How to choose correct Drivers for DIY speakers? need advice

[Santy]

All parameters being the same would be an identical driver but I understand your question. Pm me your number and we'll talk.

I would have been more keen to talk had you told that I was grossly incorrect on phone. hyeah: No offence taken.

I did not actually realise that you were talking about a sub, my bad. But the points I made remain as valid, except, you'd need not worry about baffle step.

Honestly, I am not at all disagreeing with what you said because I understood very little about it. I am actually 'baffled' as to where I went wrong.

But let's talk, I'll be happy to address what little I know towards answering any queries you may have.

My query kapvin, is the same as the one I answered to. For a DIYer what makes more sense- to build two smaller subs or one big sub. May be we will start with simpler observations first (which are pretty straight forward)?

Advantages of one 12"
Efficiency is more (power loss is less due to single amp)
Consider a class D 300 W amp has 80% efficiency. Now look at two class D 200 W amps with same efficiency. Which is more efficient?

Goes much deeper
For same class (quality/design) of drivers, I think this law would apply.

Lesser footprint
One sub takes lesser space, than two sub. Strange that you see this too as incorrect.

Advantages of two 8"
Stereo integration is better
I think it is as simple as that. One sub for each channel. Universally agreed I guess.

-Symmetry of your setup (if you place it that way)
This is to with aesthetics. You have one sub near your left speaker and one on right.

Less likely to receive complaints from neighbours
25 Hz frequencies can travel more through your walls and floor than 50 Hz, read rattling

Buy one first and add one more when budget permits
Hope this makes sense.

Disadvantages of two 8"
Doublt the effort (in case of DIY)
I am pretty sure this is true

Bass extension is limited
We replace a 12" driver in an already built sub, with an 8" driver. I am sure we will lose a lot of bottom end.

Placement / setup / configuration might become a headache
Placing one sub is difficult, two...?

Needs a receiver with two preouts (preferably) which is going to be expensive again
Unless you are ok with a Y cable. That works, too. Again, for stereo?

More power drawn
Two amps?

More floor space needed
Two subs, more space, right?

Will touch other points later. Please do correct me if I am wrong already. Specifically! I am learning too..

 

[keith_correa]

5. Placement of speakers in the room also plays important role and cannot be considered in isolation.

Would appreciate if you can explain some more on how to choose drivers based on placement of speakers.

7. Two 8" drivers can cause cancellation between common frequency if both of them emit the same freq. You need to align both the drivers properly in time to prevent cancellation effect.
8. Efficiency of the drivers will be reduced if the cross-over does not level matched to the two 8" driver.

I'm assuming you mean there are 2 different 8" drivers in play here right?

 

[Santy]

7. Two 8" drivers can cause cancellation between common frequency if both of them emit the same freq.

If two similar drivers are used in a speaker, usually they are crossed over at two different slopes. Please correct me if I am wrong. My Energy speakers have two similar bass drivers in each speaker and I can literally hear different frequencies from each and the excursions also vary, confirming my view?

 

[manoj.p]

Santy,

One big advantage of 2 subs instead of one is the room mode cancellations. If you have 4 then even better.

 

[kapvin]

Santy,

am replying in line.

i am no expert myself. but i've been making speakers off and on for some time.

I would have been more keen to talk had you told that I was grossly incorrect on phone. hyeah: No offence taken.



Honestly, I am not at all disagreeing with what you said because I understood very little about it. I am actually 'baffled' as to where I went wrong.




My query kapvin, is the same as the one I answered to. For a DIYer what makes more sense- to build two smaller subs or one big sub. May be we will start with simpler observations first (which are pretty straight forward)?

Advantages of one 12"
Efficiency is more (power loss is less due to single amp)
Consider a class D 300 W amp has 80% efficiency. Now look at two class D 200 W amps with same efficiency. Which is more efficient?


why are you looking at just the efficiency of the amp? lets take the drivers into the equation too.. becuase they are the ones which are transalating the power into sound that you hear.

let us take a typical sub 8"and 12"" which deliver 84db/w @ 1m @ 50hz. now you have one 12"fed by the 300w which gives you 109 db. with 80% efficiency that gives you 109db with 375w of power consumption.

now take your example of 2 8". also 84db and 2 x 200w. each will give 107DB. but because there are 2 and there is accoustic summing.. you will get a 6db boost -113db for 400w of output and 500w of consumption. which is more efficient? reduce the power of the 8"to 150w each --each sub will give you 106db==> 112db with summing. all for 375 watts of consumption

but my point is not to prove you wrong but to say.. as in all cases, it depends.. generally larger drivers are more efficient, which would negate this point/


Goes much deeper
For same class (quality/design) of drivers, I think this law would apply.

not true at all. depends on the parameters of the driver and the enclosure and the alignment. for eg - my new subs (10"seas") will do an f6 of 22hz in 60 llitre box. a 15"will have an f6 in the 30s or 40s.



Lesser footprint
One sub takes lesser space, than two sub. Strange that you see this too as incorrect.

not true. you can stack the subs. also you can design a sub with a low footprint. eventually what matters in most alignments is the volume that the sub sees, and a typical 12"excluding care audio woofers, require more than twice the volume of a typical 8"(again generalising) also. a 12"will need at least 12+ inches in each dimension to fit the baffle. you can manage a narrow baffle 8"sub, right?


Advantages of two 8"
Stereo integration is better
I think it is as simple as that. One sub for each channel. Universally agreed I guess.

i guess.. but again depends on phase matching at crossover. so a badly implemented 2.2 system will sound worse than a well implemented 2.1

-Symmetry of your setup (if you place it that way)
This is to with aesthetics. You have one sub near your left speaker and one on right.

i guess. though having a sub in centre is also symmetric

Less likely to receive complaints from neighbours
25 Hz frequencies can travel more through your walls and floor than 50 Hz, read rattling

but that depends on the subs LF extension and spl, which is not empirically linked to the size ( i hope you agree to that).. so wrong

Buy one first and add one more when budget permits
Hope this makes sense.

of course..

Disadvantages of two 8"
Doublt the effort (in case of DIY)
I am pretty sure this is true

designing one sub and copying that design? surely not double the effort?


Bass extension is limited
We replace a 12" driver in an already built sub, with an 8" driver. I am sure we will lose a lot of bottom end.
sorry if I sould repetitive -- but it depends on which sub is replacing which


Placement / setup / configuration might become a headache
Placing one sub is difficult, two...?

true.. but the end result will also be better with 2 subs, as per you conjecture above.. so you work harder for a better result


Needs a receiver with two preouts (preferably) which is going to be expensive again
Unless you are ok with a Y cable. That works, too. Again, for stereo?

More power drawn
Two amps? answered above. but you also do a dual mono sub poweres by the same amp

More floor space needed
Two subs, more space, right?
answered above
Will touch other points later. Please do correct me if I am wrong already. Specifically! I am learning too..

have fun...

 

[Hari Iyer]

Would appreciate if you can explain some more on how to choose drivers based on placement of speakers.

With two 8" woofer you will need to keep the speakers away from the rear and side walls to prevent boom bass. Same will apply for 12" woofer due to lobing of the low frequency behind the speakers due to diffraction effect. Typically 8" / 12" woofer have resonance from 30Hz to 40 Hz and these frequency will lobe behind the baffle. Hence the speaker has to be placed away from the rear and side walls or add some kind of bass trap.

I'm assuming you mean there are 2 different 8" drivers in play here right?

The values of the components for the filters are decided by the impedance of the driver. Typically you calculate filter values using the driver actual impedance and this decides the cross-over frequency. When you connect 2 drivers in parallel, the impedance of the driver usually do not become half as impedance is a complex function of frequency. The voice coil inductance and resistance also decides the impedance of the speaker. Just connecting 2, 8 ohms speaker in parallel does not mean that you can now design the filter for a 4 ohms load. This affects the sensitivity of the speakers and how the signal is distributed between them. Its better to use a potential divider in the filter rather than directly connecting them in Parallel.

 

[kapvin]

With two 8" woofer you will need to keep the speakers away from the rear and side walls to prevent boom bass. Same will apply for 12" woofer due to lobing of the low frequency behind the speakers due to diffraction effect. Typically 8" / 12" woofer have resonance from 30Hz to 40 Hz and these frequency will lobe behind the baffle. Hence the speaker has to be placed away from the rear and side walls or add some kind of bass trap.



The values of the components for the filters are decided by the impedance of the driver. Typically you calculate filter values using the driver actual impedance and this decides the cross-over frequency. When you connect 2 drivers in parallel, the impedance of the driver usually do not become half as impedance is a complex function of frequency. The voice coil inductance and resistance also decides the impedance of the speaker. Just connecting 2, 8 ohms speaker in parallel does not mean that you can now design the filter for a 4 ohms load. This affects the sensitivity of the speakers and how the signal is distributed between them. Its better to use a potential divider in the filter rather than directly connecting them in Parallel.

?
surely what you are talking about is moving the speaker from half space to quarter space(floor and wall) to 1/8 space (corner). what does that have to do with the resonant frequency of the woofer?

typically when you design a speaker for a room for placement away from walls, putting it next to a wall will cause accentuation due to quarter space loading. but you can design around it, most times.

as a trite example done in less than 5 minutes using a driver that I own.. please refer to the modelled graphs below, same driver, same enclosure, different tuning.

i guess as a speaker builder you'll know what i mean about how each design would behave against a wall or corner...

not sure what you meant by the part on the cross over either but we can discuss it when we meet..

 

[spirovious]

Some HT makes-
Five Channel TriTrix Build
TritrixMT_pg_1
Tritrix_pg_1

 

[Santy]

@kapvin
Yes its fun to read, especially about powering two drivers with same amp and stacking a sub on top of another. But by and large, it appears that for sake of debate some points are refuted.

When I talk about amp's efficiency in terms of power consumed to power delivered; but you are considering the entire unit's acoustic efficiency in terms of SPL. Are they not different topics? Regarding footprints, one of the main reason why people go for two subs is to achieve uniform response across the room by placing it in different places. So stacking does not make much sense. Two subs gain is quite higher - agreed but at the cost of LF extension.

If you are designing a sub with lesser cross sectional area but taller design, the same can be applied to larger drivers as well. Lets compare apples to apples. And also placing the sub at centre is easier said than done, given the fact that placement is always tricky and people tend to find a corner giving maximum performance. Given 25 hz and 40 hz at "same SPL", don't you think the former will cause a bigger impact on the walls and objects? Infact acoustic proofing of lower frequencies need denser and thicker panels. Designing a sub is one task, fabricating it is another. I was talking about physical effort in fabricating two subs. I am sure its painful enough for many.

As you can see, I am not trying to conclude which is better, merely presenting the breakup of possible merits and demerits for interested people to make a choice. Infact since you are more knowledgeable in this domain, I urge you to suggest which is better according to you and why?... in simple terms for the benefit of FMs.

 

[kapvin]

@kapvin
Yes its fun to read, especially about powering two drivers with same amp and stacking a sub on top of another. But by and large, it appears that for sake of debate some points are refuted.

When I talk about amp's efficiency in terms of power consumed to power delivered; but you are considering the entire unit's acoustic efficiency in terms of SPL. Are they not different topics? Regarding footprints, one of the main reason why people go for two subs is to achieve uniform response across the room by placing it in different places. So stacking does not make much sense. Two subs gain is quite higher - agreed but at the cost of LF extension.

If you are designing a sub with lesser cross sectional area but taller design, the same can be applied to larger drivers as well. Lets compare apples to apples. And also placing the sub at centre is easier said than done, given the fact that placement is always tricky and people tend to find a corner giving maximum performance. Given 25 hz and 40 hz at "same SPL", don't you think the former will cause a bigger impact on the walls and objects? Infact acoustic proofing of lower frequencies need denser and thicker panels. Designing a sub is one task, fabricating it is another. I was talking about physical effort in fabricating two subs. I am sure its painful enough for many.

As you can see, I am not trying to conclude which is better, merely presenting the breakup of possible merits and demerits for interested people to make a choice. Infact since you are more knowledgeable in this domain, I urge you to suggest which is better according to you and why?... in simple terms for the benefit of FMs.

You are right. I bow to your superior knowledge and deep insight. I was being argumentative and silly in front of a person who obviously knows it all. Put it down to my rapidly progressing senility. there is obviously a fount of knowledge here. I really have nothing to contribute..

 

[Santy]

You are right. I bow to your superior knowledge and deep insight. I was being argumentative and silly in front of a person who obviously knows it all. Put it down to my rapidly progressing senility. there is obviously a fount of knowledge here. I really have nothing to contribute..

I am not sure why you got so offended kapvin? I didn't know that discussing about logical stuff makes you uncomfortable. What is the need to become so sarcastic and personal is not clear to me. Did I ever say that I am more knowledgeable than you? I am sorry if I had given you any such feeling. Infact I wanted you to summarize your thoughts since I was sure you know better. Its sad to read your post. :sad:

 

[kanwar]

Santy,

One big advantage of 2 subs instead of one is the room mode cancellations. If you have 4 then even better.

If you want more spl then stack the subs close to each other, if you place them in each corner of the room you are going for awful peaking at room resonance modes with lot of ripples due to room gain. I prefer a large cone sub , atleast 18 incher to do the justice and better performance.

I have seen people come up with a link from avs forum advocating 4 subs at each corner , but hey did you ever cared to measure the FR in such setup?........Not to mention the messed up phase response.

 

[lipimanas]

now i have stepped into the DIY mode of subwoofer making. i have placed an order for oaudio 300w plate amplifier and in search of a matching driver.
searched for the driver at parts-express and found the shipping cost to be more than the driver itself. gave up the idea.

need advice from experts to help search the matching 12" driver within a price range of 10 to 15k. in india.

 

[sashijoseph]

If you want more spl then stack the subs close to each other, if you place them in each corner of the room you are going for awful peaking at room resonance modes with lot of ripples due to room gain. I prefer a large cone sub , atleast 18 incher to do the justice and better performance.

I have seen people come up with a link from avs forum advocating 4 subs at each corner , but hey did you ever cared to measure the FR in such setup?........Not to mention the messed up phase response.

A single sub placed in a corner will excite all room modes.
Subs placed in all 4 corners will cancel out all odd-order modes,as will 2 subs placed in diagonally opposite corners.

Sad part is,these are only rules of thumb and one may have to make a slightly more informed placement strategy if one is to minimize room modes and equalise the LF listening experience across the room.

But still,multi subs give the option of taming room modes better than a single sub.

 

[kanwar]

A single sub placed in a corner will excite all room modes.
Subs placed in all 4 corners will cancel out all odd-order modes,as will 2 subs placed in diagonally opposite corners.

If you care to measure the phase and impulse response with multiple subs at each corner, you will get contradicted in the hands of science.. If odd order modes are cancelled then somethings are "added" also...... Placing multiple Subs at either each corner or at center of each wall directs the response towards listener from each direction but at the same time addition and subtraction of phases happen [peaking and dips]and what you get is clustermess of phase response and you cease to listen to out of phase material in LF which is present in stereo recordings very often in such setups.

Do the same with stacked Subs placed not in the corner but in the center but far from listener and some 4-5 feet away from the wall behind it, you get the best possible single source of LF originating from that point with coherent phase. Rest of it is dependent on how well the decay contours behave in particular room having variety of physical objects such has furniture.

 

[kanwar]

need advice from experts to help search the matching 12" driver within a price range of 10 to 15k. in india.

If you like, you can try Pro-audio drivers as well and why do you want to stick to 12" only, you can get much better response with larger cones.

 

[manoj.p]

If you want more spl then stack the subs close to each other, if you place them in each corner of the room you are going for awful peaking at room resonance modes with lot of ripples due to room gain. I prefer a large cone sub , atleast 18 incher to do the justice and better performance.

I have seen people come up with a link from avs forum advocating 4 subs at each corner , but hey did you ever cared to measure the FR in such setup?........Not to mention the messed up phase response.

I think you got it all wrong. It's not that people at avs came up with the 4 sub theory. There are lot of studies done around this including JBL/Harman. They did measure response and also did listening tests with trained listeners. Also, best location for those subs is not corner, but mid-point of each wall. Next best position is in the corner.

I am not lucky enough to get 4 subs in my room, due to placement issues. I only have two 18 inch subs, place at quarter distance from each corner on front wall. And for the record, I did measure the room response in my room with a professionally calibrated mic. I use that data with BFD to take care of peaks n dips.

 

[kanwar]

I think you got it all wrong. It's not that people at avs came up with the 4 sub theory. There are lot of studies done around this including JBL/Harman. They did measure response and also did listening tests with trained listeners. Also, best location for those subs is not corner, but mid-point of each wall. Next best position is in the corner.

I am not lucky enough to get 4 subs in my room, due to placement issues. I only have two 18 inch subs, place at quarter distance from each corner on front wall. And for the record, I did measure the room response in my room with a professionally calibrated mic. I use that data with BFD to take care of peaks n dips.

Don't get me wrong here, I already know about Harman and research done by Dr. Floyde Toole in subwoofer placement. The reason i stated AVS was that its very popular in Sub placement debate. Now if you go thru the Harman white paper they clearly state :
"The LF generally goes down for larger numbers of subwoofers, possibly due to having more locations away from the
corners. "
No doubt you cancel odd modes thru 4 Subs placed at different locations and even out the response centered at listening using EQ, but in doing so the phase response and SPL gets suffered which is why i don't prefer it. This way you loose the grunt and impact of direct LF projected at the listener.

Here is proaudio placement of JBL subwoofers in iMAx theaters.

A special subwoofer with 8 JBL model 2245 H (Medium Efficiency Extended Bass) in one enclosure (a cabinet huge like a caravan) is provided to extend the range of the main channels

Here you can see they have use 8 drivers in single enclosure, just think why?

 

[sashijoseph]

Don't get me wrong here, I already know about Harman and research done by Dr. Floyde Toole in subwoofer placement. The reason i stated AVS was that its very popular in Sub placement debate. Now if you go thru the Harman white paper they clearly state :
"The LF generally goes down for larger numbers of subwoofers, possibly due to having more locations away from the
corners. "
No doubt you cancel odd modes thru 4 Subs placed at different locations and even out the response centered at listening using EQ, but in doing so the phase response and SPL gets suffered which is why i don't prefer it. This way you loose the grunt and impact of direct LF projected at the listener.

Here is proaudio placement of JBL subwoofers in iMAx theaters.

A special subwoofer with 8 JBL model 2245 H (Medium Efficiency Extended Bass) in one enclosure (a cabinet huge like a caravan) is provided to extend the range of the main channels

Here you can see they have use 8 drivers in single enclosure, just think why?

But the standing waves generated in a room do have significant magnitude and phase variations across the room.So wouldn't it make more sense in deactivating room modes as much as possible in order to reduce phase anomalies and afford better sub integration.
A symmetrical 2 sub configuration would offer the best of both worlds...not too much LF spl loss,at the same time a happier modal response.
Would this statement be true?

As for the JBL sub doing theater duty,we must consider the theatre would have been constructed keeping in mind standing waves and measures would have been taken to dampen the modes at the outset.
But for our unplanned homes multi subs offer a viable tool to smoothen out room response.

 

[kanwar]

But the standing waves generated in a room do have significant magnitude and phase variations across the room.So wouldn't it make more sense in deactivating room modes as much as possible in order to reduce phase anomalies and afford better sub integration.

I think its better to invest in modding a room in order to kill standing waves rather than applying a band-aid of purchasing 4 subwoofers just to mitigate the effect.

A symmetrical 2 sub configuration would offer the best of both worlds...not too much LF spl loss,at the same time a happier modal response.
Would this statement be true?

That would be a compromise, not a solution based on scientific approach.

As for the JBL sub doing theater duty,we must consider the theatre would have been constructed keeping in mind standing waves and measures would have been taken to dampen the modes at the outset.
But for our unplanned homes multi subs offer a viable tool to smoothen out room response.

I agree that theaters are designed that way to keep standing waves out and minimizing odd order nodes along with damping.

But again would it be a wise solution to go and invest the amount on 4 set of Subs which can tame the problem to some extent and still you are devoid of SPL and impact.

I think the wiser solution would be to invest in modding the room shape internally in order to create better acoustic resolution and stack the Subs and feel the difference.