Using DSP to get a speaker to play lower?

[Trevm]

 

Hello.

I have a set of JBL control 28t speakers I have removed all tapping equipment, and added extra deading material to the cabinets.

 

 I use these for my outdoor pergola speakers and intentionly chose them due to the fact they roll off high at around 100hz to try and keep things nice for my neighbours as they are used often and at times late at night.

 

In saying that as nice as I find these, it's now annoying me that they aren't playing low enough - so stuff the neighbours I would like to fix that.

 

If I throw some DSP at them via a minidsp and apply boost down low will I get any decent results?  I have plenty of headroom as the volume levels are usually kept well below what the JBLs can handle.

 

Any advice is appreciated.

 

[GregWormald]

You might get a bit more bass extension but the roll-off below 100 Hz is very steep and likely a character of the woofer, so it's going to be minor.

 

By the time you pay for the DSP gear and software you would probably be better off with a subwoofer.

[Dean Gale]

Just get a cheap subwoofer or two position them were you want but install some protection over the ports . Cheap computer fan covers off of ebay would work

[Keith_W]

Short answer is: no. 

 

Making a driver do what it does not want to do will create distortion. Often the distortion products are higher up the frequency range, so you will not only get distorted bass, you will also get distorted mids. 

[Trevm]

11 hours ago, Dean Gale said:

Just get a cheap subwoofer or two position them were you want but install some protection over the ports . Cheap computer fan covers off of ebay would work

 

I had considered this, but to be frank the outdoor sub options I've seen suck. 

It means an extra power cable and rcas run as the amp is inside etc plus mounting it somewhere is a pain as they cant mount up high on the pergola.

[POV]

As per the others….it’s a no.  Subwoofers are the ticket, and given you don’t want to disturb the neighbours too much just go for smaller box, smaller driver units.  It will be far easier, and much more effective.

 

Or, replace the JBLs with something with more bass and redeploy the JBLs somewhere else.  

[Ittaku]

According to the specs, they should go down to 55Hz. Check you don't have the left wired out of phase with the right speaker. Then change their position to make sure you don't have a cancellation null in your listening position (walking around the room yourself might show more and less bass.) Check the basics before getting fancy.

[aussievintage]

29 minutes ago, Ittaku said:

According to the specs, they should go down to 55Hz. Check you don't have the left wired out of phase with the right speaker. Then change their position to make sure you don't have a cancellation null in your listening position (walking around the room yourself might show more and less bass.) Check the basics before getting fancy.

 

 

Agree.  55Hz is plenty low enough  for quite acceptable listening.    Keep in mind that human hearing rolls off at low volumes, so that thing they used to call a loudness control (inversely proportional bass and treble boost), is worth implementing when you have it turned down.

[frednork]

16 hours ago, Trevm said:

If I throw some DSP at them via a minidsp and apply boost down low will I get any decent results?  I have plenty of headroom as the volume levels are usually kept well below what the JBLs can handle.

I think the above comment means it could be worth a shot but not sure buying  a minidsp is worth the trouble. If you arent playing super loud you can see what might be possible.  If you have a bass tone control anywhere in your chain give that a go first , in your amp, in your digital controller? to see what benefit it may have. Sure a minidsp will be more customisable but it doesnt sound like it warrants that level of accuracy. If you are using roon there is already dsp included in it and a lot of other players also.  If you are not sure let us know what your equipment chain is and we can help see it is possible. Worth trying for free before committing to some unnecessary expense.   another thing you can try if possible is to have them close to the wall to get extra bass reinforcement.  If its mostly for background it might just be enough. 

 

If you cant get enough bass using the above then I would look for something else or add a sub as suggested.

Edited September 17 by frednork

[Trevm]

2 hours ago, Ittaku said:

According to the specs, they should go down to 55Hz. Check you don't have the left wired out of phase with the right speaker. Then change their position to make sure you don't have a cancellation null in your listening position (walking around the room yourself might show more and less bass.) Check the basics before getting fancy.

They are mounted up against the pergola corners.  5 mtr high and 3.5 apart.

It's an outdoor area, I don't think cancellations are a factor here.

 

 

[aussievintage]

17 minutes ago, frednork said:

16 hours ago, Trevm said:

 

I think the above comment means it could be worth a shot but not sure buying  a minidsp is worth the trouble. If you arent playing super loud you can see what might be possible.  If you have a bass tone control anywhere in your chain give that a go first , in your amp, in your digital controller? to see what benefit it may have. Sure a minidsp will be more customisable but it doesnt sound like it warrants that level of accuracy

 

Definitely not a job that requires a DSP.    Tone controls, or a simple EQ function (most digital players have them).

[Keith_W]

Another speaker manufacturer that claims that their product goes down to "55Hz". It's -20dB at 55Hz! 

 

If you want more bass - either get new speakers or use a subwoofer. Simple as that. 

[AudioGeek]

17 minutes ago, Keith_W said:

Another speaker manufacturer that claims that their product goes down to "55Hz". It's -20dB at 55Hz! 

 

If you want more bass - either get new speakers or use a subwoofer. Simple as that. 

 

But is that measurement anechoic?

[Keith_W]

4 minutes ago, AudioGeek said:

 

But is that measurement anechoic?

 

Manufacturer's measurement. And JBL belongs to the Harman group, I am pretty sure they have an anechoic chamber. They are one of the most engineering focused audio companies on the market. If not THE most engineering focused given how many important publications they have contributed. 

[davewantsmoore]

18 hours ago, Trevm said:

If I throw some DSP at them via a minidsp and apply boost down low will I get any decent results?  I have plenty of headroom as the volume levels are usually kept well below what the JBLs can handle.

 

Any advice is appreciated.

 

Yes... but it depends on what sort of SPL you are looking for.

Let's say you want another octave of flat extension (ie. 50Hz)

The spec sheet shows the maximum output for the speaker is ~95dB at 50Hz.

 

What you need to do is:

Create EQ which will flatten the output of the speaker above 50Hz.

Consider the maximum output of the speaker to be 95dB.

 

 

[GregWormald]

According to the specs and the graph those speakers are not designed to produce appreciable bass below 100Hz. The data sheet shows -10dB at 55 Hz so I think you're stuck.

 

Edited September 17 by GregWormald

[davewantsmoore]

2 hours ago, frednork said:

If you have a bass tone control anywhere in your chain give that a go first

You can try this... but carefully.

 

The reason being that if you apply "some sort of boost at 50Hz" .... we need to be sure that the roll off (slope) below 50Hz, is the same as it was without the EQ.

 

Otherwise, there could the situation where.... we play the speaker at (for example) 95dB ... thinking that (for example) the max SPL possible is now 95dB (because the new rolloff being 50Hz, as in my example above) ..... but if the new SPL at 20Hz, is 85 instead of 80 due to the slope below 50Hz having EQ (or the wrong EQ) applied to it, then we have a problem.

 

This may not sound like much ... but the ~6dB of extra SPL at 20Hz is a doubling of driver excursion.   ie. double the maximum excursion that the driver can handle (using the max output specs quoted by JBL).

[AudioGeek]

Come on guys, if its an anechoic measurement then it will have reasonable output at 55Hz indoors in a room. You all know this. I dont think the claims are unressonable. Will need a bit of eq/dsp to sound good down low in a room. 

 

Obviously being outdoors, with limited "room gain", this is of no help to the OP. I agree with Keith - new speakers or a sub, maybe wireless (still needs power).

[Richard Tremain]

Speakers have NO bass in free air, DSP or not, no point change speaker either. People just position them for reinforcement. ie. in a corner.

You can even put some boarding around them cheaply.

Edited September 17 by Richard Tremain

[AudioGeek]

46 minutes ago, Richard Tremain said:

Speakers have NO bass in free air, DSP or not, no point change speaker either. People just position them for reinforcement. ie. in a corner.

You can even put some boarding around them cheaply.

 

Have you been to an outdoor gig?

It is possible to get real bass and sufficient spl. The problem is you often need multiple large drivers.

 

If OP was looking at new speakers with bass  - would probably need 15 inch drivers or multiple speakers. Probably not practical for a pergola.

[Trevm]

Some conflicting advice here.

Anyway I've been able to buy my old minidsp back so I'll have some results in a few weeks.

[davewantsmoore]

4 hours ago, AudioGeek said:

Obviously being outdoors, with limited "room gain", this is of no help to the OP. I agree with Keith - new speakers or a sub, maybe wireless (still needs power).

The data sheet clearly states the (max SPL)  measurements are half space.

 

The speaker can make 95dB at 50Hz.... so if this is enough, then great.

 

2 hours ago, Richard Tremain said:

Speakers have NO bass in free air, DSP or not

?

EQ can add back the SPL lost by moving from full-space to half-space to quarter-space.

The speaker will be in half space as it has the ground.

 

Adding "boarding" around the speaker, only help if it is larger than the wavelengths of interest .... so for bass they need to be very large.

 

So overall this is a bad take.

 

25 minutes ago, Trevm said:

Some conflicting advice here.

Anyway I've been able to buy my old minidsp back so I'll have some results in a few weeks.

As always.

 

You can EQ your speaker flat outside to get the bass back .... just be mindful of the maximum SPL limits of the speaker.

 

Eg. if you made everything (the whole frequency range) as loud as 20Hz (ie. flat bass down to 20Hz) .... then playing the speaker louder than 80dB will be too much.

 

 

 

 

 

[davewantsmoore]

4 hours ago, AudioGeek said:

with limited "room gain"

Room gain is very limited even in a room.

 

The best you can hope for is 3 or 4dB above the lowest mode of the room.

 

Below the lowest mode of the room, you get + 12dB/octave..... but because your speaker (at best) rolls off at 12dB per octave, it just means the SPL continues flat (no gain) below the lowest mode.

 

... but this is all irrelevant if the frequency of interest is (for example) 50Hz (as this is well above the lowest room mode of any sensible sized room).

[Richard Tremain]

On 17/09/2023 at 5:45 PM, AudioGeek said:

 

Have you been to an outdoor gig?

It is possible to get real bass and sufficient spl. The problem is you often need multiple large drivers.

 

If OP was looking at new speakers with bass  - would probably need 15 inch drivers or multiple speakers. Probably not practical for a pergola.

I think we are discussing a Hi-Fi system an outdoor PA system is designed for a specific function.

Also the Amp power is so many thousand watts.

[Richard Tremain]

On 17/09/2023 at 7:17 PM, davewantsmoore said:

The data sheet clearly states the (max SPL)  measurements are half space.

 

The speaker can make 95dB at 50Hz.... so if this is enough, then great.

 

?

EQ can add back the SPL lost by moving from full-space to half-space to quarter-space.

The speaker will be in half space as it has the ground.

 

Adding "boarding" around the speaker, only help if it is larger than the wavelengths of interest .... so for bass they need to be very large.

 

So overall this is a bad take.

 

As always.

 

You can EQ your speaker flat outside to get the bass back .... just be mindful of the maximum SPL limits of the speaker.

 

Eg. if you made everything (the whole frequency range) as loud as 20Hz (ie. flat bass down to 20Hz) .... then playing the speaker louder than 80dB will be too much.

 

 

 

 

 

Like you say EQ can only help if the Bass unit can take it and as this would have not been a design objective this is a bad take. Also this requires amplifer power.

I am a simple guy and leave wave lengths to measurements between 2 walls.

If you put big chipboard behind a speaker you retain sound that is lost to the rear which is mostly bass as it is omni directional.