, and send the full range signal the amp driving the hiq, but put a passive first order crossover (cap in series) to limit the lows

OR

2 - the 2 boards split the channel to high passed and low passed signals, and the HPF L&R go to the NAD, and the LPF L&R go to the T amp

 

[soundnovice]

Any reason why you chose the 15" drivers? after comparing, i saw that the 15" have some 3dB more sensitivity than the 12", but adding 2x the power was cheaper than paying 2x for the 15" drivers, especially if you're going active.

My philips HiQ are driven by an NAD 3020 at 25x2W RMS, and I was planning to use my SMSL SA 98E (with an upgraded PSU) to send 2x100W to the woofer


Eight Audio - Active Sub-Woofer Filter with Phase, Gain & Freq. Adj.

this is what I was planning to use - it has a 55-160Hz range (good enough since the philips do well till around 100hz) these are 2.1 boards, so I was planning to use a pair.

SMSL is class D amp designed for easier loads (like fullrange speakers or small bookshelf speakers). PA drivers need more current. class AB amp would help here. clean 100W class AB can work. more is better. also this depends on how low you want to go with these woofers. for reproducing frequencies below 40hz or so, more power is necessary to maintain proper headroom. SMSL 100W amp can do better upto say 60-70hz without going into distortion but not below that. below that you need more power, especially for OB speakers.

more than price or sensitivity factors, bigger woofers are preferred because they have bigger cone area and can move more air than smaller ones. they can produce lows without the need for reaching their xmax limit and hence with low distortion. a 6.5" subwoofer can also produce 20hz (assuming it has very high xmax capability like tangband one) but due to excessive cone movement distortion will be introduced. in other words, bass sounds muddy, slow or booms a lot. with bigger woofers, bass would sound 'effortless' which is good for music.

 

[greenhorn]

SMSL is class D amp designed for easier loads (like fullrange speakers or small bookshelf speakers). PA drivers need more current. class AB amp would help here. clean 100W class AB can work. more is better. also this depends on how low you want to go with these woofers. for reproducing frequencies below 40hz or so, more power is necessary to maintain proper headroom. SMSL 100W amp can do better upto say 60-70hz without going into distortion but not below that. below that you need more power, especially for OB speakers.

the datasheet for the TDA 7498E shows distortion is flat down to 20hz, and shows it capable of delivering 130WPC into 4 ohms @ 1% THD. I'm planning to upgrade the stock 5.7A PSU with a 10A unit which should help with the power.

I'm not planning to add a linkwitz transform or any other eq yet to get a flat to 20 response - and honestly since I'll be using this with my TT, i dont think i want it to go that low or loud, since it is already prone to acoustic feedback when I used it with my logitech Z2300

 

[goldyrathore]

15" isn't double the price, it costs 1800 a piece, only.

Which is this driver? make/model pls?

 

[Sumanta]

Which is this driver? make/model pls?

Ahuja Sound Solutions

I paid 1800 per piece in Baroda on 2012. Hope it helps.

 

[sureshkn]

This driver has quite low Qts and Spl for so called perceptional behaviour of any OB. But I think you can give it a try by an easy way.

1) Tell someone to hold it with bunch of news papers or any hard board folded like a cylinder on the back of the driver. Use one only. Listen to 3 major frequency ranges like 50 to 150, 500 to 2500 and 8000 to 18000 by playing some instrument or other sources (computer with internet comes handy). Then play some good vocal sources that you are very familiar with (in terms of your expectations).
I do not expect you be able to have a cylinder any longer than 1 foot.
If it sounds even 30% to your expected liking, you IMO should be happy with a OB design. If that driver is good at highs, fine, or else you can add a simple tweeter with a capacitor.
I think you can follow Jaudere's design by having non-parallel sides of your baffle to support LFs as a final design. Or else you can simply add LF drivers of Ahuja, Considering small size of your driver, it will give a good look to the LF cabinet by having a Ripole shape. We can talk about that later.



We definitely can make a TL with 12 FRX driver of Ahuja, but its size will be huge. If it is okay with you Hari, please share a preliminary dimension of the cabinet considering 45 Hz and a tapered line. ATL will be even longer and wider if I am not wrong.

Sumanta,
Last weekend I setup the driver again and did the testing as you have mentioned. I did not play any specific frequency range, instead played my favourite songs, and instrumentals. First I played in my usual speakers and then on the MarkAudio.

MarkAudio has good Highs and mid. But clearly lacked the LFs. I am not sure of the reason. The drivers ran only < 100hrs. So, probably not broken fully. And I used a haphazard way of connecting using crocodile clips. I liked the sound. Lack of LFs is not a main concern. Probably I will go with OB with just MarkAudio. And if required later add Ahuja. Please give your opinion.

Regards,
Suresh.

 

[saikatbiswas82]

@suresh,

What are your plans for xover? Are you going for bi-amping? Are there any plans for introducing any dsp in between?

 

[sureshkn]

Hi Saikat,
I don't want to add a crossover. If Sumanta can provide the dimensions then I will get help from local carpeter to make it and will directly connect to poweramp.

Regards,
Suresh.

 

[saikatbiswas82]

Hi Saikat,
I don't want to add a crossover. If Sumanta can provide the dimensions then I will get help from local carpeter to make it and will directly connect to poweramp.

Regards,
Suresh.

So I think you are going for single driver (ma alpair 10) ob design then. Correct me if I am wrong.

 

[sureshkn]

Yes, single driver only. I have a pair of Markaudio Alpair-10M Gold 6" Full Range Gen 3.

 

[Sumanta]

Hi Saikat,
I don't want to add a crossover. If Sumanta can provide the dimensions then I will get help from local carpeter to make it and will directly connect to poweramp.

Regards,
Suresh.

I definitely can, lot many design are floating in my head.
If you want to learn more, want to get more and more out of your learning and trials, I suggest you read (if not already) papers of Martin j King and Linkwitz on OB.

If you want to make it once only and enjoy it for long, it will be a bit risky for me, but I will still give you a drawing to make one.

If first one is your choice, which I prefer, we will be walking along on a wonderful journey together. My interest here is to try things that I can't try (room is already full with one set).

Please share other links of your music system. If it is an active way now or going to be, I will be even more happier.