Can A Scientist Tell Me Why My High End Speakers Sound Dramatically Better Crossed Over At 120hz?

[SadMonster]

Speakers: JBL 705P
Stereo Subwoofers: JBL LSR310s (I can localize the subwoofers at any crossover and can post videos of me doing this if you don’t believe me)

My setup sounds DRAMATICALLY better crossed over at 120hz versus 80hz.

At first I thought this might be because the built in 120hz crossover on the JBL also includes a bass boost in some frequencies as described in the manual and the in room response of that boost might be more even than without the boost on the 80hz crossover.

But I’ve since calibrated the bass to the same target curve with Dirac live and calibrated 120hz crossover still sounds dramatically better than the calibrated 80hz crossover. I have 2 sets of measurements for each crossover setting so I’m not misapplying corrections.

Despite supposedly having the same decibel output and very similar frequency responses once calibrated the bass with the 120hz crossover feels far more impactful and realistic. Additionally, the midrange at the 80hz crossover feels boxy, stuffy, bloated. This is quite noticeable on vocals. At 120hz the midrange suddenly feels freed from it’s chains and ready to soar into the sky with the beautiful doves of the sound god.

Can any of you come up with theories as to what might be happening here with science?

 

[Hayabusa]

Assuming you run your stereo subs as real stereo subs (not summed mono to both of them) we can rule out problems of having multiple sound sources (L,R) is the 80-120Hz region as a source for the differences you hear.

Maybe its just the 80-120Hz handled by the 705's stresses the sound above 120Hz?
But that would only happen at high SPL levels.
Is the difference also at low level listening?

You could also run a distortion measurement in the 80-120 range to see if the different crossover frequency makes a substantial difference there.

 

[Blumlein 88]

Maybe show us some measurements you have of both conditions. We need data to go on. If you do REW sweeps is there less distortion at high levels in one vs the other crossover point?

 

[Hayabusa]

An other one could be: time alligment between your subs and the 705's

 

[SadMonster]

1. I am running real stereo and not dual mono on the subs.
2. I don’t feel like I listen super loud but I doubt I’d be able to tell the difference with the volume mow
3. Unfortunately I don’t know how to do distortion measurements or use REW but I do have FR graphs of both setups before calibration
4. I have 0 time alignment and would not know how to go about setting that up

 

[Hayabusa]

1. I am running real stereo and not dual mono on the subs.
2. I don’t feel like I listen super loud but I doubt I’d be able to tell the difference with the volume mow
3. Unfortunately I don’t know how to do distortion measurements or use REW but I do have FR graphs of both setups before calibration
4. I have 0 time alignment and would not know how to go about setting that up

Time allignment: at least start with getting the distance of the subs and 705's to the listening position as equal as possible.

 

[SadMonster]

Time allignment: at least start with getting the distance of the subs and 705's to the listening position as equal as possible.

Already done!

 

[Chrispy]

Why would that be so unusual?

 

[StevenEleven]

Speakers: JBL 705P
Stereo Subwoofers: JBL LSR310s (I can localize the subwoofers at any crossover and can post videos of me doing this if you don’t believe me)

My setup sounds DRAMATICALLY better crossed over at 120hz versus 80hz.

At first I thought this might be because the built in 120hz crossover on the JBL also includes a bass boost in some frequencies as described in the manual and the in room response of that boost might be more even than without the boost on the 80hz crossover.

But I’ve since calibrated the bass to the same target curve with Dirac live and calibrated 120hz crossover still sounds dramatically better than the calibrated 80hz crossover. I have 2 sets of measurements for each crossover setting so I’m not misapplying corrections.

Despite supposedly having the same decibel output and very similar frequency responses once calibrated the bass with the 120hz crossover feels far more impactful and realistic. Additionally, the midrange at the 80hz crossover feels boxy, stuffy, bloated. This is quite noticeable on vocals. At 120hz the midrange suddenly feels freed from it’s chains and ready to soar into the sky with the beautiful doves of the sound god.

Can any of you come up with theories as to what might be happening here with science?

It sounds perfectly plausible to me.

I would say

A) It's perfectly fine to trust your ears on this one, IMHO, but if you are intellectually curious or rather, like me, a bit obsessive:

B) Spend $100 and some time with REW and a Umik-1 and measure your system with the two different crossovers. I bet you'll see a significant difference in FR. I've been through it myself. All may be revealed. Might well something to do with how your room affects the bass in the 80-120 hz range from the subwoofers as opposed to the speakers, at least in part.

C) Even though a 120 hz crossover may not be the ideal you've dreamed of, if it sounds better to you, well, that's a pretty big deal in audio. Don't get fixated on standards or how stuff is supposed to behave in general.

IMHO, YMMV, & etc.

 

[Hayabusa]

Already done!

View attachment 134848

looking at your picture I have an additional possible reason:
the 705s are at a distance of the side walls and back walls that can cause cancelations in the 80-120Hz areas.
distances of 1/4'th of the wave length cause problems. So for 80-120 thats somewhere between 2 and 3 feet (60-90cm).
Your subs are clearly closer to the walls and will have less of that problem.

 

[audiofooled]

I've never been a fan of downfiring subs. I'd suspect you have too much bass reinforcement from boundaries at certain frequencies (at which you can always tell where the subs are located). That would be floor and corners. If you think of it like this, the ports of the subs are facing you, also speaker drivers, but the sub drivers are very close to the floor. Not hearing where the subs are located needs not only crossover integration but also some physical placement strategies...

 

[Frank Dernie]

In the absence of further data my guess is distortion from or overload of the little bass driver in the 705 being reduced by removing the requirement to operate 80 to 120 Hz.

 

[abdo123]

the smaller the range of frequencies a diaphragm has to produce, the less distortion that diaphragm will produce (Intermodular distortion IMD).

However I think it's a combination of time alignment (phase was better aligned at 120Hz than 80Hz), room modes and IMD.

 

[Vict0r]

Room modes. The frequencies you hear between 80hz and 120hz sound "better" to you when they're playing at you from the position of the subwoofer, and they sound "worse" to you when they're played at you from the position of the speakers. It's very likely that's because they interact with the room differently from those two, different positions.

 

[tecnogadget]

This kind of posts surface every week and are pointless without Umik (or similar calibrated mic) + REW measurements.

With a proper measurement differences shows up instantaneous, maybe there are phase cancelations, unexplainable frequency response changes, or as another member pointed out different decay times on room modal modes (Bass ringing). I suspect both subs placed at the corners could be of influence on this matter.

Whithout measurements there won’t be any scientific approach, only guessing as I did above.

I highly doubt changing Xover from 80Hz to 120Hz to be that much impactful on the midrange, that range is Upper Bass & Mid Bass.

 

[alex-z]

3. Unfortunately I don’t know how to do distortion measurements or use REW but I do have FR graphs of both setups before calibration

Plug in measurement mic.

REW will ask for .txt calibration file, download it from the miniDSP website. (if using UMIK-1)

Click the measure button, enter the frequency range, sweep length, and output channel.

Repeat measurements as needed.

Click "save all" to create .mdat file that you can share with others to help diagnose your issue.

 

[Χ Ξ Σ]

What's with so many people saying buy a umik? This guy uses Dirac, he must have owned a mic.

 

[Chrispy]

What's with so many people saying buy a umik? This guy uses Dirac, he must have owned a mic.

What mic does Dirac gear typically come with? Has a calibration file you can use in REW? Umik is an affordable measurement mic and is readily available I think is its main attraction.....

 

[Ron Texas]

My LS50's sound dramatically better crossed over at 170 Hz than 100Hz. There are several reasons for the improvement, but the main one is taking the load off the LF part of the LS50 coaxial driver. It's more than IM distortion, it avoids bottoming out. It also gets rid of a quarter wave cancellation at around 145 hz. The 80 hz crossover is recommended because it prevents localization of bass (usually) with a single sub.

 

[Χ Ξ Σ]

What mic does Dirac gear typically come with? Has a calibration file you can use in REW? Umik is an affordable measurement mic and is readily available I think is its main attraction.....

From his early thread the OP is using a miniDSP DDRC24 to run Dirac. He mostly likely has a miniDSP UMIK-1. The problem is that never did any REW measurements and believed in the near-perfect predicted response that Dirac gave him a little too much.