Ask an Acoustic Engineer (me)

[Justin Zazzi]

Ok, I have an easy one for you (I think?). A lot of people seem to look "down" on 6x9 speakers. Personally, I've found that they make fantastic midbass speakers. What are you thoughts on "non-round" speakers? To me, for something like midbass, a 6x9 seems perfectly fine and has the advantage of more cone area so it can provide deeper bass than 6.5" midbass speakers.

Just curious what an engineer things about 6x9s.

Thank you!

I'm not sure where non-round speakers first got a bad name. I'm guessing the first non-round speakers were relatively immature models that didn't perform well, or maybe oval speakers have a stigma of being "oem" so therefore they must be junk.

I think oval speakers are mature enough now that they perform well and they can get you more cone area in a space that wouldn't otherwise be practical. For example we make a 6x9" woofer that fits in the top of the saddlebags on motorcycles.

View attachment 9984
These speakers make excellent use of the available space and I've been tuning something similar with stellar results.

I like them for the most part since you can get more sound out of a similar size hole. They can be tricky to simulate in terms of off-axis response for all of the discussion you're having above though. Also, oval speakers require more sophisticated tools to model the off-axis frequency response and by more sophisticated I mean more expensive and sometimes time consuming. I think non-round speakers are mature enough at this point that they offer a solid deal and they are starting to catch on as a way to get a "bigger" speaker in a similar space.

I also get tripped up on the 5x7" ovals because that's a common size to print photographs which is another hobby of mine!

 

[mikeyt]

Maybe you can dispel a myth for me. I would like to use a sub that's rated 1000 watts rms, however the 5 channel amp that I will use will only put out 660 rms out of the sub channel at 2ohms stable.

 

[Jdunk54nl]

Maybe you can dispel a myth for me. I would like to use a sub that's rated 1000 watts rms, however the 5 channel amp that I will use will only put out 660 rms out of the sub channel at 2ohms stable.

Whats the myth? That you have to use 1000 watts or you are going to hurt it? If so that is definitely a myth. There is no such thing as under powering speakers.

 

[mikeyt]

Sorry I didn't finish my post before hitting enter...lol Yes I was wondering if under powering the speaker would affect the performance of it.

 

[Justin Zazzi]

Sorry I didn't finish my post before hitting enter...lol Yes I was wondering if under powering the speaker would affect the performance of it.

If you give it a little less power, it will be a little less loud! Honestly, that's what happens when you're listening to music at a reasonable volume ... you're sending maybe 10-50w of power to your subwoofer instead of 1000w. Does your subwoofer explode? No. Actually it does the opposite by staying cool and not being stressed mechanically. If you give you subwoofer a little less power then it'll be a little less loud.

I think the myth goes like this: if you under-power your speaker then you'll want to turn up your amplifier a lot and over-drive it into clipping. Then, clipping is like momentary DC voltage which is more power than you expect so you speaker will melt. Or clipping has tremendous amounts of high-frequency energy and it will melt your tweeter.

The myth relies on you over-driving your amplifier far into clipping. If you are pushing your "small" amplifier so hard that this could actually melt your speakers, then I imagine you would also overdrive a "larger" amplifier and just melt your speakers faster. I think this myth/problem exists between radio and chair.

---

I do not believe the extra power delivered to a subwoofer would be a serious problem but I'm curious how sensitive a tweeter might be to excess power in the higher frequencies. By happy accident, I am running a few power tests at the office right now as a practical test for this *exact* question. I am tuning a system louder than before and we are making sure that running it hotter, well into clipping, will not present any reliability issues. If I learn something cool I'll share what I can!

 

[Pb82 Ronin]

Justin, great thread so far! Definitely been chasing my tail with trying to deal with what I feel is wave cancellation in the low frequencies (> 100Hz) in my Vette. My sub is a JL 10W7 in a sealed box fired upwards into curved glass. My assumption is the sound wave is colliding with itself and cancelling. Of course I could be way off too...that's why I'm asking. When we tune in the garage, everything goes well and bass response is decent. But, when i take the car to the highway, all bass just vanishes (mid-bass suffers the most). All i can hear is from about 500 Hz and up, and 60 hz and lower. It's the strangest and most frustrating phenomenon ever.

 

[TheTodd]

Justin, great thread so far! Definitely been chasing my tail with trying to deal with what I feel is wave cancellation in the low frequencies (> 100Hz) in my Vette. My sub is a JL 10W7 in a sealed box fired upwards into curved glass. My assumption is the sound wave is colliding with itself and cancelling. Of course I could be way of too...that's why I'm asking. When we tune in the garage, everything goes well and bass response is decent. But, when i take the car to the highway, all bass just vanishes (mid-bass suffers the most). All i can hear is from about 500 Hz and up, and 60 hz and lower. It's the strangest and most frustrating phenomenon ever.

I’m dealing with a similar issue in my Vette (1996) but it’s only really the sub bass that drops out but I’m attributing it to the muffler deleted exhaust & the general lack of sound deadening throughout the car. So I’m figuring more of a drowning out vs cancellation but I could be wrong. My subs are also firing straight up into the curved glass so I’m curious to hear any thoughts. It very well just could be the fact that our cars (Vettes in general) didn’t really have faithful music reproduction in mind when designed. It’s more about the power & driving experience plus being lightweight, so my non-engineer S.W.A.G. (Scientific Wild Ass Guess) is that certain frequencies are just getting drowned out. The difference in frequencies between your Corvette & mine may be due to the year difference.

 

[Pb82 Ronin]

It's not the deadening bro...I have a C6Z with CLD, MLV, and VB2, 4, etc all through it...she's SUPER quiet. This phenomenon STILL happens. I also have the M2W so I can kill my exhaust output as to not interfere. Trust me when i say my vette is very quiet. I really think the speaker orientation is killing it.

 

[TheTodd]

Yeah... you probably have a point there. Mine has just about none. I have it more for the sensory experience than the music. For mine, the music is something to occupy me on longer trips. There’s a lot of times the radio doesn’t even get turned on.

 

[Grinder]

It's not the deadening bro...I have a C6Z with CLD, MLV, and VB2, 4, etc all through it...she's SUPER quiet. This phenomenon STILL happens. I also have the M2W so I can kill my exhaust output as to not interfere. Trust me when i say my vette is very quiet. I really think the speaker orientation is killing it.

If speaker orientation remains the same when on the highway as when tuning in the garage, wouldn't something other than orientation account for the difference?

 

[Pb82 Ronin]

If speaker orientation remains the same when on the highway as when tuning in the garage, wouldn't something other than orientation account for the difference?

I don't know...truth be told, output isn't that great even when sitting in the garage tuning. It just gets worse when road noise is present.

 

[erinh]

Eliminate variables. Pull the car out of the garage and park it in the driveway or in the street, away from any large buildings/house. Does it sound the same as it did when in the garage or does all the bass vanish?

If the issue happens once the car leaves the garage then I have to think there's something going on in your garage; like you're basically at the mercy of the room within a room effect.
If the issue is only while you're driving then it would seem the road/wind noise is canceling out the response.

Though, truthfully, both of those wiping out 60-500hz seems like a stretch to me.

Anyway, answer the first question. Then you'll know what path to take toward further troubleshooting.

 

[Pb82 Ronin]

It sounds close...but a minimal change is detectable.

 

[erinh]

Do you have an RTA setup you can use to test in garage vs outside garage? You could also test while driving but I’d recommend you get help with that and make sure to have them with you in both scenarios so the only thing changing is the driving aspect.

 

[Justin Zazzi]

All i can hear is from about 500 Hz and up, and 60 hz and lower. It's the strangest and most frustrating phenomenon ever.

So if ~60hz and lower is intact, your subwoofer seems to be working alright.

A hole between ~60z and ~500hz sounds like a midbass driver problem since that's the only speaker playing that range.

I would continue looking at the difference of just parking outside like Erin suggested. I don't think that'll be the fix-all, but it's a good thing to double-check.

Also, what is the other difference between the garage and highway? Velocity. Are you using any of the factory radio or amplifier? Is there any active noise cancellation built in to the car or is there any automatic volume control that adapts the volume to the vehicle speed? This sounds like it could be a dynamic filter fighting against you somehow?

What is the signal chain between your music source (phone?) and your speaker? Bluetooth to a factory radio? Phone straight to an aftermarket DSP? That might help us think it through with you.

Also, did this problem appear suddenly or has it been like this for a while? Has it ever worked right? If it did work right before, what did you change between then and now?

 

[mauian]

Hey Justin, this might be a dumb question but is it a bad idea to set gains on an amp or input sensitivities on a DSP with a sine sweep? I’ve just seen many methods using 40hz and 1000hz sine waves and a limitation as pointed out by Andy at Audiofrog is that this doesn’t cover the whole spectrum so you could have a boost at 30Hz (or pick any other frequency) that could be generating distortion that you might not be picking up on if only using a 40hz sine wave. Some people use multiple sine waves...

While it may be overkill, any reason not to use a sine sweep?

If it’s ok, I would think a linear sine sweep would be best (as opposed to logarithmic) for consistent energy across the spectrum (if detecting distortion with a DD-1 or LED light on amp/dsp)?

On a related note, could white noise be used too to send equal energy across the spectrum all at once?

thanks!


https://m.facebook.com/audiofrogInc...ech-supporting-someone-yeste/526653370847709/


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[Pb82 Ronin]

Do you have an RTA setup you can use to test in garage vs outside garage? You could also test while driving but I’d recommend you get help with that and make sure to have them with you in both scenarios so the only thing changing is the driving aspect.

View attachment 10060 I believe this setup is slightly better than a single Mic/RTA (Courtesy of Darkridr)

So if ~60hz and lower is intact, your subwoofer seems to be working alright. It is...I wonder if the box is the butt-head here.

A hole between ~60z and ~500hz sounds like a midbass driver problem since that's the only speaker playing that range. Running the mids (6.5" KX2) from 85 -1100 Hz. We did do a quick function check to verify they're working.

I would continue looking at the difference of just parking outside like Erin suggested. I don't think that'll be the fix-all, but it's a good thing to double-check. We can try...not sure if the cords will extend that far...

Also, what is the other difference between the garage and highway? Velocity. Are you using any of the factory radio or amplifier? Is there any active noise cancellation built in to the car or is there any automatic volume control that adapts the volume to the vehicle speed? This sounds like it could be a dynamic filter fighting against you somehow?

Zero connections to anything OEM. On purpose...Bose is garbage. No noise cancellation stuff, or anything in the DSP other than the filters we choose.

What is the signal chain between your music source (phone?) and your speaker? Bluetooth to a factory radio? Phone straight to an aftermarket DSP? That might help us think it through with you.

Direct connect to HU by either 3.5MM jack (when tuning) or direct USB iPod connection. Even have FLAC files to play with.

Also, did this problem appear suddenly or has it been like this for a while? Has it ever worked right? If it did work right before, what did you change between then and now?

Been like this since we started tuning. Every time we have a great tune emerge in the garage, the sound quality goes away the moment I hit the highway. I think one of the main contributing factors could be wind/road/tire noise passively cancelling the mid-bass frequencies. I realize that's a stretch...but at this point we have HOURS of tuning in this setup and multiple tunes. Some sounded good, some sounded great, and some sounded awful. Obviously, we finish on the "great" sounding ones...then I go for a drive. Then...it all goes to crap wihtout making a single change. Poopiest feeling ever because my bro has helped me so many times that his wife probably hates me now. LOL!

Responses in blue (or pics...LOL)

 

[Fernpatch]

I honestly suspect you are having road noise masking some or all of the sound that goes missing on the road. I have battled a very similar issue in my car. my solution in progress is developing 2 eq presets. one for critical listening when parked and a second with some boosts applied to the problem areas while driving. it may not be the "correct" way to go about it but it is the best solution that I have found thus far for vanishing mid bass and lower mid range in my own vehicle.

 

[Justin Zazzi]

Hey Justin, this might be a dumb question but is it a bad idea to set gains on an amp or input sensitivities on a DSP with a sine sweep? I’ve just seen many methods using 40hz and 1000hz sine waves and a limitation as pointed out by Andy at Audiofrog is that this doesn’t cover the whole spectrum so you could have a boost at 30Hz (or pick any other frequency) that could be generating distortion that you might not be picking up on if only using a 40hz sine wave. Some people use multiple sine waves...

While it may be overkill, any reason not to use a sine sweep?

Not a dumb question.

I used to be super crazy careful about amplifier gain settings and I used an oscilloscope and everything. I realized a single sine tone can be hit or miss like you mention because there might be boosts or cuts all over the place. So then I did a sweep and looked for the hottest frequency (electrically at the speaker terminals) then I used that sine tone to set the gains.

Later I realized if you set gains, then tune, chances are you're going to make a lot of cuts and so your gain structure will not be what you thought it was. The system can wind up a lot more quiet than you intended.

How often has this happened: you set gains, you spend all day tuning until it's just right, you either share with a friend or you listen the next day, you realize it is not loud enough, you adjust the gains, you spend all day tuning until it's just right .... and round and round.

I like one of Andy's recent posts about setting gains last. I wound up with a very similar idea before I saw his post. In short it goes like this:
-if your system is not loud enough, increase gains.
-if you system has too much noise floor or hiss, reduce gains.

There are many ways to get fancy about finding the balance between loudness and quality but many of them are difficult or impossible with simple tools like REW. I find the ears are the best tool for the job unless you don't know what to listen for, then you borrow your friends' ears.

If it’s ok, I would think a linear sine sweep would be best (as opposed to logarithmic) for consistent energy across the spectrum (if detecting distortion with a DD-1 or LED light on amp/dsp)?

I'm not sure how the DD-1 works, but the C.L.E.A.N. gain setting lights on the Rockford amps I use are pretty reliable no matter what I'm doing. A linear sweep might not be a bad idea, but similar to above I think it's a bit overkill unless you have no other way to listen for it.

On a related note, could white noise be used too to send equal energy across the spectrum all at once?

You could, but setting gains is usually hunting for a threshold of clipping the input or output of a device and then looking for the resulting distortion to see when you found the threshold. White noise or any continuous noise would be a poor choice since distortion is much harder to see unless you have really sophisticated (read expensive) tools.

 

[Justin Zazzi]

I don't know...truth be told, output isn't that great even when sitting in the garage tuning. It just gets worse when road noise is present.

I think I'm with Fernpatch on this one. Driving on the highway, no matter how quiet your car is, will not sound the same as in the garage. I like the idea of two presets. I have been making use of the "bass" feature on my radio to make small adjustments as I drive. Not much else you can do unless you have access to a DSP with speed-controlled compensation.

You could get something like this Analog Devices demo board and craft your own DSP inside it complete with speed-sensitive filters, but you'd also need a speed sensor to feed it. You might use a CAN or OBDII interface to grab velocity signals. That would be a fun project.

https://www.digikey.com/product-det...inc./EVAL-ADAU1466Z/EVAL-ADAU1466Z-ND/7915254